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Managing Editor  | February 2017

New material designed to cool buildings in eco-friendly manner


Engineers at the University of Colorado at Boulder have developed a scalable, manufactured metamaterial from a glass-polymer hybrid that effectively reflects solar energy, while allowing for the dissipation of infrared thermal radiation, according to a report on the school’s website.

 

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A new metamaterial will allow for cooling buildings without requiring air conditioning. (Unsplash)

 

The material can be used to cool buildings and other structures, even in direct sunlight, without the need for thermoelectric coolers or air conditioning systems that require resources such as electricity and water.

 

Its properties were engineered by the inclusion of glass microspheres in a polymer film. The microspheres are visibly-scattering but infrared-radiant, according to the university. The film is coated with a thin layer of silver on the underside to optimize its spectral reflectance.

 

Another major development was the engineers’ ability to produce the glass-polymer hybrid material, which is just 50 micrometers thick, in rolls of film. This makes it a material that can be scaled for industrial and commercial applications, such as the production of solar cells where this material could add one or two percent to the cell’s efficiency.

 

“The engineers have applied for a patent for the technology and are working with CU Boulder’s Technology Transfer Office to explore potential commercial applications,” noted the article. “They plan to create a 200-square-meter ‘cooling farm’ prototype in Boulder in 2017.”

 

As an article from The Economist indicated, more than 6 percent of the electricity generated in the U.S. is used to air condition buildings. This is expensive in terms of dollars and resources, so this new material, which costs only $0.50 per square meter to produce, is a potential game-changer.

 

The article added, “That cooling effect, 93 watts per square meter in direct sunlight, and more at night, is potent. The team estimates that 20 square meters of their film, placed atop an average American house, would be enough to keep the internal temperature at 20°C on a day when it was 37°C outside.”

 

The work was also published in a recent edition of Science. The abstract stated:

 

“Passive radiative cooling draws heat from surfaces and radiates it into space as infrared radiation to which the atmosphere is transparent. However, the energy density mismatch between solar irradiance and the low infrared radiation flux from a near-ambient-temperature surface require materials that strongly emit thermal energy and barely absorb sunlight.

 

“We embedded resonant polar dielectric microspheres randomly in a polymeric matrix, resulting in a metamaterial that is fully transparent to the solar spectrum while having an infrared emissivity greater than 0.93 across the atmospheric window. When backed with silver coating, the metamaterial shows a noon-time radiative cooling power of 93 W/m2 under direct sunshine.

 

“More critically, we demonstrated high-throughput, economical roll-to-roll manufacturing of the metamaterial, vital for promoting radiative cooling as a viable energy technology.”

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