[BLDG-SIM] eQUEST Economizer Question

[Fred Porter]

Two  possibilities .
1. The office system is modeled/proposed with humidification. The increased OA when economizing dries out the mixed air. There are some keywords to close the economizer below user selected ambient humidity ratios. The best solution is to get rid of the humidifier, which should rarely be needed in a tight office building unless the office system transfers a great deal of air to the labs. If the humidity is really needed, and warm return air is available which would otherwise be relieved (the definition of economizing),  evaporative humidification works great and consumes no energy until the mixed air temp is so low preheat would be otherwise needed. BUT, DOE2 does not presently model control of the the evaporative cooling for humidification when not needed for cooling.
2. For a variety of possible reasons, the modeled SAT may be floating up from 55F (CHW loop or cooling scheduled off, inadequate capacity, etc.) during hours when enabling the economizer allows the SAT to be met. So reheat increases during those hours when the SAT is decreased back down to 55F.

From: Matt Edwards
Sent: Fri, 6/29/2007 6:49am
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] eQUEST Economizer Question


Hello,
 
I am using eQUEST to model an Lab/Office building with Standard VAV w/Reheat system type throughout.  The office spaces are isolated on a single VAV system, and one option I am adding by parametric run is an OA Temp economizer strategy.  The supply air temperature set point (COOL-SET-T) is held constant at 55, and the maximum system level heating is also held to 55 degrees (HEAT-SET-T).  What I'm noticing is that there is a significant heating increase with the addition of an economizer when OA-CONTROL is the only variable.  This heating increase is outweighing any significant cooling or electricity savings resulting in an energy penalty.  I had hoped that the economizer would only mix outside air with return air to maintain the 55 degree supply air temperature from the unit.  Are there additional measures necessary to clearly define economizer control to prevent a heating increase, or is there a better way to define economizer control altogether?
 
Thanks,
 
 
 
Matt Edwards LEED ® AP
Mechanical Systems | Affiliated Engineers, Inc
5802 Research Park Blvd
Madison, WI 53719
 
Phone: (608) 236-1154 (direct)
Fax: (608) 238-2614
Email: medwards at aeieng.com
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