VAV airhandler with face and bypass dampers

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Does anyone have any advice on modeling a VAV air handler with face and
bypass dampers? Essentially I have a set of dampers with a heating coil
before the cooling coil. When in heating only the discharge air
temperature is reset based between 55F and 65F. In cooling the DAT is
between 55F and 59F. Chillers and CHW loop is set to demand.

I had tried modeling a preheat coil to simulate the heating coil being
before the cooling coil, but the results were not as expected. When I
looked at the hourly reports I found the following:

1) Space temperatures for the unit were above the heating set-point
and below the cooling set-point. Yet, the cooling coil was activated. I
have a suspicion that this is due to equest turning on cooling coil if
there is any chance a space may need cooling but have been unable to
confirm. In addition, the given RAT, MAT, DAT temperatures due not make
sense. For example:
DAT (off cooling coil)=48F with cooling coil running and OAT
below 32F.
2) The %OA is constant even at night. Cfm/per has been specified at
the zone level. Should it be at the system level?

Any help would be greatly appreciated.

Andy Szczepaniak

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Joined: 2011-10-02
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