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Re: GBlist: window performance



Rod asked:
<< Question: Is there performance data for windows over the long term - 5,
10,20
 years?>> snip, and 

<< we have installed triple glazed Winnipeg windows with fiberglas frames
that appear to be good in most areas but have noticed a few structural things
that make me wonder about their long term performance (although we are pretty
pleased with them on the whole.)   
 
It seems to me test performances on brand new windows is not the whole
 picture. I once installed low - leakage, double weather stripped windows to
 later discover that the sun degenerated the strips to uselessness within 5
 years. What about low-e argon windows? Does the argon eventually disperse
 over an unacceptably short time reducing the insulating value to dry air
 again? Does the film degenerate similarily? >>

Rod, 
Unfortunately, you hit a home run with this line of thinking.  Standards for
"long term performance" and "performance degradation" have been LONG in
DEVELOPMENT and short on application.  BUT, Take Heart!  There are some
interesting activities afoot that are (hopefully) going to take some major
steps toward the answers you seek.

First, NFRC has a "long term energy performance" subcommittee that is about
to initiate a very aggressive test program to evaluate how a few SPECIFIC
performance indices change when subjected to accellerated weathering.
 (Aside.... there has been  little agreement among the technical and
standards community as to WHAT should be tested and HOW it should be tested)
 NFRC dodged THAT bullet (kinda) and developed its own proposed protocol
(based in part on some of the unheeded suggestions of the past) and testing
is about to begin on about 20 windows in a one-year program.  Hot, cold, UV,
operation, water, repeats, extremes, etc.  (For details on the test plan,
contact NFRC at 301-589-NFRC.)  Prior to, during and followinf the testing,
window air leakage and U-factor will be assessed.  In theory, these values
will be used to adjust the initial performance values based on the long term
performance expectations for that particular product.

Yes, this is STILL a long way off.... but you and those like you that are
actually THINK about long term performance should get involved in this (and
similar projects) to MAKE SURE THEY SUCCEED!!!!

and the short answers to your questions include:

Argon (and other gasses) WILL leak out over time (as long as the laws of
physics and diffusion hold up) and will be replaced by air.  In high
performanece units this is particularly bad because the moisture laden air
condenses on the metal surfaces of the films and coatings and corrosion
(RUST) will result.  "Low-e" will become "High-E" and energy performance goes
(dare I say it?) out the wi...... 

The up-side is that a good IG unit's seal SHOULD last a pretty long time....
20+ years?

Standard rant about window and IG warranties..... read the fine print and
pick a manufacturer that will be there and stand behind their product....


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