[Bldg-sim] Ashrae 90.1 - Unmet hours

[Fred Porter]

I also interpret the 90.1 PRM definition as Sureka's table illustrates.
I imagine the intent of the original writers was that you would get
about one hour/day for either morning startup or at/near design
conditions, when MANY zones might be "outside the throttling range"
during that hour. Any other interpretation penalizes buildings with more
zones. And it should not matter whether Zones 1,2 and 3 are served by
the same system or separate systems.
 
For DOE2/eQuest, as far as I know, this is essentially how the BEPS %
unmet hours are determined, though apparently the percent references
system "on" hours. I THINK this is calculated as a fraction of the
system with the greatest "on" hours, but I'm not sure how cycling "on"
is treated. I think that if a model includes any system, even a tiny
virtual independent system, with continuous operation, then the overall
% from BEPS can be multiplied by 8760 (hopefully NOT 8760 + design day
hours)!
 
Unless it has been added to the newest versions of eQuest, there are NO
DOE2/eQuest summary outputs which decompose "unmet hours" into heating
and cooling for the BUILDING, as requested by the PRM and EAc1 forms.
However this decomposition is not specifically required by the language
of the standard. AND these #s might not necessarily be additive, a good
reason NOT to try to decompose and then sum these. During startup on a
winter day, many interior zones might be "undercooled" while many
exterior zones are "underheated," yielding ONE unmet load hour, but also
ONE hour cooling loads not met and ONE hour heating loads not met...
which would appear to become TWO hours if entered separately then
summed. 
 
Fred W. Porter
Architectural Energy Corp.

P.S. Before increasing system or zone capacities, it's always wise to
check myriad other inputs to assure that some schedule or setting hasn't
turned off the heating or cooling or reset SA temps in some
unanticipated fashion.

>>> surekha tetali <surekhatetali at gmail.com> 10/27/2009 6:53 AM >>>



The unmet hour table meant to show the hours of the day in which that
particular zone is unmet and not the number of hours.
The same information is shown in the below table for one particular
day- suppose Jan 1st 
In the table below:

·Yes – represents that the hour is unmet by the system
·No – represents that the temperatures are met in the zone



Hour of the day
Zone 1
Zone 2
Zone 3
Number of unmet hours of the building

1st
No
No
No

2nd
No
No
No

3rd
No
No
No

4th
No
No
No

5th
No
No
No

6th
Yes
Yes
No
1

7th
No
No
Yes
1

8th
Yes
Yes
Yes
1

9th
No
No
No


10th
No
No
No


11th
No
No
No


12th
No
Yes
Yes
1

13th
No
No
Yes
1

14th
Yes
No
No
1

15th
No
No
No


16th
Yes
Yes
No
1

17th
No
No
No

18th
No
No
No

19th
No
No
No

20th
No
No
No

21st
No
No
No

22nd
No
No
No

23rd
No
No
No

24th
No
No
No

Total number of unmet hours in each zone
4
4
4
-

Total number of unmet hours of the building
7



As seen in the table:
Total unmet hours in the building is not the sum of number of unmet
hours in each zone (which is 12hrs) but is the sum of number of unmet
hours of the building (which is 7hrs).


I am also attaching the table as an image.In case the formatting goes
wrong in the mail, the attached image can be referred.


Regards,


Surekha Tetali
Building Science Research Centre
IIIT Hyderabad.


On Tue, Oct 27, 2009 at 5:04 PM, Seth P. Spangler <sspangle at rmf.com>
wrote:



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 
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

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