Super-Insulating Vacuum Glass
In terms of energy efficiency, windows are one of the biggest contributors to heat loss from buildings. However, a new window technology being developed by Guardian Industries could allow for windows that can provide insulation values comparable to a standard insulated 2×4 stud wall, with a new double-pane glass and a vacuum between the panes.
A thermos keeps hot beverages hot and cold beverages cold by separating the contents from the outside world with a vacuum. Heat is conducted by three modes, conduction, convection, and radiation. A vacuum prevents conduction and convection, and a reflective coating serves to reflect radiated heat back where it came from. The Guardian VIG (vacuum-insulated glass) works the same way, with a vacuum between two panes of glass, and a low-E coating to prevent radiant heat from escaping.
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Ordinary single-pane window glass is not much better than an open window when it comes to insulation value. Even a good quality double-pane window only has an R-value of 3 or 4, typically. A typical 2×4 stud wall has an R-value of 12 or better. Superinsulated houses with thick wall construction and very high R-values will often use triple glazing, and will minimize the size of the windows in order to keep the efficiency of the system as high as possible and reduce the amount of energy lost through the windows.
The new glass provides a vacuum space between two panes of glass. To keep the two sheets of glass from being drawn together by the vacuum, low thermal-conductivity spacers are placed in the space between the two panes. (These are the small dots that can be seen in the photograph.)
While the vacuum is only about 1/100th as strong as what is typically found in an ordinary thermos, it is still far better than standard double pane glass in preventing heat loss from conduction and from convection. The only other glazing systems I have come across with close to this level of insulation value have been nanogel-filled windows, but those are just translucent, and do not allow clear vision through the glass.
The manufacturer, Guardian Industries, is reportedly hoping to have this glass commercially available by the end of 2009. More importantly, while other researchers have been exploring the idea of vacuum glass for several years, Guardian is expecting to be able to produce this glass at a reasonable cost over conventional glass.
The head of the Building Technologies Division at Lawrence Berkeley National Laboratory, was quoted as saying, “This performance level would convert most windows in heating climates into net energy suppliers, providing more energy to the home via passive solar gain (even facing north) than the window looses.”
via: BuildingGreen.com
Image Sources: Passive House Institute and Bulding Green.com
What is the R-value of this window?
It’s still in development, so I don’t know that there’s a definite answer for you just yet. But they were talking about center-of-glass values of R-11 to R-12 for it, and the possibility of triple pane assemblies that could give you an R-15 window.
Sounds like a great product.
But it depends what price point this glass is at. My gut feeling is that it will be too expensive for the window industry to look at it favourably.
Some years back, other earlier researchers were having difficulty getting a similar concept down to $15/sq ft. According to BuildingGreen, a few years ago Guardian was get the cost below $6 to $8 sq ft ($65–$86/m2), but recent technological improvements have enabled them to better that.
“Guardian is in discussion with two major U.S. window manufacturers about use of this glazing.”
[...] “several times more efficient than even the best current windows available,” in their Super Insulating Vacuum Glass [...]
Hi,
a similar technic is currently used (and sold) by Velux, whereas only “cavities provide a vacuum space” (I couldn’t find more details):
http://www.velux.ch/VELUXCommon/Resources/cache/c5b764fe-da56-45d3-91f0-727869d9e2f2_Nouveautes06-F.pdf
(”Vitrage sous Vide”)… sorry, it’s in french.
Thanks for the information. My French is too weak for me to confidently translate the information from that site. (Since it’s a Swiss site, the data is in metric format, as well.)
If I’m doing the translation right, though, it’s about R-4.7, which is pretty good for a window, but not as high performance as the Guardian windows. There’s also no discussion of the maximum size that Velux makes, but as they are a residential supplier, I imagine they are not as large as what Guardian is working on. Still, it’s good to point out that other manufacturers are working with this, too.
Asaof, Uw (1,2 W/m².K) currently indicates the thermal transmittance of the window (glass+..), whereas Ug (0,6 W/m².K) is specific of the glass part (sorry for the evidence if things are the same in US, but I’ve no way to know it). If following the convertion factor given by Wikipedia (http://en.wikipedia.org/wiki/R-value_(insulation)), it roughly corresponds to R-9.4, which is terribly good, even better than triple panel glass…
Addendum: I do not work for Velux but as Environnemental Enginner in a public structure :o)
Alpen Window has windows avaliable at R15 and R20 now, from there website information.
I bought some of there R8 glass for a project last year. The make a quality product. They stay so warm that there is no condensing on the glass in a bathroom under almost all but the worst conditions.
I wonder how long the vacuum seals will last. Certainly my existing double-pane windows started leaking around the edges after only a few years. A partial vacuum can’t help that much.