[Bldg-sim] Exhaust fans

[Jeff Haberl]

Rathna,

In the DOE-2 family of simulations, “Exhaust fans” are typically modeled in one of two ways. One of the methods “models” the exhaust air (i.e., the heat gain shows up in the calculation), the other method does not. Both methods account for the electricity use of the fan.

The first way is where the “exhaust” is part of the system return air flow from a zone(s), with a certain portion of the air volume being exhausted in the systems exhaust and  replaced with new incoming air. If a pressure drop is specified for the return fan, then there is heat gain across the fan that impacts all return air flow. If no return fan is specified, then there is no heat gain and there is no electricity use associated with the fan.

If the exhaust is a zonal exhaust, then only the electricity use get recorded as any heat gain to the exhaust stream goes outside. However, since the DOE-2 family of simulations (i.e., DOE2.2 and DOE2.1e) balances the air flow into/out of a zone, there is an equal amount of air flow into the building to make up for the zonal exhaust. If both system exhaust and zone exhaust are specified, then the two add together.

If you want to see the actual equations for such models, the quickest way to see these is with the spreadsheets that come with ASHRAE RP865 project (i.e., contact Mike Vaughn), or you can download them from the ESL web site.

Jeff

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Jeff S. Haberl, Ph.D.,P.E., FASHRAE.............. jhaberl at tamu.edu<mailto:jhaberl at tamu.edu>

Professor............................................................Office Ph: 979-845-6507

Department of Architecture.............................Lab Ph:979-845-6065

Energy Systems Laboratory.............................FAX: 979-862-2457

Texas A&M University.....................................77843-3581

College Station, Texas, USA, 77843..................URL:www.esl.tamu.edu

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From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Rathna Shree
Sent: Monday, April 16, 2012 5:34 AM
To: bldg
Subject: [Bldg-sim] Exhaust fans

Dear All,

I am working on a warehouse project. Warehouse areas are non conditioned and these areas have exhaust fans. Please let me know how to model these fans. Can i just treat it as an miscellaneous equipment load? Is it required to model with fan air volume, bhp etc.

Regards,
Rathnashree
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