modelFourPipe

System model for a four-pipe fan coil unit

Information

This is a four-pipe fan coil unit system model. The system consists of the following components:

A supply fan fan of class Buildings.Fluid.Movers.FlowControlled_m_flow.
Heating coil options for no heating coil, a hot-water heating coil or an electric heating coil determined by the user selection for parameter heaCoiTyp as follows:
1. No heating coil with bypass connector pipByp of class Buildings.Fluid.FixedResistances.PressureDrop if heaCoiTyp is set to Buildings.Controls.OBC.ASHRAE.G36.Types.HeatingCoil.None.
2. A hot-water heating coil heaCoiHW of class Buildings.Fluid.HeatExchangers.DryCoilCounterFlow if heaCoiTyp is set to Buildings.Controls.OBC.ASHRAE.G36.Types.HeatingCoil.WaterBased.
3. An electric heating coil heaCoiEle of class Buildings.Fluid.HeatExchangers.HeaterCooler_u if heaCoiTyp is set to Buildings.Controls.OBC.ASHRAE.G36.Types.HeatingCoil.Electric.
A chilled-water cooling coil cooCoi of class Buildings.Fluid.HeatExchangers.WetCoilCounterFlow.

For examples of how to use the model, refer to Buildings.Examples.FanCoils.FourPipe. The following points are salient when using the model:

The connected air-loop does not need an additional fan, since the fan in this model generates flow.
The fluid loop connections for hot-water and chilled-water require an external pressure difference between the inlet and the outlet sufficient to overcome the pressure drop across the two respective coils.

The figure below shows the schematic diagram of the four pipe system when heaCoiTyp is set to water based using the enumeration Buildings.Controls.OBC.ASHRAE.G36.Types.HeatingCoil.

Parameters

Type	Name	Default	Description
System parameters
Buildings.Controls.OBC.ASHRAE.G36.Types.HeatingCoil	heaCoiTyp	Buildings.Controls.OBC.ASHRAE.G36.Types.HeatingCoil.WaterBased	Heating coil type
Modelica.Units.SI.PressureDifference	dpAir_nominal		Total pressure difference across supply and return ports in air loop
Modelica.Units.SI.MassFlowRate	mAir_flow_nominal		Nominal mass flow rate of supply air
Heating coil parameters
Modelica.Units.SI.HeatFlowRate	QHeaCoi_flow_nominal		Nominal heat flow rate of heating coil
Modelica.Units.SI.Temperature	THeaCoiWatSup_nominal	333.15	Design water temperature entering heating coil
Modelica.Units.SI.Temperature	THeaCoiAirEnt_nominal	293.15	Design air temperature entering heating coil
Modelica.Units.SI.MassFlowRate	mHeaCoiWat_flow_nominal		Nominal mass flow rate of heating hot water
Modelica.Units.SI.PressureDifference	dpHeaCoiWat_nominal		Total pressure difference across heating coil (water side)
Modelica.Units.SI.PressureDifference	dpHeaCoiVal_nominal	dpHeaCoiWat_nominal	Design pressure drop of heating water valve
Cooling coil parameters
Modelica.Units.SI.HeatFlowRate	QCooCoi_flow_nominal		Nominal heat flow rate of cooling coil
Modelica.Units.SI.Temperature	TCooCoiWatEnt_nominal	279.83	Design water inlet temperature of cooling coil
Modelica.Units.SI.Temperature	TCooCoiAirEnt_nominal	296.15	Design air inlet temperature of cooling coil
Modelica.Units.SI.MassFraction	wCooCoiAirEnt_nominal	0.012	Design humidity ratio of inlet air of cooling coil (in kg/kg dry air)
Modelica.Units.SI.MassFlowRate	mCooCoiWat_flow_nominal		Nominal mass flow rate of chilled water
Modelica.Units.SI.PressureDifference	dpCooCoiWat_nominal		Total pressure difference across cooling coil (water side)
Modelica.Units.SI.PressureDifference	dpCooCoiVal_nominal	dpCooCoiWat_nominal	Design pressure drop of chilled water valve

Connectors

Type	Name	Description
Buildings.Controls.OBC.CDL.Interfaces.RealInput	uHea	Heating loop control signal
Buildings.Controls.OBC.CDL.Interfaces.RealInput	uCoo	Cooling loop control signal
Buildings.Controls.OBC.CDL.Interfaces.RealInput	uFan	Fan normalized speed control signal
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yFan_actual	Normalized actual fan speed signal
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	TAirSup	Measured supply air temperature
Modelica.Fluid.Interfaces.FluidPort_a	port_air_a	Return air port from zone
Modelica.Fluid.Interfaces.FluidPort_b	port_air_b	Supply air port to the zone
Modelica.Fluid.Interfaces.FluidPort_a	port_CHW_a	Chilled water supply port
Modelica.Fluid.Interfaces.FluidPort_b	port_CHW_b	Chilled water return port
Modelica.Fluid.Interfaces.FluidPort_a	port_HW_a	Hot water supply port
Modelica.Fluid.Interfaces.FluidPort_b	port_HW_b	Hot water return port

Components

Type	Name	Description
Buildings.Fluid.Sensors.TemperatureTwoPort	TAirHea	Heating coil discharge air temperature sensor
Buildings.Fluid.HeatExchangers.DryCoilEffectivenessNTU	hex	Hot water heating coil
Buildings.Fluid.Actuators.Valves.TwoWayLinear	valHW	Hot water flow control valve
Buildings.Fluid.HeatExchangers.WetCoilEffectivenessNTU	hexWetNtu	Chilled-water cooling coil
Buildings.Fluid.Actuators.Valves.TwoWayLinear	valCHW	Chilled-water flow control valve
Buildings.Fluid.Sensors.TemperatureTwoPort	TAirLvg	Supply air temperature sensor
Buildings.Fluid.Movers.Preconfigured.SpeedControlled_y	fan	Supply fan
Buildings.Fluid.FixedResistances.PressureDrop	totResAir	Total resistance of air path
Buildings.Fluid.HeatExchangers.HeaterCooler_u	heaCoiEle	Electric heating coil

Name	Description
MediumA	Medium for air
MediumHW	Medium for hot water
MediumCHW	Medium for chilled water

Revisions

September 22, 2025, by Michael Wetter:
Exposed parameters, reviewed model for first release.
This is for issue 2885.
August 03, 2022 by Karthik Devaprasad, Sen Huang:
First implementation.