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How does the VRFwithDOAS measure set terminal unit fan parameters?

asked 2017-07-06 12:21:04 -0500

pajordan gravatar image

updated 2017-07-07 19:49:20 -0500

I’m applying the VRFwithDOAS measure (available on BCL: to the DOE OfficeSmall prototype model and I am wanting to have the measure set some of the indoor unit fan parameters (at least the Pressure Rise). When I run the measure, it appears to be setting the indoor unit fan parameters to match the OS:Fan:OnOff defaults defined in my hvac_library.osm file.

I don’t understand how the measure.rb file for this measure is defining these fan parameters; I think it is calling the OsLib_HVAC.rb file to do so but in that script I don’t see any if case for when “zoneHVAC” == “VRF”. How can I modify the VRFwithDOAS measure to set these fan parameters? I'm most interested in having it set the Pressure Rise to be something lower than the 300 default defined in my hvac_library.osm file (probably closer to 125).

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answered 2017-07-06 13:10:29 -0500

The VRF terminal units are constructed in the OsLib_HVAC.createVRFAirConditioners method in the OsLib_HVAC library. When the ZoneHVACTerminalUnitVariableRefrigerantFlow object is created, it creates a default FanOnOff object and assigns it to the VRF terminal unit.

To change the pressure rise, once the object is constructed, you can get the supply fan and set the pressure rise.

Add this code block right after the vrf_terminalUnit = constructor.

supply_fan = vrf_terminalUnit.supplyAirFan
supply_fan = supply_fan.to_FanOnOff.get

Related forum question on pressure rise for VRF units..

You may also want to use different VRF curves from the OS default.

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This worked great - thanks for the help and suggestions!

pajordan gravatar image pajordan  ( 2017-07-10 11:07:39 -0500 )edit

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Asked: 2017-07-06 12:21:04 -0500

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Last updated: Jul 06 '17