[Equest-users] Has anyone had issues with EXHAUST-SOURCE energ consumption

Min-Hwan Yang yangm at kjww.com
Wed Oct 14 07:44:50 PDT 2009


When you input the EXHAUST-SOURCE as Air Handler, the EXHAUST-FLOW is made up via outdoor air supplied by the air handler. In this mode, The minimum outside air requirement of the air handler will be forced to be at least the exhaust flow.  In addition, the default minimum airflow requirement of VAV terminals will be at least the exhaust requirement.  This may be why OSA Ventilation rate for the RTU is more than the sum of the individual OSA rates you set.

When you input the EXHAUST-SOURCE as INFILTRATION, your heating or cooling energy use go up because outdoor air infiltration increases and the exhaust fan operates independently of the space conditioning system, and may be working longer than the RTU.

Min-Hwan Yang, CEM, LEED AP
Mechanical Engineer | yangm at kjww.com

200 West Jackson Boulevard, Suite 1200 | Chicago, Illinois 60606
312-294-0501 | Direct: 312-356-3750 | Fax: 312-294-0003

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I am trying to model exhaust fans for a building and have had a couple of issues regarding the EXHAUST-SOURCE input under the zone Outside Air and Exhaust section.  I have two RTU's, one is a 100% OA constant volume system with constant volume fume hood exhausts.  The other RTU is a VAV system with a couple exhaust fans. 

Starting with the VAV system, when I input the EXHAUST-SOURCE as Air Handler, my OSA Ventilation rate for the RTU is quite a bit more than the sum of the individual OSA rates.  I cannot figure this out.  When I change the EXHAUST-SOURCE to Balanced Infiltration my RTU ventilation rate matches the sum of the zones, but my energy use goes up.  Is there something I am missing here?

For the 100% OA CV system, if I model the EXHAUST-SOURCE as Balanced Infiltration or Infiltration vs Air Handler my space heating energy rate over doubles.  This does not seem correct and makes me nervous to use the Balanced Infiltration input for my VAV fans.

Has anyone run into this issue before?  Is this a bug or would these results be expected?


Ryan Del Balso
Building Performance Engineer
ryan at ambient-e.com
130 W. 5th Avenue, Denver, CO 80204 
t 303.278.1532x210 | f 303.278.8533 |

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