Researchers from Indiana’s public research university – Purdue University – have developed a new ultra-white paint that reflects more than 95% of sunlight. Applying this paint to a building can cool the surface lower than the ambient temperature, resulting in lower cooling costs and energy use.
Over the years, scientists have explored how white paint could be used to cool down buildings and their surrounding microclimate. Some studies even suggest that painting buildings white can cool entire cities. In 2012, a NASA study found that white coatings in New York City could drop peak roof temperatures by an average of 43°F (24°C).
Many existing radiative cooling paints reflect sunlight using titanium oxide as their main ingredient. These paints are very effective at reflecting visible and near-infrared light. However, they have their drawbacks, including how it absorbs violet and ultra-violet light, something the team wanted to modify.
For the study, published in the Cell Reports Physical Science, the Purdue researchers developed a new formula. They substituted titanium dioxide with calcium carbonate fillers, which are cheaper, more abundant, and absorb less ultra-violet light. The paint uses various particle sizes, with a particle concentration of 60%; both factors help with cooling because it scatters the sunlight.
Over two days, the team tested the paint outdoors during the day and night. They found that it remained 3°F (1.7°C) cooler than the ambient temperature under direct sunlight, demonstrating a cooling capacity of 37 W/m2. The paint dropped as low as 18°F (10°C) below the ambient temperature at night.
The researchers also performed another set of tests, which involved painting some parts of a pattern with the new ultra-white paint, and others with regular white paint, all with the same thickness. Using an infrared camera, the team could see the difference in temperatures between the two materials by how clearly they could see the pattern.
The outcome was a new radiative cooling paint that reflects 95.5% of the incoming light, which is better than many other paints in development that manage between 80 to 90%. However, it falls short of the record holder, which reflects 98% of light.
In addition to cooling buildings, the new paint could also prevent outdoor electrical systems from overheating. The team’s next steps will be to study how well the paint lasts out in the environmental elements, to ensure that it’s commercially viable.
Xiulin Ruan, one of the study’s authors, explained:
Our paint is compatible with the manufacturing process of commercial paint, and the cost may be comparable or even lower. The key is to ensure the reliability of the paint so that it is viable in long-term outdoor applications.
The record-breaking ultra-white paint that reflects 98% of the sun’s heat was developed by a team of material scientists from the University of California, Los Angeles. These scientists substituted titanium oxide with barite, polytetrafluoroethylene, and Teflon and used fewer polymer binders in the paint, which are typically served to absorb heat.
