Revolutionary white paint could cool Greek island buildings better than AC

Professor Xiulin Ruan, who developed a revolutionary new white paint that cools buildings. Credit: Facebook/Xiulin Ruan

A revolutionary new ultra-white paint, which looks like the shiny lime used on so many buildings in the Cyclades and other Greek islands, could eventually replace air conditioning one day because it radiates so much heat back into space.

Recently developed by researchers at Purdue University, the paint reflects a staggering 98.1% of sunlight, far more than the average 10-20% of sunlight that most commercial white paints are doing today.

The new product is so effective that it cools buildings down to an incredible 19 degrees Fahrenheit. Xiulin Ruan, a professor of mechanical engineering at Purdue University, was a co-author of the published scientific paper on the findings.

He and his colleagues believe the paint can help fight global warming and reduce our reliance on air conditioning and even electric air exchangers.

White paint
The Greek island of Mykonos and many other islands in the Cyclades are known for their whitewashed buildings. A fresh white paint job can help keep them – and the planet – looking much cooler in the future. Credit: Cifo Buscemi /Wikimedia Commons/ CC0

Once applied, the new paint can keep surfaces up to 19 degrees Fahrenheit cooler than their surrounding environment, according to Purdue. The new paint, which researchers say may even be available for purchase within the next year.

The scientists responsible for this groundbreaking discovery belong to Purdue’s mechanical engineering department. They recently published their groundbreaking findings in the journal Applied materials and ACS interfaces.

The Greek island of Naxos. Credit: Sergio Alvarez Creative Commons Identical Attribution-Share

The research study was funded by both Purdue’s Cooling Technologies Research Center and the Air Force Office of Scientific Research (AFOSR).

“Our paint only absorbs 1.9% of sunlight, while commercial paint absorbs 10-20% of sunlight,” Ruan explains.

Contrary to intuition, even white paint absorbs the sun’s rays and heat rather than reflecting most of the heat skyward. On sunny days, the white paint heats up, making it harder to keep interior spaces cooler.

Even the whitest white paints on the commercial market today reflect at most 80 to 90 percent of the light, according to Ruan.

Credit: The Church of the Taxiarches in the village of Vathy on Sifnos. Photo credit: Zde /Wikimedia Commons/CC BY-SA 4.0

The new Purdue paint not only reflects nearly all of the sun’s rays back into space, but also sends infrared heat away from a building’s surface. This equates to an average cooling power of 113 watts per square meter (10.7 square feet).

When paint is applied to the roof of a building, researchers say, it results in powerful cost savings.

The cooling effect exceeds that of an air conditioner

On the roof of a 1,000 square foot house, 10 kilowatts of cooling power will be generated by the paint, which Ruan says is more powerful than most residential central air conditioners.

In scorching Indiana heat, researchers tested the new paint on a building on the Purdue campus at noon on a sunny day, proving that the paint kept outside temperatures a respectable eight degrees cooler than the ambient temperature inside. era.

However, it was at night, when they discovered that the paint caused surfaces to stay 19 degrees cooler than their surroundings, that the paint’s breakthrough performance came to the fore.

“Our paint can lose heat by its own emission – it radiates heat into deep space,” Ruan explained to Smithsonian magazine.

“With so little absorption from the sun, our paint loses more heat than it absorbs. It’s really exciting for us. In the sun, it cools below room temperature and it’s difficult to achieve,” Ruan said.

Barium Sulfate Particles are a Game Changer for Ultra White Paint

Video produced by the team using an infrared camera shows exactly how much the paint cools the surfaces it is applied to, with the whitest of all white paints represented by a dark purple square in the middle to indicate its cold temperature.

Naturally, commercially available white paints, even those marketed as heat-rejecting products, are cooler than dark paints, but they are still made with titanium dioxide, which absorbs the sun’s ultraviolet rays, causing heat to any surface they are used on. at the top.

“Commercial white paints are cooler than other darker colored paints, but they are still warmer than room or surrounding temperature,” Ruan notes.

The researchers naturally declined to try to use materials that could reflect, rather than absorb, the harsh UV rays. Testing over 100 different materials over the past seven years, they finally discovered barium sulphate after discovering that calcium carbonate reflects 95.5% of the sun’s rays.

Incredibly, barium sulfate was even more effective than calcium carbonate. Already used in cosmetics as well as photographic papers, the substance is created by reacting
barium hydroxide and other sources of barium with sulfuric acid.

Ruan and the other researchers also took two additional steps to improve the reflective nature of the paint, using six times the concentration of barium sulfate particles as most heat-resistant paints on the market. They also used barium particles of different sizes in the mix.

“We have found that if you put different particle sizes in your paint, each particle size can scatter and reflect different wavelengths and together they reflect the entire wavelength spectrum of light from the sun,” says Ruan.

The new paint is truly revolutionary, not only because it would clearly reduce the need for air conditioning.

Painting would reduce heat convection in cities, use of fossil fuels

When air conditioners are used, they simply remove heat and humidity from inside and transfer it outside, increasing the overall heat sink effect of a city or town.

Of course, using paint would also reduce the need for electricity and/or fossil fuels for air conditioning.

According to the researchers, the types of electromagnetic waves emitted by the surface of the ultra-white paint can pass through the atmosphere and return to deep space.

“Air conditioners can cool your home, but they move the heat from the inside out. The heat is still in the city, it’s still on the Earth, in our air,” Ruan explains.

“So even if you don’t care about the electricity bills you pay, it’s going to warm the Earth anyway. Our paint doesn’t use any energy but, more importantly, it sends the heat out into space. The heat doesn’t stay on the Earth, which really helps the Earth cool down and can stop the warming trend,” Ruan says.

According to Purdue researchers, ultra-white paint could reduce air conditioning by up to 70% in desert cities such as Reno, Nevada, and Phoenix, Arizona.

Taking the experiment to the extreme, they extrapolated that if they covered 0.5-1% of the earth’s surface, including buildings, roads, and unused land, among others, with the ultra- white, it would be enough to control global warming.

“It’s a lot of space, but if we ever need to use this approach to help reverse global warming, it’s still affordable – the paint is cheap,” says Ruan.

Purdue scientists have already filed a patent application on the ultra white paint and have pledged to clarify its durability in residential and commercial use.

Price shouldn’t be an issue, Ruan says, with a gallon costing almost exactly the same price as a gallon of regular paint right now, around $30 to $40 a gallon.

Elizabeth Thompson, vice president of the US Green Building Council, is fascinated by the future prospects of paint.

“When I first heard about it, I imagined, ‘Wow, this could be used in all kinds of different urban conditions in the United States and around the world,'” she says.

“This potential is so strong and compelling. It will be great to see how this evolves and how researchers are able to develop its applications,” Thompson says hopefully.

The US Green Building Council is the nonprofit group that developed the LEED (Leadership in Energy and Environmental Design) rating system for green buildings. It now offers a “heat island reduction credit” for buildings whose owners are working towards LEED certification levels.

According to Thompson, the new Ultra White paint is a game-changer in this area.

Using materials that have an initial solar reflectance of 33% upon installation or 28% over three years is one way homeowners are currently trying to make buildings more energy efficient, Thompson says. The 98.1% solar reflectance of Purdue paint completely eliminates these requirements.

“It’s just a whole other stage of chilling, which is very exciting,” Thompson says.

“It’s hopeful,” she says, adding that “these are the kinds of things that we all hope scientists and researchers will help us discover, opportunities we didn’t know existed for a living. more sustainable way.


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