If you’ve ever revamped a room in your house and went to the hardware store to get some fresh paint, you know there is a a lot of of different shades of white on the market. Apparently there’s a new shade of white in town – and it could have some pretty cool (literally) climate implications.
In a study published Thursday in ACS Applied Materials & Interfaces, researchers at Purdue University say they have now created the whitest paint in the world. By creating the whitest paint ever, which researchers say reflects up to 98.1% of light, the Purdue researchers beat their own record set last fall when they took a paint that reflects 95.5% of the sunlight
It may seem pointless to nitpick to race for the whitest paint of all by just a few percentage points, when many of us can’t tell the difference between most of the white monster chips at Home Depot. However, when it comes to the cooling effects of white paint, those small percentages matter.
Anyone who has gone out on a hot summer day knows to wear white clothes; white reflects light, black absorbs. But white paints currently on the market with labels like “ultra reflective” or “high reflective” reflect only about 80% to 90% of the light, said Xiulin Ruan, a lead author on the study. That might be enough to keep your kitchen sparkling clean every day, but when it comes to cooling properties, it’s less effective.
“We don’t consider 90% to 98% to be very different, but we have to think about the absorption of the sunlight,” said Ruan. “Our paint absorbs 1.9% of the sunlight, but that commercial paint, even with reflective fabrics, absorbs 10% of the sunlight – five times as much as our paint absorbs. They look white, they are quite white, but they are not white enough – they cannot cool beyond the ambient temperature. “
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Ruan said efforts to develop the whitest paint possible that could also serve as a coolant go back to the 1970s. Ruan’s team has spent about seven years alone making white paint whiter, working out methods to add reflective materials to the paint to help it beat the sun. This successful white paint contains high concentrations of barium sulfate – a chemical compound used to make white cosmetics and photo paper – with different sized particles dispersed throughout the paint.
“The sunlight has different colors because it has different wavelengths,” Ruan explains. “We need different particle sizes to scatter each wavelength.”
The development of this type of ultra-reflective paint could be a game-changer for the way we design buildings as our world gets hotter and hotter. More and more work is being done on the way urban design choices: replacing super hot and super absorbent asphalt roofs with reflective surfaces, or building in parks or other green spaces in cities to literally cool the area – can help us reduce the heat in cities and other built spaces without using more energy for air conditioners.
Ruan and his team have big visions of the paint’s potential; They estimate that using super-reflective white paint extensively in cities like Reno or Phoenix can save up to 80% on the cost of air conditioning. “If you have really hot days, our paint alone might not work, but on other days it could keep you from turning on your air conditioner,” he said.
These kinds of climate hacks sound like the solution to all of our problems, but there are still many of them real-world considerations to hammer out when you think about designing cities to beat the heat. “To make cities more reflective, one has to be very, very, very practical,” said Hashem Akbari, professor of construction, civil and environmental engineering at Concordia University.
Akbari pointed out that regular wear and tear on reflective roofs or walls can affect reflectivity rates measured in a lab environment. “Soot and dust reduce surface reflection,” he said. “If they start with a super-duper 95% reflectivity, the airborne pollutants, droplets, soot can collect on the surface and reduce reflectivity.”
Still, Akbari said that starting now to replace roofs regularly, which should be updated every few decades, with more reflective materials – regardless of the whiteness of the paint you’re using or the percentage it actually reflects – would be a good start are for most cities. .
“If every roof to be replaced could be replaced by a highly reflective roof, then within a period of 10 to 30 years all roofs will be highly reflective. You don’t have to press on a particular technology, such as a coating, ”he said. “We need to encourage marketing and insulation of reflective materials while the roofs are being transformed.”