[Bldg-sim] Do I need to use the actual window shape?

[Nick Caton]

I have modeled cases like this both ways and will continue to approach them leaving options open.

Sometimes a combined area of windows is an acceptable approximation, and sometimes it is not.  It very much depends on the purpose and intent of the model (notably, what degree of accuracy is expected of the envelope).

One can have a self-imposed 'standard' and that's fine (I personally choose to regularly do/avoid some things it might be weird to expect others to do/avoid), but in the end such approximations are the call of the person constructing the model.  All such choices may be fairly made on a case-by-case basis if you are comfortable doing so and justifying your choices.

In the case of a LEED model, I would personally match the actual window layout in normal practice, and in doing so match the actual framing perimeter sums.  That said, I think LEED (really, 90.1 Appendix G) is intentionally constructed to permit a range of choices in this regard.  If you're made to approximate windows by combining their areas for whatever reason (I can think of a few good ones), provided your baseline has a matching layout you've maintained a level playing field and should be able to sleep easy at night =).

If your absolute concern is modeled accuracy of the envelope/glazing systems (read: not necessarily a LEED performance rating model) - certainly you should pay close mind to the actual framing areas and developed lengths for all the reasons discussed so far.

~Nick

[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.
SENIOR ENGINEER

Smith & Boucher Engineers
25501 west valley parkway, suite 200
olathe, ks 66061
direct 913.344.0036
fax 913.345.0617
www.smithboucher.com

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of RobertWichert
Sent: Wednesday, February 29, 2012 12:48 PM
To: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Do I need to use the actual window shape?

There would be a difference, for instance, if there were ten windows, all with metal frames, and you modeled that as one big window with ten times the area.  I wouldn't do that.  Maybe not important, but I wouldn't do it.

The soffit only comes into the question of there is an overhang, which is shading, and must be modeled if you want to take credit for it.

I think.





Robert Wichert P.Eng. LEED AP

+1 916 966 9060

FAX +1 916 966 9068















===============================================

On 2/29/2012 10:02 AM, Morgan Heater wrote:
You can model whatever size and shape you want as long as your area weighted SHGC, and U-value are correct, and your shading is modeling correctly.  Daylighting performance might be affected slightly, along with passive solar performance, but I am fairly certain that the affect would be very small compared with the annual building energy use.  If you're genuinely curious, try it.  Model a couple of different scenarios, all with the same total area, u-value, and SHGC, and see what happens.


Morgan Heater, P.E.
BEMP, LEED AP
morgan at ecotope.com<mailto:morgan at ecotope.com>
206-322-3753 ext 209

From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of JRR
Sent: Tuesday, February 28, 2012 6:24 PM
To: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: Re: [Bldg-sim] Do I need to use the actual window shape?

YES  SEE  Passive Solar Handbook Extended Professional Edition,  Mazria,   1979.  try  Amazon.com

IT"S the header space at the top of the window, the width of the soffit,  that turns off the summer heat................

bye.......


On 2/24/2012 12:10 PM, Alex Krickx wrote:
Hi Esmireta,

I'm not sure about what LEED requires, but I would be aware that in addition to Window-Wall Ratio, you should also consider Glass-Frame ratio. Depending on the software and method that you model windows, two 3'x5' windows with a 1" frame are NOT the same as one 6'x5' window (the 6'x5' would have two vertical components, whereas the two 3'x5' would have four vertical components). I'm not sure a LEED reviewer would notice the difference, but I think best practice is to include the correct frame area in your model.

Kind regards,
Alex Krickx

Alex Krickx, LEED AP
Building Energy Specialist
Serious Energy, Inc.
1250 Elko Dr, Sunnyvale, CA 94089
(t) 408.541.8124
akrickx at seriousenergy.com<mailto:akrickx at seriousenergy.com>

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From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Esmireta
Sent: Thursday, February 23, 2012 5:45 PM
To: BLDGSIM
Subject: [Bldg-sim] Do I need to use the actual window shape?

When doing the LEED project, do I need to use the actual window shape, or just keep the window-wall ratio in each direction?
I don't think the window shape will influence the energy cost if the window-wall ratio is the same. But I don't know if the LEED reviewer care about it.
Thanks a lot!






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