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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
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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
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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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Goal 2: Minimize the likelihood and
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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Goal 2: Minimize the likelihood and
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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Goal 2: Minimize the likelihood and
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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Goal 2: Minimize the likelihood and
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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Goal 2: Minimize the likelihood and
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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Goal 3: Establish a repeatable plan for bringing the plant
into control during excursions
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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Goal 3: Establish a repeatable plan for bringing the plant
into control during excursions
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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Goal 3: Establish a repeatable plan for bringing the plant
into control during excursions
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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Goal 3: Establish a repeatable plan for bringing the plant
into control during excursions
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
Recommended