Fan formula System 1 & 2 ASHRAE 90.1 - 2007

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Hi All,

Appendix G3.1.2.9 of ASHRAE 90.1-2007 gives the formula for systems 1
& 2:Pfan = CFMs x 0.3where CFMs is the supply fan airflow rate in
cfm and Pfan is in watts. I just noticed that in SI version, the
formula is the same Pfan = CFMs x 0.3 where Pfan is also in watts but
CFMs is in lps. Which is version correct? I have already looked into the erratas and addendum but did not find any corrections.

Thank you all in advance.

Jaigath Chandraprakash

Jaigath Chandraprakash's picture
Joined: 2011-10-02
Reputation: 0

The IP version is correct.


Jason Glazer's picture
Joined: 2011-09-30
Reputation: 0

Yes, it appears to be part of the SI edition that hasn't been fully
converted from IP.

For System 7 (I haven't done a system 1 or 2), I used the SI calc and found
that it matched the fan power of a VAV system in E+ with 1300Pa pressure
drop and about 70% fan efficiency. You just have to do half of the calc in
IP units!

Chris Yates's picture
Joined: 2011-10-02
Reputation: 0