[Bldg-sim] Ashrae 90.1 - Unmet hours

[Kendra Tupper]

I agree that Nick's interpretation is correct, but this is my biggest
frustration with 90.1. For multi-zone buildings, the limit should be on the
sum of "non-concident" unmet load hours for each zone. For standard energy
modeling output reports, you can determine the total annual unmet hours for
each zone, but you don't know which hours of the year they occur.

In Jim's example, what if each of the 300 zones had 1 unmet load hour that
all occurred during the same hour of the year? Or better yet, what if you
had 300 zones with 30 hours of unmet loads (all at the same hours)? By the
90.1 reasoning, you would have 9000 unmet load hours (greater than the
number of hours in a year!).

I have thought about requesting a change to 90.1, but if the standard were
to require people to determine the sum of non-coincident unmet load hours
for each zone, it would put a large burden on the energy modeler to develop
hourly output reports for each zone and hand calculate this. It seems like
we're stuck with what we have until the energy modeling programs can produce
an output report that describes the sum of non-coincident unmet load hours.

Kendra Tupper, PE, LEED AP
Senior Consultant
Built Environment Team

Rocky Mountain Institute  |  T  303-567-8641 |  F  303-245-7213  |
www.rmi.org


On Mon, Oct 26, 2009 at 6:38 PM, Rosenberg, Michael I <
michael.rosenberg at pnl.gov> wrote:

>  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).
>
>
>
> [image: cid:489575314 at 22072009-0ABB]**
>
> * *
>
> *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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