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Most “radiative cooling” designs involve roofs that are engineered to absorb and release infrared wavelengths of solar energy as it radiates out of the Earth’s atmosphere into space. Such roofs may be decorated with vegetation, painted white to better reflect sunlight, or coated with materials that are both highly reflective and highly emissive (seeSN: 2/6/23).
Vertical walls are difficult to cool, says Yuan Yang, a materials scientist at Columbia University, because they’re not only exposed to space, but also absorb heat from the ground at the same time — an efficient radiative cooling design must take both effects into account.
Namely, a zigzag wall: Yang and his team hypothesized that by corrugating a vertical surface and coating it with different materials (a more reflective material facing downwards, a more emissivity material facing upwards), the wall would absorb less heat than a traditional straight wall.
Simulations comparing how much heat a traditional wall and a zigzag wall get from the ground on a hot day backed up that hypothesis: The average difference in wall temperature was about 2.3°C, rising to 3.1°C during the hottest hours of the day. The team found similar differences when they tested a miniature backyard version of their design in New Jersey in summer 2022.
Effect of zigzag on wall temperature
Yang says the goal was to design something that would be commercially appealing: Corrugated walls already exist, he notes, making the design easy to manufacture and scale, and consumers might find a way to zigzag when the weather suddenly changes.
