SECTION 230993 - SEQUENCES OF OPERATION - · Web viewMONITOR and display status of sump pump high water level alarm dry contact provided by pump manufacturer as DI point, as indicated

GUIDE SPECIFICATION SECTION 230993- 1 Revised 4 January 2017 Sequences of Operation

SECTION 230993 - SEQUENCES OF OPERATION

PART 1 - GENERAL

SCOPE

This section includes basic requirements for sequences of operation for Division 23 equipment, as well for equipment furnished under other Divisions.

RELATED DOCUMENTS

Drawings and general provisions of Contract, including General and Supplementary Conditions and Division 01 Specification sections, apply to the work of this section.

The requirements of Sections 230913, 230923, 230924, and 290933 apply to the work of this section.

SUBMITTALS

General: Submittals shall demonstrate compliance with technical requirements by reference to each subsection of this specification. Where a submitted item does not comply fully with each and every requirement of the Specifications, the submittal shall clearly indicate such deviations. Identification requirements for non-complying features of items are very specific. See Section 019913 for exact requirements.

Sequences of Operation: Provide complete documentation of the sequences of operation required by this project, as hereinafter specified:

Include narrative sequence of operation for each HVAC system, subsystem, and component as defined herein, within other specification sections referenced herein, and/or defined on the project Drawings.

Narratives shall not be verbatim copies of the sequences provided herein, but shall reflect the actual sequence of operation as applied by the contractor.

Sequences of operation must include setpoints and/or control ranges, digital alarms, analog alarm setpoints (both high and low), time delays, I/O point names, hardware/software interlocks, analog control mode (e.g., proportional [P] or proportional plus integral [PI]), and any other specifics needed for the user to fully understand and utilize the DDC system for operation of each HVAC system and its individual components in compliance with the design intent.

Sequences of operation for each item of equipment that is controlled by integral original equipment manufacturer (OEM)controls, with or without control logic through the DDC system, shall be incorporated in the applicable narrative.

Control Schematics: Provide schematic diagrams of each HVAC system/subsystem sufficient to define the location of all control sensors, final control devices, etc. that are utilized as part of any sequence of operation and that confirm all input and output points required by any sequence of operation.

PART 2 - PRODUCTS (Not Used)

PART 3 - EXECUTION

GENERAL REQUIREMENTS

Sequences of operation specified herein, which indicate the functional intent of HVAC systems, subsystems, and/or components operation, are general in nature and may not fully define every aspect of programming that may be required to fulfill the design intent. Contractor shall provide all programming necessary to obtain the

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sequences/system operation indicated, resulting in stable HVAC system operation in accordance with the design intent.

The following standard abbreviations, along with abbreviations defined on the Drawings, shall apply to all control schematics and sequences:

Abbreviation

Definition Abbreviation Definition

I/O Points HVAC Components/ConditionsAI Analog Input ACWS, ACWR Air-Conditioning Water Supply, ReturnAO Analog Output AHU Air-Handling UnitAV Analog Value BCU Blower Coil UnitDI Digital (Binary) Input CAV Constant Air VolumeDO Digital (Binary) Output CC Cooling CoilDV Digital (Binary) Value CDWS, CDWR Condenser Water Supply, Return

Control Conditions/Actions CHWS, CHWR

Chilled Water Supply, Return

BP Barometric Pressure FCU Fan Coil UnitBTU British Thermal Unit HC Heating CoilDA Direct Acting HX Heat ExchangerDB Dry Bulb HWS, HWR Hot Water Supply, ReturnDP Differential Pressure OA Outdoor Air

DPT Dew Point Temperature OEM Original Equipment ManufacturerDT Differential Temperature (Range) PHC Preheat CoilNC Normally Closed RA Return AirNO Normally Open RF Return Air FanP Pressure; Proportional SA Supply Air

RA Reverse Acting SF Supply FanSP Static Pressure VA Ventilation AirT Temperature VAV Variable Air Volume

TP Total Pressure XA Relief AirVP Velocity Pressure XF Relief Air FanWB Wet Bulb

Sequences of operation shall incorporate the following control point/object requirements, as applicable:

PointDescription

Hardware Point Software PointGRAPHICAI AO DI BI AV DV SCHED TREND

BTU X X XDamper End Switch X XDP X X XDPT X X XDT X X XDrain Pan Water Level Sensor X XElectrical Power X X XEnthalpy X X XFlow (Air, Water, Steam, etc.) X X XGas Concentration X X XHumidity X X XOccupancy/Vacancy X X XOccupied/Unoccupied X x X XOn/Off X x X XOpen/Close X X XOutput (Percent) X X XPosition (Percent from Normal) X X XP X X XSpeed (%, setpoint) X XSpeed (%, feedback) X X XStatus X X X

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PointDescription

Hardware Point Software PointGRAPHICAI AO DI BI AV DV SCHED TREND

T X X X

All sequences of operation are based on one or more sensed variables, with an associated controlled variable, changing in one direction. Each sequence shall operate in reverse when the sensed variable(s) changes in the opposite direction.

HVAC control setpoints are defined or implied within the sequences of operation specified hereinafter and/or elsewhere on the Drawings.

Where a setpoint is not explicitly defined or implied, determine the appropriate setpoint based on scheduled performance data for HVAC equipment. Confirm setpoint with A-E.

Defined or implied setpoints and setpoint reset requirements shall, as necessary, be adjusted based on test data provided by the testing/adjusting/balancing (TAB) subcontractor and control system calibration and verification testing as required by Section 230923 to provide stable, satisfactory HVAC systems operation in compliance with the design intent.

AO setpoints and control ranges shall be user-adjustable.

DO points that depend on a specific analog value to change shall be user-adjustable.

The minimum speed setting for each pump and fan under VFD control shall be as low as possible, while avoiding inertial stalling. Adjust each VFD minimum speed and ramp-up and -down times based on test data provided by the TAB subcontractor. Default times for acceleration/deceleration shall be 30 seconds for motors less than 40 hp and 60 seconds for motors 40 hp and larger.

Two independent schedules for HVAC system operation and control are required by Sequence 1.14, established as follows:

"ON/OFF" schedule(s) shall determine HVAC systems and/or equipment start/stop times, define applicable operating setpoints, and define when specific sequences of operation are to be utilized.

“ON” hour is defined as the estimated latest hour at which the HVAC system/equipment may be “ENABLED” and commanded “ON” so that setpoint conditions are maintained within the space(s) served at the “OCCUPIED” start hour. This “ON” hour shall be adjusted by the “Optimum Start” application specified in Section 230923.

“OFF” hour is defined as the hour at which the HVAC system/equipment shall be “DISABLED.”

"OCCUPIED/UNOCCUPIED" schedule(s) shall determine ventilation modes.

These schedules define 5 specific operating periods for the HVAC systems to which they are applied:

“On” period is the elapsed time between the scheduled “On” hour, defined as the latest allowable hour at which the HVAC system must be “On,” and the “Off” hour, during which the HVAC operates to maintain the spaces served at the defined “On” period temperature and/or humidity setpoints.

“Off” period is the elapsed time between the scheduled “Off” and “On” hours during which the HVAC system does not operate unless it is required to cycle “On” to maintain the spaces served at the defined “Off” period high and low limit temperature and/or humidity setpoints.

“Occupied” period is the elapsed time between the scheduled “Occupied” start and end hours during which people, to a greater or lesser extent, are expected to be present and required ventilation air.

“Unoccupied” period is the elapsed time between the scheduled “Occupied” end and start hours during which people, except at de minimis levels , are not expected to be present and, therefore, no ventilation air is required.

“Pre-Occupied” period is the elapsed time between the scheduled “On” hour and the actual “On”

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hour computed by the Optimum Start algorithm so that setpoint conditions are maintained within the space(s) served at the beginning of the “Occupied” period. (This period typically overlaps the “Unoccupied” period by 1-3 hours depending on input schedules.)

Provide operator-defined maintenance “lockout” for each HVAC component. When initiated, any component defined to be locked out for maintenance shall be deleted from any applicable control sequence of operation.

SEQUENCES OF OPERATION

[Guideline: These sequences comply with the draft of BSR/ASHRAE Guideline 36P, High Performance Sequences of Operation for HVAC Systems, published June 2016, and with the current edition of ASHRAE Standards 62.1 and 90.1.

The control sequences are presented in “narrative” format since experience has proven that this format is the better understood method by which HVAC designers can describe their design intent, for owners and contractors to understand how each HVAC system is to operate, and for control vendors to determine DDC system requirements.

These sequences of operation are presented as individual sequences for each HVAC system “element.” It is required that the HVAC designer assemble these “element” control sequences to define the complete control requirements for each specific HVAC system. Upon completion of editing of this section, delete the following “Index to Sequences” and the “Return to Top” links at the end of each sequence.]

Index to Sequences of Operation

Section ID DescriptionGENERAL

1.10 Emergency Stop Control1 . 1 4 Schedules of Operation1.18 Input Point Monitoring and Alarm Initiation1.20 Output Point Control1. 2 1 Constant Speed Single-Phase or Polyphase Motor Control1.22 Two-Speed Polyphase Motor Control1.23 Variable Speed Single-Phase Motor Control1.24 Variable Speed Polyphase Motor Control1.25 Single-Phase and Polyphase Motor Status Monitoring

1.26.1 Lead/Lag/Cascade Sequencing of Parallel-Configured Components1.26.2 Lead/Lag/Standby Sequencing of Alternating Components1.27 Exhaust Air Fan Start/Stop1.30 Outdoor Piping/Equipment Trace Heating Cable1.33 Final Control Element Operators (Valves and Dampers)1. 3 9 Electric Resistance Heating Control

SITE CONDITIONS AND UTILITIES2. 0 1 Outdoor Air Conditions2.03 Cooler or Freezer Temperature Alarm2.04 Sump Pump High Water Level2 . 07 Utilities Consumption

CENTRAL PLANTS3.1 Chilled Water Systems

3.11.1 Chiller Controller Interface3.11.2 Chilled Water System Enable/Start/Stop3.12.1 Chilled Water System, Single Chiller, Primary Constant Flow3.12.2 Chilled Water System, Single Chiller, Primary-Secondary Variable Flow3.12.3 Chilled Water System, Single Chiller, Primary Variable Flow3.14 Chilled Water System, Multiple Chillers

3. 1 4.1 Primary-Secondary Variable Flow3.1 4 .2 Primary Variable Flow

3.15 Condenser Water System, Dedicated Cooling Tower3.16 Condenser Water System, Multiple Cooling Towers

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Section ID Description3.17 Condenser Water System, Cooling Tower Operating and Safety Controls3. 1 8 Refrigeration Machinery Room Ventilation and Purge

3.2 Hot Water Systems3.20 Boiler Room Safety Control3.21 Boiler Controller Interface

3.2 1 .1 Non-Condensing Boilers3.2 1 .2 Condensing Boilers

3.22 Hot Water System Enable/Start/Stop3.23 Hot Water System, Multiple Non-Condensing Boilers, Primary-Secondary

Variable Flow3.24 Hot Water System, Multiple Condensing Boilers

3.24 . 1 Primary-Secondary Variable Flow3.24.2 Primary Variable Flow

3.25 Hot Water System, Steam-to-HW Heat Exchanger(s), Variable Flow3. 2 6 Hot Water Unit Heater3.27 Hot Water Convection/Radiation

3.3 Steam Systems3.20 Boiler Room Safety Control3 . 31 Boiler Controller Interface3.3 3 Steam System, Multiple Boilers3.35 Steam Unit Heater3.38 Steam Convection/Radiation

3.4 Closed Loop Water Source Heat Pump Systems3.41 Heat Pump Water Loop, Variable flow

AIR-HANDLING SYSTEMS4.0 Air-Handling Systems Operations and Monitoring

4. 0 0 Start/Stop Control4. 0 1 Space Temperature/Humidity Setpoints and Monitoring4.05 Drain Pan Condensate Level Alarm4.06 Filter Differential Pressure Alarm4.07 Low Limit Thermostat Control and Alarm4.08 Preheat Control4. 0 9 Duct Steam Humidifier

4.1 Single Zone Air-Handling Systems4.1 0 Single Zone Air-Handling Systems, Operations and Monitoring4.11 Space Temperature and Humidity Control, Single Zone System

4.11.1 CAV4.11.2 VAV

4.12 Minimum Outdoor Air Control, Single Zone System4.1 2 .1 CAV4.1 2 .2 VAV

4 . 1 4 Demand Control Ventilation Control (DCV) Enable/Disable, Single Zone System4.14.1 DCV Based on Occupancy Schedule + Occupancy/Vacancy Sensing4.14.2 DCV Based on Occupancy Schedule + Operator/Manual Schedule Override4.14.3 DCV Based on Occupancy Schedule + CO2 Sensing4.14.4 DCV Based on Occupancy Schedule + People Counting/Sensing

4.15 Airside Economizer Control4.2 Multiple Zone Single Duct Air-Handling Systems

4.20 Multiple Zone Single Duct Air-Handling Systems, Operations and Monitoring4.21 Discharge Air Temperature Control, Multiple Zone System4.22 Airflow Volume Control, Multiple Zone System4. 2 3 Minimum Outdoor Air Control, Multiple Zone System4.24 Demand Controlled Ventilation (DCV) Enable/Disable, Multiple Zone System

4.24.1 DCV Based on Occupancy Schedule + Return Air CO2 Sensing4.24.2 DCV Based on Occupancy Schedule + Zone Occupancy/Vacancy Sensing

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Section ID Description4.24.3 DCV Based on Occupancy Schedule + Zone CO2 Sensing4.24.4 DCV Based on Zone People Counting/Sensing

4.26 “OFF” Period Space Temperature/Humidity Control, Multiple Zone System4.27 Terminal Unit Control, Single Duct

4.27.1 CAV Terminal Reheat4.27.2 VAV Cooling Only4.27 . 3 VAV Terminal Reheat, Single Maximum Airflow Setpoint4.27.4 VAV Terminal Reheat, Dual Maximum Airflow Setpoints4.27.5 Supplemental Perimeter Heating

4.28 Terminal Unit Control, Single Duct, Fan-Powered,4.28.1 Series-Configured4.28.2 Parallel-Configured

PACKAGED DX COOLING SYSTEMS5.10 Packaged/Split Air-Cooled DX Unit, CAV or VAV Single Zone System5.11 Space Temperature and Humidity Control, Single Zone Heating and Cooling

System5.13 Space Temperature and Humidity Control, Single Zone Air Source Heat

Pump System5.15 Space Temperature and Humidity Control, Single Zone Water Source Heat

Pump System5.20 Packaged/Split Air-Cooled DX Unit, VAV Multiple Zone System5.30 Packaged/Split Air-Cooled DX Unit, Outdoor Air Preconditioning System5.31 Packaged Water-to-Water Heat Pump, Outdoor Air Preconditioning System

SERVICE HOT WATER HEATING6.10 Service Hot Water Heater

SPECIAL EXHAUST SYSTEMS7.10 Type I Kitchen Hood Interface [FUTURE]7.12 Type II Kitchen Hood [FUTURE]7.13 Laboratory: Room Controls7.14 Laboratory: Fume Hood Exhaust, Variable Air Volume, Multi-Fan Manifold

AIR-TO-AIR HEAT RECOVERY8.10 Run-Around Air-to-Air Heat Recovery

LIGHTING9.10 Exterior Lighting9.13 Interior Lighting [FUTURE]

GENERAL DDC SEQUENCES

1.10 Emergency Stop Control:

The following elements shall be incorporated into sequences of operation, whether specifically defined in individual sequences of operation hereinafter or not, and shall initiate an alarm upon occurrence of any emergency stop:

[Guideline: Emergency stop control must be edited for each project…the following sequence does not address smoke purge and evacuation requirements for health care facilities.]

Application Configuration Emergency Stop RequirementsFCU/BCU/AHU supply air fan(s) and return/relief air fan(s).

Unit serves a single space and is incapable of spreading smoke beyond the space in which smoke is generated.

Duct smoke detectors not required. Emergency stop by fire alarm system shutdown relay/software interlock not required.

Unit serves multiple spaces and is capable of spreading smoke beyond

Unit airflow ≤ 2,000 cfm

No duct smoke detectors required. Emergency stop by fire alarm system shutdown relay/ software interlock not required.

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Application Configuration Emergency Stop Requirementsthe space in which smoke is generated.

Unit airflow > 2,000 cfm

Duct smoke detectors required in both unit return air and supply air. Emergency stop of all unit fans shall be initiated by auxiliary contacts of duct smoke detectors or by fire alarm system shutdown relay/software interlock.

Unit airflow > 15,000 cfm, serving 2 or more stories

Duct smoke detectors required in both unit return air and supply air. Additional smoke detector required in the return air at each story. Emergency stop of all unit fans shall be initiated by auxiliary contacts of duct smoke detectors or by fire alarm system shutdown relay/software interlock.

CAV unit with minimum outdoor airflow (no economizer cycle).

Low limit thermostat not required.

CAV or VAV unit with economizer cycle operation.

Low limit thermostat required when any coil utilizes water or steam as primary heat transfer medium. (See Sequence 4.07)

Unit with return or relief fan(s).

If a supply fan is stopped by any safety interlock, all associated supply and return/relief fan(s) shall be commanded “OFF” via software interlock.

If return/relief fan(s) is stopped by any safety interlock, the associated supply fan(s) shall be commanded “OFF” via software interlock.

Unit with supply and/or return air smoke isolation dampers.

If supply or return air smoke isolation damper fails to open upon unit start-up or closes while unit is running, as indicated by damper end switch, emergency stop shall be initiated for all system fans.

Water chiller system motors, including chiller(s), pumps(s), and cooling tower fan(s).

Indoor or outdoor water chiller(s).

Fire alarm Emergency stop of all system motors shall be initiated by fire alarm system shutdown relay/software interlock. Shut down chilled water system in reverse start sequence to avoid damage.

Indoor water chiller(s) located within a refrigeration machinery room equipped with refrigerant monitor.

Refrigerant monitor

Emergency stop of all system motors shall be initiated by software interlock. Shut down chilled water system in reverse start sequence to avoid damage. (See Sequence 3.18 for refrigeration machinery room hardwired ventilation/refrigerant purge requirements.)

Boiler system motors, including burner(s) and pump(s).

Indoor or outdoor boiler(s).

Fire alarm Emergency stop of all system motors and closing of main fuel valve(s) shall be initiated by fire alarm system shutdown relay/software interlock. Shut down boiler system in reverse start sequence to avoid damage.

Indoor boiler(s) located within a mechanical equipment room.

Emergency switch(es)

Emergency stop of all system motors and closing of main fuel valve(s) shall be initiated by manual activation of emergency switch.Shut down boiler system in reverse start sequence to avoid damage.

1.14. Schedules of Operation:

[Guideline: Two independent schedules for HVAC system operation and control are required:

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"ON/OFF" schedule(s) shall establish HVAC systems and/or equipment start/stop times, define applicable operating setpoints, and define when specific sequences of operation are to be utilized.

“ON” hour is defined as the estimated latest hour at which the HVAC system/equipment may be commanded “ON” so that setpoint conditions are maintained within the space(s) served at the “OCCUPIED” period start hour. The actual “ON” hour is adjusted by the “Optimum Start” application as specified in Section 230923.

“OFF” hour is defined as the hour at which the HVAC system/equipment shall be commanded “OFF.”

"OCCUPIED/UNOCCUPIED" schedule(s) shall determine ventilation modes.

The time period between the “ON” hour and the scheduled “OCCUPIED” period start hour may be defined as the “PRE-OCCUPANCY” period, the length of which varies based on “Optimum Start” application. By default, the period between end of the “OCCUPIED” period and the “ON” hour is defined as the “UNOCCUPIED” period.

Determine daily/weekly specific operating times and occupancy periods for each area of the facility and establish "ON/OFF" schedule for each HVAC system operation and, for air systems, the "OCCUPIED/ UNOCCUPIED" periods.

“System(s)” can be defined individually (e.g., AHU-3 or Chiller) or in groups (e.g., AHU-1 thru AHU-9 or Chillers 1 and 2).

“Hours” define the times (use 24-hour clock to avoid am/pm confusion) for each day of the week for on/off and, as applicable, occupancy start/stop (note that times outside of the occupancy period, by default, define the unoccupied period).

Enter “weeks” of the year (1-52) during which each weekly schedule applies (e.g., 1-52 for offices, etc. or 1-24 and 34-52 for schools).

Define multiple schedules as needed. For example, for the same systems there may be a “normal” schedule, but also schedules for “holidays,” “vacation periods,”, and/or one or more seasonal schedules.]

System(s) Period

Hours (1-24) Each Day of The Week Weeks to Apply (1-

52)MON TUE WED THR FRI SAT SUN

“ON” Hour for Latest System Start“OFF” Hour to Stop SystemOccupied Period Start HourOccupied Period End Hour

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1.18 Input Point Monitoring and Alarm Initiation

Digital inputs (DI or DV):

MONITOR each DI and DV point for alarm condition.

MONITOR each motor status and initiate alarms in accordance with Sequence 1.25.

Set digital point alarm condition the basis of field adjusted differential setpoints.

Where start/stop or other two-position control sequence is based on a digital input status condition or input sensed variable value(s) (AI or AV), set time delays or digital filters to prevent any equipment item or final control element from "short-cycling" in response to small changes of the sensed variable(s).

Incorporate user-adjustable time inhibit alarm(s) to prevent nuisance alarms and/or "tripping" under

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normal operation and during equipment start-up and shut-down.

For devices that have Form “C” relay contacts available for alarm monitoring, use NC contacts for the “Off” or “Normal” condition and NO contacts on “Alarm” condition.

Analog inputs (AI or AV):

Set high and/or low alarm setpoints for each point.

The following default values shall be used if alarm setpoints are not defined within a specific sequence operation or indicated on the Drawings:

Space temperature 5ºF below low setpoint of comfort zone or5ºF above high setpoint of comfort zone

Space humidity ≥70% RHAHU mixed air low limit ≤38ºFCooling coil leaving air ≥60ºFHeating coil leaving air ≤90ºFCHW supply ≥48ºFHW supply ≤120ºFLow pressure steam supply 5 psig below setpointHigh pressure steam supply 15 psig below setpoint

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1.20 Output Point Control

Set each control loop to utilize one of the following control modes:

Digital (binary) output: Two position (e.g., on-off, slow-fast)

Analog output: Proportional (P) or proportional + integral (PI) function control, as follows:

Controlled Variable Control ModeSpace Temperature PMixed Air Temperature PICoil Discharge Temperature PI (cooling), P (heating)Chilled Water Supply Temperature PIHot Water Supply Temperature PAirflow PI (with wide proportional band and fast reset rate)Fan Static Pressure (Fan Speed) PIHumidity PDewpoint Temperature POther (not listed above or indicated on the Drawings)

Consult A-E

Analog output proportional band and gain setpoints:

Set on basis of actual sensor span, zero bias, and minimum proportional bands/throttling ranges, as follows, for all analog control loops to prevent "hunting:"

Set proportional bands/throttling ranges to provide stable control around setpoints and as determined on an individual point basis based on test data provided by the TAB subcontractor.

Default deadbands/throttling ranges are as follows

Space temperature (cooling) ± 1.5°FSpace temperature (heating) ± 2.0°FSpace humidity ± 5% RHMixed/discharge air temperature ± 0.25°FCHWS/CDWS temperature ± 0.50°F

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HWS/ACWS temperature ± 2.0°FDuct/plenum static pressure ± 0.05” wgBuilding static pressure ± 0.01” wgAirflow (cfm) and water flow (gpm) ± 2% of design flowWater pressure ± 0.25 psi

Analog output integral gain setpoint:

Set to bring the measured variable to its setpoint without abrupt changes to HVAC equipment operation and, with the exception of condenser water bypass valve control, to limit every control loop output signal to a maximum rate of change of 25% per minute.

Only if this found to be impossible, may the proportional gain, as determined above, be adjusted.

Analog output derivative gain setpoint:

Derivative function for any control loop is prohibited unless reviewed by the A-E for each specific point. Set derivative gain to 0.

Setpoint reset: For air or water systems in which the sequence of operation requires temperature, pressure, etc. setpoint to be reset based on valve or damper position of the zone(s) requiring cooling or heating, the following method shall be employed:

A floating reset algorithm shall be used that increments the secondary variable (e.g., temperature, pipe or duct pressure) setpoint on a periodic basis to maintain primary variable (e.g. cooling valve, heating valve, damper position) setpoint of 85% open. The reset increment shall be calculated based on the average position of the quantity of the worst (most open valve/damper) zone(s) as specified. The recalculation time, reset increment and control device position influence shall be chosen to maintain the primary variable within the specified maximum allowable variance while minimizing overshoot and settling time.

Final control element operation:

Normally open/normally closed: Two-way final control element position in response to 0% control loop output signal. Except as otherwise specified herein or indicated on the Drawings, “OFF” or “NORMAL” position of final control elements shall be as follows:

Final Control Element Off/Normal Position Reheating coil control valve closedHeating/Preheating coil control valve openCooling coil control valve openOutside air damper closedReturn air damper openExhaust/relief air damper closed

Direct acting/response: 0% to 100% change of final control element state or position in response to 0% to 100% control loop output signal.

Reverse acting/response: 100% to 0% change of final control element state or position in response to 0% to 100% control loop output signal.

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1.21 Constant Speed Single-Phase or Polyphase Motor Control:

Motor shall be commanded “ON/OFF” via DO point.

MONITOR motor status as DI point in accordance with Sequence 1.25.

Emergency stop:

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Hard-wired contact(s) shall “STOP” motor in accordance with motor emergency stop requirements defined hereinbefore.

Initiate alarm upon emergency stop.

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1.22 Two-Speed Polyphase Motor Control:

Motor shall be commanded “ON” at low speed, commanded to switch from one speed to the other (high to low or low to high), and commanded “OFF” via two (2) DO points.

