modelChillerDXHeatingEconomizer

HVAC system model with a dry cooling coil, air-cooled chiller, electric heating coil, variable speed fan, and mixing box with economizer control.
Diagram of ChillerDXHeatingEconomizerOpen the diagram
▶ Check in your browser

Information

This is a conventional single zone VAV HVAC system model. The system contains a variable speed supply fan, electric heating coil, water-based cooling coil, economizer, and air-cooled chiller. The control of the system is that of conventional VAV heating and cooling. During cooling, the supply air temperature is held constant while the supply air flow is modulated from maximum to minimum according to zone load. This is done by modulating the fan speed. During heating, the supply air flow is held at a constant minimum while the heating coil is modulated accoding to zone load. The mass flow of chilled water through the cooling coil is controlled by a three-way valve to maintain the supply air temperature setpoint during cooling. The mixing box maintains the minimum outside airflow fraction unless conditions for economizer are met, in which case the economizer controller adjusts the outside airflow fraction to meet a mixed air temperature setpoint. The economizer is enabled if the outside air drybulb temperature is lower than the return air temperature and the system is not in heating mode.

There are a number of assumptions in the model. Pressure drops through the system are collected into a single component. The mass flow of return air is equal to the mass flow of supply air. The mass flow of outside air and relief air in the mixing box is ideally controlled so that the supply air is composed of the specified outside airflow fraction, rather than having feedback control of damper positions. The cooling coil is a dry coil model.

Parameters

TypeNameDefaultDescription
Modelica.Units.SI.DimensionlessRatioCOP_nominal5.5Nominal COP of the chiller
Modelica.Units.SI.TemperatureTSupChi_nominalDesign value for chiller leaving water temperature
Modelica.Units.SI.MassFlowRatemChiEva_flow_nominal-QCoo_flow_nominal/Buildings.Utilities.Psychrometrics.Constants.cpWatLiq/4Design chilled water supply flow
Modelica.Units.SI.MassFlowRatemChiCon_flow_nominal-QCoo_flow_nominal*(1 + 1/COP_nominal)/Buildings.Utilities.Psychrometrics.Constants.cpAir/10Design condenser air flow
Air design
Modelica.Units.SI.MassFlowRatemAir_flow_nominalDesign airflow rate of system
Modelica.Units.SI.PressureDifferencedp_nominal500Design pressure drop of flow leg with fan
Heating design
Modelica.Units.SI.PowerQHea_flow_nominalDesign capacity of heating coil
RealetaHea_nominalDesign heating efficiency of the heating coil
Cooling design
Modelica.Units.SI.PowerQCoo_flow_nominalDesign capacity of cooling coil

Connectors

TypeNameDefaultDescription
Modelica.Blocks.Interfaces.BooleanInputchiOnOn signal for chiller plant
Modelica.Blocks.Interfaces.RealInputuFanFan control signal
Modelica.Blocks.Interfaces.RealInputuHeaControl input for heater
Modelica.Blocks.Interfaces.RealInputuCooValControl signal for cooling valve
Modelica.Blocks.Interfaces.RealInputTSetChiSet point for leaving chilled water temperature
Modelica.Blocks.Interfaces.RealInputuEcoControl signal for economizer
Modelica.Fluid.Interfaces.FluidPort_asupplyAirSupply air
Modelica.Fluid.Interfaces.FluidPort_breturnAirReturn air
Modelica.Blocks.Interfaces.RealOutputPFanElectrical power consumed by the supply fan
Modelica.Blocks.Interfaces.RealOutputQHea_flowElectrical power consumed by the heating equipment
Modelica.Blocks.Interfaces.RealOutputPCooElectrical power consumed by the cooling equipment
Modelica.Blocks.Interfaces.RealOutputPPumElectrical power consumed by the pumps
Modelica.Blocks.Interfaces.RealOutputTMixMixed air temperature
Modelica.Blocks.Interfaces.RealOutputTSupSupply air temperature after coils
Buildings.BoundaryConditions.WeatherData.BusweaBusWeather bus
Modelica.Blocks.Interfaces.RealOutputTRetReturn air temperature
Modelica.Blocks.Interfaces.RealOutputy_actualActual supply fan speed

Components

TypeNameDefaultDescription
Buildings.Fluid.Sensors.TemperatureTwoPortsenTSupSupply air temperature sensor
Buildings.Fluid.HeatExchangers.HeaterCooler_uheaCoiAir heating coil
Buildings.Fluid.Movers.FlowControlled_m_flowfanSupSupply fan
Buildings.Fluid.FixedResistances.PressureDroptotalResTotal resistance
Modelica.Blocks.Math.GaineffHeating efficiency
Buildings.Fluid.Sources.OutsideoutBoundary conditions for outside air
Buildings.Fluid.Sensors.TemperatureTwoPortsenTMixAirMixed air temperature sensor
Buildings.Fluid.HeatExchangers.DryCoilEffectivenessNTUcooCoiCooling coil
Buildings.Fluid.Sources.MassFlowSource_TsouChiWatMass flow source for chiller
Buildings.Fluid.Movers.FlowControlled_m_flowpumChiWatPump for chilled water loop
Buildings.Fluid.Chillers.ElectricEIRchiAir cooled chiller
Buildings.Fluid.Sources.Boundary_pTbouPreChiPressure boundary condition for chilled water loop
Modelica.Blocks.Math.GaingaiFanGain for fan mass flow rate
IdealValveideValIdeal valve
Modelica.Blocks.Math.BooleanToRealbooToIntBoolean to integer conversion
IdealValveideEcoIdeal economizer
Fluid.Sensors.TemperatureTwoPortsenTRetAirReturn air temperature sensor
Fluid.Sensors.TraceSubstancesTwoPortsenTraSubSensor for trace substance

Contents

NameDescription
MediumAMedium model for air
MediumWMedium model for water
IdealValveprotected

Revisions

  • March 27, 2024, by Michael Wetter:
    Corrected wrong assignment of out.C.
  • November 1, 2021, by Hongxiang Fu:
    Refactored the model by replacing not use_powerCharacteristic with the enumeration Buildings.Fluid.Movers.BaseClasses.Types.HydraulicEfficiencyMethod. This is for #2668.
  • February 25, 2021, by Baptiste Ravache:
    Inverse the sign of cooCoi.Q_flow_nominal to respect the heat flow convention.
  • September 08, 2017, by Thierry S. Nouidui:
    Removed experiment annotation.
  • June 21, 2017, by Michael Wetter:
    Refactored implementation.
  • June 1, 2017, by David Blum:
    First implementation.