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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Hi everyone!<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>A recent discussion with a mechanical mentor brought up a question I’d like to share with the list… If anyone has a partial or complete response I think we’d all benefit and appreciate it if you’d share your thoughts!<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>For a given duct distribution system, you’ve got a certain static drop. At full flow, your supply fan also has to deal with a certain velocity pressure drop due to friction with the duct distribution. If you lower the volume of your supply airstream, you also lower the velocity and therefore the velocity pressure drops for the given duct distribution. The net result is system supply fan has a lower total pressure drop to overcome, and so should operate more efficiently.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Does anyone know: Whether we choose “variable speed” fan control, use the FAN-EIR-FPLR curve generated by the wizards, or use the VSD curve defined in 90.1 appendix G… are we simultaneously accounting for the efficiency gains due to lowered velocity pressure drop in addition to the drop in fan energy from lower RPMs? If this is not accounted for inside/outside the fan curves, is there a direct way to define that or logically work it into the curves?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>If it helps anyone answer, I can illustrate from recent checks that the wizard-generated FAN-EIR-FPLR curve has a “Nike Swoosh” shape with an inflection around the 20% mark. This shape best matches the (limited) data I’ve seen for “real world” VSD input measurements. Here’s a screenshot:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><img width=508 height=307 id="_x0000_i1028" src="cid:image002.png@01CC7E8A.A7C00E30"><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The following illustrates the 90.1-2007 VAV curve we’re made to use for baseline systems 5-8 (I haven’t checked to see if this still applies to 2010). It does not have the same “inflection point” as zero is approached. I think it’s based on the fan law power equation or something similar that doesn’t account for motor/VSD losses:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><img width=508 height=304 id="Picture_x0020_2" src="cid:image003.png@01CC7E8C.6C6150E0"><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The help files illustrate a different, third shape for “variable speed” control different from both of the above…<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><img width=418 height=371 id="Picture_x0020_5" src="cid:image004.png@01CC7E93.0F166540"><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Seeing these side-by-side raises another question for me regarding 90.1-2007 intent/practice… not specific to eQuest… but I’ve already spent too much of my time today writing this out! Another day =)…<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thanks in advance for anyone joining in the discussion!<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>~Nick<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><img width=119 height=37 id="Picture_x0020_1" src="cid:image001.jpg@01CC7E87.344D2EE0" alt="cid:489575314@22072009-0ABB"><b><span style='font-family:"Stylus BT","sans-serif";color:#2D4D5E'><o:p></o:p></span></b></p><p class=MsoNormal><b><span style='font-family:"Stylus BT","sans-serif";color:#2D4D5E'><o:p> </o:p></span></b></p><p class=MsoNormal><b><span style='font-size:12.0pt;font-family:"Stylus BT","sans-serif";color:#2D4D5E'>NICK CATON, P.E.</span></b><b><span style='font-size:12.0pt;font-family:"Stylus BT","sans-serif";color:#2D4D5E'><o:p></o:p></span></b></p><p class=MsoNormal><span style='font-size:7.5pt;color:#CC9900'>SENIOR ENGINEER<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:7.5pt;color:#CC9900'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;color:#2D4D5E'>Smith & Boucher Engineers</span><span style='font-size:7.5pt;font-family:"Times New Roman","serif";color:#CC9900'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;color:#2D4D5E'>25501 west valley parkway, suite 200<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;color:#2D4D5E'>olathe, ks 66061<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;color:#2D4D5E'>direct 913.344.0036<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;color:#2D4D5E'>fax 913.345.0617<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><a href="www.smithboucher.com" title="blocked::www.smithboucher.com"><span style='font-size:10.0pt;color:blue'>www.smithboucher.com</span></a></span><u><span style='font-size:10.0pt;color:blue'> </span></u><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>