MONITOR motor status as DI point in accordance with Sequence 1.25. Emergency stop:

Hard-wired contact(s) shall “STOP” motor in accordance with motor emergency stop requirements defined by Sequence 1.10.

Initiate alarm upon emergency stop.Back to Top

1.23 Variable Speed Single-Phase Motor Control:

Provide interface between DDC system and manufacturer-provided electronically commutated motor (ECM) integral speed controller.

Command motor “ON/OFF” via DO point.

MONITOR motor status as DI point in accordance with Sequence 1.25.

Emergency stop:



Modulate motor speed from minimum speed to 100% speed in direct response to AO point.

Adjust minimum speed setpoint to value, as reviewed by A-E, using the following procedure:

Manually set ECM controller minimum speed output to 6 Hz (10% of maximum) unless (1) dictated otherwise by the equipment manufacturer or (2) defined otherwise by sequence(s) of operation.

Observe driven equipment to ensure that it is visibly rotating.

If not, increase controller minimum speed output in increments of 2 Hz until the unit driven equipment is visibly rotating.

Ensure that the current sensing relay required by Sequence 1.25 confirms operation at the minimum speed setting.

Initiate alarm via DI point if ECM controller status/fault contact closes.

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1.24 Variable Speed Polyphase Motor Control:

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Provide interface between DDC system and manufacturer-provided variable frequency drive (VFD) for motor speed control.

Command motor “ON/OFF” via DO point.

MONITOR motor status in accordance with Sequence 1.25.

Emergency stop:



Modulate motor speed from minimum speed to maximum speed in direct response to AO point.

Set minimum speed setpoint to value, as reviewed by A-E, using the following procedure:

Manually set VFD minimum speed output to 6 Hz (10% of maximum) unless (1) dictated otherwise by the equipment manufacturer or (2) defined otherwise by sequence(s) of operation herein defined.

Observe driven equipment to ensure that it is visibly rotating. If not, increase controller minimum speed output in increments of 2 Hz until the unit driven equipment is visibly rotating.

Ensure that the current sensing relay required by Sequence 1.25 confirms operation at the minimum speed setting.

Set maximum speed setpoint to value determined during TAB operations in order to obtain design flow.

MONITOR motor speed feedback from VFD via AI point.

Initiate alarm via DI point if VFD status/fault contact closes.

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1.25 Single-Phase and Polyphase Motor Status Monitoring:

Motor "ON" or "OFF" status shall be determined via DI point contact closure by current monitoring relay as illustrated above.

Adjust current monitoring relay “trip” setpoint to 5% above the minimum operating motor amperage.

For variable speed motors, coordinate “trip” setpoint with minimum motor speed.

Monitor motor status anytime motor has been commanded “ON.”

Inhibit motor status monitoring for the first 10 seconds after motor is commanded “ON.”

If motor status DI point indicates motor failure:

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For single pump or fan configurations, command motor “OFF,” terminate associated start sequence, and initiate pump/fan failure alarm.

For dual pumps or fans operating in lead/standby configuration in accordance with Sequence 1.26.2, command operating pump/fan “OFF,” command standby pump/fan “ON,” and initiate pump/fan failure alarm.

If standby pump/fan motor status DI point indicates motor failure, terminate associated start sequence and initiate pump/fan failure alarm.

For multiple pumps or fans operating in parallel lead/lag/cascade configuration in accordance with Sequence 1.26.1, command failed pump/fan “OFF,” initiate pump/fan failure alarm, and continue associated start sequence with remaining pump(s)/fan(s) in operation.

If two or more motor status DI points indicate motor failure, command all motors “OFF,” terminate associated start sequence, and initiate pump/fan failure alarm.

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[Guideline: This sequence is required for HVAC components such as fans, pumps, chillers, etc. that operate in parallel and must be staged on and off as function of imposed load.]

1.26.1 Lead/Lag/Cascade Sequencing of Parallel-Configured Components:

DDC system shall incorporate “Lead/Lag” sequence as part of any sequence of operation requiring sequential “ON/OFF” staging and cascading of multiple HVAC components designed to operate in parallel, as follows:

Designate HVAC each component as “Lead” in the reverse order of its number of operational hours.

Designate HVAC each component as “Lag” in the direct order of its number of operational hours.

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[Guideline: The following sequence is required for HVAC components such as fans, pumps, chillers, etc. that operate in alternatively, i.e., one or more is always “OFF” in standby mode.]

1.26.2 Lead/Standby Sequencing of Alternating Components: DDC system shall incorporate “Lead/Standby” sequence as part of any sequence of operation requiring the “ON/OFF” alternating use of two or more HVAC components, as follows:

Designate HVAC components as “Lead/Standby” on a weekly schedule to equalize operational hours of each HVAC component.

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1.27 Exhaust Fan Start/Stop: Exhaust fan start/stop control methods shall be as indicated on the Drawings, in accordance with the following:

[Guideline: Ensure that fan schedule(s) on the Drawings indicate the required type of start/stop control for each exhaust fan.]

IndicatedControl Method Exhaust Fan Start/Stop Control Method

DDCStart/stop exhaust fan(s) in accordance with(1) associated air-handling system “OCCUPIED/UNOCCUPIED” schedule or (2) operator command in compliance with Sequence 1.21.

Independent Thermostat

Start/stop exhaust fan(s) based on stand-alone, wall-mounted line-voltage thermostat; no DDC connection required. On a rise in space temperature to above setpoint, exhaust fan shall be energized to maintain space temperature at setpoint. See control schematic below.

Manual Start/stop exhaust fan(s) via manual switches or breakers. See Division 26 Drawings, as applicable.

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1.30 Outdoor Piping/Equipment Trace Heating Cable: On a fall in liquid temperature to below setpoint, trace heating cable, where indicated on the Drawings, shall be energized by pipe surface mounted line voltage thermostat ("aquastat") to maintain liquid temperature at setpoint.

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1.33 Final Control Element Operators (Valves and Dampers):

Two-position control operator shall “OPEN” or “CLOSE” final control element (valve/damper), as indicated on the Drawings, in direct response to DO point.

MONITOR final control element position as DI point equal to the DO point.

Final control element position shall be confirmed by visual inspection during the calibration and verification procedures required by Section 230923.

Modulating control operator shall modulate 0% to 100% from its Normal state, as indicated on the Drawings, in direct response to AO point.

MONITOR final control element position as AI point whose value (percent) is equal to the AO point value (percent).

Final control element position shall be confirmed as equal to the AO point value (percent) during the calibration and verification procedures required by Section 230923.

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1.39 Electric Resistance Heating Coil Control:

[Guideline: Select one or both of the following based on the type(s) of heating coil control utilized for the project.]

Mechanical Relay/Contactor Control: Energize each circuit (“stage”) of heating capacity, as scheduled on the Drawings, via DO point(s) in accordance with indicated sequence of operation.

Silicon Control Rectifier (SCR) Control: Interface with SCR type controller via AO point to modulate heating capacity, as scheduled on the Drawings, from 0% to 100% in accordance with indicated sequence of operation.

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SITE CONDITIONS AND UTILITIES

2.01 Outdoor Air Conditions:

[Guideline: On the Drawings, locate sensors to monitor ambient (outdoor) air conditions on a north-facing wall of the building, sheltered from both direct sunlight and prevailing wind(s).]

MONITOR ambient outdoor air conditions as AI points:

DB Temperature (ºF)RH (%)

Compute enthalpy (Btu/Lbm) as AV point as a function of monitored DB and RH.

Compute DPT (ºF) as AV point as a function of monitored DB and RH.

Compute WB temperature (ºF) as AV point as a function of monitored DB and RH.

AI and AV point values shall serve as global inputs to any sequence of operation requiring an ambient outdoor air condition as a control or computational variable.

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2.03 Cooler/Freezer Temperature Alarm:

MONITOR and display cooler or freezer temperature, as indicated on the Drawings, as AI point.

Initiate high temperature alarm if cooler or freezer temperature rises above high limit temperature setpoint.

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2.04 Sump Pump High Later Level:

MONITOR and display status of sump pump high water level alarm dry contact provided by pump manufacturer as DI point, as indicated on the Drawings.

Initiate high water level alarm when contact closes.

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2.07 Utilities Consumption:

MONITOR facility primary utilities consumption where indicated on the Drawings:

Electricity:

Provide utility electrical power voltage monitor (three phase where applicable) for each building or indicated area of each building to determine availability of utility power status as DI.

In absence of utility power in any phase, command all equipment/components "OFF" within 7 seconds.

If utility power is recovered within 5 seconds, command all equipment/components "ON" as defined by each system/component sequence of operation.

When utility power has been restored after a period exceeding 7 seconds, all affected equipment/components shall be automatically commanded “ON” in sequence at 5 second intervals.

Coordinate with electric utility to utilize one of the following methods for monitoring electrical energy via AI point for consumption computation(s):

Pulse output provided from utility metering.

Contractor-installed current and voltage transformers.

[Guideline: For projects that include an emergency/essential power system that supports HVAC component operation, include the following requirements. Coordinate with Division 26 design.] MONITOR emergency/essential power system status as DI point to determine when emergency/essential power is available.

When emergency/essential power is indicated to be available, command all equipment/components served by emergency/essential power "ON," as defined by each system/component sequence of operation.

When utility power is restored, command equipment/components “ON” as follows:

Equipment/components operating on emergency/essential power shall continue to operate as electrical service automatically transitions to utility power.

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Command equipment/components served only by utility power "ON" in accordance with each system/ component sequence of operation defined in this Section.

Fuel Gas: Coordinate with natural gas utility or propane supplier, as applicable, to utilize one of the following methods for monitoring fuel gas consumption via AI point and consumption computation(s):


Contractor-installed fuel gas flow meter.

Fuel Oil: Provide contractor-installed fuel oil flow meter to provide AI point and consumption computation(s). Water: Coordinate with water utility to utilize one of the following methods for monitoring facility water consumption to provide AI point and consumption computation(s):


Contractor-installed water flow meter.

Chilled Water: Provide contractor-installed hydronic Btu metering station to provide AI point for consumption computation(s).

Heating Hot Water: Provide contractor-installed hydronic Btu metering station to provide AI point for consumption computation(s).

Steam: Provide contractor-installed steam flow meter to provide AI point for consumption computation(s).

Condensate: Provide contractor-installed condensate flow meter to provide AI point for consumption computation(s).

Where indicated on the Drawings and/or as follows, provide contractor-installed sub-metering of specific utilities:

Electricity: Current and voltage transformers to provide AI point for consumption computation(s).

Fuel gas: Fuel gas flow meter to provide AI point for consumption computation(s).

Water: Water flow meter(s) to provide AI point for consumption computation(s) at the following locations:

Cooling tower(s) make-up water connection(s).

Steam system make-up water connection(s). [Guideline: Chilled and hot water systems are closed systems rarely need make-up water, so the following two points may be eliminated unless required by the Owner.] Chilled water system make-up water connection(s).

Hot water system make-up water connection(s).

Chilled Water: Hydronic Btu metering station to provide AI point for consumption computation(s).

Heating Hot Water: Hydronic Btu metering station to provide AI point for consumption computation(s).

Steam: Steam flow meter to provide AI point for consumption computation(s).

Condensate: Condensate flow meter to provide AI point for consumption computation(s).

Archive monitored data every 15 minutes, along with computed hourly, daily, and monthly consumption totals.

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CENTRAL PLANTS

3.1 CHILLED WATER SYSTEMS

[Guideline: A chilled water system consists of one or more water chillers, associated pumps, and, for evaporatively- cooled systems, associated condenser water system(s). The elements and control sequences for each chilled water system will vary based on the number of chillers and the chilled water distribution piping configuration. However, each chiller will include an OEM controller provided by the chiller manufacturer that must be interfaced with DDC system. The scope of control provide by the OEM controller and the interface requirements are defined by this sequence, but the designer is cautioned that careful analysis of the OEM BACnet “Protocol Interface Compliance Statement” (PICS) is required to ensure that the required control sequence for the chiller is integrated correctly. ]

3.11.1 Chiller Controller Interface: PRIMARY CHILLER CONTROL IS PROVIDED BY OEM CONTROLLER INTERFACED WITH DDC SYSTEM.

Chiller leaving chilled water temperature shall be controlled by OEM controller, based on CHWS temperature setpoint defined via AO point.

MONITOR the following chiller operation/status points via the OEM controller:

Chiller operating hours (AV point)

Evaporator refrigerant temperature (AI point)

Condenser refrigerant temperature (AI point)

Percent (%) rated load amps (AI point)

Minimum CHWS flow status (DI point)

Minimum CDWS flow status (DI point)

Low Load Shutdown Status (Di point)

Chiller status/fault alarm (DI point)

Initiate alarm via DI point if chiller controller status/fault alarm is issued by OEM controller.

Evaporator water temperature (AI point) (air-cooled chillers only).

Initiate alarm via DI point if evaporator water temperature falls below 40ºF.

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3.11.2 Chilled Water System Enable/Start/Stop:

“ENABLE” system via DO point upon operator command [and/or when the outdoor air temperature is greater than ______ F].

When ”ENABLED,” chilled water system shall:

Start if [Enter number or percentage of AHUs listed below that will “trigger” the chilled water system starting] of the following AHU/BCU/FCUs initiate a “REQUEST FOR COOLING” in accordance with Sequence 4.01:

Stop if OEM controller cycles chiller off, as indicated by DI or DV point provided by OEM controller, for at least 40 minutes.

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Chiller(s) shall be commanded “ON/OFF” via DO point in accordance with Sequence 3.12.1, 3.12.2, 3.12.3, 3.14.1, or 3.14.2, as applicable.

Hard-wired safety interlocks shall be incorporated through OEM controller, as follows:

Chilled water pump starter(s)/VFD(s) NO auxiliary contact(s).

Chilled water NO flow sensor.

Condenser water pump starter(s)/VFD(s) NO auxiliary contact(s) (as applicable).

Condenser water NO flow sensor (as applicable).

3.12.1 Chilled Water System, Single Chiller, Primary Constant Flow:

[Guideline: This chilled water system consists of a single chiller, air-cooled or water-cooled, with a constant chilled water flow rate. This configuration is recommended only for small system applications were three-way control valves must be used for temperature control at AHUs, heat exchangers, etc. served.]

Chilled water system start sequence shall be as follows:

Command chilled water pump(s) "ON" via DO point(s) in accordance with Sequence 1.21.

Confirm each pump operation based on pump status via DI point in accordance with Sequence 1.25.

Confirm chilled water flow via differential pressure flow switch via DI point.

For a water-cooled chiller, command condenser water system “ON” via DO point in accordance with Sequence 3.15.

Command chiller "ON" via DO point through interface with OEM controller in accordance with Sequence 3.11.

If chiller OEM controller indicates chiller fault via DI point, command chiller, chilled water pump(s), and, as applicable, condenser water system "OFF" via DO points and initiate alarm.

If chiller fails to start within 3 minutes after being commanded "ON", command chiller, chilled water pump(s), and, as applicable, condenser water system "OFF" via DO points and initiate alarm.

Upon resumption of power after a power outage, chiller shall restart in accordance with sequence above, after 3 minutes time delay.

CHWS temperature control:

MONITOR CHWS temperature as AI point.

MONITOR CHWR temperature as AI point.

Compute CHWS temperature setpoint as a linear function of outdoor air temperature, as follows, and set chiller OEM controller via AO point to maintain leaving water temperature at setpoint:

Outdoor Air Temperature

CHWSTemperature Setpoint

≤ 60ºF Chiller design leaving water temperature plus 5ºF≥ 70ºF Chiller design leaving water temperature

Reset CHWS temperature setpoint input to OEM controller via AO point as follows:

Every 15 minutes, evaluate all space temperatures and all chilled water control valves' positions to identify potential under-cooling.

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If any space temperature exceeds its maximum comfort zone temperature setpoint, as defined by Sequence 4.01, while the associated chilled water control valve is more than 95% open, decrease CHWS temperature setpoint 0.5ºF every 15 minutes until all space temperatures are at or below their maximum comfort zone temperature setpoint.

Every 15 minutes, evaluate all space humidity conditions and chilled water control valves' positions to identify potential inadequate dehumidification.

If any space humidity exceeds its high limit setpoint, as defined by Sequence 4.01, while the associated chilled water control valve is more than 95% open, decrease CHWS temperature setpoint 0.5ºF every 15 minutes until all space humidity conditions are at or below its high limit humidity setpoint.

Chilled water pump(s) shall continue to run for 1 minute after chiller is commanded “OFF” or is cycled “OFF” by OEM controller when imposed cooling load falls below minimum cooling load requirement for the chiller.

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3.12.2 Chilled Water System, Single Chiller, Primary-Secondary Variable Flow:

[Guideline: This chilled water system consists of a single chiller, air-cooled or water-cooled, with a variable chilled water flow rate. Two water “loops” are included: a primary loop that maintains a constant, low head flow through the chiller and a secondary loop that distributes variable flow to the imposed loads. The secondary flow rate is controlled on the basis of maintaining a constant differential temperature (“range”) in the secondary loop. This configuration is recommended only for small system applications were two-way control valves can be used for temperature control at AHUs, heat exchangers, etc. served.]


Command secondary chilled water pump(s) "ON" via DO point(s) in accordance with Sequence 1.21.

Confirm each pump operation based on pump status via DI point in accordance with Sequence 1.25.

Confirm secondary chilled water flow via differential pressure flow sensor via DI point.

Command primary chilled water pump(s) "ON" via DO point(s) in accordance with Sequence 1.21.

Confirm each pump operation based on motor status via DI point in accordance with Sequence 1.25.

Confirm primary chilled water flow via differential pressure flow sensor via DI point.

For a water-cooled chiller, command condenser water system “ON” via DO point in accordance with Sequence 3.15.

Command chiller "ON" through OEM controller via DO point in accordance with Sequence 3.11.

If OEM controller indicates chiller fault via DI point, command chiller, chilled water pump(s), and, as applicable, condenser water system "OFF" via DO points and initiate alarm.

If chiller fails to start within 3 minutes after being commanded "ON", command chiller, chilled water pump(s), and, as applicable, condenser water system "OFF" via DO points and initiate alarm.

Upon resumption of power after a power outage, chiller shall restart in accordance with sequence above, after 3 minutes time delay.

Primary CHWS temperature control:


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MONITOR CHWR temperature as AI point.





Reset CHWS temperature setpoint input to OEM controller via AO point as follows:

Every 15 minutes, evaluate all space temperatures and chilled water control valves' positions to identify potential under-cooling.

If any space temperature exceeds its maximum comfort zone temperature setpoint while the associated chilled water control valve is more than 95% open, decrease CHWS temperature setpoint 0.5ºF every 15 minutes until all space temperatures are at or below their maximum comfort zone temperature setpoint.


If any space humidity exceeds its high limit setpoint while the associated chilled water control valve is more than 95% open, decrease CHWS temperature setpoint 0.5ºF every 15 minutes until all space humidity conditions are at or below its high limit humidity setpoint.

Primary chilled water pump(s) shall continue to run for 1 minute after chiller is cycled “OFF” by OEM controller when imposed cooling load falls below minimum cooling load requirement for chiller.

Secondary CHWS temperature/flow control:

MONITOR secondary CHWS temperature as AI point.

MONITOR secondary CHWR temperature as AI point.

MONITOR differential pressure as AI point(s) at locations(s) indicated on the Drawings.

During TAB of secondary chilled water distribution, set differential pressure setpoint(s) to value(s) recommended by TAB subcontractor, as reviewed by A-E.

Set secondary CHWS temperature setpoint to equal primary CHWS temperature setpoint.

Set secondary CHWR temperature setpoint as secondary CHWS temperature setpoint plus chilled water system design temperature rise.

Modulate secondary chilled water pump(s) speed via AO point(s) interfaced with VFD(s), in accordance with Sequence 1.24, to maintain secondary CHWR temperature at setpoint.

If any differential pressure AI point falls below setpoint, increase secondary chilled water pump(s) speed to maintain differential pressure(s) at setpoint.

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3.12.3 Chilled Water System, Single Chiller, Primary Variable Flow:

[Guideline: This chilled water system consists of a single chiller, air-cooled or water-cooled, with a variable chilled water flow rate. This control sequence is based on a chiller being equipped with a high quality flow meter for determining chilled water flow rate for control of the bypass valve and primary pump speed to maintain minimum flow as required by the manufacturer. To reduce costs, a high quality differential pressure sensor across the evaporator

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may be used to indicate flow rate. However, without careful field testing and calibration, this method is typically less accurate since (1) differential pressure varies as the square of flow and (2) flow vs. pressure drop data provided by chiller manufacturers is often inaccurate.

There are several issues related to variable primary flow chilled water systems before making the decision to apply this configuration for a project:

Basic operating criteria for this system include the following:

1. Flow through chiller must be maintained in the range of 3 to 11 pfs. Consequently a good quality flow meter, which must have periodic recalibration, are required.

2. If flow rates through the chiller change too rapidly, the chiller controls cannot keep up. Therefore load fluctuations must be limited to not more that 25-30% per minute.

Chapter 3 of the 2016 ASHRAE Handbook – HVAC Systems and Equipment states that the designer should avoid this configuration where there are poor controls or limited operator training (implying that this is never the first choice for new systems unless the Owner already has experience with other existing systems of this configuration)

The simpler primary-secondary system configuration remains the recommended approach for the majority of multiple chiller systems. This recommendation was borne out by a December 2010 report in HPAC Engineering wherein the authors performed a study of primary-secondary systems vs. variable primary flow systems, finding that the energy savings from primary flow systems, overall, was essentially non-existent and that primary-secondary systems "…have the advantage of more accurate, flexible, and stable control and operational conditions."]


Command primary chilled water pump(s) "ON" at minimum speed via DO point(s) in accordance with Sequence 1.21.

Confirm each pump’s operation based on motor status via DI point in accordance with Sequence 1.25.

Confirm chilled water flow via differential pressure flow sensor via AI point.

If differential pressure flow sensor indicates flow failure, terminate start sequence and initiate alarm.

Increase pump(s) speed via AO point to maintain minimum required flow rate through chiller as indicated by flow meter AI point.

For water-cooled chiller, command condenser water system “ON” via DO point in accordance with Sequence 3.16.

Confirm condenser water flow via differential pressure flow sensor.


Command chiller "ON" through interface with chiller OEM controller in accordance with Sequence 3.11.

MONITOR chiller status/fault.

If OEM controller indicates a chiller fault via DI point, command chiller and primary chilled water pump(s) "OFF" via DO points and initiate alarm.

If chiller fails to start within 3 minutes after being commanded "ON", command chiller and primary chilled water pump(s) "OFF" via DO points and initiate alarm.

Upon resumption of power after a power outage, chiller shall restart, if commanded "ON", after 3 minutes time delay.

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CHWS temperature and flow control:


MONITOR CWHR temperature as AI point.

Chiller CHWS temperature setpoint shall be controlled as follows:





Reset CHWS temperature setpoint through OEM controller via AO point as follows:





Leaving water temperature for each chiller shall be maintained via chiller controller at primary CHWS temperature setpoint input by AO point in accordance with Sequence 3.11.

Modulate primary chilled water pump(s) speed through VFD via AO point at a rate not faster than 25% per minute to maintain the chilled water temperature range (CHWR temperature minus CHWS temperature) at setpoint.

MONITOR differential pressure(s) as AI point(s) as indicated on the Drawings.

During TAB of chilled water distribution, adjust differential pressure setpoint(s) to value(s) recommended by TAB subcontractor, as reviewed by A-E.

If any differential pressure AI point falls below setpoint, increase chilled water pump(s) speed to maintain differential pressure(s) at setpoint.

If chilled water flow through chiller falls below the minimum flow required by the chiller manufacturer, as evidenced by the chiller flow meter AI point, modulate the NC bypass valve “OPEN” and increase chilled water pump(s) speed to maintain minimum flow rate at setpoint.

Primary chilled water pump(s) shall continue to run for 1 minute after chiller is commanded “OFF” or is cycled “OFF” by OEM controller.

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3.14.1 Chilled Water System, Multiple Chillers, Primary-Secondary Variable Flow:

[Guideline: This chilled water system consists of a two or more chillers, air-cooled or water-cooled. Two water “loops” are included: a primary loop that maintains a constant, low head flow through each chiller and a secondary loop that

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distributes variable flow to the imposed loads. The secondary flow rate is controlled on the basis of maintaining a constant differential temperature (“range”) in the secondary loop.]


Command secondary chilled water pump(s) "ON" via DO point(s) in accordance with Sequence 1.21.


Confirm secondary chilled water flow via differential pressure flow sensor via DI point.


For water-cooled chillers, command condenser water system “ON” via DO point in accordance with Sequence 3.16.

Primary flow vs. secondary water flow control as hereinafter specified is illustrated by with the following graphic:

Secondary CHWS temperature/flow control:

MONITOR secondary CHWS temperature as AI point.

MONITOR secondary CHWR temperature as AI point.

MONITOR differential pressure(s) at each location indicated on the Drawings as AI point(s).

Set secondary CHWS temperature setpoint to equal primary CHWS temperature setpoint defined below.

Compute secondary CHWR temperature setpoint as CHWS temperature setpoint plus chilled water system design temperature range.

Modulate secondary chilled water pump(s) speed via AO point through interface with VFD(s) in accordance with Sequence 1.24 to maintain secondary CHWR temperature at setpoint.

If any differential pressure AI point falls below setpoint, increase secondary chilled water pump(s) speed to maintain differential pressure(s) at setpoint.

During TAB of secondary chilled water distribution, adjust differential pressure setpoint(s) to value(s) recommended by TAB subcontractor, as reviewed by A-E.

Primary CHWS temperature/flow control:

MONITOR primary CHWR temperature as AI point.

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Start/stop each chiller in sequence to maintain primary CHWR temperature at or below secondary CHWR temperature setpoint, as follows:

If primary CHWR temperature is above secondary CHWR temperature setpoint for 30 minutes, command a chiller "ON" through OEM controller via DO point in accordance with Sequence 3.11.

