[Equest-users] Chiller ROI - HELP!

[Jim Marsh]

Brett, attached are some example kw/ton curves for existing chillers on a
recent project.  Chiller #1 is a 250 ton unit, and chillers 2 thru 4 are 550
ton units.  Chillers 1 and 2 are ~ 15 years old, and chillers 3 and 4 are
newer with better efficiencies.  All 4 chillers are water cooled.  The
curves show efficiencies with and without Adjustable Frequency Drives.  It's
hard to tell the difference between the "w/AFD" and "w/o AFD" curves, but
the "w/AFD" curves have a lower kw/ton except at full load.
 
Jim Marsh, PE, LEED AP
SEG, Inc.
2550 Walsh Avenue
Suite 120
Santa Clara, CA 95051
Desk: 408 260 8008 Ext 210
Cell: 408 656 3096
Fax: 408 260 8018
 <http://seg-corp.com/> http://seg-corp.com/
 
 
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From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Pasha
Korber-Gonzalez
Sent: Thursday, April 01, 2010 1:11 PM
To: James Hansen
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Chiller ROI - HELP!


Brett,
 
to get better part load data and efficiency of your proposed chiller
replacement, call your chill sales engineer and ask them to generate a part
load performance report for you in 10% unloading increments, then you can
see the decrease in performance efficiency for each part-load step of the
chiller.  Also be sure that you recognize if you are looking at RATED
Conditions (which means chiller performance at ARI standard conditions), or
at DESIGN conditions (which are your project's specified operating
conditions--this would account for part load efficiencies if you were
running a 12-or 14 Degree delta-T across your chiller.)
 
Before you set up a new performance curve you will need to get this data
supplied from the manufacturer.
 
Pasha


On Thu, Apr 1, 2010 at 2:01 PM, James Hansen <JHANSEN at ghtltd.com> wrote:


KW/ton drops off with decreasing part load, and since the chiller isn't
always operating at ARI full load conditions, you can't just divide total
chiller energy consumption (in KWH) by the total cooling load (in btu) and
hope to get anywhere near the full load rated KW/ton.

 

As you go about this ROI study, make sure that when you are analyzing your
proposed chiller replacement, that you create a custom EIR vs PLR curve
based on manufacturer's data, otherwise you're using a default DOE-2 curve
that isn't necessarily correct.

 

Furthermore, to make the study worthwhile, the existing chiller model really
needs to be normalized as best as possible to actual building operating
conditions.  You can get away without doing it for a simple comparison, but
it would be more accurate if you normalized to utility bills.

 

GHT Limited
James Hansen, PE, LEED AP

Senior Associate

1010 N. Glebe Rd, Suite 200

Arlington, VA  22201-4749

703-338-5754 (Cell)

703-243-1200 (Office)

703-276-1376 (Fax)

 <http://www.ghtltd.com/> www.ghtltd.com

 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Brett
Sanicola
Sent: Thursday, April 01, 2010 2:38 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Chiller ROI - HELP!

 

I've been attempting to calculate a simple ROI for a new 250 ton chiller our
client wants to install to replace his older chiller.  I ran the simulation
for the default "high rise hotel" construction which, to my luck, is quite
similar to the actual building.  The detailed results, however, are not
making sense to me.  Specifically, when I look at Equipment Loads and Energy
Use for the Chiller, the Elec Use and Cool Load don't coincide given the
default Chiller efficiency of .67kw/ton.  For example they give a Chiller
Elec Use of 535453 KWH and a Cool Load of 3294 MBTU.  However, according to
my calculations, at .67KW/TON, 535453 KWH should give me closer to 9590
MBTU.  I see most of the hours are in part load range, but does the
efficiency drop off that dramatically at part load that it would explain the
discrepancy?  Which numbers should I base my analysis on, the Cool Load
number or the Elec Use number.

 

Also, on the same page (Equipment Loads and Energy Usage), it gives me a
peak load of 2436 KBTU/HR.  However, when I go to the section titled
"Building Peak Load Components" the peak cooling load is significantly less
(1619 KBTU/HR)

 

At this point, I have no idea what any number represents, since I don't know
how it was calculated.

 

I greatly appreciate any help!  Thanks.

 

Respectfully,

 

Brett Sanicola

Engineer

ASB Engineering

(516) 785-4200



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