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<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=852420619-11082008>For those interested, I think I figured out how to do
this (with some direction from Linda). I set up a "dummy" water-cooled
chiller with an associated drycooler for heat rejection. The chiller EIR
was set to 0, the condenser water circulating pump horsepower was set to 0, and
the EIR of the drycooler was set to the power that I think the air-cooled
chiller condenser fans will use during free-cooling
operation.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=852420619-11082008></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=852420619-11082008>I then set up two Equipment Control components called
"Greater than 38" and "Less than 38". "Less than 38" has my dummy chiller
set up to handle the load, and "Greater than 38" has my normal air-cooled
chillers set to handle the load. I then set up a Load Management
component. Management Seq 1 references the "Less than 38" Eqpm Ctrl with
the Max OSA Temp set to 38 degrees. Management Seq 2 references the
"Greater than 38" Eqpm Ctrl with the Max OSA Temp set to 110 degrees. (You
could set the switchover point to whatever you prefer).</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=852420619-11082008></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=852420619-11082008>I didn't spend that much time fiddling with this, but
it looks like it may have worked. My dummy chiller operates 6 hrs in
October, 19 in November, 106 in December, 149 in January, 133 in February, 47 in
March and 4 in April (Washington, DC area). That looks about
right.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=852420619-11082008></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=852420619-11082008>For reference, the utility bills dropped from $247,931
to $246,744 (for a 140,000 sq ft office building in DC). This worked out
to a 6% reduction in total space cooling energy for the year, but only about a
0.5% decrease in total utility bills.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=852420619-11082008></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=852420619-11082008>And this doesn't take into account the added pressure
drop across the air-cooled chiller condenser fans for the rest of the
year. This relatively minor increase in savings is probably why
free-cooling coils in air-cooled chillers in this climate are not particularly
favorable. And also why the took the economizer requirement out of
90.1-2004 and the 2006 IECC (for our climate zone).</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=852420619-11082008></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=852420619-11082008>I welcome any comments if I did something
incorrectly....</SPAN></FONT></DIV>
<DIV> </DIV>
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Limited<BR></SPAN></B><st1:PersonName><B><SPAN
style="FONT-SIZE: 11pt; FONT-FAMILY: Arial">James
Hansen</SPAN></B></st1:PersonName><B><SPAN
style="FONT-SIZE: 11pt; FONT-FAMILY: Arial">, <FONT size=2>PE, LEED
AP</FONT></SPAN></B></P>
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<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> bldg-sim-bounces@lists.onebuilding.org
[mailto:bldg-sim-bounces@lists.onebuilding.org] <B>On Behalf Of </B>James
Hansen<BR><B>Sent:</B> Monday, August 11, 2008 1:51 PM<BR><B>To:</B>
bldg-sim@lists.onebuilding.org<BR><B>Subject:</B> [Bldg-sim] Air-cooled chiller
economizer<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV><SPAN class=399204817-11082008><FONT face=Arial size=2>Does anyone have
insight on a relatively easy way to model free-cooling coils on air-cooled
chillers? I thought adding a drycooler might help simulate this, but I
don't even think you can attach a heat-rejection device directly to a chilled
water loop. Is this one of those things that you have to "estimate"
by approximating the total # of available free-cooling hours and
subtracting compressor energy?</FONT></SPAN></DIV>
<DIV><SPAN class=399204817-11082008><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=399204817-11082008><FONT face=Arial
size=2>Thanks</FONT></SPAN></DIV>
<DIV><SPAN class=399204817-11082008><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><B><SPAN style="COLOR: teal; FONT-FAMILY: Arial">GHT
Limited<BR></SPAN></B><B><SPAN style="FONT-SIZE: 11pt; FONT-FAMILY: Arial">James
Hansen</SPAN></B><B><SPAN style="FONT-SIZE: 11pt; FONT-FAMILY: Arial">, <FONT
size=2>PE, LEED AP</FONT></SPAN></B></DIV>
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align=left><SPAN style="FONT-SIZE: 11pt; FONT-FAMILY: Arial"><FONT size=1>1010
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