[Equest-users] Chiller ROI - HELP!

[Paul Riemer]

IPLV and NPLV values are not perfect by any means but I think you should get comfortable with what they represent before you try to use a detailed energy model to overcome their short comings.

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 3:11 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<mailto: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)
www.ghtltd.com<http://www.ghtltd.com/>


From: equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org> [mailto: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<mailto: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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