[BLDG-SIM] Question about Fan Power
Brandon Nichols
BrandonN at Hargis.biz
Thu Jul 5 13:35:32 PDT 2007
BHP must be in the numerator else it would take less power to run motors of increasing horsepower, QED?
Brandon Nichols, PE
Mechanical
HARGIS ENGINEERS
600 Stewart Street
Suite 1000
Seattle, WA 98101
www.hargis.biz
d | 206.436.0400 c | 206.228.8707
o | 206.448.3376 f | 206.448.4450
_____
From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Vikram Sami
Sent: Thursday, July 05, 2007 1:12 PM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Question about Fan Power
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
Responsive Design * Technological Expertise * Exceptional Service
www.lordaecksargent.com <file://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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