Which software can model a low temp VAV with PFP boxes.

asked 2016-04-19 15:25:56 -0500

edixon16
358 ●10

updated 2016-04-19 21:59:24 -0500

Can a low temperature VAV system be modeled explicitly in any of the energy modeling softwares? The system I am trying to model tempers the SA down to 46F at the AHU cooling coil, then a parallel fan power box (variable speed ECM running continuously when the AHU is on) mixes RA with the low temp SA to about 55F before it is delivered to the space to avoid occupant comfort problems associated with dumping cold air. During cooler months the cooling coil leaving air temp would be reset to 55F in order to reduce the amount of reheat required.

I have spoke with a Trane product support and Trace cannot model the 46F LAT from the coil with 55F SA temp to the space unless I were to add 9F of duct loss, which would negate the benefit of using a low temp VAV system. Is it possible to model this in any of the other programs such as eQuest, EnergyPlus or IES?

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2

I've recently modeled a VAV with PFP boxes using OpenStudio with more standard supply air temperatures. While I can't think of any issue with lowering the supply air temperature, I believe the fan on parallel PIUs need to be constant volume and not variable speed as your design suggests.

pflaumingo ( 2016-04-19 17:59:19 -0500 )edit

1

That's an answer, not a comment.

__AmirRoth__ ( 2016-04-19 20:02:18 -0500 )edit

I second @pflaumingo. If you decide to take EnergyPlus route, AirTerminal:SingleDuct:ParallelPIU:Reheat is what you'll need. But the limitation is that PIU fan should be constant speed and not variable speed.

Chandan Sharma ( 2016-04-19 21:14:32 -0500 )edit

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answered 2016-04-19 18:17:14 -0500

crduggin

800 ●4 ●5

That would be easy to model in the VE. The pfpb is setup as CV by default, but making them variable is a simple control change.

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Why is it "the VE" rather than just "VE"? More importantly, why is it "the Ohio State University"? I can sort of see using "the VE" to disambiguate from other the-less uses of "VE" like "Value Engineering". But "The Ohio State University" is "Ohio State University"...

__AmirRoth__ ( 2016-04-19 20:01:41 -0500 )edit

Lol, don't forget THE University of the South. I suppose it sounds better when you say what it stands for. Model in the Virtual Environment rather than model in Virtual Environment.

crduggin ( 2016-04-19 20:23:23 -0500 )edit

Do you mean IES VE ?

BL ( 2016-04-20 08:03:13 -0500 )edit

Yes, I mean IESVE. Prototype system 6 and 8 are PFPB, depending on whether you want DX or CHW. Simply change the cooling coil LAT to the required 46F and adjust the PFPB airflow control to be variable. You will have to make some adjustments to the PFPB volume to ensure you get the SAT desired though.

crduggin ( 2016-04-20 08:30:23 -0500 )edit

1

I know I'm over a year late to this party, but - can't comment on the universities syntax, but it's THE VE, because it wouldn't be grammatically correct without the article once you spell out the acronym (...to model in THE Virtual Environment...)