modelPartialDirect

Partial direct ETS model for district energy systems with in-building pumping and deltaT control

Extends from Buildings.DHC.ETS.BaseClasses.PartialETS.

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

TypeNameDefaultDescription
Nominal condition
Modelica.Units.SI.MassFlowRatemBui_flow_nominalNominal mass flow rate of building side
Modelica.Units.SI.PressureDifferencedpConVal_nominal50Nominal pressure drop in the control valve
Modelica.Units.SI.PressureDifferencedpCheVal_nominal6000Nominal pressure drop in the check valve
PID controller
Modelica.Blocks.Types.SimpleControllercontrollerTypeModelica.Blocks.Types.SimpleController.PIType of controller
Realk0.1Gain of controller
Modelica.Units.SI.TimeTi60Time constant of integrator block
Modelica.Units.SI.TimeTd0.1Time constant of derivative block
RealyMax1Upper limit of output
RealyMin0Lower limit of output
Advanced
Modelica.Fluid.Types.DynamicsenergyDynamicsModelica.Fluid.Types.Dynamics.FixedInitialType of energy balance: dynamic (3 initialization options) or steady state
Realbandwidth0.2Bandwidth around reference signal for on/off controller

Components

TypeNameDefaultDescription
Modelica.Blocks.Interfaces.RealInputTDisRetSetSetpoint for the district return temperature (min for cooling, max for heating)
Modelica.Blocks.Interfaces.RealOutputQ_flowMeasured heating demand at the ETS
Modelica.Blocks.Interfaces.RealOutputQMeasured energy consumption at the ETS
Buildings.Fluid.Sensors.TemperatureTwoPortsenTDisSupDistrict supply temperature sensor
Buildings.Fluid.Sensors.MassFlowRatesenMasFloDistrict supply mass flow rate sensor
Buildings.Fluid.FixedResistances.JunctionjunBypass junction
Buildings.Fluid.Sensors.TemperatureTwoPortsenTDisRetDistrict return temperature sensor
Buildings.Fluid.FixedResistances.JunctionsplBypass junction, splitter
Buildings.Fluid.Actuators.Valves.TwoWayEqualPercentageconValControl valve
Buildings.Fluid.Sensors.TemperatureTwoPortsenTBuiRetBuilding return temperature sensor
Fluid.FixedResistances.CheckValvecheValCheck valve (backflow preventer)
Modelica.Blocks.Math.AdddTDisTemperature difference on the district side
Modelica.Blocks.Math.ProductproProduct
Modelica.Blocks.Math.GaincpSpecific heat multiplier to calculate heat flow rate
Modelica.Blocks.Continuous.IntegratorintIntegration
Controls.OBC.CDL.Reals.PIDconDistrict return temperature controller
Buildings.Fluid.Sensors.TemperatureTwoPortsenTBuiSupBuilding supply temperature sensor

Revisions

  • March 11, 2024, by Michael Wetter:
    Corrected wrong displayUnit string.
  • April 7, 2023, by David Blum:
    Changed to partial base class for direct so can extend to heating and cooling ETS.
  • 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.