Heat killer paint more powerful than air conditioner

The whitest paint in the world that can curb global warming has been developed. The researchers argued that painting buildings with the paint they developed could provide enough cooling effect to avoid the need for air conditioning.


Developed by Professor Xiulin Ruan of the Department of Mechanical Engineering at Purdue University, the white paint reflects up to 98.1% of sunlight and emits infrared heat from the surface. On the other hand, white paint on the market can't make the surface cooler than the surroundings because it only reflects 80-90% of sunlight.

Professor Shurin Luan from the Department of Mechanical Engineering at Purdue University shows a sample of the whitest paint in the world made in his laboratory. ©Purdue University/Jared Pike
Professor Shurin Luan from the Department of Mechanical Engineering at Purdue University shows a sample of the whitest paint in the world made in his laboratory. ©Purdue University/Jared Pike
 

Using high-precision temperature measurement equipment called thermocouples, the researchers demonstrated that the newly developed paint can maintain a temperature of 7.2°C cooler than its surroundings at night. In addition, it was 13.3℃ lower than the ambient temperature under strong sunlight at noon.


The paint has been shown to be effective even in winter when sunlight is relatively weak. When the outdoor temperature was 6.1℃, the painted sample kept the temperature 7.7℃ lower than that. The results of this study were published in the April 15th issue of ACS Applied Materials and Interface', an international journal in the field of biomaterials and biotechnology published by the American Chemical Society.


The two features that make the paint whitenest


According to him, it is thanks to two characteristics that make the paint extremely white. The first is a compound called barium sulfate, which is contained in a very dark concentration in paint. This compound is used to whiten photo paper and cosmetics.


The second characteristic is that the sizes of the barium sulfate particles in the paint are all different. The degree to which each particle scatters light depends on its size, so the wider the particle size, the more the light spectrum the paint can scatter from the sun.


In other words, high-concentration particles of different sizes provide the widest spectral scattering to the paint, resulting in the highest reflectivity.

Researchers measuring temperature outdoors ⓒPurdue University
Researchers measuring temperature outdoors ⓒPurdue University
 

Xiangyu Li, a postdoctoral researcher at the Massachusetts Institute of Technology, who participated in the project as a doctoral student in Prof. Luan's lab, said, I found that using barium sulfate can theoretically make things very reflective. I mean white.


Prof. Luan's team revealed that they initially listed more than 100 different materials as candidates, and then selected barium sulfate as a result of conducting 50 different experiments on 10 of the selected materials.


In October of last year, Professor Luan's team also developed a white paint that can reflect 95.5% of sunlight. The material used by the researchers at this time was calcium carbonate, a compound commonly found in rocks and shells.


It is known that the newly developed paint is not only thinner than then but also can keep the surface cooler. It has more cooling power than home air conditioners.


The researchers revealed that the newly developed paint may be the most similar concept to Vantablack, which is the blackest in the world.


Vanta Black, developed by a British nano research company in 2014, can absorb 99.96% of light, so it is a new material that produces the darkest black color without leaving any traces when light is illuminated. Conventional black absorbs only visible light, whereas Vanta Black absorbs infrared rays.


Professor Luan said, If you paint a roof of about 93 square meters with this paint, we estimate that you can get 10 kW of cooling power. This is more powerful than the air conditioner used in most homes insisted.

If you paint the exterior walls of the building with the paint developed by Professor Luan's research team, you will be able to enjoy a cool life even in hot summer.
If you paint the exterior walls of the building with the paint developed by Professor Luan's research team, you will be able to enjoy a cool life even in hot summer.
 

He also said that the paint has a positive effect on discharging heat into space, unlike air conditioners that leave the heat on the surface of the earth. Air conditioners use a lot of energy and have the disadvantage of accelerating global warming and a heat island phenomenon due to the hot heat emitted from outdoor units.


The researchers explained that if the roof was painted with this paint, covering 0.5 to 1% of the earth's surface with the paint, the ongoing global warming could be reversed.


In order for this paint to retain its reflective properties, it must be resistant to dust. To do this, the researchers say they are working on a way to make the paint particulate.


Prof. Luan argues that a study could be done to increase the sunlight reflectivity of this paint to close to 100%, but that is not practical. This is because manufacturing costs can be more expensive compared to the additional cooling effect that can be obtained.

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