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2018-09-27. Cooling paint drops the temperature of any surface.

posted Sep 29, 2018, 9:17 PM by Alan Gould   [ updated Sep 29, 2018, 9:17 PM ]
By Robert F. Service, Science Magazine. [https://www.sciencemag.org/news/2018/09/cooling-paint-drops-temperature-any-surface] For GSS Energy Use chapter 8. Excerpt: Homes in Greece and other sunbaked countries are regularly painted white to reflect as much sunlight as possible. Researchers are building on that age-old strategy with a new wave of "passive radiative cooling" materials that shed sunlight and heat. Most are not easy to apply to existing roofs and walls, but a team of U.S. researchers has now created a cooling paint that can coat just about any surface, lowering its temperature by 6°C. ...new materials, Yin says, could drop cooling costs by up to 15% in some climates. "It's quite a big number," he says. And with 17% of all residential electricity use in the United States going toward air conditioning, the savings could be substantial. White paints typically reflect only about 80% of visible light, and they still absorb ultraviolet (UV) and near-infrared (near-IR) rays, which warm buildings. To do better, the new materials start by incorporating materials or structures that reflect nearly all the sun's incoming rays, including near-IR heat and, in some cases, UV as well. They also contain polymers or other substances that, because of their chemical makeup, radiate away additional heat as mid-IR light, at wavelengths of 8 to 13 micrometers. The atmosphere does not block these wavelengths, effectively allowing the materials to shed excess heat into space without warming the surrounding air....