14 Nov 2024

Angularly asymmetric emitter cools a vertical surface below ambient in peak sunlight

Advanced materials and metamaterialsClimate and environment
AI illustration · Illustrative scene, not a photograph of the specific device or experiment.

What was demonstrated

A hierarchically designed, angularly asymmetric, spectrally selective thermal emitter mounted vertically reached about 2.5 degrees C below ambient temperature under peak sunlight of about 920 W per square metre. This was about 4.3 degrees C cooler than a silica-polymer hybrid radiative cooler and 8.9 degrees C cooler than commercial white paint under the same conditions.

Why it matters

Earlier subambient daytime demonstrations needed sky-facing surfaces. Walls and vehicle sides are mostly vertical, so this extends passive cooling to a much larger share of real surfaces.

Caveats

  • The cooling margin is modest (about 2.5 degrees C below ambient) and was measured on test samples, not whole buildings.
  • Performance depends on local sky conditions, surroundings and orientation.
  • Durability, soiling and manufacturing cost at building scale are not reported in the abstract.

Technology profiles

Sources

  1. peer reviewed paper
    Subambient daytime radiative cooling of vertical surfaces
    Fei Xie, Weiliang Jin, J. Ryan Nolen et al.. Science, 14 Nov 2024. DOI: 10.1126/science.adn2524.

Last reviewed 20 Oct 2026.