[BLDG-SIM] ASHRAE 90.1 - window SHGC

[Jeff Haberl]

FYI. 

There is a MS thesis on this topic at the ESL's web site "ecalc.tamu.edu" go to "public" then "reports" then "thesis". Look for the thesis by Jaya Mukhopadyay. 

CWF plays a big role as well as SHGC vs SC. 

Jeff
BB 8=!  8=)  :=)  8=)  ;=)  8=)  8=(  8=)  :=')  8=)  8=)  8=? BB

Jeff S. Haberl, Ph.D., P.E.............................jhaberl at esl.tamu.edu

Professor......................................................Office Ph: 979-845-6507

Department of Architecture.......................Lab Ph: 979-845-6065 

Energy Systems Laboratory.......................FAX: 979-862-2457 

Texas A&M University..............................77843-3581

College Station, Texas, USA.......................URL: www-esl.tamu.edu

BB 8=/  8=)  :=)  8=)  ;=)  8=)  8=()  8=) 8=?  8=)  8=)  8= BB
 

----- Original Message -----
From: BLDG-SIM at gard.com <BLDG-SIM at gard.com>
To: BLDG-SIM at gard.com <BLDG-SIM at gard.com>
Sent: Mon Apr 09 15:10:20 2007
Subject: [BLDG-SIM] ASHRAE 90.1 - window SHGC

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: 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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