The Highlights and Summary from the article follow.

Highlights

• A novel, passive radiative thermoregulation mechanism for walls and windows
• Buildings lose narrowband heat to the sky but exchange broadband heat with the earth
• Vertical LWIR emitters stay cooler than broadband ones in hot weather and warmer in cold
• Thermoregulation by this simple and static design yields untapped energy savings

Summary

Efficient passive radiative cooling of buildings requires an unimpeded view of the sky. However, vertical facades of buildings mostly see terrestrial features that become broadband-radiative heat sources in the summer and heat sinks in the winter. The resulting summertime terrestrial heat gain by buildings negates or overwhelms their narrowband longwave infrared (LWIR) radiative cooling to space, while the wintertime terrestrial heat loss causes overcooling. We show that selective LWIR emitters on vertical building facades can exploit the differential transmittance of the atmosphere toward the sky and between terrestrial objects to achieve higher summertime cooling and wintertime heating than conventionally used broadband emitters. The impact of this novel and passive thermoregulation is comparable to that of painting dark roofs white and is achievable with both novel and commonplace materials. Our findings represent new and remarkable opportunities for materials design and untapped thermoregulation of entities ranging from buildings to human bodies.

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