Cooling paint could reduce buildings’ CO2 emissions

Photo credit: Purdue University

Greek islands’ picturesque villages whitened with lime are not only picture-postcard landscapes. They effectively keep the houses cool inside by reflecting light, according to a known principle of physics. 

Inspired by this architectural curiosity, American researchers from Purdue University in Indiana have developed an even whiter paint that reflects 95.5% of sunlight. “We put a painted surface outside under direct sunlight, the surface cooled 1.7°C below the ambient temperature and during night time it even cooled up to 10°C below the ambient temperature,” explained Xiulin Ruan, one of the researchers, to the BBC.

What’s more, this paint not only diverts heat away from the painted surface, it sends it far out into space: heat therefore does not remained trapped in the atmosphere and does not contribute to global warming.

The team achieved this result after six years’ research, adding high concentrations of different-sized particles of calcium carbonate — in other words, limestone — to the paint. It has just published its conclusions in the journal Cell Reports Physical Science

A paint versus air conditioning 

Xiulin Ruan believes that the paint has the potential to significantly reduce a building’s carbon footprint: “This cooling power can offset the majority of the air conditioning needs.”

For decades, scientists have been working on ways to improve buildings’ air conditioning efficiency. Many reflective paints already exist, but none of them is able to sufficiently deflect the sun’s rays to cool the interior of houses and offices.

This ultra-high-performance paint could therefore interest the construction sector, which represents one of the major sources of CO2 emissions, especially data centers. According to the World Green Building Council, lighting and air conditioning — heating and cooling — are responsible for around 28% of CO2 worldwide. They are mainly powered by fossil fuels, including in Europe, where 75% of these needs are met by coal, oil or gas.

The paint still has to be tested for its long-term reliability and efficacy before it is put on the market. However, manufacturers are already taking an interest in it and the researchers are working on developing other colors that could present the same cooling properties. 

Sources: 

“Climate change: 'Cooling paint' could cut emissions from buildings,” BBC, October 21, 2020 https://www.bbc.com/news/science-environment-54632523

“Full Daytime Sub-ambient Radiative Cooling in Commercial-like Paints with High Figure of Merit,” Cell Reports Physical Science, October 21, 2020 https://www.cell.com/cell-reports-physical-science/fulltext/S2666-3864(20)30236-8

Radiative Cooling Paint https://www.youtube.com/watch?v=caFzYvYAUo4