[Bldg-sim] Appendix G Window to wall ratio

Mon Apr 18 09:40:21 PDT 2016

Hi,

As a side point, if you use eQuest, be careful when using the simulation
output to calculate the W2W ratio.  If you modify the roof, which I do
regularly because of overlapping building shells, the W2W ratio from the
LV-D report may not be correct.    Only EXTERIOR-WALL with LOCATION =TOP is
counted as ROOF.   Anything else is counted as EXTERIOR-WALL.   On a recent
school, the LV-D said the W2W ratio = 16.3% when the real number was 20.6%.
Also, make sure to check that the baseline model generator has assigned the
correct constructions.

Shaun Martin LEED-AP, BEMP

Principal

Shaun Martin Consulting

#90 – 425 Carrall Street

Vancouver, BC  V6B 6E3

p. 604-789-1095

From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of
via Bldg-sim
Sent: April 15, 2016 12:17 PM
To: jglazer at gard.com; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Appendix G Window to wall ratio

Hi there K!

As far as LEED/GBCI reviews are concerned, the User’s manual is a very
strong a resource to cite in my experience, especially where it can serve to
clarify something less clear in the Standard.

That said, I’ll admit to being shifty at times on this issue (there are
certainly grey areas the standard doesn’t clearly address), but I would
probably lean towards Jason’s interpretation as well for most cases.  In my
own phrasing:  Draw the WWR area line to exclude “conditioned envelope that
faces dirt.”  

If you are dealing with a building featuring tons of glass facade, do keep
in mind that opaque glass façade areas (i.e. spandrel) may be excluded when
tallying the window area (be sure your model reflects such a distinction).  

If the quantity of windows in your semi-underground levels is pushing you
just past the “40% mark” for the building as a whole (I assume that’s what
you’re referencing), then do acknowledge/communicate with your design team
that they are toe-ing the line with the Standard.  Some project-specific
sensitivity analysis may be helpful for your own understanding before waving
a big red flag over the issue:  bumping slightly past that 40% mark often
won’t hurt performance rating much, but a building with 80% WWR is almost
certain to feel the burn.  

Also note that if you are making more use out of the building’s relatively
high WWR from an energy perspective (i.e. natural ventilation for thermal
comfort, daylighting controls, deliberate solar load shading considerations
for certain climates
), there’s nothing stopping your team from claiming a
net credit considering everything together.  

Finally, as a fellow who LOVES energy modeling but also likes getting
outside every so often, I personally reckon extra daylighting and views are
subjectively “worth” a net energy penalty.  I think most building
owners/tenants outside of the vampire population would generally agree.
Consider me a fan of higher window distributions, so long as you’re keeping
me thermally and visually comfortable (glare control please!).

As to whether Appendix G  intends to “penalize” below grade floors with
windows
 that might just be a stretch.  If you were to flip around the
situation (include below grade envelope for WWR calcs) – it would be weird
to generally “encourage/discourage” the use of below grade windows facing
dirt, right?  As a general rule, I try to remind myself that it’s probably
safe to assume the committee drafting this language never had any
specific/given project in mind, and were just trying to come up with a
generally fair (if occasionally arbitrary/silly) line to draw in the sand
that would suit most cases.

Hope this helps you enjoy the weekend a little more!

~Nick

----------------------------------------------------------------------------
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Nick Caton, P.E.

  Senior Energy Engineer
  Energy and Sustainability Services
  North America Operations
  Schneider Electric

D  913.564.6361 
M  785.410.3317 
E   <mailto:nicholas.caton at schneider-electric.com>
nicholas.caton at schneider-electric.com
F  913.564.6380

15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States

From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of
Jason Glazer via Bldg-sim
Sent: Friday, April 15, 2016 1:17 PM
To: bldg-sim at lists.onebuilding.org <mailto:bldg-sim at lists.onebuilding.org> 
Subject: Re: [Bldg-sim] Appendix G Window to wall ratio

I would suggest that you count only the portion of the wall that is above
grade. Just my opinion.

Jason

On 4/14/2016 5:17 PM, k bk via Bldg-sim wrote:

Appendix G (LEED) indicates that when we calculate the window to wall ratio
only the above grade walls shall be included.

We have a building design where the conditioned basement wall partially
protrudes above ground and also has windows that let in sunlight. It is
unclear if in this circumstance we could count the whole wall in the window
to wall ratio. Any body have any hints.

Surprisingly, this definition of below grade wall appears to apply only to
appendix G & LEED. As per the user manual to 90.1 the below grade wall can
be included towards the window to wall ratio, for the prescriptive path and
chapter 11.

Frankly speaking, it is unfortunate that Appendix G & LEED, Would discourage
the construction of below grade conditioned spaces in this manner. In
essence aren't we increasing the efficiency of the building if we put
conditioned spaces below grade. 

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