modelElectricChillerParallel

District cooling plant model

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Extends from Buildings.DHC.Plants.BaseClasses.PartialPlant (Partial class for modeling a plant).

Information

This model implements a generic district central cooling plant as illustrated in the schematics below.

The cooling is provided by two parallel chillers instantiated from Buildings.Applications.BaseClasses.Equipment.ElectricChillerParallel.
The chilled water bypass loop is controlled to ensure a minimum flow of chilled water running through the chillers all the time.
The condenser water is cooled by two parallel cooling towers with a bypass loop. See Buildings.DHC.Plants.Cooling.Subsystems.CoolingTowersWithBypass for the details of the modeling of the cooling towers.
The chilled water loop is equipped with two parallel constant speed pumps, which run one-and-one with each chiller. The condenser water pumps are constant speed with prescribed mass flow rates.
The plant operates when it receives an on signal from the external control.

The staging of the chillers is based on the calculated cooling load.

See Buildings.DHC.Plants.Cooling.Controls.ChillerStage for the detailed control logic.

System schematics .

Parameters

Type	Name	Default	Description
Boolean	have_fue (from PartialPlant)	nFue > 0	Set to true if the plant has fuel use
Buildings.Fluid.Data.Fuels.Generic[nFue]	fue (from PartialPlant)		Fuel type
Buildings.Fluid.Movers.Data.Generic	perCHWPum
Buildings.Fluid.Movers.Data.Generic	perCWPum
Modelica.Units.SI.PressureDifference	dpCooTowVal_nominal		Nominal pressure difference of the cooling tower valve
Configuration
Buildings.DHC.Types.DistrictSystemType	typ (from PartialPlant)	Buildings.DHC.Types.DistrictSystemType.CombinedGeneration2to4	Type of district system
Boolean	have_fan (from PartialPlant)	false	Set to true if fan power is computed
Boolean	have_pum (from PartialPlant)	false	Set to true if pump power is computed
Boolean	have_eleHea (from PartialPlant)	false	Set to true if the plant has electric heating system
Integer	nFue (from PartialPlant)	0	Number of fuel types (0 means no combustion system)
Boolean	have_eleCoo (from PartialPlant)	false	Set to true if the plant has electric cooling system
Boolean	have_weaBus (from PartialPlant)	false	Set to true to use a weather bus
Assumptions
Boolean	allowFlowReversal (from PartialPlant)	false	Set to true to allow flow reversal in service lines
Chiller
Integer	numChi	2	Number of chillers
Buildings.Fluid.Chillers.Data.ElectricEIR.Generic	perChi		Performance data of chiller
Modelica.Units.SI.MassFlowRate	mCHW_flow_nominal		Nominal chilled water mass flow rate
Modelica.Units.SI.Pressure	dpCHW_nominal		Pressure difference at the chilled water side
Modelica.Units.SI.HeatFlowRate	QChi_nominal		Nominal cooling capacity of single chiller (negative means cooling)
Modelica.Units.SI.MassFlowRate	mMin_flow		Minimum mass flow rate of single chiller
Cooling Tower
Modelica.Units.SI.MassFlowRate	mCW_flow_nominal		Nominal condenser water mass flow rate
Modelica.Units.SI.Pressure	dpCW_nominal		Pressure difference at the condenser water side
Modelica.Units.SI.Temperature	TAirInWB_nominal		Nominal air wetbulb temperature
Modelica.Units.SI.Temperature	TCW_nominal		Nominal condenser water temperature at tower inlet
Modelica.Units.SI.TemperatureDifference	dT_nominal		Temperature difference between inlet and outlet of the tower
Modelica.Units.SI.TemperatureDifference	dTApp		Approach temperature
Modelica.Units.SI.Temperature	TMin		Minimum allowed water temperature entering chiller
Modelica.Units.SI.Power	PFan_nominal		Fan power
Pump
Modelica.Units.SI.Pressure	dpCHWPumVal_nominal		Nominal pressure drop of chilled water pump valve
Modelica.Units.SI.Pressure	dpCWPumVal_nominal		Nominal pressure drop of condenser water pump valve
Dynamics › Pump
Modelica.Units.SI.Time	tau	1	Pump time constant at nominal flow (if energyDynamics <> SteadyState)
Boolean	use_riseTime	false	Set to true to continuously change motor speed
Modelica.Units.SI.Time	riseTime	30	Time needed to change motor speed between zero and full speed
Modelica.Blocks.Types.Init	init	Modelica.Blocks.Types.Init.InitialOutput	Type of initialization for pumps (no init/steady state/initial state/initial output)
Real	yCHWP_start	fill(0, numChi)	Initial value of CHW pump signals
Real	yCWP_start	fill(0, numChi)	Initial value of CW pump signals
Dynamics › Valve
Boolean	use_strokeTime	use_riseTime	Set to true to continuously change valve position
Modelica.Units.SI.Time	strokeTime	riseTime	Time needed to open or close valve
Control Settings
Modelica.Units.SI.Time	tWai		Waiting time
Dynamics › Conservation equations
Modelica.Fluid.Types.Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamics.DynamicFreeInitial	Type of energy balance: dynamic (3 initialization options) or steady state
Advanced › Dynamics
Modelica.Fluid.Types.Dynamics	massDynamics	energyDynamics	Type of mass balance: dynamic (3 initialization options) or steady state, must be steady state if energyDynamics is steady state

