[Equest-users] Constructing chiller part load curves

[Afaan Naqvi]

Thanks to all for the feedback. It seems all are in agreement that I need more data points, and also data points at CHW supply temperatures other than 44 F, even if other CHW temperatures are not supplied. A follow up question then, is where in e-Quest would you enter 20 (or even 9 ) data points? When I look into constructing a curve there are only 4 possible entries for dependant, delta T and independent data points.

To give this some context, I am trying to model Smardt chillers which are marketed to have superior part load performance which I am not sure is being captured by the default library chiller curves.

Thanks again for your help.


Afaan Naqvi  PE  LEED AP

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Wednesday, January 19, 2011 9:01 AM
To: David Eldridge; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Constructing chiller part load curves

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

[cid:image001.jpg at 01CBB7B9.8CAF69D0]

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_%20HVAC_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> [mailto: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<mailto: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
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