[Equest-users] Chiller ROI - HELP!

[Brett Sanicola]

Thanks!  I was starting to conclude that as well, but then I spoke to
Carrier, and they said that there is no way that it would drop off that
significantly.  For example, they said they have a unit that is full
load rated at .6KW/ton and .7KW/ton down to 25% part load.  The numbers
I'm getting is nearing 2KW/ton, even though the full load rating remains
at .67KW/ton.  I did mention that the vast majority of my hours are
operating below the 10 percent part load, but he still said it wouldn't
be that high.  Any thoughts?

 

Respectfully,

 

Brett Sanicola

Engineer

ASB Engineering

(516) 785-4200

From: James Hansen [mailto:JHANSEN at ghtltd.com] 
Sent: Thursday, April 01, 2010 4:02 PM
To: Brett Sanicola; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Chiller ROI - HELP!

 

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)

www.ghtltd.com <http://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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