IES VE Unmet Hours Setpoints

asked 2021-01-26 12:55:44 -0500

Josh Roth

21 ●3

updated 2021-01-26 17:33:44 -0500

Aaron Boranian

14070 ●81 ●24 http://bigladdersoftware.com/

I am working through a LEED v4 energy model and am trying to reconcile the unmet load hours that I am getting from the Range command in IES VE. Unfortunately I am finding that the setpoints it is referencing are the HVAC zone setpoints, not the room setpoints.

This presents an issue in some areas, for example, where I have an open office with a nearby storage room that is on the zone with it. The acceptable temperatures for the storage room are 60°F-80°F cooling. The open office setpoints are 70/75. Even though the storage room stays within its acceptable range, the fact that it is outside of the open office setpoints (since the open office is the master room and its setpoints drive the HVAC zone setpoints) produces UMLH.

Are there any insights on how I can work with IES VE to get it to ignore UMLH if they are within a room's acceptable range?

I've also looked at this previous post, for reference.

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answered 2021-01-26 16:30:57 -0500

crduggin

800 ●4 ●5

This could be a little different depending on which version of the VE you are in. The unmet load hours test and HVAC controls are going to use the set point that shows up for that layer in the ApHVAC system for that layer. Assuming you have them still linked, it would be the same as the master room on the zone.

I'm confused when you say the storage room is inside its acceptable range but the open office isn't even though the open office is the master room. It really should be over cooling or heating the storage room in order to get the office within range.

If you think about it the only set point that a real HVAC system is controlling to is the one for the space where the thermostat is, so the storage room set point can't actually be different.

Based on what you have described about the office not meeting but the storage does even though it is the master room, you need to reapportion the zone airflow in the zone airflow distribution dialog of the ApHVAC system. Give the office more air and the storage room less. The % used for distribution are calculated based on the last room loads results you ad applied to the system.

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answered 2021-03-18 21:00:20 -0500

Greg Collins

530 ●8 http://www.zeroenvy.com/

updated 2022-04-11 10:59:15 -0500

edit: There is a great 4-part series of articles from Timothy Moore at IES on resolving unmet load hours:

--- original post ---

Aaand you face the "problem" with IES-VE that it is confuses people by aligning with real-life. Most people have the eQUEST mentality w.r.t. spaces and thermal zones being the same thing. (I started in eQUEST too and still think it's great, but it's dated). 90.1 and other modeling standards were developed around the same.

If, in real life, you had a VAV box serving an office and a storage room, and the thermostat is in the office, you're absolutely going to have poor temp control in the storage room. The HVAC system has no idea what's happening there and no way to control for it.

While this SHOULD make us re-think what rooms are grouped together into zones and/or adjust your expectations re: resultant temperature in non-primary (I'm trying to get away from master/slave) spaces, that's annoying and overkill for 99% of situations.

Long story short, I do the same as Cory and use spaces instead of zones in the VE (mostly). Had to point out the irony though.. :)

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Yep, that's the conclusion that I came to as well - too overkill for most simulations. But it definitely can provide insights into thermal comfort and controls issues, as you said!

Josh Roth ( 2021-03-19 08:21:43 -0500 )edit

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answered 2021-01-28 13:46:08 -0500

Josh Roth

21 ●3

Thanks for the response! I should probably clarify-when I am saying "acceptable range" for the storage room, I don't mean thermostat set point. I mean that, in the example I gave, when the open office thermostat is satisfied and has no UMLH, having the storage room be within 60-80 as a byproduct (since the control is in the open office) would be ok and shouldn't be considered an UMLH for the storage room.

From my understanding of 90.1, a non-master-room being outside of the zone setpoints shouldn't be an UMLH if it is within an acceptable design range. Is that correct?

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I would agree. I just haven't had time to go back and see what the VE is doing with the zone components. The other solution is to just not use zone components :). What version of the VE are you using?

crduggin ( 2021-01-28 18:17:37 -0500 )edit

I'm using 2019.3.2.0.

I'm intrigued by your suggestion to not use zone components. I was under the impression that the only time when room components should be used would be when each room is its own zone (e.g. a chilled beam building or something along those lines). Is there a way to use room components in a multi-room zone application?

Josh Roth ( 2021-01-29 10:32:22 -0500 )edit

Eh... so this is a bit more subjective of an answer. It depends on what you are doing. I come from using eQuest originally. Then we had to make larger thermal blocks that might encompass multiple rooms or very similar space types. Combining spaces like storage rooms that just get a little air into a larger zone was pretty standard. I avoid using zone components except in certain situations. If it is a cheap, single-zone VAV system that serves multiple differing spaces, i use zone components for the reason you said above. If we want room by room airflows for loads I use zone components.

crduggin ( 2021-01-29 10:38:53 -0500 )edit

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When doing an energy model, especially for LEED, zone components, where they represent a real life scenario, complicate troubleshooting unmet hours pretty substantially. I prefer to avoid that if i can.

crduggin ( 2021-01-29 10:41:00 -0500 )edit

That makes sense. Thanks!

Josh Roth ( 2021-01-29 10:41:22 -0500 )edit

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