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Gaurdian must be getting close to releasing their latest high tech glazing system, it was at the Remodeler Show. They have been playing with vacuum to eliminate convective and conductive heat transfer and are getting very impressive performance with simple two layer low E coatings. You can read about it here: http://www.enn.com/sci-tech/article/31817

Given the recent thread about melted siding caused by convetional low E glazings, I thought some of you might be interested.

Tom

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Fantastic if they can make it work long term? Will the unit will still be susceptible to glazing seal leaks like gas filled units? 1 - 3 years down the road what will happen? Should you size your mechanical system for the higher R value? The other thing I noticed is "a center-of-glass insulating value of R-12 to R-13", where exactly is the center of glass? Are they ignoring the thermal bridging at the frame, and if so what is the size of the IGU?

What are your opinions?

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The R-value of an IG unit is always measured at the center of glass, that is where it is most efficient. I was impressed with the U-factors in the .18 - .19 range. U-factor is the measure of actual energy transfer (not just resistance) and as such the entire IG unit is considered. They got to that level of performance with a very primative and inexpensive low E coating, one that doesn't meet today's energy star criteria in an argon filled unit, nearly of that performance comes from the vacuum. To reach .18 with a typical unit one needs at least three pieces of glass, 12 or more low E coatings on at least two different surfaces, and krypton gas, and the Solar Heat Gain Coefficient ususally ends up around .20 and Visable Transmittance is way low too (looks tinted). Gaurdian managed to keep VT and SHGC in the realm of high end dual pane low E products and beat the U factor of triple panes in a unit less than 1/2 the overall thickness, I'm impressed.

I don't think that Seal Failure is going to be a significant issue, most of the failures I see have more to do with how the glazing fits into the sash assembly than with spacer failures. There are a couple of argon unit manufacturers that are asking for trouble though. They have been assembling IGs in an argon atmosphere for 100% fill. The last time a big glass company tried for 100% fill rates there were major failures. Argon molecules are small enough to pass through the molecules of the other materials in an IG assembly creating a vacuum that the unit wasn't designed to withstand. If the airspace temp falls far enough, fast enough the stresses can be impressive. I've seen lots of imploded argon IGs as a result. Argon evacuation happens much slower at the industry standard 93-95% fill rate, less than 1/2% per year, and the stresses build much slower and units will seal fail or stress crack or adjust and work fine.

Tom

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