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This paint was developed by researchers at Purdue University and reflects 98.1% of sunlight

The new paint coating is an easy way to give your home a new look. Soon, it may also help keep your house cool.

Researchers at Purdue University have developed a new type of ultra-white paint that reflects 98.1% of sunlight and makes the surface temperature 19 degrees Fahrenheit lower than the surrounding environment. This new paint may be on the market within the next year or two, one day it can help fight global warming and reduce our dependence on air conditioning.

A team of scientists from Purdue University’s Department of Mechanical Engineering recently published their coatings research results in ACS Applied Materials & Interfaces. The research was funded by the University’s Cooling Technology Research Center and the Office of Air Force Science Research.

"Our paint only absorbs 1.9% of sunlight, while commercial paint absorbs 10% to 20% of sunlight," said Ruan Xiulin, a professor of mechanical engineering at Purdue University and one of the co-authors of the study.

This coating is a significant improvement of the heat-resistant coatings currently on the market. When exposed to sunlight, the surface covered by the white paint available today becomes hotter, not colder. Ruan said that these heat-resistant coatings can reflect 80% to 90% of sunlight at best.

Researchers call this new ultra-white paint the coolest paint ever recorded. It can reflect almost all sunlight and radiate infrared heat from the surface. The average cooling power is 113 watts per square meter. Ruan said that if applied to the roof of a 1,000-square-foot house, it would be equivalent to 10 kilowatts of cooling power, which is greater than the power of most residential central air conditioners.

In a test conducted on the roof of a campus building in West Lafayette, Indiana, during a sunny noon, the paint made the outdoor surface temperature 8 degrees lower than the ambient temperature. At night, the paint makes the surface temperature 19 degrees lower than the surrounding environment.

"Our paint can dissipate heat through its own radiation-it will radiate heat into the depths of space," Ruan said. "Because of so little absorption of the sun, our paint loses more heat than it absorbs. This is really exciting for us. In the sun, it will cool below the ambient temperature, which is difficult Achieved."

Ruan said that heat-resistant white paints on the market today are usually made of titanium dioxide, which can reflect certain wavelengths of sunlight—mainly visible and near-infrared wavelengths—but absorb the sun’s ultraviolet rays, causing the surface to heat up. .

"Commercial white paints are cooler than other darker paints, but they are still hotter than the environment or the surrounding temperature," Ruan said.

These existing paints are better than none, but the researchers want to experiment with materials that reflect rather than absorb the sun’s ultraviolet rays. In the past seven years, they tested more than 100 different materials, and finally narrowed the selection to barium sulfate, which is a known ultraviolet reflective compound that has been used in cosmetics, reflective photo paper, oil paint, X Radiographic inspection and other applications. (In the process, they also developed an earlier ultra-white paint made of calcium carbonate that reflects 95.5% of sunlight.)

Although barium sulfate is a good starting point, the researchers also took two new steps to enhance the paint’s ability to reflect light and dissipate heat: They used a high concentration of barium sulfate particles—60%, which is usually 10%-They added particles of different sizes.

"We found that if you add different particle sizes to the paint, each particle size scatters and reflects different wavelengths, and together they reflect the entire wavelength spectrum of sunlight," Ruan said.

The potential benefits of ultra-white coatings are twofold. By keeping the surface cool and reducing the use of air conditioners that are usually powered by electricity, this coating may help reduce the burning of fossil fuels. In addition, the working method of air conditioners is usually to discharge the heat of the indoor space to the outside. This method is called convection. This heat transfer and other reasons can cause the urban heat island effect, which occurs when the city becomes hotter than the surrounding area, so more air-conditioning is needed. On the other hand, ultra-white paint uses radiation to transfer heat and emit electromagnetic waves that can pass through the atmosphere and enter deep space.

"Air conditioners can cool your house, but they will transfer heat from the inside of the house to the outside-the heat still exists in the city, it still exists on the earth, it exists in our air," Ruan said. "So even if you don’t care about the electricity bills you pay, it will warm the earth anyway. Our paint does not use any electricity, but more importantly, it transmits heat to space. The heat does not stay on the earth, so This really helps the planet cool down and stops the warming trend."

Researchers used statistical models to estimate that their ultra-white paint could reduce air conditioning usage in popular cities such as Reno, Nevada and Phoenix, Arizona by as much as 70%. In a rather extreme model, they also found that covering 0.5% to 1% of the earth's surface with ultra-white paint-buildings, roads, unused land, almost everything-is enough to stop the trend of global warming .

"This is a large area, but if we need to use this method to help reverse the warming trend one day, it will still be affordable-the paint is not expensive," Ruan said.

Researchers have applied for a patent, and they are doing additional tests to understand the long-term durability and reliability of this coating outdoors, as they are working hard to provide this coating to consumers. They have not yet determined the exact price of the paint, but Ruan said he expects the paint to be similar to paints on the market today—about $30 to $40 per gallon.

At the same time, sustainable construction experts can easily imagine the potential future impact of the invention.

"When I first heard about it, I was imagining,'Wow, this can be used in a variety of different urban conditions in the United States and internationally,'" said Elizabeth Thompson, vice president of the U.S. Green Building Council. "It is this potential that is so powerful and compelling. It is great to see how this has evolved and how researchers can develop its applications."

The U.S. Green Building Council is a non-profit organization that has developed a Leadership in Energy and Environmental Design (LEED) rating system for sustainable buildings, and provides heat island reduction credits for buildings that reach LEED certification.

Thompson said one way for a building to get the credit is to use materials or equipment with an initial solar reflectance of 33% or 28% within three years. The solar reflectance of ultra-white paint is 98.1%, which far exceeds these requirements.

"This is just a completely different cooling process, very exciting," Thompson said. "This is hopeful. This is something we all hope scientists and researchers will help us discover. We don't know how there is an opportunity to live more sustainably."

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