[Bldg-sim] Ashrae 90.1 - Unmet hours
Vishal Garg
vishal at iiit.net
Tue Oct 27 11:48:12 PDT 2009
You are right. The Unmet hours of the proposed design can be less than base
case unmet hours and the difference can be more than 50 hours (or upto 300
hours as shown by you).
However, the ASHRAE 90.1 2004 user manual on page G37states:
"If the number of hours that loads are unmet by either the systems or plant
of either the baseline or the proposed model exceeds 300 hours of the 8760
hours simulated, or *differs by more than 50 hours between the two models*,
these simulation results will not be accepted as valid." I think this is
incorrect.
According to ASHRAE 90.1 2004 - "unmet load hours for the proposed
design *shall
not exceed* the number of unmet load hours for the baseline building design
by more than 50." Reverse is not required.
So, the unmet load hours for the proposed design can be less than the number
of unmet load hours for the baseline building design by more than 50.
Vishal
Head, Center for IT in Building Science | IIIT-H | Research University |
Gachibowli | Hyderabad 500 032
Website: cbs.iiit.ac.in | Tel#+91 40 6653 1125| Fax: #+91 40 6653 1413|
Mobile # +919949990900| Email: vishal at iiit.ac.in
On Tue, Oct 27, 2009 at 11:57 PM, Crockett, Jim <Jcrockett at nexant.com>wrote:
> It’s splitting hairs, but one item in the email from Ashu is not quite
> correct. The following sentence is from his email, and the incorrect line
> is in bold:
>
> - As per ASHRAE 90.1-2004, the unmet hours of the total building should
> be less than or equal to 300 hours and *the difference in the base case
> and proposed case should be less than or equal to 50 hours.*
>
>
>
> What Ashrae actually says is, “. . .unmet load hours for the *proposed*design shall not exceed the number of load hours for the
> *baseline building design* by more than 50.”
>
>
>
> If you have a building where the baseline has 300 unmet hours, and the
> proposed has 0 unmet hours, no correction is needed. A correction is only
> needed if the unmet hours in the *proposed* exceeds those in the *baseline
> *by more than 50. (or if either exceeds 300). Worded differently, if the
> baseline has 300 unmet hours, and the proposed system has 0 unmet hours, you
> do not need to make the baseline more stringent.
>
>
>
>
> ------------------------------
>
> *From:* Scott Criswell [mailto:scott.criswell at doe2.com]
> *Sent:* Tuesday, October 27, 2009 10:09 AM
> *To:* Rosenberg, Michael I
> *Cc:* ashu gupta; Nick Caton; Crockett, Jim; Kendra Tupper;
> bldg-sim at lists.onebuilding.org
>
> *Subject:* Re: [Bldg-sim] Ashrae 90.1 - Unmet hours
>
>
>
> I can confirm Mike's understanding of the DOE-2/eQUEST results. To get the
> correct number of hours of unmet loads, people should MULTIPLY the Percent
> hours outside throttling range from BEPS or BEPU by the total annual "hours
> fans on" listed in report SS-E.
>
> One other comment re: Ashu's write-up - I believe that (for DOE-2/eQUEST) a
> zone temperature has to be more than one degree outside the throttling range
> for that hour to be counted as an hour outside throttling range. So for a
> zone with a heating thermostat setpoint of 72 and a 2 degree throttling
> range (=> 71-73 degree "throttling range"), the zone temperature would have
> to be LESS THAN 70 in order for that hour to be counted.
>
> related info -
> We are contemplating a change to the Air-Side HVAC Summary view in the
> eQUEST interface to report this total number of hours as opposed to just the
> percent in the totals section at the bottom of the report.
> We have also just in the past several days (thanks to the efforts of Steve
> Gates) added precision to the percent hours outside throttling range
> reported on BEPS & BEPU and ALSO added separate reporting of hours any zone
> is either under cooled or under heated, intended for reporting to LEED
> submission templates. Assuming no further changes (which is certainly not
> out of the question), future releases of DOE-2/eQUEST will report the
> following in the BEPS & BEPU reports:
> PERCENT OF HOURS ANY SYSTEM ZONE OUTSIDE OF THROTTLING RANGE =
> 4.45
> PERCENT OF HOURS ANY PLANT LOAD NOT SATISFIED =
> 0.00
> HOURS ANY ZONE ABOVE COOLING THROTTLING RANGE =
> 98
> HOURS ANY ZONE BELOW HEATING THROTTLING RANGE =
> 25
>
> - Scott
>
>
> Rosenberg, Michael I wrote:
>
> Ashu,
>
>
>
> I am in agreement with everything you stated except possibly this;
>
>
>
> “When percentage of unmet is specified, than this is the percentage of
> total number of hours (1 year- 8760 hours) for which the simulation is
> performed (not just the occupied hours)”
>
>
>
> My understanding is that some simulation programs (DOE2 and eQuest in
> particular) report this as a percentage of hours that the fan is running. I
> could be wrong, and I am sure some of you DOE2 experts can comment on what
> is reported in the DOE2 BEPS report.
