[Equest-users] Centrifugal Chiller Curves

Nicholas Caton ncaton at catonenergy.com
Wed Apr 8 16:55:08 PDT 2015


With respect to WSE, my practice to handle simultaneous chiller/WSE
operations is to “roll my own” waterside economizer
“chiller/heat-exchanger” leveraging load management inputs.  I’ve attached
a discussion wherein I provided an outline for a starting point, and have
also copied that text below this response since my attachments haven’t been
working of late.

In short, you should be able to have your WSE operation function
independently of the other chillers on the same loop.  It will be up to you
to build on this framework to be sure to account for the pumping/fan
energies/additional head associated with that “free cooling” operation (as



*Caton Energy Consulting*
  1150 N. 192nd St., #4-202

  Shoreline, WA 98133
  office:  785.410.3317


Hi Nikola, good to hear from you!

An approach I like to start with (sometimes this is a rough approximation,
other times it is very accurate & appropriate), is:

1.       Establish an outside temperature at and below which the waterside
economizer is designed to handle the building’s cooling loads (or largely

2.       Create a “free cooling” chiller with an EIR a hair above zero
(something like 0.0000001), attach it to the CHW loop(s) servicing your
coils, alongside the regular chiller(s)

3.       Create a pair of equipment control sequences:  “Free” and “Normal”

a.       For the “Free” control sequence, assign the “free cooling chiller”
in the first row to handle loads first. You may optionally also assign the
actual chillers and associated capacity ranges for each.

b.      For the “Normal” control sequence, specify your normal chiller
sequence of operations

4.       Then create a Load Management of type OA-TEMP.

a.       Set the outside air temperature below which free cooling is active
under management sequence 1, and assign the free cooling control sequence
defined in the previous step.

b.      Set management sequence 2 to a maximum OSA temp of 999, and assign
the normal control sequence from the previous step

Integrating WSE into eQuest is one of those things I always plan on
spending extra time on – the devil is in the details!  I don’t believe
waterside economizer systems are something you can make a simple rote
procedure around, as actual waterside economizer system
operations/limitations are varied and nuanced.  Consider this a simple
outline to convey the approach concept & get you started.  I would
particularly advise paying close attention to your pumping and heat
rejection energies from this point forward.

Hope that helps get you started - Happy new year!



*Caton Energy Consulting*
  1150 N. 192nd St., #4-202

  Shoreline, WA 98133
  office:  785.410.3317


*From:* Equest-users [mailto:equest-users-bounces at lists.onebuilding.org
<equest-users-bounces at lists.onebuilding.org>] *On Behalf Of *Nikola Kravik
*Sent:* Tuesday, December 30, 2014 8:45 AM
*To:* equest-users at lists.onebuilding.org
*Subject:* [Equest-users] Water side economizer

Hi eQuest users,

Can you please share your experiences with implementing WSE successfully
and workarounds in v3.65?

Thank you,


Nikola Kravik, BEMP, LEED AP

Energy Engineer

ASHRAE Golden Gate BOG

IBPSA USA San Francisco Committee

*Willdan Energy Solutions*

*Celebrating 50 years of service*

6120 Stoneridge Mall Road, Suite 250
Pleasanton, CA 94588

T. 925.416.4200 ext. 1228
D. 925.416.4228

C. 925.719.5883
F. 925.737.0174

Email: nkravik at willdan.com


*From:* Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] *On
Behalf Of *Brian Fountain
*Sent:* Wednesday, April 08, 2015 4:12 PM
*To:* jordan jackson; Michael Busman; equest-users at lists.onebuilding.org
*Subject:* Re: [Equest-users] Centrifugal Chiller Curves

DOE-2.3 (eQUEST 3.70) does serial chillers. DOE-2.2 does not and as you
observed the WSE will only work when it can take all the load. Have not
tried. The DOE-2.3 WSE in series.

*From: *jordan jackson

*Sent: *Wednesday, April 8, 2015 6:31 PM

*To: *Michael Busman; equest-users at lists.onebuilding.org

*Subject: *Re: [Equest-users] Centrifugal Chiller Curves


Thanks for the spreadsheet. That is definitely more elaborate than the one
I put together.

I was able to successfully model air-cooled screws using the spreadsheet I
attached, but the issue I'm running into with the water-cooled centrifugals
is that the capacity provided by the rep does not change as a result of
entering condenser water temperature. KW changes, but tonnage does not.
This creates an unrealistic curve for CAPFT and EIRFT.

I'm at the mercy of the reps to provide this data and so far I have struck
out. I was just curious if there was something I'm missing. Does something
need to be held constant that will allow the capacity to change based on
entering condenser water temperature and leaving chilled water temperature?

On a similarly frustrating note... I'm trying to come up with a workaround
to model series chillers in eQuest with free cooling on the upstream
chiller. From reading the DOE manual it seems waterside economizer won't do
what I need it to since I can't be in WSE and supplementing with the
downstream chiller. I considered combining performance of the two chillers
into one machine, but I haven't totally figured out how that will work.

Any ideas are welcome.


Jordan Jackson.

On Tue, Apr 7, 2015 at 8:44 AM, Michael Busman <mbusman at opterraenergy.com>


Many, many years ago I used to do a lot of modeling in VisualDOE.  I don’t
do much in eQUEST or other simulation program anymore.

Anyway, I’ve attached a spreadsheet I put together way back when that is
based on calculation methodology that was published by Pacific Gas &
Electric.  If you look through the tabs you’ll see that I have some sample
data that is used to calculate the curve coefficients.  Originally it was
based on a constant speed chiller, however, a few years ago I added a tab
for a variable speed chiller.

Don’t expect the manufacturers’ reps to produce the curves for you but they
should be able to generate the data you need.  Key to this for reasons I
don’t recall is that the reps need to generate at least 10 data points of
full load data at different chilled and condenser water temperatures in
order to map the chiller.  You will also need several part load data points
at different water temps also.  If you give the reps the blank data sheet
they should be able to run their software to generate the data you need.

Browse through the spreadsheet tabs and hopefully it will make sense to
you.  Any questions, I’ll do my best to answer you, however, please
remember that it’s been a long time since I’ve developed custom curves.

My best,


*Mike Busman, C.E.M.*

Lead Project Engineer

765 The City Dr South Suite 475

Orange, CA 92868

T.   657-216-3261

M. 310.387.2083

mbusman at opterraenergy.com

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*From:* Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] *On
Behalf Of *jordan jackson
*Sent:* Monday, April 06, 2015 3:55 PM
*To:* equest-users at lists.onebuilding.org
*Subject:* [Equest-users] Centrifugal Chiller Curves

I have been using eQuest to evaluate chiller performance for retrofit
projects. I have not had a problem modeling air-cooled, but I can't seem to
get the data from the reps that I would like for water-cooled centrifugal
projects. I have settled on using standard curves for CAPFT and EIRFT and
using a cubic curve with coefficients created through a curve fit in excel

The manufacturers reps aren't able to produce a capacity or EIR curve as a
function of temperature (entering condenser water temp). Has this been
everyone's experience with this.

I'm attaching the excel file I created to calculate all of this.

Any feedback is appreciated. I'm just concerned about the data I'm
reporting to the client without touching those curves.


Jordan Jackson.
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