United States. A team of engineers at the University of Colorado, Boulder, has developed a scalable manufactured metamaterial — an engineering material with extraordinary properties not found in nature — to act as a type of air conditioning system for structures.
The system has the ability to cool objects even under direct sunlight with zero energy and water consumption.
When applied to a surface, the metamaterial film cools the object below by efficiently reflecting incoming solar energy back into space while allowing the surface to spew its own heat in the form of infrared thermal radiation.
The new material could provide an environmentally friendly means of supplemental cooling for thermoelectric power plants, which currently require large amounts of water and electricity to maintain the operating temperatures of their machines.
The researchers' hybrid glass-polymer material measures just 50 micrometers thick — slightly thicker than the aluminum foil found in a kitchen — and can be economically fabricated in rolls, making it a potentially viable technology on a large scale for both residential and commercial applications.
The material takes advantage of passive radiative cooling, the process by which objects naturally give off heat in the form of infrared radiation, without consuming energy. Thermal radiation provides some natural nighttime cooling and is used for residential cooling in some areas, but daytime cooling has historically been more than a challenge. For a structure exposed to sunlight, even a small amount of directly absorbed solar energy is enough to negate passive radiation.
The challenge for the researchers was to create a material that could provide a double whammy: reflecting incoming solar rays into the atmosphere while still offering an escape route for infrared radiation. To solve this, the researchers incorporated visibly dispersing but radial infrared glass microspheres into a polymer film. They then added a thin silver coating underneath in order to achieve maximum spectral reflectance.
Source: University of Colorado.
