TSI Incorporated – Critical Environments Copyright© 2006 TSI Incorporated Critical Environments Laboratory Control Basics and Room Control Strategies

Copyright© 2006 TSI Incorporated

TSI Incorporated – Critical Environments

Critical Environments

Laboratory Control Basics and

Room Control Strategies



Insert Agenda slide

•Laboratory customers and goals•Laboratory environment

–Safety–Comfort–Experiment integrity–Energy efficiency

•Room pressurization control–Constant Volume–Direct pressure–Flow tracking, a.k.a. “Airflow Tracking” or “Volumetric Offset” –Flow tracking with pressure feedback

•VAV control types–Constant Volume–Direct pressure–Flow tracking, a.k.a. “Airflow Tracking” or “Volumetric Offset” –Flow tracking with pressure feedback

•Temperature control•Laboratory control



Laboratory Customer Types

• Universities– Teaching labs– Research labs

• High Schools/Middle Schools• Hospitals




• Government Facilities– USDA– FDA– GSA & ATF– CSI




• Industry– Technology companies– Pharmaceutical manufacturers



Laboratory Goals

• Safety– Containment

• Primary: fume hood containment• Secondary: Directional room airflow-net

negative airflow labs– Ventilation (dilution)

• Comfort– Temperature– Ventilation – Sound



Laboratory Goals

• Experiment Integrity– Protection of research– Uniform airflow, reduce drafts– Stable room pressurization

• Energy-efficiency– Current energy costs (Q1,2006): $7.50/cfm; 1000 cfm

hood costs $7,500/yr)



Laboratory Goals

Concerning your past involvement in lab controls:

Has there been any other laboratory goals or needs

that you were asked to address or meet?



Laboratory Environments

• Use determines Requirements– Animal Research– Clinical labs– Analytical Chemistry– Teaching labs– Biocontainment– Forensic labs– Nanotechnology



Laboratory Environments

• Ideal laboratory configuration– Designed to meet specific requirements for a given

application or task– Chemical lab will have different needs than a

pharmaceutical lab or vivarium



Laboratory Safety

• Minimize long-term exposure to chemicals and fumes

• Primary Containment– Fume hood– Laminar flow bench– BSC– Snorkels

• Secondary Containment– Laboratory itself



Laboratory Safety

Objectives of Lab Ventilation– A laboratory is built to accommodate materials and

processes that contaminate air which may pose a health risk to the occupants

– Lab exhaust devices capture contaminants– Lab exhaust system removes contaminants– Lab ventilation system provides dilution air

• 100% Outside Air (4-12 air changes per hour)

• No Recirculation

• 24 hours/day, 7 days per week



Laboratory Safety

• Ventilation rate examples– OSHA

• 4-12 ACPH

– Prudent Practices• 6-12 ACPH

– ASHRAE Laboratory Ventilation• 6-10 ACPH

– NFPA• Minimum of 4 ACPH

• Typically greater than 8 ACPH when occupied



Calculate Air Exchange Rate (ACPH)Air Changes Per Hour

To calculate air exchanges per hour, use the following formula:L= LengthW= WidthH= HeightCF= Cubic Feet (of lab space)ACPH = Air Changes (or exchanges) Per Hour

• Measure your room and work the following equation:L’ x W’ x H’ = CF (ex: 10’ X 12’ X 8’ = 960 CF with 180 cfm)

• 180 cfm / 960 CF = .1875/m• .1875/m x 60m/h = 11.25 ACPH



Examples of Air Changes per Hour Lab Space ACH OA

Chemistry (standard Wet Lab) 10 100%

Biological (Tissue Culture, DNA) 12 100%

Special Lab (High Odor Generation) 30 100%

Chemical Storage & Distribution 10 100%

Analytical Lab (Instrument Room) 12 100%

Equipment Room (autoclaves, centrifuges, freezers) 15 100%

Computer server or dry electronics lab 12 to 60 20 cfm/person

Animal rooms 15 100%

ISO Class 4 Clean room 660 20 cfm/person







Laboratory Comfort

• Maintain space temperature– More challenging with VAV

• Maintain ventilation– Normally covered by ACPH for a

given lab application– Limit infiltration from sources

other than HVAC system– Reduce drafts or odd airflow

patterns

• Minimize noise



Experiment Integrity

• Protection of research and personnel is accomplished with:

