A project boasting the “window of the future,” complete with “switchable” coatings, has European Union experts shelling out some dough.
The Winsmart project, developed by Matthias Koebel, a materials science and technology researcher at Empa Research Institute in Switzerland, received a grant of 3.8 million euros ($4.8 million) through the EU’s Seventh Framework Programme.
EControl Glas, Plauen, Germany
|Switchable glazing in operation at the Fraunhofer Institute IST in Brunswick, Germany. The windows on the left side of the passageway are darkened; those on the right are not. |
The program supports research and innovation efforts throughout the EU.
Researchers say the Winsmart project will develop “intelligent” windows for the next generation of buildings and achieve a new level of air tightness—30 years.
Besting 21 competing proposals for the grant, the project is intended to develop technologies that improve the insulating ability of windows made of conventional glass and add functional properties, such as optically “switchable” coatings.
Koebel says that he’s confident that the first Winsmart window will be on the market in five to 10 years.
Coatings Replace Blinds, Shades
Part of the project concentrates on developing a glass pane coating that will allow the windows to autonomously darken and lighten themselves.
A process called “vacuum sputtering” is used to deposit thin layers of material 100-200 nm thick on the glass. The process is done in a vacuum chamber, with the materials being vaporized at high temperatures, then condensating onto the glass surface, researchers explain.
The experimental setup at Empa used to produce glazing prototypes with the new edge sealing technique. The cylindrical, copper-colored injection head is clearly visible—it injects a liquid tin alloy between the panes.
The process creates an electrically conducting layer, topped by a “switchable” layer made of, for example, tungsten oxide. This type of functional device layer is therefore always enclosed between two electrically conducting layers.
At the press of a button, a battery or power supply lets current flow through the layered device and the tungsten oxide reacts to darken the glass.
If the “window of the future” were able to measure the illuminance (the amount of light falling on it), it could autonomously darken or lighten itself as necessary, obviating the need for a power supply, according to the researchers.
In theory, a number of additional coatings could be applied on top of each other to make the glass water-repellent or scratch-resistant, in addition to the optical switching functionality.
Koebel's team is developing alternative wet-chemical processes to do this, replacing the vacuum sputtering technique, which is both energy and cost intensive.
Conventional double-glazed windows consist of two glass sheets mounted in an aluminum frame. This frame also encloses a 1.5 to 2 cm thick gap between the panes, which is sealed with silicone and filled with a noble gas. The gas prevents the transmission of heat through the window.
Winsmart researchers say they have developed a “new vacuum insulating system” that is one-third the thickness of conventional double-glazed windows.
Further, the space between the panes is evacuated to a high vacuum, giving the window superior insulation performance, researchers add. The gap between the panes is 0.2 to 2.7 mm wide and is maintained by a large number of tiny spacers placed between the glass sheets.
Firming Up Framing
The kind of aluminum frame used today in conventional window production would, however, immediately buckle under atmospheric pressure and no longer be able to maintain its structural integrity. In addition, the leak tightness of conventional construction techniques is inadequate for a vacuum glazing.
For these reasons, the researchers say, the surrounding frame has to be made more robust. The team is working on a patented process, in which the two glass panes are placed in a vacuum chamber and a liquid tin alloy is injected all around the edges of the cavity to form the so-called edge seal.
The researchers say that because of the differences in surface tension between glass and liquid tin, the latter behaves like rainwater on a lotus leaf—water droplets run off.
“The scientists overcame this problem by applying an electric voltage to the tin metal for a short period of time, a necessary process step to ensure that the metal adheres properly to the glass and that, after solidifying, the seal strengthens and remains airtight for the next 30 years as required,” the researchers say.
Mass Production Plans
“Cutting the glass to size, applying switchable layers, sealing the edges under high vacuum—all these steps should in future take place one after the other on a production line,” according to the researchers.
So, in cooperation with the industrial partners, the project is also developing advanced production technologies. For example, the research team is developing robots to inject the liquid metal between the glass panes.
The project partners include Danish Technological Institute DTI; Fraunhofer-Gesellschaft, ISE & IWM, Frieburg, Germany; University of Ljubljana, Slovenia; AGC Glass Europe, Belgium; PhotoSolar A/S, Denmark; EControl-Glas GmbH & Co. KG, Germany; and Scandia Windows, Denmark.
Knowledge = Currency
“Knowledge is the currency of the global economy,” says European Research, Innovation and Science Commissioner Máire Geoghegan-Quinn, in an announcement on the grant.
“If Europe wants to continue to compete in the 21st century, we must support the research and innovation that will generate growth and jobs, now and in the future. The high level of competition for EU funding makes sure that taxpayers' money goes to the best projects that tackle issues that concern all of us.”