- Kelly Shen ’23, image from Unsplash.com
A new coat of paint is a simple way to freshen up your home. Soon, it could also help keep your house cool. Researchers at Purdue University have developed an ultra-white paint that reflects 98.1 percent of sunlight, and could possibly keep surfaces up to 19 degrees Fahrenheit cooler than their surroundings.
The team of scientists in Purdue’s engineering department recently published the findings, stating “Our paint only absorbs 1.9 percent of the sunlight, whereas commercial paint absorbs 10 to 20 percent of sunlight.”
The paint may be a marked improvement from current heat-rejecting paints on the market. When struck by the sun’s rays, surfaces covered in today’s available white paints get warmer, not cooler. At best, these heat-combatting paints can reflect 80 to 90 percent of sunlight.
The new ultra-white paint, which the researchers say is the coolest on record, reflects nearly all of the sun’s rays and sends infrared heat far from the surface, providing an average cooling power of 113 watts per square meter. If painted onto the roof of a 1,000-square-foot home, that translates to a cooling power of 10 kilowatts, which is more powerful than most residential central air conditioners. In tests conducted during sunny, midday hours on the roof of a campus building in West Lafayette, Indiana, the paint kept outdoor surfaces 8 degrees cooler than the ambient surrounding.
Heat-rejecting white paints on the market now are typically made with titanium oxide, which reflects certain wavelengths of sunlight—mainly, the light and near-infrared wavelengths—but absorbs the sun’s ultraviolet rays, causing the surface to heat up. These existing paints work better than ordinary walls, but the researchers wanted to experiment with materials that reflect, instead of absorb, the sun’s UV rays. They tested quite 100 different materials over the past seven years, eventually narrowing down their selection to barium sulphate, a known UV-reflecting compound that was already used in cosmetics, reflective photo paper, oil paints, x-ray examinations and other applications. (Along the way, they also developed an earlier ultra-white paint made up of carbonate that reflected 95.5 percent of sunlight.)
Though barium sulphate was a start, the researchers also took two novel steps to improve the paint’s ability to reflect light and emit heat: They used a high concentration of barium sulphate particles—60 percent compared to the standard 10 percent in current paints—and they incorporated particles of varying sizes.
In the future, this new reflective paint could be used in place of air conditioning, and could be used to combat emissions.