modelFourPipe

Model of a five zone floor with fan coil units
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Extends from Modelica.Icons.Example (Icon for runnable examples).

Information

This model demonstrates the usage of Buildings.Controls.OBC.ASHRAE.G36.FanCoilUnits.Controller, a controller for four-pipe fan coil units based on the sequences defined in ASHRAE Guideline 36, 2021. A generic schematic for such a system is shown below.

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This model consists of

  • 3 identical thermal zone models with time-varying internal heat gains and interaction with ambient air through building envelope.
  • 3 fan-coil units serving each zone.
  • 3 fan coil unit controllers that output the supply fan enable signal and speed signal, the supply air temperature setpoint, the zone air heating and cooling setpoints, and valve positions for heating and cooling coils.

The 3 fan coil units each have a supply fan and a chilled-water cooling coil. The heating coil varies as follows for each instance:

  • fanCoiUni has no heating coil.
  • fanCoiUni1 has a hot-water heating coil.
  • fanCoiUni2 has an electric heating coil.

The HVAC system switches between occupied, unoccupied, unoccupied warm-up and unoccupied pre-cool modes. The cooling coil and heating coil output are modulated to maintain the heating and cooling setpoints. The supply air temperature is modulated based on the differential between the temperature setpoint and the zone temperature to avoid unecessary heating and cooling use and avoid extreme temperature fluctuations.

See the model Buildings.Fluid.ZoneEquipment.FourPipe and Buildings.Controls.OBC.ASHRAE.G36.FanCoilUnits.Controller for a description of the fan coil unit and the controller, respectively.

The thermal zone is a south-facing thermal zone of the medium office building that is also used in Buildings.Examples.VAVReheat, but here only this one room is modeled, and instanciated three times for the three different fan coil units. The external facade is 49.91 meters long, the north-facing interior wall is 40.76 meters, and the room width is 4.58 meters. The room height is 2.74 meters.

Parameters

TypeNameDefaultDescription
Modelica.Units.SI.LengthwSou49.91Length of south facing exterior wall
Modelica.Units.SI.LengthwNor40.76Lenght of north facing interior wall
Modelica.Units.SI.LengthwSid6.47Length of each of the two side walls
Modelica.Units.SI.LengthdRoosqrt(wSid^2 - ((wSou - wNor)/2)^2)Room depth
Modelica.Units.SI.LengthhRoo2.74Room height
Modelica.Units.SI.AreaAFlo(wSou + wNor)/2*dRooFloor area
Modelica.Units.SI.VolumeVRooAFlo*hRooRoom volume
RealwinWalRat0.33Window to wall ratio for exterior wall
Modelica.Units.SI.LengthhWin1.5Height of windows
RealkInt1Gain factor to scale internal heat gain in each zone
HeatTransfer.Data.Solids.PlywoodmatCarTraWood for floor
HeatTransfer.Data.Solids.PlywoodmatFurMaterial for furniture
HeatTransfer.Data.Solids.ConcretematConConcrete
HeatTransfer.Data.Solids.PlywoodmatWooWood for exterior construction
HeatTransfer.Data.Solids.GypsumBoardmatGypGypsum board
HeatTransfer.Data.Resistances.CarpetmatCarCarpet
HeatTransfer.Data.Solids.GenericmatInsSteelframe construction with insulation
HeatTransfer.Data.Solids.GypsumBoardmatGyp2Gypsum board
HeatTransfer.Data.GlazingSystems.DoubleClearAir13ClearglaSysData record for the glazing system
HeatTransfer.Data.OpaqueConstructions.GenericconExtWalExterior construction
HeatTransfer.Data.OpaqueConstructions.GenericconIntWalInterior wall construction
HeatTransfer.Data.OpaqueConstructions.GenericconFurConstruction for internal mass of furniture
HeatTransfer.Data.OpaqueConstructions.GenericconFloFloor construction (opa_a is carpet)

