[Bldg-sim] Chiller part load raw data points into eQuest

Fred Porter FPorter at archenergy.com
Thu Dec 20 08:02:40 PST 2007


The way I "deal" with this is by using a spreadsheet I've built which
evaluates groups of the DOE-2.2 chiller curves at any combination of
temperatures and loads. In this situation I would evaluate a number of
DOE2 chiller curves' output EIRs and CAPs at the IPLV or NPLV condensing
and evaporating temperatures, delta Ts, and PLRs. Then compare these
with the rated values at the four "EIRs" given by the IPLV/NPLV values.
Then pick the curves with the best match (hopefully all in the same
family!). If that fails, simply make an educated guess of the difference
between reality and the model and correct the model result with that, or
try to create some better curves. If the real chiller seems to have much
better low-load performance, possibly model more chillers than the real
proposed case, though I have seen that backfire.
 
Having said that, I think USGBC should disallow any claims for improved
chiller (or really any equipment) part load performance vs the baseline
unless the manufacturer has supplied off-design performance data
adequate to characterize the chiller and usable in the analyst's
simulation program. For their part USGBC, ASHRAE, or the IRS need to
define similar off-design performance data that correspond with the
minimum performance IPLVs in Table 6.8. Maybe the USGBC could hire
someone quickly to do this with some of the million bucks they have
budgeted for "green bldg research." The ASHRAE App G text should
probably stick to the big picture. In the ACM, the California Energy
Commission has defined chiller curves for the T24 "standard" case model
(these evaluate to better than the ASHRAE minimum IPLVs) and they also
have some restrictions on claims of improved part load performance in
the "design" model. 
 
Fred Porter
AEC


>>> "Aulbach, John" <jaulbach at nexant.com> 12/19/2007 6:02 PM >>>
So I cannot "reverse engineer" a part load curve that uses condenser
water relief in calculating the points, knowing what condenser temps are
used at what part load point (100%, 75%, 50%, etc) ???

From: Steven Gates [mailto:steve.gates at doe2.com] 
Sent: Wednesday, December 19, 2007 4:57 PM
To: Aulbach, John; bldg-sim at lists.onebuilding.org 
Subject: RE: [Bldg-sim] Chiller part load raw data points into eQuest


Unfortunately the IPLV is of little or no value when setting up chiller
curves. To set up the EIR-fT and EIR-fPLR curves requires more data
points than is available in the IPLV. IPLV basically describes a
two-dimensional curve, whereas the actual chiller performance is
3-dimensional.  The IPLV assumes that condenser temperature drops as
chiller load drops, but this is not necessarily the case. Examples:A
cooling tower has a fixed setpoint of 85°F.  Or, the condenser water
source is a lake or river.  In this case condenser temperature does not
drop as chiller load drops. A large plant has 3 chillers utilizing a
single cooling tower.  The current load is 33% of design, so one chiller
is running at full load. IPLV assumes an entering condenser temperature
of 85°F (full load), whereas the cooling tower is actually lightly
loaded and can achieve a smaller approach to wetbulb. The building is on
the West coast (low wetbulb) vs. Florida (high wetbulb). Tower
performance and condenser temperature vs. load is entirely different in
these two climates. 

So while IPLV may be an interesting figure for rough comparisons, it is
insufficient for an hourly simulation program. This is true for all
energy simulation programs, not just eQUEST. Ultimately this issue will
need to be addressed by standards organizations such as ARI, and/or
equipment manufacturers.
Steve Gates
eQUEST development team


From:bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Aulbach,
John
Sent: Wednesday, December 19, 2007 4:04 PM
To: bldg-sim at lists.onebuilding.org 
Subject: [Bldg-sim] Chiller part load raw data points into eQuest

 
Hi Gang:
 
I have a part load curve from a chiller manufacturer for input into
eQuest. Unfortunately, it has condenser temperature relief (this is an
evaporatively cooled chiller, so we are speaking of dry bulb outdoor
temperatures.
 
Normally, I ask for a part load curve with a constant condenser
temperature, and let eQuest modify this curve based on changing outdoor
air conditions.
 
But now I have the IPLV data and it deals with condenser relief. I DO
have at what part load a particular condenser temperature occurs
(complimenting this IPLV data.
 
Can anyone help me?
 
John R. Aulbach, PE, CEM
Project Manager
Nexant, Inc.
100 North Barranca, Suite 820
West Covina, CA 91791 USA
Phone: 626-430-9054
Fax: 626-430-9060
email: jaulbach at nexant.com

 
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