[Bldg-sim] CAV to VAV issues in EnergyPlus

[Studer, Daniel]

Ryan,

In terms of debugging your model, it would be constructive to know where the energy use differs: increased heating, cooling, or fan energy? Also, you may want to take a look at the table file and double-check that the coil and fan sizes, and design OA flow rates are identical between the two models. It's possible that in your conversion you modified something that is causing your system to size differently (presuming you're not hard-sizing everything). That's where I'd start.

Thanks,
Danny

Daniel Studer
Engineer | Commercial Buildings Research Group
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO  80401


From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Ryan Del Balso
Sent: Friday, October 04, 2013 1:16 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] CAV to VAV issues in EnergyPlus

I will start out by saying I am not an EnergyPlus expert. I am trying to convert one of the DOE commercial building E+ prototypes from a CAV system to a VAV system to determine the energy savings. I have modified the baseline CAV model for one of the zones thus far to a VAV system, but the VAV model is using more energy than the CAV model. I also have a lot more unmet hours for both heating and cooling. I cannot figure out what is causing these issues (I assume they are related). My current guess is that I continue to use the same cooling coil (Coil:Cooling:DX:SingleSpeed) in the VAV model, rather than converting the coil to Coil:Cooling:DX:TwoSpeed as I see in most of the other DOE prototype VAV models.
My questions are:
1. Is it ok to use the Coil:Cooling:DX:SingleSpeed in a VAV system, or should I convert that to a Coil:Cooling:DX:TwoSpeed?
2. If it I convert the VAV model to the Coil:Cooling:DX:TwoSpeed is this analogous to modifying the baseline compressor to a variable speed compressor?
Thanks for any help.
Ryan
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