Compute "temperature rise per chiller" as design secondary chilled water temperature rise divided by the number of chillers commanded "ON".

If primary CHWR temperature is below secondary CHWR temperature setpoint minus computed temperature rise per chiller for 30 minutes, command a chiller "OFF" through OEM controller via DO point.

Rotate chiller “ON/OFF” sequence to equalize runtime between chillers.

Chiller start sequence shall be as follows:

Command primary chilled water pump(s) "ON" via DO point in accordance with Sequence 1.21.

Confirm pump operation based on motor status as DI point in accordance with Sequence 1.25.


If differential pressure flow sensor indicates flow failure, terminate start sequence, close chiller isolation valve(s), initiate alarm, and initiate starting of next chiller in the sequence.

Command chiller "ON" via DO point through interface with chiller OEM controller in accordance with Sequence 3.11.

MONITOR chiller status/fault as DI point.

If OEM controller indicates a chiller fault, command chiller and primary chilled water pump(s) "OFF" via DO points, close chiller isolation valve(s), initiate alarm, and initiate starting of next chiller in the sequence.

If chiller fails to start within 3 minutes after being commanded "ON", command chiller and primary chilled water pump(s) "OFF" via DO points, close chiller isolation valve(s), initiate alarm, and initiate starting of next chiller in the sequence.


Each chiller's CHWS temperature setpoint shall be controlled as follows:





Reset CHWS temperature setpoint through chiller OEM controller via AO point as follows:


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MONITOR chiller entering water temperature as AI point.

MONITOR chiller's leaving water temperature as AI point.

Leaving water temperature for each chiller shall be maintained via chiller OEM controller at primary CHWS temperature setpoint input by AO point in accordance with Sequence 3.11.

Primary chilled water pump(s) shall continue to run for 1 minute after chiller is cycled “OFF” by OEM controller when imposed cooling load falls below minimum cooling load requirement for chiller.

Rotate chillers “ON/OFF” in accordance with Sequence 1.26.1.

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3.14.2 Chilled Water System, Multiple Chillers, Primary Variable Flow:

[Guideline: This sequence is based on two or more water chillers piped in parallel on a common “primary” chilled water loop, each equipped with a high quality flow meter for determining individual chiller rates for control of the bypass valve and primary pump speed to maintain minimum. To reduce costs, a high quality differential pressure sensor across the evaporator or each chiller may be used to indicate flow rate. However, without careful field testing and calibration, this method is typically less accurate since (1) differential pressure varies as the square of flow and (2) flow vs. pressure drop data provided by chiller manufacturers is often inaccurate.

There are several issues related to variable primary flow chilled water systems before making the decision to apply this configuration for a project:

Basic operating criteria for this system include the following:

1. Flow through each chiller must be maintained in the range of 3 to 11 fps. Consequently a good quality flow meter, which must have periodic recalibration, is required for each chiller.

2. If flow rates through the chiller change too rapidly, the chiller controls cannot keep up. Therefore load fluctuations must be limited to not more that 25-30% per minute.

As recommended in the Design Guidelines, for large systems with high flow rates and long distribution piping runs, the additional savings in pumping energy produced by this configuration may be advantageous. But, it is a much more complex system and has operating limitations. Chapter 3 of the 2016 ASHRAE Handbook – HVAC Systems and Equipment states that the designer should avoid this configuration where there are poor controls or limited operator training (implying that this is never the first choice for new systems unless the Owner already has experience with other existing systems of this configuration).

The simpler primary-secondary system configuration remains the recommended approach for the majority of multiple chiller systems. This recommendation was borne out by a December 2010 report in HPAC Engineering wherein the authors performed a study of primary-secondary systems vs. variable primary flow systems, finding that

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the energy savings from primary flow systems, overall, was essentially non-existent and that primary-secondary systems "…have the advantage of more accurate, flexible, and stable control and operational conditions."]


Modulate chilled water (and, for water-cooled chillers, condenser water) isolation valve “OPEN” for “Lead” chiller.

Monitor chilled water flow meter to for “Lead” chiller.

Command primary chilled water pump(s) "ON" at minimum speed via DO point(s) in accordance with Sequence 1.21.

Confirm each pump(s) operation based on motor status as DI point in accordance with Sequence 1.25.


If differential pressure flow sensor indicates flow failure, terminate start sequence, close chiller isolation valve(s), and initiate alarm.

Increase pump(s) speed via AO point to maintain minimum required flow rate through “Lead” chiller as indicated by flow meter AI point.

For water-cooled chiller, command condenser water system “ON” via DO point in accordance with Sequence 3.16.


Confirm condenser water flow via differential pressure flow sensor.

If condenser water pump status input or differential pressure flow sensor indicates flow failure, terminate start sequence, initiate alarm, and initiate starting of “Lag” pump in the sequence.

Command “Lead” chiller "ON" through interface with chiller OEM controller in accordance with Sequence 3.11.

MONITOR “Lead” chiller status/fault via DI point.

If OEM controller indicates a chiller fault, command chiller "OFF" via DO points, close chiller isolation valve(s), initiate alarm, and initiate starting of next chiller in the sequence.

If chiller fails to start within 3 minutes after being commanded "ON", command chiller and primary chilled water pump(s) "OFF" via DO points, close chiller isolation valve(s), initiate alarm, and initiate starting of next chiller in the sequence.


CHWS temperature and flow control:

MONITOR CHWS temperature at each chiller as AI point.

MONITOR common CHWS temperature as AI point

MONITOR common CHWR temperature as AI point

Each chiller's CHWS temperature setpoint shall be controlled as follows:


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Reset CHWS temperature setpoint through chiller OEM controller via AO point as follows:





Leaving water temperature for each chiller shall be maintained via chiller controller at primary CHWS temperature setpoint input by AO point in accordance with Sequence 3.11.

Modulate primary chilled water pump(s) speed via AO point at a rate not faster than 25% per minute to maintain the common chilled water temperature range (CHWR temperature minus CHWS temperature) at setpoint

MONITOR differential pressure(s) as AI point(s) as indicated on the Drawings.

During TAB of chilled water distribution, adjust differential pressure setpoint(s) to value(s) recommended by TAB subcontractor, as reviewed by A-E.

If any differential pressure AI point falls below setpoint, increase chilled water pump(s) speed to maintain differential pressure(s) at setpoint.

If chilled water flow through any operating chiller falls below the minimum flow required by the chiller manufacturer, as evidenced by the individual chiller flow meters AI points, modulate the NC bypass valve “Open” and increase chilled water pump(s) speed to maintain minimum flow rate(s) at setpoint.

Start/stop each chiller via DO point through chiller OEM controller, in sequence, as follows:

For each operating chiller, compute chiller percent running load amps (%RLA) as [actual RLA] / [design (scheduled) RLA].

Set %RLA high limit setpoint to 95%.

Set %RLA low limit setpoint to 15% when only one chiller is operating or to 45% when multiple chillers are operating.

If the “Lead” chiller’s %RLA exceeds the high limit setpoint for 30 minutes, command a “Lag” chiller "ON" in accordance with “Lead” chiller start sequence defined above.

“Lag” chiller’s chilled water isolation valve shall be modulated “Open” at a rate not faster than 25% per minute prior to commanding “Lag” chiller “ON.”

[Guideline: Delete the following two sentences for systems with only two chillers.]

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If each operating chiller’s %RLA exceeds the high limit setpoint for 30 minutes, command a “Lag” chiller "ON."

“Lag” chiller’s chilled water isolation valve shall be modulated “Open” at a rate not faster than 25% per minute prior to commanding “Lag” chiller “ON.”

If all operating chillers’ %RLA falls to or below the low limit setpoint for 30 minutes, command a “Lag” chiller "OFF."

“Lag” chiller’s chilled water isolation valve shall be modulated “Closed” at a rate not faster than 25% per minute after commanding “Lag” chiller “OFF.”

Primary chilled water pump(s) shall continue to run for 1 minute after last operating chiller is commanded “OFF” or is cycled “OFF” by its OEM controller.

Rotate chillers “ON/OFF” in accordance with Sequence 1.26.1.

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3.15 Condenser Water System, Dedicated Cooling Tower:

[Guideline: This sequence is required for condenser water distribution with one cooling tower dedicated to serving one chiller, typical of a single chiller system. If multiple chillers and cooling towers are utilized, Sequence 3.16 is recommended…it is far more energy efficient.]

“ENABLE” condenser water system when associated chiller is commanded "ON".

[Guideline: If condenser water bypass is piped directly to the tower basin, include the following. If condenser water bypass is piped to the condenser water pump suction, delete the following.]

If the average outdoor air temperature has been less than 60°F over the preceding “OFF” period, modulate bypass control valve to 100% bypass position (i.e., no flow to tower) via AO point prior to commanding chiller “ON.”

Condenser water system start/stop and flow control:

Command condenser water pump(s) "ON" via DO point(s) in accordance with Sequence 1.21.

Confirm pump(s) operation based on motor status via DI point in accordance with Sequence 1.25.

Confirm condenser water flow via differential pressure switch via DI point.

Condenser water temperature control:

MONITOR condenser water return temperature as AI point.

MONITOR condenser water supply temperature as AI point.

Maintain condenser water supply temperature at 75ºF setpoint as follows:

[Guideline: Large 3-way control valves are formed by mounting two 2-way butterfly valves on a piping tee. Butterfly valves have equal percentage flow characteristics and work well when used to control flow through coils and heat exchangers. However, when coupled-together to form a 3-way condenser water bypass control valve, individual valve operators are required for each of the two butterfly valves so the two valves can be modulated independently to overcome the non-linearity, percent flow vs. percent open, for each valve.]

If condenser water bypass valve has been modulated to 100% bypass upon chiller start-up, on a rise of condenser water supply temperature above setpoint, modulate bypass control valve operators via AO points in sequence to divert condenser water flow through the cooling tower, while maintaining constant condenser water flow rate, as follows:

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Percent (%) OpenTo Cooling Tower (NO) To Bypass (NC)

100 080 8560 9040 9320 960 100

[Guideline: Select/edit the cooling tower fan control sequence for the project from the following three options.]

Single Speed Cooling Tower Fan Motor Control Sequence: On a continued rise of condenser water supply temperature above setpoint, command cooling tower fan "ON" via DO point in accordance with Sequence 1.21.

Confirm fan operation based on motor status via DI point in accordance with Sequence 1.25.

Two-Speed Cooling Tower Fan Motor Control Sequence:

On a continued rise of condenser water supply temperature to above setpoint, command cooling tower fan "ON" at low speed via DO point in accordance with Sequence 1.22.


On a continued rise of condenser water supply temperature to above setpoint, command cooling tower fan "ON" at high speed via DO point in accordance with Sequence 1.22.

Variable Speed Cooling Tower Fan Motor Control Sequence:

On a continued rise of condenser water supply temperature above setpoint, command cooling tower fan "ON" at minimum speed through VFD via DO point, in accordance with Sequence 1.24.


On a continued rise of condenser water supply temperature to above setpoint, modulate fan speed from minimum to maximum through VFD via AO point in accordance with Sequence 1.24.

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3.16 Condenser Water System, Multiple Cooling Towers:

[Guideline: Condenser water distribution is based on a common loop configuration that allows any cooling tower to serve any chiller condenser. Each chiller condenser and cooling tower is isolated by two-way, two-position control valves. Equalizer piping maintains water level at same level in all cooling towers. Condenser water bypass control valve enables "cold starting" of a chiller. This configuration allows use of as many cooling towers as possible under any load condition so as to minimize the CDWS temperature and improve chiller efficiency.]

ENABLE condenser water system when first chiller is commanded "ON".

[Guideline: If condenser water bypass is piped directly to the tower basin, include the following. If condenser water bypass is piped to the condenser water pump suction, delete the following.]

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If the average outdoor air temperature has been less than 60°F over the preceding “OFF” period, modulate bypass control valve to 100% bypass position (i.e., no flow to tower) via AO point prior to enabling chiller to start.

Condenser water system start/stop and flow control:

Command variable speed condenser water pump(s) "ON" at minimum speed through VFD(s) via DO point in accordance with Sequence 1.24.

Confirm pumps operation based on motor status via DI point in accordance with Sequence 1.25.

Confirm condenser water flow via differential pressure sensor via DI point.

Modulate pump(s) speed through VFD(s) via AO point in accordance with Sequence 1.24 to provide flow equivalent to percentage of total number of chillers commanded "ON."

Condenser water temperature control:

MONITOR condenser water return temperature as AI point.

MONITOR condenser water supply temperature as AI point.

Maintain condenser water supply temperature at 75ºF setpoint as follows:

[Guideline: Large 3-way control valves are formed by mounting two 2-way butterfly valves on a piping tee. Butterfly valves have equal percentage flow characteristics and work well when used to control flow through coils and heat exchangers. However, when coupled-together to form a 3-way condenser water bypass control valve, individual valve operators are required for each of the two butterfly valves so the two valves can be modulated independently to overcome the non-linearity of percent flow vs. percent open for each valve.]

If condenser water bypass valve has been modulated to 100% bypass upon chiller start-up, on a rise of condenser water supply temperature above setpoint, modulate bypass control valve operators via AO points in sequence to divert condenser water flow through the cooling tower, while maintaining constant condenser water flow rate, as follows:

Percent (%) OpenTo Cooling Tower (NO) To Bypass (NC)

100 080 8560 9040 9320 960 100

Command isolation valves "OPEN" via DO points for number of cooling towers or tower cells matching the number of chillers commanded "ON".

On a continued rise of condenser water temperature above setpoint, command isolation valves of additional cooling towers or tower cells "OPEN" via DO points, in sequence.

[Guideline: Select/edit the cooling tower fan control from the following three options.]

Single Speed Cooling Tower Fan Motor Control Sequence:

On a continued rise of condenser water supply temperature above setpoint, command cooling tower fan "ON" via DO point in accordance with Sequence 1.21.


Two-Speed Cooling Fan Motor Control Sequence:

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On a continued rise of condenser water supply temperature to above setpoint, command cooling tower fan "ON" at low speed via DO point, in accordance with Sequence 1.22.


On a continued rise of condenser water supply temperature to above setpoint, command cooling tower fan "ON" at high speed via DO point, in accordance with Sequence 1.22.

Variable Speed Cooling Fan Motor Control Sequence:

On a continued rise of condenser water supply temperature above setpoint, command cooling tower fan "ON" at minimum speed through VFD via DO point, in accordance with Sequence 1.24.


On a continued rise of condenser water supply temperature to above setpoint, modulate fan speed from minimum to maximum through VFD via AO point in accordance with Sequence 1.24.

Rotate multiple cooling towers “ON/OFF” in accordance with Sequence 1.26.1.

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3.17 Condenser Water System, Cooling Tower Operating and Safety Controls:

[Guideline: Cooling towers supporting water-cooled chillers are, due to their higher efficiencies, expected to be induced draft, crossflow or counterflow, type and this sequence is based on that configuration. If multi-fan forced draft towers are applied, this sequence must be edited accordingly. Note that this sequence also applies to evaporatively cooled closed circuit coolers.]

Vibration switch lockout:

MONITOR cooling tower vibration switch NC contact(s) as DI point(s).

If switch contact(s) open, DISABLE cooling tower operation as follows:

For dedicated cooling tower configuration, command cooling tower and associated condenser water pump(s), chiller, and chilled water pump(s) “OFF” via DO points and initiate alarm.

For a multiple cooling tower configuration, command cooling tower “OFF” via DO point and initiate alarm. Command tower isolation valves “CLOSED” via DO points and DISABLE cooling tower within condenser water temperature control sequence.

Basin water level control:

Five-probe level sensor/controller(s) provided with cooling towers/evaporative coolers shall control water level in basin and provide control and alarm functions as follows:

At low operating level, normally closed make-up water valve shall “OPEN.”

At high operating level, normally closed make-up water valve shall “CLOSE.”

MONITOR “low alarm level” contact as DI point. When switch contact opens, “DISABLE” cooling tower operation as follows:

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For dedicated cooling tower configuration, command cooling tower and associated condenser water pump(s), chiller, and chilled water pump(s) “OFF” via DO points and initiate alarm.

For multiple the cooling tower configuration, command cooling tower “OFF” via DO point and initiate alarm. Command tower isolation valves to “CLOSE” via DO points and DISABLE cooling tower within the condenser water temperature control sequence.

MONITOR “high alarm level” contact as DI point.

When switch contact opens, initiate alarm.

Basin water freeze protection:

NO line voltage electric thermostat shall close upon fall of basin water temperature to 40ºF, energizing electric basin heater, and open when water temperature rises to 42ºF, de-energizing heater.

Basin water level controller contact shall interrupt the heater control circuit to prevent heater operation if basin water level is below “low alarm level.”

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3.18 Refrigeration Machinery Room Ventilation and Purge

[Guideline: This sequence addresses control of two-speed exhaust air fan, with outdoor air intake damper, to ventilate and/or purge refrigerant gas from refrigeration machinery room on the basis of alarm outputs from a refrigerant monitor and space thermostat.]

Via refrigerant monitor, MONITOR refrigerant concentration level alarm condition(s) as DI point(s), as follows:

[Guideline: Level 1 and Level 2 alarms may not warrant monitoring and initiating an alarm. Edit the following as required for the project.]

Level 1: Initiate DDC alarm.

Level 2: Initiate DDC alarm.

Level 3: Initiate DDC alarm and initiate refrigeration machinery room ventilation sequence as defined below.

MONITOR refrigeration machinery room temperature via AI point.

MONITOR refrigeration machinery room occupancy via DI point.

MONITOR exhaust fan status in accordance with Sequence 1.25.

Upon a rise in refrigeration machinery room temperature to above the high limit temperature setpoint (default=85°F), command outdoor intake air damper "OPEN" via DO point and command exhaust fan “ON” at low speed in accordance with Sequence 1.22.

Any time the refrigeration machinery room is occupied, as indicated by the occupancy sensor DI point, command the exhaust air intake damper “OPEN” via DO point and command exhaust fan “ON” at low speed in accordance with Sequence 1.22.

Via hard-wired interlock indicated below, the refrigerant monitor shall, upon alarm level 3, open the exhaust air intake damper and start the exhaust fan on high speed. Damper shall remain open and exhaust fan shall remain in operation until the refrigerant monitor resets.

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3.2 HOT WATER SYSTEMS

3.20 Boiler Room Safety Control

Manual boiler room safety switch(es) are required by Sections 235213, 235216, 235223, 235233, or 235240, as applicable.

Hardwired switch interlock shall close main fuel supply control valve and prevent boiler system from starting/operating when safety switch is activated as indicated by N.O. contactor closing.

Emergency stop shall be provided in accordance with Sequence 1.10.

3.21.1 Boiler Controller Interface, Non-Condensing Boiler(s):

[Guidelines: For conventional boilers, the specifications require each boiler to fitted with OEM-installed operating and safety controls. Operating setpoints, ON/OFF control, and staging/cascading of multiple boilers shall be under control of the DDC system. The scope of control provide by the OEM controller and the interface requirements are defined by this sequence, but the designer is cautioned that careful analysis of the OEM BACnet “Protocol Interface Compliance Statement” (PICS) is required to ensure that the required control sequence for the chiller is integrated correctly.]

PRIMARY BOILER CONTROL IS PROVIDED BY OEM CONTROLLER FOR EACH BOILER INTERFACED WITH DDC SYSTEM.

Boiler leaving hot water temperature shall be controlled by OEM controller based on hot water temperature setpoint defined via AO point.

Boiler controller/DDC interface for each boiler shall include the following:

DDCPoint

Boiler Controller

PointFunction

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DO ENABLE Allow boiler operationDI Alarm Boiler fault alarmAI - Boiler leaving HW temperatureAI Firing Rate Boiler load/firing rate

Initiate alarm if the boiler controller status/fault contactor closes.

MONITOR boiler firing rate.

3.21.2 Boiler Controller Interface, Condensing Boiler(s):

[Guidelines: The specifications require that the condensing boiler(s) manufacturer provide a OEM-installed Boiler Management System (BMS), including sensors and final control elements, and interface to the DDC system. The BMS is required to control up to four (4) boilers and to cascade/stage these boilers on/off as necessary and modulate individual boiler burners to maintain HWS temperature at setpoint defined by the DDC system. As applicable, integral primary pump and 2-position isolation valve(s) for each boiler shall be start/stop under command of the BMS. The scope of control provide by the OEM controller and the interface requirements are defined by this sequence, but the designer is cautioned that careful analysis of the OEM BACnet “Protocol Interface Compliance Statement” (PICS) is required to ensure that the required control sequence for the chiller is integrated correctly. ]

PRIMARY BOILER CONTROL IS PROVIDED BY BOILER MANAGEMENT SYSTEM (BMS) INTERFACED WITH DDC SYSTEM.

HWS temperature shall be controlled by BMS based on HWS temperature setpoint defined via AO point from DDC system.

BMS/DDC interface shall include the following:

DDCPoint

BMSPoint Function

AO HWS Setpoint Temperature

Define setpoint temperature for BMS boiler control

DO ENABLE Allow boiler system operationDI Alarm Boiler status/fault alarm

MONITOR flue gas temperature as AI point.

Initiate alarm via DI point if the BMS “status/fault” contactor closes.

The BMS shall automatically control multiple boiler lead/lag/cascade operation/rotation in accordance with boiler manufacturer’s recommendations in accordance with Section 235216.

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3.22 Hot Water System Start/Stop:

“ENABLE/DISABLE” hot water system via DO point in accordance with "ON/OFF" schedule defined by Sequence 1.14 or upon operator command.

When “ENABLED”, hot water system shall:

Start if [Enter number or percentage of AHUs listed below that will “trigger” the hot water system starting] of the following AHU/BCU/FCUs initiate a “REQUEST FOR HEATING” in accordance with Sequence 4.01:

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Hardwired safety interlock shall prevent boiler(s) starting if hot water flow not established as indicated by boiler water loop differential pressure switch.

Stop if none of the user-defined AHU/BCU/FCUs initiate a “REQUEST FOR HEATING” in accordance with Sequence 4.01 for 30 minutes.

3.23 Hot Water System, Multiple Non-Condensing Boilers, Primary-Secondary Variable Flow:

[Guideline: For all but the smallest of systems, a multiple boiler configuration is recommended (see design guidelines).]

System start sequence shall be as follows:

Command main fuel supply control valve "OPEN" via DO point.

Command secondary hot water pump(s) "ON" via DO point(s).

Confirm each pump(s) operation based on motor status via DI point(s) in accordance with Sequence 1.25.

Confirm secondary loop hot water flow via differential pressure flow sensor as DI point.

Command primary hot water pump "ON".

Confirm pump(s) operation based on motor status via DI point(s) in accordance with Sequence 1.25.

Confirm primary loop hot water flow via differential pressure switch DI point.

Command boiler "ON" through interface to OEM controller via DO point in accordance with Sequence 3.21.

MONITOR boiler status/fault.

If boiler OEM controller indicates a boiler fault, command boiler and hot water pump(s) "OFF" via DO points and initiate alarm.

If boiler fails to start within 5 minutes after being commanded “ON,” command primary and secondary hot water pump(s) and boiler "OFF" via DO points and initiate alarm.

Upon resumption of power after a power outage, boiler shall restart, if commanded "ON", after 5 minute time delay.

Primary HWS temperature control:

MONITOR primary HWS temperature as AI point.

MONITOR primary HWR temperature as AI point.

Compute primary HWS temperature setpoint as a linear function of outdoor air temperature as follows:


(ºF)

Primary HWS Temperature Setpoint

(ºF)≤ 20ºF 180ºF≥ 60ºF 130ºF

Secondary hot water temperature/flow control:

Compute secondary HWR temperature setpoint as primary HWS temperature minus hot water design system delta-T (30ºF default).

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Modulate secondary hot water pump(s) speed via AO point(s) in accordance with Sequence 1.24 to maintain secondary HWR temperature at setpoint.

MONITOR differential pressure sensor(s) at location(s) indicated on the Drawings as AI point(s).

If differential pressure sensor input(s) falls below setpoint, increase secondary hot water pumps speed via AO point(s) to maintain differential pressure(s) at setpoint.

During TAB of secondary hot water distribution, adjust differential pressure setpoint(s) to value(s) recommended by TAB subcontractor, as reviewed by A-E.

Multiple boilers sequencing: Start/stop each boiler in sequence through each OEM controller interface in accordance with Sequence 3.21 to maintain secondary HWS temperature at setpoint, as follows:

If secondary HWS temperature falls below setpoint temperature for 30 minutes, start a boiler via DO point.

If secondary HWS temperature rises above setpoint temperature for 30 minutes, stop a boiler via DO point.

Rotate multiple boilers "ON/OFF" in accordance with Sequence 1.26.1 to equalize runtime.

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3.24.1 Hot Water System, Multiple Condensing Boilers, Primary-Secondary Variable Flow:

[Guideline: Edit the following sequence as required for a primary/secondary variable flow system. This configuration is normally required with smaller firetube condensing boilers. Primary pump and isolation control valve are specified to be provided with each boiler by the boiler manufacturer.]



Command secondary hot water pump(s) "ON" via DO point(s).

Confirm each pump(s) operation based on motor status via DI point(s).

Confirm secondary loop hot water flow via differential pressure flow switch as DI point.

Primary hot water temperature/flow control: Primary HWS temperature setpoint, multiple boiler/pump boiler lead/lag and cascading/rotating shall be controlled by BMS in accordance with Section 235216.

MONITOR differential pressure switch as DI point at each boiler to confirm boiler operation when energized.

Secondary hot water temperature/flow control:

Compute secondary HWR temperature setpoint as primary HWS temperature minus hot water design system range.

Modulate secondary hot water pump(s) speed through VFD(s) via AO point(s) to maintain secondary HWR temperature at setpoint.

