[BLDG-SIM] Question about Fan Power

[Neeraj Kapoor]

Forwarding my reply to Vikram.
Just wanted to keep this on the thread . . .

----- Forwarded Message ----
From: Neeraj Kapoor <near_ej at yahoo.com>
To: VSami at lasarchitect.com
Sent: Thursday, 5 July, 2007 5:09:32 PM
Subject: Re: [BLDG-SIM] Question about Fan Power

Vikram,

The second answer is correct, i.e. the bhp goes in as a numerator. (746*BHP)/(1-EXP{[-0.243789*LN(BHP)]-1.685541})

I figured it out by trial and error. In one case that when I used the bhp in the denominator, the fan power increased 3 to 4 times. That immediately added heat to the supply air stream and terminated my simulation run due to an error. I hope the equation is clarified better in the next version of the document.

bests,
Neeraj


----- Original Message ----
From: Vikram
 Sami <VSami at lasarchitect.com>
To: BLDG-SIM at gard.com
Sent: Thursday, 5 July, 2007 4:12:10 PM
Subject: [BLDG-SIM] Question about Fan Power

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



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





Send free SMS to your Friends on Mobile from your Yahoo! Messenger. Download Now! http://messenger.yahoo.com/download.php




Send free SMS to your Friends on Mobile from your Yahoo! Messenger. Download Now! http://messenger.yahoo.com/download.php

===========================
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/20070705/6b9bae49/attachment-0008.htm>