It is a simple, low-tech solution that can help cool homes. It is used in response to an unprecedented heat wave in France. Some stores are running out of stock of a simple, cheap and unexpected product: crushed chalk. It is known as blanc de Meudon (Meudon white). This product is typically used to make paints or as a cleaning item. But now chalk is used to combat extreme heat. As?
The windows of schools and private homes are being covered with chalk. When mixed with water and applied to glass, it forms a whitish, milky layer. It lets some light through but reflects heat. There could be a solid scientific basis behind this homemade trick to refresh spaces. Heat waves are becoming more frequent and intense due to rising global temperatures and pose a special danger to the urban population.
Cooling as possible
It is well known that white paint – generally applied to walls and roofs – has a cooling effect. They reflect sunlight and heat. This principle can be used to cool buildings and cities. Commercial white paint can reduce the temperature of the opposite side by at least 1.7°C compared to the ambient temperature at noon. One type of ultra-white paint could reflect up to 98.1% of sunlight. Combining it with an undercoat of ultra-black paint could reduce daytime temperatures by up to 7.6°C.
Why use chalk to combat extreme heat? Due to the properties of its main component, calcium carbonate (CaCO₃). It is not only highly reflective but also resistant to solar radiation. It absorbs very little sunlight, including that of the visible spectrum, which gives it its white color. Does not absorb ultraviolet radiation. This property has led some researchers to use calcium carbonate nanoparticles in new types of "supercooling" paint. Chalk has also been used as a coating for fabrics that help keep the person wearing them cool. It is considered relatively harmless to health and the environment.
Economic
The demand for blanc de Meudon It is causing shortages throughout the country. And the population faces temperatures above 40 °C. It was after the trick of painting windows with this chalk mixture spread on social networks that demand for the product skyrocketed.
Some French schools have also applied this chalk paint on their windows. If the windows are painted white, the indoor temperature is reduced considerably, with a greater effect than painting the walls. Chalk, like white paint in general, is inexpensive. Unlike air conditioning, it only requires energy during its manufacturing.
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