Million Cool Roofs
From dark to light: painting roofs with light-reflecting paint is one of the simplest measures against heat stress.

Can a little paint on the roof lower the electricity bill and also curb climate change? Xiulin Ruan, professor of mechanical engineering at Purdue University in the USA, is convinced of it. For years he worked with his students on a color that was finally presented in April 2021 as "the whitest white". The special feature: the acrylic paint containing barium sulphate particles reflects up to 98,1 percent of sunlight. 

Xiulin Ruan
The ultra white was produced in a laboratory at Purdue University. Pictured: Prof. Xiulin Ruan

According to the scientists, roofs coated with it remain cooler than their surroundings, even in the hottest midday sun, because the paint can even emit thermal radiation in the infrared range. It develops a cooling capacity of ten kilowatts on a roof area of ​​around 90 square meters, and according to Ruan, this is better than what conventional air conditioning systems in residential buildings can achieve. 

 

Cooling is a must

The ultra white can already be found in the Guinness Book of Records. According to the inventor, as soon as the path to retail has been made, a lot is possible: Not only would the need for air conditioning decrease, the color could even reverse global warming - if just under one percent of the earth's surface were painted with the new white.

It is still a bold vision. However, one thing seems certain: the desire for cooling is likely to increase dramatically in the coming decades. This is due to rising temperatures and a growing urban population worldwide that has to come to terms with the extreme heat.

The International Energy Agency (IEA) estimates that around two billion air conditioners deliver goosebumps at the touch of a button, 70 percent of them in residential buildings. And the prospects for the manufacturers seem sunny: for the year 2050, a stock of 4,5 billion devices is forecast, because above all people from the new middle class from India to Brazil are likely to fuel demand. It will be a boom with a downside: Air conditioning systems are likely to become a main factor in global electricity demand and, since the devices are known to emit a lot of heat, make the heat problem even worse. 

Air conditioning
Air conditioners don't just use electricity, they give off heat - making the heat problem worse. Pictured: Singapore

According to the IEA, many people who cool artificially today usually do so with a model that is “two to three times less efficient” than the best in its class. In order to persuade people to buy more efficient devices, you have to come up with something – like Rwanda is trying to do now. The small East African country has "R-COOL GO" presented a new financing product a few weeks ago: Local banks offer attractive loans for the purchase of efficient refrigerators and air conditioning systems, which can be paid off in small installments. For many Rwandans, this makes cooling affordable for the first time. A similar funding scheme exists in Ghana.

In the future, significantly more powerful systems could also provide a fresh breeze. An impetus for this comes from an innovation competition supported by the Indian government: The Global Cooling Prize called on manufacturers to develop cooling technologies that use less electricity and use more climate-friendly coolants. In 2021, the two winners - Gree Electric Appliances from China and Daikin India - were chosen. They succeeded in building prototypes that require 80 percent less energy than conventional devices. They also use refrigerants with a low GWP - the abbreviation stands for Global Warming Potential. The new temperature reducers should be on the market by 2025 at the latest. 

Down with the heat

Hundreds of millions of people living in hot countries and in poverty at that cannot afford cooling. Many live in densely populated neighborhoods where cabins are poorly designed and built with cheap, heat-retaining materials. "When it gets hot, residents cover their tin roofs with cardboard and sleep directly on the floor," says Indian environmental expert Vivek Gilani, explaining how people in Pune and Bangalore are fighting heat stress.

Interview with Vivek Gilani, Founder of cBalance in India

Vivek Gilani

The cardboard on the hot tin roof

Environmental engineer Vivek Gilani advises Indian citizens on how to protect the climate and how sustainable and affordable cooling is possible.

Gilani founded cBalance, a social enterprise that helps families transform their homes. He relies on simple, passive cooling solutions that require little or no energy. 

