WASHINGTON — Researchers at Columbia University have invented a high-quality polymer coating that can cool down buildings in daytime by reflecting sunlight and radiating heat to the colder atmosphere.
The study published on Thursday in the journal Science described the new material with nano-to-microscale air voids that could act as a spontaneous air cooler and be fabricated, dyed, and applied like paint on rooftops, buildings, water tanks, vehicles, even spacecraft.
The passive daytime radiative cooling (PDRC), an alternative to these energy-intensive cooling methods, is most effective if a surface has a high solar reflectance that minimizes solar heat gain, and a high, thermal emittance that maximizes radiative heat loss to the sky, according to the study.
The researchers led by Yang Yuan and Yu Nanfang, both from Columbia University, gave the polymer a porous foam-like structure that can effectively scatter and reflect sunlight.
They essentially replace the pigments in white paint with air voids that reflect all wavelengths of sunlight, from UV to infrared, according to the study.
The researchers found their polymer coating’s high solar reflectance (96 percent more) and high thermal emittance (97 percent more) kept it significantly cooler than its environment under widely different skies.
An experiment showed 6 Celsius degrees decrease in dry desert in Arizona and 3 Celsius degrees decrease in humid environment of Bangladesh.
“The fact that cooling is achieved in both desert and tropical climates, without any thermal protection or shielding, demonstrates the utility of our design wherever cooling is required,” said Yang.
They also created colored polymer coatings with cooling capabilities by adding dyes.