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<p class="MsoNormal">Hi Rathnashree,<o:p></o:p></p>
<p class="MsoNormal">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></p>
<p class="MsoNormal">Regards,<o:p></o:p></p>
<p class="MsoNormal">~Bill<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Franklin Gothic Medium",sans-serif;color:black">William Bishop, PE, BEMP, BEAP, CEM, LEED AP<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:black">Senior Energy Engineer<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span style="font-size:3.0pt;font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></b></p>
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</v:shapetype><v:shape id="Picture_x0020_4" o:spid="_x0000_s1026" type="#_x0000_t75" alt="Pathfinder-EA-logo-2" style='position:absolute;margin-left:0;margin-top:63.6pt;width:68.45pt;height:43.9pt;z-index:-251657216;visibility:visible;mso-wrap-style:square;mso-width-percent:0;mso-height-percent:0;mso-wrap-distance-left:9pt;mso-wrap-distance-top:0;mso-wrap-distance-right:9pt;mso-wrap-distance-bottom:0;mso-position-horizontal:left;mso-position-horizontal-relative:text;mso-position-vertical:absolute;mso-position-vertical-relative:text;mso-width-percent:0;mso-height-percent:0;mso-width-relative:page;mso-height-relative:page'>
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</v:shape><![endif]--><![if !vml]><img width="91" height="59" style="width:.9479in;height:.6145in" src="cid:image004.jpg@01D690BB.8F44C060" align="left" hspace="12" alt="Pathfinder-EA-logo-2" v:shapes="Picture_x0020_4"><![endif]><b><i><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:#002060">T:
(585) 698-1956</span></i></b><b><i><span style="color:#002060"> </span>
</i></b><span style="color:#1F497D"> </span><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:#1F497D">F: (585) 325-6005<o:p></o:p></span></p>
<p class="MsoNormal"><a href="mailto:wbishop@pathfinder-ea.com"><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:blue">bbishop@pathfinder-ea.com</span></a><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:black"> </span><a href="http://www.pathfinder-ea.com/"><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:blue">www.pathfinder-ea.com</span></a><span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:#1F497D">134 South Fitzhugh Street<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:#1F497D">Rochester, NY 14608
<img border="0" width="26" height="23" style="width:.2708in;height:.2395in" id="Picture_x0020_1" src="cid:image003.png@01D690BB.2FB08530">
</span><i><span style="font-size:7.0pt;font-family:"Verdana",sans-serif;color:#00B0F0">Ask me why Carbon Fee & Dividend may be right for you.</span></i><span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b>From:</b> Bldg-sim <bldg-sim-bounces@lists.onebuilding.org>
<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 <bldg-sim@lists.onebuilding.org><br>
<b>Subject:</b> [Bldg-sim] Constant air volume systems<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif">Dear All,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif">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?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif">Regards,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica",sans-serif">Rathnashree<o:p></o:p></span></p>
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