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A New Smart Roof Coating Keeps Houses Warm in Winter and Cool in the Summer

Scientists from Berkeley Lab developed a smart roof coating that keeps buildings warm during cold periods of weather, and cool when it gets hot, a report from New Atlas reveals.

The coating is comprised of a radiative cooling system that reflects sunlight and heat when it's warm and then automatically switches off in the winter. The researchers say their system will help to reduce energy use all year round.

Radiative cooling systems have great potential for conserving energy and also for sourcing energy at off-peak times. Last year, for example, a group of researchers from Stanford University revealed that they were working on "anti-solar panels" that could produce electricity at night via radiative cooling.

Radiative cooling itself is a naturally occurring and common phenomenon where a surface facing the sky ejects its heat into the air in the form of thermal radiation.

For their new smart roof coating, the Berkeley Lab scientists set out to develop a material that would cool a building in summer, but could automatically switch to trapping heat in winter. After initial testing and development, they came up with a material they call temperature-adaptive radiative coating (TARC). Their findings were outlined in a paper in the journal Science.

Scientists create a physics-defying roof coating material

The main component in TARC is a compound called vanadium dioxide (VO2). In 2017, the same team found that when this unusual compound reaches a temperature of 153°F (67°C), it conducts electricity, but not heat. Thanks to this physics-defying material, TARC absorbs and emits thermal-infrared light in hot weather, keeping it away from the interior of the building. When the weather gets cold though, the material lets the heat from sunlight pass right through into the building.

In tests, the researchers showed that TARC reflected approximately 75 percent of sunlight in cold and hot weather — as a point of reference, the world's whitest paint reflects 98.1 percent of sunlight. Crucially though, it reflected up to 90 percent of heat when temperatures rose above 86°F (30°C), and only 20 percent of heat when temperatures fell below 59°F (15°C). According to the researchers' estimations, based on those findings, the average U.S. household would be able to save up to 10 percent on their electricity bill using TARC.

The team says it will continue to run experiments with different variations on its TARC material, which it says might also be viable for applications in electric vehicles, satellites, and electronics devices.



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