[L’industrie c’est fou] This building material changes color to reduce energy consumption

To reflect light and hope to gain a few degrees in buildings, we knew the “cool roof” technique, which consists of painting the roofs white. A solution with limited effects. Having a building material that can change its infrared color depending on the outside temperature, and therefore the amount of heat it absorbs or emits, might prove more efficient. This is at least the conviction of researchers from the Pritzker school of molecular engineering at the University of Chicago (United States). “You add a layer when you’re cold, and you take off a layer when you’re hot”they simplify.

The answer provided lies in an electrochromic material (capable of changing color under the effect of an electrical impulse), non-flammable (an advantage in the world of construction, subject to various standards), integrating copper (to retain the infrared heat) and an aqueous electrolyte (to emit heat). Between the solid layers of the material, only 0.5 millimeters thick, a liquid is inserted, in the form of a sandwich panel also carrying a PE film and a layer of graphene. “At any chosen trigger temperature, the device can use a minute amount of electricity to induce the chemical shift between states by depositing copper in a thin film or removing that copper”summarizes the University of Chicago.

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Limited energy consumption

Tested for the time being on small plates 6 centimeters in diameter, the material, intended to be affixed to the facade, is already proving promising: up to 92% of the infrared heat it contains can be emitted in hot weather. , a means of helping to cool the interior of a building. To keep a building warm, the material only reflects 7% infrared heat. One way of hoping to limit, in the long term, the energy consumption of the heating-ventilation-air conditioning (HVAC) package, recognized as one of the most energy-consuming buildingsespecially tertiary.

In a typical commercial building, 0.2% of the total electricity consumption would be required to change the state of the material, but the use of the latter might save 8.4% of the annual energy consumption. of the HVAC batch. Pending possible industrial developments, the theme is already being debated in several countries. Thus, in France for example, the new environmental regulation RE2020 integrates the concept of “summer comfort”.

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