<div dir="ltr">Fred,<div><br><div>The reason for "forcing" zero power at zero mass flow rate is because the temperature raise across the fan is dT = P/m_flow/cp, where P is the power of the fan, m_flow is the mass flow rate and cp is the specific heat capacity. If P were not zero at m_flow=0, one would get an infinite large temperature raise. Forcing P=0 if m_flow=0 is for numerical reasons, which is important as continuous time simulators cross the region of very small flow rates when equipment is switched on or off. However, proper implementation of controls will not simulate the fan at such low speed for extended periods of time, as this region is outside of the capability of the real equipment. Therefore, this treatment does not affect your energy saving calculations.</div>
<div><br></div><div>For a more in-depth discussion about this topic, see Section 4 in <a href="http://www.tandfonline.com/doi/pdf/10.1080/19401493.2013.765506">http://www.tandfonline.com/doi/pdf/10.1080/19401493.2013.765506</a></div>
<div><br></div><div>All the best,</div><div><br></div><div>Michael</div></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Wed, Feb 26, 2014 at 11:08 AM, Porter, Fred AEC <span dir="ltr"><<a href="mailto:FPorter@archenergy.com" target="_blank">FPorter@archenergy.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal"><span style="color:#1f497d">Thank you Nathan,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d">I think a reasonable sp reset fan curve is better than the ASHRAE baseline curve at most values of interest.
<u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d">I did just notice that the ASHRAE curve appears to have been “forced” through 30% power at 50% flow which is the minimum performance listed in 6.5.3.2.1. For some reason, it was also “forced” through zero power
at zero flow. <u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d">Fred<u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d"><u></u> <u></u></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""> Nathan Miller [mailto:<a href="mailto:nathanm@rushingco.com" target="_blank">nathanm@rushingco.com</a>]
<br>
<b>Sent:</b> Wednesday, February 26, 2014 11:42 AM<br>
<b>To:</b> Porter, Fred AEC; bldg-sim@lists. onebuilding. org (<a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a>)<br>
<b>Subject:</b> [External] RE: ASHRAE App G VAV Fan Curve<u></u><u></u></span></p>
</div>
</div><div><div class="h5">
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><span style="color:#1f497d">I think it is pretty clear the way 90.1 App. G is written that you SHALL use that specific curve for the baseline VAV system fan power. Now it is a different discussion about whether that curve properly accounts
for any ASHRAE required controls strategies, fan performance requirements, etc, but that doesn’t really matter, here is the curve to use.
<u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d">Proposed, as always, should accurately reflect how the system will operate. If you think a more advantageous fan curve is appropriate, such as to account for static pressure reset, go ahead and use it, just as
you could create a custom curve for boiler or chiller part-load efficiencies. Don’t hide the fact, make it clear to the reviewer that you are using different curves, state the source for your proposed curve and see if they want to comment or challenge the
results. <u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d">For what it is worth (keeping in mind that past rulings do not set precedent), on multiple projects I have worked on I have used “static pressure reset” fan curves in the proposed, the mandatory baseline fan
curve in the baseline, and it has never even been questioned by the reviewer. <u></u>
<u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d"><u></u> <u></u></span></p>
<div>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#632423">Nathan Miller
</span></b><b><span style="font-size:8.0pt;font-family:"Verdana","sans-serif";color:#1f497d">-</span></b><b><span style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#632423">
</span></b><b><span style="font-size:8.0pt;font-family:"Verdana","sans-serif";color:#632423">PE, LEED<sup>®</sup>AP BD+C, CEM<u></u><u></u></span></b></p>
<p class="MsoNormal" style="margin-bottom:4.0pt"><i><span style="font-size:8.0pt;font-family:"Verdana","sans-serif"">Mechanical Engineer/Senior Energy Analyst
<u></u><u></u></span></i></p>
<p class="MsoNormal" style="line-height:115%"><b><span style="font-size:8.0pt;line-height:115%;font-family:"Verdana","sans-serif";color:#632423">RUSHING</span></b><span style="font-size:8.0pt;line-height:115%;font-family:"Verdana","sans-serif";color:#bfab7f">
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</span><span style="line-height:115%;font-size:8.0pt;font-family:"Verdana","sans-serif""><a href="tel:206-788-4577" value="+12067884577" target="_blank">206-788-4577</a> |</span><span style="font-size:8.0pt;line-height:115%;font-family:"Verdana","sans-serif";color:#bfab7f">
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<p class="MsoNormal"><span style="color:#1f497d"><u></u> <u></u></span></p>
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<div style="border:none;border-top:solid #e1e1e1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b>From:</b> <a href="mailto:bldg-sim-bounces@lists.onebuilding.org" target="_blank">
bldg-sim-bounces@lists.onebuilding.org</a> [<a href="mailto:bldg-sim-bounces@lists.onebuilding.org" target="_blank">mailto:bldg-sim-bounces@lists.onebuilding.org</a>]
<b>On Behalf Of </b>Porter, Fred AEC<br>
<b>Sent:</b> Wednesday, February 26, 2014 9:40 AM<br>
<b>To:</b> bldg-sim@lists. onebuilding. org (<a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a>)<br>
<b>Subject:</b> [Bldg-sim] ASHRAE App G VAV Fan Curve<u></u><u></u></p>
</div>
</div>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">All,<u></u><u></u></p>
<p class="MsoNormal">Does anyone know, particularly through having claims accepted by GBCI, whether the ASHRAE App G VAV fan curve is supposed to represent a fan system with or without static pressure reset. I always thought it was supposed to represent a system
with sp reset, conforming to 6.5.3.2.3. However, most of the curve power values are even higher than curves representing VAV/VFD systems without sp reset. A confusing aspect is that compared to other VFD fan curves, the power values are high at high flows,
but low at low flows, even going to zero at zero flow, though that is really meaningless.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">As an aside, the 2013 Title 24 ACM now defines fan curves for central VAV systems with and without sp reset, taken from Taylor’s VAV design guide. SP reset is the “baseline” or “standard.”A<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Thanks for any experience or thoughts on this.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Fred<u></u><u></u></p>
<p class="MsoNormal"><b><span style>Fred Porter, BEMP, LEED</span><span style="color:#1f497d">©</span><span style> AP<u></u><u></u></span></b></p>
<p class="MsoNormal" style="margin-bottom:2.0pt"><span style="color:#7f7f7f">Senior Energy Analyst<u></u><u></u></span></p>
<p class="MsoNormal"><b><span style="color:#005daa">Architectural Energy Corporation<u></u><u></u></span></b></p>
<p class="MsoNormal"><i><span style="font-size:9.0pt;color:#005daa">A Member of NORESCO Energy and Sustainability Services<u></u><u></u></span></i></p>
<p class="MsoNormal"><span style="font-size:10.0pt;color:#7f7f7f">2540 Frontier Ave, Suite 100, Boulder, CO 80301<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;color:#7f7f7f">Phone <a href="tel:303.459.7425" value="+13034597425" target="_blank">303.459.7425</a> |
<a href="mailto:fporter@archenergy.com" target="_blank">fporter@archenergy.com</a><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;color:#807f83"><a href="http://www.archenergy.com" target="_blank">www.archenergy.com</a></span><span style="font-size:9.0pt;color:#807f83"><u></u><u></u></span></p>
<p class="MsoNormal"><b><span style="font-size:8.0pt;color:#7f7f7f"><u></u> <u></u></span></b></p>
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