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Can I use a Fan:ZoneExhaust in a zone that is not served by an AirLoop?

asked 2017-08-10 12:30:45 -0500

Molly Curtz gravatar image

updated 2018-04-21 08:45:15 -0500

In Energy Plus, I am modeling toilet exhaust fans. All of the air to the toilet zone is supplied by transfer air from adjacent conditioned zones. There is no supply air or return air from/to an AHU at the toilet zone, and there is no active temperature control in the zone. For these reasons, the toilet zone is not served by any AirLoopHVAC. I have read this post concerning modeling transfer air. I have followed the advice suggested by the answer there posted by Archmage and

  • Used a ZoneMixing object to send air from the source zone into the toilet zone.
  • Used a Fan:ZoneExhaust object to remove air from the source zone to reduce return air flow to the AHU serving that zone, and to force additional OSA supply from the AHU if needed to balance the zone EA.

Finally, I need to figure out a way to remove air from the toilet zone. I need to do that without introducing outdoor air directly to the toilet zone as would occur with ZoneVentilation:DesignFlowRate Is it possbile to set up a Fan:ZoneExhaust for the toilet zone, which is not on an AirLoopHVAC? If it is possible, what other objects will I need in addition to the Fan:ZoneExhaust? Is there a different way to do this?

Thanks in advance for advice.

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answered 2017-08-10 12:59:27 -0500

updated 2017-08-10 19:29:59 -0500

Molly Curtz gravatar image

Yes, that's possible, with certain requirements. The simulation assumes neutral pressure unless AirflowNetwork is used. This is because the outdoor air system exhausts an amount equal to the outdoor air. So to ensure that the zones do not result in a negative pressure you need to ensure that the amount of outdoor air equals or exceeds the amount of exhaust air. Exhaust air is accounted for when it occurs in a zone attached to the air loop. For non-air loop zones, a review of the results is required to make sure the air mass balance is correct for this simulation. I would look at the infiltration reporting to see if that amount would offset the toilet zone exhaust. Maybe others have a better solution.

To summarize the conclusion of the below comment discussion: An additional Fan:ZoneExhaust in the toilet zone is unnecessary. The energy impact of the transfer air on the receiving toilet zone is accounted for by the ZoneMixing object. The toilet exhaust fan power can be accounted for in the Fan:ZoneExhaust that is in the source zone.

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Thanks @rraustad.

RE: "Exhaust air is accounted for when it occurs in a zone attached to the air loop"; I would be accounting for the EA with a Fan:ZoneExhaust used in the transfer air source zone, which is attached to the air loop.

RE:"For non-air loop zones, a review of the results is required to make sure the air mass balance is correct"; My understanding is that ZoneMixing does not impact the mass in the source zone. My hope was that the air supplied into the receiving toilet zone by the ZoneMixing object can be balanced by air removed by a Fan:ZoneExhaust object at the toilet zone.

Molly Curtz gravatar imageMolly Curtz ( 2017-08-10 13:15:57 -0500 )edit

If I add Fan:ZoneExhaust to the toilet zone, I am trying to figure out if I will also need a ZoneHVAC:EquipmentList, where this fan is listed, and further, given that I don't have thermostats setup for the toilet zone, how would the inputs therein be made for Cooling Load Sequence and Heating or No-Load Sequence?

Molly Curtz gravatar imageMolly Curtz ( 2017-08-10 13:20:15 -0500 )edit

OK, I read your description again. You are accounting for toilet zone exhaust air by installing the exhaust fan in an adjacent zone and using a mixing object to transfer air to the toilet zone. This sounds fine to me since you don't need to actually exhaust air from the toilet zone (your simulating that with the zone exhaust fan in the adjacent zone). What I need to check on is if the mixing object air transfer is included somehow in the air balance. I seem to recall that it is. I'll get back to you when I hear something.

rraustad gravatar imagerraustad ( 2017-08-10 13:21:58 -0500 )edit

Yes, I am asking about using two Fan:ZoneExhaust objects (only one of the two would account for the fan power of the zone EA fan). One would be located in the source zone, and another would be located in the receiving toilet zone. The reason I'm considering this is that I thought that I should also exhaust air from the toilet zone. I'm not clear what would happen to the temperature in the toilet zone if I just let air mass accumulate there (without removing the mass that is supplied to it by the Zone:Mixing object).

Molly Curtz gravatar imageMolly Curtz ( 2017-08-10 13:28:26 -0500 )edit

Not sure I got the answer I wanted. Here's what I would do. Run the sim as you have it now (no exhaust in the toilet zone) and check the adjacent zone inlet node mass flow rate and zone return node mass flow rate. If they are different by the amount of exhaust air, you are OK.

rraustad gravatar imagerraustad ( 2017-08-10 13:33:01 -0500 )edit

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Asked: 2017-08-10 12:30:45 -0500

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Last updated: Aug 10 '17