[BLDG-SIM] Question about Fan Power

[Brandon Nichols]

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>  

Please don't print this email unless you really have to. 
One tree makes 16.67 reams of copy paper or 8,333.3 sheets
~Conservatree, September 2002

************************************************************************** 
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. 
*************************************************************************** 




==================
You received this e-mail because you are subscribed 
to the BLDG-SIM at GARD.COM mailing list.  To unsubscribe 
from this mailing list send a blank message to 
BLDG-SIM-UNSUBSCRIBE at GARD.COM


===========================
You received this e-mail because you are subscribed 
to the BLDG-SIM at GARD.COM mailing list.  To unsubscribe 
from this mailing list send a blank message to 
BLDG-SIM-UNSUBSCRIBE at GARD.COM
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20070705/1eae6f35/attachment-0008.htm>