[Bldg-sim] Ashrae 90.1 - Unmet hours

[Timothy Moore]

We also interpreted the unmet loads hours as Sureka's table illustrates below. We believe this to be the correct interpretation and have included tools in the Virtual Environment for assessing unmet load hours accordingly. The tools counts only occupied hours for each zone (per the schedule for that particular zone), and unmet load hours are determined in keeping with the controls throttling ranges established by the user for heating and cooling of individual zones. The occupied hours and set points can thus vary from one zone to another, without double-counting a particular hour during which two or more zones are out of range. That said, in support of other needs and interpretations, we also provide means for users to count unmet loads or other hourly bin data for any set of hours in the day and to total all hours or just the non-coincident hours via a logical “OR” test

 

Regards,

Timothy 

 

 


Timothy Moore 
Senior Consultant
Special Projects 

Office: 415 983-0603
timothy.moore at iesve.com <mailto:timothy.moore at iesve.com> 
www.iesve.com <http://www.iesve.com/> 

**Design, Simulate + Innovate with the <Virtual Environment>**

Email Disclaimer <http://www.iesve.com/disclaimer.html> 

 

 

 

 

 

 

 

 

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Fred Porter
Sent: Tuesday, October 27, 2009 8:59 AM
To: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Ashrae 90.1 - Unmet hours

 

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 <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

Error! Filename not specified.

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 <http://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).

Error! Filename not specified.

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 <http://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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