<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman,new york,times,serif;font-size:10pt">Nick:<br><br>For a supply duct passing through a plenum return ceiling during the cooling season, the temperature difference between the supply air and return air can be as much as 25 degrees.<br><br>During the heating season, this difference could be as much as 30 degrees during morning warm up.<br><br>Paul Diglio<br><br><div style="font-family: times new roman,new york,times,serif; font-size: 10pt;"><br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><font face="Tahoma" size="2"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> Nick Caton <ncaton@smithboucher.com><br><b><span style="font-weight: bold;">To:</span></b> Paul Diglio <paul.diglio@sbcglobal.net>; "McArdle, Mike" <Mike.McAardle@state.vt.us>; xiaoyang shi
<xs2144@gmail.com>; equest-users@lists.onebuilding.org<br><b><span style="font-weight: bold;">Sent:</span></b> Tue, March 29, 2011 8:03:32 PM<br><b><span style="font-weight: bold;">Subject:</span></b> RE: [Equest-users] question about inefficiency of duct<br></font><br>
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<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">I think Mike’s general point is fair and isn’t to be
taken in absolutes. </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">When a ducted return air stream is passing through a conditioned
space or plenums/chases in between other conditioned spaces, it’s
probably a safe bet to claim any duct gains/losses are *negligible* (not nonexistent),
particularly if said return ducts are insulated, due to the relatively small
delta-T.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">On the other hand, winter losses and summertime gains at extreme
temperatures may be considerable if any ductwork is routed exterior to the building,
even if insulated. </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">Xiaoyang, if you wish to calculate it as a percentage at design
conditions: ( U x A x deltaT )<sub>DUCT</sub> / (total building
heating or cooling load) x 100</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">If you wanted to model such exterior duct heat losses/gains in
eQuest… I haven’t considered that before – but depending on
your system setup, it might be as simple as a small exterior wall surface
with appropriate U-value and area equal to the duct surface area… in the event
the solar loads incident on the duct might be significant, make a point to correctly
locate the surface in 3D (over the roof, along a wall, etc.) to avoid any incorrect
self-shading from other surfaces.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">If anyone has delved into this and knows a better/simpler way
please do share =).</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">~Nick</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
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<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"><img id="Picture_x0020_1" src="cid:1.3376215159@web83305.mail.sp1.yahoo.com" alt="cid:489575314@22072009-0ABB" width="119" height="37"></span><b><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(45, 77, 94);"></span></b></p>
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<p class="MsoNormal"><b><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(45, 77, 94);">NICK CATON, E.I.T.</span></b><b><span style="font-family: "sans-serif"; color: rgb(45, 77, 94);"></span></b></p>
<p class="MsoNormal"><span style="font-size: 7.5pt; font-family: "sans-serif"; color: rgb(204, 153, 0);">PROJECT ENGINEER</span></p>
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<p class="MsoNormal"><span style="font-size: 10pt; font-family: "sans-serif"; color: rgb(45, 77, 94);">olathe ks 66061</span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family: "sans-serif"; color: rgb(45, 77, 94);">direct 913 344.0036</span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family: "sans-serif"; color: rgb(45, 77, 94);">fax 913 345.0617</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"><a rel="nofollow" title="blocked::www.smithboucher.com"><span style="font-size: 10pt;">www.smithboucher.com</span></a></span><u><span style="font-size: 10pt; font-family: "sans-serif"; color: blue;"> </span></u><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"></span></p>
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<p class="MsoNormal"><b><span style="font-size: 10pt; font-family: "sans-serif";">From:</span></b><span style="font-size: 10pt; font-family: "sans-serif";">
equest-users-bounces@lists.onebuilding.org
[mailto:equest-users-bounces@lists.onebuilding.org] <b>On Behalf Of </b>Paul
Diglio<br>
<b>Sent:</b> Tuesday, March 29, 2011 4:59 PM<br>
<b>To:</b> McArdle, Mike; xiaoyang shi; equest-users@lists.onebuilding.org<br>
<b>Subject:</b> Re: [Equest-users] question about inefficiency of duct</span></p>
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<p class="MsoNormal"><span style="font-size: 10pt;">Michael:<br>
<br>
"if the air in duct is the same air as the air being supplied to the
space, there is no net effect"? What do you mean by net effect?<br>
<br>
The duct heat loss/gain depends on the difference of the temperature of the air
in the duct and the temperature of the air surrounding the outside of the
duct. It is highly unlikely that these temperature will be the same.<br>
<br>
Paul Diglio</span></p>
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<p class="MsoNormal"><span style="font-size: 10pt;"> </span></p>
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<div class="MsoNormal" style="text-align: center;" align="center"><span style="font-size: 10pt; font-family: "sans-serif";">
<hr align="center" width="100%" size="1">
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<p class="MsoNormal" style="margin-bottom: 12pt;"><b><span style="font-size: 10pt; font-family: "sans-serif";">From:</span></b><span style="font-size: 10pt; font-family: "sans-serif";"> "McArdle, Mike"
<Mike.McAardle@state.vt.us><br>
<b>To:</b> xiaoyang shi <xs2144@gmail.com>; "equest-users@lists.onebuilding.org"
<equest-users@lists.onebuilding.org><br>
<b>Sent:</b> Tue, March 29, 2011 5:39:40 PM<br>
<b>Subject:</b> Re: [Equest-users] question about inefficiency of duct</span></p>
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<p class="MsoNormal"><span style="font-size: 10pt; font-family: "sans-serif";">Dear
xiaoyang shi</span><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">It Depends on the temperature differentials between air in duct
and space and insulation thickness </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">But more importantly , if the air in duct is the same air
as the air being supplied to the space there is no net effect </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">Thank you, Sincerely,</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">Michael J. McArdle , P.E.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">Buildings Engineer II, Project Manager </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">State of Vermont, </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">Buildings and General Services (BGS)</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">2 Governor Aiken Avenue</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">Montpelier, Vt. 05633</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family: "sans-serif"; color: rgb(31, 73, 125);">Office: 802-828-5650; cell: 802-272-4828</span></p>
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<p class="MsoNormal"><b><span style="font-size: 10pt; font-family: "sans-serif";">From:</span></b><span style="font-size: 10pt; font-family: "sans-serif";">
equest-users-bounces@lists.onebuilding.org
[mailto:equest-users-bounces@lists.onebuilding.org] <b>On Behalf Of </b>xiaoyang
shi<br>
<b>Sent:</b> Tuesday, March 29, 2011 5:37 PM<br>
<b>To:</b> equest-users@lists.onebuilding.org<br>
<b>Subject:</b> [Equest-users] question about inefficiency of duct</span></p>
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<p class="MsoNormal"> </p>
<p class="MsoNormal" style="margin-bottom: 12pt;">Hi folks,<br>
<br>
In the winter time, some heat loss in HVAC is from duct.<br>
<br>
What is the percentage of heat loss through the duct to the total building heat
load, due to the inefficiencies of duct delivery system?<br>
<br>
Thank you guys.<br>
<br>
</p>
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