Most people are familiar with the idea that painting the roof of a building white can help cool it down by reflecting sunlight. But just how much temperature reduction is possible depends on the type of paint used. Since the 1970s, radiative cooling paints have been used to enhance this effect. However, no paints have been able to cool below the ambient temperature. Perhaps up until now, that is.
Engineers at Purdue University have developed a new formulation for white paint that’s able to reduce the temperature of surfaces by up to 18 degrees Fahrenheit (-7 degrees Celsius) below the temperature of their surroundings. Furthermore, it achieves this impressive refrigeration effect without consuming energy. That could make it a valuable weapon in the battle against climate change.
“This sounds quite counterintuitive but it actually works,” Xiulin Ruan, a Purdue professor of mechanical engineering, told Digital Trends. “First, our paint can reflect 95.5% sunlight, meaning it is nearly not heated by the sunlight at all. Also, it emits radiant heat in the infrared, and that heat goes through the atmosphere which has a transparent window in the wavelength range of 8-13 microns directly to the deep space, which is an extremely cold heat sink at -270 degree Celsius. [With] these two factors together, the paint can be cooled below the surrounding temperature by the deep space.”
The paint formulation has several variations from regular paint, such as calcium carbonate fillers instead of titanium oxide, and a variety of particle sizes, which helps it scatter sunlight more effectively. Ruan suggested that the paint could have a wide range of possible applications. In addition to cooling buildings (which, as a result, may not have to power up the AC), it could also be used in massive data centers, utility systems, on cars, in outdoor electrical equipment, and, well, basically anywhere else you want cooling to take place.
“It not only saves energy, but [can] also reduce CO2 emissions associated with producing [this] saved energy,” Ruan said.
He noted that the team is actively exploring ways to bring this to market. “We are already in the process of trying to commercialize the technology by talking to major manufacturers,” Ruan noted. “Some of the next steps include investigating the long-term durability and developing colored cooling paints.”
A paper describing the work was recently published in the journal Cell Reports Physical Science.
