[Equest-users] Constructing chiller part load curves

Wed Jan 19 09:00:37 PST 2011

Hi Afaan,

The first table below contains the sort of information you will need to
make a centrifugal EIR curve, but as David says you're lacking in the
minimum # of data points.  I believe the bare minimum to extrapolate an
accurate bi-quadratic curve would require 9 rows of data (minimum 3
PLR's for a minimum 3 dT's), though you should probably use the maximum
number of data entry points permitted when allowing eQuest to determine
the coefficients (20 per curve).  

dT is simply the difference between the chilled and condenser water
temps.

I'm not sure exactly what we're looking at in the second table, but it
doesn't look like data for creating a curve...  If you want to make
CAP-FT and EIR-FT curves (and if you don't, that's okay too - see below)
you'll need a rep who understands and can provide you with "maximum
capacity" (not the designed capacity, or where PLR = 1.0) and power
drawn under different conditions.  I've previously selected 5 CW temps
and 4 CHW temps around and including the design conditions being
normalized to, totaling the maximum 20 data entry points we're permitted
to input.  

The attached email contains an overview of materials you should review
to understand the process of custom chiller curve creation (includes a
reference to the same EDR guideline David brings up below).  Once you
feel comfortable understanding the required data collection described
towards the end of the referenced EDR chapter, you might do well to also
read through a fairly lengthy discussion on this list that I started:
"Chiller Curves (oh boy!)."   There, I eventually provided an
illustrated breakdown of each default curve and its
function/implications, eventually realizing and providing visuals of
their combined effects analogous to what equipment reps often provide
for "chiller efficiency curves."  You should be able to follow this
discussion from start to finish, and should come away knowing exactly
what eQuest is doing "under the hood" moving forward.  Carol Gardner
also provided a writeup within that discussion that is similar to the
EDR... oh I see she just posted it again =)!

One final suggestion:  Your collected data suggests a possible pitfall -
if you want to make the CAP-FT and EIR-FT curves, you MUST gather data
for multiple CHW temps, even if the design should only ever call for 44
degree water to be produced.  If you don't understand why, then honestly
you need further review of what the curves are functionally doing - see
suggested reading above and attached.  

If you and your reps are struggling with producing the data required to
make CAP-FT and EIR-FT curves, it's advisable to stick with the
defaults, and ensure your custom EIR-fPLR&dT curve entries are all
normalized to ARI rather than a design condition.

Best of luck!

~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: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of David
Eldridge
Sent: Wednesday, January 19, 2011 7:38 AM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Constructing chiller part load curves

You may want to run through this document before you get too much
further.  Skip ahead to "Part 2" of the document.

http://www.energydesignresources.com/media/2654/EDR_DesignGuidelines_%20
HVAC_Simulation.pdf

In a nutshell - you should acquire a few more data points to develop a
more comprehensive matrix.  Right now your matrix would be equivalent to
a line through the middle of possible conditions, you need to extend
your data set over a wider range of water temperatures and load
conditions.

David

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, HBDP

Project Manager

Direct: (847) 316-9224 | Fax: (847) 328-4550

http://www.grummanbutkus.com

Grumman/Butkus Associates | 820 Davis Street, Suite 300 | Evanston, IL
60201

Energy Efficiency Consultants and Sustainable Design Engineers

From: equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] On Behalf Of Afaan Naqvi
Sent: Tuesday, January 18, 2011 8:33 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Constructing chiller part load curves

After browsing the forums, it seems there are many users that have
constructed custom chiller curves based on selection data. I believe I
have all the data I need to do this, but am coming up with polynomial
coefficients and hourly results that do not make sense at all. Can
someone please walk me through how to go about building the 3 curves for
a centrifugal, water cooled chiller with a VSD based on the following
data:

% Load

Capacity

kW in

Perf

Evap T in

Evap T out

Conden T in

Coned T out

100

85

53.6

0.63

54

44

85

94.8

75

63.8

29.8

0.47

51.5

44

75

82

50

42.5

13.3

0.31

49

44

65

69.5

25

21.3

6.9

0.32

46.5

44

65

67.2

I believe the additional data I need is calculated below, except for the
dT term which I am unclear on:

Load

PLR

kW

f PLR

85

1

53.6

1

63.8

0.751

29.8

0.556

42.5

0.500

13.3

0.248

21.3

0.251

6.9

0.129

Not sure if the dT term required by the curves is the difference in
condenser supply and return, or condenser and evaporator supply,
condenser supply and evaporator return, etc. Can someone please clarify?

Thanks

Afaan Naqvi  PE  LEED AP

____________________________________________________________
Electronic mail messages entering and leaving Arup  business
systems are scanned for acceptability of content and viruses

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