[bldg-sim] Turning one number into four..

Busman, Michael mbusman at noresco.com
Thu Feb 8 15:46:54 PST 2007


John,

I could be wrong, but this is my rough understanding of how IPLV is
calculated.

The kW/ton at the different load points are multiplied by an assumed
weighting factor % that may or may not represent the amount of time
spent operating at that load point.  The product of the kW/ton and
weighting factor are added up to get the IPLV.  The kW/ton has an
inherent assumption of condenser relief of a varying amount for air or
water-cooled machines for each % load reduction.  The reality of this is
also questionable if you are comparing performance in Houston and the
less humid Southwest.

I'm not aware of any software that spits out your chiller curves from a
single IPLV value.  If one existed, I would still be a bit skeptical
based on the potential slop that can go into the IPLV.  You might just
have to find a chiller that meets the COP and IPLV requirements and get
the mfg. local sales engineer to run you enough full and part-load data
at varying CHW and CW temperatures so that you can create the curve
coefficients yourself.

Good luck, old buddy.

Mike Busman
NORESCO

-----Original Message-----
From: bldg-sim at gard.com [mailto:bldg-sim at gard.com] On Behalf Of Aulbach,
John
Sent: Thursday, February 08, 2007 2:54 PM
To: bldg-sim at gard.com
Subject: [bldg-sim] Turning one number into four..

Hi all:

The infamous "one equation, four unknowns".  Namely, IPLV (or NPLV, if
you are of that persuasion).

Utility incentive Programs and LEED say to use an ASHRAE 90.1-2004 code
chiller with a COP of xx and an IPLV of xx. As I understand it, IPLV is
a curve created as a standardization to compare chiller part load
characteristics, one to another.  However, no analysis program that I
know of (certainly not of the DOE-2/eQuest flavor) can extract such a
curve from a single number.

I believe you are losing out if a new high efficiency chiller with a 4
mile long condenser (just kidding) happens to perform quite well at part
load. You will not get a fair comparision, only the default program
curves.

Is there some accepted ASHRAE magic that will take an IPLV number and
make the 75%, 50%, and 25% kW/ton numbers, so that a true "apples and
apples" comparison between a code chiller and a super chiller can be
made?

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