MONITOR differential pressure sensor at location(s) indicated on the Drawings as AI point(s).

If differential pressure sensor input(s) falls below setpoint, increase secondary hot water pumps speed via AO point(s) to maintain differential pressure(s) at setpoint.

During TAB of secondary hot water distribution, adjust differential pressure setpoint(s) to value(s) recommended by TAB subcontractor, as reviewed by A-E.

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During “OFF” periods, hot water system shall be DISABLED unless a requirement for heating or dehumidification is indicated by Sequence 4.11.1, 4.11.2, or 4.26, as applicable.

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3.24.2 Hot Water System, Multiple Condensing Boilers, Primary Variable Flow:

[Guideline: Edit the following sequence as required for a primary-only variable flow system. This configuration is normally used with larger water-tube condensing boilers. An isolation control valve is specified to be provided with each boiler by the boiler manufacturer.]



Command hot water pump(s) "ON" via DO point(s).

Confirm each pump(s) operation based on motor status via DI point(s.

Confirm hot water flow via differential pressure flow switch as DI point.

Hot water temperature control: HWS temperature setpoint, multiple boiler/pump boiler lead/lag and cascading/rotating shall be controlled by BMS in accordance with Section 235216.

MONITOR differential pressure switch as DI point at each boiler to confirm boiler operation when energized.

Hot water flow control:

Compute HWR temperature setpoint as HWS temperature minus hot water design system range.

Modulate hot water pump(s) speed through VFD(s) via AO point(s) to maintain HWR temperature at setpoint.

MONITOR differential pressure sensors at location(s) indicated on the Drawings as AI point(s).

If differential pressure sensor input(s) falls below setpoint, increase hot water pumps speed via AO point(s) to maintain differential pressure(s) at setpoint.

During TAB of hot water distribution, adjust differential pressure setpoint(s) to value(s) recommended by TAB subcontractor, as reviewed by A-E.


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3.25 Hot Water System, Steam-to-Hot Water Heat Exchanger(s), Variable Flow:


Command hot water pump(s) "ON" via DO point(s) in accordance with Sequence 1.24.

Confirm each pump(s) operation based on motor status via DI point in accordance with Sequence 1.25.

Confirm secondary loop hot water flow via differential pressure switch DI point.

Modulate hot water pump(s) speed through VFD(s) via AO point(s) in accordance with Sequence 1.24 to maintain HWR temperature at setpoint defined below.

MONITOR differential pressure at location(s) indicated on the Drawings as AI point(s).

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If differential pressure sensor(s) falls below setpoint, increase secondary hot water pump(s) speed to maintain differential pressure(s) at setpoint.

During TAB of secondary chilled water distribution, adjust differential pressure setpoint(s) to value(s) recommended by TAB subcontractor, as reviewed by A-E.

MONITOR HWS temperature as AI point.

MONITOR HWR temperature as AI point.

Compute HWS temperature setpoint as a linear function of outdoor air temperature, as follows:

Outdoor AirTemperature

(ºF)

HWSTemperature Setpoint

(ºF)≤ 20ºF 180ºF 75ºF 110ºF

Every 15 minutes, evaluate all space temperatures and hot water control valve positions to identify potential under-heating.

If 90% or more hot water valves are more than 95% open, increase the HWS temperature setpoint 2ºF every 15 minutes until the quantity of hot water control valves that are more than 95% open decreases to 75% or less.

Compute HWR temperature setpoint as primary HWS temperature plus hot water design system temperature range.

[Guideline: Select one of the two following subsections based on the heat exchanger configuration.]

Single heat exchanger HWS temperature control:

Modulate N.C. steam control valves “OPEN” via AO points to maintain HWS temperature at setpoint:

For HWS temperature control AO point output from 0-33%, modulate the 1/3-capacity control valve to maintain HWS temperature setpoint.

On an increase of the HWS temperature control AO output to above 33% for more than 2 minutes, the 1/3-capacity control valve shall be modulated “CLOSED” as the 2/3-capacity control valve shall be modulated 0-100% “OPEN” to maintain HWS temperature setpoint.

On a continued increase of the HWS temperature control AO output to above 66% for more than 2 minutes, the 2/3 capacity control valve shall remain 100% “OPEN” and the 1/3 capacity control valve shall be modulated 0-100% “OPEN” to maintain HWS temperature setpoint.

Reset control valve modulation sequence when the HWS temperature control AO output falls to 0%.

Multiple heat exchanger HWS temperature control:

Command each heat exchanger “ON” in sequence.

On a fall in HWS temperature to below setpoint, command lead heat exchanger “ON” by opening the N.C. flow isolation valve via DO.

Maintain HWS temperature at setpoint by modulating the lead heat exchanger control valves via AO points as defined below.

On a continued fall in HWS temperature below setpoint after the AO control output increases to 100%, command each lag heat exchanger “ON,” in sequence, by opening each N.C. flow isolation valve via DO.

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Maintain HWS temperature at setpoint by modulating the lag heat exchanger(s) control valves via AO points as defined below.

Modulate N.C. steam control valves “OPEN” via AO points to maintain HWS temperature at setpoint:

For HWS temperature control AO point output from 0-33%, modulate the 1/3-capacity control valve to maintain HWS temperature setpoint.

On an increase of the HWS temperature control AO output to above 33% for more than 2 minutes, the 1/3-capacity control valve shall be modulated “CLOSED” as the 2/3-capacity control valve shall be modulated 0-100% “OPEN” to maintain HWS temperature setpoint.

On a continued increase of the HWS temperature control AO output to above 66% for more than 2 minutes, the 2/3 capacity control valve shall remain 100% “OPEN” and the 1/3 capacity control valve shall be modulated 0-100% “OPEN” to maintain HWS temperature setpoint.

Reset control valve modulation sequence when the HWS temperature control AO output falls to 0%.

Rotate multiple heat exchangers "ON/OFF" in accordance with Sequence 1.26.1 to equalize runtime.


Back to Top3.26 Hot Water Unit Heater:

On a fall in space temperature to below minimum comfort zone temperature setpoint in accordance with Sequence 4.01, NO line-voltage electric thermostat temperature shall close to energize the unit heater fan and open NC hot water control valve to maintain space at minimum comfort zone temperature setpoint.

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3.27 Hot Water Convection/Radiation:

On a fall in space temperature to below minimum comfort zone temperature setpoint in accordance with Sequence 4.01, modulate NC hot water control valve from 0% to 100% “OPEN” via AO point to maintain space at minimum comfort zone temperature setpoint.

3.3 STEAM SYSTEMS

[The scope of control provide by the OEM controller and the interface requirements are defined by this sequence, but the designer is cautioned that careful analysis of the OEM BACnet “Protocol Interface Compliance Statement” (PICS) is required to ensure that the required control sequence for the chiller is integrated correctly.]

3.31 Boiler Controller Interface:

PRIMARY CONTROL IS PROVIDED BY OEM CONTROLLER FOR EACH BOILER INTERFACED WITH DDC SYSTEM.

“ENABLE/DISABLE” system via DO point in accordance with "ON/OFF" schedule defined by Sequence 1.14 or upon operator command.

Boiler OEM controller shall maintain steam supply pressure at setpoint provided to OEM controller via AO point in accordance with Sequence 3.33.

Boiler shall start/stop in accordance with Sequence 3.32 or 3.33, as applicable.

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Command boiler "ON/OFF" through interface to OEM controller via DO point in accordance with Sequence 3.21.1.

Boiler controller/DDC interface for each boiler shall include the following:

DDCPoint

Boiler ControllerPoint Function

DO Start/Stop Allow boiler operationDI Alarm Boiler status/fault alarmAI - Boiler steam pressure setpointAI Firing Rate Boiler load/firing rate

Hardwired safety interlock shall prevent boiler starting if hot water flow not established as indicated by boiler water loop differential pressure switch.

MONITOR boiler firing rate as AI point.

MONITOR boiler status/fault as DI point:

If boiler OEM controller indicates a boiler fault, command boiler "OFF" via DO point and initiate alarm.

If boiler fails to start within 5 minutes after being commanded “ON,” command boiler "OFF" via DO point and initiate alarm.

Upon resumption of power after a power outage, boiler shall restart, if commanded "ON", after 5 minute time delay.

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3.33 Steam System, Multiple Boilers:

[Guideline: For all but the smallest of systems, a multiple boiler configuration is recommended (see design guidelines). If a single boiler is required, edit this sequence accordingly.]

“ENABLE/DISABLE” steam system via DO point in accordance with "ON/OFF" schedule defined by Sequence 1.14 or upon operator command.

When “ENABLED”, steam system shall:

Start if [Enter number or percentage of AHUs listed below that will “trigger” the hot water system starting] of the following AHU/BCU/FCUs initiate a “REQUEST FOR HEATING” in accordance with Sequence 4.01:

Stop if none of the user-defined AHU/BCU/FCUs initiate a “REQUEST FOR HEATING” in accordance with Sequence 4.01 for 30 minutes.

Steam system start sequence shall be as follows:

MONITOR header (main) steam pressure as AI point.

Start/stop each boiler in accordance with Sequence 1.26.1, through OEM controllers to maintain header steam pressure at setpoint, as follows:

If header steam pressure falls 10% below setpoint for 30 minutes, start “Lead” boiler via DO point.

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On a continued fall in header steam pressure after 15 minutes, start “Lag” boiler(s) via DO point(s).

If header steam pressure rises 10% above setpoint for 30 minutes, stop “Lead” boiler via DO point.

On a continued rise in header steam pressure after 15 minutes, stop “Lag” boiler(s) via DO point(s) in same order as each boiler was started.

Boiler start/stop sequence and capacity control:


Command boiler "ON" via DO point through OEM controller in accordance with Sequence 3.21.

Maintain boiler steam pressure:

Set boiler steam pressure setpoint as 5 psig above steam header pressure setpoint via AO point interface with OEM controller.

OEM controller shall MONITOR boiler steam pressure and modulate burner firing rate to main boiler steam pressure at setpoint.

Rotate multiple boilers "ON/OFF" in accordance with Sequence 1.26.1.

During “OFF” periods, steam system shall be DISABLED unless a requirement for heating or dehumidification is indicated by Sequence 4.11.1, 4.11.2, or 4.26, as applicable.

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3.35 Steam Unit Heater: On a fall in space temperature to below minimum comfort zone temperature setpoint in accordance with Sequence 4.01, NO line-voltage electric thermostat temperature shall close to energize the unit heater fan and open NC steam control valve to maintain space at minimum comfort zone temperature setpoint.

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3.38 Steam Convection/Radiation: On a fall in space temperature to below minimum comfort zone temperature setpoint in accordance with Sequence 4.01, modulate NC steam control valve from 0% to 100% “OPEN” via AO point to maintain space at minimum comfort zone temperature setpoint.

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3.4 CLOSED LOOP WATER SOURCE HEAT PUMP SYSTEM

3.41 Heat Pump Water Loop, Variable Flow:

[Guideline: This sequence is based on the use of at least two condensing water hot water boilers that provide supplemental heating; at least two closed circuit evaporative coolers, each with 2-speed fans, for rejecting excess heat; and two loop distribution pumps operating in parallel. Edit as required for different system configuration.]

“ENABLE/DISABLE” system in accordance with (1) "ON/OFF" schedule defined by Sequence 1.14, (2) demand for heating or cooling indicated by ______ [Guideline: Enter number or percentage] of water source heat pumps being commanded "ON", or (3) operator command, as follows:

Command ACWS pump(s) "ON" via DO points in accordance with Sequence 1.24.

Confirm pump(s) operation based on motor status as DI point(s) in accordance with Sequence 1.25.

Confirm water flow via differential pressure flow switch via DI point.

If differential pressure flow switch indicates flow failure, command ACWS pump(s) “OFF” and initiate alarm.

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Loop water temperature control:

MONITOR ACWS temperature as AI point.

MONITOR ACWR temperature as AI point.

Maintain low limit ACWR setpoint temperature range as follows:

When ACWR temperature falls to 60ºF, ENABLE boiler system.

When ACWR temperature rises to 70ºF, DISABLE boiler system.

Maintain high limit ACWR setpoint temperature range as follows:

When ACWR temperature rises to 90ºF, ENABLE evaporative cooler system.

When ACWR temperature falls to 80ºF, DISABLE evaporative cooler system.

Boiler system control:

[Guideline: Include/edit Sequence 3.24.2 for boiler system control.]

When “ENABLED,” hot water system shall operate in accordance with Sequence 3.24.2.

Evaporative cooler system control:

When “ENABLED”, command evaporative cooler isolation valve(s) “OPEN” via DO point(s).

On a rise of ACWR temperature above the high limit setpoint range, command evaporative cooling spray pump(s) "ON" via DO point(s) in accordance with Sequence 1.21.

Confirm each pump operation based on motor status as DI point in accordance with Sequence 1.25.

On a continued rise of ACWR water temperature to above the high limit setpoint range, command cooler fan(s) "ON" at low speed via DO point(s) in accordance with Sequence 1.22.

Confirm each fan operation based on motor status as DI point in accordance with Sequence 1.25.

On a continued rise of ACWR temperature to above the high limit setpoint range, command cooler fan(s) "ON" at high speed via DO point(s) in accordance with Sequence 1.22.

Confirm each fan operation based on motor status as DI point in accordance with Sequence 1.25.

Back to TopAIR-HANDLING SYSEMS

4.0 GENERAL AIR-HANDLING SYSTEMS OPERATIONS AND MONITORING

4.00 Start/Stop Control:

Start/stop air-handling system supply air fan(s) and associated return or relief air fan(s), as applicable, in accordance with Sequence 1.21, 1.22, 1.23, or 1.24, as applicable, based on (1) user-defined "ON/OFF" schedule defined by Sequence 1.14, (2) optimum start time computation, or (3) operator command.

During "ON" periods, command air-handling system "ON" (start) unless inhibited by optimum start time computation, operator command, or an emergency stop interlock in accordance with Sequence 1.13.

Command, as applicable, supply air and return air smoke isolation damper(s) “OPEN” via DO point(s)

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Hardwire isolation damper end switch(es) as part of fan interlock wiring to confirm that dampers are open.

If any isolation damper fails to “OPEN,” terminate start sequence and initiate alarm.

During "OFF" periods, command air-handling system "OFF" via DO point unless there is a need for heating, cooling, or dehumidification as evidenced by space temperature or humidity being out of zone “OFF” period low or high limit setpoint(s) defined by Sequence 4.01.

Each exhaust fan associated with an air-handling system, as tabulated below, shall be commanded "ON" via DO point when the air-handling system is "ON" and commanded "OFF" via DO point when the air-handling system is "OFF," in accordance with Sequence 1.27:

Air-Handling System Tag

ExhaustFan Tag Area(s) Served

MONITOR fan motors(s) status via DI point(s) in accordance with Sequence 1.25.

[Guideline: The following requirements may be deleted for single zone air systems with which there is no risk of fire, smoke, or isolation damper accidental closure.]

MONITOR supply fan and, as applicable, return/relief fan static pressures as AI points at two locations:

High limit static pressure (locate immediately downstream of the fan).

During TAB of air-handling system, adjust setpoint to value recommended by TAB subcontractor, as reviewed by A-E.

If high limit static pressure exceeds setpoint, command system “OFF” via DO point.

Issue high pressure alarm.

Low limit static pressure (locate immediately upstream of the fan).


If low limit static pressure falls below setpoint, command system “OFF” via DO point.

Issue low pressure alarm.

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4.01 Space Temperature/Humidity Setpoints and Monitoring:

Space temperature and humidity control setpoints:

"ON" Period: Temperature Range: 70-75ºF Comfort ZoneMax. Humidity: 60% RH High Limit

[Guideline: For comfort conditioning, low limit humidity control is not normally provided and the following setpoint requirement can be deleted. But, for critical occupancies, such as hospitals, labs, etc., or in very cold climates, it may be needed. If so, include the following setpoint requirement.]

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Min. Humidity: 30% RH Low Limit

"OFF" Period: Max. Temperature: 85ºF High LimitMin. Temperature: 55ºF Low Limit

[Guideline: High limit humidity control during unoccupied hours is recommended. However, discuss this with the owner before including it in the project scope.]

Max. Humidity: 70% RH High Limit

Space temperature setpoints shall not be adjustable by space occupants unless (1) specifically indicated on the Drawings or (2) the project is to be constructed to meet the requirements of the USGBC “LEED Rating System.”

Where setpoint adjustment is required, adjustment range shall be limited to +/- 2°F from temperature range defined above.

Space humidity setpoints shall not be adjustable by space occupants.

MONITOR each space temperature and humidity as individual AI point.

[Guideline: Delete the following section for projects that do not have a central chilled water system, a central hot water system, and/or a central steam system.]

Cooling/Heating “REQUESTS” for Central Plant Start/Stop Control:

For spaces served by single zone air systems:

A “REQUEST FOR COOLING” shall be initiated when a space sensor indicates a space temperature rising above either the maximum comfort zone temperature setpoint during “ON” periods or the high limit temperature setpoint during “OFF” periods or a space humidity rising above the high limit humidity setpoint for a period of 30 minutes.

A “REQUEST FOR HEATING” shall be initiated when a space sensor indicates a space temperature falling below either the minimum comfort zone temperature setpoint during “ON” periods or the low limit temperature setpoint during “OFF” periods or a space humidity rising above the high limit humidity setpoint for a period of 30 minutes.

For spaces served by multiple zone air systems:

A “REQUEST FOR COOLING” shall be initiated when at least five (5) space sensors indicate a space temperature rising above either the maximum comfort zone temperature setpoint during “ON” periods or the high limit temperature setpoint during “OFF” periods or a space humidity rising above the high limit humidity setpoint for a period of 30 minutes.

A “REQUEST FOR HEATING” shall be initiated when at least five (5) space sensors indicate a space temperature falling below either the minimum comfort zone temperature setpoint during “ON” periods or the low limit temperature setpoint during “OFF” periods or a space humidity rising above the high limit humidity setpoint for a period of 30 minutes

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4.05 Drain Pan Condensate Level Alarm:

MONITOR drain pan condensate level sensor integral NO dry contact as a DI point.

Upon sensor detection of drain pan moisture, and after user-defined time delay (default = 3 minutes), stop air-handling system via DO point and initiate an alarm.

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4.06 Filter Differential Pressure Alarm:

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MONITOR filter differential pressure gauge integral NO dry contact as DI point.

Upon filter differential pressure exceeding setpoint, initiate maintenance alarm for filter replacement.

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4.07 Low Limit Thermostat Control and Alarm:

[Guideline: This sequence requires manual reset of the low limit thermostat for the air-handling system to restart.]

Stop air-handling system fan(s) via hardwired interlock when mixed air temperature falls to 38ºF.

MONITOR low limit thermostat auxiliary SPDT line voltage switch as DI point and initiate the following actions when thermostat “trips”:

In accordance with Sequence 4.08, as applicable, initiate maximum preheating capability.

Modulate the outdoor air damper(s) and relief air dampers 100% “CLOSED” and modulate return air dampers 100% “OPEN” via AO points.

Modulate chilled water coil control valve via AO point to provide 0% cooling capacity.

Initiate alarm.

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4.08 Preheat Control:

[Guideline: See “Design Guidelines” to determine if/when preheat is required for an air system. For systems with a separate heating coil located downstream of the chilled water cooling coil, the preheat coil discharge temperature should be set at 40ºF to protect the cooling coil from freezing and to prevent the low limit thermostat for tripping. For systems without a separate downstream heating coil, the preheat coil setpoint must be determined on the basis of the unit discharge air temperature requirement.]

Mixed air temperature setpoint shall be the greater of 40⁰F or the air-handling system discharge air temperature setpoint.

MONITOR mixed air temperature as AI point.

[Guideline: Select/edit preheat coil control from the following four options.]

Hot water preheat coil with circulating pump:

Provide 3-way modulating hot water control valve and circulating pump as detailed on the Drawings.

On a fall of mixed air temperature to below setpoint, command preheat coil hot water pump “ON” via DO point to provide 100% water flow through coil and modulate NC preheat hot water control valve via AO point to maintain mixed air at setpoint.

Hot water or steam preheat coil with integral face and bypass dampers:

Provide two-way modulating hot water or steam control valve, as indicated on the Drawings.

Provide preheat coil, as indicated on the Drawings, with integral modulating face and bypass (F&B) dampers.

When preheat coil entering air temperature is above the design mixed air temperature setpoint, modulate F&B dampers via AO point to 100% “bypass” and modulate the heating control valve “CLOSED” via AO point.

When preheat coil entering air temperature is between 40°F and the mixed leaving air temperature setpoint,

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modulate F&B dampers via AO point to provide 100% air flow to the preheat coil and modulate the preheat coil control valve via AO point to maintain mixed air temperature setpoint.

When preheat coil entering air temperature is less than 40°F, modulate preheat coil control valve via AO point to provide 100% flow through preheat coil and modulate F&B dampers via AO point to maintain mixed air temperature setpoint.

Steam preheat coil with dual control valves:

Provide Stage 1 NC two-position steam control valve sized for 20% of the preheat coil scheduled capacity with a pressure drop of 50% of the available steam pressure. Provide Stage 2 NC modulating steam control valve sized for 80% of the preheat coil scheduled capacity with a pressure drop of 25% of the available steam pressure.

On a fall of mixed air temperature to below setpoint, command Stage 1 steam control valve “OPEN” via DO point to maintain mixed at setpoint.

On further fall of mixed air temperature to below setpoint, modulate Stage 2 steam control valve from 0% to 100% “OPEN” via AO point to maintain mixed air temperature at setpoint.

Electric preheat coil:

Staged Control: On a fall in mixed air temperature to below setpoint, command each stage of the preheat coil “ON,” in sequence, via DO points, to maintain mixed air temperature at setpoint.

SCR Control: On a fall of mixed air temperature to below setpoint, modulate integral SCR controller via AO point to maintain mixed air temperature setpoint.

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4.09 Steam Distributing Type Duct Humidifier:

“ENABLE” humidifier operation if air-handling system is “ON,” the supply air fan is operating at ≥ 20% speed, and the outdoor air temperature is below 50ºF.

Connect integral humidifier temperature switch located in condensate line to prevent humidifier operation until steam condensate has reached 205ºF temperature.If space humidity falls below low limit humidity setpoint as defined in Sequence 4.01, modulate humidifier NC steam control valve from 0% to 100% “OPEN” via AO point to maintain space humidity at low limit humidity setpoint.

MONITOR supply air humidity downstream of humidifier absorption zone as AI point.

Limit humidifier AO point value to maintain downstream humidity at maximum 90% RH. DISABLE humidifier operation if any ENABLE condition is/becomes not true.

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4.1 SINGLE ZONE AIR-HANDLING SYSTEMS

[Guideline: Single zone air-handling systems are designed to maintain temperature and humidity high limit setpoint in a single control zone, a single space or a group of spaces that share common HVAC requirements and operating schedules.

Each single zone air-handling system required to have VAV control must be configured to maintain minimum design ventilation airflow at any total airflow during scheduled “OCCUPIED” periods.

For each single zone air-handling system required to have an airside economizer cycle, a return air fan or relief air fan is required unless barometric relief dampers located within the space served are provided (note that barometric relief air dampers located in return air ductwork represents a design error).]

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4.10 Single Zone Air-Handling Systems Operation and Monitoring:

The following sequences of operation indicated by check boxes shall apply to each of the following single zone air-handling systems:

See “Schedules” and “Details” drawing sheets and applicable specification sections that define the components and configuration of each air-handling system listed above.

[Guideline: Fill in each check box below to indicate the configuration and control requirements for each of the single zone air-handling systems listed above. Check boxes that are already filled in indicate mandatory requirements. Note that this subsection may have to be repeated for each different air-handling system configuration used for this project.]

Basic control elements (Sequences 1.xx and 2.xx, as applicable) General operations and monitoring

Start/stop control (Sequence 4.00) Space temperature/humidity monitoring (Sequence 4.01) Drain pan condensate monitoring (Sequence 4.05) Filter differential pressure monitoring (Sequence 4.06) Low limit thermostat alarm (Sequence 4.07) Preheat (Sequence 4.08)

Hot water coil with circulating pump option Hot water coil with integral face and bypass dampers option Steam coil with dual control valves option Steam coil with integral face and bypass dampers option Electric coil with stages option Electric coil with silicon controlled rectifier option

Primary humidifier (Sequence 4.09) Constant air volume temperature/humidity control (Sequence 4.11.1)

Minimum outdoor air flow control (Sequence 4.12.1) Cooling

Chilled water option Direct refrigerant (DX) option (Sequence 5.10.1)

Heating/reheating Hot water coil option Steam coil option Electric coil with stages option Electric coil with silicon controlled rectifier option

Variable air volume temperature/humidity control (Sequence 4.11.2) Minimum outdoor air flow control (Sequence 4.12.2) Cooling

Chilled water coil option Direct refrigerant (DX) coil option (Sequence 5.10.1)

Heating/reheating Hot water coil option Steam coil option Electric coil with stages option Electric coil with silicon controlled rectifier option

Demand control ventilation enable/disable (Sequence 4.14) Occupancy schedule + occupancy/vacancy sensing option (Sequence 4.14.1) Occupancy schedule + manual override option (Sequence 4.14.2) Occupancy schedule + CO2 sensing option (Sequence 4.14.3) Occupancy schedule + people counting option (Sequence 4.14.4)

Economizer cycle (Sequence 4.15)

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Dry bulb temperature option Differential enthalpy option Relief air control

Barometric damper option Return air fan option

Flow tracking control Building/plenum pressure monitoring/control

Relief air fan option Flow tracking control Building pressure monitoring/control

[Guideline: The following air system elements and sequences of operation apply to single zone units utilizing chilled water coils for cooling and hot water, steam, and/or electric coils for preheating, heating, and/or reheating…edit as required.]

