[BLDG-SIM] ASHRAE 90.1 - window SHGC

David S Eldridge DSE at grummanbutkus.com
Tue Apr 10 12:14:37 PDT 2007


Remember that those total annual energy quantities include
heating/cooling for the outside air which may be different than envelope
heating loads, and that the energy costs are not the same per BTU.  (Not
sure where the EIA totals come from - DHW may also be included?)
 
That said, a typical "square" design would have perimeter zones that
would/wouldn't need heating even while the core of the building required
cooling.  That effect would be captured by an ECB analysis or Appendix G
analysis with the baseline building being "penalized' for using the
standard's glazing.  The trade-offs between additional cooling and
beneficial solar heating could be quantified then, including the costs.
 
Obviously, a building that might benefit from reduced glazing
requirements will now have to do a simulation to document that fact in
the code or LEED process.  They could probably commission a much
simplified model to determine what level of glazing works best and then
either build a prescriptive building or pursue ECB as necessary.
 
A LEED building would normally have much of this modeling work included
in their scope anyway for EAC1, so an additional modeling exercise to
determine the optimal glazing wouldn't be a big deal.
 
I only see this as a major problem for buildings in the northerly
climates that wanted to use 90.1 prescriptively, and that weren't going
to run an energy model already.  I don't have a feel for how many
buildings would fall into that category.
 
--------------------------------------------------------------
David S. Eldridge, Jr.
Project Engineer
LEED v2.0 Accredited Professional
Grumman/Butkus Associates
820 Davis St., Suite 300
Evanston, IL  60201
847.328.3555  ext. 224
dse at grummanbutkus.com
-------------------------------------------------------------


________________________________

	From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of
Leonard Sciarra
	Sent: Monday, April 09, 2007 1:43 PM
	To: BLDG-SIM at gard.com
	Subject: [BLDG-SIM] ASHRAE 90.1 - window SHGC
	
	
	Charlie,
	 
	(this maybe off topic) 
	 
	Good point, however, you must remember, that the development of
the prescriptive tables in 90.1 is based on a generic office building
with an floor plan aspect ratio of 1:1.  it is an internally load
dominated building, so even up to climate zone 7 (maybe not 8) in
calculating ANNUAL energy consumption, reducing solar heat gain (while
allowing some light in for assumed daylighting) was the key factor in
the glazing selection that comes out of the model.  Again, it was annual
energy consumption.  
	 
	Prescriptive codes are blunt instruments of change.   I think we
all agree that if you change the building aspect ratio, choose good
glass/shading and install a daylight harvesting/dimming system, design
the interior to take advantage of all of this, you are 70% of the way to
a kick ass energy efficient design.
	 
	Leonard Sciarra, AIA, LEED ap

	312.577.6580 (Dir)

	G E N S L E R | Architecture & Design Worldwide

	30 West Monroe Street

	Chicago IL, 60603

	312.456.0123

	
	 
________________________________

	From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of
D. Charlie Curcija
	Sent: Monday, April 09, 2007 8:50 AM
	To: BLDG-SIM at gard.com
	Subject: [BLDG-SIM] ASHRAE 90.1 - window SHGC
	
	
	International Glazing Database (IGDB), which is part of WINDOW
5.2 program (windows.lbl.gov) contains several hundred individual glass
layers whose solar transmittance is at or below 0.3, which, as a part of
glazing system and whole fenestration product, would produce SHGC of
0.25 or lower, which meets ASHRAE 90.1 for all climate zones.  The best
choice for low SHGC windows is so called spectrally selective low-e, and
there are at least 100 glass products with this type of low-e coating.
The cost of these products is only marginally higher than the cost of
clear glass.
	 
	I think that you are definitely overlooking something.
	 
	Having said that, I do want to state that the use of low SHGC
products in heating dominated climates (anything at or above climate
zone 5) is wrong and is the major flaw of both ASHRAE 90.1 and IECC
2006, particularly for orientations with potentially high solar gain in
the winter, such as South orientation.
	 
	D. Charlie Curcija
	Carli, Inc.
	18 Tanglewood Rd.
	Amherst, MA 01002
	 
	Tel: (413) 256-4647
	Fax: (413) 256-4823
	cell: (413) 575-3487
	email: curcija at fenestration.com
<blocked::mailto:curcija at fenestration.com> 
	web: http://www.fenestration.com <http://www.fenestration.com/> 
	 
	
	
	Support open document format as the best way to assure full
compatibility and interoperability! 
	 
	
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