USF develops white cooling paint reflecting up to 98% of sunlight, tested for 28 days outdoors in Tampa
The University of South Florida tested a self-cooling roof paint on small samples outdoors. Surfaces ran up to 13.5 degrees below ambient air temperature, the authors report.
Researchers at the University of South Florida (USF) have developed a white self-cooling paint for roofs that reflects up to 98% of sunlight, according to usf.edu. usf.edu
usf.eduusf.eduOpen source ↗ The paint was created in the lab of Distinguished University Professor Yogi Goswami at the USF TECO Clean Energy Research Center. In outdoor testing it cooled surfaces by up to 13.5 degrees below ambient air temperature.
Goswami notes that 25% of all energy used in the United States goes toward cooling buildings. Air conditioning is also becoming more common in Europe, while countries such as India and China are gaining access to cooling technologies. These trends prompted the work.
How radiative cooling works in the paint
The paint uses outer space as a heat sink. Earth's atmosphere has a natural window that lets certain wavelengths of heat pass through instead of being trapped near the surface. The team engineered the paint, which is made from natural materials designed to reflect sunlight, to release heat in those wavelengths so that it escapes toward space.
Conventional cool-roof paints mainly reduce heat absorption. In these tests the new paint cooled surfaces below the temperature of the surrounding air. usf.edu
usf.eduusf.eduOpen source ↗
Outdoor test in Tampa
The researchers used three samples. Each had thermal insulation at the base with aluminum foil on top. One was coated with the new paint, one with a commercial cool-roof paint, and one was left as bare foil.
Thermometers on each sample recorded temperatures from 10 a.m. to 5 p.m. over 28 days in Tampa, Florida. The new paint reached the lowest temperatures and consistently stayed below ambient air temperature, with a peak reduction of 13.5 degrees. According to Goswami, earlier external studies tested the paint only indoors in controlled conditions.
Protective coating and next steps
The technology is covered by a provisional patent application. The lab is now developing a transparent protective coating to go over the paint. It is intended to help the paint withstand wind and rain while preserving its cooling performance. usf.edu
usf.eduusf.eduOpen source ↗
Goswami said it would not be difficult for the paint to cut energy bills by 50%. He expects commercial buildings to adopt it first, followed by residential ones, and says his group is working to make it commercially available.
