This Ancient Technology Is Helping Millions Stay Cool

This summer, India has endured possibly its worst ever heatwave. The capital, Delhi, logged a record high of 52.9 degrees Celsius (127 degrees Fahrenheit) on May 29, while India’s northern states have baked at sustained temperatures of more than 42 degrees during the daytime. Only now, as the rainy season starts, are temperatures cooling. But in the coming years, things will only get worse.

For many, respite from the relentless heat has come from an improbable source: the earth. Special pots made from clay, when combined with water, can be used to chill drinking water and the surrounding air. They are helping millions of households that don’t have air conditioning and refrigerators stay cool. Companies are also creating earthen building materials that are better at keeping out heat than bricks and mortar, drawing on knowledge that has helped keep people cool for thousands of years.

“We have lost track of traditional systems that have worked for us in the past,” says Monish Siripurapu, the founder of CoolAnt. His company is working to revive these preindustrial cooling techniques at scale, creating clay-based cladding and cooling units that can be installed in both homes and businesses.

These, along with other, smaller clay cooling devices, achieve their effects through evaporation. The simplest and most popular are matka, earthen pots available in a variety of shapes, sizes, and decorative forms. Costing as little as $1 a piece, they’re simple to operate: They just need to be filled with water, and physics does the rest. Their clay is porous, with the water passing through tiny pores to reach the pots’ outer surface. Once there it evaporates, pulling heat from the surrounding air and from the water inside to do so, cooling both. Matka are often covered on top with a wet cloth to help keep their water cool.

Importantly, they don’t use electricity, making them easily deployable and cheap to run. Because of their simplicity, religious bodies and nonprofits across India often put earthen pots in public places for commuters to quench their thirst.

In the Rajkot district of the state of Gujarat, homeware producer Mitticool sells hundreds of different clay and terracotta items, many of which can be used for evaporative cooling. But its biggest draw is its 50-liter, electricity-free refrigerator made from baked clay—which works, essentially, like a giant matka.

Users fill a 10-liter reservoir tank at the top, which, through evaporative cooling, chills both the water and a separate insulated chamber for food below. Priced at 8,000 Indian rupees ($95), the fridge must be kept in a ventilated space to allow for evaporation, and requires regular scrubbing to keep the surface pores open. “The temperature inside the fridge is up to 15 degrees Celsius lower than the surroundings, and it can preserve fruits and vegetables for up to a week,” company founder Mansukhbhai Prajapati says.

Down in the Coimbatore district of Tamil Nadu, at the southern tip of India, 72-year-old potter M. Sivasamy sells his own version of a clay refrigerator that can keep food items fresh for three to four days. His is a cylindrical fridge that comes in two parts, each costing approximately $25. A larger outer chamber is filled with water to generate a cooling effect, while inside it a floating vessel stores edible items. A lid sits on top to keep everything chilled. “I get all the clay from my village,” says Sivasamy. “My customers also appreciate the rainlike smell of food items kept in the fridge.”

Because they don’t use electricity, earthen pots and clay fridges are eco-friendly, and they’re resilient in the face of power cuts too, which can affect households during heat waves when the energy demand spikes. But crucially, they’re affordable.

According to India’s fifth National Family Health Survey, only a third of the more than 300 million households in the country have access to a refrigerator, and fewer than a quarter are able to afford cooling solutions like air conditioning or a water cooler. The International Energy Agency estimates only around 5 percent of Indian households have AC. Cost is a huge factor in explaining the enduring popularity of the millions of matka silently at work across the country.

Then, there are companies like Delhi’s CoolAnt working on creating larger nonelectrical cooling systems. Among its solutions, which are made from baked clay, is Beehive, an assembly of open-ended earthen cones placed in a frame and installed as a window unit. The whole kit is watered periodically—either manually, twice a day, or using an electric pump—to allow evaporative cooling and ventilation. Another variant—a circular cone-filled frame that sits fully inside a building, called Beehive Deki—can cool internal air.

Image may contain Adult and Person

Beehive Deki being built.

Photograph: CoolAnt

Beehive uses the same cooling concept as the earthen pots, but slightly differently. The cones have a wide rear opening for letting in hot air from the outside, and a narrower inner opening. Evaporative cooling chills the air when it’s inside the cone, and the difference in the size of the openings means that the cold air is propelled through the smaller opening to the interior of the building.

