With the energy crisis on the one hand and the continuing warming of the climate on the other, the question of how we will cool our architectures in the future is becoming increasingly recurrent. Gathering data, in 2019 alone, cooling devices accounted for 8.5 per cent of the world’s total electricity consumption, equivalent to around 1 billion tonnes of CO2 emissions. And in the coming years, consumption is likely to become even higher.

To overcome this vicious circle, MIT researchers are investigating a system capable of cooling rooms without consuming energy, a passive device. This type of technology absorbs heat from its surroundings and then uses physical effects, such as insulation, evaporation and radiation, to transfer the heat away from the system being cooled, all without adding energy.

Within a flat three-layer panel, the scientists combined several passive cooling techniques. The top layer of the panel consists of a highly insulating aerogel, an ultralight, sponge-like material characterised by sparse networks of cross-linked polymers, in which most of the volume is occupied by empty space. Next is hydrogel, a material characterised by a similar network of insoluble polymers, this time immersed in water. This layer is insulated from the aerogel above, but when the thermal energy that manages to pass through the top layer is absorbed, the water it contains is partially evaporated into vapour, which rises through the aerogel. Finally, the researchers placed a reflective material similar to a mirror. This layer reflects the heat that manages to pass through the top two layers, ensuring that the hydrogel absorbs as much heat as possible.

To test the performance of the device, the team placed it on a rooftop of MIT’s Cambridge campus, next to a purely radiative cooling system. The result is about three times as efficient as the state-of-the-art system. During the summer months, it cooled the space under the panel to 9.3°C below room temperature, even in direct sunlight.