BY CARISSA WONG | 18 OCTOBER 2023
Biomimicry once again provides a solution.
A chameleon-inspired coating that changes colour depending on the weather could save energy and help to keep homes warm or cool across the seasons.
The Namaqua chameleon, which dwells in the desert regions of southern Africa, adjusts its body temperature by altering its skin colour to reflect more or less sunlight.
Inspired by this adaptation, researchers created a coating that turns white – and reflects more sunlight – at temperatures above 25°C but turns black to absorb more heat at lower temperatures.
Conventional paints that cool buildings by reflecting sunlight are useful in the summer but also increase energy consumption during the winter, says Yan Dong, an engineer at the Harbin Institute of Technology in China.
Instead, the new coating, called a temperature-adaptive radiative cooling coating (TARCC), can switch between cooling in the summer and warming in the winter, says Dong.
The coating is a mixture of silicon dioxide, aluminium oxide and barium sulfate nanoparticles held together by the binding agents polyvinylidene fluoride and N-methylpyrrolidone.
‘Variations in temperature trigger a switch in the chemical bonds of these particles, resulting in colour changes,’ says Dong. The TARCC can be sprayed or painted onto wood, plastic, metal, and stone roofs, he adds.
To test the coating’s performance, the researchers covered the steel roofs of 1m wide concrete ‘houses’ with either the TARCC or a conventional cooling paint. By placing them outside on a hot summer’s day with an average air temperature of around 29°C, the team found that TARCC and the conventional cooling paint kept the roof about 4°C cooler than the surrounding air, on average.
By repeating the tests on a winter’s day, with an air temperature of around 17°C, the researchers found that the TARCC kept the roof about 4°C warmer than the surrounding air, and 8°C warmer than the conventional cooling paint.
They then used a computational model and weather data to simulate the heat gain and loss of small houses – a few metres wide and with heating systems – in different regions of the world, that had roofs coated in a TARCC, or standard white paint. They estimated that, in mid-latitude regions such as Atlanta, US, the TARCC could reduce annual energy consumption by up to 20%, compared with white paint.
However, these findings and the durability of the coating will need to be validated in the real world, says Dong.
‘We are in the process of patenting our research and exploring collaborations with companies to facilitate larger-scale real-world applications,’ says Dong.
‘It would be a cheap and relatively easy way to adapt buildings to extreme weather,’ says Yao Zhai, a professor of mechanical and aerospace engineering at the University of Missouri Columbia, US, who was not involved in the study.
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