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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Joshua,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>If the velocity in the main duct is
extremely high, it could be sucking air into the duct. The high velocity
pressure of the air in the main duct can lower the static pressure in the duct below
the room static pressure. This aspirating effect is used in chemistry labs to produce
a vacuum in a system by hooking a hose as a side tap to another hose with water
running through it. It can also be demonstrated with a simple experiment. Hold the
short end of a dollar bill directly below your lower lip, with the other end of
the dollar bill hanging down. Now blow. The dollar bill will fly up like a
flag. Your high-velocity air is like the air in the duct, and the low pressure
in the main air stream is sucking up the dollar bill like the air in the duct
is sucking air out of the room. I recommend estimating the velocity pressure
and the static pressure at the problem points to see if aspiration is causing
the problem.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
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<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'>Sincerely,</span></font><font color=navy><span style='color:navy'><o:p></o:p></span></font></p>
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w:st="on"><font size=2 color=navy face=Arial><span style='font-size:10.0pt;
font-family:Arial;color:navy'>Keith Swartz</span></font></st1:PersonName><font
size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'>, PE, LEED® AP</span></font><font color=navy><span
style='color:navy'><o:p></o:p></span></font></p>
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w:insAuthor="Keith Swartz" w:insDate="2008-01-14T14:35:00Z"
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w:st="on"><font color=navy><span style='color:navy'>Energy</span></font></st1:PlaceName></ns0:PlaceName><font
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w:insAuthor="Keith Swartz" w:insDate="2008-01-14T14:35:00Z"
w:endInsAuthor="Keith Swartz" w:endInsDate="2008-01-14T14:35:00Z"><st1:PlaceType
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w:insAuthor="Keith Swartz" w:insDate="2008-01-14T14:35:00Z"
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w:endInsAuthor="Keith Swartz" w:endInsDate="2008-01-14T14:35:00Z"><ns0:State
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Science Drive</span></font></st1:address></st1:Street></ns0:address></ns0:Street><font
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w:endInsAuthor="Keith Swartz" w:endInsDate="2008-01-14T14:35:00Z"><ns0:Street
w:insAuthor="Keith Swartz" w:insDate="2008-01-14T14:35:00Z"
w:endInsAuthor="Keith Swartz" w:endInsDate="2008-01-14T14:35:00Z"><st1:address
w:st="on"><st1:Street w:st="on"><font color=navy><span style='color:navy'>Suite</span></font></st1:Street></ns0:Street></st1:address><font
color=navy><span style='color:navy'> 200</span></font></ns0:address><font
color=navy><span style='color:navy'><o:p></o:p></span></font></span></font></p>
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w:insAuthor="Keith Swartz" w:insDate="2008-01-14T14:35:00Z"
w:endInsAuthor="Keith Swartz" w:endInsDate="2008-01-14T14:35:00Z"><ns0:City
w:insAuthor="Keith Swartz" w:insDate="2008-01-14T14:35:00Z"
w:endInsAuthor="Keith Swartz" w:endInsDate="2008-01-14T14:35:00Z"><font
color=navy><span style='color:navy'>Madison</span></font></ns0:City><font
color=navy><span style='color:navy'>, </span></font><ns0:State
w:insAuthor="Keith Swartz" w:insDate="2008-01-14T14:35:00Z"
w:endInsAuthor="Keith Swartz" w:endInsDate="2008-01-14T14:35:00Z"><font
color=navy><span style='color:navy'>WI</span></font></ns0:State><font
color=navy><span style='color:navy'> </span></font><ns0:PostalCode
w:insAuthor="Keith Swartz" w:insDate="2008-01-14T14:35:00Z"
w:endInsAuthor="Keith Swartz" w:endInsDate="2008-01-14T14:35:00Z"><font
color=navy><span style='color:navy'>53711</span></font></ns0:PostalCode></ns0:place><font
color=navy><span style='color:navy'><o:p></o:p></span></font></span></font></p>
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color:navy'>Phone: 608-238-8276 ext. 123<o:p></o:p></span></font></p>
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color=navy><span style='color:navy'><o:p></o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> Brain, Joshua
[mailto:JBrain@Vanderweil.com] <br>
<b><span style='font-weight:bold'>Sent:</span></b> Friday, January 11, 2008
7:44 AM<br>
<b><span style='font-weight:bold'>To:</span></b> bldg-sim@lists.onebuilding.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> [Bldg-sim] IES CFD
Modeling Issue: Reverse Flow through Diffusers</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Hello,</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>I am using IES to conduct a CFD model on a
long and narrow room (283ft by 60ft) with three large ducts (square 4ft by 4ft)
running along the ceiling (280ft long, 28ft off the floor). I have 18 diffusers
equally spaced along each of the three 280ft ducts for a total of 54. Each
diffuser has a CFM of 1110, an area of 3.75 sf, and a discharge velocity of 300
fpm. There is a single return grill at one end of the building. </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>My problem is: when I look at the velocity
vectors in the MicroFlo Viewer some of the diffusers have the air flowing
backwards or into the diffuser, not flowing out as it is supposed to. This
occurs across all three duct lengths at the same diffuser location. </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Has anyone else run into this and have
they resolved the issue? IES took my model and made changes to it only to
find that they could not fix it. </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Thank you in advance for any advice, </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Josh</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 color=navy face="Times New Roman"><span
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<p class=MsoNormal><font size=2 color=navy face="Times New Roman"><span
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Boston, MA 02210 </span></font><o:p></o:p></p>
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