3C1 Russell ChilledWaterLoadShedding

8/13/2019 3C1 Russell ChilledWaterLoadShedding

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Chilled Water Load

Shedding: Planning and

Procedures

IDEA ConferenceFeb. 2008Jay Russell, PE

University of Michigan


2/23

Overview Definitions

Background - Palmer Chiller Plant Communicate with the Stakeholders

Minimize the Likelihood and Severity ofExcursions

Regain Control of the Plant During

Excursions Conclusions


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Definitions Load Shedding (CHW System): Restricting

or turning off the flow of chilled water forselected users in a controlled, repeatablemanner.

Excursion (CHW system): Period ofelevated supply temperatures due tocapacity shortfall, equipment or control

problems


4/23

Background -

Palmer Drive Chiller Plant

3,000-ton electric centrifugal chiller plant

(2) x 1,250-ton plus (1) x 500-ton w/generator backup

Primary-Secondary-Tertiary system w/

14-degree design Delta T

Serves about 600,000 GSF of laboratory,

vivarium, office, conference, classroom,and admin space.

Plant does not have full N-1 reliability


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Life Sciences Institute (LSI) ~350K GSF

Background - Palmer Drive Chiller Plant


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Background - Palmer Drive Chiller Plant LSI Cooling Coil Design Conditions: 92 Fdb, 72

Fwb (40% RH)

Actual daytime conditions, July 31 August 2,2006: 95 Fdb, 84 Fwb (65% RH)

Worst conditions Ive seen in 19 years trackingHVAC systems BAS staffer

Result: most air handlers could not meetsetpoint, CHW valves opened wide, causingmassive negative flow through decoupler


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Chilled Water System Reliability PlanThree major goals for reliability plan:

1. Maintain communication betweenstakeholders at all times, but especially duringunforeseen outages or excursions.

2. Minimize the likelihood and severity of chilledwater outages and excursions

3. Establish a repeatable plan for bringing the

plant back into normal control ranges duringexcursions


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Goal 1: Maintain Communication

Between Stakeholders Communication must be timely and must

be maintained at all times Use existing shutdown notification system

and building contact database

Use Building Automation System to trendand analyze plant performance

Establish load database for planning andfor emergency response


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Goal 2: Minimize the likelihood and

severity of excursions Limit flows for tertiary systems

Establish alarms for critical flows andtemperatures

Add flexiblility to temperature setpoints


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severity of excursionsFlow limitations for tertiary systems

Tertiary Max. Flow (gal/min)

LSI-AHU 2,500

LSI-Vivarium 700

LSI-Process 250LSI-Server 95

Palmer Commons 450

Undergraduate Science Bldg 1,050TOTAL 5,045

Max. primary CHW flowrate: 4,800


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severity of excursionsFlow limitations for tertiary systems

Progam maximum tertiary flow limits intotertiary valve control code. These limitvariables can then be altered automatically byload shedding algorithm.


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severity of excursionsAlarms for critical flows and temperatures

Program alarms into Building AutomationSystem to alert operators of excursionsbefore they get out of hand.

Cut through the chaff of routine alarmsby using email, phone, or pagernotification for critical stakeholders.


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severity of excursionsAdding flexibility to temperature setpoints

Load Type Critical CHWS Temp? Critical DAT Temp?

AHU-Offices NO NO

AHU-Labs YES, BUT CAN RANGE YES, BUT CAN RANGE

AHU-Vivarium YES, BUT CAN RANGE YES, BUT CAN RANGE

AHU/Fan Coils-Server Rms YES, BUT CAN RANGE YES, BUT CAN RANGE

AHU-Stairwells NO NO

Fan Coils-Elec. Rooms NO NO

Fan Coils-Telecom Rooms NO NO

Fan Coil-BDF NO NO

Fan Coils-Elevator Rooms NO NO

Cold Rooms NO-condenser water DOES NOT APPLY

Environmental Rooms NO-condenser water DOES NOT APPLY


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severity of excursionsAdding flexibility to temperature setpoints

Most air handling systems, even critical vivariumfans, can accommodate a few degrees of chilledwater supply temp variation, since in manycases reheat coils can compensate.

Emphasize stable versus unstable

During excursions, allow tertiary supplysetpoints to rise, especially in non-critical areas.

Consider floating DAT setpoints

DAT SP = (CHWS Temp) + (Design coil approach)


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Goal 3: Establish a repeatable plan for bringing the plant

into control during excursions

Bodys response to shock

Establish multi-level load shedding modes Establish stakeholder responsibilities in

advance


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Establish multi-level load shedding modesLevel 1: ~ 430 tons shed total

Tertiary Normal Max.Flow

(gal/min)

Level 1 Max.Flow

(gal/min)

Expected dischargeair temp

increase (deg F)

LSI-AHU 2,500 2,150 2

LSI-Vivarium 700 600 2

LSI-Process 250 205 2

LSI-Server 95 80 2Commons 450 385 2

USB 1,050 900 2

Total 5,045 4,320


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Establish multi-level load shedding modesLevel 2: ~ 1,200 tons shed total

Tertiary Normal Max.Flow (gal/min)

Level 2 Max.Flow (gal/min)

Expected dischargeair temp increase

(deg F)

LSI-AHU 2,500 1,400 6

LSI-Vivarium 700 550 3

LSI-Process 250 110 6

LSI-Server 95 55 6Commons 450 250 6

USB 1,050 600 6

Total 5,045 2,965


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Establish multi-level load shedding modesLevel 3-Start to shut off non-critical systems:~1,850 tons shed totalShut-offSequence

Load Name Service Area Design Demand(Tons)

1 LSI Systems AHU-7, -8 Offices 160 total

2 USB Systems AHU-2, -3 Offices, Classrooms 200 total

3 Commons Systems AHU-1, -2 Offices, Meeting Rooms 240 total

4 Commons Systems AHU-3 Kitchen/Food Service 50 total

Total 650 tons


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Establish multi-level load shedding modesLevel 4 All loads shut off except Vivarium, to

match capacity of 500-ton chiller withemergency power


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Load Shedding in Action: August 8, 2007


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Load Shedding in Action: August 8, 2007


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Conclusions Know your customers and communicate

with them regularly Know your loads

Think of bending but not breaking: let

temperature/flow setpoints flex ratherthan outright shutoff if possible

Establish a consensus on load sheddingplans in advance of emergency outage orexcursion

Documents

3C1 Russell ChilledWaterLoadShedding