Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.SetPoints

Sequences for setting the setpoints for chilled water control

Information

This package contains chilled water plant reset control sequences. The implementation is based on section 5.20.5.2. in ASHRAE Guideline 36-2021.

Package Content

Name	Description
ChilledWaterPlantReset	Sequences to generate chilled water plant reset
ChilledWaterSupply	Sequences to generate setpoints of chilled water supply temperature and the differential pressure
Validation	Collection of validation models

Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.SetPoints.ChilledWaterPlantReset

Sequences to generate chilled water plant reset

Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.SetPoints.ChilledWaterPlantReset

Information

Block that output chilled water plant reset yChiWatPlaRes according to ASHRAE Guideline 36-2021, section 5.20.5.2.

Following implementation is for plants with primary-only and primary-secondary systems serving differential pressure controlled pumps.

Chilled water plant reset yChiWatPlaRes shall be reset using trim-respond logic with the following parameters:

Variable	Value	Definition
Device	Any chilled water pump	Associated device
SP0	`iniSet`	Initial setpoint
SPmin	`minSet`	Minimum setpoint
SPmax	`maxSet`	Maximum setpoint
Td	`delTim`	Delay timer
T	`samplePeriod`	Time step
I	`numIgnReq`	Number of ignored requests
R	`TChiWatSupResReq`	Number of requests
SPtrim	`triAmo`	Trim amount
SPres	`resAmo`	Respond amount
SPres_max	`maxRes`	Maximum response per time interval

Plant reset loop shall be enabled when the plant is enabled (any chilled water pump is enabled, uChiWatPum = true) and disabled when the plant is disabled (all chilled water pumps are disabled, uChiWatPum = false).

When the plant stage change is initiated (uStaCha=true), the plant reset yChiWatPlaRes shall be disabled and the value fixed at its last value for the longer of holTim and the time it takes for the plant to successfully stage.

For primary-secondary plants serving more than one set of differential pressure controlled pumps, a unique instance of the reset shall be used for each set of differential pressure controlled secondary pumps.

Chilled water reset requests from all loads served by a set of pumps shall be directed to those pumps reset loop only.
The differential pressure setpoint output from each reset shall be used in the pressure control loop for the associated set of pumps only.

Parameters

Type	Name	Default	Description
Integer	nPum	2	Total number of chilled water pumps
Real	holTim	900	Time to fix plant reset value [s]
Trim and respond parameters
Real	iniSet	1	Initial setpoint
Real	minSet	0	Minimum setpoint
Real	maxSet	1	Maximum setpoint
Real	delTim	900	Delay time after which trim and respond is activated [s]
Real	samplePeriod	300	Sample period time [s]
Integer	numIgnReq	2	Number of ignored requests
Real	triAmo	-0.02	Trim amount
Real	resAmo	0.03	Respond amount (must be opposite in to triAmo)
Real	maxRes	0.07	Maximum response per time interval (same sign as resAmo)

Connectors

Type	Name	Description
input IntegerInput	TChiWatSupResReq	Chilled water supply temperature setpoint reset request
input BooleanInput	chaPro	Plant staging status that indicates if the plant is in the staging process
input BooleanInput	uChiWatPum[nPum]	Chilled water pump status
output RealOutput	yChiWatPlaRes	Chilled water plant reset [1]

