[Bldg-sim] Ashrae 90.1 - Unmet hours

[Nick Caton]

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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