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unmet hour - heating too high in eQuest

asked 2015-01-16 09:16:48 -0500

updated 2015-01-16 10:04:48 -0500

Hey everyone,

I am doing a high raise office building (14 levels, about 800,000 sf) energy model use eQuest, VAV system, chillers and boilers, core and shell, Ashrae system 7. When I run the result, unmet hour is high, 36 for cooling (Thats OK), 414 for heating.

I tried to increase air flow - Minimum flow ratio from 0.3 to 0.5 or higher, no working. Tried increase air-flow - design flow from 0.5 cfm/sf to 0.6 or higher, no working. Tried turn on night fan (cycle on any) - no working Increased heating capacity, no working. all the zones assignment seems right.

Could any masters here help me troubleshooting with this? Really really appreciate!!!! Please let me know if you need any other information~~~

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answered 2015-01-16 12:17:45 -0500

updated 2015-01-16 13:21:01 -0500

First, read through this thread:

https://unmethours.com/question/359/w...

Although many suggestions are for EnergyPlus/OpenStudio, the same techniques will apply to eQuest.

There are many possible solutions. Examine your SS-R report, and find which zones are having issue - it may all be in one zone which can help to focus your efforts.

First, I'd look at your Throttling Range (at the zone level) - it defaults to 2F, which is a fairly tight range. Try 4F or even 6F, and see how much of an impact it has. This is particularly relevent for VAV systems.

Try autosizing the airflow/heat capacities, and see what eQuest thinks the capacities should be.

If you are using Floor Multipliers, heating and cooling capacities need to be entered at the zone level rather than the system level. In this case, it would show up in the SS-R report with the Mid level zones having the underheated/cooled hours, but the Bottom and Top floors are fine.

Also check your outdoor air rates - are you bringing in too much outdoor air? This would cause the systems to have to work harder to condition the air.

At the end of the day, if it is just one or two zones, you can add an electric resistance baseboard to cover the unmet capacity and reduce the hours to an acceptable range. This would be the very last resort though...

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Hey Ben, Thank you very much for your answer, it helps.

I tried increase the Throttling Range, but not too many change, unmet hour just decrease like 10hr. I leave the cooling/heating capacity (At zone level) all blank - which I think means auto sizing, the result shows same unmet hour from BEPS report. Are you mean look at the capacity from other places? could you tell me which report? I leave outdoor air rate blank too.....

Jenny Gao's avatar Jenny Gao  ( 2015-01-16 13:56:49 -0500 )edit

Try autosizing your system heating/cooling capacities as well, if you've input these values - leaving it blank will cause eQuest to autosize the values.

Other reports which may or may not be helpful in diagnosing the problem: SS-P (System heating and cooling performance summaries), SV-A (system design parameters), SS-F (zone demand summary), PS-C (plant equipment summary)

Without seeing the actual model it's hard to nail down a specific cause... If you are willing, post the .inp and .pd2 files and I can try to have a look at it over the weekend, or perhaps others here can help you as well.

Benjamin's avatar Benjamin  ( 2015-01-16 16:07:26 -0500 )edit

Problem solved! You know what? Some of the zones' Heating source did not assign to HW loop, kept none. That's the reason lol. I Learn a lot from your commends!!! Really appreciate man! Add your LinkedIn BTW

Jenny Gao's avatar Jenny Gao  ( 2015-01-16 17:54:04 -0500 )edit

Glad you solved it, Jenny :) Like I said, it really depends on the building on what solution will solve the problem. Every building is unique, and eQuest in my experience is a peculiar program - the most unexpected thing can be the cause of the problem.

Benjamin's avatar Benjamin  ( 2015-01-16 23:39:24 -0500 )edit

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Asked: 2015-01-16 09:16:48 -0500

Seen: 2,466 times

Last updated: Jan 16 '15