Dear all,
When you are rotating the building through 4 different orientations, do you
change the glazing so that the glazing with the highest SHGC is always faces
north, or do you put the glazing with high SHGC on the original north
facade, and then rotate the building so that the high SHGC glazing faces the
east, south and west orientations in subsequent simulations?
Yours faithfully,
*Ulrik Welle-Strand Horn *
Dear Ulrik,
Since the intent of the Standard is to assign the better glazing performance
to non-North walls, I always rotate the glazing characteristics with the
building. (e.g., I assign the "North" glazing characteristics to the
elevation that, after rotating, faces North)
James V. Dirkes II, P.E., LEED AP
I read Table G3.1 section 5 sub item (c) under the baseline building performance column to require use of the "SHGC_all" for all vertical glazing. Have others read that and reached a different conclusion? Did I miss an addenda? or a CIR?
I agree and was looking for that reference as we speak!
Brenda V. Morawa, PE LEED AP QCxP
Paul,
That's a VERY valid point. Thanks for pointing it out.
*Ulrik Welle-Strand Horn *
A90.1-2007 removed the reference to SHGC_All and refers to the Chapter 5
tables. You should be able to use the SHGC_north in the baseline if you
follow 2007.
Regards,
Bill Talbert, PE, LEED? AP
AM >>> Paul,
That's a VERY valid point. Thanks for pointing it out.
Ulrik Welle
This is an interesting discussion (one that may have already occurred
previously). According to the 90.1 User Manual:
"SHGC - The budget building design's fenestration solar heat gain
coefficient is set to the maximum required for the climate. The
prescriptive standards give SHGC criteria for all orientations and
provide an exception for north facing fenestration. The exception is
not used for the baseline building; the criteria for all orientations
are used for all orientations..."
However, even the LEED-NC EAc1 template differentiates between the North
SHGC and the rest of the fenestration....if the exception is not to be
used, why would the USGBC have a place to enter the SHGC(north) for the
baseline building?? And why would they accept two different SHGCs for
the baseline building on the template?
I can't seem to find any NC or CS CIRs that address this.
James Hansen, PE, LEED AP
Sorry, I should have read further before posting. In the LEED-NC
reference guide, it states:
"The four Baseline Design energy models are identical to each other,
except that the building orientation for each model is modified as
described in ASHRAE Std 90.1 Table G3.5.1a, and the window SHGCs are
revised to reflect the minimum ASHRAE Building Envelope Requirements for
the revised building orientation."
In other words, the USGBC, whether on purpose or not, has provided its
own exception to 90.1 that allows you to use the SHGC(north) in the
baseline models. And yes, after rotating, you have to reassign the
proper SHGCs to the new "north".
James Hansen, PE, LEED AP
All;
I certainly do NOT think the 2007 PRM requires that the baseline glazing "North" SHGCs be "moved" as the "North" exposures change in each of the simulations that generates the "baseline building performance." I could see how one might think that, but say it ain't so. I assume the baseline "North" SHGC is applied to what would be "North" glazing in the proposed and unrotated baseline models, and those glazing parameters are left in place for that facade as the baseline model is rotated. I don't think this has been fodder for a USGBC CIR or ASHRAE interpretation yet, but maybe I'm out of touch. Addendum A to 2004, which removed the glazing redistribution requirement, still used SHGC_all for all baseline glazing. I thought this had been incorporated verbatim in the 2007 edits but noooooo. Time to get out the magnifier and channel my inner attorney.
Fred
Aha. Yes, there it is in the NC 2.2 revised EAc1 section, not under the
envelope heading of course. But if using the PRM from the 2007 App G, I
would reference the 2007 Users' Manual for further explanation and find
on G-16:
SHGC
"... The prescriptive standards give SHGC criteria
for all orientations and provide an
exception for north facing fenestration.
The exception is not used for the baseline
building; the criteria for all orientations are
used for all orientations. The maximum
SHGC is a function of the glazing
percentage, which is taken from the
proposed design or 40% of the gross
above-grade exterior wall, which ever is
less."
Which happens to be exactly the same text as in the 2004 UM. Of course,
if using 2007 App G, baseline models are supposed to reflect the more
stringent window parameters in Chapter 5.
Fred