[Equest-users] using IPLV in eQuest

Fri Feb 25 12:58:27 PST 2011

Nick:

I come from a mechanical contracting and service  background.  Condenser water 
temperature is a hotly debated item.  Some  manufacturers define a very narrow 
range of acceptable condenser water  temperature and others define a very narrow 
range of the temperature  difference between entering and leaving condenser 
water temperature.

During one investment-grade audit I performed recently, Trane told me that the 
condenser water dt can be no less than 5 degrees for maximum efficiency on the 
650 ton CVHE chillers I  was working with.  The water temperature could be 
anywhere to 50-80  degrees.  This machine had hot-gas bypass to keep the head 
pressure up.

Other chillers that I have overhauled require a very narrow band of  condenser 
water temperature, such as 75-78 degrees supply temperature.   So modeling a 
wide condenser water range does not make much sense to me  since it is not a 
real world application.  The chillers I have worked on  either have a tower 
bypass loop or a hot gas bypass to keep the  condensing pressure up where it 
belongs.  Energy is wasted when too cold a condenser water temperature is 
specified.

Other manufacturers say the colder the better.

Specifying variable primary chilled water flow and variable condenser  water 
flow has a large impact on chiller efficiency.  I ask the  manufacturers to 
provide me the kW/Ton for minimum flow, standard flow  and maximum flow for the 
evaporator and condenser bundles.  A chiller  that has an kW/Ton of .56 at AHRI 
conditions can often have a 1.3 kW/Ton  at minimum condenser flow (3 gpm/ton) at 
30% load.

The IPLV is really a useless rating for a real world application since  it 
assumes a certain percentage load a certain percentage of the time.   It all 
depends on the design of the system and the load profile.  It is a  good rating 
to compare various chillers if they conform to the load  profile.  I see more 
chillers that run in the 40-60% range 90% of the  time than I see chillers that 
match the IPLV conditions.

During my investment-grade reviews with our local utility, the lift of the 
chiller is always an important consideration.

There was an e-mail for someone, I believe York, that offered to model  any 
manufacturers chiller on this forum a few months ago.  I have had  good luck 
getting the rep to provide the information that I requested as  long as I find 
the right person.

Paul

________________________________
From: Nick Caton <ncaton at smithboucher.com>
To: Paul Diglio <paul.diglio at sbcglobal.net>; equest-users at lists.onebuilding.org
Sent: Fri, February 25, 2011 2:50:44 PM
Subject: RE: [Equest-users] using IPLV in eQuest

Paul, I may not have been crystal-clear, but if someone is merely making a 
comparative analysis between two screw chillers, aren’t the relative effects of 
varying lift between the two chillers negligible?  My general understanding is 
that lift is a more critical variable when comparing VSD centrifugal chillers…  
This is why I suggested a simpler EIR-fPLR curve would be sufficient in lieu of 
an EIR-fPLR&dT – I was trying to simplify Rohini’s comparative analysis.

I’d agree that an EIR-fPLR&dT curve would be more precise and more appropriate 
if the goal is to better match the chiller behavior (and creating custom CAP-FT 
and EIR-FT would be even better), but I was thinking this would require an 
unnecessary amount of extra work for Rohini’s comparative purpose.

My “suggested information to request” below for constructing EIR-fPLR&dT curves 
is based on my past experience with limitations of my local manf. rep’s software 
– they need to set certain items constant to get the numbers to crunch…  Have 
you had luck collecting PLR runs where the evaporator and/or condenser temp was 
allowed to float?  I’ve picked up through the lists that a better way to skin 
the cat may be to approach the chiller controls reps where they may exist, as 
they may have more flexible software…

I throw this disclaimer out sometimes:  I certainly haven’t been doing this for 
decades!  If I’m misunderstanding something, I very much welcome corrections 
;).  

Thanks,

~Nick

NICK CATON, E.I.T.
PROJECT ENGINEER
Smith & Boucher Engineers
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
www.smithboucher.com

From:Paul Diglio [mailto:paul.diglio at sbcglobal.net] 
Sent: Friday, February 25, 2011 12:44 PM
To: Nick Caton; James Waechter; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] using IPLV in eQuest

Actually what everyone is calling dt is more accurately referred to as lift.  It 
is the difference between the saturated evaporating temperature and the 
saturated condensing temperature, which is different than the condenser water 
temperature and the evaporator water temperature.

A more accurate curve can be built if you have the chiller manufacturer model 
both these variables for you, rather than leaving the evaporator water 
temperature constant and just varying the condenser water temperature.  Any 
change in the evaporator pressure will effect the condensing pressure and any 
change in the condensing pressure will effect the evaporator pressure.
Paul

________________________________

From:Nick Caton <ncaton at smithboucher.com>
To: James Waechter <jamesw at McKinstry.com>; equest-users at lists.onebuilding.org
Sent: Fri, February 25, 2011 1:21:42 PM
Subject: Re: [Equest-users] using IPLV in eQuest
James et al,

Rohini will need to create performance curves to make this particular 
comparison.  Otherwise using the default curves will result in identical part 
load performances.

