Cooling Film

A new plastic film has been developed that can cool buildings without the need for refrigerants – and without using power – even in direct sunlight. Best of all, it can be manufactured using standard roll-to-roll methods for about 50 cents per square meter.

The material exploits an “infrared window” in the Earth’s atmosphere that allows certain wavelengths of heat-carrying infrared radiation to pass into space. As objects shed heat through passive radiative cooling, the source of that heat will remain cool. The trick was to convert the heat from a building to the proper wavelength so that it can escape without any bounce-back effect from the atmosphere. This was done by embedding tiny glass beads into a commercially available transparent plastic to create a film that’s about 50 microns thick (slightly thicker than aluminum foil). The diameter of the beads – in this case, about eight microns – determines the wavelength of the radiation emitted. In addition, the back of the film is coated with silver to reflect incident sunlight and further reduce heat buildup.

The net effect is 93 watts per square meter of cooling when exposed to direct sunlight, and even better at night. According to estimates, 20 square meters of the film placed on the roof of an average home would be adequate to maintain an inside temperature of 68 degrees Fahrenheit (20 degrees Celsius) on a typical hot summer day.

Besides cooling homes and other buildings, the film could provide supplementary cooling for thermoelectric power plants, where large amounts of water and electricity are needed to maintain equipment temperatures within a certain range. It may also be used to improve the efficiency of solar panels, which can overheat, reducing their generating capacity. The developers plan to build a 200-square meter prototype “cooling farm” this year to further evaluate the commercial applications.