# wwr calculation

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Hi all I have a question about calculating WWR. for example, if the south wall area is 700sf and total window area is 70sf then the WWR should be 10%. but if 50% of south wall is part of a garage and is unconditioned, then in calculating WWR , should I include only the wall area for conditioned space or it should include complete facade? Thanks Deepika [image: image.png]
DEEPIKA KHOWAL
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It should be the gross wall area for everything above ground. Use the lv-d report to find the numbers to calculate the overall WWR for your entire bldg. There is a summary page at the end of the lv-d report. Look for the line called-'all walls'. You can use those numbers to calc WWR percentage. Pashalu
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Thanks Pasha yes , i have been using LV-d report. Am confused how it work for an unconditioned space. Thanks
DEEPIKA KHOWAL
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It doesn't change for unconditioned or conditioned. It is only a function of gross wall area (ft2) and window area (ft2). Don't think too hard about this. You are looking for a needle in the wrong haystack. This one is straight forward with no tricks... WWR is for whole bldg not space by space. Pashalu
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ok. Thanks Pasha. I know I think too much... prevention is better than cure :) Deepika
DEEPIKA KHOWAL
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I don't think I agree with this advice

Under ASHRAE 90.1-2007, Section 5.2.1, part of the requirements for the PRESCRIPTIVE method requires that "the vertical fenestration area does not exceed 40% of the gross wall area for each space-conditioning category".

The definition for "space conditioning category" simply says:

non-residential conditioned space,

residential conditioned space, and

nonresidential and residential semiheated space

It doesn't list unconditioned space. Now I know this info is listed in the prescriptive requirements, but if it was my model, and I had a garage that had 100% window area, there is no way I would count that towards the gross WWR, particularly if I was applying for LEED, and these inconsequential windows pushed my WWR above 40% and thus penalized my proposed building. In fact, I might not even model the windows, unless I felt they were going to superheat the garage and start impacting adjacent space cooling loads.

Just my opinion...

James Hansen, P.E., LEED AP

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I agree with James . if its unconditioned space, we should not claim the window area . that way we can have higher WWR for rest of conditioned spaces.
DEEPIKA KHOWAL
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I model garages all the time. I haven't done a building in a while that didn't have some sort of conditioned space in the garages that needed an adjacent unconditioned space (but without exterior walls) to properly analyze. Plus for LEED these days, they want all of your building areas in the model to match those entered by the architect in the PI forms. So you are supposed to model garage elevator lobbies, semi-heated mechanical spaces, main electric rooms, unheated garage space, etc. Also, my garage at work has windows :) -James
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Do they provide mechanical cooling for your garage at work? or does it have windows with no roof area....I'm sure your garage at work is not considered a "regularly occupied, fully conditioned (i.e. T-stat controlled) space". Pasha
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I agree with James. Modeling the garage is necessary to model the associated conditioned spaces within that floor (heated storage rooms, elevator lobbies, occupiable space adjacent to the garage). Obviously the garage is modeled as unconditioned, so I'm not sure what your point about mechanical cooling is. When you exclude the parking garage from your model do you model all of the adjacent spaces with exterior walls adjacent? -Robby
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Robby--- No, I don't model adjacent walls as exposed unless they are exposed...you can detail adiabatic constructions if you want, don't you do this? Also--I agree that if there are conditioned spaces in commercial parking garages that are *included in the LEED project definition*, however if the parking garage is not included for LEED than I have the right to omit it from my model as I see fit (as the professional simulator of course.) Therefore, we are arguing professional judgements of opinion, where as this initial discussion uncovered that Deepika was referencing a commercial building model Energy Standard, where he should have been referencing a Residential Energy Standard. So why has this discussion turned so wildly away from the subject at hand? I model my commercial garages correctly when they are required no matter what compliance program I am modeling for (i.e. LEED, Oregon ETO guidelines, Title-24, Savings by Design, etc.) My point about mechanical cooling is that if James is parking his car in a garage that has windows, doesn't the solar load into the garage space warrant that some amount of mechanical cooling is needed in his parking garage at work. I can't imagine a sealed parking garage with windows not needing any mechanical cooling, otherwise I am sure that it would be like a Sauna when James leaves work at 6:00pm on the hottest day of the summer in the humidity-laden climate of Arlington, VA. My guess--and it is purely a guess, based on realistic assumptions and whole building science that his commercial/public parking garage at work has some sort of "open air" concept or extremely MASSIVE ventilation fans, to keep the conditions of the parking garage thermally acceptable AND ventilated so as not to "trap" all of the CO from the car exhausts that are entering and leaving the garage throughout the day. If this is the case, or something similar, then it would not make his parking garage a very sustainable or energy efficient building due to the additional energy needed to manage the thermal temperatures inside and the toxic exhaust fumes that are now contained with in a parking garage that has windows. let's keep this discussion friendly and professional and not get too far off the original topic of discussion where the garage that Deepika was referring too was not a commercial parking garage---it is an attached garage to a private residence, in which he is not modeling for LEED for Commercial buildings and in which the WWR value of 40% does not apply to his project requirements. Pasha :)
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I never mentioned am using 90.1 standard. it was a generic question about calculating wwr . and if you say its not important to model unconditioned spaces, how do you account for heat transfer between conditioned and unconditioned spaces? Thanks Deepika
DEEPIKA KHOWAL
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Hmm*...

