Good morning everyone,

We are having an issue with the calculated total fan flow of the baseline case and was wondering if someone could help me out. We are modeling a 12 floor hotel, with a VRF system in the first three floors and PTAC's in the remaining 9 (rooms); for a total conditioned area of about 92325 sf. The baseline case is modeled with a system 2 per ASHRAE appendix G.
The following table summarizes our issue:

Baseline case

Proposed case

Total cooling capacity

281.5 tons

247 tons

Design airflow rate

39700 cfm

80500 cfm

We used the automatic calculation from eQuest (leaving both capacity and fan flow blank) for the baseline case, and the actual mechanical design for the proposed case. For some reason, the baseline calculation for the fan flow seems to be very low, and was wondering if anyone has had a similar issue regarding the automatic calculations from eQuest. If so, has anyone found a solution?

If we analyze other estimates, eQuest is calculating about 0.43 cfm/sf for the baseline, which also seems very low compared to other projects we have worked with. We are also thinking of using the following formula to estimate the baseline fan flow: Sensible btu=1.09*cfm*dT; but with this approach we get a fan flow about 50% more that the proposed, which also seems unlikely. Any suggestions for estimating the baseline fan flow which LEED reviewers accept?

Thanks you very much, hope someone can help us out.

Ing. Gast?n Michaud F.