I was curious if anyone could confirm their experience with App G fan
power calculations for FCUs vs real life equipment values.
For AHUs, VAV boxes, etc, most average equipment consumes power nearly
identical to the fan power calculations of App G. Usually a little bit
better, but nothing major unless you start specifying ECM motors in VAV
boxes, fan walls for AHUs, etc.
But for FCUs: I've got a project with 100+, and most of them come out
to about 0.0008 KW / cfm per the calculations.
However, fairly standard FCU selections (from McQuay, not that it
matters), use about 0.0003 KW / cfm. That's almost a third of the
energy use, and when the entire building is FCU, it makes a huge
difference.
Can someone confirm their experience? I'm not complaining, but I just
want to make sure there isn't some addendum that changes the fan power
calcs for very low CFM HVAC systems.
Thanks!
James Hansen, PE, LEED AP
James,
That's an error in ASHRAE 90.1-2004 that was later corrected in the
addenda and incorporated into the 2007 version. With the correction, the
fan power allowance drops by more than 50% (from what I recall) for
these small systems.
Regards,
Jonathan M. Curtin, EIT, LEED(r) AP
Sorry, I meant PTACs....(FCU is the proposed system).
And Jonathan informed me that ASHRAE corrected this is a later addendum,
as well as in the 2007 version of 90.1