You might be aware that air conditioning is not a particularly eco-friendly technology. It cools down the space you are occupying, yet the energy used (e.g. roughly 6% of all the electricity produced in the United States) contributes to global warming. As our planet gets warmer, the effect could be self-perpetuating: hotter air resulting in higher AC usage, which could create more heat. “Cool walls” are an interesting alternative.

Cool wall 101

Homes in Greece and other warm countries are commonly painted white (or other light colors) to reflect as much sunlight as possible. Researchers are exploring such age-old strategy with a new wave of “passive radiative cooling” materials that shed sunlight and heat. Cooling paint that can now coat many surfaces, lowering their temperature by up to 6°C.

“Houses in Greece” by Maria Michelle (Pixabay)

This advancement highlights “terrific progress in this field,” stated Xiaobo Yin, a materials scientist at the University of Colorado in Boulder whose team has conceived a passive radiative cooling plastic film and has set up a company called Radi-Cool, in order to commercialize it. Yin believes the new materials could drop cooling costs by up to 15% in some climates. “It’s quite a big number,” he added.

White paints typically reflect about 80% of visible light, and still absorb ultraviolet (UV) and near-infrared (near-IR) rays, which warm buildings. To build upon that technique, the new materials start by incorporating materials or structures which reflect nearly all the sun’s incoming rays, including near-IR heat (and in some cases UV heat). Moreover they contain polymers or other substances that, do to their their chemical makeup, radiate away additional heat. Essentially, the materials shed excess heat into space without warming the surrounding air.

White paints typically reflect about 80% of visible light, and still absorb ultraviolet (UV) and near-infrared (near-IR) rays, which warm buildings.

New cost-savings insights

Recently, researchers from the Berkeley Lab studied warm U.S. cities from Miami, Florida, to Albuquerque, New Mexico (map: climate zones 1A to 4B), and determined that cool walls could lead to yearly heating, ventilation, and air conditioning (HVAC) energy cost savings up to 11% for stand-alone retail stores, 8.3% for single-family homes, as well as 4.6% for medium-sized office buildings. For single-family homes across all California climates, the study found potential energy cost savings of 4% to 27%.