Modelica definition

block ChilledWaterPlantReset "Sequences to generate chilled water plant reset" parameter Integer nPum = 2 "Total number of chilled water pumps"; parameter Real holTim(unit="s")=900 "Time to fix plant reset value"; parameter Real iniSet=1 "Initial setpoint"; parameter Real minSet = 0 "Minimum setpoint"; parameter Real maxSet = 1 "Maximum setpoint"; parameter Real delTim(unit="s")=900 "Delay time after which trim and respond is activated"; parameter Real samplePeriod(unit="s")=300 "Sample period time"; parameter Integer numIgnReq = 2 "Number of ignored requests"; parameter Real triAmo = -0.02 "Trim amount"; parameter Real resAmo = 0.03 "Respond amount (must be opposite in to triAmo)"; parameter Real maxRes = 0.07 "Maximum response per time interval (same sign as resAmo)"; Buildings.Controls.OBC.CDL.Interfaces.IntegerInput TChiWatSupResReq "Chilled water supply temperature setpoint reset request"; Buildings.Controls.OBC.CDL.Interfaces.BooleanInput chaPro "Plant staging status that indicates if the plant is in the staging process"; Buildings.Controls.OBC.CDL.Interfaces.BooleanInput uChiWatPum[nPum] "Chilled water pump status"; Buildings.Controls.OBC.CDL.Interfaces.RealOutput yChiWatPlaRes( final min=minSet, final max=maxSet, final unit="1") "Chilled water plant reset"; Buildings.Controls.OBC.ASHRAE.G36.Generic.TrimAndRespond triRes( final have_hol=true, final iniSet=iniSet, final minSet=minSet, final maxSet=maxSet, final delTim=delTim, final samplePeriod=samplePeriod, final numIgnReq=numIgnReq, final triAmo=triAmo, final resAmo=resAmo, final maxRes=maxRes, final dtHol=holTim) "Calculate chilled water plant reset"; protected Buildings.Controls.OBC.CDL.Logical.Not not1[nPum] "Logical not"; Buildings.Controls.OBC.CDL.Logical.MultiAnd mulAnd( final nin=nPum) "Logical and"; Buildings.Controls.OBC.CDL.Logical.Not not2 "Check if these is any CHW pump is proven on"; Buildings.Controls.OBC.CDL.Reals.Switch swi1 "Set reset value to zero when device is disabled"; Buildings.Controls.OBC.CDL.Reals.Sources.Constant con1( final k=0) "Zero request when device is OFF"; equation connect(not1.y, mulAnd.u); connect(mulAnd.y, not2.u); connect(uChiWatPum, not1.u); connect(TChiWatSupResReq, triRes.numOfReq); connect(not2.y, triRes.uDevSta); connect(not2.y, swi1.u2); connect(con1.y, swi1.u3); connect(swi1.y, yChiWatPlaRes); connect(chaPro, triRes.uHol); connect(triRes.y, swi1.u1); end ChilledWaterPlantReset;

Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.SetPoints.ChilledWaterSupply

Sequences to generate setpoints of chilled water supply temperature and the differential pressure

Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.SetPoints.ChilledWaterSupply

Information

Block that outputs setpoints for the chilled water supply of primary-only and primary-secondary systems serving differential pressure controlled pumps. The outputs include supply temperature setpoint TChiWatSupSet and the differential pressure setpoint dpChiWatSet, according to ASHRAE Guideline 36-2021, section 5.20.5.2.

Chilled water supply temperature setpoint TChiWatSupSet and the differential pressure setpoint dpChiWatSet shall be reset based on the current value of chilled water plant reset uChiWatPlaRes.

Image of chilled water supply setpoints

Parameters

Type	Name	Default	Description
Integer	nRemDpSen	1	Total number of remote pressure differential sensor
Real	dpChiWatMin[nRemDpSen]	fill(34473.8, nRemDpSen)	Minimum chilled water differential pressure setpoint [Pa]
Real	dpChiWatMax[nRemDpSen]		Maximum chilled water differential pressure setpoint [Pa]
Real	TChiWatSupMin		Minimum chilled water supply temperature. This is the lowest minimum chilled water supply temperature of chillers in the plant [K]
Real	TPlaChiWatSupMax	288.706	Maximum plant chilled water supply temperature, default 60 degF [K]
Real	minSet	0	Minimum plant reset value
Real	maxSet	1	Maximum plant reset value
Real	halSet	0.5	Half plant reset value

Connectors

Type	Name	Description
input RealInput	uChiWatPlaRes	Chilled water plant reset [1]
output RealOutput	dpChiWatSet[nRemDpSen]	Chilled water differential pressure setpoint [Pa]
output RealOutput	TChiWatSupSet	Chilled water supply temperature [K]

