Scientists have designed a chameleon-like building material that changes its infrared color (and therefore the amount of heat it absorbs or emits) depending on the outside temperature. On hot days, the material can emit up to 92% of the heat it contains to the outside in the form of infrared radiation, helping to cool the interior of a building. However, on the coldest days, the material emits only 7% of the internal heat, helping to keep the building warm.
This achievement is the work of the team led by Po-Chun Hsu, from the Pritzker School of Molecular Engineering at the University of Chicago in the United States.
This type of intelligent material helps to maintain a comfortable temperature in a building without requiring large amounts of energy.
According to some estimates, buildings account for 30% of global energy consumption and emit 10% of all greenhouse gas. Approximately half of this energy footprint is attributed to heating and cooling indoor spaces.
Radiative cooling materials have been around for some time and help keep buildings cool by increasing their ability to emit heat emitted by people and objects in the form of infrared radiation to the outside. There are also materials that prevent the emission of infrared to the outside in cold climates.
But neither of these two kinds of materials is ideal for regions where the climate varies a lot throughout the year, oscillating between the cold of winter and the heat of summer.
Hsu and his colleagues designed a nonflammable electrochromic building material that contains a layer that can take two configurations: solid copper that retains most of the infrared heat, or an aqueous solution that emits infrared.
The material contains a layer that can take two configurations: solid copper that retains most of the heat, helping to keep the building warm; or an aqueous solution with a large emission of infrared radiation to the outside, which helps to cool the building. (Image: University of Chicago PME/Hsu Group)
At whatever activation temperature is chosen, the material uses a small amount of electricity to induce the chemical change between the two states.
Once the change is executed, no more energy is required to keep the material in the state it is in.
Hsu and his colleagues have found that the material retains its efficiency after up to 1,800 change cycles.
Hsu’s team discusses the technical details of their new material in the academic journal Nature Sustainability, under the title “Dynamic electrochromism for all-season radiative thermoregulation.” (Fountain: NCYT by Amazings)