New paint formulation can help buildings rely less on air conditioning
WEST LAFAYETTE, India – In an effort to curb global warming, Purdue University engineers have created the whitest paint to date. Coating buildings with this paint can cool them down in a day enough to reduce the need for air conditioning, the researchers say.
In October, the team created an ultra-white paint that pushed boundaries on how white paint can be. Now they have surpassed that. The newer paint is not only whiter, but can also keep surfaces cooler than the formulation the researchers have previously shown.
“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 homes, ”said Xiulin Ruan, a Purdue professor of mechanical engineering.
The researchers believe that this white may be the closest equivalent of the blackest black, “Vantablack”, which absorbs up to 99.9% of visible light. The new whitest paint formulation reflects up to 98.1% of sunlight – compared to the 95.5% of sunlight reflected by the researchers’ earlier ultra-white paint – and at the same time sends infrared heat away from a surface.
Typical commercial white paint is warmer instead of cooler. Paints on the market that are designed to repel heat only reflect 80% -90% of sunlight and can not make surfaces cooler than their surroundings.
The team’s research paper showing how the paint works will be published Thursday (April 15) as a cover of the journal ACS Applied Materials & Interfaces.
What makes the whitest paint so white
Two features give the paint its extreme whiteness. One is the very high concentration of the paint of a chemical compound called barium sulfate, which is also used to whitewash photo paper and cosmetics.
“We saw several commercial products, basically anything white,” said Xiangyu Li, a postdoctoral fellow at the Massachusetts Institute of Technology who worked on this project as a Purdue Ph.D. student in Ruan’s lab. “We found that using barium sulfate can theoretically reflect your things really, really, which means they are really, really white.”
The second feature is that the barium sulphate particles are all different sizes in the paint. How much each particle emits light depends on its size, so a wider range of particle sizes allows the paint to scatter more of the sun’s light spectrum.
“A high concentration of particles that also have different sizes gives the paint the widest spectral distribution, which contributes to the highest reflectance,” said Joseph Peoples, a Purdue Ph.D. student in mechanical engineering.
There is little room to whiten the paint, but not much without compromising the paint.
“Although a higher particle concentration is better to make something white, you can not increase the concentration too much. The higher the concentration, the easier it is for the paint to break off or peel off, ” Li said.
How the whitest paint is also the coolest
The whiteness of the paint also means that the paint is the coolest on record. Using high-temperature temperature reading devices called thermocouples, the researchers demonstrated outside that the painted surfaces can keep 19 degrees Fahrenheit cooler than their surrounding environment at night. It can also cool surfaces over 8 degrees Fahrenheit below its surroundings under strong sunlight in the afternoon.
The sun’s reflection of the paint is so effective, it even works in the middle of winter. During an outdoor test with an ambient temperature of 43 degrees Fahrenheit, the paint still managed to lower the sample temperature by 18 degrees Fahrenheit.
This white paint is the result of six years of research building on attempts dating back to the 1970s to develop radiant cooling paint as a viable alternative to traditional air conditioners.
Ruan’s lab had overseen 100 different materials, reduced them to 10 and tested about 50 different formulations for each material. Their previous ultra-white paint was a formulation made of calcium carbonate, an earth-abundant compound often found in rocks and shells.
The researchers showed in their study that their paint based on barium sulfate based on commercial paint can potentially outside conditions. The technique used by the researchers to make the paint is also compatible with the process of commercial paint manufacturing.
Patent applications for this paint formulation have been submitted via the Purdue Research Foundation Office of Technology Commercialization, This research was supported by the Cooling Technologies Research Center at Purdue University and the Air Force Office of Scientific Research through the Defense University Research Instrumentation Program (Grant No.427 FA9550-17-1-0368). The research was conducted in Purdue’s FLEX Lab en Ray W. Herrick Laboratories en the Birck Nanotechnology Center of Discovery Park of Purdue.
About Discovery Park
Discovery Park is a place where Purdue researchers move beyond traditional boundaries, collaborating across disciplines and with policymakers and business leaders to create solutions for a better world. Major challenges of global health, global conflict and security, and those that lie at the nexus of sustainable energy, world supply, water and the environment are the focus of researchers at Discovery Park. The translation from discovery to influence has been integrated into the fabric of Discovery Park through entrepreneurship programs and collaborations.