Modeling ERV's in Equest

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Hi all,

We are using Equest to model a 500,000 sq ft federal prison facility. More than half of the AHU's have energy recovery, so we modeled this at each applicable unit. When we run the model with ERV's vs. the model with no ERV's, it appears as though the ERV's are actually hurting us on the cooling energy. Is there a quirk when modeling ERV's in Equest (much like the bug fix in the Advanced Edit section of VisDOE)? Does anyone have any suggestions, or has anyone run into a similar problem before?

Thanks in advance for the advice...

P.S. Kim - are you happy I'm finally asking a question about Equest?? :)

Kristy M. Walson, PE, LEED AP

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What is the climate like? If you have a lot of cooling hours where the outside air temperature is lower than the space temperature it will hurt your cooling. For example, if it is 60 outside and your building is calling for cooling. With a 74 degree space temperature, if your running your ERV your actually raising the outside air temp to lets say 65 then cooling it back down. One way to help this out is to set your ERV to run "when minimum outside air" rather than "when fans on". This will allow the unit to economize. You can then continue to play with the controls until you get the best savings out of it. If the units cant economize you can also set the ERV to run based on outside air delta t's or delta h's. You can also set the ERV to put off a particular temperature, such as 55. I believe you can set both a cooling and a heating temp. You will then have to choose the method of either bypassing air or modulating the wheel speed to give you your specified leaving air temperature.
Hope this helps.

Charles Land's picture
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Here are a couple of other items to check when modeling ERVs in eQuest.

1. If the system does not have dedicated fans, manually set the
pressure drop across your recovery unit? The default pressure drops on the
supply and exhaust sides are pretty high. If there are dedicated fans, make
sure the actual fan power is entered.
2. Depending on the make-up air temperature control method and system
design, check the capacity control setting. If the design does not bypass
the recovery section when it is not in use, the parent HVAC fans must
overcome that additional pressure drop during all operating hours.

Also, right clicking on an input field and choosing "Item Help" will provide
a good amount of information as to how eQuest accounts for each input.

Good Luck! ERVs can be tricky sometimes.

John T. Forester, LEED AP BD+C

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