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4.11.1 Space Temperature and Humidity Control, CAV Single Zone System:

In accordance with Sequence 4.01, space temperature and high limit humidity shall be maintained at setpoint as follows:

Where an air-handling system serves a single space, provide a single temperature + humidity sensor for the space served.

[Guideline: The design should avoid having a single zone system that serves multiple spaces. However, if this configuration is required, select the number and location for space temperature and humidity sensor(s) from the following two options.]

Where an air-handling system serves multiple spaces, provide temperature sensors for each space served and a humidity sensor in a single “key” space as indicated on the Drawings.

Where an air-handling system serves multiple spaces, provide a single temperature + humidity sensor in a single “key” space as indicated on the Drawings.

Where a single space is served by multiple air-handling systems, provide a single space temperature + humidity sensor to serve as input for all air-handling systems serving that space.

During “ON” periods:

Where indicated on the Drawings, temperature control shall be based on a single space temperature sensor AI point as follows:

On a rise in space temperature to above the maximum comfort zone temperature, modulate the chilled water control valve via AO point to maintain space temperature at the maximum comfort zone temperature.

On a fall in space temperature to below the minimum comfort zone temperature, modulate the heating coil final control element in sequence with preheat coil control element(s), as applicable, via AO points to maintain space temperature at the minimum comfort zone temperature, as follows:

Hot Water Coil Control: Modulate NC hot water control valve 0-100% “OPEN.”

Steam Coil Control: Modulate NC steam control valve 0-100% “OPEN.”

Staged Electric Coil Control: Modulate each stage of the heating coil “ON,” in sequence.

SCR Electric Coil Control: Modulate integral SCR controller 0-100% “ON.”

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When the space temperature is within the limits of the minimum and maximum comfort zone temperatures, both cooling coil control valve and heating coil final control elements shall be modulated “CLOSED/OFF” via AO points.

Where indicated on the Drawings, temperature control based on multiple space temperature sensors AI points, as follows:

Routinely (at least every 5 minutes) MONITOR and sort space temperature AI points to determine which spaces are within the comfort temperature zone.

If all AI points are within the comfort zone defined, both cooling coil and heating coil control valves shall be modulated “CLOSED” via AO points.

If all AI points are above the maximum comfort zone temperature, modulate the chilled water control valve via AO point until the highest space temperature is decreased to the maximum comfort zone temperature.

If all AI points are below the minimum comfort zone temperature, modulate the heating coil final control element via AO point, in sequence with preheat coil control elements, as applicable, until the lowest space temperature is increased to the minimum comfort zone temperature.

If at least 1 AI point is above the maximum comfort zone temperature and at least 1 AI point is below the minimum comfort zone temperature, compute the “percentage dissatisfied factor” (PDF) for each space as follows:

R = [-8.6479 + (0.2431 X C)] + [0.3442 – (0.0073 X C)] X T

where C = month of year (1-12)T = sensor temperature, °C

PD = 100 – {95 EXP [ -(0.03353 X R4 + 0.2179 X R2)]}

PDF = 0.9 X (PD – 0.1)

Modulate the cooling chilled water control valve via AO point to provide cooling or modulate the heating coil final control element(s) via AO point, in sequence with preheat coil final control element(s), as applicable, to minimize the PDF at each sensor.

Humidity control, based on a single space humidity sensor AI point rising above the high limit humidity setpoint, shall be as follows, as applicable:

Hot Water Coil Control:

If HWS is not available, as evidenced by the HWS temperature being less than 100°F, initiate alarm and terminate humidity control sequence.

If HWS is available, as evidenced by the HWS temperature being equal to or greater than 100°F, modulate the NO chilled water control valve 100% “OPEN” via AO point and modulate the NC heating coil hot water control valve via AO point to maintain space temperature at the maximum comfort zone temperature.

Steam Coil Control:

If steam is not available, as evidenced by the steam supply pressure being less than 5 psig, initiate alarm and terminate humidity control sequence.

If steam is available, as evidenced by the steam supply pressure being equal to or greater than 5 psig, modulate the NO chilled water control valve 100% “OPEN” via AO point and modulate the NC heating coil steam control valve via AO point to maintain space temperature at the maximum comfort zone temperature.

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Staged Electric Coil Control: Modulate the NO chilled water control valve 100% “OPEN” via AO point and modulate each stage of the heating coil “ON,” in sequence via AO point to maintain space temperature at the maximum comfort zone temperature.

SCR Electric Coil Control: Modulate the NO chilled water control valve 100% “OPEN” via AO point and modulate integral SCR controller 0-100% “ON” via AO point to maintain space temperature at the maximum comfort zone temperature.

During “OFF” periods, modulate all final heating and cooling control elements “CLOSED/OFF” via AO points unless a need for heating or cooling is dictated as follows:

On a rise in any space temperature to above the high limit temperature setpoint, command chilled water system “ON” via DO point:

If chilled water is not available, as evidenced by the CHWS temperature being greater than 45°F after 15 minutes of operation, initiate alarm and terminate sequence.

If chilled water is available, as evidenced by CHWS temperature being less than or equal to 45°F:

Command air-handling system “ON” via DO point in accordance with Sequence 4.00.

Modulate NO cooling coil chilled water control valve via AO point to maintain space at high limit temperature minus 5°F.

On a fall in any space temperature to below the low limit temperature setpoint:


If HWS is not available, as evidenced by the HWS temperature being less than 100°F after 15 minutes of operation, initiate alarm and terminate sequence.

If hot water is available, as evidenced by the HWS temperature being equal to or greater than 100°F:


Modulate NC heating coil hot water control valve via AO point to maintain space at low limit temperature plus 5°F.

Steam Coil Control:

If steam is not available, as evidenced by the steam supply pressure being less than 5 psig after 15 minutes of operation, initiate alarm and terminate sequence.

If steam is available, as evidenced by the steam supply pressure being equal to or greater than 5 psig after 15 minutes of operation:


Modulate the NC heating coil steam control valve via AO point to maintain space temperature at low limit temperature plus 5°F.

Staged Electric Coil Control:


Modulate each stage of the heating coil “ON,” in sequence, via AO point to maintain space temperature at low limit temperature plus 5°F.

SCR Electric Coil Control:

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Modulate integral SCR controller 0-100% “ON” via AO point to maintain space temperature at low limit temperature plus 5°F.

[Guideline: Delete the following subsection if high limit humidity control during “OFF” periods is not required.]

On a rise in any space humidity to above the high limit humidity setpoint, command chilled water system “ON” via DO point.






Modulate NO cooling coil chilled water control valve 100% “OPEN” via AO point until space humidity falls to high limit setpoint minus 5% RH.

Modulate NC heating coil hot water control valve via AO point to maintain space temperature at the high limit temperature.

Steam Coil Control:





Modulate the NC heating coil steam control valve via AO point to maintain space temperature at low limit temperature.




Modulate each stage of the heating coil “ON,” in sequence to maintain space temperature at low limit temperature.



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Modulate integral SCR controller 0-100% “ON” to maintain space temperature at low limit temperature.

Once space condition(s) return to within setpoint limit conditions +/- 5°F and/or -5% RH, as defined above, for 5 minutes, command the air-handling system “OFF” via DO point, modulate both heating and cooling final control elements “CLOSED/OFF” via AO points, and command the chilled water system and hot water or steam system, as applicable, “OFF” via DO points.

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4.11.2 Space Temperature and Humidity Control, VAV Single Zone System:

In accordance with Sequence 4.01, space temperature and high limit humidity shall be maintained at setpoint as follows:

Where an air-handling system serves a single space, provide a single temperature + humidity sensor for the space served.

[Guideline: The design should avoid having a single zone system that serves multiple spaces. However, if this configuration is required, select the number and location for space temperature and humidity sensor(s) from the following two options.]

Where an air-handling system serves multiple spaces, provide temperature sensors for each space served and a humidity sensor in a single “key” space as indicated on the Drawings.

Where an air-handling system serves multiple spaces, provide a single temperature + humidity sensor in a single “key” space as indicated on the Drawings.

Where a single space is served by multiple air-handling systems, provide a single space temperature + humidity sensor to serve as input for all air-handling systems serving that space.

During “ON” periods:

Where indicated on the Drawings, temperature control based on a single space temperature sensor AI point shall be as follows:

On a rise in space temperature above the maximum comfort zone temperature setpoint, provide cooling as follows:

From 0% to 49% AI point signal, cooling supply air flow shall be minimum air-handling system airflow. Modulate the cooling coil chilled water control valve from 0% to 100% “OPEN” to maintain space temperature at maximum comfort zone temperature setpoint.

From 50% to 100% AI point signal, modulate chilled water control valve 100% “OPEN” via AO point and then modulate supply fan speed through the VFD via AO point from minimum speed to maximum speed to maintain space temperature at maximum comfort zone temperature setpoint.

On a fall is space temperature to below the minimum comfort zone temperature setpoint, provide heating as follows:

From 0% to 49% AI point signal:

Modulate supply fan speed through the VFD via AO point to minimum.

Modulate the heating coil final control element, as applicable, in sequence with preheat coil control element(s), as applicable, via AO points to maintain space temperature at the minimum comfort zone temperature, as follows:

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Modulate the heating coil final control element, as applicable, in sequence with preheat coil control element(s), as applicable, via AO points to 100% “OPEN/ON” via AO points, as follows:

Hot Water Coil Control: Modulate NC hot water control valve to 100% “OPEN.”

Steam Coil Control: Modulate NC steam control valve to 100% “OPEN.”

Staged Electric Coil Control: Modulate each stage of the heating coil “ON.”

SCR Electric Coil Control: Modulate integral SCR controller to 100% “ON.”

Modulate supply fan speed through VFD via AO point from minimum speed to maximum speed to maintain space temperature at minimum comfort zone temperature setpoint.

When the space temperature is within the limits of the minimum and maximum space temperature setpoints, both cooling coil control valve and heating final control elements shall be modulated “CLOSED/OFF” and fan speed shall be set at minimum.

[Guideline: Delete the following subsection when unless multiple space temperature sensors are utilized for single zone unit control.]

Where indicated on the Drawings, temperature control based on multiple space temperature sensors AI points shall be as follows:

Routinely (at least every 5 minutes) MONITOR and sort AI points from all space temperature sensors to determine which spaces are within the comfort temperature space.

If all space temperatures are within the limits of the zone minimum and maximum temperature setpoints, both cooling coil and heating coil final control element(s) shall be modulated “CLOSED/ OFF” via AO points and supply fan speed shall be modulated through VFD via AO point to minimum.

If all spaces are above the maximum comfort zone temperature setpoint, increase air-handling system cooling output, as follows, until the highest space temperature is decreased to the maximum comfort zone temperature.

From 0% to 49% AI point signal, modulate supply airflow though VFD via AO point to minimum. Modulate cooling coil chilled water control valve from 0% to 100% “OPEN” via AO point to maintain space temperature at maximum comfort zone temperature setpoint.

From 50% to 100% AI point signal, modulate supply airflow through VFD via AO from minimum to maximum to maintain space temperature at maximum comfort zone temperature setpoint.

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If all spaces are below the minimum comfort zone temperature setpoint, increase air-handling system heating output, as follows, until the lowest sensor temperature is increased to the minimum comfort zone temperature.


Modulate supply fan speed through the VFD via AO point to minimum.

Modulate the heating coil final control element, as applicable, in sequence with preheat coil control element(s), as applicable, via AO points to maintain space temperature at the minimum comfort zone temperature, as follows:






Modulate the heating coil final control element, as applicable, in sequence with preheat coil control element(s), as applicable, via AO points to 100% “OPEN/ON” via AO points, as follows:






If 1 or more spaces are above the maximum comfort zone temperature setpoint while 1 or more spaces are below the minimum comfort zone temperature setpoint, compute the "percentage dissatisfied factor" (PDF) for each sensor as follows:

R = [-8.6479 + (0.2431 X C)] + [0.3442 - (0.0073 X C)] X T

where C = Month of year (1-12)T = Sensor temperature, °C

PD = 100 - {95 EXP [ -(0.03353 X R4 + 0.2179 X R2)]}

PDF = 0.9 X (PD - 0.1)

Modulate the cooling chilled water control valve via AO point to provide cooling or modulate the heating coil hot final control element(s) in sequence with preheat coil final control element(s), as applicable, along with fan speed, as necessary to minimize the PDF at each space.

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Humidity control, based on a single space humidity sensor AI point, where indicated on the Drawings, rising above the high limit humidity setpoint, shall be as follows, as applicable:

Modulate supply airflow to maximum through VFD via AO point.


If HWS is not available, as evidenced by the HWS temperature being less than 100°F, initiate alarm and terminate humidity control sequence.

If HWS is available, as evidenced by the HWS temperature being equal to or greater than 100°F, modulate the NO chilled water control valve 100% “OPEN” via AO point and modulate the NC heating coil hot water control valve via AO point to maintain space temperature at the maximum comfort zone temperature.

Steam Coil Control:

If steam is not available, as evidenced by the steam supply pressure being less than 5 psig, initiate alarm and terminate humidity control sequence.

If steam is available, as evidenced by the steam supply pressure being equal to or greater than 5 psig, modulate the NO chilled water control valve 100% “OPEN” via AO point and modulate the NC heating coil steam control valve via AO point to maintain space temperature at the maximum comfort zone temperature.

Staged Electric Coil Control: Modulate the NO chilled water control valve 100% “OPEN” via AO point and modulate each stage of the heating coil “ON,” in sequence via AO point to maintain space temperature at the maximum comfort zone temperature.

SCR Electric Coil Control: Modulate the NO chilled water control valve 100% “OPEN” via AO point and modulate integral SCR controller 0-100% “ON” via AO point to maintain space temperature at the maximum comfort zone temperature.

During “OFF” periods, modulate all final control elements “CLOSED/OFF” via AO points, unless a need for heating or cooling is dictated as follows:

On a rise in space temperature to above the high limit temperature setpoint, provide cooling as follows:


If chilled water is available, as evidenced by CHWS temperature being less than or equal to 45°F:

Command air-handling system "ON" via DO point in accordance with Sequence 4.00 with supply airflow modulated to minimum through VFD via AO point.

As applicable, command return fan "ON" via DO point and modulate return airflow through VFD via AO point to maintain 0 cfm difference between supply and return airflows.

As applicable, command relief fan "OFF" via DO point.

Modulate cooling coil chilled water control valve via DO point to maintain space at high limit temperature setpoint minus 5°F.

On a fall in any space temperature to below the low limit temperature setpoint, provide heating by the final control element, as applicable, as follows:



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Steam Coil Control:
















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[Guideline: Delete the following subsection if high limit humidity control during “OFF” periods is not required.]

On a rise in any space humidity to above the high limit humidity setpoint, provide cooling and heating, as applicable, as follows:









Modulate NC heating coil hot water control valve via AO point to maintain space temperature at the high limit temperature.

Steam Coil Control:







Modulate the NC heating coil steam control valve via AO point to maintain space temperature at low limit temperature.



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As applicable, command relief fan "OFF" via DO point.4.00.


Modulate each stage of the heating coil “ON,” in sequence to maintain space temperature at low limit temperature.






Modulate integral SCR controller 0-100% “ON” to maintain space temperature at low limit temperature.

Once space condition(s) return to within setpoint limit conditions +/- 5°F and/or -5% RH, as defined above, for 5 minutes, command the air-handling system “OFF” via DO point, modulate both NO chilled water and NC heating coil hot water control valves “CLOSED” via AO points, and command the chilled water system and hot water systems “OFF” via DO points.

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4.12.1 Minimum Outdoor Airflow Control, CAV Single Zone System:

[Guideline: VA, EA, and PA must be defined by the Designer and these requirements verified by the test and balance contractor. ]

Set the minimum outdoor airflow OA setpoint as the greater of VA or (EA + PA) based on the following:

Variable Description"ON"

Period"OFF" Period

VA

MinimumVentilation

Airflow (CFM)

Occupied PeriodMinimum Required

Ventilation Air as Scheduled on

Drawings 0UnoccupiedPeriod

Va (Area Component of

Minimum Required

Ventilation Air)

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Period"OFF" Period

EASum of Exhaust Fan Airflows (CFM) In Building or Portion of Building Served by Air-Handling System.

As Indicated on Drawings


PAExcess Airflow (CFM) Required to Maintain Positive Pressure in Building or Portion of Building Served by Air-Handling System.

10% of EA 10% of EA

[Guideline: Typically, 10% excess airflow (PA) is sufficient to maintain building at a positive internal pressure. However, adjust this value upward as required by project conditions.]

During “OCCUPIED” periods and during “UNOCCUPIED” periods prior to the air-handling system being commanded “OFF,” “ENABLE” minimum outdoor airflow and modulate [minimum] outdoor air damper to preset “OPEN” positions to maintain OA at setpoint. [Minimum] outdoor air damper positions [percent “OPEN”] for each outdoor airflow required by this sequence shall be determined by the TAB subcontractor.

[Guideline: Delete the following sentence unless barometric dampers are incorporated into the deisgn. But, for high density occupancies, the outdoor airflow required for ventilation may result in excess barometric pressure (e.g., >0.10” wg) in the occupied area. While rare, this condition requires barometric pressure relief and the simplest, lest costly method is to use spring-loaded adjustable setpoint barometric pressure relief dampers. This option is feasible only if a direct, low pressure drop relief air path from the space to outdoors can be created…locating the relief damper in the return air path is typically a mistake if the pressure drop through that path exceeds 0.10” wg. Barometric damper(s) must be installed within or behind a wind and rain barrier such as a louvered relief penthouse, rain hood, or sidewall louver.]

Maintain space barometric pressure at not greater than +0.05” wg by adjusting pressure relief setting of gravity/spring actuated damper(s).

Anytime the air-handling system is “OFF,” modulate [minimum] outdoor air damper 0% “OPEN” via AO point.

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4.12.2 Minimum Outdoor Airflow Control, VAV Single Zone System:




Period"OFF" Period

VA

MinimumVentilation

Airflow (CFM)


Ventilation Air as Scheduled on the



Minimum Required

Ventilation Air)




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Period"OFF" Period


10% of EA 10% of EA


During “OCCUPIED” periods and during “UNOCCUPIED” periods prior to the air-handling system being commanded “OFF,” “ENABLE” minimum outdoor airflow control maintain OA at setpoint, as follows:

[Guideline: Select/edit one of the following two options complying with ASHRAE Std. 62.1 for minimum outdoor airflow control.]

Outdoor airflow rate monitoring and control:

[Guideline: This option for control of minimum outdoor airflow rate is based on direct measurement of that airflow, which requires an airflow monitoring station in the minimum outdoor air intake.]

MONITOR minimum outdoor airflow OA as AI point.

Maintain minimum outdoor airflow OA at setpoint by modulating the [minimum] outdoor air damper and, as necessary, the return air damper, via AO point(s) as follows:

If OA falls below the minimum ventilation airflow VA and the [minimum] outdoor air damper is modulated 100% “OPEN,” modulate return air damper from 100% to 0% “OPEN” via AO point.

If OA falls below the minimum ventilation airflow VA after the [minimum] outdoor air damper is modulated 100% “OPEN” and the return air damper is modulated 100% “CLOSED,” reset the minimum supply fan speed setpoint upward.

Outdoor airflow differential pressure monitoring and control:

[Guideline: This option for control of minimum outdoor airflow rate is based on direct measurement of the differential air pressure drop across the outdoor intake louver and damper. Generally, the direct measurement of airflow (see above option) is more accurate and only marginally more expensive…it is the recommended option. However, for small air systems (<3,000 cfm), and especially for small packed units, space constraints may limit use of airflow sensors.]

MONITOR differential pressure across the outdoor air intake louver and damper as AI point.

Modulate [minimum] outdoor air damper 0-100%“OPEN” via AO point to maintain minimum outdoor air differential pressure at setpoint.

During TAB of air-handling system, determine pressure drop across outdoor air intake louver and damper at minimum outdoor airflow and establish setpoint for this control sequence.

Maintain minimum outdoor air differential pressure at setpoint by modulating the [minimum] outdoor air damper and, as necessary, the return air damper, as follows:

If outdoor air differential pressure falls below setpoint and the [minimum] outdoor air damper is modulated 100% “OPEN,” modulate return air damper from 100% to 0% “OPEN” via AO point

If outdoor air differential pressure falls below setpoint after the [minimum] outdoor air damper is modulated 100% “OPEN” and the return air damper is modulated 100% “CLOSED,” reset the minimum supply fan speed setpoint upward.

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[Guideline: Normally, delete the following sentence. But, for high density occupancies, the outdoor airflow required for ventilation may result in excess barometric pressure (e.g., >0.10” wg) in the occupied area. While rare, this condition requires barometric pressure relief and the simplest, lest costly method is to use spring-loaded adjustable setpoint barometric pressure relief dampers. This option is feasible only if a direct, low pressure drop relief air path from the space to outdoors can be created…locating the relief damper in the return air path is typically a mistake if the pressure drop through that path exceeds 0.10” wg. Barometric damper(s) must be installed within or behind a wind and rain barrier such as a louvered relief penthouse, rain hood, or sidewall louver.]



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4.14 Demand Control Ventilation (DCV) Enable/Disable, Single Zone System:

[Guideline: Compliance with the ASHRAE Standard 90.1 requires that DCV be provided for spaces larger than 500 square feet that have an average occupant load of ≥25 people per 1000 square feet of floor area (as established on the basis of the Mechanical Code) and are served by systems with one or more of the following elements: an airside economizer; automatic modulating control of the outdoor air damper; or a design outdoor airflow greater than 3,000 cfm.

DCV is not required for systems with a design outdoor airflow less than 1,200 cfm or for spaces where the supply airflow rate minus any makeup or outgoing transfer air requirement is less than 1,200 cfm.

Select DCV control sequences required for the project from options 4.14.1, 4.14.2, 4.14.3, and 4.14.4, as applicable.]

During “OCCUPIED” periods, ENABLE demand control ventilation, as follows:

Inhibit Sequence 4.14.1, 4.14.2, 4.14.3, and 4.14.4, as applicable, during the first hour after beginning of each "OCCUPIED" period.

During “UNOCCUPIED” periods and anytime the air-handling system is “OFF,” DISABLE demand control ventilation.

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4.14.1 Demand Control Ventilation (DCV) Based on Occupancy Schedule + Occupancy/Vacancy Sensing, Single Zone System:

Anytime occupancy/vacancy sensor(s) determine(s) that all spaces served by an air-handling system become unoccupied, minimum ventilation airflow, VA, setpoint in Sequence 4.12.1 shall be reduced to the greater of (EA + PA) or the area component of the design ventilation airflow, Va, dictated by ASHRAE Standard 62.1.

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4.14.2 Demand Control Ventilation (DCV) Based on Occupancy Schedule + Operator/Manual Schedule Override, Single Zone System:

[Guideline: For certain spaces, such as gymnasiums, auditoriums, and other assembly occupancies, the minimum ventilation required for routine use is significantly less than the minimum ventilation required for peak occupancy during assembly “events.” Therefore, two minimum ventilation airflow requirements can be defined:

“Normal” Occupancy: The number of persons that may occupy the space during routine use. (For a gymnasium, this may be 40-60 people, the occupancy for two physical education classes. For an auditorium, the normal occupancy may be only 10-40 people for drama or music classes, play rehearsals, etc.)

“Event” Occupancy: The maximum number of persons that may occupancy the space under “full house” conditions. (For a gymnasium, this would be the occupancy count during a basketball game or school assembly. For an auditorium, this would be the maximum seating capacity, plus stage occupancy.)

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While the “normal” occupancy period occurs routinely, the “event” occupancy occurs infrequently and, often, unpredictably, so a schedule for controlling the ventilation rate cannot be readily developed. Therefore, it is recommended that a local key-operated switch be provided so that manual changeover from normal ventilation rate to event ventilation rate.]

During “NORMAL OCCUPIED” periods, minimum ventilation airflow, VA, setpoint in Sequence 4.12.1 or 4.12.2, as applicable, shall be the “NORMAL” ventilation airflow as scheduled on the Drawings.

During “EVENT OCCUPIED” periods defined by (1) manual “event override switch” in accordance with Section 230913 or (2) operator override of Sequence 1.14, minimum ventilation airflow VA setpoint in Sequence 4.12.1 or 4.12.2, as applicable, shall be the “EVENT” outdoor airflow as scheduled on the Drawings.

Maximum length of “EVENT OCCUPIED” period (override) shall be 3 hours.

If “EVENT OCCUPIED” period extends past midnight, terminate “EVENT OCCUPIED” period override of Sequence 1.14 at 12:01 a.m.

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4.14.3 Demand Control Ventilation (DCV) Based on Occupancy Schedule + CO2 Sensing, Single Zone System:

[Guideline: CO2 sensors have been found to be both inaccurate and unreliable and their use is not recommended. However, it their use is required by the Owner and/or for LEED compliance, the following sequence may be utilized.

Where a single zone system serves multiple spaces, provide a single CO2 sensor in a “key” space indicated on the Drawings or in the system return air duct, upstream of the outdoor air intake connection.

It is critical that the A-E review the Design Guidelines to become familiar with the issues associated with CO2 sensors and make sure the Owner understands the significant maintenance burden that is required to maintain sensor accuracy.]

MONITOR carbon dioxide (CO2) indoor and outdoor concentration levels (ppm), as indicated on the Drawings, and average monitored levels over a sliding 5 minute period to establish input values for computation below:

Minimum outdoor airflow VA for Sequence 4.12.1 or 4.12.2, as applicable, shall be reduced in response to monitored CO2 concentration levels, as follows:

Modulate the [minimum] outdoor air damper to maintain the maximum differential between indoor and outdoor CO2 levels in any space not to exceed 700 ppm.

Inhibit sequence if ventilation airflow, VA, is reduced to the greater of (EA + PA) or to the sum of zone area component of the minimum design ventilation airflows, Va, dictated by ASHRAE Standard 62.1.