• Laminar flow bench• BSC• Fume hoods• Chemical storage



Energy-Efficiency

• Exhaust as little air as possible without impacting safety or comfort– Using less air is the most promising tactic

• VAV system• Occupied and unoccupied modes

– Recover the heat– Move air more efficiently– Increased initial cost– Saves operating expenses in the long-term



Room Pressurization Control

To maintain directional airflow by controlling supply and exhaust air flows in order to pressurize or depressurize the room relative to an adjacent space and to maintain a comfortable, non-fluctuating air temperature.

• Primary containment– Laboratory fume hoods

– Biological safety cabinets

– Snorkels

• Secondary containment– Laboratory room itself



Room Control Strategies

• Constant Volume (CV)– Control and/or balance supply & exhaust flows– Monitor pressure only

• Constant Volume (CV) – Two Position– Control and/or balance supply & exhaust flows– Monitor pressure only

• Variable Air Volume (VAV)– Control supply & exhaust flows under varying loads– Monitor critical parameters

NOTE: CV and VAV also used on lab hoodsNOTE: Dampers and flow stations or Venturi valves can be used for either CV or VAV systems



Constant Volume

• May monitor ΔP• No ΔP Control

– Simple– Read only

• 8635-M• 8610/12,8650-MON• CVV (Venturi Valve)• Temp by others• Requirements

– Closed door– Low Traffic– Stable reference

8650-MON

8635-M



Constant Volume

• Use Constant Volume when– Low hood density (large room with one hood)– Low concern regarding energy usage– Room ventilation rates of 10 ACPH or more

• Advantages– Easy to design– Minimizes cost of controls– Few controls to maintain

• Disadvantages– Equipment sized for full flows

• High initial and operating costs – Difficulties arise when relocating equipment– Limits future expansion– Wastes energy



Variable Air Volume (VAV)• Use a Variable Volume System when

– High hood density– If fume hood energy usage exceeds lab ventilation or thermal requirements

• Advantages– Reduced energy costs

• less air conditioned• supplied and exhausted air vary depending on loads

– Use of unoccupied mode with reduced flows saves energy – Applying diversity factors

• Sizing equipment based on expected flows as opposed to maximum flows– Pressure-independent VAV controls adapt to system changes

• Maintain constant face velocity regardless of sash position• Modulate supply and exhaust based on room ΔP or temperature demand

• Disadvantages– Reduced airflows and energy usage are dependent on good hood user sash

position management– Increased HVAC system complexity– Higher installation costs



VAV Control Types

• Direct pressure– Measure room pressure differential – Maintain it

• Flow tracking– Measure supply and exhaust air flows– Maintain an offset between supply and exhaust flows



VAV Control Types

• Flow tracking with pressure monitoring– Measure supply and exhaust air flows– Monitor pressure differential– Maintain an offset between supply and exhaust flows

• Flow tracking with pressure reset (AOC)– Measure supply and exhaust air flows– Maintain an offset between supply and exhaust flows– Measure pressure differential– Adjust offset between supply and exhaust flows

based on pressure measurement



VAV Control Type Features

Direct Pressure Control

Flow Tracking Control

Flow Tracking Control with ΔP

monitoring

Flow Tracking

Control with ΔP

feedback

Measures room ΔP X X X

Modulates supply and exhaust flows X X X X

Measures supply and exhaust flows X X X X

Fixed flow offset X X

Adjusts flow offset to meet room ΔP set point X



Factors to consider in Determining Control System Strategy

• Number of hoods• Room volume• Energy costs• Room Ventilation Rates• Hours of Operation

(occupied/unoccupied hours)

