Working on a building with an air handling unit which serves
the entire floor. In the exterior rooms there are Fan coils to supply further heating
and cooling to the floor. I have split the floor up into interior zones and
exterior zones (each containing a fan coil unit). The AHU I have modeled as a
power induction unit which serves all the zones on the floor, the interior
zones have terminal type std VAV and the exterior zones have series PIU. With
in the exterior zones I have specified flow rates, heat/cool capacity
reflecting the FC. However I am getting lots of unmet hours from these exterior
zones (~500 hrs each). I inputted a REHEAT-DELTA-T in of 57F (based on fan flow
rates and heat capacity) into each of the exterior zones. This greatly reduced
the unmet hours; however I find it strange because the unmet hours are
completely dependent on REHEAT-DELTA-T and completely independent of the zone
heat capacity. I appear to have a poor understanding of how the PIU system
works, if anyone could provide further insight it would be much appreciated.
John