Modelica definition

block ChilledWaterSupply "Sequences to generate setpoints of chilled water supply temperature and the differential pressure" parameter Integer nRemDpSen=1 "Total number of remote pressure differential sensor"; parameter Real dpChiWatMin[nRemDpSen]( final min=fill(0,nRemDpSen), final unit=fill("Pa",nRemDpSen), final quantity=fill("PressureDifference",nRemDpSen), displayUnit=fill("Pa",nRemDpSen)) = fill(34473.8, nRemDpSen) "Minimum chilled water differential pressure setpoint"; parameter Real dpChiWatMax[nRemDpSen]( final min=dpChiWatMin, final unit=fill("Pa",nRemDpSen), final quantity=fill("PressureDifference",nRemDpSen), displayUnit=fill("Pa",nRemDpSen)) "Maximum chilled water differential pressure setpoint"; parameter Real TChiWatSupMin( final quantity="ThermodynamicTemperature", final unit="K", displayUnit="degC") "Minimum chilled water supply temperature. This is the lowest minimum chilled water supply temperature of chillers in the plant"; parameter Real TPlaChiWatSupMax( final quantity="ThermodynamicTemperature", final unit="K", displayUnit="degC") = 288.706 "Maximum plant chilled water supply temperature, default 60 degF"; parameter Real minSet = 0 "Minimum plant reset value"; parameter Real maxSet = 1 "Maximum plant reset value"; parameter Real halSet = 0.5 "Half plant reset value"; Buildings.Controls.OBC.CDL.Interfaces.RealInput uChiWatPlaRes( final min=minSet, final max=maxSet, final unit="1") "Chilled water plant reset"; Buildings.Controls.OBC.CDL.Interfaces.RealOutput dpChiWatSet[nRemDpSen]( final unit=fill("Pa", nRemDpSen), final quantity=fill("PressureDifference", nRemDpSen)) "Chilled water differential pressure setpoint"; Buildings.Controls.OBC.CDL.Interfaces.RealOutput TChiWatSupSet( final unit="K", displayUnit="degC", final quantity="ThermodynamicTemperature") "Chilled water supply temperature"; protected Buildings.Controls.OBC.CDL.Reals.Line chiWatPumPre[nRemDpSen] "Chilled water pump differential pressure setpoint"; Buildings.Controls.OBC.CDL.Reals.Sources.Constant zerRes[nRemDpSen]( final k=fill(minSet, nRemDpSen)) "Minimum plant reset"; Buildings.Controls.OBC.CDL.Reals.Sources.Constant halRes[nRemDpSen]( final k=fill(halSet, nRemDpSen)) "Half one plant reset"; Buildings.Controls.OBC.CDL.Reals.Sources.Constant oneRes( final k=maxSet) "Maximum plant reset"; Buildings.Controls.OBC.CDL.Reals.Sources.Constant minChiWatPumPre[nRemDpSen]( final k=dpChiWatMin) "Minimum chilled water differential pressure setpoint"; Buildings.Controls.OBC.CDL.Reals.Sources.Constant maxChiWatPumPre[nRemDpSen]( final k=dpChiWatMax) "Maximum chilled water differential pressure setpoint"; Buildings.Controls.OBC.CDL.Reals.Sources.Constant maxChiWatTem( final k=TPlaChiWatSupMax) "Maximum chilled water supply temperature"; Buildings.Controls.OBC.CDL.Reals.Sources.Constant minChiWatTem( final k=TChiWatSupMin) "Minimum chilled water supply temperature"; Buildings.Controls.OBC.CDL.Reals.Line chiWatTem "Chilled water temperature setpoint"; Buildings.Controls.OBC.CDL.Routing.RealScalarReplicator reaRep( final nout=nRemDpSen) "Distribute reset value to each remote sensor"; equation connect(zerRes.y, chiWatPumPre.x1); connect(minChiWatPumPre.y, chiWatPumPre.f1); connect(halRes.y, chiWatPumPre.x2); connect(maxChiWatPumPre.y, chiWatPumPre.f2); connect(maxChiWatTem.y, chiWatTem.f1); connect(oneRes.y, chiWatTem.x2); connect(minChiWatTem.y, chiWatTem.f2); connect(chiWatPumPre.y, dpChiWatSet); connect(chiWatTem.y, TChiWatSupSet); connect(uChiWatPlaRes, chiWatTem.u); connect(uChiWatPlaRes, reaRep.u); connect(halRes[1].y, chiWatTem.x1); connect(reaRep.y, chiWatPumPre.u); end ChilledWaterSupply;