Components

TypeNameDefaultDescription
Buildings.Fluid.Sources.Boundary_pTsouHeaSource for hot water
Buildings.Fluid.Sources.Boundary_pTsinHeaSink for hot water
Buildings.Fluid.Sources.Boundary_pTsinCooSink for chilled water
Buildings.Fluid.Sources.Boundary_pTsouCooSource for chilled water
Buildings.Fluid.ZoneEquipment.FourPipefanCoiUni1Fan coil unit with no heating coil
Buildings.Controls.OBC.ASHRAE.G36.FanCoilUnits.ControllerconFCU1Fan coil unit controller
Buildings.BoundaryConditions.WeatherData.ReaderTMY3weaDatWeather data reader
Buildings.Controls.OBC.ASHRAE.G36.FanCoilUnits.ControllerconFCU2Fan coil unit controller
Buildings.Controls.OBC.ASHRAE.G36.FanCoilUnits.ControllerconFCU3Fan coil unit controller
MixedAirzon1Zone-1
Modelica.Thermal.HeatTransfer.Sensors.TemperatureSensorsenTRooAir1Air temperature sensor
Modelica.Blocks.Sources.ConstantuShaControl signal for the shading device
Modelica.Blocks.Routing.Replicatorreplicator
Modelica.Blocks.Sources.CombiTimeTableintGaiFraFraction of internal heat gain
Modelica.Blocks.Math.MatrixGaingaiMatrix gain to split up heat gain in radiant, convective and latent gain
Modelica.Blocks.Math.Gain[3]gaiIntGain for internal heat gain amplification for each zone
Buildings.Fluid.ZoneEquipment.FourPipefanCoiUni2Fan coil unit with hot-water heating coil
MixedAirzon2Zone-2
Modelica.Thermal.HeatTransfer.Sensors.TemperatureSensorsenTRooAir2Air temperature sensor
Buildings.Fluid.ZoneEquipment.FourPipefanCoiUni3Fan coil unit with electric heating coil
MixedAirzon3Zone-3
Modelica.Thermal.HeatTransfer.Sensors.TemperatureSensorsenTRooAir3Air temperature sensor
Buildings.Controls.OBC.CDL.Integers.Sources.ConstantlimLevCooling and heating demand limit level
Buildings.Controls.SetPoints.OccupancyScheduleoccSchOccupancy schedule
Buildings.Controls.OBC.CDL.Reals.Sources.ConstantTOccHeaSetPoiOccupied heating temperature setpoint
Buildings.Controls.OBC.CDL.Reals.Sources.ConstantTUnOccCooSetUnoccupied cooling temperature setpoint
Buildings.Controls.OBC.CDL.Reals.Sources.ConstantTUnOccHeaSetUnoccupied heating temperature setpoint
Buildings.Controls.OBC.CDL.Reals.GreaterThreshold[3]greThrCheck if fan speed is above threshold for proven on signal
Buildings.Controls.OBC.CDL.Logical.Timer[3]timGenerate fan proven on signal
Buildings.Controls.OBC.CDL.Reals.Sources.ConstantTSetAdjUnoccupied cooling temperature setpoint
Buildings.Controls.OBC.CDL.Reals.Sources.ConstantcooWarTimCooldown and warm-up time
Buildings.Controls.OBC.CDL.Reals.Sources.ConstantTOccCooSetPoiOccupied cooling temperature setpoint
Modelica.Blocks.Math.Gain[3]gaiInt1Gain for internal heat gain amplification for zone with no heating coil service

Contents

NameDescription
MediumAMedium for air
MediumWMedium for hot-water and chilled-water
MixedAirThermal zone model

Revisions

  • November 20, 2025, by Karthik Devaprasad:
    Updated PI controller parameters on controller instances. Added schematic of generic fan coil unit system integration with controller and thermal zone.
  • September 23, 2025, by Cerrina Mouchref, Karthik Devaprasad and Michael Wetter:
    First implementation.