.Buildings.Examples.FanCoils.FourPipe

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.

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.

Contents

Name	Description
MediumA	Medium for air
MediumW	Medium for hot-water and chilled-water
MixedAir	Thermal 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.