• Heat generation in labs• Number of researchers• Type of lab work being

performed

• Open or closed lab• Tightness of constructed

envelope• Complexity of cleanliness

requirements• Speed of disturbances and

response• Duct conditions for flow

measurement



VAV Control Loops

• Direct pressure – Closed loop on pressure

• Flow tracking – Closed loop on flow

– Open loop on pressure

• Flow tracking with pressure monitoring– Closed loop on flow

– Open loop on pressure

• Flow tracking with room pressure feedback– Closed loop on flow

– Closed loop on pressure



Open Loop on Pressure – Closed Loop on Flow



Closed Loop on Pressure – Closed Loop on Flow




8650

Model 8636




• Measure room pressure differential with thru-the-wall sensor

• Modulate supply and exhaust to maintain room pressure differential set point

• Measure the supply flow to set minimum ventilation rate and to determine ACPH




• Closed loop on pressure– Adjusts supply and exhaust to

maintain room pressure differential and reheat

• Easy to implement• Safest




• Requirements– Closed door with low traffic– Stable reference

• Fluctuations in reference space will cause disturbances within the lab

– Supply flow measurement is required for ventilation control and to determine ACPH

• TSI Models 8635, 8636




• Used In– Labs where containment is

critical

– Small closed labs

– Low cost is key




• Most engineers / consultants understand

• Works very well when properly applied

• ΔP guaranteed



Direct Pressure Control Sequence of Operations

If fume hood flow increases and makes space more

negative, then …

1. Controller senses an increased exhaust flow

2. Controller gradually closes the general exhaust damper to minimum if required

3. If ΔP set point is still not achieved …

4. Controller gradually opens supply until ΔP set point is achieved




If fume hood flow decreases and makes space more

positive, then …

1. Controller senses a decreased exhaust flow

2. Controller gradually opens the general exhaust damper to maximum if required


4. Controller gradually closes supply until ΔP is achieved




If the door to the lab opens, then …

1. Controller senses the room ΔP go toward neutral

2. Controller quickly closes supply to minimum if required


4. Controller quickly opens the general exhaust damper to maximum if required until ΔP is achieved




If the lab temperature increases, then …

1. Controller senses temperature increase

2. Controller closes reheat valve

3. If, after 3 minutes, the lab is still too warm …

4. Controller gradually increases supply

5. Controller senses ΔP decrease

6. Controller increases general exhaust to meet ΔP set point




If the lab temperature decreases, then …

1. Controller senses temperature decrease

2. Controller opens reheat valve

3. If, after 3 minutes, the lab is still too cold …

4. Controller gradually decreases supply

5. Controller senses ΔP increase

6. Controller decreases general exhaust to meet ΔP set point



Direct Pressure Controller Components8635-C, 8636

8635-C includes:

• 800199 Controller Output Cable, 4-cond., 25 ft.

• 800224 SureFlow Room Pressure Controller

• 800326 SureFlow Room Pressure Sensor w/ Cable

• 800420 24-VAC Transformer with Cable

8636 includes:• 800199 Controller Output

Cable, 4-cond., 25 ft.• 800326 SureFlow Room

Pressure Sensor w/ Cable• 800420 24-VAC

Transformer with Cable• 800775 8636 SureFlow

Room Pressure Controller




8681

8650




– Measure supply and exhaust air flows– Exhaust flow is more than supply flow (negative lab)

• Difference is referred to as “offset” air– Determine an offset between supply and total exhaust

flows• Total exhaust includes fume hoods, general exhaust,

snorkels, plus other exhaust devices• Offset value is generally listed on the room schedule

– Determined by the number of doors or other penetrations into the lab space

• If unknown, use 10% of maximum exhaust




– Modulate supply and exhaust flows to maintain offset

• Once lab is completed, offset value may be adjusted to sufficiently create a negative space

– Measure the supply flow to set minimum ventilation rate and to determine ACPH




• Controls flows to numerical set points– Exhaust flow greater than supply flow (labs)– Difference is referred to as offset

