[Bldg-sim] Ashrae 90.1 - Unmet hours
Nick Caton
ncaton at smithboucher.com
Mon Oct 26 20:19:40 PDT 2009
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
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).
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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