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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'>Bill<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'>The DOAS System is preconditioning the
Outside Air before it is sent to the Main AHU. The Ratio of Fresh Air to
Return Air is based on the how you are controlling your system. <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'>By specifying “Sum of Zone OA”
within Equest, the system is simply summing up the necessary Outside Air to
meet the cfm/occ and cfm/ft2. Yet this strategy is not the best way to
determine Ventilation Requirements. For example, a fully occupied
classroom may require an OA Ratio of 40%. Yet other spaces served by the
same AHU need an OA Ratio of 15%. As a result, the final OA Ratio
supplied will be somewhere in between, probably around 20%. Therefore the
fully occupied classroom is not being provided a sufficient level of
Ventilation. This control strategy does not meet ASHRAE Standard 62-2004.<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'>The other option of “Set by Critical
Zone” is based on the Multi-Zone Ventilation Strategy specified by ASHRAE
Standard 62-2004. If you are conducting an Energy Model to meet LEED,
then you must use this control strategy.<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 your model just has AHUs, then Equest
works with the “Set by Critical Zone” strategy.<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'>Yet, if you have connected a DOAS to an
AHU, then everything gets messed up. The AHU provides Ventilation Air
based on the “Set by Critical Zone” strategy. Yet the DOAS
unit provides Ventilation Air based on the “Sum of Zone OA”
strategy. To be correct EQUEST needs to have the DOAS provide the same
Ventilation Air as the attached AHU based on the “Set by Critical Zone”
strategy.<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'>I hope that I explained it properly.<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'>Ian<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>
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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'> William Bahnfleth
[mailto:wbahnfleth@psu.edu] <br>
<b><span style='font-weight:bold'>Sent:</span></b> Monday, September 01, 2008
8:31 PM<br>
<b><span style='font-weight:bold'>To:</span></b> Doebber, Ian<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [Equest-users] Using
Dedicated Outdoor Air System defies ASHRAE 62.1</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Ian-<br>
<br>
A DOAS system (by my definition) supplies 100% outside air, so the concept of
the critical zone (requiring the largest fraction of OA in SA), which relates
to recirculating multiple-space systems, doesn't apply. Am I missing
something?<br>
<br>
Bill Bahnfleth<br>
<br>
At 08:26 PM 9/1/2008, you wrote:<br>
<br>
<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Content-class: urn:content-classes:message<br>
Content-Type: multipart/alternative;<br>
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boundary="----_=_NextPart_001_01C90C92.93E93E65"<br>
<br>
</span></font><font size=2><span style='font-size:10.0pt'>FYI : When using
“OA-FROM-SYSTEM” in to model a Dedicated Outdoor Air System (DOAS),
you must specify “Sum of Zone OA” both for the DOAS and the AHU
that it is serving. The “OA-FROM-SYSTEM” does not correctly
update the DOAS Flow Rate to meet the AHU Outdoor Air Design Ventilation if you
specify “Set by Critical Zone”. <br>
<br>
This causes a problem as “Set by Critical Zone” is the correct way
to Design the Maximum Ventilation Rate according to ASHRAE 62-2004. Based
on my 200,000 <st1:place w:st="on"><st1:PlaceName w:st="on">ft2</st1:PlaceName>
<st1:PlaceType w:st="on">School</st1:PlaceType></st1:place> model, the
“Sum of Zone OA” undersizes the amount of Ventilation Air by
25%. Obviously significant.<br>
<br>
Note that this is using Equest 3.6. Can someone tell me whether this has
been fixed in Equest 3.61. <br>
<br>
Regards,<br>
Ian Doebber<br>
<br>
<br>
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<br>
<div>__________</div>
<br>
<div>William P. Bahnfleth, PhD, PE, FASHRAE</div>
<div>Professor of Architectural Engineering and Director, Indoor
Environment Center</div>
<br>
<div>The Pennsylvania State University / 104 Engineering Unit A /
University Park, PA 16802 USA</div>
<br>
<div>voice: 814.863.2076 / fax: 814.863.4789 / e-mail:
wbahnfleth@psu.edu</div>
<div>
<a href="http://www.engr.psu.edu/ae/faculty/bahnfleth/" EUDORA=AUTOURL>
http://www.engr.psu.edu/ae/faculty/bahnfleth/</a> ,
<a href="http://www.engr.psu.edu/ae/iec/" EUDORA=AUTOURL>
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<br>
Here's a good rule of thumb: too clever is dumb. - Ogden Nash
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