I think my experience and present thinking sandwiches me somewhere in
the middle of these proposed approaches/assertations... Aboveground
parking garages in my models are never "excluded" entirely, but like
Pasha typically manifest as a collection of building shades, external
lighting loads and process fan loads to represent mechanical
ventilation. Ventilation/lighting loads are defined with unique
scheduling to capture their controls at the meter or sub-meters for easy
documentation/model verification. Building walls against the garage are
modeled as exterior surfaces, shaded but otherwise exposed to outside
ambient conditions

Modeling an unconditioned garage as an unconditioned space/zone (in
eQuest terms) is something I did starting out, and if the garage is very
large/enclosed may allow for a better representation of temperatures for
"semi-conditioned partitions," but it just seems like more work to me
altogether, particularly in LEED documentation and reviewer
clarifications like those bringing this discussion up...

I personally model conditioned and semi-conditioned garage spaces (like
elevator lobbies) as eQuest spaces/zones exactly where they are located
- within the garage or along the actual building perimeter. To one of
James' & Robby's points, these are modeled with exterior walls and in
spite of the garage building shades may experience more extreme
temperatures than in reality as the tempering effects of big slabs of
concrete are present even in fully open garages. For the context of
LEED: the baseline/proposed remain on level footing however by 90.1's
design, and I've yet to run into the case where such "more extreme"
conditions resulted in unmet hours, forcing a more accurate
representation.

Suffice to say, I believe there's more than one "right" way to model a
garage, with different approaches having unique qualities considering
degree-of-accuracy & time-efficiency. We should remember an
"appropriate" degree of accuracy for one model may be overkill for
another (time better spent improving the accuracy of something else).
In energy modeling it's normally difficult to generalize and say any
single approach is "right."

WWR with my approach remains a calculation using the gross exterior wall
& fenestration areas of the non-garage building. The exterior surfaces
of the garage (conveniently) don't wedge their way into eQuest's outputs
to be removed later, because they are not modeled as space surfaces.
Note the alternative of including the garage surfaces for WWR calcs
could ultimately either help OR hurt your performance rating - not sure
if everyone is picking up on that. It would appear both interpretations
have made it through the LEED reviewer gauntlet in any case.

To an earlier point/query somebody touched on: "Enforcement" of
not-quite-matching areas for LEED is something I find to reflect a
reviewers general familiarity (or not) with building modeling practice.
If it's noted my models' totals are very different because they don't
include the gross area of a garage and someone else filled out their
LEED templates in a different fashion, I explain/reiterate the garage is
in fact modeled, the difference in areas are appropriate/expected and
merely the result of how areas are tallied for spaces within eQuest. If
a reviewer should thereafter insist the areas match exactly, an
obstinate response would cost our project team money due to an
additional review, or has otherwise annoyed me to the point I don't feel
like educating him/her, I might just add a dummy space of the
appropriate area to make the tallies match. I haven't run into that
particular reviewer just yet though =).

I cannot speak to modeling fully conditioned (heated and cooled) parking
garages, but if I that crossed my desk I would intuitively define a
conditioned space - I think that places fully conditioned garages out of
the current discussion.

~Nick

* I observe multiple individuals oversimplifying/re-interpreting valid
points others are trying to share... take note that's not furthering the
discussion and only making you look quarrelsome...

NICK CATON, P.E.

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