Modulate the [minimum] outdoor air damper to maintain the maximum indoor CO2 level in any space not to exceed 1000 ppm.

Initiate alarm if indoor CO2 level exceeds 1200 ppm for 30 minutes or more.

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4.14.4 Demand Control Ventilation (DCV) Based on Occupancy Schedule + People Counting/Sensing, Single Zone System:

[Guideline: While “people counting” technology is still new to the industry, it is already considered to be more accurate and reliable than CO2 sensing, though significantly more expensive. Its use is a better option than Sequence 4.14.3 and is recommended for spaces such as auditoriums, large classrooms or lecture halls, dining areas, etc. that may have widely varying populations.]

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Every 5 minutes, MONITOR the total actual population in the space(s) served by an air-handling system.

If actual population is 0 (zero), the minimum ventilation airflow, VA, setpoint in Sequence 4.12.1 or 4.12.2, as applicable, shall be reduced to the greater of (EA + PA) or the area component of the design ventilation airflow Va, whichever is greater.

If the actual population is 1 or more, compute the population ratio, PR, as follows:

PR = (Actual Population) / (Design Population)

If computed PR exceeds 1.0, reset PR to 1.0.

The minimum ventilation airflow, VA, setpoint in Sequence 4.12.1 or 4.12.2, as applicable, shall be reduced to the greater of (EA + PA) or the population-adjusted area component of the design ventilation airflow (Va x PR).

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4.15 Airside Economizer Control:

[Guideline: Every economizer requires that relief of indoor barometric pressure be provided via barometric relief dampers, return air fan(s), or relief air fan(s).]

During “ON” periods, ENABLE airside economizer control. Each [maximum] outdoor air damper, return air damper, and relief air damper shall be modulated as an individual AO point, as follows:

[Guideline: Two optional sequences of operation for airside economizer control are the fixed dry bulb enthalpy control option, which uses outdoor dry bulb temperatures to establish enthalpy limits, and the differential enthalpy option.]

Dry bulb enthalpy control:

When the air-handling system is providing cooling, as evidenced by the space temperature being above the maximum comfort temperature setpoint, and the outdoor air temperature is at or below 55°F, modulate the cooling coil control valve “CLOSED” via AO point and maintain space temperature at setpoint by modulating the [maximum] outdoor air, return air, and relief air dampers via AO points.

[Guideline: The outdoor air temperature setpoint for switching to/from 100% outdoor airflow operation, applied below, must be determined by psychrometric analysis as the temperature below which the outdoor air enthalpy will be at or below the return air enthalpy. For example, in Climate Zone 3A, a switchover temperature of 65°F would result in little risk of the outdoor air enthalpy exceeding the return air enthalpy. However, in Climate Zone 5A, the switchover temperature setpoint can raised to 69°F. Note the required high limit temperatures for switchover imposed by the 2012 Energy Conservation Code.]

When the air-handling system is providing cooling, as evidenced by the space temperature being above the maximum comfort temperature setpoint, and the outdoor temperature is above 55°F but at or below ____ºF [Guideline: Enter temperature.], modulate the [maximum] outdoor air and relief air dampers 100% “OPEN” and return air damper 100% “CLOSED” via AO points so that the system operates with 100% outdoor air supply. Maintain the space temperature by modulating the cooling coil chilled water control valve via AO point.

When the outdoor air temperature is above _____ºF [Guideline: Enter temperature.], modulate the [maximum] outdoor air and relief air dampers 100% “CLOSED” and return air damper 100% “OPEN” via AO point so that the system operates with only minimum outdoor air supply. Maintain space temperature setpoint by modulating cooling coil chilled water control valve via AO point.

Differential enthalpy control:

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When the air-handling system is providing cooling, as evidenced by the space temperature being above the maximum comfort temperature setpoint, and the outdoor air temperature is at or below 55°F, modulate the cooling coil control valve “CLOSED” via AO point and maintain space temperature at setpoint by modulating the [maximum] outdoor air, return air, and relief air dampers via AO points.

When the outdoor air temperature is greater than 55°F and the outdoor enthalpy is less than the space enthalpy, modulate the [maximum] outdoor air and relief air dampers 100% “OPEN” and the return air damper 100% “CLOSED” via AO points so that the system operates with 100% outdoor air supply. Maintain space temperature by modulating the cooling coil chilled water control valve via AO point.

When the outdoor air enthalpy is greater than the space enthalpy, modulate [maximum] outdoor air and relief air dampers 100% “CLOSED” and the return air damper 100% “OPEN” via AO points so that the system operates with minimum outdoor air supply. Maintain space temperature setpoint by modulating cooling coil chilled water control valve via AO point.

[Guideline: Select the relief air sequence to be used from the following options.]

Relief air control via barometric pressure relief damper(s):

[Guideline: From single large spaces, direct barometric pressure relief utilizing gravity/spring actuated dampers may be used. This option is feasible only if a direct, low pressure drop relief air path from the space to outdoors can be created…locating the relief damper in the return air path is typically a mistake if the pressure drop through that path exceeds 0.10” wg. Barometric damper(s) must be installed within or behind a wind and rain barrier such as a louvered relief penthouse, rain hood, or sidewall louver.]


Return air fan control (Flow Tracking):

MONITOR supply fan airflow SA as AI point.

MONITOR return fan airflow RA as AI point.

Modulate return fan speed through VFD via AO point to maintain building outdoor airflow OA at setpoint.

Modulate relief air damper via AO point “OPEN” to maintain relief airflow computed as [RA - (SA - OA)].

Return air fan control (Building/Plenum Pressure Control):

[Guideline: This option should be used ONLY when required/requested by the Owner. The designer must take extra care in selecting the control parameters that determine the dynamic response of the digital filters and feedback controllers.]

MONITOR the pressure in the relief/return air plenum downstream of the return air fan as AI point.

Modulate the return air fan speed via AO point to maintain the relief/return air plenum pressure at +0.25 hPa (0.10” wg) setpoint.

MONITOR outdoor barometric pressure as AI point.

[Guideline: Indicate sensor location on the Drawings. Locate outdoor sensor at least 8 feet above the roof and remote from exhaust fans. Install the sensor in a wind-proof enclosure.

In order to obtain accurate outdoor pressure measurements, the sensor needs to be both stable and routinely calibrated against a known reference atmospheric pressure source, i.e. one that is professionally maintained. The National Weather Service (NWS) tests their pressure gauges

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annually using calibrated instruments from the national pressure standards laboratory. Routine recalibration the outdoor sensor using the air pressure measurement of the nearest NWS automated weather station is required.]

MONITOR indoor barometric pressure as AI point.

[Guideline: Indicate sensor location on the Drawings. Locate indoor sensor in interior space served with a constant volume terminal unit, with no direct exhaust from the space. The selected space should be remote from elevators, stair towers, adjacent spaces with variable pressure conditions (such a toilets, laboratories, etc.) and, ideally, should be an unoccupied space with minimum door opening/closing.]

Average monitored barometric pressures over a sliding 5 minute period to establish input values for differential pressure computation below:

Compute building differential pressure as (indoor barometric pressure – outdoor barometric pressure).

Modulate relief air damper 0-100% “OPEN” via AO point to maintain building differential pressure at +0.25 hPa (0.10” wg).

To minimize conflict between the fan and damper control loops, the following is required:

To prevent excessive control loop interaction, the closed loop response time of the building pressurization loop shall not exceed 20% of the closed loop response time of the return air fan control loop. This may be accomplished by decreasing the gain of the building pressure controller.

To prevent fluctuations in outdoor air pressure attributed from wind gusts “exciting” the control system, digital filters shall be incorporate to reject input spikes.

Relief air fan control (Flow Tracking):

If [OA - (EA + PA] > 0, relief air fan shall be commanded "ON" via DO point.

Confirm fan operation based on fan motor status as DI point in accordance with Sequence 1.25.

MONITOR relief air fan airflow as AI point.

Modulate relief air fan speed through VFD via AO point to maintain relief airflow at [OA - (EA + PA)].

Modulate relief air damper 0-100% “OPEN” via AO point in direct proportion to relief air fan speed.

Relief air fan control (Building Pressure Control):

MONITOR outdoor barometric pressure as AI point.

[Guideline: Indicate sensor location on the Drawings. Locate outdoor sensor at least 8 feet above the roof and remote from exhaust fans. Install the sensor in a wind-proof enclosure.

In order to obtain accurate outdoor pressure measurements, the sensor needs to be both stable and routinely calibrated against a known reference atmospheric pressure source, i.e. one that is professionally maintained. The National Weather Service (NWS) tests their pressure gauges annually using calibrated instruments from the national pressure standards laboratory. Routine recalibration the outdoor sensor using the air pressure measurement of the nearest NWS automated weather station is required.]

MONITOR indoor barometric pressure as AI point.

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[Guideline: Indicate sensor location on the Drawings. Locate indoor sensor in interior space served with a constant volume terminal unit, with no direct exhaust from the space. The selected space should be remote from elevators, stair towers, adjacent spaces with variable pressure conditions (such a toilets, laboratories, etc.) and, ideally, should be an unoccupied space with minimum door opening/closing.]

Average monitored barometric pressures over a sliding 5 minute period to establish input values for differential pressure computation below:

Compute building differential pressure as (indoor barometric pressure – outdoor barometric pressure).

If the building differential pressure rises above +0.25 hPa (0.10” wg), relief fan shall be commanded “ON” via DO point

Modulate relief air fan speed through VFD via AO point to maintain building differential pressure at +0.25 hPa (0.10” wg).

Modulate relief air damper 0-100% “OPEN” via AO point in direct proportion the relief air fan speed.

If building differential pressure falls below +0.12 hPa (0.05” wg) for 15 minutes, command relief air fan “OFF” via DO point and modulate relief air damper “CLOSED” via AO point.

During “OFF” periods, modulate all dampers to their “normal” position.

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4.2 MULTIPLE ZONE SINGLE DUCT AIR-HANDLING SYSTEMS

[Guidelines: Multiple zone single duct air-handling systems are configured to serve a significant number of independent control zones, each consisting of a space or small number of spaces, with varying HVAC requirements and, to some extent, varying operating schedules. These systems, to minimize energy consumption, are almost always controlled for VAV operation.]

4.20 Multiple Zone Air-Handling System, Operations and Monitoring:

The following sequences of operation indicated by check boxes shall apply to each of the following single zone air-handling systems:




Start/stop control (Sequence 4.00) Drain pan condensate monitoring (Sequence 4.05) Filter differential pressure monitoring (Sequence 4.06) Low limit thermostat alarm (Sequence 4.07) Preheat (Sequence 4.08)

Hot water coil with circulating pump option

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Hot water coil with integral face and bypass dampers option Steam coil with dual control valves option Steam coil with integral face and bypass dampers option Electric coil with stages option Electric coil with silicon controlled rectifier option

Primary humidifier (Sequence 4.09) Variable air volume supply air control

Discharge air temperature control (Sequence 4.21) Supply fan air volume control (Sequence 4.22) Minimum outdoor air flow control (Sequence 4.23)

Demand control ventilation enable/disable (Sequence 4.24) Occupancy schedule + return air CO2 sensing option (Sequence 4.24.1) Occupancy schedule + zone occupancy/vacancy sensing option (Sequence 4.24.2) Occupancy schedule + zone CO2 sensing option (Sequence 4.24.3) Occupancy schedule + zone people counting option (Sequence 4.24.4)

Economizer cycle (Sequence 4.15) Dry bulb temperature option Differential enthalpy option Relief air control




Space temperature and humidity control via terminal units (Sequences 4.26 and as follows) Single duct, CAV terminal reheat (Sequence 4.27.1) Single duct, VAV cooling only (Sequence 4.27.2) Single duct, VAV terminal reheat, single maximum airflow setpoint (Sequence 4.27.3) Single duct, VAV terminal reheat, dual maximum airflow setpoints (Sequence 4.27.4) Single duct, supplemental perimeter heating (Sequence 4.27.5) Single duct, fan powered, series configured (4.28.1) Single duct, fan powered, parallel configured (4.28.2)

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[Guideline: The following air system elements and sequences of operation apply to multiple zone units utilizing chilled water coils for cooling; hot water, steam, and/or electric coils for preheating; and hot water heating and/or reheating…edit as required.]

4.21 Discharge Air Temperature Control, Multiple Zone System:

During “ON” periods, define discharge air temperature setpoint, as follows:

MONITOR discharge air temperature as AI point.

MONITOR return air temperature and humidity as individual AI points.

Set discharge air temperature setpoint as AV point as follows:

Routinely (at least every 5 minutes), evaluate air-handling system return air temperature and humidity to establish discharge air temperature setpoint.

If the return air temperature is ≤ 70ºF and return air humidity is ≤ 50%, discharge air temperature setpoint shall be 60ºF.

If the return air temperature is ≥ 75ºF or return air humidity is > 50%, discharge air temperature setpoint shall be 55ºF.

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Reset discharge air temperature setpoint via AV point as follows:

Routinely (at least every 5 minutes), evaluate space temperatures and terminal units damper positions to identify potential under-cooling. If 90% or more terminal unit dampers are more than 95% open, decrease discharge air temperature setpoint by 0.5ºF until the quantity of terminal air-handling system dampers that are more than 95% “OPEN” decreases to 60% or less.

Routinely (at least every 5 minutes), evaluate space humidity conditions to identify potential high humidity. If humidity in any space served exceeds the high limit humidity setpoint for that space, decrease discharge air temperature setpoint by 0.5ºF until all space humidity conditions are at or below the space high limit humidity setpoint.

Modulate NO cooling coil chilled water control valve via AO point from 0% to 100% “OPEN” to maintain discharge air temperature at setpoint.

During “OFF” periods, DISABLE discharge air temperature setpoint.

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4.22 Supply Air Fan VAV Control, Multiple Zone System:

During “ON” periods, ENABLE supply air fan volume control, as follows:

MONITOR supply air operating static pressure as AI point:

If location is not indicated on the Drawings, locate sensor at a point approximately 2/3 distance downstream in supply ductwork.

MONITOR supply air fan airflow rate (cfm) as AI point.

Modulate supply fan speed through VFD via AO point to maintain supply duct operating static pressure setpoint as follows:

Initial supply operating static pressure setpoint shall be set at 0.75" wg.


Operating static pressure setpoint shall be reset based on terminal unit airflow "requests", derived from terminal units damper position/airflow and space temperature requirements as follows:

When all terminal unit dampers are less than 90% “OPEN” and all space temperatures are within the comfort zone defined by Sequence 4.01, operating pressure setpoint shall be incrementally reset downward by 0.10” wg every 15 minutes to a minimum of 0.30" wg or until the supply fan reaches its it minimum allowable airflow as defined below.

When at least one terminal unit damper is greater than 95% “OPEN” and corresponding space temperature is not within the comfort zone defined by Sequence 4.01, the reverse shall occur and the operating static pressure setpoint shall be reset upward by 0.10” wg every 15 minutes to final setpoint of 1.25" wg.

Supply airflow shall not be less than required minimum outdoor airflow defined by Sequence 4.23.

During “OFF” periods, DISABLE supply fan airflow control.

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4.23 Minimum Outdoor Air Control, VAV Multiple Zone System:


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Period"OFF" Period

VA

MinimumVentilation

Airflow (CFM)


Ventilation Air as Scheduled on the



Minimum Required

Ventilation Air)





10% of EA 10% of EA


During “OCCUPIED” periods and during “UNOCCUPIED” periods prior to the air-handling system being commanded “OFF,” “ENABLE” minimum outdoor airflow control to maintain OA at setpoint, as follows:

[Guideline: Select/edit one of the following two options complying with ASHRAE Std. 62.1 for minimum outdoor airflow control.]

Outdoor airflow rate monitoring and control:

[Guideline: This option for control of minimum outdoor airflow rate is based on direct measurement of that airflow, which requires an airflow monitoring station in the minimum outdoor air intake.]

MONITOR minimum outdoor airflow OA as AI point.

Maintain minimum outdoor airflow OA at setpoint by modulating the [minimum] outdoor air damper and, as necessary, the return air damper, via AO point(s) as follows:

If OA falls below the minimum ventilation airflow VA and the [minimum] outdoor air damper is modulated 100% “OPEN,” modulate return air damper from 100% to 0% “OPEN” via AO point.

If OA falls below the minimum ventilation airflow VA after the [minimum] outdoor air damper is modulated 100% “OPEN” and the return air damper is modulated 100% “CLOSED,” reset the minimum supply fan speed setpoint upward.

Outdoor airflow differential pressure monitoring and control:

[Guideline: This option for control of minimum outdoor airflow rate is based on direct measurement of the differential air pressure drop across the outdoor intake louver and damper. Generally, the direct measurement of airflow (see above option) is more accurate and only marginally more expensive…it is the recommended option. However, for small air systems (<3,000 cfm), and especially for small packed units, space constraints may limit use of airflow sensors.]

MONITOR differential pressure across the outdoor air intake louver and damper as AI point.

Modulate [minimum] outdoor air damper 0-100% “OPEN” via AO point to maintain minimum outdoor air differential pressure at setpoint.

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During TAB of air-handling system, determine pressure drop across outdoor air intake louver and damper at minimum outdoor airflow and establish setpoint for this control sequence.

Maintain minimum outdoor air differential pressure at setpoint by modulating the [minimum] outdoor air damper and, as necessary, the return air damper, as follows:

If outdoor air differential pressure falls below setpoint and the [minimum] outdoor air damper is modulated 100% “OPEN,” modulate return air damper from 100% to 0% “OPEN” via AO point

If outdoor air differential pressure falls below setpoint after the [minimum] outdoor air damper is modulated 100% “OPEN” and the return air damper is modulated 100% “CLOSED,” initiate alarm.

[Guideline: Normally, delete the following sentence. But, for high density occupancies, the outdoor airflow required for ventilation may result in excess barometric pressure (e.g., >0.10” wg) in the occupied area. While rare, this condition requires barometric pressure relief and the simplest, lest costly method is to use spring-loaded adjustable setpoint barometric pressure relief dampers. This option is feasible only if a direct, low pressure drop relief air path from the space to outdoors can be created…locating the relief damper in the return air path is typically a mistake if the pressure drop through that path exceeds 0.10” wg. Barometric damper(s) must be installed within or behind a wind and rain barrier such as a louvered relief penthouse, rain hood, or sidewall louver.]



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4.24 Demand Control Ventilation (DCV) Enable/Disable, VAV Multiple Zone System:

[Guideline: Compliance with the International Energy Conservation Code requires that DCV be provided for spaces larger than 500 square feet that have an average occupant load of ≥25 people per 1000 square feet of floor area (as established on the basis of the International Mechanical Code) and are served by systems with one or more of the following elements: an airside economizer; automatic modulating control of the outdoor air damper; or a design outdoor airflow greater than 3,000 cfm.

DCV is not required for systems with a design outdoor airflow less than 1,200 cfm or for spaces where the supply airflow rate minus any makeup or outgoing transfer air requirement is less than 1,200 cfm.

Va and Vo used in DCV computations are the area and occupancy ventilation airflows based on ASHRAE Standard 62.1, as scheduled on the Drawings.

Select DCV control sequences required for the project from options 4.2.1, 4.24.2, 4.24.3, and 4.24.4, as applicable.]

During “OCCUPIED” periods, ENABLE demand control ventilation.

Inhibit Sequence 4.24.1, 4.24.2, 4.24.3, and/or 4.24.4, as applicable, during the first hour of each "OCCUPIED" period.

During “UNOCCUPIED” periods and anytime the air-handling system is “OFF,” DISABLE demand control ventilation.

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4.24.1 Demand Control Ventilation (DCV) Based on Occupancy Schedule + Return Air CO2 Sensing, VAV Multiple Zone System:

[Guideline: CO2 sensors have been found to be both inaccurate and unreliable and their use is not recommended. However, it their use is required by the Owner, the following sequence may be utilized.

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When ventilation air in a multiple zone system is controlled by a single CO2 sensor, the sensor is generally located in the return air duct. The sensor controls the dampers to maintain return air at approximately 800 ppm CO2 concentration (based and outdoor CO2 level of 400 ppm and the assumption that 75% of spaces served will be at 700 ppm or lower CO2 concentration, while 25% of spaces will be at no greater than 1,000 ppm). The sensor monitors average concentration; thus some zones are over-ventilated and some zones under-ventilated…this type of control successfully reduces energy use at low first cost, but doesn’t strictly meet code or guarantee occupant comfort.]

Every minute, average monitored carbon dioxide (CO2) return and outdoor air concentration levels (ppm) over a sliding 5 minute window to obtain levels for calculations below:

When DCV is “ENABLED,” minimum outdoor air airflow setpoint, OA, defined by Sequence 4.23 shall be reduced in response to monitored carbon dioxide concentration levels, as follows:

Modulate the minimum outdoor air damper to maintain the maximum differential between return air and outdoor air CO2 levels at 400 ppm.

Inhibit sequence if ventilation airflow, VA, is reduced to the greater of (EA + PA) or the sum of zone area component of the minimum design ventilation airflows, Va, dictated by ASHRAE Standard 62.1.

Modulate the minimum outdoor air damper to maintain the maximum return air CO2 level in any space at 1000 ppm.

Initiate alarm if return CO2 level exceeds 1200 ppm for 30 minutes or more.

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4.24.2 Demand Control Ventilation (DCV) Based on Occupancy Schedule + Zone Occupancy/Vacancy Sensing, VAV Multiple Zone System :

[Guideline: This sequence is a simplified version of the requirements of ASHRAE Standard 62.1.]

When DCV is “ENABLED,” minimum outdoor air airflow setpoint OA defined by Sequence 4.23 shall be reduced in response to occupancy in each terminal unit zone as follows:

Every 5 minutes, determine occupancy status, on the basis of space occupancy/vacancy sensors, for each terminal unit zone.

Compute air-handling system VA airflow requirement as follows:

VA = [Σ Va/0.5 for all unoccupied terminal unit zones] + [Σ (Va + Vo)/0.9 for all occupied terminal unit zones]

Compute reduced OA airflow setpoint for Sequence 4.23.


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4.24.3 Demand Control Ventilation (DCV) Based on Occupancy Schedule + Zone CO2 Sensing, VAV Multiple Zone System:

[Guideline: CO2 sensors have been found to be both inaccurate and unreliable and their use is not recommended. However, it their use is required by the Owner and/or for LEED compliance, the following sequence may be utilized.

With a CO2 sensor in each terminal unit zone as required by ASHRAE Standard 90.1, the DDC system can determine how much OA is needed in each zone and can reset the building outdoor airflow to meet the need of the most critical zone. Thus, some zones are over-ventilated, but no zone is under-ventilated, thus complying with ASHRAE Standard 62.1 requirements.

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To minimize control costs and reduce control sequence complexity, CO2 sensors should be installed only in zones requiring DCV control by the current edition of ASHRAE Standard 90.1.

This sequence is a simplified version of the requirements of ASHRAE Standard 62.1.]

Every 1 minute, average monitored carbon dioxide (CO2) indoor and outdoor concentration levels (ppm), as indicated on the Drawings, over a sliding 5 minute window to obtain levels for calculations below:

When DCV is “ENABLED,” minimum outdoor air airflow setpoint OA defined by Sequence 4.23 shall be reduced in response to CO2 concentration level in each terminal unit zone as follows:

Every 5 minutes, compute the CO2 Concentration Ratio, CR for each terminal unit zone as follows:

CR = [(Outdoor CO2 Concentration) – (Indoor CO2 Concentration)] / 700

If computed CR exceeds 1.0, reset CR to 1.0.


VA = Σ {[Va + (Vo x CR)]/0.7} for all terminal unit zones



Initiate alarm if any terminal unit zone CO2 level exceeds 1200 ppm for 30 minutes or more.

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4.24.4 Demand Control Ventilation (DCV) Based on Occupancy Schedule + Zone People Counting/Sensing, VAV Multiple Zone System:

[Guideline: While “people counting” technology is still new to the industry, it is already considered to be more accurate and reliable than CO2 sensing, though significantly more expensive. Its use is a better option than Sequence 4.24.3 and is recommended for spaces such as auditoriums, large classrooms or lecture halls, dining areas, etc. that may have widely varying populations.

This sequence is a simplified version of the requirements of ASHRAE Standard 62.1.]

When DCV is “ENABLED,” minimum outdoor air airflow setpoint OA defined by Sequence 4.23 shall be reduced in response to population within each terminal unit zone as follows:

Every 5 minutes, MONITOR actual population and compute population ratio (PR) for each terminal unit zone as follows:

If actual population is 0 (zero), PR = 0.

If population is 1 or more, compute population ratio, PR, as follows

PR = (Actual Zone Population) / (Design Zone Population)

If computed PR exceeds 1.0, reset PR to 1.0.


VA = Σ {[Va + (Vo x PR)]/0.7} for all terminal unit zones



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4.26 “OFF” Period Space Temperature/Humidity Control, Multiple Zone System:

During “OFF” periods, command air-handling system and exhaust fans associated with that air-handling system “OFF” via DO points.

Modulate [minimum] outdoor air damper, [maximum outdoor air damper,] and relief air damper 100% “CLOSED”and return air damper to 100% open.

MONITOR temperature and humidity in each zone served by the air-handling system.

If any space temperature exceeds the “OFF” period high limit temperature defined by Sequence 4.01 for 15 minutes, cooling shall be provided as follows:

If chilled water is not available, as indicated by the CHWS temperature being greater than 45°F after 15 minutes of operation, initiate alarm and terminate sequence.

If chilled water is available, as indicated by CHWS temperature being less than or equal to 45°F, command air-handling system “ON” in accordance with Sequence 4.00.

As applicable, command return fan "ON" in accordance with Sequence 4.00, modulate return air fan speed to 100% airflow through VFD via AO point, and modulate supply fan speed through VFD via AO point to maintain 0 cfm difference between supply and return airflows.

As applicable, command relief fan "OFF" via DO point and modulate supply fan speed through VFD via AO point to maximum.

