30 September 2023

Warm in Winter and Cool in Summer: The temperature-adaptive radiative cooling coating with color variability is designed and fabricated

The highly reflective solar radiation of passive daytime radiative cooling (PDRC) increases heating energy consumption in the cold winter. Inspired by the temperature-adaptive skin color of chameleon, we efficiently combine temperature-adaptive solar absorption and PDRC technology to achieve “warm in winter and cool in summer”.

The temperature-adaptive radiative cooling coating (TARCC) with color variability is designed and fabricated, achieving 41% visible light regulation capability. Comprehensive seasonal outdoor tests confirm the reliability of the TARCC: in summer, the TARCC exhibits high solar reflectance (∼93%) and atmospheric transmission window emittance (∼94%), resulting in a 6.5 K subambient temperature. In the winter, the TARCC’s dark color strongly absorbs solar radiation, resulting in a 4.3 K temperature rise. Compared with PDRC coatings, the TARCC can save up to 20% of annual energy in midlatitude regions and increase suitable human hours by 55%. With its low cost, easy preparation, and simple construction, the TARCC shows promise for achieving sustainable and comfortable indoor environments.

The team mixed thermochromic microcapsules, specialized microparticles and binders to form a suspension, which they then brushed or sprayed onto metal surfaces. The coated surface began to change color from dark to light gray when heated to 69 degrees Fahrenheit. When temperatures reach 86 degrees (F), the light film reflects up to 93% of solar radiation. When heated to temperatures above 175 degrees over the course of a day, the coated materials showed no signs of damage.

According to the researchers, this color-changing system is easy and cheap to make, saving energy for regions with different seasons.

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