[Greenbuilding] Desert windows - fiberglass?

[wmdorsett at sbcglobal.net]

Dan, your dilemma is very similar to one that I've been working through 
for the Midwest. We can (or used to have) cold winters and hot summers. 
Today cooling is becoming the predominant concern. Most of the programs 
available (i.e. RESFEN)  treat all the windows of the house the same 
regardless of orientation. Of course all windows should have as high a 
U-value as possible and ideally have high visible light transmission 
(VT). Our sun is high overhead during the summer, so the incidence on 
the glass reflects most of the light that would overheat a space. So 
south windows can be spec'd for high solar heat gain (SHGC).  Those on 
east and west sides contribute little heat in the winter and are a 
generally terrible in the summer, so they need to be designed for low 
solar heat gain.

The only independent lab testing windows, NFRC has a database which 
rates windows from participating manufacturers. The only problem is that 
at this time the database is not searchable. One of their staff did a 
search for me which listed and ranked windows by U Val<=0.25 SHGC<=0.30 
VT>=0.55. There were only seven manufacturers which met this criteria. 
Of their 14 tested windows only three were not vinyl. Those three were 
wood/aluminum composite. To widen our selection he did a search of their 
database using U Val<=0.30 SHGC<=0.35 VT>=0.55. This brought back a much 
wider group of manufacturers. Instead of a spreadsheet with 11 windows, 
this one lists 6642 windows. Still the highest rated windows are 
predominantly vinyl, with a couple Canadian companies, Fibertec 
(fiberglass) and the Wilmar Challenger line of Jeld-Wen (aluminum clad 
wood) performing best. This database tests just out of the factory 
performance not durability. Their performance can dramatically change 
with for example the failure of weatherstripping.

I have the same hesitations with vinyl: weatherability, and the fact 
that vinyl expands and contracts with temperature than glass (effecting 
the seals especially in your climate), and they are unpaintable.  Wilmar 
Challenger is available in a couple northern states, but draws blank 
looks from Jeld-Wen dealers elsewhere. In pricing for a few small awning 
windows, Fibertec would ship by common carrier for about $1000/window 
plus freight. At this point, I'm looking at Loewen Windows, which still 
are available in Kansas City, and have given enough thought to their 
design to use Santoprene weatherstripping and extruded aluminum cladding 
and offer a glazing option that gives an R-7 for center of glass. 
(http://architect.loewen.com/architect_site.nsf/glazing_heatsmart). 
These may well be $1000/window as well. I'm calling today.

Anyone who wants a copy of the spreadsheet, please contact me off list. 
And I would be grateful any further thoughts.

Bill Dorsett
Sunwrights
Manhattan, KS



Dan Johnson wrote:
> Looking for windows to put in a new house in Phoenix, with a very low
> U-value (0.3 or less) to fight against 115 deg F heat.  I'm concerned
> about the durability of fiberglass frames in that intense UV
> environment.  In my experience, anything synthetic left in the sun
> turns to powder in a few years.  Are fiberglass actually OK?  
>
> Desert window options:
> 1. Fiberglass frames - UV degradation?
> 2. Aluminum frames - hard to find thermally broken Alu frames for
> residential windows, otherwise splendid
> 3. Wood - forget wood in the desert. It will last a year
> 4. Vinyl - avoid vinyl (see dialogue elsewhere); same UV degradation
> as fiberglass?
>
> FYI: also have a good shading scheme, exterior blinds, etc.
>
>
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