<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:arial,helvetica,sans-serif;font-size:10pt"><div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">Forwarding my reply to Vikram.<br>Just wanted to keep this on the thread . . .<br><br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;">----- Forwarded Message ----<br>From: Neeraj Kapoor <near_ej@yahoo.com><br>To: VSami@lasarchitect.com<br>Sent: Thursday, 5 July, 2007 5:09:32 PM<br>Subject: Re: [BLDG-SIM] Question about Fan Power<br><br><div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;"><div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">Vikram,<br><br>The second answer is correct, i.e. the bhp goes in as a numerator. <span style="font-weight: bold;">(</span>746*BHP<span style="font-weight: bold;">)</span>/<span style="font-weight:
bold;">(</span>1-EXP{[-0.243789*LN(BHP)]-1.685541}<span style="font-weight: bold;">)</span><br><br>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.<br><br>bests,<br>Neeraj<br><br><br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;">----- Original Message ----<br>From: Vikram
Sami <VSami@lasarchitect.com><br>To: BLDG-SIM@gard.com<br>Sent: Thursday, 5 July, 2007 4:12:10 PM<br>Subject: [BLDG-SIM] Question about Fan Power<br><br><title>Question about Fan Power</title>
<p><font face="Arial" size="2">So I'm trying to calculate fan power, and came across this mindbender</font>
</p>
<p><i><font face="Times New Roman">Pfan</font></i> <font face="Times New Roman">= 746 / (1 - e[ -0.2437839 × ln( bhp ) - 1.685541 ])<u><b> </b></u></font><u><b><font color="#ff0000" face="Times New Roman">× bhp</font></b></u><b></b>
</p>
<p><font face="Arial" size="2">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?</font></p>
<p><font face="Arial" size="2">i.e. - Should the equation read</font>
</p>
<p><i><font face="Times New Roman">Pfan</font></i> <font face="Times New Roman">= 746 / [(1 - e[ -0.2437839 × ln( bhp ) - 1.685541 ]) × bhp]</font>
</p>
<p><font face="Times New Roman">Or</font>
</p>
<p><i><font face="Times New Roman">Pfan</font></i> <font face="Times New Roman">= [746 / (1 - e[ -0.2437839 × ln( bhp ) - 1.685541 ])] × bhp</font>
</p>
<p><font face="Arial" size="2">Any help is much appreciated.</font>
</p>
<p><font face="Arial" size="2">Thanks</font>
</p>
<p><b><font color="#000000" face="Garamond">Vikram Sami,</font></b> <font color="#000000" face="Garamond">LEED AP</font><b></b>
<br><font color="#000000" face="Garamond">Direct Phone 404-253-1466 | Direct Fax 404-253-1366</font>
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<br><font face="Arial" size="2">**************************************************************************</font>
<br><font face="TT12B7o00" size="2">G3.1.2.9</font><b></b><b> <font face="Times New Roman" size="2">Supply Fan Power.</font></b> <font face="Times New Roman" size="2">System fan electrical power</font>
<br><font face="Times New Roman" size="2">for supply, return, exhaust, and relief (excluding power to fanpowered</font>
<br><font face="Times New Roman" size="2">VAV boxes) shall be calculated using the following</font>
<br><font face="Times New Roman" size="2">formulas:</font>
<br><i><font face="Times New Roman" size="2">P</font><font face="Times New Roman" size="1">fan</font></i> <font face="Times New Roman" size="2">= 746 / (1 - e</font><font face="Times New Roman" size="1">[ -0.2437839 × ln( bhp ) - 1.685541 ]</font><font face="Times New Roman" size="2">) × bhp</font>
<br><font face="Times New Roman" size="2">where</font>
<br><i><font face="Times New Roman" size="2">P</font><font face="Times New Roman" size="1">fan</font></i> <font face="Times New Roman" size="2">= electric power to fan motor (watts) and</font>
<br><font face="Times New Roman" size="2">bhp = brake horsepower of</font><i> <font face="Times New Roman" size="2">baseline</font></i> <font face="Times New Roman" size="2">fan motor from Table</font>
<br><font face="Times New Roman" size="2">G3.1.2.9, where cfm represents design supply flow</font>
<br><font face="Times New Roman" size="2">rate.</font>
<br><font face="Arial" size="2">***************************************************************************</font>
</p>
<br>
<br>
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