Modulate cooling coil chilled water control valve 100% “OPEN” via AO point.

Terminal units served by air handling system shall operate in accordance with “ON” period sequence of operation defined for each terminal unit type to maintain space temperature at “OFF” period high limit temperature setpoint minus 5°F.

If any space temperature falls below the “OFF” period low limit temperature defined by Sequence 4.01 for 15 minutes, command the hot water system "ON” and provide heating as follows:

If hot water is not available, as indicated by the HWS temperature being less than 100°F after 15 minutes of operation, initiate alarm and terminate sequence.

[Guideline: Delete the following sequence if the system utilizes predominately fan-powered terminal units.]

If hot water is available, as indicated by the HWS temperature being equal to or greater than 100°F, command air-handling system “ON” in accordance with Sequence 4.00:

As applicable, command return fan "ON" in accordance with Sequence 4.00, modulate return air fan speed through VFD via AO point to 100% airflow, and modulate supply fan speed through VFD via AO point to maintain 0 cfm difference between supply and return airflows.


Terminal units served by air handling system shall operate in accordance with “ON” period sequence of operation defined for each terminal unit type to maintain space temperature at “OFF” period low limit temperature setpoint plus 5°F.

[Guideline: Delete the following sequence if the system utilizes predominately standard (no-fan) terminal units.]

If hot water is available, as indicated by the HWS temperature being equal to or greater than 100°F and the air handling system predominately serves fan-powered terminal units, air-handling system shall remain

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“OFF” and each terminal unit shall be ENABLED to operate in accordance with “ON” period sequence of operation defined for each terminal unit type to maintain space temperature at “OFF” low limit temperature setpoint plus 5°F.

[Guideline: The following subsection may be deleted if “OFF” period high limit humidity control is not required.]

If any space humidity exceeds the high limit humidity setpoint, command hot water system "ON" and provide humidity control as follows:

If hot water is not available, as indicated by the HWS temperature being less than 100°F after 15 minutes of operation, initiate alarm and terminate sequence.

If chilled water is not available, as indicated by the CHWS temperature being greater than 45°F after 15 minutes of operation, initiate alarm and terminate sequence.

If both hot water, as indicated by the HWS temperature being equal to or greater than 100°F, and chilled water, as indicated by CHWS temperature being less than or equal to 45°F, are available, command air-handling system “ON” in accordance with Sequence 4.00:

As applicable, command return fan "ON" in accordance with Sequence 4.00, modulate return air fan speed through VFD via AO point to 100% airflow, and modulate supply fan speed through VFD via AO point to maintain 0 cfm difference between supply and return airflows.


Modulate cooling coil chilled water control valve 100% “OPEN” via AO point to maintain all space humidity conditions at “OFF” period high limit setpoint minus 5% RH.

Terminal units served by air handling system shall operate in accordance with “ON” period sequence of operation defined for each terminal unit type to maintain space temperature a “OFF” period high limit temperature setpoint minus 5°F.

Once all space condition(s) return to within setpoint limit conditions, +/- 5°F and/or -5% RH as defined above, for 5 minutes, command the air-handling system “OFF” via DO point, modulate both NO chilled water and NC heating coil hot water control valves “CLOSED” via AO points, DISABLE all terminal units, and command the chilled water system and hot water systems “OFF” via DO points.

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4.27.1 Terminal Unit, Single Duct, CAV Terminal Reheat:

[Guideline: Do not utilize multiple space temperature and humidity sensors for a terminal unit serving multiple spaces…select the most representative “key” space in which to locate one zone temperature and humidity sensor.

CAV terminal units may be used (only) in critical applications such as laboratories, hospitals, etc., since airflow balance/space pressurization control requirements fall under the “process” exemption of the Energy Conservation Code.]

Terminal unit (TU) airflow setpoints (cfm) shall include the following, as applicable and as scheduled on the Drawings:

VmaxVaVo

TU airflow setpoint, cooling and heatingMinimum space ventilation airflow, area basisMinimum space ventilation airflow, occupancy basis

MONITOR each terminal unit NO primary airflow damper as AI point.

MONITOR each terminal unit discharge air temperature as AI point.

During “ON” periods, TU shall operate as follows:

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Modulate primary air volume damper via AO point to maintain Vmax airflow at setpoint.

Hot Water Heating Coil: If space temperature falls below minimum comfort zone temperature setpoint, modulate hot water control valve via AO point to maintain space temperature at minimum comfort zone temperature setpoint.

Electric Resistance Heating Coil: If space temperature falls below minimum comfort zone temperature setpoint, energize heating coil via DO or AO point(s) in accordance with Sequence 1.39, as applicable, to maintain space temperature at minimum comfort zone temperature setpoint.

If space humidity rises above high limit humidity setpoint, initiate alarm.

“ON” period sequence of operation for TU is illustrated by the following graphic:

During “OFF” periods, TU shall operate as follows:

When the air-handling system is “OFF,” modulate the TU damper 100% “CLOSED” via AO point and DISABLE reheat coil control.

If the air-handling system, chilled water system, and, as applicable, hot water system start in accordance with Sequence 4.26, TU shall operate in accordance with “ON” period sequence defined above.

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4.27.2 Terminal Unit, Single Duct, VAV Cooling Only:

[Guideline: Do not utilize multiple space temperature and humidity sensors for a terminal unit serving multiple spaces…select the most representative “key” space in which to locate one zone temperature and humidity sensor.]


VmaxVminVaVo

Maximum TU airflow setpoint, coolingMinimum TU airflow setpoint, coolingMinimum space ventilation airflow, area basisMinimum space ventilation airflow, occupancy basis




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If space temperature rises above the maximum comfort zone temperature setpoint, modulate primary air volume damper via AO point between Vmin airflow setpoint and Vmax airflow setpoint to maintain space at maximum comfort zone temperature setpoint.

If space humidity rises above high limit humidity setpoint, initiate alarm.

If the space is determined to be “UNOCCUPIED” on the basis of a space occupancy/vacancy sensor(s) or people-counting technologies sensor(s), reset Vmin airflow setpoint to Va airflow and control terminal unit in as above.

“ON” period sequence of operation for TU is illustrated by the following graphic:


When the air-handling system is “OFF,” modulate the TU damper 100% “CLOSED” via AO point.

If the air-handling system and chilled water system start in accordance with Sequence 4.26, TU shall operate in accordance with “ON” period sequence defined above.

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4.27.3 Terminal Unit, Single Duct, VAV Terminal Reheat, Single Maximum Airflow Setpoint:


VmaxVminVaVo

Maximum TU airflow setpointMinimum TU airflow setpointMinimum space ventilation airflow, area basisMinimum space ventilation airflow, occupancy basis



During scheduled “ON” periods defined by Sequence 1.14, TU shall operate as follows:


If space temperature falls below minimum comfort zone temperature setpoint, modulate primary air volume damper via AO point to maintain Vmin airflow setpoint and modulate heating control via AO point to maintain space at minimum comfort zone temperature setpoint.

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Hot Water Heating Coil: Modulate NC hot water control valve to maintain space temperature at minimum comfort zone temperature setpoint.

Electric Resistance Heating Coil: Energize heating coil in accordance with Sequence 1.39, as applicable, to maintain space temperature at minimum comfort zone temperature setpoint.

If space humidity rises above high limit humidity setpoint, modulate primary air volume damper via AO point to maintain space humidity at high limit humidity setpoint and modulate heating AO to maintain space temperature at maximum comfort zone temperature setpoint as above.

When space temperature is within the comfort temperature zone, modulate the primary air volume damper to maintain Vmin airflow setpoint and modulate the heating hot water control valve closed.

If the space is determined to be “UNOCCUPIED” as evidenced by space occupancy/vacancy sensor(s) or people-counting technology sensor(s), reset Vmin airflow setpoint to Va airflow and control terminal unit as defined above.

“ON” period sequence of operation for terminal unit is illustrated by the following graphic:


When the air-handling system is “OFF,” modulate the TU damper 100% “CLOSED” via AO point and DISABLE heating control.

If the space temperature exceeds the “OFF” period high temperature limit and the air-handling system and chilled water systems start in accordance with Sequence 4.26, TU shall provide cooling in accordance with its “ON” period cooling sequence above.

If the space temperature falls below the “OFF” period low temperature limit and the air-handling system and hot water systems start in accordance with Sequence 4.26, TU shall provide heating in accordance with its “ON” period heating sequence above.

If the space humidity exceeds the “OFF” period high humidity limit and the air-handling system and both chilled and hot water systems start in accordance with Sequence 4.26, TU shall provide humidity control in accordance with its “ON” period sequence above.

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4.27.4 Terminal Unit, Single Duct, VAV Terminal Reheat, Dual Maximum Airflow Setpoints:


Vmaxcool

Vmaxheat

VminVa

Maximum TU airflow setpoint, coolingMaximum TU airflow setpoint, heatingMinimum TU airflow setpoint, cooling and heatingMinimum space ventilation airflow, area basis

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Vo Minimum space ventilation airflow, occupancy basis


MONITOR each terminal unit discharge air temperature as n AI point.


If space temperature rises above the maximum comfort zone temperature setpoint, modulate primary air volume damper via AO point between Vmin airflow setpoint and Vmaxcool airflow setpoint to maintain space at maximum comfort zone temperature setpoint.

If space temperature falls below minimum comfort zone temperature setpoint, unit control sequence shall be as follows:

From 0% to 49% AI point signal, modulate primary air volume damper via AO point to maintain Vmin airflow setpoint. Modulate the heating AO point to increase supply air temperature to maintain 90ºF setpoint.

From 50% to 100% AI point signal, modulate heating AO to maintain supply air temperature at 90ºF setpoint and modulate primary air volume damper via AO point between Vmin airflow setpoint and Vmaxheat airflow setpoint to maintain space at minimum comfort zone temperature setpoint.



When space temperature is within the comfort temperature zone, modulate the primary air volume damper via AO point to maintain Vmin airflow setpoint and modulate the heating AO point to 0% signal.


If space humidity rises above high limit humidity setpoint, modulate primary air volume damper via AO point to maintain space humidity at high limit humidity setpoint and modulate heating AO point to maintain space temperature at maximum comfort zone temperature setpoint.

“ON” period sequences of operation for terminal unit is illustrated by the following graphic:


When the air-handling system is “OFF,” modulate the TU damper 100% “CLOSED” via AO point and DISABLE heating control.

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4.27.5 Terminal Unit, Single Duct, with Supplemental Perimeter Heating:

[Guideline: For space(s) that have high heat losses, perimeter baseboard heating may be applied to provide supplemental heating (and to eliminate the need for using a fan-powered terminal unit).]

When terminal unit heating output is modulated to 100% via AO point, on a continued fall in space temperature below the minimum comfort zone temperature setpoint, modulate perimeter heating AO to maintain minimum comfort zone temperature setpoint less 1.5ºF.

Hot Water Perimeter Heating: Modulate NO hot water control valve to maintain space temperature at minimum comfort zone temperature setpoint.

Electric Resistance Perimeter Heating: Energize heating in accordance with Sequence 1.39, as applicable, to maintain space temperature at minimum comfort zone temperature setpoint.

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4.28.1 Terminal Unit, Fan Powered, Single Duct, Series-Configured:


VmaxVminVaVo





Command TU supply fan “ON” via DO point


If space temperature falls below minimum comfort zone temperature setpoint, modulate primary air volume damper via AO point to maintain Vmin airflow setpoint and modulate heating AO to maintain space at minimum comfort zone temperature setpoint.


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If space humidity rises above high limit humidity setpoint, modulate primary air volume damper via AO point to maintain space humidity at high limit humidity setpoint and modulate heating AO to maintain space temperature at maximum comfort zone temperature setpoint, as above.

When space temperature is within the comfort temperature zone, modulate the primary air volume damper to maintain Vmin airflow setpoint and modulate the heating AO output to 0%.




When the air-handling system is “OFF,” command TU supply fan “OFF” via DO point, modulate the primary air damper 100% “CLOSED” via AO point, and DISABLE heating control.




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4.28.2 Terminal Unit, Fan Powered, Single Duct, Parallel-Configured:


VmaxVminVaVo



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If space temperature rises above the maximum comfort zone temperature setpoint, command TU supply fan “OFF” via DO point, modulate primary air volume damper via AO point between Vmin airflow setpoint and Vmax airflow setpoint to maintain space at maximum comfort zone temperature setpoint.

If space temperature falls below minimum comfort zone temperature setpoint, command TU supply fan “ON” via DO point at minimum speed, modulate primary air volume damper via AO point to maintain Vmin airflow setpoint, and modulate heating AO point to maintain space at minimum comfort zone temperature setpoint.



On a further fall in space temperature after heating AO signal is at 100%, modulate TU fan speed from minimum to maximum.

If space humidity rises above high limit humidity setpoint, modulate primary air volume damper via AO point to maintain space humidity at high limit humidity setpoint and modulate heating AO point to maintain space temperature at maximum comfort zone temperature setpoint as above.

When space temperature is within the comfort temperature zone, modulate the primary air volume damper via AO point to maintain Vmin airflow setpoint and modulate heating AO point to 0% output.




When the air-handling system is “OFF,” command TU supply fan “OFF,” modulate the primary air damper 100% closed, and DISABLE heating control.



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PACKAGED AIR-COOLED AND WATER-COOLED DX SYSTEMS

[Guideline: Packaged or split systems utilize direct expansion (DX) cooling. Heating, as applicable, may be provided via a direct fuel fired heat exchanger (furnace), a hot water or electric resistance heating coil, or heat pump cycle operation. The guidelines and sequences of operation provided in Section 4 generally apply to the air-handling side of these systems and must be utilized. However, the use of DX cooling requires certain control variations included in this section.

The number one control design issue with any packaged DX system is resolving the interface between the DDC system and the OEM controls. The scope of control provide by the OEM controller and the interface requirements are defined by this sequence, but the designer is cautioned that careful analysis of the OEM BACnet “Protocol Interface Compliance Statement” (PICS) is required to ensure that the required control sequence for the chiller is integrated correctly. ]

For single-zone systems, a “thermostatic interface” OEM controller is generally available and is preferred since this type of interface is well understood, is fairly simple, and is adequate for comfort air-conditioning operational control. The basic connections and functions associated with a thermostatic interface are as follows:

R –R terminal is the power provided by (typically) a 24v transformer provided as part of the system by manufacturers.

RC and RH –RC terminal is designated for the power for cooling control, while the RH terminal is designated for the power for heating. Some systems use two transformers. one for cooling and one for heating. In this case, power from the transformer in the air-conditioning system would go to the RC terminal and power from the heating system would go to the RH terminal. For a heating and cooling system equipped with a single transformer, a “jumper” is be installed between RC and RH to power both terminals from a common source.

Y (or Y1) – This is the terminal for cooling and goes to the compressor start/stop circuit for systems with one compressor or the first stage of cooling when there are multiple compressors.

Y2 – This is the thermostat terminal for second stage cooling.

W (or W1) – This is the thermostat terminal for heating when there is only one stage, or the first stage of heating where two stages are provided.

W2 – This is the thermostat terminal used for second stage of heating. (There are gas furnaces with low fire/ high fire control that may depend on two-stage heating control. Likewise, heat pumps use staging for multiple compressors and/or auxiliary heat.)

W3 – Terminal for third stage of heating (if required).

G – This is the thermostat terminal used to energize the indoor fan.

C – This is the thermostat “common” terminal that originates from the transformer(s) and is the “neutral” connection that completes a 24 volts power circuit.

O or B – These thermostat terminals are for heat pumps only. The B thermostat terminal is used when a OEM controller energizes the reversing valve in heating mode. However, most manufacturers energize the reversing valve for cooling and the O thermostat terminal is utilized for this purpose.

E – This thermostat terminal is for heat pumps and stands for “Emergency Heating.” If the heat pump compressor or condenser fails and it is necessary to provide heating, this terminal is used to energize the supplemental heating source as “back-up” without initiating compressor operation.

The Specifications require that all DX packaged units have two states of heating and two stages of cooling with, preferably, modulating hot gas reheat.

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For more complex packaged DX systems, such as VAV multiple zone units, dedicated ventilation air units, etc., OEM digital controllers, mounted and wired at the OEM, are normally required for their operation. In this case, interface/communication between the OEM controller and the DDC system, using the BACnet protocol, is also required. See Sections 230923 and 230924 of the specifications for the requirements imposed on the equipment manufacturer/vendor for ensuring that this interface is “seamless” and functional as specified by this sequence of operation. Unfortunately, this requirement is rarely met. First, there is the issue of the interface itself…just because two devices are both 100% BACnet compatible does not necessarily mean the two devices fully communicate. Second, manufacturers may include control schemes and sequences that do not comply with the project specification and are not desired by the A-E. The A-E, therefore, will almost always have to work with the equipment supplier and the DDC system to ensure proper interface. And, even then, the results are not always successful and it may be necessary to retain a “control systems integrator” to develop an working interface.

Potential design/control issues that may require modification/editing of these sequences include the following:

1. The sequences in Section 5 envision that the packaged/split systems have VAV operation on the basis of modulating speed control between the minimum airflow setpoint and maximum airflow. The sequences must be revised if 2-speed fan control is provided (typical for units under 5 tons capacity).

2. The use of fuel-fired furnaces is an option that must be carefully considered. The sequences required 2-stage heating control if this option is selected.

3. Modulating hot gas reheat control may not be available from some manufacturers and the use of on/off hot gas reheat control may be acceptable. In that case, on/off reheat control must be cycled to maintain space temperature setpoint when in the unit is in a humidity control mode.]

5.10 Packaged/Split Air-Cooled DX Unit, CAV or VAV Single Zone System:

PRIMARY UNIT CONTROL IS PROVIDED BY OEM CONTROLLER INTERFACED WITH DDC SYSTEM.

[Guideline: Single zone systems are designed to maintain temperature and humidity high limit setpoint in a single control zone, a single space or a group of spaces that share common HVAC requirements and operating schedules.

Each single zone system required to have VAV control must be configured to maintain minimum design ventilation airflow at any total airflow during scheduled “OCCUPIED” periods.

For each single zone system required to have an airside economizer cycle, a return air fan or relief air fan is required unless barometric relief dampers located within the space served can be utilized (note that locating barometric relief air dampers in return air ductwork is a design error).]

Thermostatic interface between the DDC system and each single zone packaged unit OEM controller shall be based on the following:

Packaged/Split Single Zone HVAC SystemDDC I/O

PointControl Sequence

FunctionOEM Controller

Thermostatic Interface TerminalsL1 24v power R, RC, RHC 24v neutral C

DO Indoor fan start/stop GDO First stage of cooling on/off Y or Y1DO Second stage of cooling on/off Y2DO First stage of heating on/off W or W1DO Second stage of heating on/off W2DO Third stage of heating on/off W3DO Heat pump reversing valve actuation O, BDO Hot gas reheat valve HGV (on/off)AO Hot gas reheat valve HGV (modulating)DO Auxiliary/back-up heating on/off EDI Packaged unit internal fault/failure/alarm Varies

The following sequences of operation indicated by check boxes shall apply to each of the following

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packaged single zone air-handling systems:




Start/stop control (Sequence 4.00) Space temperature/humidity monitoring (Sequence 4.01) Drain pan condensate monitoring (Sequence 4.05) Filter differential pressure monitoring (Sequence 4.06) Low limit thermostat alarm (Sequence 4.07) Preheat (Sequence 4.08)


Primary humidifier (Sequence 4.09) Temperature/humidity control (Sequence 4.11.1 single sensor location option)

DX cooling, with separate heating, system w/hot gas reheat (Sequence 5.11) Fuel-fired furnace option Hot water coil option Steam coil option Electric coil with stages option Electric coil with silicon controlled rectifier option

Air source heat pump system w/hot gas reheat and electric supplemental heater (Sequence 5.13) Water source heat pump system w/hot gas reheat (Sequence 5.15)

Demand control ventilation enable/disable (Sequence 4.14) Occupancy schedule + occupancy/vacancy sensing option (Sequence 4.14.1) Occupancy schedule + manual override option (Sequence 4.14.2) Occupancy schedule + CO2 sensing option (Sequence 4.14.3) Occupancy schedule + people counting option (Sequence 4.14.4)

Minimum outdoor air flow control (Sequence 4.12.1 or 4.12.2, as applicable) Economizer cycle (Sequence 4.15)

Dry bulb temperature option Differential enthalpy option Relief air control





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5.11 Space Temperature and Humidity Control, Single Zone CAV or VAV Heating/Cooling System:


Space temperature and humidity setpoints shall be in accordance with Sequence 4.01.

CAV System:

"ON" period temperature and high limit humidity control:

On a rise in space temperature to above the maximum comfort zone temperature setpoint, initiate stage 1 of cooling via DO point.

On a continued rise in space temperature to above the maximum comfort zone temperature setpoint, initiate stage 2 of cooling via DO point.

On a rise in any space humidity to above the high limit humidity setpoint, initiate stage 1 of cooling via DO point to maintain space humidity at high limit setpoint.

On a continued rise in any space humidity to above the high limit humidity setpoint, initiate stage 2 of cooling via DO point to maintain space humidity at high limit setpoint.

Modulate hot gas reheat valve via AO point to maintain space temperature at the maximum comfort zone temperature setpoint.

On a fall in space temperature to below the minimum comfort zone temperature, modulate the heating coil final control element(s) in sequence with preheat coil control element(s), as applicable, via AO points to maintain space temperature at the minimum comfort zone temperature, as follows:

[Guideline: Select/edit one of the following heating options.]

Fuel-Fired Furnace: Modulate stage 1 (low fire) heating “ON” via AO point. On a further fall in space temperature, modulate stage 2 (high fire) heating “ON” via AO point.





When the space temperature is within the limits of the minimum and maximum comfort zone temperatures, both cooling and heating coil final control elements shall be modulated “CLOSED/OFF” via AO points.

"OFF" period high limit temperature and humidity control:

On a rise in space temperature to above the high limit setpoint temperature, energize the supply fan via DO point and initiate stage 1 of cooling via DO point to maintain space temperature at the high limit setpoint temperature minus 5°F.

On a continued rise in space temperature to above the high limit setpoint temperature, initiate stage 2 of cooling via DO point to maintain space temperature at the high limit setpoint temperature minus 5°F.

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On a rise in any space humidity to above the high limit humidity setpoint, initiate stage 1 of cooling by DO point and modulate the hot gas reheat valve via AO point to maintain space temperature at the high limit setpoint temperature.

On a continued rise in any space humidity to above the high limit humidity setpoint, initiate stage 2 of cooling via DO point and modulate the hot gas reheat valve via AO point to maintain space temperature at the high limit setpoint temperature.

On a fall in space temperature to below the low limit setpoint temperature:


Fuel-Fired Furnace Control:

Modulate stage 1 (low fire) heating “ON” via AO point to maintain space temperature at low limit setpoint temperature plus 5°F.

On a further fall in space temperature, modulate stage 2 (high fire) heating “ON” via AO point to maintain space temperature at low limit setpoint temperature plus 5°F.


Command hot water system “ON” via DO point.







Steam Coil Control:

Command steam system “ON” via DO point.





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Once space conditions return to within limit conditions, ± 5°F and/or minus 5% RH as above, for 5 minutes, de-energize supply fan via DO point.

VAV System:

"ON" period space temperature and high limit humidity control:

On a rise in space temperature above the maximum comfort zone temperature, provide cooling as follows:

From 0% to 49% space temperature AI signal, cooling airflow shall be minimum unit airflow. Initiate stage 1 cooling via DO point to maintain space temperature at maximum comfort zone temperature setpoint.

From 50% to 100% space temperature AI signal, increase fan speed from minimum speed to maximum speed. Cycle stage 2 cooling “ON/OFF” via DO point to maintain space temperature at maximum comfort zone temperature setpoint.

On a rise in any space humidity to above the high limit humidity setpoint, provide dehumidification as follows:

Set dehumidification airflow at maximum unit airflow and initiate stage 1 cooling via DO point to maintain space humidity at high limit humidity setpoint.

On a continued rise in any space humidity to above the high limit humidity setpoint, initiate stage 2 cooling via DO output to maintain space humidity at high limit humidity setpoint.

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Modulate the hot gas reheat valve via AO point to maintain space temperature at the maximum comfort zone temperature.

On a fall is space temperature to below the minimum comfort zone temperature setpoint, provide heating as follows:


Modulate supply fan speed through the VFD via AO point to minimum speed.

Modulate the heating coil final control element in sequence with preheat coil control element(s), as applicable, via AO points to maintain space temperature at the minimum comfort zone temperature, as follows:


Fuel-Fired Furnace Control: Modulate stage 1 (low fire) heating “ON.”






Modulate heating final control element(s) in sequence with preheat coil control element(s), as applicable, to 100% “OPEN/ON” via AO points, as follows:


Fuel-Fired Furnace Control: Modulate stage 2 (high fire) heating “ON.”






When the space temperature is within the limits of the minimum and maximum space temperature setpoints, both cooling and heating final control elements shall be modulated “CLOSED/OFF” and fan speed shall be set at minimum.


On a rise in space temperature to above the high limit setpoint temperature, energize the unit fan at maximum speed via DO point and initiate stage 1 of cooling via DO point to maintain space temperature at the high limit setpoint temperature minus 5°F.

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On a rise in any space humidity to above the high limit humidity setpoint, energize the unit fan at maximum speed via DO point and initiate stage 1 of cooling via DO point to maintain space humidity at high limit setpoint minus 5% RH.

On a continued rise in any space humidity to above the high limit humidity setpoint, initiate stage 2 of cooling via DO point to maintain space humidity at high limit setpoint minus 5% RH.

Modulate hot gas reheat valve via AO point to maintain space temperature at the high limit setpoint temperature.

On a fall in space temperature to below the low limit temperature setpoint:

[Guideline: Select/edit one of the following three heating options.]