Connectors

Type	Name	Description
Modelica.Fluid.Interfaces.FluidPort_a	port_aSerAmb (from PartialPlant)	Fluid connector for ambient water service supply line
Modelica.Fluid.Interfaces.FluidPort_b	port_bSerAmb (from PartialPlant)	Fluid connector for ambient water service return line
Modelica.Fluid.Interfaces.FluidPort_a	port_aSerHea (from PartialPlant)	Fluid connector for heating service supply line
Modelica.Fluid.Interfaces.FluidPort_b	port_bSerHea (from PartialPlant)	Fluid connector for heating service return line
Modelica.Fluid.Interfaces.FluidPort_a	port_aSerCoo (from PartialPlant)	Fluid connector for cooling service supply line
Modelica.Fluid.Interfaces.FluidPort_b	port_bSerCoo (from PartialPlant)	Fluid connector for cooling service return line
Buildings.BoundaryConditions.WeatherData.Bus	weaBus (from PartialPlant)	Weather data bus
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	PHea (from PartialPlant)	Power drawn by heating system
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	PCoo (from PartialPlant)	Power drawn by cooling system
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	PFan (from PartialPlant)	Power drawn by fan motors
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	PPum (from PartialPlant)	Power drawn by pump motors
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	QFue_flow (from PartialPlant)	Fuel energy input rate
Modelica.Blocks.Interfaces.BooleanInput	on	On signal of the plant
Modelica.Blocks.Interfaces.RealInput	TCHWSupSet	Set point for chilled water supply temperature

Components

Type	Name	Description
Buildings.Applications.BaseClasses.Equipment.ElectricChillerParallel	mulChiSys	Chillers connected in parallel
Buildings.DHC.Plants.Cooling.Subsystems.CoolingTowersWithBypass	cooTowWitByp	Cooling towers with bypass valve
Buildings.Applications.BaseClasses.Equipment.FlowMachine_y	pumCHW	Chilled water pumps
Buildings.Applications.BaseClasses.Equipment.FlowMachine_m	pumCW	Condenser water pumps
Buildings.Fluid.Actuators.Valves.TwoWayEqualPercentage	valByp	Chilled water bypass valve
Buildings.Fluid.Sensors.TemperatureTwoPort	senTCHWSup	Chilled water supply temperature
Buildings.DHC.Plants.Cooling.Controls.ChillerStage	chiStaCon	Chiller staging controller
Buildings.Fluid.Sensors.TemperatureTwoPort	senTCHWRet	Chilled water return temperature
Buildings.Fluid.Sources.Boundary_pT	expTanCW	Condenser water expansion tank
Buildings.Fluid.Sources.Boundary_pT	expTanCHW	Chilled water expansion tank
Buildings.Fluid.Sensors.MassFlowRate	senMasFlo	Chilled water return mass flow
Buildings.Controls.OBC.CDL.Conversions.BooleanToReal[numChi]	chiOn	Convert chiller on signal from boolean to real
Buildings.Controls.OBC.CDL.Reals.MultiSum	totPPum	Total pump power
Buildings.Controls.OBC.CDL.Reals.MultiSum	totPFan	Total fan power
Buildings.Controls.OBC.CDL.Reals.MultiSum	totPCoo	Total cooling power
Buildings.Fluid.FixedResistances.Junction	joiCHWRet	Flow joint for the chilled water return side
Buildings.Fluid.FixedResistances.Junction	splCHWSup	Flow splitter for the chilled water supply side
Buildings.DHC.Plants.Cooling.Controls.ChilledWaterBypass	chiBypCon	Chilled water bypass control
Fluid.Sensors.MassFlowRate	senMasFloCHW	Total chilled water pump mass flow rate

Revisions

January 2, 2023, by Kathryn Hinkelman:
Revised chilled water pump control to be constant speed and running 1-and-1 with chillers.
December 14, 2022, by Kathryn Hinkelman:
Corrected chiBypCon to control mass flow rate through the chillers.
This is for issue 2912.
November 16, 2022, by Michael Wetter:
Corrected wrong assignments for chiller system mulChiSys which assigned chilled water to condenser water parameters and vice versa.
Changed rise time of valve to 30 seconds so that it is the same as the one for the pumps.
September 15, 2022, by Kathryn Hinkelman:
Propagated dynamics and initialization parameters for pumps.
March 3, 2022, by Michael Wetter:
Moved massDynamics to Advanced tab and added assertion for correct combination of energy and mass dynamics.
This is for issue 1542.
August 6, 2020 by Jing Wang:
First implementation.