[Equest-users] Building area method ASHRAE 90.1 (UNCLASSIFIED)

Eurek, John S NWO John.S.Eurek at usace.army.mil
Wed May 23 09:19:05 PDT 2012

Classification: UNCLASSIFIED
Caveats: NONE

Do both and use the one that gets more points!

-----Original Message-----
From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bishop, Bill
Sent: Wednesday, May 23, 2012 9:45 AM
To: Patrick J. O'Leary, Jr.; Nick Caton
Cc: eQuest Users; Oscar B.
Subject: Re: [Equest-users] Building area method ASHRAE 90.1

Building Area and Space-by-Space are not methods for designing lighting systems. They are prescriptive requirements for demonstrating lighting energy compliance in 90.1. The LPD allowances in Tables 9.5.1 and 9.6.1 do not need to be complied with if using energy modeling to demonstrate compliance for 90.1 and for LEED. (Only the Mandatory Provisions of 9.4 need to be met for the lighting design.) Energy modelers only need to know the lighting power and space use categorizations of the design as shown on the drawings (along with schedules and controls), not the process used to design it (which typically considers light levels in footcandles or lux).


I think that if a lighting system has been designed, a strong argument can be made that the space-by-space method needs to be used in both the proposed and baseline cases, and that lighting power needs to be entered individually for each space/zone.

                "If construction documents are complete, the proposed building lighting system power is modeled as shown on the design documents." (ASHRAE 90.1 User's Manual, p. G-17)  

"The LPD for the proposed design is taken from the design documents for the building. The LPD specified in the models must correspond to the spaces within each thermal block." (ASHRAE 90.1 User's Manual, p. 11-14 and also p. G-18)

The only obvious case for using the Building Area Method to determine modeled LPD is the case that Nick mentioned where lighting neither exists nor is specified.


As Maria Karpman, Nick and Patrick have mentioned, you are likely to show higher energy savings using the Space-by-Space method. Beyond that, using Space-by-Space allows you to give valuable feedback to the design team, which I would argue is a responsibility of energy modelers. It is routine for me to point out areas of potential improvement of the lighting design in every project I model, based on the allowances in Table 9.6.1. "Yes, Ms. Architect, that is a lovely looking light fixture, but 2.6 W/ft2 of lounge lighting is more than twice the baseline allowance." I don't know how you give helpful feedback if you are just comparing two building-averaged lighting power densities.





 <mailto:wbishop at pathfinder-ea.com> 



From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Patrick J. O'Leary, Jr.
Sent: Tuesday, May 22, 2012 7:28 PM
To: Nick Caton
Cc: eQuest Users; Oscar B.
Subject: Re: [Equest-users] Building area method ASHRAE 90.1


actually nick, i agree with you.  since i don't design lighting systems i always ask the lighting designer which method they're using before i start building a model.  almost all of the lighting designer's i've worked with use the whole building area method, though as you point out the space-by-space method can actually do a bit better for energy savings.

my point is that there isn't a mandate to use either the space-by-space or whole building area method and there is no justification as far as 90.1-200x is concerned for a usgbc reviewer to claim that the space-by-space method be used.  the requirement per 90.1 is that the method be consistent in both the proposed and baseline models.  space-by-space in both or whole building in both.  this is what i've had to point out to reviewer's when i've received comments.  just quote chapter & verse to show that the method (space-by-space or whole building) used meets the 90.1 app g requirement and is applied the same in both models.

as far as comcheck, comcheck reports from lighting designers are only as good as the individual filling them out.  i've had lighting designers (with all of their extra letters including pe after their names) fill them out incorrectly.  i.e. not having all the lighting fixtures the same in drawing schedules as input into comcheck, not having same number of fixtures in drawings and in comcheck, not having the same floor areas in drawings and in comcheck, and worst of all, not using the same methodology in comcheck that they've used to design the lighting system in the first place.   yes, i've seen comcheck reports that indicate space-by-space when the lighting designer has told me whole building method.  and vice versa.  so i always end up confirming my lighting take-offs (from the lighting plans) and methodology with the lighting designer/electrical engineer and their comcheck report.

On 5/22/12 3:58 PM, Nick Caton wrote: 

Hmm, I think I'm on the fence here.  

My practice is identical to Vikram's description for both energy modeling and when documenting compliance for my lighting designs:  Choose whatever method you wish, but always use the same approach for baseline and proposed.  This is pretty clear outside of Appendix G, when documenting compliance.  For modeling, I don't use either approach predominantly - it depends on the project.


