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<div class=Section1>
<p class=MsoNormal><span style='color:#1F497D'>Jason,<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>ASHRAE 90.1 2007 (and 2004) uses
CFMs = “the baseline system maximum design supply fan airflow rate in cfm”<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>So it should be method 2. As
Michael points out, you’re not actually calculating the amount of power
it takes to <b>supply</b> 100,000 cfm. You’re calculating your “system
allowance” based on that supply / total system airflow. The calculations
already are based on the idea that a supply of that quantity will have to
return and/or exhaust that quantity as well. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>The Advanced Energy Modeling for
LEED manual also points out that a common error is “Additional fan power
allowance is claimed in baseline for return, exhaust, or relief fans”.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>-Corinne<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
bldg-sim-bounces@lists.onebuilding.org
[mailto:bldg-sim-bounces@lists.onebuilding.org] <b>On Behalf Of </b>Michael A.
Eustice<br>
<b>Sent:</b> Friday, June 17, 2011 10:52 AM<br>
<b>To:</b> 'Jason Wendel'; 'bldg-sim'<br>
<b>Subject:</b> Re: [Bldg-sim] Fan Power<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:black'>You seem to be directly
correlating fan energy consumption and airflow rate. Remember, fan energy
is proportional to the product of airflow rate and differential pressure.
<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal>Here are my thoughts:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>If we have:<o:p></o:p></p>
<p class=MsoNormal>SA fan: 100,000 cfm @ 4”wc<o:p></o:p></p>
<p class=MsoNormal>RA fan: 90,000 cfm @ 1” wc<o:p></o:p></p>
<p class=MsoNormal>EA fan: 10,000 cfm @ 1” wc<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>And let’s say they result in:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>SA fan: 95 KW<o:p></o:p></p>
<p class=MsoNormal>RA fan: 20 KW<o:p></o:p></p>
<p class=MsoNormal>EA fan: 2 KW<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The total airflow of the system is 100,000 cfm, since the RA
and EA fan are in series with the SA fan. Remember, in a series
arrangement the differential pressure of the fans are summed, not the airflow
quantity; therefore, we meet the LEED criteria that says that the system total
fan power<u> is based on</u> the baseline system design supply airflow
rate. The system total fan power, however, is 117 KW, which can be
calculated by adding the individual fan’s KW together, or by using total
system airflow (100,000 cfm) and total system static pressure (5” wc) to
calculate total system KW directly. The system total differential
pressure is 5”, not 6”, because the RA and EA fans are in parallel
with each other, and both are in series with the SA fan.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Then I guess you’d simply apply that proportion of fan
power (81% for SA fan, 17% for RA fan, and 2% for EA fan) to the proposed
system configuration.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Can anyone else confirm? I haven’t done this
calculation for LEED before so I am not saying this IS the correct approach.
This is simply my initial reaction to your question.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Thanks,<o:p></o:p></p>
<p class=MsoNormal>Michael Eustice, PE, LEED AP<o:p></o:p></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
bldg-sim-bounces@lists.onebuilding.org
[mailto:bldg-sim-bounces@lists.onebuilding.org] <b>On Behalf Of </b>Jason
Wendel<br>
<b>Sent:</b> Friday, June 17, 2011 10:02 AM<br>
<b>To:</b> 'bldg-sim'<br>
<b>Subject:</b> [Bldg-sim] Fan Power<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>So, which is it, I have received LEED Review comments back
stating two different ways to calculate fan power and no matter what I do, the
next reviewer for the next project sees it differently and has me revise it.<o:p></o:p></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo2'><![if !supportLists]><span
style='mso-list:Ignore'>1.<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>Calculate the baseline fan power from the sum of all
the supply, return & exhaust airflows combined to get a total fan
power. Then proportion out the total fan power between each of the fans
(supply, return, exhaust, etc).<o:p></o:p></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo2'><![if !supportLists]><span
style='mso-list:Ignore'>2.<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>Calculate the baseline fan power for the supply fan
only, and then proportion out the power from that calculation into each of the
fans (supply, return, exhaust, etc.)<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Method #1 takes all the airflow in all the fans in the
building added together, calculates the fan power to move that much air, and
then proportions it out to each of the fans. For example,
100,000 cfm supply air, 90,000 return air and 10,000 exhaust air. Totals
to 200,000 cfm airflow in the building. Calculate the airflow for the
200,000 cfm and lets say you get 200 kW. Then you proportion out the fan
power between the fans – but the sum is 200 kW of power.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>So, method #2 doesn’t make sense to me. You take
calculate the amount of power required to blow the supply air (lets say 100,000
cfm, for example) throughout the building (say 100 kW for simplicity), and then
say that the 100 kW is then divided out between all the fans in the building,
resulting in the supply fan using ˝ of the power that you calculated it should,
and the rest of the power is divided out between each of the other fans in the
building. So you calculate that 100 kW of energy is needed to move
100,000 cfm of air, but then you change your mind and say that the baseline
system is actually only going to use 50 kW of energy and the other 50 kW is
used in the return and exhaust fans? That doesn’t make sense to me.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>So, which is it? I’ve received review comments
back from LEED stating each of them, for different projects. It appears
to be interpreted differently from different LEED Reviewers so apparently they
don’t know either.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='font-size:8.0pt;font-family:"Arial","sans-serif";
color:#1F497D'>-Jason<o:p></o:p></span></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p> </o:p></span></p>
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