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Modeling Self-contained Units with a Variable Speed Heat Pump

asked 2015-05-12 12:39:56 -0500

pflaumingo's avatar

updated 2015-11-14 16:14:04 -0500

Has anyone been successful or tried to use the Coil:Cooling:WaterToAirHeatPump:VariableSpeedEquationFit component on an AirLoopHVAC:UnitarySystem as a way of modeling a self-contained VAV with a variable speed compressor? I have used the OpenStudio API to set up a self-contained VAV with the unitary system and a Coil:Cooling:WaterToAirHeatPump:EquationFit component, which works fine, and I also used the setString method to set the control type to SetPoint rather than load based (sorry!). No problems here. However, when I changed the heat pump out with the variable speed component then no load was seen on the unitary system and the compressor didn't turn on. The EnergyPlus example file that has the variable speed heat pump on a unitary system uses a load control type on a zone so I tried adjusting my IDF and got the error below. It is wanting me to use a Fan:OnOff object, but this defeats the purpose of the VAV if I have to do this.

* Severe * AirLoopHVAC:UnitarySystem = AIR LOOP HVAC UNITARY SYSTEM 1 * ~~~ * Supply Fan Object Type = * ~~~ * Fan type must be Fan:OnOff when Supply Air Fan Operating Mode Schedule Name = Blank. * Fatal * GetUnitarySystemInput: Errors found in input. Program terminates.

If anyone has encountered this before, or if they have any advice, it'd be much appreciated.

EDIT: The file has been sent to @Kyle Benne directly.

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To note, I have seen this post and followed it to the corrected issues here, which seems to show an adjustment was made for the equation fit and parameter estimation model, but makes no mention of the variable speed equation fit object.

pflaumingo's avatar pflaumingo  ( 2015-05-12 12:41:55 -0500 )edit

@pflaumingo where is the variable speed fan in this setup? Do you have it inside the unitary? In any case this sure smells like a bug in the unitary model, but let's try to narrow in before making a bug report that isn't real. AirLoopHVAC:UnitarySystem allows so many variations that you can be sure they haven't all been tested.

Kyle Benne's avatar Kyle Benne  ( 2015-05-13 09:12:46 -0500 )edit

@Kyle Benne, the above is with a Fan:VariableVolume outside of the unit. Since then, I have moved the fan into the unit and it works with the control type as load with a controlling zone. The issue is that this building is 200,000sqft and is essentially one massive PVAV with a 70% WWR so a lot of the zones won't get the required cooling capacity - especially with a supply air reset tied to a zone. When I change the control type to SetPoint then the Cooling Coil within the system again sees no load.

pflaumingo's avatar pflaumingo  ( 2015-05-13 13:44:59 -0500 )edit

Cont... So whether the fan is in the unitary system or not, when the control type is SetPoint then the the coil seems to experience no load if the variable speed water to air heat pump component is used.

pflaumingo's avatar pflaumingo  ( 2015-05-13 13:47:19 -0500 )edit

OK. Sounds like we have an E+ bug to me. Would you mind sending me the file and I'll create an E+ issue?

Kyle Benne's avatar Kyle Benne  ( 2015-05-13 16:10:54 -0500 )edit

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answered 2015-08-03 15:15:28 -0500

An EnergyPlus issue has been filed.

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Asked: 2015-05-12 12:39:56 -0500

Seen: 457 times

Last updated: Aug 03 '15