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CHW FCU with Electric Heat in OpenStudio

asked 2018-06-27 09:01:25 -0500

JCR562's avatar

updated 2018-06-27 09:46:44 -0500

I'm wanting to model a chilled water FCU with electric heat in OpenStudio but am having trouble finding the best way to do so. The FCU equipment is for a 4-pipe unit that uses heating water as the heat source and I don't see an option to use an electric heat strip instead. I thought about creating an airloop but I have ~75 of these scenarios so it would be a major haul to create 75 airloops (I don't see a way to copy an airloop).

I also thought about overwriting the 4-pipe FCU heating coil to 0 btu/hr, but am not sure how I would add heat to the space.

Does anyone have any ideas? Thanks!

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answered 2018-06-27 10:41:30 -0500

gokul's avatar

Have you tried setting the heating coil capacity to zero in your FourPipeFanCoil, and adding a UnitHeater:Electric for the electric space heating?

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Thanks for the quick response. This seems like a good work around.

JCR562's avatar JCR562  ( 2018-06-27 21:16:01 -0500 )edit

this won't capture fan energy use associated with the fan coil in heating mode.

mdahlhausen's avatar mdahlhausen  ( 2018-06-28 16:53:15 -0500 )edit

answered 2018-06-27 12:15:56 -0500

This is straightforward with the OpenStudio SDK.

Create a ZoneHVACFourPipeFanCoil object for each zone. Each FCU requires a schedule, fan, cooling coil, and a heating coil to create the object. The heating coil can be an electric resistance coil.

Example script:

require 'openstudio' # load the OpenStudio SDK

# logic to load the model in the current version of the SDK
osm_path ="C:/Users/yourname/Desktop/model.osm")
translator =
model = translator.loadModel(osm_path)
model = model.get

# create an array of zones served by FCUs
zones = model.getThermalZones # this returns all zones in the model
# there are many other ways you can create an array of zones, e.g. by space names, zone names, from a .csv file, etc.
# for example, choose only zones with "served by FCU" in name
zones = {|zone| "served by FCU"}

# reference a chilled water loop in your model
chilled_water_loop = model.getPlantLoopByName("Chilled Water Loop").get

# loop through each zone and add an FCU
zones.each do |zone|

  # create a coil cooling water
  clg_coil =
  clg_coil.setName("#{} FCU Cooling Coil")
  chilled_water_loop.addDemandBranchForComponent(clg_coil) # add to chilled water loop
  # set cooling coil design temperatures if desired
  # clg_coil.setDesignInletWaterTemperature()
  # clg_coil.setDesignInletAirTemperature()
  # clg_coil.setDesignOutletAirTemperature()
  # coil controller properties
  clg_coil_controller = clg_coil.controllerWaterCoil.get
  clg_coil_controller.setName("#{} Controller")

  # create an electric heating coil
  htg_coil =
  htg_coil.setName("#{} FCU Electric Heating Coil")

  # create a fan onoff
  fan =
  fan.setName("#{} FCU Fan")
  fan.setPressureRise(300.0) # pa
  fan.setEndUseSubcategory("FCU Fans")

  # create a fan coil unit with these objects
  fcu =,
  fcu.setName("#{} FCU")
  fcu.setMaximumOutdoorAirFlowRate(0.0) # no outdoor ventilation from FCUs

path = "C:/Users/yourname/Desktop/model_new.osm",true)

The Prototype.hvac_system has plenty of examples for building all different kinds of HVAC systems. Use can use the methods directly with require 'openstudio-standards', or copy them into your own scripts.

See the OpenStudio measure writing guide if you'd like to expand this into an OpenStudio measure.

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Thank you for your help. Unfortunately, my OS skills are limited at the moment and your answer is going over my head a little. I'll need some time to fully comprehend your answer but this seems to be the most appropriate and accurate way.

JCR562's avatar JCR562  ( 2018-06-27 21:19:48 -0500 )edit

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Asked: 2018-06-27 09:01:25 -0500

Seen: 518 times

Last updated: Jun 27 '18