These Walls Cool Themselves, No A/C Needed

As the thermometer outside rises, your air will be at least 10 degrees cooler.

As climate change makes summer heat more unbearable and incomes rise in developing nations, the world will be using a lot more air conditioning–30 times as much by the end of the century, according to one prediction. Ironically, all of that A/C also makes climate change worse. In the U.S. alone, people already use nearly 200 billion kilowatt hours of electricity for cooling each year, and countries like India and China will soon dwarf that.


But what if buildings could start to cool themselves without plugging into the grid? A team of students and professors from Barcelona’s Institute for Advanced Architecture of Catalonia is developing a design for walls that automatically cool–using zero energy–when temperatures rise outside.

The system uses a material called hydrogel that swells to 400 times its size when placed in water. In hot weather, the hydrogel slowly begins to evaporate, cooling the indoor air by about 9 or 10 degrees. The designers incorporated the hydrogel into a new composite called “hydroceramic,” which sandwiches the gel between layers of clay and fabric to create walls that maximize the effect.

“As a system, it is meant to be 100% passive, as it uses recycled rainwater and/or greywater from the building itself,” the team says. “It also cools more when it is hotter because it relies on evaporation as a mechanism.”

Unlike conventional evaporative coolers, it doesn’t require a continuous supply of water. “The hydrogel can retain the water for several days, sometimes even months,” the designers explain. “The rate of evaporation of water which is also the reason of the cooling is dependant upon the outside temperature, humidity and wind conditions.”

The system could theoretically be used on its own in a low-cost building. But since most people will probably want extra cooling–if it’s 100 degrees outside, cooling by 10 degrees might not be enough–it can also be combined with more traditional air conditioning. The material can help save up to 28% of the energy used by A/C (though no word on how much energy is required in the material’s manufacture).

“We believe that the project is a low-cost alternative to meet energy needs and as a system relies on a simple natural process,” the designers say. “In this way it is moving design and technology to a more sustainable future that is respectful of its environment.”


The design, which is close to being market-ready, was developed by masters students Akanksha Rathee, Pong Santayanon, and Elena Mitrofanova, along with professor Areti Markopoulou and assistants Alexandre Dubor and Moritz Begle.

About the author

Adele Peters is a staff writer at Fast Company who focuses on solutions to some of the world's largest problems, from climate change to homelessness. Previously, she worked with GOOD, BioLite, and the Sustainable Products and Solutions program at UC Berkeley.