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A team of engineers from the University of Colorado in Boulder, United States, developed an expandable manufactured metamaterial. It is a material with extraordinary properties not found in nature, which acts as a kind of air conditioning system for structures.
It has the ability to cool objects even under direct sunlight without consuming energy or water. When applied to a surface, the metamaterial film cools the object underneath by efficiently reflecting incoming solar energy back to the outside while simultaneously allowing the surface to expel its own heat in the form of thermal infrared radiation.
The news about this new development was published in the journal ‘Science’. It is a hybrid glass-polymer material that is slightly thicker than the aluminum foil used in the kitchen, and can be inexpensively manufactured in rolls, making it a potentially viable technology on a large scale for both residential and commercial applications.
"We believe that this low-cost manufacturing process will be able to transform real-world applications with this radiative cooling technology," said Xiaobo Yin, co-director of the research, assistant professor in CU Boulder's Department of Mechanical Engineering and Program. Materials Science and Engineering.
The material takes advantage of passive radiative cooling, the process by which objects naturally release 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 cooling during the day has historically been more of a challenge. For a structure exposed to sunlight, even a small amount of directly absorbed solar energy is sufficient to prevent passive radiation.
Thus, the challenge for the CU Boulder researchers was to create a material that could reflect incoming solar rays back into the atmosphere and still provide a means of escape for infrared radiation. To solve this, the authors incorporated visibly scattered, infrared radiating glass microspheres into a polymer film. A fine silver coating was then added underneath in order to achieve maximum spectral reflectance.
"Only between 10 and 20 square meters of this material on the roof could cool a single-family house well in summer", gives as an example another of the authors of this work, Gang Tan, associate professor in the Department of Civil and Architectural Engineering of the University of Wyoming, United States.
As well as being useful for cooling buildings and power plants, the material could also help improve the efficiency and lifespan of solar panels. In direct sunlight, panels can overheat to temperatures that hinder their ability to convert sunlight into electricity.