2023-09-29 06:30:06
What biotechnological innovation should we not miss this month? A covering inspired by the chameleon to do without a radiator or air conditioning…
When autumn arrives, the air conditioning turns off while the radiators start heating up again. These traditional temperature management systems tend to be expensive in terms of energy – often of fossil origin. To act in a more sustainable manner, other options have gradually emerged. Unfortunately, cooling paints and colored steel tiles are limited to only one type of operation (cooling and heating respectively). An international research team led by Yan Dong, doctoral student at the Harbin Institute of Technology (China), wanted to remedy this by inventing an adaptive coating that is “warm in winter and cool in summer”. Their work, inspired by a chameleon whose skin color varies depending on the outside temperature, is presented in the Nano Letters from September 20, 2023.
A covering that varies with the seasons
Namaqualand is a desert located in the southwest of Africa, and known for its large daily temperature variations. This is where a rather unusual chameleon lives, Chameleo namaquensis. When temperatures are high, the latter appears gray. The sunlight then reflects on his skin, allowing him to stay cool. Conversely, cooling the air sees it change to a dark brown which absorbs ambient heat. To reproduce this feat, Yan Dong’s team suspended thermochromic microcapsules – which change color depending on temperature – with other specialized microcapsules. The mixture was then sprayed onto a metal surface. Above 20°C, the coating changed from a dark color to a grayish color. And once 30°C was reached, this protective film reflected up to 93% of the radiation received.
To validate their invention, the researchers carried out a battery of tests comparing the effectiveness of their coating to existing techniques: white paint, passive effect paint and bluish steel tiles. The four coatings were applied to a building constructed outdoors on the scale of a niche and studied over the four seasons that make up a year. The new system first showed its reliability in summer, with its high reflectance leading to a temperature reduction of 6.5°C inside the “niche” compared to ambient conditions. It performed just as well in winter, its dark color effectively absorbing the sun’s rays for an increase in the building’s internal temperature of 4.3°C. But where this new invention really makes the difference is in its ability to adapt according to the seasons, and particularly during variable periods such as spring and autumn. In the future, up to 20% energy savings per year could be achieved using this protection device installed in mid-latitudes.
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