Researchers from Purdue University have developed an ultra-white paint that can reflect solar heat and therefore decrease the need for cooling technologies like air conditioning. The white paint, while not the first developed with this cooling effect in mind, is by far the whitest yet designed and has significantly greater cooling capacities than any other paint to date.
"If you were to use this paint to cover a roof area of about 1,000 square feet, we estimate that you could get a cooling power of 10 kilowatts. That's more powerful than the central air conditioners used by most houses," said Xiulin Ruan, who is a Purdue professor of mechanical engineering.
Current commercial heat-reflecting paints only are able to reflect between 80-90% of solar heat and are unable to cool surfaces more than their surroundings. This paint, which is described in the journal ACS Applied Materials & Interfaces, reflects up to 98.1% of sunlight and disperses infrared heat away from the surface on which it is applied. The researchers compare it to Vantablack, which is known as the blackest black and absorbs 99.9% of visible light.
The paint’s ultra-whiteness comes from the high concentration and varied particle size of a chemical compound barium sulfate. "A high concentration of particles that are also different sizes gives the paint the broadest spectral scattering, which contributes to the highest reflectance," explained Joseph Peoples, who is a Purdue Ph.D. student in mechanical engineering. Its super reflectivity also means that it is able to keep surfaces 19 degrees Fahrenheit cooler than their ambient surroundings at night and 8 degrees Fahrenheit cooler under strong sunlight during the peak midday heat.
Finding the right balance of particle concentration is crucial for making sure that the paint remains usable. "Although a higher particle concentration is better for making something white, you can't increase the concentration too much. The higher the concentration, the easier it is for the paint to break or peel off," said Xiangyu Li, a postdoctoral researcher at the Massachusetts Institute of Technology.
Radiative cooling paint offers an alternative to keeping air conditioner use low and reducing energy costs. The researchers are confident that their barium sulfate-based paint is ready for the commercial paint fabrication process, assuring that it remains effective in outdoor conditions.