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 disagree with both of you.

First of all, who models Garages in their models anyway? What a waste of
time.---this scews the gross floor area, and nothing in a parking garage
impacts the HVAC equipment loads of the conditioned spaces....you can always
input your garage vent fans and lighting as single exterior load input
numbers in your model which simplifies the whole modeling project and
billable time spent WITHOUT compromising on the calculations of energy
use....

Second of all---poor example for offering windows in a parking garage--this
is never real life, and a non-applicable example doesn't "hold water". At
least give an example that is comparable to real life situations... Parking
garages are either open air, or underground (without fenestration...) Have
you ever had a project where Mechanical cooling needed to be provided to a
parking garage? I hope not because these are considered transient space
types.

If you are modeling your LEED buildings according to appendix G --90.1 you
do not include the above grade garage wall area in your gross building WWR
calculation.

FOURTH---Deepika---you are modeling a residential home from your picture you
sent us. YOU CANNOT USE ASHRAE STANDARD 90.1 TO MODEL LOW-RISE RESIDENTIAL
BUILDINGS!

You are using and interpreting the wrong standard, you need to use ASHRAE
Standard 90.2 for Non-commerical Residential buildings. You will need to
use this new reference as everything you are referring to does not apply for
your project or your project model.

The real answer to your question is the Nebraska Cornhusker football team IS
BETTER than the Virgina Tech Hoakies! GO BIG RED!!!!
Pasha

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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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Hi Pasha & Deepika,

Just trying to have a conversation here regarding your methods of modeling
parking garages. Perhaps we can learn from one another in this exchange?

I find very little benefit to not including the parking garage in the model.
You're increasing your project load and simulation run times by a marginal
amount, but you're gaining a more realistic model which accounts for the
temperature float of the unconditioned parking garage and the heat transfer
that will occur between it and the adjacent conditioned spaces. Walls
between conditioned space and unconditioned space should not be modeled as
adiabatic, they should be modeled as Standard walls with a wall construction
per your architectural drawings. These are also technically above grade
walls that should be included in your WWR calculation.

Going back to the original topic, WWR should be calculated based on the
gross area of exterior walls between conditioned spaces and
exterior/unconditioned spaces. The LV-D report includes above-grade walls
that are adjacent to unconditioned spaces, so this incorrectly increases
gross above-grade wall area that should be used in your WWR calculation.
Gross above-grade wall area should be calculated by the energy modeler or
architect based on the actual design drawings and then used to determine the
appropriate amount of glazing in the baseline model. The LV-D reports can
be useful for calibrating the glazing in your model to the calculated
glazing area from the drawings.

Hope this helps,
-Robby

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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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