[Bldg-sim] Ashrae 90.1 - Unmet hours

[Griffith, Brent]

EnergyPlus produces a simple summary table for this called "Time Setpoint Not Met." It has hours not met by zone and for entire facility, taking into account coincidence. Results are separated by heating and cooling as well as total time vs occupied times.

EnergyPlus uses a deviation from setpoint of 0.2C to trigger unmet time.  I hear DOE2 uses a deviation of 1.0F as a trigger.  I think this is one area where 90.1 could be clearer.


________________________________
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Monday, October 26, 2009 9:20 PM
To: Rosenberg, Michael I; Crockett, Jim; Kendra Tupper
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Ashrae 90.1 - Unmet hours

Mike,

I appreciate you bringing this up.  This definition drives straight to the heart of defining the issue-at-hand...  Since I kinda presented both sides of the issue at once - I'd like to clarify where I stand regarding what the correct interpretation should be.

The logic is as follows:  If a modeled year has 8,760 hours, can there be 10,000 unmet load hours?  By strict reading of the standard's definition below, I would put my foot down stating there can only be 8,760, at most.

By common practice however, it appears a majority (myself included) sum unmet cooling/heating hours between the zones, even if they should fall on the same modeled hour, against the intent of the standard.

My pure speculation (for what it's worth, as a young EIT) is this practice developed because eQuest BDL reports don't present the crunched numbers in a way that makes the sum of unmet load hours, as intended by 90.1, easy to determine.  I wouldn't be shocked to learn other energy modeling software packages generate LEED compliance summaries featuring unmet load hour totals in sync with the real intent of ASHRAE 90.1.

If there's anything I've learned from going out on a limb, it's that I'm sure to learn something whether I fall or not!

~Nick

[cid:image001.jpg at 01CA56FF.CDA93C70]

NICK CATON, E.I.T.
PROJECT ENGINEER
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
Check out our new web-site @ www.smithboucher.com

From: Rosenberg, Michael I [mailto:michael.rosenberg at pnl.gov]
Sent: Monday, October 26, 2009 7:39 PM
To: Nick Caton; Crockett, Jim; bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] Ashrae 90.1 - Unmet hours

Nick,

Your interpretation is the correct one. According to the definitions in Standard 90.1.

unmet load hour: an hour in which one or more zones is outside of the thermostat setpoint range.


Mike
__________________________
Michael Rosenberg
Senior Commercial Buildings Energy Analyst
ENERGY & ENVIRONMENT DIRECTORATE
Pacific Northwest National Laboratory
2032 Todd Street
Eugene, OR 97405
(541) 844-1960
michael.rosenberg at pnl.gov
www.pnl.gov
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Monday, October 26, 2009 5:33 PM
To: Crockett, Jim; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Ashrae 90.1 - Unmet hours

Jim,

That's actually a really good question that I was afraid to ask when I first encountered it - kudos to you!  I've currently resolved to follow what others seemed to be doing within and outside of my office:  Sum up all unmet hours for cooling and heating between the zones just as you describe.   In your example, I'd agree that the unmet hours of your 301 zone building total 301.

I do agree that this doesn't seem intuitively to be the intent of the standard, however between what is suggested within 90.1, the LEED handbook, and the LEED credit templates - I honestly can't see any clear indication either way on which is the appropriate interpretation.

I think the appropriate metric for ensuring appropriately sized systems should be something like: "hours of the modeled year in which at least one zone has an unmet cooling/heating load,"  but I think that was avoided by all concerned parties because it's too wordy!

My acting interpretation, again referencing your example, is that all systems of your 301 zone example affecting the zones with unmet cooling/heating hours should have their heating/cooling/overall sizing capacity ratios increased incrementally until the design hours fall below 300 (and/or within 50 of the sum from the other model, depending on your situation).

Afraid I'm only really adding to the discussion here without providing a solid answer.  Would like to echo the desire to see anyone's experiences that would help us know the "right" way to interpret this (in my case, specifically in the context of a LEED submittal).

[cid:image001.jpg at 01CA56FF.CDA93C70]

NICK CATON, E.I.T.
PROJECT ENGINEER
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
Check out our new web-site @ www.smithboucher.com

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Crockett, Jim
Sent: Monday, October 26, 2009 4:27 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Ashrae 90.1 - Unmet hours

Ashrae 90.1 (2004) Appendix G3.1.2.2 requires a baseline building to have less than 300 unmet hours.  What exactly does this mean?

To illustrate my question:  assume you have a building with 301 zones, and each zone has 1 unmet hour per year.  This gives you a total of 301 unmet hours, and requires you to increase your baseline equipment capacity.  But you could argue that, on average, the building has only 1 unmet hour per year.

Have any of you run into this?  Is it addressed in an addendum somewhere, etc?

Any help is appreciated.  Thanks,



Jim Crockett, P.E.

Senior Project Engineer
Energy & Carbon Management
Nexant, Inc.
4021 S. 700 E., Suite 250
Salt Lake City, Utah 84107

(801) 639-5603 - phone
(801) 266-4786 - fax

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