Fuel-Fired Furnace Control:




Modulate stage 1 (low fire) heating “ON” via AO point to maintain space at low limit temperature plus 5°F.

On a further fall in space temperature, increase fan speed from minimum speed to maximum speed and modulate stage 2 (high fire) heating “ON” via AO point to maintain space at low limit temperature plus 5°F.


Command hot water system “ON” via DO point.







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Steam Coil Control:

Command steam system “ON” via DO point.

















Once space conditions return to within limit conditions, ± 5°F and/or minus 5% RH as above, for 5 minutes, de-energize air-handling unit.

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5.13 Space Temperature and Humidity Control, Single Zone CAV or VAV Air Source Heat Pump:



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CAV System:

"ON" period temperature and high limit humidity control:

On a rise in space temperature to above the maximum comfort zone temperature setpoint, initiate stage 1 of cooling via DO point.

On a continued rise in space temperature to above the maximum comfort zone temperature setpoint, initiate stage 2 of cooling via DO point.

On a rise in any space humidity to above the high limit humidity setpoint, initiate stage 1 of cooling via DO point to maintain space humidity at high limit setpoint.



On a fall in space temperature to below the minimum comfort zone temperature setpoint, initiate stage 1 of heating via DO point to maintain space temperature at minimum comfort zone temperature setpoint.

On a further fall in space temperature to below the minimum comfort zone temperature setpoint, initiate stage 2 of heating via DO point to maintain space temperature at minimum comfort zone temperature setpoint.

If stage 2 heating is maintained for 15 minutes, but the space temperature continues to fall, energize the stage 3 supplemental electric resistance heater via DO point to maintain the space temperature at the minimum comfort zone temperature setpoint.

When the space temperature is within the limits of the minimum and maximum zone temperature setpoint and space humidity is at or below the high limit humidity setpoint, unit fan shall operate and no cooling or heating shall be initiated.


On a rise in space temperature to above the high limit setpoint temperature, energize the unit fan via DO point and initiate stage 1 via DO point of cooling to maintain space temperature at the high limit temperature setpoint minus 5°F.

On a continued rise in space temperature to above the high limit setpoint temperature, initiate stage 2 of cooling via DO point to maintain space temperature at the high limit temperature setpoint minus 5°F.

On a rise in any space humidity to above the high limit humidity setpoint, energize unit fan via DO point, initiate stage 1 of cooling via DO point to maintain space humidity at high limit humidity setpoint minus 5% RH.

On a continued rise in any space humidity to above the high limit humidity setpoint, initiate stage 2 of cooling via DO point to maintain space humidity at high limit humidity setpoint minus 5% RH.

Modulate the hot gas reheat valve via AO point to maintain space temperature at the high limit temperature setpoint.

On a fall in space temperature to below the low limit setpoint temperature, energize the unit fan via DO point and initiate stage 1 of heating to maintain space temperature at the low limit temperature setpoint plus 5°F.

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On a further fall in space temperature to below the low limit setpoint temperature, initiate stage 2 of heating via DO point to maintain space temperature at the low limit temperature setpoint plus 5°F.

If stage 2 heating is maintained for 15 minutes, but the space temperature continues to fall, energize the supplemental electric resistance heater (in stages, as applicable) to maintain the space temperature at the low limit temperature setpoint plus 5°F.

Once space conditions return to within limit conditions, ± 5°F and/or minus 5% RH as above, for 5 minutes, de-energize unit.

VAV System:

"ON" period space temperature and high limit humidity control:

On a rise in space temperature above the maximum comfort zone temperature, provide cooling as follows:

From 0% to 49% space temperature AI signal, cooling supply airflow shall be minimum unit airflow. Initiate stage 1 of cooling via DO point to maintain space temperature at the maximum comfort zone temperature setpoint.

From 50% to 100% space temperature AI signal, increase fan speed from minimum speed to maximum speed. Initiate stage 2 of cooling via DO point to maintain space temperature at the maximum comfort zone temperature setpoint.

On a rise in any space humidity to above the high limit humidity setpoint, provide dehumidification as follows:

Set dehumidification airflow at maximum unit airflow and initiate stage 1 cooling via DO point to maintain space humidity at high limit humidity setpoint.

On a continued rise in any space humidity to above the high limit humidity setpoint, initiate stage 2 cooling via DO output to maintain space humidity at high limit humidity setpoint.

Modulate the hot gas reheat valve via AO point to maintain space temperature at the maximum comfort zone temperature.

On a fall in space temperature below the minimum comfort zone temperature, provide heating as follows:

From 0% to 49% space temperature AI signal, heating air flow shall be minimum unit airflow. Initiate stage 1 heating via DO point to maintain space temperature at minimum comfort zone temperature setpoint.

From 50% to 100% space temperature AI point signal, increase fan speed from minimum speed to maximum speed. Initiate stage 2 heating via DO point to maintain space temperature at minimum comfort zone temperature setpoint.

If 100% stage 2 heating is maintained for 15 minutes or more, but the space temperature continues to fall, energize the supplemental electric resistance heater (in stages, as applicable) via DO point(s) to maintain space temperature at minimum comfort zone temperature setpoint.

When the space temperature is within the limits of the minimum and maximum zone temperature setpoint and space humidity is at or below the high limit humidity setpoint, unit fan shall operate at minimum speed and no cooling or heating shall be initiated.


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On a rise in space temperature to above the high limit setpoint temperature, energize the unit fan at maximum speed via DO point and initiate stage 1 of cooling via DO point to maintain space temperature at the high limit setpoint temperature minus 5°F.


On a rise in any space humidity to above the high limit humidity setpoint, energize the unit fan at maximum speed via DO point and initiate stage 1 of cooling via DO point to maintain space humidity at high limit setpoint minus 5% RH.


Modulate hot gas reheat valve via AO point to maintain space temperature at the high limit setpoint temperature.

On a fall in space temperature below the low limit temperature setpoint, provide heating as follows:

From 0% to 49% space temperature AI signal, energize unit fan at minimum speed via DO point. Initiate stage 1 heating via DO point to maintain space temperature at low limit temperature setpoint plus 5°F.

From 50% to 100% space temperature AI signal, increase fan speed from minimum speed to maximum speed. Initiate stage 2 heating via DO point to maintain space temperature at low limit temperature setpoint plus 5°F.

If 100% stage 2 heating is maintained for 15 minutes or more, but the space temperature continues to fall, energize the supplemental electric resistance heater (in stages, as applicable) via DO points to maintain space temperature at low limit temperature setpoint plus 5°F.

Once space conditions return to within limit conditions, ± 5°F and/or minus 5% RH as above, for 5 minutes, de-energize unit.

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5.15 Space Temperature and Humidity Control, Single Zone CAV or VAV Water Source Heat Pump System:



"On" period temperature and humidity control:

When the space temperature is within the limits of the minimum and maximum comfort zone temperature setpoints, neither cooling nor heating shall be initiated.

[Guideline: Include the following only two subsections when there is an economizer water coil in the unit.]

Cooling: If the ACWS temperature is at or below 55ºF, on a rise in space temperature to above the maximum comfort zone temperature setpoint, modulate loop water flow via AO point through the economizer water coil to maintain space at maximum comfort zone temperature setpoint.

On a continued rise in space temperature to above the maximum comfort zone temperature setpoint, initiate stage 1 of cooling via DO point to maintain space at maximum comfort zone temperature setpoint.

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On a continued rise in space temperature to above the maximum comfort zone temperature setpoint, initiate stage 2 of cooling to maintain space at maximum comfort zone temperature setpoint.

Cooling: If the ACWS temperature is above 55ºF, on a rise in space temperature to above the maximum comfort zone temperature setpoint, initiate stage 1 of cooling via DO point.


[Guideline: Include the following subsection when there is no economizer water coil in the unit.]

Cooling: At any ACWS temperature, on a rise in space temperature to above the maximum comfort zone temperature setpoint, initiate stage 1 of cooling via DO point.


[Guideline: Include the following subsections for every unit.]

Heating: At any ACWS temperature, on a fall in space temperature to below the minimum comfort zone temperature setpoint, initiate stage 1 of heating via DO point to maintain space at minimum comfort zone temperature setpoint.

On a continued fall in space temperature to below the minimum comfort zone temperature setpoint, initiate stage 2 of heating via DO point to maintain space at minimum comfort zone temperature setpoint.

Humidity: On a rise in any space humidity to above the high limit humidity setpoint, initiate stage 1 of cooling via DO point to maintain space humidity at high limit setpoint.



"OFF" period temperature and humidity limit control:

On a rise in space temperature to above the high limit setpoint temperature, command ACWS pump(s) “ON” via DO point(s), command unit fan "ON" via DO point, and initiate stage 1 of cooling via DO point to maintain space at high limit setpoint temperature minus 5°F.

On a continued rise in space temperature above the high limit setpoint temperature, initiate stage 2 of cooling to maintain space at high limit setpoint temperature minus 5°F.

If space humidity rises above high limit humidity setpoint, command ACWS pump(s) “ON” via DO point(s), command unit fan "ON" via DO point, on a rise in any space humidity to above the high limit humidity setpoint, initiate stage 1 of cooling via DO point to maintain space humidity at high limit setpoint minus 5% RH.


Modulate hot gas reheat control valve via AO point to maintain space at minimum temperature setpoint.

On a fall in space temperature to below the low limit setpoint temperature, command ACWS pump(s) “ON” via DO point(s), command unit fan "ON" via DO point, and initiate stage 1 of heating via DO point to maintain space at the low limit setpoint temperature plus 5°F.

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On a continued fall in space temperature to below the low limit setpoint temperature, initiate stage 2 of heating via DO point to maintain space at the low limit setpoint temperature plus 5°F.

Once space conditions return to within limit conditions, ± 5°F and/or minus 5% RH as above, for 5 minutes, command unit "OFF".

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5.20 Packaged/Split Air-Cooled DX Unit, Multiple Zone VAV System:


The following sequences of operation indicated by check boxes shall apply to each of the following packaged multiple zone air-handling systems:




Start/stop control (Sequence 4.00) Space temperature/humidity monitoring (Sequence 4.01) Drain pan condensate monitoring (Sequence 4.05) Filter differential pressure monitoring (Sequence 4.06) Low limit thermostat alarm (Sequence 4.07) Preheat (Sequence 4.08) Fuel-fired furnace option


Primary humidifier (Sequence 4.09) Multiple zone VAV supply air control

Discharge air temperature control (Sequence 4.21) DX cooling option

Supply fan air volume control (Sequence 4.22) Minimum outdoor air flow control (Sequence 4.23) Demand control ventilation enable/disable (Sequence 4.24)

Occupancy schedule + return air CO2 sensing option (Sequence 4.24.1) Occupancy schedule + zone occupancy/vacancy sensing option (Sequence 4.24.2) Occupancy schedule + zone CO2 sensing option (Sequence 4.24.3) Occupancy schedule + zone people counting option (Sequence 4.24.4)

Economizer cycle (Sequence 4.15) Dry bulb temperature option Differential enthalpy option Relief air control

Barometric damper option

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Return air fan option Flow tracking control Building/plenum pressure monitoring/control


Space temperature and humidity control via terminal units (Sequence 4.26 and as follows) Single duct, CAV terminal reheat (Sequence 4.27.1) Single duct, VAV cooling only (Sequence 4.27.2) Single duct, VAV terminal reheat, single maximum airflow setpoint (Sequence 4.27.3) Single duct, VAV terminal reheat, dual maximum airflow setpoints (Sequence 4.27.4) Single duct, supplemental perimeter heating (Sequence 4.27.5) Single duct, fan powered, series configured (4.28.1) Single duct, fan powered, parallel configured (4.28.2)


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5.30 Packaged/Split Air-Cooled DX Unit, Outdoor Air Preconditioning System:


Command unit and associated exhaust fans “ON/OFF,” as defined by Sequence 4.00, as defined below or upon operator command.

Where ventilation air is supplied to air-handling systems, unit shall start/stop via software interlock with air-handling systems served.

Where ventilation air is supplied directly to occupied spaces, unit shall start/stop in accordance with user-defined “ON/OFF” schedule defined by Sequence 1.14 or upon operator command.

MONITOR HVAC unit OEM controller fault/failure/alarm as DI point.

MONITOR fan motors(s) status as AI point(s) in accordance with Sequence 1.25.

Ventilation air temperature and humidity control:

MONITOR discharge air dry bulb temperature and discharge air dewpoint temperature as AI points.

Discharge air dry bulb temperature setpoint for OEM controller shall be input via AO point from the DDC system as follows:


(ºF)

Discharge Air Dry Bulb Temperature

(ºF)≤ 50ºF 72ºF≥ 85ºF 55ºF

OEM controller shall maintain discharge air dry bulb and dewpoint temperatures as follows:

Discharge air dry bulb temperature shall be maintained at setpoint temperature input to OEM controller from the DDC system.

Discharge air dewpoint temperature shall maintained at or below 50ºF.

Ventilation Airflow Control:

When DVA unit is "ON":

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MONITOR supply airflow as AI point, computed on the basis of velocity pressure input and supply duct cross sectional area.

MONITOR ventilation supply air duct static pressure as AI input.

[Guideline: Edit the following two subsections based on the way in which ventilation air is distributed.]

When ventilation air is ducted to each air-handling unit, ventilation air supply to each unit shall be controlled by 2-position minimum ventilation air damper positioned via AO point based on user-defined "OCCUPIED/ UNOCCUPIED” schedule in conjunction with space occupancy/vacancy sensor(s) or people-counting technologies sensor(s), as applicable.

During "OCCUPIED" periods, when sensor(s) confirms that any space served is occupied, the damper shall be 100% “OPEN”.

Anytime sensor(s) determine that the space is unoccupied, the damper shall be closed.

When ventilation air is distributed into each space through air outlet(s), 2-position air damper(s) shall “OPEN” and close based on user-defined "OCCUPIED/ UNOCCUPIED” schedule in conjunction with space occupancy/vacancy sensor(s) or people-counting technologies sensor(s), as applicable.

During "OCCUPIED" periods, when sensor(s) confirms that any space served is occupied, the damper shall be 100% “OPEN”.

Anytime sensor(s) determine that the space is unoccupied, the damper shall be closed.

Modulate NC bypass damper via AO point to maintain supply air duct pressure setpoint established by test during TAB work.

MONITOR unit airflow via AI point.

Modulate bypass damper position via AO point to maintain constant supply airflow.

When unit is "OFF", bypass damper shall be modulated “CLOSED” via AO point.

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5.31 Packaged Water-to-Water Heat Pump, Outdoor Air Pre-Conditioning System


During “ON” period for any air-handling system connected to the preconditioning system, ENABLE outdoor air pre-conditioning system operation as follows:

Monitor differential pressure for ACWS/ASWR system as AI point

Confirm that ACWS/ACWR system flow is maintained.

Command preconditioning pump “ON” via DO point in accordance with Sequence 1.21.

Confirm preconditioning pump status in accordance with Sequence 1.25 .

If preconditioning pump fails, as indicated by pump status, initiate alarm and terminate sequence.

Command water-to-water heat pump “ON” via DO point through OEM controller interface.

Monitor heat pump “fault/status” through OEM controller as DI point.

If heat pump fails as indicated by unit controller, initiate alarm and terminate sequence.

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Supply water temperature control:

Water supply temperature shall be controlled by the OEM controller on the basis of setpoint temperature provided by the DDC system. as follows:

When the outdoor air temperature is at or above 70ºF, water supply temperature setpoint shall be 45ºF.

When the outdoor air temperature is at or below 65ºF, water supply temperature setpoint shall be as follows:

Outdoor air temperature

(ºF)

Leaving water temperature setpoint (ºF)

65 9020 130

Outdoor air temperature control:

Modulate each 3-way preconditioning coil control valve via AO point to maintain coil discharge air temperature setpoint as follows:

Outdoor air temperature

(ºF)

Discharge air dry bulb temperature

(ºF)≤ 65 72≥ 70 55

During “OFF” period for all air-handling systems connected to the preconditioning system, both pre-conditioning pump and water-to-water heat pump shall be commanded “OFF” via DO points.

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SERVICE HOT WATER HEATING

6.10 Service Hot Water Heater:

[Guideline: Service hot water heater, electric or gas-fired condensing type, with 120/1/60 control power circuit and with integral water temperature control.]

“ENABLE” service hot water heater and start/stop recirculation pump(s) in accordance with Sequence 1.21 based upon (1) user-defined "ON/OFF" schedule in accordance with sequence 1.14 or (2) operator command.

Low hot water temperature alarm:

Set pipe surface mounted thermostat low supply temperature setpoint (default = 100ºF)

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When heater is commanded "ON", initiate alarm if pipe surface mounted thermostat switch closes, indicating low temperature condition, after 30 minutes.

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SPECIAL EXHAUST SYSTEMS

7.10 Type I Kitchen Hood Interface [FUTURE]:

7.12 Type II Kitchen Hood Interface [FUTURE]:

7.13 Laboratory: Room Controls:

CAV laboratory: Laboratory equipped with CAV fume hood(s), CAV terminal reheat unit, and CAV air valves.

MONITOR terminal reheat unit supply airflow as AI point.

MONITOR each CAV air valve exhaust airflow as AI point.

MONITOR laboratory differential pressure as AI point.

Maintain laboratory at negative air pressure by modulating terminal unit damper and CAV air valve(s) via AO point to maintain each airflow at setpoint.

If laboratory pressure becomes non-negative at any time, initiate alarm.

CAV laboratory with two-state switching: Laboratory equipped with CAV fume hood(s), terminal reheat type terminal unit, and two-state CAV air valves.


MONITOR each CAV air valve exhaust airflow as AI point.


When fume hood sash switch indicates the hood sash is “OPEN” via DI point, maintain laboratory at negative air pressure by modulating terminal unit damper and CAV air valves via AO point(s) to maintain each airflow at maximum setpoint.

When fume sash switch indicates that hood sash is “CLOSED” via DI point, maintain laboratory at negative air pressure by modulating terminal unit damper and two state CAV air valves via AO point(s) to maintain each airflow at minimum setpoint.

Where laboratory is equipped with more than one two-stage fume hoods, all fume hood sashes must be indicated “CLOSED” before any airflow is reduced.

If laboratory pressure becomes non-negative at any time, initiate alarm.

VAV laboratory: Laboratory equipped with VAV fume hood(s), VAV terminal reheat type terminal unit, and VAV air valves.


MONITOR each VAV air valve exhaust airflow as AI point.


Fume hood VAV air valve shall modulate via AO point to maintain exhaust airflow between minimum and maximum setpoints in direct response to AI point provided by the fume hood controller that monitors/controls hood face velocity at setpoint.

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Terminal unit airflow shall be the greater of (1) airflow required to satisfy space temperature and humidity setpoints or (2) airflow to track exhaust airflow and maintain a differential airflow setpoint between supply airflow and hood exhaust airflow.

If terminal unit airflow exceeds 90% of the hood exhaust airflow, the room exhaust VAV air valve shall modulate “OPEN” to maintain total exhaust airflow (hoods + room) at 110% of supply airflow.

If laboratory differential pressure becomes non-negative, initiate alarm and increase hood and room exhaust airflows to maintain total exhaust airflow (hoods + room) at 110% of supply airflow.

Laboratory purge: Upon occupant activation of laboratory “Panic Button”, terminal unit supply airflow shall be reduced to minimum and all CAV/VAV air valves shall be modulated 100% open.

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7.14 Laboratory: Fume Hood Exhaust, VAV, Multi-Fan Manifold:

[Guideline: Fume hood exhaust system is a variable volume system consisting of manifold exhaust with four (4) exhaust fans, each with VFD for variable speed control, one exhaust fan designated as "lead"; two fans designated "first lag" and "second lag", and one fan designated as "standby".]

Command exhaust fans "ON/OFF" via their VFDs in accordance with sequence 1.24 via DO points.

Lead/lag/standby fan selection:

One exhaust fan shall be designated "lead"; two fans designated "first lag" and "second lag", and one fan designated as "standby".

Two exhaust fans shall operate and a third fan shall cycle “ON/OFF” as needed.

The fourth fan will be “standby” and shall started only if required by a failure of one or more “lead/lag” fans.

Lead/lag/standby fans selection shall be based on rotational sequence defined by sequence 1.26.1/1.26.2.

Start lead exhaust fan:

Confirm lead exhaust air flow on the basis of differential pressure flow via AI point.

If lead fan status DI point or differential pressure flow AI point indicates flow failure, terminate start sequence, initiate alarm, and initiate starting of next exhaust fan in the sequence.

Exhaust fan start/stop:

Sequence fans on based on exhaust fan flow and outside air bleed damper position in the order designated by the "static pressure control" sequence below.

When “lead” exhaust fans speed is at 95% or more for 15 minutes, start the “lag” exhaust fan in the sequence and modulate all operating fans to operate at the same speed via AO points.

When operating exhaust fan(s) speed falls to minimum for 15 minutes and the outside air bypass damper is fully open, stop “lag” exhaust fan.

When starting any exhaust fan:

Command exhaust fan to start at minimum speed set in the VFD via DO point.

Command the isolation damper open.

If isolation damper end switch DI point does not indicate "DAMPER OPEN" condition within 2 minutes, command the exhaust fan “OFF” and the isolation

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damper closed, initiate alarm, and initiate starting of next exhaust fan in the sequence.

When stopping any exhaust fan:

Command isolation damper to close via AO point.

Ramp fan speed down to minimum at the same rate as the damper actuator stroke time via AO point.

After the fan is at minimum speed and the damper end switch indicates the damper is closed, command the fan "OFF" via DO point.

When switching lead fans or stopping a lag fan, prove operation of the new lead fan and allow 2 minutes for the fan to come up to speed before initiating the stop fan sequence.

Static pressure control:

Modulate exhaust fan VFDs and outside air bypass dampers via AO points in sequence to maintain static pressure setpoint as sensed by the static pressure sensors. Default static pressure setpoint is -1.0 in. wg. Final setpoint shall be determined during test and balance of the exhaust fans, as recommended by the TAB subcontractor and reviewed by the A-E.

As exhaust airflow requirements decrease and the static pressure becomes more negative than setpoint, decrease the exhaust fans VFD speed simultaneously and in parallel to maintain the static pressure setpoint until the minimum fan flow setpoint is reached.

If the static pressure continues to fall, modulate open the outside air bleed dampers (in parallel, if more than one) to maintain the static pressure setpoint.

If static pressure continues to fall below setpoint, stage “OFF” lag exhaust fan as described in the "exhaust fan start/stop" sequence above.

As exhaust airflow requirements increase and duct static pressure becomes less negative than setpoint, the fans shall continue to operate at their minimum fan flow setpoints and the outside air bleed dampers shall be modulated “CLOSED” via AO point to maintain duct static setpoint.

When the outside air bleed dampers are fully closed, the exhaust fans speed shall be increased to maintain static pressure at setpoint.

If exhaust airflow requirement continues to increase and duct static pressure cannot be maintained, initiate the start sequence for the lag fan as described in the "Exhaust fan start/stop" sequence above.

If multiple static pressure sensing locations are indicated on the Drawings, maintain the static pressure setpoint based on the lowest reading sensor AI point.

If the static sensors deviate by more than 0.05 in. wg, initiate alarm.

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AIR-TO-AIR HEAT RECOVERY

8.10 Run-Around Air-To-Air Heat Recovery:

[Guideline: The system has two modes of operation: (1) recover sensible heat from the exhaust air stream for preheating ventilation outdoor air when the outside air is below 50ºF and (2) pre-cool the ventilation outdoor air when the outside air temperature is above 80ºF . The system is inactive when the outside air temperature is between these two setpoints.]

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ENABLE/DISABLE heat recovery system on the basis of (1) user-defined "ON/OFF" schedule(s) of associated air-handling system(s) and exhaust air fan(s) when the outdoor air temperature is above 80ºF or below 55ºF or (2) operator command, as follows:

Heat recovery/outdoor air preconditioning control:

When heat recovery is ENABLED and the outdoor air temperature is below 55ºF, the outdoor air preconditioning coil(s) shall serve as the first stage of preheat:

Command heat recovery pump "ON" in accordance with Sequence 1.21.

Confirm pump operation based on motor status in accordance with Sequence 1.25.

Confirm heat recovery solution flow via differential pressure flow switch as DI point.

If pump or flow fails, command pump “OFF,” initiate alarm, and terminate sequence.

Modulate three-way control valve in direct response to AO point to maintain coil leaving air temperature at 55ºF setpoint.

If the heat recovery solution temperature entering the exhaust air falls to 30ºF, limit control loop output signal to three-way control valve via AO point to maintain entering solution temperature at 30ºF setpoint.

When heat recovery is ENABLED and the outdoor air temperature is above 80ºF, the outdoor air preconditioning coil(s) shall serve as to pre-cool entering outdoor:

Command heat recovery pump "ON" in accordance with Sequence 1.21.

Confirm pump operation based on motor status in accordance with Sequence 1.25.

Confirm heat recovery solution flow via differential pressure flow switch as DI point.

If pump or flow fails, command pump “OFF,” initiate alarm, and terminate sequence.

Modulate three-way control valve in direct response to AO point to maintain coil leaving air temperature at 80ºF setpoint.

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LIGHTING

9.10 Exterior Lighting:

Each exterior lighting control relay, as indicated on the Drawings, shall be “OPEN”/”CLOSED” via DO point in accordance with user-defined “ON/OFF” schedule in accordance with Sequence 1.14.

Provide manually adjustable setpoint photocell sensor(s), as indicated on the Drawings, to inhibit exterior lighting during daylight hours.

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9.13 Interior Lighting:

[Guideline: Insert lighting sequences in accordance with edition of ASHRAE 90.1 adopted in the North Carolina State Building Code. Review with Electrical Designer.]

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Documents

SECTION 230993 - SEQUENCES OF OPERATION - · Web viewMONITOR and display status of sump pump high water level alarm dry contact provided by pump manufacturer as DI point, as indicated