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Scientists have developed a new kind of white paint that is so white it reflects 95.5% of the sunlight that falls on it back into space. The net effect of this is that even under direct sunlight, the paint cools the ambient surroundings down by 1.7 degrees.
In terms of the battle against climate change, this is a big deal since buildings are one of the biggest contributors to greenhouse gas emissions.
According to the World Green Building Council, building and construction are responsible for 39% of all carbon emissions in the world and the energy necessary to heat, cool and light buildings account for 28% of global emissions.
During the summer months, some places are unbearable to live and work in unless buildings are air- conditioned. These air conditioners take the hot air inside the buildings to the outside, contributing to the so-called ‘’heat islands’’ effect in urban areas, which contribute to global warming.
Making matters worse, the energy necessary to run the air conditioners is derived from burning fossil fuels. In Europe, according to 2018 figures from Eurostat, 75% of heating and cooling comes from burning fossil fuels while and only 19% comes from renewable energy.
While scientists have been working on radiative cooling paints since the 1970s, the paints that they have developed thus far were not able to reflect enough of the sun’s heat to reduce temperatures inside buildings. They could not come up with a commercially viable paint alternative for air conditioners.
What is different about this new paint?
The new paint has high concentrations of calcium carbonate added to it, which is an abundant resource and highly reflective.
“Sunlight is a broad spectrum of wavelengths,” said Prof Xiulin Ruan from the School of Mechanical Engineering at Purdue University
“We know that each particle size can only scatter one wavelength effectively so we decided to use different particle sizes to scatter all the wavelengths. This is an important contributor eventually resulting in this very high reflectance.”
Ruan and his team did cooling tests in West Lafayette, Indiana to demonstrate the new paint’s radiative cooling abilities. The paint itself remained 10 degrees C below the ambient temperature at night and at least 1.7 degrees C below the temperature of the ambient surroundings at noon.
Then the team did another test. They painted part of a surface with their new paint and part of the same surface with a commercial white paint. Using an infrared camera, they could see that their paint maintained a lower temperature than the commercial paint under direct sunlight.
The team’s research demonstrates a radiative cooling technology that could be used in commercial paints to cool buildings and eliminate the need for air conditioning.
“Our paint is compatible with the manufacturing process of commercial paint, and the cost may be comparable or even lower,” says Ruan. “The key is to ensure the reliability of the paint so that it is viable in long-term outdoor applications.”
The paper was published in the journal Cell Reports Physical Science.
