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[EnergyPlus_Support] VAV with reheat - PIU not cycling - temperature below setpoint

Hi All,

I'm trying to model a simple VAV system with local reheat (PIU). When I set up the availability of the air terminals to - always on - The indoor temperature is maintained within the setpoints. The problem is that at night the parallel fan runs all the time. When I set up a schedule with the fans off at night there is a short swing in temperature in the evening below the setpoint (17 deg C). Then the temperature goes back to normal. 
I checked the sizing of the heating coils and flow. Entered the values back manually and tried to oversize as well (doubles the capacity) without any effect. 
I also checked the timestep and bumped it to 30. No change.
If you check the attached file the problem occurs in the winter (there's an example around 4th Dec).
There's an old post from 06 refering to a similar problem. http://tech.groups.yahoo.com/group/EnergyPlus_Support/message/6649
Not sure if this is still the same.

Thanks for your help!

The idf file is in the Files/Problem_submittals folder.



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