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<p class="MsoNormal"><span style="color:#1F497D">The critical zone fraction as explained by ASHRAE 62.1 will, in most cases, increase outside air intake in a VAV system. This is due to the need for the entire system to increase its outside air fraction if
one zone’s airflow dips to its minimum VAV airflow. To maintain the ventilation fraction in the one zone that reduced airflow, the entire system ingests large amounts of outside air to make sure it gets enough air to that particular zone.<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">It’s a bit more complicated than that, but that’s the simplest explanation. There are ways around it, but it takes time to ‘correct’ for small, high ventilation-fraction areas that tend to drive the system towards
high ventilation rates when they modulate to minimum position.<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">Hope this makes sense.<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">Michael <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<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>Jim Dirkes<br>
<b>Sent:</b> Tuesday, August 16, 2011 9:12 AM<br>
<b>To:</b> 'Anne Juran'; bldg-sim@lists.onebuilding.org<br>
<b>Subject:</b> Re: [Bldg-sim] DOAS and baseline OA<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Dear Anne,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I’m not sure why you think the OA requirement varies by system. I’m not well versed in Standard 62, but my basic understanding is that one of the calculation methods is the result of building area and number
of occupants. Those are unchanged by system selection … which is why it makes sense for Appendix G to require matching volumes.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" align="center" style="text-align:center"><b><span style="font-size:13.5pt;color:#1F497D">The Building Performance Team<br>
</span><span style="color:#1F497D">James V. Dirkes II, P.E., BEMP , LEED AP<br>
</span></b><span style="color:#1F497D">1631 Acacia Drive NW<br>
Grand Rapids, MI 49504<br>
616 450 8653<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<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>Anne Juran<br>
<b>Sent:</b> Tuesday, August 16, 2011 8:33 AM<br>
<b>To:</b> bldg-sim@lists.onebuilding.org<br>
<b>Subject:</b> [Bldg-sim] DOAS and baseline OA<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman","serif";color:black">I’m curious how everyone is handling the OA for Appendix G simulations when using a DOAS in the proposed system. We have a design that is DOAS + FCU with
a total OA of 8,000 CFM. When you run the OA calcs for this same building with a VAV system (the baseline), the total OA required to meet Standard 62 is 39,000 CFM. This difference in OA represents a significant energy savings (in climate zone 4A), yet
Appendix G requires the OA volumes to match. It does not seem “fair” to me that the proposed case cannot take credit for design choice when it comes to OA. I feel like Appendix G should make an exception for DOAS. Am I missing something? Is there a way
around this? Any thoughts are appreciated!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman","serif";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman","serif";color:black">Anne<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman","serif";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman","serif";color:black"><o:p> </o:p></span></p>
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