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
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DEEPIKA KHOWAL
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
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.