Whitewashed buildings that stay cool by reflecting heat are a mainstay in the Mediterranean. But not all white paint is created equal. Now researchers have made an ultra-white cooling paint that reflects up to 98 percent of the sun’s heat.
The new paint, reported in the journal Joule, could cool buildings more efficiently and significantly bring down cooling costs compared to conventional white cool-roof paints.
Cooling living environments in an energy-efficient manner has become an “urgent challenge” as climate changes causes heat islands, researchers at the University of California, Los Angeles write in the paper.
White cooling paints are an established cooling technology that help bring down indoor temperatures and thus save the electricity used for air-conditioning in hot climates. These paints work by reflecting heat-producing infrared radiation, and are typically made of titanium dioxide pigments in an acrylic or other polymer base. The best white cool-roof paints available today reflect about 85 percent of solar radiation falling on them.
Titanium dioxide reflects most visible and near-infrared light well, but it absorbs ultraviolet rays, while the polymer binder can absorb near-infrared light. This causes some heating under sunlight, so the paints don’t work very efficiently under harsh, bright sunshine.
So the researchers replaced the titanium oxide with inexpensive and easily available ingredients such as barite, which are natural pigments used in paints and coatings, and powered Teflon. These compounds help the paint reflect ultraviolet rays. The researchers also reduced the concentration of the polymer binders, which further reduce the heat absorbed by the paint.
These changes to paint formulation are within the means of today’s paints and coatings industry, said paper co-author Jyotirmoy Mandal. In the paper, Mandal and his colleagues highlight chemical and optical techniques that could be used to address technical challenges such as bringing down cost by reducing materials usage; enhancing the paint’ durability and resistance to soiling; reducing glare; and adding color to the paints.
“We hope that the work will spur future initiatives in super-white coatings for not only energy savings in buildings, but also mitigating the heat island effects of cities, and perhaps even showing a practical way that, if applied on a massive, global scale could affect climate change.”
Source: Jyotirmoy Mandal et al. Paints as a Scalable and Effective Radiative Cooling Technology for Buildings. Joule, 2020.