The following is excerpted from the following (short) recommended reading 
concerning what IPLV means:  
http://ashrae-cfl.org/2010/03/understanding-iplvnplv/
IPLV (or NPLV) = 0.01A+0.42B+0.45C+0.12D
Where:
A = COP or EER @ 100% Load
B = COP or EER @ 75% Load
C = COP or EER @ 50% Load
D = COP or EER @ 25% Load
John is saying knowing only the IPLV and the 100% load condition efficiency 
(variable ‘A,’ above) is not enough information to extrapolate the IPLV curves 
to compare the two chillers.  

For the exercise of comparing the two non-centrifugal chillers of the same 
technology/type, I would just focus on making a custom EIR-FPLR (not 
EIR-fPLR&dT) for each chiller, and use the library CAP-FT AND EIR-FT curves.  My 
understanding is the effects of temperature on capacity and EIR outside of 
centrifugal VSD chillers is negligible.  NOTE:  Whenever using any of the 
default library chiller performance curves, that means you MUST normalize to and 
specify the chiller at ARI conditions – those curves aren’t normalized to 
anything else.

So!  If you can find the IPLV A, B, C and D values for both chillers’ curves, 
you could come up with your EIR-FPLR curve coefficients (curve type = quadratic 
or cubic) using a curve-fit in excel… or alternatively make eQuest figure the 
coefficients by entering those points as raw data.

You may more easily just make your own curves, following John’s advice and 
getting part load unloading curves (100%, 90%, 80%... etc) held at a constant 
chilled & condenser temperature to match the ARI* conditions (85CWT if this is 
water cooled) at which you’re specifying the chiller capacity/EIR.  Again, you 
could either go into excel, normalize the data (review DOE2 help entry for 
EIR-FPLR), make a scatter chart, and get the coefficients using a curve fit… or 
enter the data as raw points into eQuest and the coefficients will be figured by 
eQuest… whatever makes more sense to you.

For others and personal future reference…. If you are looking to make an 
EIR-fPLR&dT curve (for centrifugal chillers or otherwise):  Ask your rep instead 
for multiple (minimum 3) part load unloading runs, holding the delivered chilled 
water temp constant, and vary the condenser water temperature incrementally for 
each run (i.e. 85, 75, 65).  Choose a range of CWT’s that cover the anticipated 
range to be encountered in the actual design. This will get you enough data to 
have the minimum 3 delta-T’s represented in your part load data points to build 
this curve correctly.  You’ll be using eQuest “raw-data” entry method to make it 
generate the coefficients.

~Nick

* Rather than ARI conditions (85F CWT), you could be normalizing to Design 
condition EIR/CAP, provided you’re making a full set of custom curves in the 
same fashion.

NICK CATON, E.I.T.
PROJECT ENGINEER
Smith & Boucher Engineers
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
www.smithboucher.com

From:equest-users-bounces at lists.onebuilding.org 
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of James Waechter
Sent: Friday, February 25, 2011 10:55 AM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] using IPLV in eQuest

John,

If the only parameter Rohini enters into the program is the full-load EIR – 
which he said is the same for both chillers – how will eQuest know to bend the 
curves differently for the two chiller options.  It is my understanding that 
program would use the same chiller efficiency curves for both machines even 
though their IPLVs are different.

In order to overcome this issue, are you saying Rohini should get chiller 
performance data from each of the manufacturers and enter his own custom 
curves?  I recall there was a discussion on that topic a few months back.

Regards,
James Waechter Jr., P.E., CEM, LEED A.P.
Energy Engineer – Rocky Mountain Region
p 303 215 4062 | m 727 686 3248
McKinstry
Consulting | Construction | Energy | Facility Services
www.mckinstry.com 

From:equest-users-bounces at lists.onebuilding.org 
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of John Aulbach
Sent: Friday, February 25, 2011 9:41 AM
To: R B; eQUEST Users List
Subject: Re: [Equest-users] using IPLV in eQuest

Rohini:

Won't happen. IPLV is a number which has one equation and 4 unknowns. Actually, 
three unknowns as you know the 100% point. You need a manufacturer's curve run 
at 85F constant condenser water temperature. Let eQuest do the curve bending 
after that. ARI curve won't work right.

John R. Aulbach, PE, CEM
Senior Energy Engineer

________________________________

PartnerEnergy
1990 E. Grand Avenue, El Segundo, CA 90245
W: 888-826-1216, X254| D: 310-765-7295 | F: 310-817-2745
www.ptrenergy.com| jaulbach at ptrenergy.com

________________________________

From:R B <slv3sat at gmail.com>
To: eQUEST Users List <equest-users at lists.onebuilding.org>
Sent: Fri, February 25, 2011 7:25:18 AM
Subject: [Equest-users] using IPLV in eQuest
Hi All, 
I would like to compare two screw chillers with same full load kW/ton and 
different IPLV kW/ton. I am using the full load number for the EIR. Where can 
the IPLV number be used? Is there some way to scale the performance curves to 
reflect different IPLV's?
-Rohini

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