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
Mr philip, we keep on seeing press release about the guardian VIG. Can you please mail me more about this technology and if it is manual or automated? The final Price and the application of Use? if it is a big commercial project, the production is high enought to cover it? any brochure? or sample???
Thank you for your collaboration
how well would these work in southern humid climates?
Great solution! But how glass panels with vacuuumed air from the cavity will stay flat in temperature changes. Lets say in Dubai climate where AC keeep air cool inside, and outdoor air is extremally hot? Are there any invisible to human eye partitions between glass panels?
This SIVG window pane w/ 15 r factor will probably be suitable for our off grid green residential and commercial structures under design now for north America. As this product is sold in volume the cost will come down as with most products.
As to how long the windows will hold vacuum: it mostly depends on the edge seals. There is no reason in principle not to make the windows re-evacuatable. The article mentions that the vacuum level is 100X typical pressure in a thermos (which is around 10^-7 torr. I’m guessing they picked the initial vacuum level so that not too much change will occur in one year.
I did calculations years ago (on plastic extruded glazing) which showed that the energy cost to run a vacuum pump occasionally to re-establish a vacuum is very well energy justified.
The edge seal is an air tight glassy compound fused to the glass sheets - nothing like the organic sealants used in traditional IG units. Therefor the life expectancy is targeted at more than the 10 or 20 years of traditional IG units. The vacuum cannot be “refreshed”. The units are pumped down and remain under vacuum for the lifetime. There is a threshold vacuum that has to be maintained in order that gas conduction is virtually eliminated, which maintains the high R-value. The low-E double silver or triple silver coating is the workhorse for reducing thermal (radiant) transfer. The pillars that hold the glass apart are a clear compound - very hard and 1mm in diameter by 0.25mm thick - which is the cavity thickness as well. The VIG will work in any climate - it is really just a calculation of energy cost to heat or cool (plus smaller HVAC) vs. the benefit from VIG. Achieving R-10 (COG) at the cost of a (less efficient) triple pane along with pending government and energy star initiatives will be the main drivers to commercialization.
I have an idea for what I feel will provide a very low-cost approach to vacuum-insulated glass, with an extended life. Would Guardian or some other manufacturer be interested in talking to me?
S.M.Hunter, Ph.D
The cacuum seals last for about 10 years.
Our company Qingdao Hengda Glass in China can produce vacuum glass. If you are in need of them, please let us know.
email:phoebe-wang86@hotmail.com
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