[Equest-users] Baseline chiller unusual part load COP

[Daric Adair]

Rushi;

David beat me to it, those are good resources. But you might get a headache.
The default curves unloading unrealistically well is problem we are aware of and have run into many times. It has a real impact; chillers don’t unload like the curves describe.
For history, I believe the default curves are based on data from the COMNET 2011 reference guide, but don’t think I’ve been able to get to the root source of what chiller data they’re supposed to be based on. These are also reproduced in the PNNL Guides for ASHRAE 90.1-2010 & 2016. If any one knows original source for data, would love to review it.

The path I’ve taken typically is to either 1-run default curves in Proposed & Baseline if we can’t get data needed from a rep. 2- get Proposed Curve information and if the chiller types are the same in Proposed &  Baseline (Screw/ Centrifugal) use the same in both 3-if the rep will get us data for Proposed & Baseline, use that data.
The availability of generic, but realistic curves would greatly assist modelers.


Thanks,
daric adair

From: Rushi Quest <rushiquest at gmail.com>
Sent: Thursday, March 25, 2021 5:22 AM
To: David Eldridge <DEldridge at grummanbutkus.com>; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Baseline chiller unusual part load COP

Thanks David for taking out time to reply, will go through your suggestions and follow up for any further queries.

On Thursday, March 25, 2021, David Eldridge <DEldridge at grummanbutkus.com<mailto:DEldridge at grummanbutkus.com>> wrote:
Here’s another paper on the topic, the paper is old the methods should hold up if you make your own spreadsheet.
Tools and Techniques to Calibrate Electric Chiller Component Models (taylor-engineering.com)<http://www.taylor-engineering.com/wp-content/uploads/2020/04/ASHRAE_Symposium_AC-02-9-1_Electric_Chiller_Model.pdf>

David

David S. Eldridge, Jr., P.E., BEMP, BEAP, HBDP, GGA
Associate

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From: Equest-users <equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org>> On Behalf Of Rushi Quest via Equest-users
Sent: Wednesday, March 24, 2021 12:36 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Baseline chiller unusual part load COP

Hi everyone,

I am working on a office building project (e-quest 3.65-7175) in which baseline case is modelled following ASHRAE-90.1-2010 standard.

Two centrifugal type chillers of 690TR each are assigned to the chilled water loop with full load COP value entered as 6.16 in chiller input tabs.

As I was analysing the hourly reports for chiller, it was observed that chiller COP values (based on corrected EIR values in hourly report) are quite high ranging from 11 to around 25 at part load values in the range of 50% to 0.1%.

This seems very unusual considering that as per chiller manufacturer part load datapoints the part load COP values starts decreasing below 35-30% part load; whereas using e-quest default chiller curves, the chiller COP value seems to go on increasing even at lower part load values.

Has anyone observed this before, or am I going wrong somewhere?

Also due to above issue, when part load data points provided by chiller manufacturer are entered in proposed model and default e-quest performance curves are used in baseline model, expected energy savings under space cooling consumption are not achieved during comparison.

I have attached screen-shots showing e-quest default curve coefficients (EIR-FT, EIR,-fPLR & Cap-FT curves) for centrifugal chiller and a sample manufacturer's part load details for reference.

Do I need to change the default curve coefficients from e-quest to get more accurate results? If so, please kindly let me know the changes to be made or the process for finding correct part load curve coefficients for chiller.

Thanks in advance.





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