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<p class="MsoNormal">Hello Rathna,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I would like to add a couple of thoughts. First, we are finding more
<u>single zone VAV </u>units that will vary the airflow when the load is reduced, as the fan energy savings can be significant. As you probably know, for a given system, as you reduce the airflow by 25% you can reduce the power required by over 50%.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Second, the energy code is often requiring two speed control at a minimum for single zone systems, which also can greatly improve humidity control as well. With the cost of variable frequency drives so low today, some are finding a VFD
more cost effective than a 2-speed motor. Another reason for a VFD on a system without VAV boxes.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">As Bill noted, this application should be defined by the design engineer, etc.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hope this is helpful.<o:p></o:p></p>
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<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Robert L. (Bob) Towell, P.E., LEED AP, CCP, FASHRAE<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:#1F497D">20A Edwardsville Professional Park<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:#1F497D">Phone: 618-307-5882<o:p></o:p></span></p>
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<p class="MsoNormal"><i>CxE Group is a women (and veteran) owned business.<o:p></o:p></i></p>
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<p class="MsoNormal"><b>From:</b> Rathna Shree <rathnashreep@yahoo.in> <br>
<b>Sent:</b> Wednesday, September 23, 2020 8:19 AM<br>
<b>To:</b> Bishop, Bill <bbishop@pathfinder-ea.com><br>
<b>Cc:</b> bldg-sim@lists.onebuilding.org<br>
<b>Subject:</b> Re: [Bldg-sim] Constant air volume systems<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif">Thank you Mr. Bill for the clarification. This helps.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A">On Tuesday, 22 September, 2020, 06:07:15 pm IST, Bishop, Bill <<a href="mailto:bbishop@pathfinder-ea.com">bbishop@pathfinder-ea.com</a>> wrote:
<o:p></o:p></span></p>
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<p class="yiv4310010346msonormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A">Hi Rathnashree,<o:p></o:p></span></p>
<p class="yiv4310010346msonormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A">You need to know more about the air handling unit and system (controls, ductwork and zone dampers, if any) to know how to simulate the minimum
flow associated with a VFD. An AHU may be designed as a constant volume unit and still use a VFD to balance the system at a fixed flowrate. You don’t automatically get energy savings by using a VFD, and you actually incur a small energy penalty associated
with drive losses. If the system does not have any adjustable zone dampers that are automatically controlled, it may be designed to operate at constant volume, and you would use a minimum flow ratio of 1. If the unit only handles a small number of zones, it
may be designed to run at constant volume. I suggest you ask the design engineer how the unit will be controlled. You can also look for a controls drawing or talk to a factory rep for that unit.<o:p></o:p></span></p>
<p class="yiv4310010346msonormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A">Regards,<o:p></o:p></span></p>
<p class="yiv4310010346msonormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A">~Bill<o:p></o:p></span></p>
<p class="yiv4310010346msonormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A"> <o:p></o:p></span></p>
<p class="yiv4310010346msonormal"><b><span style="font-size:10.0pt;font-family:"Gothic sans-serif",serif;color:black">William Bishop, PE, BEMP, BEAP, CEM, LEED AP</span></b><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A"><o:p></o:p></span></p>
<p class="yiv4310010346msonormal"><b><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:black">Senior Energy Engineer</span></b><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A"><o:p></o:p></span></p>
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<p class="yiv4310010346msonormal"><b><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A">From:</span></b><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A"> Bldg-sim <<a href="mailto:bldg-sim-bounces@lists.onebuilding.org">bldg-sim-bounces@lists.onebuilding.org</a>>
<b>On Behalf Of </b>Rathna Shree via Bldg-sim<br>
<b>Sent:</b> Tuesday, September 22, 2020 7:39 AM<br>
<b>To:</b> bldg <<a href="mailto:bldg-sim@lists.onebuilding.org">bldg-sim@lists.onebuilding.org</a>><br>
<b>Subject:</b> [Bldg-sim] Constant air volume systems<o:p></o:p></span></p>
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<p class="yiv4310010346msonormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A"> <o:p></o:p></span></p>
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<p class="yiv4310010346msonormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#26282A">Dear All,</span><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A"><o:p></o:p></span></p>
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<p class="yiv4310010346msonormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#26282A"> </span><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A"><o:p></o:p></span></p>
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<p class="yiv4310010346msonormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#26282A">In many of our projects, we have Air handling units with VFD and no VAV system. When simulated with minimum flow ratio as 1 and AHU with VFD, there
is no difference in energy consumption. The impact of with and without VFD is negligible. Since there will be a small amount of variation in Airflow in zones due to VFD in AHU, can we reduce the minimum flow ratio from 1 to about 0.8 or 0.7?</span><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A"><o:p></o:p></span></p>
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<p class="yiv4310010346msonormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#26282A"> </span><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A"><o:p></o:p></span></p>
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<p class="yiv4310010346msonormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#26282A">Regards,</span><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A"><o:p></o:p></span></p>
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<p class="yiv4310010346msonormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#26282A">Rathnashree</span><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif;color:#26282A"><o:p></o:p></span></p>
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