# [Equest-users] Baseline PTAC Fan Energy for a Proposed Merv13 + Return Duct System - Goodness Me I had No Idea

Kathryn Kerns kathryn.kerns at bceengineers.com
Wed Feb 27 15:23:45 PST 2013

```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
0.012167

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.

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Kathryn
Kerns
Sent: Monday, February 25, 2013 5:57 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Baseline PTAC Fan Energy for a Proposed Merv13 +
Return Duct System

Everyone, I have been modeling some dormitories with a proposed HVAC
system involving a DOA with a full exhaust air HX and MERV 13 filters.
The puzzle is what to do about the baseline PTAC fan power energy? If I
use 0.3 w/cfm as Appendix G suggests, my PTAC baseline system does not
account for a fully ducted return\exhaust or MERV 13 filters. The
commercial fan power equation for systems 3-8 accounts for this, but I
am not supposed to use that formula for System 1 and 2.

Another puzzle is if I develop an cooling EIR value for my baseline PTAC
using the 365 w/kCFM conversion rule and equate that with 0.3 w/cfm,
what happened to the other 65 w/kCFM?

Maybe ARI 310/380 doesn't use 365 w/cfm fan power?  I read it and didn't
find any statement regarding fan power requirements, but I assume it
works the same as ARI 210/240?

I am wondering if a compromise of

PTAC fan power = CFMs *0.000365 + A
where A= PD*CFMs /4131 and PD = 1.4

might be a reasonable solution?

PTAC fan power = 0.00063 kw/cfm

Does anyone else have experience with this puzzle?

Kathryn Kerns

Systems Specialist

BCE Engineers, Inc.

| Ph: 253.922.0446 | Fx: 253.922.0896 |

Kathryn Kerns

Systems Specialist

BCE Engineers, Inc.

| Ph: 253.922.0446 | Fx: 253.922.0896 |

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