>
>
>
> 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:* ashu gupta [mailto:kce2 at kamalcogentenergy.com<kce2 at kamalcogentenergy.com>]
>
> *Sent:* Monday, October 26, 2009 10:17 PM
> *To:* Rosenberg, Michael I; 'Nick Caton'; 'Crockett, Jim'; 'Kendra Tupper'
> *Cc:* bldg-sim at lists.onebuilding.org
> *Subject:* RE: [Bldg-sim] Ashrae 90.1 - Unmet hours
>
>
>
> Dear All,
>
>
>
> Explanation of Unmet Hours is as follows:
>
>
>
> *Unmet Hours:*
>
> Unmet hours of a building are the summation of the number of hours when the
> heating or the cooling set point temperature of a zone is not met either by
> the HVAC system or by the plant.
>
> *Understanding/Interpreting/Calculating the number of unmet hours:*
>
> - Unmet hour is for a particular zone when the zone indoor temperature
> is higher than the heating or cooling set point specified in that hour.
> - The number or the percentage of unmet hours in a building is usually
> given as one of the outputs of the simulation.
> - Zone wise unmet can also be read from the various output files
> provided by the software used for simulation.
>
> (Example:
>
> Visual DOE: “SS-J System Peak Heating and Cooling Days” report &
>
> Energy Plus: Output Variable, “Time Cooling Set point Not met”)
>
> - When two zones are unmet at the same hour, this will count to one
> unmet hour for the building.
> - When two zones have unmet hours during different non overlapping
> times of a day, the total number of unmet hours in that day is the summation
> of these unmet hours of each zone. This total for the year should be
> considered as the total unmet hours of the building.
>
> *Example: *
>
> When each zone is unmet in the specified hours as beside,
>
>
>
> Zone 1 unmet during: 6 8 14
> 16
>
> Zone 2 unmet during: 6 8 12
> 16
>
> Zone 3 unmet during: 7 8 12
> 13
>
>
>
> Total number of unmet hours of the building: *7 hrs* and not 12hrs.
>
> 6 7 8 12 13 14 16
>
>
>
> - When percentage of unmet is specified, than this is the percentage of
> total number of hours (1 year- 8760 hours) for which the simulation is
> performed (not just the occupied hours)
> - As per ASHRAE 90.1-2004, the unmet hours of the total building should
> be less than or equal to 300 hours and the difference in the base case and
> proposed case should be less than or equal to 50 hours.
> - If unmet load hours in the proposed building exceed the unmet load
> hours in the baseline building by more than 50, then the size of equipment
> in the baseline building shall be reduced incrementally, until the condition
> is satisfied.
>
>
>
>
>
> Thanks
>
> Ashu Gupta,
> Project Engineer,
> Kamal Cogent Energy,
> Kamal Ratan Chanbers 1st Floor,
> Opp. GPO, M.I. Road,
> Jaipur 302001
> Ph 141 2373185(W)
> Ph 9251665008(M)
> kce2 at kamalcogentenergy.com
> www.kamalcogentenergy.com
> ------------------------------
>
> *From:* bldg-sim-bounces at lists.onebuilding.org [
> mailto:bldg-sim-bounces at lists.onebuilding.org<bldg-sim-bounces at lists.onebuilding.org>]
> *On Behalf Of *Rosenberg, Michael I
> *Sent:* Tuesday, October 27, 2009 9:07 AM
> *To:* Nick Caton; Crockett, Jim; Kendra Tupper
> *Cc:* bldg-sim at lists.onebuilding.org
> *Subject:* Re: [Bldg-sim] Ashrae 90.1 - Unmet hours
>
>
>
> I think eQuest and any DOE2 based software does report the hours of loads
> not being met as required by Appendix G. In the BEPS report it gives
> “PERCENT OF HOURS ANY SYSTEM ZONE OUTSIDE OF THROTTLING RANGE”. My
> understanding of this number is that it is a percentage of scheduled fan
> run-time hours, so some calculation may be necessary.
>
>
>
> *__________________________*
>
> *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:* Nick Caton [mailto:ncaton at smithboucher.com<ncaton at smithboucher.com>]
>
> *Sent:* Monday, October 26, 2009 8:20 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
>
>
>
> [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:* Rosenberg, Michael I [mailto:michael.rosenberg at pnl.gov<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<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<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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>
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