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The Whitest Paint Could Revolutionise Air-Cooling

Updated: Jun 13, 2021

Ziryan Aziz explores how a new material could be used to cool buildings and limit global carbon emissions.

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Researchers in the US have developed the whitest paint ever made. With the ability to reflect 98.1% of sunlight, it has the potential to cool buildings and fight climate change.

Professor Xiulin Ruan at Purdue University, Indiana, is the lead researcher on the project. His team previously developed a paint capable of reflecting 95.5% of sunlight using calcium carbonate particles. By revising the size of the particles and replacing the calcium carbonate with barium sulphate, however, the paint now reflects 98.1% of sunlight back into space.

Because the whiteness of the paint reflects so much of the sun’s light, surfaces of buildings will stay below the ambient temperature as infrared radiation cannot be absorbed by air, being dispersed into deep space instead. As such, the team hopes that the new paint will be able to help limit the global energy usage:

“Our paint can help fight against global warming by helping to cool the Earth – that’s the cool point” – Professor Xiulin Ruan

Tests have shown both that the paint is able to cool surfaces 4.5 degrees Celsius below the ambient temperature, and that painting white rooftops on homes and buildings in cities will require less air conditioning (and hence limit the carbon emissions they produce). Prof Ruan has said that painting a 93 sq. meter rooftop with the new paint has the cooling power of 10 kilowatts, which is more powerful than the central air conditioners used by most houses.

White painted ‘cool roofs’ are not entirely new, however, having been traditionally used in many countries to help cool homes. Currently, it is being applied in Ahmedabad, India and New York City, where 10 million sq. ft of white rooftops have already been painted.

The Air Conditioning problem

According to figures in 2020, there are at least 1.9 billion air conditioning units in the world, with that number set to rise to 5.5 billion units by 2050. The growing energy consumption of air conditioning is often overlooked in climate change debates: figures from the International Energy Agency (IEA) predict that air conditioning will be the biggest factor in electricity demand by 2050. The IEA also projects that by 2050 the CO2 emissions sourced from air conditioning will equate to 2 billion tonnes annually, roughly equal to India’s daily emissions.

Aside from the emissions generated through electric energy consumption, older air conditioning units leak hydrofluorocarbons (HFCs) which are hundreds or thousands of times more potent than CO2. Although HFC-leaking units are being phased out, many older air conditioning units are still in operation around the world.

The research team at Purdue University hopes that their ultra-reflective white paint may have positive effects in helping cool down temperatures to decrease the energy consumption caused by air conditioning. A study looking at the effects of employing white painted rooftops within cities has found that ambient city temperatures could be reduced by 1 to 1.5 degrees Celsius, resulting in a reduction of water consumption of up to 9%, as lawns, parks, and other green spaces require less irrigation.

What’s next?

One factor that will need to be taken into consideration is the environmental impact caused by the mining needed to extract the barium sulphate required for the paint. It has been suggested that a more sustainable alternative is to plant more trees within cities, and on home rooftops. Trees, which are often removed in construction of suburban areas, provide a natural cooling effect; not only do their branches and leaves provide shade but the effects of transpiration allow for the water vapour generated from the sunlight hitting the leaves to cool the air below.

Nevertheless, white paint might well be coming to your local towns and cities in the near future: a patent has been submitted by the researchers, who are currently working with a company to introduce the paint into the market. There is hope that it will have a similar cost to regular paint in the coming years.

“We think this paint will be made widely available to the market, in one or two years, I hope, if we do it quickly.” – Professor Xiulin Ruan


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