If using a water pump to keep the structure wet, the system does require electricity, but the company estimates only about a third as much as a comparable AC unit. CoolAnt says that on a hot day when temperatures exceed 40 degrees Celsius, the Beehive can produce a temperature drop of around 6 degrees. However, the company stresses, exactly how much cooling a device offers will depend both on the weather and the specifics of the building.

CoolAnt also creates cooling facades—terra-cotta structures that can cover windows or even entire exterior walls of buildings to help keep the inside cool, and which are akin to the jali (or lattice) designs that can be seen on medieval-era monuments, including the Taj Mahal. In addition to shading the building, facades are kept wet with recycled water using a pump, and push cool air inside—thanks again to evaporative cooling—while also providing shade. CoolAnt says its facades require up to 30 percent less energy to run than comparable AC. When the company tested its facades in conjunction with AC, it found that running the two systems together could provide similar levels of cooling as with AC alone, but with a lower energy input.

The facades are also highly customizable, chemical-free, and completely recyclable, says CoolAnt’s founder Siripurapu. “Our ideas are easier to adopt in rural areas, where the raw material is readily available, and people have time to build these solutions at a much lower cost.”

Image may contain Architecture Balcony Building Indoors Interior Design and Window

A type of CoolAnt facade, called “Binary,” that’s made from clay leaves.

Photograph: CoolAnt

CBalance is another company working to tackle the heat problem, specifically for underprivileged households living in tightly packed slums, ghettos, and poorly planned neighborhoods. Led by Vivek Gilani, it has experimented with simple and affordable cooling ideas like insulating ceiling boards made out of recycled compressed Tetra packs and plastic objects, rooftop gardening in grow bags, and wood-wool cement composites. In houses made using sheets of tin or asbestos, having roofs and walls made with these insulating materials can cut down how much heat gets in.

The health risks of living in asbestos or tin-topped homes are severe, especially in tightly packed dwellings where indoor temperatures can be higher than outdoors, and high humidity makes the situation even worse. But getting more houses and businesses to adopt materials like those from CoolAnt and CBalance is tough.

There’s sometimes resistance from residents. People prefer a traditional house made out of brick and cement for its structural integrity, says Fatema Mohammad Chappalwala, an environmentalist and program coordinator at the Sambhaavnaa Institute of Public Policy and Politics. “It is seen as a status symbol,” she says. Plus, earth-based materials need to be maintained.

And, in the absence of government support for alternative materials, there’s a lack of uptake by commercial builders. “Elite policymakers who have never spent a single day in heat-stricken houses are tasked with making policies,” says Gilani, exasperated.

When it comes to cooling solutions, “price sensitivity is a crucial factor for the Indian market,” says Shayak Sengupta, an energy and climate fellow at the think tank the Observer Research Foundation. Therefore, to expand access to things like alternative materials and building designs, “capital injection has to come from foreign stakeholders.”

Bhavna Maheriya, who handles the energy and climate change portfolio at the nonprofit Mahila Housing Trust, which works with women from low-income households on climate resilience, says it has piloted at least half a dozen low-cost cost cooling solutions, including white solar reflective paints, but the lack of government subsidies means locals aren’t ready to embrace them despite facing the worst of brutal summers.

The lack of any serious attempts so far to scale up climate-resilient infrastructure is lamentable, says J. Srinivasan, distinguished scientist at the Divecha Center for Climate Change. “We can’t wait for the temperatures to rise any further, or we will run into an energy shortage crisis for cooling. Unfortunately, politicians don’t see it as an urgency, and they forget about it until the problem repeats like a cycle next year,” he says.

But with simpler, more affordable solutions, like Mitticool’s fridge, the public are striding ahead with adoption. Founder Prajapati says they move thousands of units each day. Even during nonsunny seasons, the artisanal value, sentimental attachment, and environmental appeal of their products are enough to keep their production lines rolling, he says. Sales of their refrigerator and similar products have reached such a level that the Indian government has created a standard for nonelectric cooling cabinets.

Prajapati is proud to be able to help others with a useful and affordable solution. “I have seen rough times in my life,” he says. “I won’t wish the same for others struck by poverty and deadly heat.”