[Equest-users] using IPLV in eQuest

[Paul Diglio]

Nick:

I agree with your analysis.  A curve built using different kW/Ton for the four 
different load ratios that are used in the IPLV calculation would be sufficient.

I would just be careful when creating a curve that uses different condenser 
water supply temperatures.  It is more of a design issue.  There has to be a 
reason why the condenser water temperature varies.  It will effect the lift and 
kW/Ton.  For example, current chillers will tolerate a much lower condenser 
water temperature.  Does this mean that it is more efficient to provide the 
lower condenser water temperature?  Not necessarily, since energy will be wasted 
running the cooling tower fans to achieve the lower temperature and energy will 
be wasted for the hot-gas bypass to bring the condenser pressure up.

In my experience, the lower condenser water temperature is most often an issue 
on chiller start-up in cold weather.  Some chillers will surge until the chiller 
warms the condenser water loop.  Surging sounds like someone with advanced COPD 
breathing.  


So, if Rohini's chillers are supplied with a nearly constant condenser water 
temperature, the EIR f(PLR&Lift) would not be critical.

Please see attached modeling data from Trane for a CVHE 450 ton chiller.  All 
the data to build the various curves is shown.  Note the difference in condenser 
bundle pressure drop for standard flow v. minimum flow.  Much energy can be 
saved with a variable condenser water pumping strategy. 


This data was used to calculate the loss of chiller efficiency due to reduced 
condenser water flow.  In this particular project, I had three existing 
chillers.  Total savings realized by the variable condenser water scenario was 
250,000 kWh/Year.  The reduced chiller efficiency consumed 50,000 kWk per year 
so the net energy savings was 200,000 kWh/Year.  Notice that the condenser water 
temperature varies in the data.  That was based on the maximum heat rejection of 
the towers during the cooling season with a minimum of 65 degrees condenser 
water supply temperature.  If I assumed a constant 78 degrees condenser water 
supply temperature the kW/Ton values would be much different.

It takes a little time to find the right person to provide this chiller data, 
but it is well worth it.

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 4:38:43 PM
Subject: RE: [Equest-users] using IPLV in eQuest

 
Thanks very much for the informed response, Paul!  
 
With all respect, I want to be sure I’m picking up the right lessons here =):
 
Accepting the arbitrary nature of IPLV ratings, what I’ve proposed for Rohini’s 
case is to define a curve that will utilize his model’s unique annual part-load 
profile (tossing IPLV’s weightings out the window), and would isolate the 
effects of PLR to make his equipment comparison.
 
Am I correctly understanding that any comparative analysis that isolates only 
the effects of part-load in comparing two chillers is pretty much pointless?  

 
I am not trying to make a case that lift, variable flows, and their effects on 
capacity and efficiency are not important (and I have also experienced responses 
all over the map from different manufacturers).  I agree that at least 
considering all of these in many cases is necessary when one wants to model 
accurate behavior, particularly from a commissioning/servicing context.  With 
all other things being equal, I’m however proposing these factors shouldn’t be 
critical if the specific goal is to determine whether chiller A or chiller B 
fits a model’s part load profile better.
 
So to clarify and make our bridges meet:  Is it critical that Rohini creates an 
EIR-fPLR&dT curve for his analysis (between two screw chillers with everything 
else presumed identical), or is it fair to say this may be overkill considering 
what he’s trying to achieve?
 
I for one will continue the good fight to obtain more solid input data for my 
curves, sometimes I have to settle for “the best I can get” with the people I’m 
supposed to be talking to, but your experiences are further motivation to try to 
find the right people =)!
 
Thanks again,
 
~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 2:58 PM
To: Nick Caton; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] using IPLV in eQuest
 
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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