Buildings.DHC.ETS.Cooling

This package contains models for energy transfer stations used in district cooling systems

Information

This package contains models for energy transfer stations used in district cooling systems.

Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).

Package Content

Name	Description
Direct	Direct cooling ETS model for district energy systems with in-building pumping and deltaT control
Indirect	Indirect cooling energy transfer station for district energy systems
Examples

Buildings.DHC.ETS.Cooling.Direct

Direct cooling ETS model for district energy systems with in-building pumping and deltaT control

Buildings.DHC.ETS.Cooling.Direct

Information

Direct cooling energy transfer station (ETS) model with in-building pumping and deltaT control. The design is based on a typical district cooling ETS described in ASHRAE's District Cooling Guide. As shown in the figure below, the district and building piping are hydronically coupled. The control valve ensures that the return temperature to the district cooling network is at or above the minimum specified value. This configuration naturally results in a fluctuating building supply tempearture.

DC ETS Direct

Reference

American Society of Heating, Refrigeration and Air-Conditioning Engineers. (2019). Chapter 5: End User Interface. In District Cooling Guide, Second Edition and Owner's Guide for Buildings Served by District Cooling.

Extends from Buildings.DHC.ETS.BaseClasses.PartialDirect (Partial direct ETS model for district energy systems with in-building pumping and deltaT control).

Parameters

Type	Name	Default	Description
replaceable package MediumSer		Water	Service side medium
replaceable package MediumSerHea_a		Water	Service side medium at heating inlet
replaceable package MediumBui		Water	Building side medium
Generic	fue[nFue]		Fuel type
Configuration
DistrictSystemType	typ	Buildings.DHC.Types.District...	Type of district system
Boolean	have_heaWat	false	Set to true if the ETS supplies heating water
Boolean	have_chiWat	true	Set to true if the ETS supplies chilled water
Nominal condition
HeatFlowRate	QHeaWat_flow_nominal	0	Nominal capacity of heating system (>=0) [W]
HeatFlowRate	QHotWat_flow_nominal	0	Nominal capacity of hot water production system (>=0) [W]
HeatFlowRate	QChiWat_flow_nominal	0	Nominal capacity of cooling system (<=0) [W]
MassFlowRate	mBui_flow_nominal		Nominal mass flow rate of building side [kg/s]
PressureDifference	dpConVal_nominal	50	Nominal pressure drop in the control valve [Pa]
PressureDifference	dpCheVal_nominal	6000	Nominal pressure drop in the check valve [Pa]
PID controller
SimpleController	controllerType	Modelica.Blocks.Types.Simple...	Type of controller
Real	k	0.1	Gain of controller [1]
Time	Ti	60	Time constant of integrator block [s]
Time	Td	0.1	Time constant of derivative block [s]
Real	yMax	1	Upper limit of output
Real	yMin	0	Lower limit of output
Assumptions
Boolean	allowFlowReversalSer	false	Set to true to allow flow reversal on service side
Boolean	allowFlowReversalBui	false	Set to true to allow flow reversal on building side
Advanced
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Type of energy balance: dynamic (3 initialization options) or steady state
Real	bandwidth	0.2	Bandwidth around reference signal for on/off controller

Connectors

Type	Name	Description
FluidPorts_a	ports_aHeaWat[nPorts_aHeaWat]	Fluid connectors for heating water return (from building)
FluidPorts_b	ports_bHeaWat[nPorts_bHeaWat]	Fluid connectors for heating water supply (to building)
FluidPorts_a	ports_aChiWat[nPorts_aChiWat]	Fluid connectors for chilled water return (from building)
FluidPorts_b	ports_bChiWat[nPorts_bChiWat]	Fluid connectors for chilled water supply (to building)
FluidPort_a	port_aSerAmb	Fluid connector for ambient water service supply line
FluidPort_b	port_bSerAmb	Fluid connector for ambient water service return line
FluidPort_a	port_aSerHea	Fluid connector for heating service supply line
FluidPort_b	port_bSerHea	Fluid connector for heating service return line
FluidPort_a	port_aSerCoo	Fluid connector for cooling service supply line
FluidPort_b	port_bSerCoo	Fluid connector for cooling service return line
output RealOutput	PHea	Power drawn by heating system [W]
output RealOutput	PCoo	Power drawn by cooling system [W]
output RealOutput	PFan	Power drawn by fan motors [W]
output RealOutput	PPum	Power drawn by pump motors [W]
output RealOutput	QFue_flow[nFue]	Fuel energy input rate [W]
Bus	weaBus	Weather data bus
input RealInput	TDisRetSet	Setpoint for the district return temperature (min for cooling, max for heating) [K]
output RealOutput	Q_flow	Measured heating demand at the ETS [W]
output RealOutput	Q	Measured energy consumption at the ETS [J]

Modelica definition

model Direct "Direct cooling ETS model for district energy systems with in-building pumping and deltaT control" extends Buildings.DHC.ETS.BaseClasses.PartialDirect( final typ=Buildings.DHC.Types.DistrictSystemType.Cooling, final have_chiWat=true, final have_heaWat=false, con(reverseActing=false), nPorts_aChiWat=1, nPorts_bChiWat=1); equation connect(port_aSerCoo, senTDisSup.port_a); connect(ports_aChiWat[1], senTBuiRet.port_a); connect(senTDisRet.port_b, port_bSerCoo); connect(senTBuiSup.port_b, ports_bChiWat[1]); end Direct;

Buildings.DHC.ETS.Cooling.Indirect

Indirect cooling energy transfer station for district energy systems

Buildings.DHC.ETS.Cooling.Indirect

Information

Indirect cooling energy transfer station (ETS) model that controls the building chilled water supply temperature by modulating a primary control valve on the district supply side. The design is based on a typical district cooling ETS described in ASHRAE's District Cooling Guide. As shown in the figure below, the building pumping design (constant/variable) is specified on the building side and not within the ETS.

