[Equest-users] Baseline chiller unusual part load COP

[David Eldridge]

Yes – you should develop curve fit parameters for your specific chillers, with the appropriate reset conditions, etc. eQUEST includes a curve-building function if you enter the performance data there.

Also see what the weighted average of the COP is against load, maybe it isn’t as far off as it seems at first with a few outliers, or it may be way off if the majority of hours are at part-load.

The idea that you should use a consistent set of curves is true though, using the default curves based on some historical piece of equipment vs the curves from a modern chiller today may not be consistent, it would be best if your chiller vendor can provide some data for a code-minimum unit to make curves for the baseline based on the baseline capacity, etc.

David


David S. Eldridge, Jr., P.E., BEMP, BEAP, HBDP, GGA
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From: Equest-users <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
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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