[BLDG-SIM] ASHRAE 90.1 - window SHGC

[D. Charlie Curcija]

Len,
 
I knew that I would touch sensitive subject.  Actually, we ran number of
different simulations using both DOE2 and EnergyPlus and in vast majority of
cases for commercial buildings low SHGC products use more energy in climate
zones 5 and above than comparable high solar gain products.  One of the
reasons that this may not have been the case when ASHRAE 90.1 ran scalar
studies, is that it used overly simplified methodology, embedded in a
spreadsheet, which assumes constant SHGC and U-factor.  We have shown (and
some others, like Jeff Haberl from ESL) that this oversimplification causes
errors upwards of 30%!   I have been pointing this to the 90.1 envelope
subcommittee for quite some time now, but it pretty much fell on deaf ears
and was ignored.
 
The contention that commercial buildings are internal load dominated and
that the heating load is not a factor, is a myth, which is easily verified
by looking at the DOE energy information agency data, where it is evident
that commercial buildings in United States use more energy for heating than
for cooling on a national level, which includes all climate zones, such as
1, 2, etc.  If the building stock uses more energy for heating than for
cooling when cooling climate zones are accounted for, it is easy to deduce
that they are using much more energy for heating than for cooling for
climate zones 5 and above.  If the argument is to reduce peak cooling load,
then there is some merit in using low solar gain products in the North, but
we should be very clear on this.
 
We have developed a new tool EFEN, which calculates energy use of commercial
buildings using EnergyPlus simulation engine, and we have interface to
WINDOW5 program, so this is all easily verified.  The program is currently
in Beta testing, so feel free to check it out at:
www.designbuildersoftware.com/efen.php.   The program provides parametric
analysis, so you can easily compare different options.
 
Regards,
Charlie

  _____  

From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Leonard
Sciarra
Sent: Monday, April 09, 2007 2:43 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:  <blocked::mailto:curcija at fenestration.com> 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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