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<HTML><HEAD><TITLE>Major disagreement on Chiller Performance Curves in DOE-2.1E and DOE-2.2</TITLE>
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<DIV><FONT face=Arial size=2>Unfortunately, the ARI data for performance at
partial loads is not useful in an hourly simulation program, precisely because
it makes an assumption about reduced condenser temperature at reduced
load. The assumptions in the ARI curve might be reasonable for a single
chiller in a given building and climate, and where you allow the condenser
temperature to drop with load and wetbulb. However, many plants have more
than one chiller, the cooling tower(s) may be controlled to a fixed
condenser temperature, and/or you might be running the chiller in Florida
vs. New Mexico, which have very different load/wetbulb
relationships.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>It would be useful if ARI recognized these
issues, and developed a standard method for reporting chiller performance for
use in hourly simulation programs (the same problem also applies to packaged
rooftop equipment). </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Note that "standard" ratings assume the evaporator
is operating at 44F leaving temperature and 2.4 gpm/ton, and the
condenser is operating at 85F entering and 3.0 gpm/ton. However a
centrifugal chiller is custom built to the engineer's specifications. A
chiller in a low-wetbulb climate may be configured to run with 75F entering
condenser water, and will surge if operated at 44F/85F. In other words,
many centrifigal chillers cannot operate at the "standard"
conditions!</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The default curves in recent versions of 2.2 are
based on a manufacturer's proprietary data. They are an improvement
over the 2.1e curves, but do not necessarily represent all chillers and all
manufacturers.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>DOE-2 uses three curves to model chiller
performance. The use of these curves is documented in the Topics
manual. More recent versions of 2.2 modify performance for off-rated
condenser flow. In addition, the PLR curve includes a second term
(PLR,dT) to model the condenser relief necessary to achieve savings with a
variable-speed drive.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=JAulbach@semprasolutions.com
href="mailto:JAulbach@semprasolutions.com">Aulbach, John</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=BLDG-SIM@GARD.COM
href="mailto:BLDG-SIM@GARD.COM">BLDG-SIM@GARD.COM</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, October 15, 2003 11:23
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [BLDG-SIM] Major disagreement on
Chiller Performance Curves in DOE-2.1E and DOE-2.2</DIV>
<DIV><BR></DIV>
<P><FONT size=2>I am having a "friendly" disagreement with a colleague on what
chiller curves to ask for from a manufacturer to input into DOE-2 (could be
either 2.1E or 2.2). We both agree that the infamous ARI point for a 100% load
should be input. But the curves are where we disagree.</FONT></P>
<P><FONT size=2>Is the Default DOE-2 curve for % Power versus % Tons the ARI
curve with the allowable reduction in condenser water temperature, or is it
based on the FIXED 85°F entering condenser water and FIXED 44°F leaving
chilled water ALL the way down the curve?</FONT></P>
<P><FONT size=2>Therefore, when I am given a chiller with a variable speed
drive installed, what parameters should I ask for in such a Power/Tons to be
FIXED ???</FONT></P><BR><BR><BR><BR>
<P><FONT size=2>John R. Aulbach, PE, CEM</FONT> <BR><FONT size=2>Project
Engineer</FONT> <BR><FONT size=2>Sempra Energy Solutions</FONT> <BR><FONT
size=2>555 West Fifth Street</FONT> <BR><FONT size=2>Mail Location 27F3</FONT>
<BR><FONT size=2>Los Angeles, CA 90013</FONT> <BR><FONT size=2>Tel: (213)
244-8551 Cell (213) 219-4875</FONT> <BR><FONT size=2> </FONT> </P>
<P><FONT size=2>"Sempra Energy Solutions is not the same company as SDG&E/
SoCalGas, the Utilities. Sempra Energy Solutions is not regulated by the
California Public Utilities Commission, and you do not have to buy Sempra
Energy Solutions products or services to continue to receive quality regulated
service from the Utilities." </FONT></P><PRE>
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