Chiller oversizing problem in eQuest

asked 2014-09-28 00:50:31 -0500

capaula
31 ●1

updated 2020-03-08 11:30:42 -0500

I let eQuest auto-size the chillers for a project I am working on, and it comes out that the report "PS-D Circulation Loop Loads" shows a peak of 4,964 kBtu/h and "PV-A Plant Design Parameters" as well as "PS-H Loads and Energy Usage for Chilled Water Loop" shows the chillers sized for 7.314 MBTU/h. It is sizing the chillers for almost 2x the peak load.

On a second run I sized each chiller (2x) for half the peak load, but I still see the same numbers on PV-A and PS-H. What does it mean, a bug that nobody fixed yet?

Can anybody tell me what is going on, or if I am making an interpretation mistake?

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@capaula Good question! I suggest rephrasing the title of the question to capture more of what you are asking. Maybe something like: "Why do PV-A and PS-H reports in eQuest give different sizing results?".

Neal Kruis ( 2014-09-29 09:41:42 -0500 )edit

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answered 2014-11-23 21:51:33 -0500

301_Hours
548 ●2 ●5

Autosizing can be problematic for any component in eQUEST, but it appears to be problematic randomly.

I've had to hard enter capacities for chillers, boilers, and preheat coils in the past to get them to work properly.

It's important to look at the hourly reports to confirm set point temperatures are being met for every hour.

If you're early in the design, you can use ASHRAE 90.1 guidance and over size your chiller by 15%, and your boiler by 25% to have a realistic capacity.

Good luck.

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answered 2014-09-30 10:35:20 -0500

DancingDavidE

580 ●6 http://www.linkedin.co...

updated 2014-09-30 12:44:44 -0500

Neal Kruis

4675 ●9 ●17 http://bigladdersoftware.com/

I believe that there is actually a separate question pertaining to the auto-sizing for multiple chillers which has been buggy in the past, which is separate from the issue of why the values might vary between the two reports in a general sense.

This issue has frequently come up when auto-sizing multiple chillers unless this has been remedied in recent versions of the software. You'll need to go back and enter the capacity for each chiller and re-run the simulation once you've established the loads.

For your design case models, you should have the proposed capacity from the engineers, auto-sizing will only be in the early stages of the project where the capacity may not yet be determined and for the baseline case where there isn't a designed chiller.

As far as the variance between the two reports, verify what method you are using to size the plant equipment either the connected coil capacity or the modeled coil load (which often will be less), and if any oversizing is included.