• Closed-Loop on Flow– Measure and control supply and exhaust flows

• Open-Loop on Pressure– Differential pressure set point not guaranteed

• Requirements– All flows are measured– Stable air flows

• TSI Models: 8680, 8681 & 8682



Flow Tracking Control, Calculating Offset Flow

Measured fume hood flows = 1400 cfm

Measured snorkel flows = 150 cfm

Measured general exhaust + = 350 cfm

Total exhaust = 1900 cfm

“Offset” requirement per schedule - = 200 cfm

Supply air flow rate set to = 1700 cfm




• The only option for open labs or labs with no suitable reference space

• Labs where containmentis not critical

• Labs designed around competition

• Remember– Doesn’t measure or

guarantee room differential pressure




• Engineers/Consultants understand

• ΔP not guaranteed



Flow Tracking Control Sequence of Operations

If fume hood flow increases and makes space more

negative, then …

1. Controller senses an increased exhaust flow

2. Controller gradually closes the general exhaust damper to minimum if required

3. If offset is still not achieved …

4. Controller gradually opens supply until offset is achieved




If fume hood flow decreases and makes space more

positive, then …

1. Controller senses a decreased exhaust flow

2. Controller gradually opens the general exhaust damper to maximum if required

3. If offset is still not achieved …

4. Controller gradually closes supply until offset is achieved





1. Controller does nothing since it cannot sense the loss of room ΔP









5. Controller gradually increases general exhaust to offset

6. ΔP unknown









5. Controller gradually decreases general exhaust to offset

6. ΔP unknown



Flow Tracking Controller Components8681-NS, 8682-NS

8681-NS includes:• 800420 24-VAC

Transformer with Cable• 800776 8681 SureFlow

Adaptive Offset Controller

8682-NS includes:• 800420 24-VAC

Transformer with Cable• 1203217 TYPE 1 NEMA

Hinged Box• 800416 DIM COMM cable,

shielded 2-wire, 25 ft.• 800228 8682 SureFlow

Digital Interface Module• 800235 8682 SUREFLOW

DDC CNTL W/O LON

Note: All damper/actuators and flow stations must be added separately. Adaptive offset and flow tracking controllers require the addition of factory start-up.



Flow Tracking with Pressure Monitoring

• Measure supply and exhaust air flows• Maintain an offset between supply and exhaust

flows • Monitor pressure differential• Differential pressure may vary



Flow Tracking with Room Pressure Feedback




• Flow tracking with room pressure feedback – Formerly referred by TSI as Adaptive Offset Control

(AOC)– Combines Direct Pressure and Flow Tracking controls– Measures supply and exhaust air flows– Measures room pressure differential– Maintains an offset between supply and exhaust flows,

more exhaust than supply– Adjust offset between supply and exhaust flows to

ensure differential pressure set point




• Closed loop on Flow– Measures and controls supply and exhaust flows

• Closed loop on Pressure– Measures room differential pressure– Differential pressure measurement is used to

adjust offset to maintain room pressure set point

• Models: 8680, 8681, 8682




• Safety of direct pressure with stability of flow tracking

• Requires suitable reference pressure

• Maximum offset limits configurable

• Not used for – Open labs– Labs without suitable

reference space• NOTE:

– Controls on flowfirst

– Pressure is slow reset back to set point




• Engineers/Consultants don’t understand

• TSI is unique to this type of control strategy

• Need to sell value of this strategy

• Used to lock-out competition



Flow Tracking with Room Pressure Feedback Sequence of Operations

If fume hood flow increases and makes space more negative, then …1. Controller senses an increased exhaust flow2. Controller gradually closes the general exhaust

damper to minimum if required3. If offset is still not achieved …4. Controller gradually opens supply until offset is

achieved5. Controller adjusts offset to meet ΔP set point




If fume hood flow decreases and makes space more positive, then …1. Controller senses a decreased exhaust flow2. Controller gradually opens the general exhaust

damper to maximum if required3. If offset is still not achieved …4. Controller gradually closes supply until offset is

achieved5. Controller adjusts offset to meet ΔP set point





1. Controller senses low ΔP

2. Increases offset to meet ΔP set pointa) Controller gradually opens the general exhaust damper

to maximum if required

b) Controller gradually closes supply to minimum if required









5. Controller gradually decreases general exhaust to offset

6. Controller adjusts offset to meet ΔP set point









5. Controller gradually increases general exhaust to offset

6. Controller adjusts offset to meet ΔP set point



Temperature Control

• To meet comfort demands in a lab environment, integral temperature control is a standard feature on Models 8636, 8681 and 8682 controllers which feature adjustable:1. Temperature dead band range

2. Temperature set point throttling range

3. Temperature set point integral value

4. Reheat valve control direction



Temperature Control

Temperature Dead Band (TEMP DB, ±0.1° - 1.0°F)

• Defines how sensitive controller needs to be regarding space temperature above and below temp set point

• If the TEMP DB is set to its maximum value (±1.0°F), the controller will not react to changes unless the space temperature rises above or below the set point by 1.0°F.

