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Smart glass reacts to the weather

By Julie Clothier for CNN
The intelligent coating lets in infrared rays or blocks them out, depending on the outside temperature.
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LONDON, England (CNN) -- Scientists in London have created a coating for glass, which reflects or absorbs heat, depending on the temperature outside.

Professor of inorganic and materials chemistry, Ivan Parkin, and Troy Manning, both of the chemistry department at University College London, developed the intelligent window coating as part of Mr Manning's PhD studies.

The thin film is made out of a material called vanadium dioxide, and it undergoes a change depending on the weather outside.

On cold days the "thermochromic coating" allows all sunlight in, while on hot days, once the outside temperature reaches a certain level, the film begins acting as a filter, blocking infrared rays, which are responsible for generating heat.

Parkin told CNN the film could be manufactured to have a predetermined heat threshold of between zero and 70 C, although it would be most useful if it were set to work at 25 C.

Its altering properties meant it could act as a replacement or partial replacement for air-conditioning systems, reducing electricity costs.

"It acts as a semi-conductor when the temperature is below a certain level, and is transparent. When the temperature rises, it turns into a metal, and becomes reflective," Parkin said.

He has had a huge amount of interest about turning the idea into a commercial reality, particularly from architects, but also from space agency NASA and greenhouse manufacturers.

"The current trend towards using glass extensively in building, poses a dilemma for architects. Do they tint the glass, which reduces the benefit of natural light or face hefty air conditioning bills?" he said.

"It's the architectural holy grail of coating on a building. An intelligent facade like this would allow architects to use more glass in their designs."

Parkin said the idea had been around for a while but most efforts had not been durable enough to make them commercially viable.

"While the heat reflective properties of vanadium dioxide are well recognized, the stumbling block has been the switching temperature," he said.

"We've shown it's possible to reduce the switching temperature to just above room temperature and manufacture it in a commercially viable way."

Parkin said there was still a lot of development needed to turn it into a commercial reality, including altering the color of the film, which is currently yellow. He is currently in negotiations with a manufacturer.

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