[Bldg-sim] FW: Apparent error on ASHRAE 90.1-2007 (and perhaps 2010)

[Jim Dirkes]

Dear forums,
I think I have discovered an error in the SI version of ASHRAE 90.1 regarding fan power for Baseline Systems 1 & 2.  I sent the message below to ASHRAE, but then thought, "Perhaps someone else has also noticed this and received some guidance from ASHRAE".  Regardless, if it is actually an error, it's worth mentioning to all of you so that you can be aware of it.
Please  let me know if you are aware of this, and how you have dealt with the discrepancy.  My plan is to use the IP formula because it allows more fan power :).

James V Dirkes II, PE, BEMP, LEED AP
www.buildingperformanceteam.com<http://www.buildingperformanceteam.com/>
Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653

From: Jim Dirkes
Sent: Friday, April 26, 2013 5:59 AM
To: 'change.proposal at ashrae.org'
Cc: Santiago Velez (santiago at zondae.com); francisco at zondae.com; 'Jason Glazer'
Subject: Apparent error on ASHRAE 90.1-2007 (and perhaps 2010)

Dear ASHRAE,
I am comparing Appendix G fan power calculations for ASHRAE 90.1 in both SI and IP units.  It appears that they do not agree for Baseline Systems 1 & 2.
The formulae for Systems 1 & 2 are:
(IP): Pfan (watts) = CFMs (cfm) * 0.3
(SI): Pfan (watts) = CFMs (L/s) * 0.3

Calculating fan power for Systems 1&2:
Given:
L/s * 1000 = m3/s
m3/s * 2118.64 = cfm

Substituting these into the fan power equations for Baseline Systems 1 & 2:
(SI): (1 L/s * 1000) * .3 = 300 W
(IP): 2118.64 cfm * .3  = 636 W

The fan power should be identical, but isn't even close! Have you ever noticed this?  I could not find an errata sheet that corrected the formula. Will you please check to see if there is a correction?  Please make a correction if I am not missing something!
Thank you!

p.s., In a smaller way, the fan power calculations do not agree for the other System types.  This appears to be due in part to using 5 digit precision for IP units and 4 digits for SI (e.g., 0.00094 for IP and 0.0015 for SI)  If you use SI factors of 0.0014857 and 0.0020547 for Systems 3-4 and 5-8 respectively, the agreement is better.

James V Dirkes II, PE, BEMP, LEED AP
www.buildingperformanceteam.com<http://www.buildingperformanceteam.com/>
Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653

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