• If the TEMP DB is set to its minimum value (±0.1°F), the controller will react to space temperature changes 0.1°F above or below set point.



Temperature Control

If TEMP DB is set to

1.0°F, and the TEMP

SETP is set to 70.0°F,

the controller will not

take corrective action

unless the space

temperature is below

69.0°F or above

71.0°F.



Temperature Control

Temperature Throttling Range (TEMP TR, ±2.0°-20.0°F)• The temperature range in which the controller fully

opens or closes the reheat valve• Defines reheat valve movement

– Smaller TEMP TR range provides more precise control– Larger TEMP TR range provides more stable control



Temperature Control

• If TEMP TR is set to ±3.0°F, and the TEMP SETP is set to 70.0°F, the reheat valve will be fully open when the space temperature is 67°F. Similarly, the reheat valve will be fully closed when the space temperature is 73.0°F.



Temperature Control

Temperature Set Point Integral Value (TEMP Ti VAL)• Manually changes the temperature control PI

integral control loop variable– Increasing TEMP Ti VAL will slow the control system

which will increase stability – Decreasing TEMP Ti VAL will speed up the control system

which may cause system instability



Temperature Control

Reheat Control Direction (REHEAT DIR)• Determines the temperature control signal’s

output direction– can be set to DIRECT or REVERSE– if the control system closes the reheat valve instead of

opening the valve, this option will reverse the control signal to now open the valve.



Laboratory Control

• How Does This All Work?– A Model 8636, Model 8681 or Model 8682 controller

receives a temperature input from a temperature sensor (1000 Ω Platinum RTD). The controller maintains temperature control by:

1. Controlling supply and general exhaust for ventilation and cooling

2. Controlling the reheat coil for heating



Laboratory Control

• The controllers have three configurable supply flow minimum set points. – The ventilation set point (VENT MIN SET) is the minimum flow

volume required to meet ventilation needs of the laboratory (ACPH).

– The temperature supply set point (COOLING FLOW) is the theoretical minimum flow required to meet cooling flow needs of the laboratory.

– The unoccupied set point (UNOCC SETP) is the minimum flow required when the lab is not occupied.

• the supply flow will not be modulated for space cooling when in UNOCC SETP mode; space temperature control will be maintained by modulating the reheat coil.



Laboratory Control

• The controller continuously compares the temperature set point to the actual space temperature. If set point is being maintained, no changes are made.

• If the space temperature is rising above set point:1. The controller will first modulate the reheat valve

closed.

2. Once the reheat valve has been fully closed for three minutes, the controller will then gradually begin increasing the supply volume by 1 CFM/second up to the COOLING FLOW set point.



Laboratory Control

• If the space temperature decreases below the set point:1. The controller will first reduce the supply volume.

2. Once the supply volume reaches its minimum (VENT MIN SET), the controller will then start a 3 minute time period.

3. If, after 3 minutes the supply flow is still at the VENT MIN SET flow rate, the controller will begin modulating the reheat coil open to meet the heating demand.


TSI Incorporated – Critical EnvironmentsCapabilities Model 8635-M 8635-C 8636 8680 8681 8682

Room pressure monitor x

Room pressure controller x x

Flow tracking controller x x x

Flow tracking controller with room pressure feedback x x x

Low alarm relay x x x x

High alarm relay x x x x

Alarm relay x x

Switch input (occupied/unoccupied) x x x x

Analog output (pressure) x x

Supply flow input 1 1 2 1 1 4

Supply control x x x x x

Exhaust flow input 1 1 1 2

Exhaust control x x x x x

Temperature input (0 - 10V) x x

Temperature input (RTD) x x x

Temperature control x x x

Hood flow input 1 2 7



TSI’s Position

• Full-featured controls– Local support– Choice of laboratory control method– Fully digital controls – easy to configure & calibrate– Software specials

• Tailor made to meet specific requirements– Integration into BAS via:

• LON• BacNet (currently via gateway)• Modbus• N2



Questions?



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TSI Incorporated – Critical Environments Copyright© 2006 TSI Incorporated Critical Environments Laboratory Control Basics and Room Control Strategies