Since Patrick is pushing one side, I'll play devil's advocate =):  I can affirm I've used "whole building" averaged LPD in proposed models for successful LEED submission without incident multiple times, documenting that clearly along the way, but I was using "whole building" for the baseline as well in each instance.  I do not personally read 90.1 or LEED to explicitly require LPD be defined with space-by-space for a proposed model.  Patrick, I just checked each of your citations and the only specific call for either method is when the lighting system has not been designed, in which case the whole building approach is prescribed.  Keep in mind both methods should sum to the same total installed watts for the proposed design.


Back to the neutral perspective:  I'll emphasis I do use both approaches.


To Oscar's case:  My general experience has been the whole building method is less generous in net allowable watts when you run the numbers both ways.  In other words, you may stand to earn more LEED points by making your baseline more detailed, using space by space.  My suggestion for Oscar is to simply go with the reviewer's flow and possibly walk away with another point tucked under your arm... it'll probably be a similar amount of effort on your part relative to composing an opposing response, and you won't have to worry about the reviewer disagreeing =).  


I agree space-by-space is 'better' for that reason alone - if different at all, it tends to yield a better performance rating.  I will acknowledge space-by-space is also "more accurate," notably so if you're simultaneously defining distinct & accurate lighting schedules space-by-space, but whether the corresponding additional time investment and resulting "accuracy boost" are advantageous for a given LEED model is a toss-up.  I personally feel the role accuracy plays in a LEED model is often overblown to a point of silliness, but that's a personal call we each need to make and a whole 'nother discussion.


Hot related tip:  energy modelers and MEP designers alike need to be aware of COMcheck.  I find it an invaluable time saver for speeding up takeoffs for whole bldg & space by space calcs, and it's only as costly as eQuest.



cid:489575314 at 22072009-0ABB





Smith & Boucher Engineers

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From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Patrick J. O'Leary, Jr.
Sent: Tuesday, May 22, 2012 4:49 PM
To: Sami, Vikram
Cc: eQuest Users; Oscar B.
Subject: Re: [Equest-users] Building area method ASHRAE 90.1


as long as a lighting system has been designed:

according to ashrae/appendix g the uniform/whole building method applies a uniform lpd to the BASELINE building only while the PROPOSED uses what is designed - so long as the design is based on the whole building area method.  the lpd of the PROPOSED design should not be applied uniformly to the PROPOSED building simulation.  

see appendix g, table g3.1, section 6 lighting, subsection b, page 173 (2004), page 179 (2007).  user's manual pages g-17/18 (2004 & 2007)

i would suggest to quote table g3.1 when replying to the reviewer's comment.  i have had reviewer's tell me i have to use the space-by-space method in a simulation for both proposed and baseline buildings.  this is not correct.  what is correct is that the simulation reflect the methodology used by the lighting designer.  if the lighting design is based on the whole building method then the whole building method maximum lpd is used in the BASELINE building.  if the design is based on the space-by-space method then the space-by-space maximum lpd for each space type is used in the BASELINE building.  in either case the PROPOSED building should reflect what is designed.  by 'what is designed' i mean look at the lighting plans, lighting schedules, and enter the lpd for each space/zone (thermal block) based on the number of fixtures, watts per fixture, and square feet of space.

On 5/22/12 2:15 PM, Sami, Vikram wrote: 

The building area method applies a uniform LPD to the entire building. If you do that in your baseline, you need to apply a uniform LPD to you proposed building too. 

In general, I don't recommend using the building are method - the space by space method is a better approach. 



Vikram Sami, LEED AP BD+C

Sustainable Design Analyst

1315 Peachtree St. NE, Atlanta, GA 30309

t: 404-443-7462    f: 404.892.5823       e: vikram.sami at perkinswill.com   www.perkinswill.com <http://www.perkinswill.com/> 

Perkins+Will.  Ideas + buildings that honor the broader goals of society



From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Oscar B.
Sent: Tuesday, May 22, 2012 4:38 PM
To: eQuest Users
Subject: [Equest-users] Building area method ASHRAE 90.1




How does the building area method work?


I just got a comment from the review team for a project pursuing LEED certification.


I used the building area method for the baseline case and in the proposed case I put the LPD from the lighting design. However they told me that the same method has to be used in both cases.


Any help would be appreciate.

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Classification: UNCLASSIFIED
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