DHC.ETS.Indirect

Reference

Extends from Buildings.DHC.ETS.BaseClasses.PartialIndirect (Partial indirect energy transfer station for district energy systems).

Parameters

Type	Name	Default	Description
replaceable package MediumSer		Water	Service side medium
replaceable package MediumSerHea_a		Water	Service side medium at heating inlet
replaceable package MediumBui		Water	Building side medium
Generic	fue[nFue]		Fuel type
Configuration
DistrictSystemType	typ	Buildings.DHC.Types.District...	Type of district system
Boolean	have_heaWat	false	Set to true if the ETS supplies heating water
Boolean	have_chiWat	true	Set to true if the ETS supplies chilled water
Nominal condition
HeatFlowRate	QHeaWat_flow_nominal	0	Nominal capacity of heating system (>=0) [W]
HeatFlowRate	QHotWat_flow_nominal	0	Nominal capacity of hot water production system (>=0) [W]
HeatFlowRate	QChiWat_flow_nominal	-Q_flow_nominal	Nominal capacity of cooling system (<=0) [W]
MassFlowRate	mDis_flow_nominal		Nominal mass flow rate of district side [kg/s]
MassFlowRate	mBui_flow_nominal		Nominal mass flow rate of building side [kg/s]
PressureDifference	dpConVal_nominal	6000	Nominal pressure drop of fully open control valve [Pa]
Heat exchanger
PressureDifference	dp1_nominal		Nominal pressure difference on primary side [Pa]
PressureDifference	dp2_nominal		Nominal pressure difference on secondary side [Pa]
Boolean	use_Q_flow_nominal	true	Set to true to specify Q_flow_nominal and temeratures, or to false to specify effectiveness
Temperature	T_a1_nominal		Nominal temperature at port a1 (district supply) [K]
Temperature	T_a2_nominal		Nominal temperature at port a2 (building return) [K]
Efficiency	eta	0.8	Constant effectiveness [1]
PID controller
SimpleController	controllerType	Modelica.Blocks.Types.Simple...	Type of controller
Real	k	1	Gain of controller [1]
Time	Ti	120	Time constant of integrator block [s]
Time	Td	0.1	Time constant of derivative block [s]
Real	yMax	1	Upper limit of output
Real	yMin	0.01	Lower limit of output
Assumptions
Boolean	allowFlowReversalSer	false	Set to true to allow flow reversal on service side
Boolean	allowFlowReversalBui	false	Set to true to allow flow reversal on building side

Connectors

Type	Name	Description
FluidPorts_a	ports_aHeaWat[nPorts_aHeaWat]	Fluid connectors for heating water return (from building)
FluidPorts_b	ports_bHeaWat[nPorts_bHeaWat]	Fluid connectors for heating water supply (to building)
FluidPorts_a	ports_aChiWat[nPorts_aChiWat]	Fluid connectors for chilled water return (from building)
FluidPorts_b	ports_bChiWat[nPorts_bChiWat]	Fluid connectors for chilled water supply (to building)
FluidPort_a	port_aSerAmb	Fluid connector for ambient water service supply line
FluidPort_b	port_bSerAmb	Fluid connector for ambient water service return line
FluidPort_a	port_aSerHea	Fluid connector for heating service supply line
FluidPort_b	port_bSerHea	Fluid connector for heating service return line
FluidPort_a	port_aSerCoo	Fluid connector for cooling service supply line
FluidPort_b	port_bSerCoo	Fluid connector for cooling service return line
output RealOutput	PHea	Power drawn by heating system [W]
output RealOutput	PCoo	Power drawn by cooling system [W]
output RealOutput	PFan	Power drawn by fan motors [W]
output RealOutput	PPum	Power drawn by pump motors [W]
output RealOutput	QFue_flow[nFue]	Fuel energy input rate [W]
Bus	weaBus	Weather data bus
input RealInput	TBuiSupSet	Setpoint temperature for building supply
output RealOutput	Q_flow	Measured heating demand at the ETS [W]
output RealOutput	Q	Measured energy consumption at the ETS [J]

Modelica definition

model Indirect "Indirect cooling energy transfer station for district energy systems" extends Buildings.DHC.ETS.BaseClasses.PartialIndirect( QChiWat_flow_nominal=-Q_flow_nominal, final typ=Buildings.DHC.Types.DistrictSystemType.Cooling, final have_chiWat=true, final have_heaWat=false, Q_flow_nominal(max=0), nPorts_aChiWat=1, nPorts_bChiWat=1, con(reverseActing=false)); equation connect(senTBuiRet.port_a, ports_aChiWat[1]); connect(senTBuiSup.port_b, ports_bChiWat[1]); connect(senTDisRet.port_b, port_bSerCoo); connect(port_aSerCoo, senTDisSup.port_a); end Indirect;