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I have had the same question for years and years. Unfortunately,
the only motor part load efficiency curves available are for constant speed
motors a various percent loading, where frequency remains constant.
<p>To my knowledge... and this was confirmed by a recent Engineered Systems
magazine article (August 2003). In this article, "How to Calculate
Motor Efficiency for Variable Speed Centrifugal Pumps" by Burt Rishel,
Burt states there are no part load motor efficiency curves available in
the industry. I agree with Burt recommendation... they should be
developed and would be quite useful. Burt is an elder pump guru who has
been around since time began, as is considered by many as an authority
on pumping systems.
<p>Which is why Burt stated the best one can expect when comparing caclulated
part load energy use on a variable speed pump (or fan) to field measured
part load results are +/- 10%.
<p>If by chance you should come across such curves, I'd certainly be interested
in seeing them.
<dl>
<dd>
<font size=-1>Thomas E. Anderson</font></dd>
<dd>
<font size=-1>President</font></dd>
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<font size=-1>Cx Associates, Ltd.</font></dd>
<dd>
<font size=-1>Building Commissioning Specialists</font></dd>
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<i><font size=-1><a href="http://www.cx-assoc.com">http://www.cx-assoc.com</a></font></i></dd>
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<i><font size=-1>933 Road 101</font></i></dd>
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<i><font size=-1>Jeffersonville, Vermont 05464 USA</font></i></dd>
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<i><font size=-1>hvac@cx-assoc.com</font></i></dd>
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<i><font size=-1>Tel: 802-644-5616 Fax: 802-644-6797</font></i></dd>
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<br>
<p>Alec Stevens wrote:
<blockquote TYPE=CITE><style></style>
<font face="Arial"><font size=-1>Hello,</font></font> <font face="Arial"><font size=-1>Does
anyone know of published research that relates motor efficiency to percent
load as well as drive frequency?</font></font><font face="Arial"><font size=-1>We
have motor curves for efficiency vs. percent load, but these curves all
assume a nominal speed that is being maintained as load decreases.
What happens to your motor efficiency when you are also changing the drive
frequency?</font></font> <font face="Arial"><font size=-1>Thanks for
any leads.</font></font><font face="Arial"><font size=-1>Sincerely,</font></font> <font face="Arial"><font size=-1>Alec
Stevens, PE</font></font>
<br><font face="Arial"><font size=-1>DMI</font></font>
<br><font face="Arial"><font size=-1>450 Lexington St, Newton, MA 02466</font></font>
<br><font face="Arial"><font size=-1>p: 617-527-1525 x105 f: 617-527-6606</font></font>
<br><font face="Arial"><font size=-1>e: <a href="mailto:astevens@dmiinc.com">astevens@dmiinc.com</a></font></font></blockquote>
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