Baseline PTAC Fan Energy for a Proposed Merv13 + Return Duct System - Goodness Me I had No Idea

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Well everyone, it seems I have hit a nerve with my original inquiry and
thank you all for your responses. After reading over the responses I
think I am going to run both the baseline and proposed fans continuously
(it seems the most conservative case) and use 0.0003 kw/cfm for the
baseline fan energy but add an A value equal to 1.4 to cover the
proposed system Merv 13 filters and return ductwork.

I think I will also modify the EIR cooling equation to use 300 w/cfm fan
power instead of 365 w/cfm power.

So baseline PTAC fan power = CFMs *0.0003 + (1.4* CFMs/4131) which works
out to be 0.00057 kw /cfm for a small 0.83 efficient motor

and baseline PTAC Cooling EIR will have a 0.10 constant instead of a

If I ever have to submit this to LEED I will probably regret it, but it
seems to be the most logical approach. Of course logic and LEED don't
necessarily go together.

Oh well, thanks again for the feedback.

Kathryn Kerns's picture
Joined: 2011-09-30
Reputation: 0


If you do submit you model for a LEED project you will not be permitted to
make any pressure drop adjustments to the Baseline residential system fan
power calculations. The formula for system types 1 and 2 in Section G3.1.2.9
is: Pfan = CFMs*0.3. Note that there is NO "A" factor in the formula. If the
project intends to pursue LEED certification, you may wish to consider an
inquiry to GBCI before you overestimate the projected savings (and those
ever-important points) and find yourself trying to justify your initial
modeling approach to the powers that be.

Just come friendly advice J

Cam Fitzgerald's picture
Joined: 2011-09-30
Reputation: 0