In the average U.S. home, heating and cooling units are the largest single consumers of energy accounting for 50% of household energy use that equates to roughly $950 per household per year. Much of that energy inefficiency is due to heat loss in winter (or gain in summer) through a home’s exterior, or envelope. That could soon change. Researchers at Rensselaer Polytechnic Institute report that they are several steps closer to creating a film that could allow homes, windows, cars, and possibly even soda cans to cool or heat themselves.
The Active Building Envelope (ABE) system could one day allow for radiant heat walls in the winter and self-cooling walls and windows in the summer. The system would have no moving parts, consume only sunlight, and emit only heat or cool air.
ABE uses solar or photovoltaic technology to convert energy from the sun’s rays into electricity. But rather than use that electricity to power an energy-intensive device like a compressor, the electric current would pass through “heat pumps” or a set of dissimilar semiconductors embedded in a sheet of film. When current moves through dissimilar conductors, heat is either released or absorbed depending on the direction of the current (a phenomenon referred to as the Peltier effect). The individual junctions where the semiconductors meet can be connected in a series, thus spreading the heating or cooling effect across a vast surface area.
Previous attempts to harness the Peltier effect for home cooling have involved the use of bulky components such as photovoltaic panels. The newest efforts by the Rensselaer team (working under a grant from the National Science Foundation) involve a microscale version of the same technology. According to the research Web site, recent advances in thin-film thermoelectric systems, coupled with improvements in solar technologies, could result in a cooling or heating film that is extremely efficient, low cost, and as thin as 50-500 micrometers. These thin-film advances could lead to vastly improved climate control systems, according to researcher Steven Van Dessel.
“Applying the system to selected parts of a building’s envelope creates the ability to control the temperature of internal surfaces, which, in turn, regulates the indoor temperature. Essentially, internal surfaces could become warm in the winter and cool in the summer,” says Van Dessel. “Additionally, because the thin-film ABE technologies are based on solidstate materials, they are completely silent and virtually maintenance free. The ease of application would make it possible to seamlessly attach the system to various building surfaces, possibly rendering conventional air-conditioning and heating equipment obsolete.”
It may be possible one day to reduce the ABE technology to a level of thinness and malleability so fine that the “system” essentially becomes not a film but a glaze-an air-conditioning paint. An ABE paint could then be applied to car windshields and sunroofs, as well as equipment to go into space.
“It also may be possible to one day use the ABE system to create packaging materials for thermal control,” Van Dessel adds, “which could lead to things like self-cooling soda bottles.” -Patrick Tucker
Source: Steven Van Dessel, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, New York 12180. Telephone 518-276-2011; Web site http://www.rpi.edu.