[Bldg-sim] [SPAM] Re: Ashrae 90.1 - Unmet hours
David Wasserman
dwasserman at southface.org
Tue Oct 27 05:39:18 PDT 2009
To get 7 unmet hours you need to interpret the numbers listed as hours of the day when the load was unmet. There are 7 unique hours when the load was not met. There are differing opinions on how unmet load hours should be calculated but this seems like the most logical but possibly not the most practical depending on the simulation software used.
David Wasserman, Senior Research Engineer, MS ME, LEED EB AP
Southface - Responsible Solutions for Environmental Living
241 Pine St., NE, Atlanta, GA 30308
Direct: 404-604-3588; Main: 404-872-3549; Fax: 404-872-5009
david at southface.org <mailto:david at southface.org> ; www.southface.org
________________________________
From: bldg-sim-bounces at lists.onebuilding.org on behalf of Seth P. Spangler
Sent: Tue 10/27/2009 7:34 AM
To: bldg-sim at lists.onebuilding.org
Subject: [SPAM] Re: [Bldg-sim] Ashrae 90.1 - Unmet hours
Am I missing something or does this table and the corresponding answer (7 unmet hours) not make sense.
Zone 1 unmet during: 6 8 14 16
Zone 2 unmet during: 6 8 12 16
Zone 3 unmet during: 7 8 12 13
If the columns (hours outside of throttling range) all represent simultaneous hours in the model then wouldn't the total number of hours be the sum of the maximum number of hours for each time period? (7+8+14+16=45 hours outside of range) I have looked at the chart multiple ways and do not see how seven (7) could ever be the correct value.
Yes, projects with hundreds of zones may be penalized however ASHRAE allows similar spaces(orientation, load , HVAC system) to be combined into a single zone which can reduce the impact of this issue.
I personally sum all of the hours ANY zone is outside of range without regard to when the time period is. I feel that this is the most accurate method of correctly sizing the HVAC systems.
Seth Spangler, LEED® AP
Project Engineer
RMF Engineering, Inc
Ph: (843) 971-9639 ext:1497
Fax: (843) 971-9641
sspangle at rmf.com
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of ashu gupta
Sent: Tuesday, October 27, 2009 1:17 AM
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 <mailto:kce2 at kamalcogentenergy.com>
www.kamalcogentenergy.com <http://www.kamalcogentenergy.com>
________________________________
From: bldg-sim-bounces at lists.onebuilding.org [mailto: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]
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
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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20091027/ab8fec99/attachment-0002.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/jpeg
Size: 1459 bytes
Desc: image001.jpg
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20091027/ab8fec99/attachment-0002.jpeg>
More information about the Bldg-sim
mailing list