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AHU Modelling - OpenStudio

asked 2015-11-20 12:52:42 -0600

Dustin's avatar

updated 2015-11-20 13:10:41 -0600

My question is regarding OpenStudio AHU modelling. For instance I have a building where 1 AHU supplies air to 2 zones for cooling. This AHU also takes in exhaust (return) air from other zones of the building. Is there a way to directly model this?

My problems comes that I can hook the two cooling zone up to the AHU and apply the thermostat with ease and it will run. I just don't know how I can tie the exhaust air back into the AHU system. I understand you can apply an exhaust fan to any zone of interest, but does it attach into an AHU or does it treat it as direct exhaust to the outdoors. They aren't directly fans but are exhaust grilles. Any suggestions are greatly appreciated.

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Anything labeled as exhaust implies that the air is going outside, whether its is going through some sort of heat recovery or something it would still not mix with other return air.

This sounds like a plenum return where multiple spaces return to a common plenum, however the AHU is not directly serving all spaces?

nickj's avatar nickj  ( 2015-11-20 17:15:00 -0600 )edit

Yes that is the exact scenario I am looking at. Any advice on how I would model this?

Dustin's avatar Dustin  ( 2015-12-09 13:23:30 -0600 )edit

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answered 2015-11-20 14:58:09 -0600

updated 2015-11-24 19:03:40 -0600

Is this picture something like what you are describing?

image description

If so, you can model the transfer air via the ZoneMixing object. Unfortunately, this object is currently isn't available in the GUI, so you'll need to add it via a Measure. Something like this:

# Create a zone mixing object in air_to_zone
zone_mixing =
# Tell it where to pull the air from
# Set the flow rate and the schedule
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Yes this is exactly what I am describing. I am wondering if OpenStudio/EnergyPlus just takes this kind of scenario into account and you don't have to model it. I am assuming it does.

Dustin's avatar Dustin  ( 2015-11-23 09:48:48 -0600 )edit

@aaron Boranian might be able to give more details.

aparker's avatar aparker  ( 2015-11-24 19:05:31 -0600 )edit

Don't forget to balance the zone mixing with infiltration or other in the passive zones. Also ensure that the zone inlet and exhaust node air flow rate matches what is expected.

rraustad's avatar rraustad  ( 2015-11-24 21:50:05 -0600 )edit

Ok, I realize now I may have worded the question wrong and misunderstood what I was trying to ask. My problem is I have an AHU that supplies a floor. It supplies air through VAV boxes which I can model fine. My problem arises in the center of the floor, no air is being supplied but air is being exhausted or returned to the AHU where it may be mixed or just exhausted.

So when looking at the figure you produced, the return air lines would be from zone 1 and 4, not 2 and 3. Can someone help me out if this makes sense. If not I will try and explain further.

Dustin's avatar Dustin  ( 2015-11-25 13:02:16 -0600 )edit

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Asked: 2015-11-20 12:52:42 -0600

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Last updated: Nov 24 '15