modelDirect

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

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

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.

Parameters

Type	Name	Default	Description
Buildings.Fluid.Data.Fuels.Generic[nFue]	fue (from PartialETS)		Fuel type
Configuration
TypDisSys	typ (from PartialETS)	Buildings.DHC.Types.DistrictSystemType.CombinedGeneration2to4	Type of district system
Integer	nPorts_aHeaWat (from PartialETS)	0	Number of heating water return ports
Integer	nPorts_bHeaWat (from PartialETS)	0	Number of heating water supply ports
Integer	nPorts_aChiWat (from PartialETS)	0	Number of chilled water return ports
Integer	nPorts_bChiWat (from PartialETS)	0	Number of chilled water supply ports
Boolean	have_heaWat (from PartialETS)	false	Set to true if the ETS supplies heating water
Boolean	have_hotWat (from PartialETS)	false	Set to true if the ETS supplies hot water
Boolean	have_chiWat (from PartialETS)	false	Set to true if the ETS supplies chilled water
Boolean	have_fan (from PartialETS)	false	Set to true if fan power is computed
Boolean	have_pum (from PartialETS)	false	Set to true if pump power is computed
Boolean	have_eleHea (from PartialETS)	false	Set to true if the ETS has electric heating system
Integer	nFue (from PartialETS)	0	Number of fuel types (0 means no combustion system)
Boolean	have_eleCoo (from PartialETS)	false	Set to true if the ETS has electric cooling system
Boolean	have_weaBus (from PartialETS)	false	Set to true to use a weather bus
Assumptions
Boolean	allowFlowReversalSer (from PartialETS)	false	Set to true to allow flow reversal on service side
Boolean	allowFlowReversalBui (from PartialETS)	false	Set to true to allow flow reversal on building side
Nominal condition
Modelica.Units.SI.HeatFlowRate	QHeaWat_flow_nominal (from PartialETS)	0	Nominal capacity of heating system (>=0)
Modelica.Units.SI.HeatFlowRate	QHotWat_flow_nominal (from PartialETS)	0	Nominal capacity of hot water production system (>=0)
Modelica.Units.SI.HeatFlowRate	QChiWat_flow_nominal (from PartialETS)	0	Nominal capacity of cooling system (<=0)
Modelica.Units.SI.MassFlowRate	mBui_flow_nominal (from PartialDirect)		Nominal mass flow rate of building side
Modelica.Units.SI.PressureDifference	dpConVal_nominal (from PartialDirect)	50	Nominal pressure drop in the control valve
Modelica.Units.SI.PressureDifference	dpCheVal_nominal (from PartialDirect)	6000	Nominal pressure drop in the check valve
PID controller
Modelica.Blocks.Types.SimpleController	controllerType (from PartialDirect)	Modelica.Blocks.Types.SimpleController.PI	Type of controller
Real	k (from PartialDirect)	0.1	Gain of controller
Modelica.Units.SI.Time	Ti (from PartialDirect)	60	Time constant of integrator block
Modelica.Units.SI.Time	Td (from PartialDirect)	0.1	Time constant of derivative block
Real	yMax (from PartialDirect)	1	Upper limit of output
Real	yMin (from PartialDirect)	0	Lower limit of output
Advanced
Modelica.Fluid.Types.Dynamics	energyDynamics (from PartialDirect)	Modelica.Fluid.Types.Dynamics.FixedInitial	Type of energy balance: dynamic (3 initialization options) or steady state
Real	bandwidth (from PartialDirect)	0.2	Bandwidth around reference signal for on/off controller

Connectors

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

Components

Type	Name	Description
Buildings.Fluid.Sensors.TemperatureTwoPort	senTDisSup (from PartialDirect)	District supply temperature sensor
Buildings.Fluid.Sensors.MassFlowRate	senMasFlo (from PartialDirect)	District supply mass flow rate sensor
Buildings.Fluid.FixedResistances.Junction	jun (from PartialDirect)	Bypass junction
Buildings.Fluid.Sensors.TemperatureTwoPort	senTDisRet (from PartialDirect)	District return temperature sensor
Buildings.Fluid.FixedResistances.Junction	spl (from PartialDirect)	Bypass junction, splitter
Buildings.Fluid.Actuators.Valves.TwoWayEqualPercentage	conVal (from PartialDirect)	Control valve
Buildings.Fluid.Sensors.TemperatureTwoPort	senTBuiRet (from PartialDirect)	Building return temperature sensor
Fluid.FixedResistances.CheckValve	cheVal (from PartialDirect)	Check valve (backflow preventer)
Modelica.Blocks.Math.Add	dTDis (from PartialDirect)	Temperature difference on the district side
Modelica.Blocks.Math.Product	pro (from PartialDirect)	Product
Modelica.Blocks.Math.Gain	cp (from PartialDirect)	Specific heat multiplier to calculate heat flow rate
Modelica.Blocks.Continuous.Integrator	int (from PartialDirect)	Integration
Controls.OBC.CDL.Reals.PID	con (from PartialDirect)	District return temperature controller
Buildings.Fluid.Sensors.TemperatureTwoPort	senTBuiSup (from PartialDirect)	Building supply temperature sensor

Revisions

March 27, 2024, by David Blum:
Update icon and fix port orientation to align with convention.
This is for issue #3606.
May 5, 2023, by David Blum:
Removed assignment of check valve allowFlowReversal=false.
This is for #3389.
April 7, 2023, by David Blum:
Change to extend from Buildings.DHC.ETS.BaseClasses.PartialDirect.
January 11, 2023, by Michael Wetter:
Changed controls to use CDL. Changed PID to PI as default for controller.
January 2, 2023, by Kathryn Hinkelman:
Set pressure drops at junctions to 0 and removed parameter dp_nominal
December 28, 2022, by Kathryn Hinkelman:
Simplified the control implementation for the district return stream. Improved default control parameters.
December 23, 2022, by Kathryn Hinkelman:
Removed extraneous m*_flow_nominal parameters because mBui_flow_nominal can be used across all components. This is for #2912.
November 11, 2022, by Michael Wetter:
Changed check valve to use version of Buildings library, and hence no outer system is needed.
March 20, 2022, by Chengnan Shi:
Update with base class partial model and standard PI control.
Novermber 13, 2019, by Kathryn Hinkelman:
First implementation.