Watery windows mimic blood vessels to boost building efficiency

Researchers at the University of Toronto say they can improve the energy of efficiency buildings by fitting window panes with tiny channels of water. The scientists says that these channels, inspired by vascular systems in nature such as the network of blood vessels in the human body, can provide 7º to 9º C of cooling in the summer, and reduce heat loss during winter.

The researchers developed a sheet of transparent flexible polymer with a "cooling layer" of clear silicone, inside which there are the tiny channels with a cross section 1 or 2 mm high and 100 micrometers across. Through these, room temperature water was circulated to and from an external source at a rate of 2 ml per minute.

The sheet was applied to a model window 10 x 10 cm (3.9 x 3.9 in) in size, an analyzed with an infrared camera. The researchers say that the temperature of the window, which had been artificially heated, was reduced by 7º to 9º C. Because the temperature of the water is lower relative to the window, it is able to absorb heat energy and take it away. The process would be the opposite during the winter, when room temperature water would supply heat to the rest of the window. In either case the idea is that the window would become a more effective barrier to convective heat transfer, making the building more energy efficient.

When filled with water, the researchers say that the channels are "not clearly visible," but that when filled with a different liquid which refracts light a similar amount to the surrounding material, they become almost invisible. They suggest that different liquids could be used for various aesthetic effects such as altering color and transparency.

The researchers were inspired by vascular systems in nature such as blood vessels in the human body which can expand and contract to increase or reduce heat loss when too warm or cold. The technology may also be applicable to photovoltaic solar panels which are more efficient at lower temperatures.