[Bldg-sim] Ashrae 90.1 - Unmet hours

[ashu gupta]

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)
 <mailto:kce2 at kamalcogentenergy.com> kce2 at kamalcogentenergy.com
 <http://www.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

 

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] 
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).

 

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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