[BLDG-SIM] Question about Fan Power

[Vikram Sami]

So I'm trying to calculate fan power, and came across this mindbender

Pfan = 746 / (1 - e[ -0.2437839 × ln( bhp ) - 1.685541 ]) × bhp

Having done the hard part (I figured out how to automate the process in XL with just the CFM input using the natural log function ), I have only one question - does the bhp (highlighted at the end) go in the numerator or denominator of the equation?

i.e. - Should the equation read

Pfan = 746 / [(1 - e[ -0.2437839 × ln( bhp ) - 1.685541 ]) × bhp]

Or

Pfan = [746 / (1 - e[ -0.2437839 × ln( bhp ) - 1.685541 ])] × bhp

Any help is much appreciated.

Thanks

Vikram Sami, LEED AP
Direct Phone 404-253-1466 | Direct Fax 404-253-1366

LORD, AECK & SARGENT ARCHITECTURE
1201 Peachtree Street NE, Suite 300, Atlanta, GA 30361
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www.lordaecksargent.com

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**************************************************************************
G3.1.2.9 Supply Fan Power. System fan electrical power
for supply, return, exhaust, and relief (excluding power to fanpowered
VAV boxes) shall be calculated using the following
formulas:
Pfan = 746 / (1 - e[ -0.2437839 × ln( bhp ) - 1.685541 ]) × bhp
where
Pfan = electric power to fan motor (watts) and
bhp = brake horsepower of baseline fan motor from Table
G3.1.2.9, where cfm represents design supply flow
rate.
***************************************************************************





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