[bldg-sim] air-side economizer...increase in heating load???

[Jeff Haberl]

This is one of the drawbacks of an economizer on a single-fan, dual-duct system. It happens in the free-cooling mode when the mixed air temp is less than the return air temp, and less than the cold deck but more than the preheating coil temp. It can be reduced with a hot deck reset, or heating plant shut-down schedule that is near to this range. You can see what is happening by looking at the hourly outputs. You can also see this with the spreadsheets that were used for ASHRAE RP865. 

Jeff
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Jeff S. Haberl, Ph.D., P.E.............................jhaberl at esl.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.......................URL: www-esl.tamu.edu

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-----Original Message-----
From: bldg-sim at gard.com <bldg-sim at gard.com>
To: bldg-sim at gard.com <bldg-sim at gard.com>
Sent: Thu Oct 20 12:26:36 2005
Subject: [bldg-sim] air-side economizer...increase in heating load???


Greetings,
 
Has anyone out there experienced a situation where DOE-2 predicted an increase in heating energy consumption when using the air-side economizer?  I was using the OA Temperature as the control (set at 65F, and I tried min temp at both 52 and 55, where 55 was also my cold deck supply temp).
 
I saw an expected decrease in cooling energy consumed, but there was an increase in heating and a small increase in fan energy.  I am modeling a building in Appleton, WI.  However, I made a simple base model as well to see if the problem was my original model.  For Appleton, Albuquerque, and Boulder (I only looked at 3), all three locations showed this increase in heating energy and decrease in cooling for the simple building.
 
Does anyone know if the RA damper modulates when the economizer is used, or does it fully close and thus provide 100% OA to the supply duct?
 
Any thoughts would be much appreciated.  THanks in advance.

Regards,

Paul


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