[BLDG-SIM] : eQuest Underfloor Air

I’m trying to use eQuest to compare an Underfloor Air System and conventional VAV system. I have modeled the Underfloor case according to the Addison/Nall paper, and am having some issues with the return air temperatures.

I have modeled two stratified zones (a lower occupied 5’ zone, and an upper 8’ plenum space). A portion of the internal gains and window conduction is modeled in the plenum space, and the return air path is set to PLENUM. I expected a portion of the cooling loads to be transferred to the return air, raising the return air temperatures, and allowed the loads in the occupied zone to be met with a higher supply air temp (SAT).

However, when I increase my SAT for the underfloor case, my cfm and fan energy increases accordingly. I output hourly return air temps for the two cases and found that they were the same – adding heat gains to the plenum space did not increase the return air temps. Further, I adjusted my heating and cooling setpoints for the zones, and found that the return air temps are equal to these zonal setpoints, regardless of what load is imposed on the plenum spaces.

Has anyone experienced this problem?

Thanks!

Kendra

Kendra Tupper
LEED® AP
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