There are many hacks against heat: These include green walls and roofs as well as shady constructions, for example made of coconut palm leaves. Windows in corrugated iron huts are cut to improve air circulation, and insulation is made from old plastic or aluminum packaging to protect against heat. The Eco-Cooler, an invention from Bangladesh, is a wall insert made from plastic bottles cut in half. If a breeze blows into the open bottles, the air escapes cooled on the other side. In huts, cooling of up to five degrees is possible – without any electricity. 

Eco cooler
Do-it-yourself: A few degrees of cooling can be achieved indoors with an insert in the outer wall, in which halved plastic bottles are mounted (photo: example from Malaysia)

white for the world

The aforementioned whitening of roofs is also very useful, even if the paint available today reflects a maximum of 90 percent of the light and cannot emit heat. An example from the World Bank's "Primer for Cool Cities" report makes it clear: if the sun's rays hit a black roof at temperatures of 37 degrees, it heats up to 80 degrees, while a white one only has 44 degrees. 

With a light roof, interiors can be cooled by an average of two to three degrees. The more roofs in the neighborhood reflect the sun's rays, the cooler it gets between the houses. In many countries, however, there is a lack of awareness of this effective measure, says the Clean Cooling Collaborative from San Francisco. In 2019, the philanthropic initiative launched the Million Cool Roofs Challenge to make cool roofs popular worldwide. Teams from ten countries -- several in Africa, Mexico, Bangladesh, Indonesia and the Philippines -- each received $125.000 to upgrade homes, schools, factories and hospitals with solar-reflective coatings -- hoping to start a trend. 

Million Cool Roofs
The ten teams in the Million Cool Roofs Challenge have recolored 1,1 million square meters of roof space.

Despite the pandemic, a lot has been achieved in the past two years: around 1,1 million square meters of roof area - equivalent to around 250.000 small houses - has been recolored. 

At the beginning of March, the project from Indonesia was chosen as the winner because, according to the jury, it represents the best sustainable and scalable model. "We had to overcome a number of hurdles to bring cool roofs to Indonesia," says project manager Beta Paramita, "which included finding suitable materials for the tropical climate, building knowledge about cooling colors and implementing it despite limited resources." 

With the help of universities and city governments, the team was finally able to achieve cool roofs on 70 homes, schools and factories in 15 cities. In individual cases, the indoor temperature dropped by an impressive ten degrees. A total of around 10.000 people are benefiting from the measures today. The prize money of 750.000 dollars will now be invested in further research work and the expansion of the company's own color production.

The design factor

Architect Sarah El Battouty says that heat stress must be taken into account when planning buildings. With your consulting company ECOnsult she relies on climate-friendly living in Egypt and uses traditional cooling techniques. In a project in the Egyptian desert, she was able to demonstrate that, with skillful planning, quality of life can be achieved even in hot zones without an air conditioner. El Battouty is also contributing her expertise to a large-scale Egyptian government infrastructure program designed to improve living standards in 4.000 villages.

Built cool
Clever architecture and cooling materials reduce heat stress.
Anti-heat architecture
The Egyptian architect Sarah El Battouty and her consulting firm ECOnsult rely on well-established techniques when constructing new buildings. El Battouty's goal is to keep indoor spaces cool without air conditioning. Their Bahareya Village housing project, in which 150 farm workers from the tea manufacturer Royal Herbs live, is considered groundbreaking.
Outside temperatures in the desert oasis reach up to 50 degrees. In the residential buildings themselves, the thermometer shows a pleasant 19 to 26 degrees. This is made possible by a broad mix of structural measures: These include raising the building foundations, shading through projecting roofs, the use of natural air currents, light-reflecting roofs and limestone cladding.
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The Indian Monish Siripurapu is also working on alternatives and uses the interplay of clay and water: The architect (Ant Studio in New Delhi) has developed an unusual terracotta façade that works with evaporative cooling. 

Cool facade
In India, terracotta pots are traditionally used to cool water. The New Delhi-based architect Monish Siripurapu and his architecture firm Ant Studio use the proven material to cool residential buildings and businesses: With "Beehive" they have developed a terracotta façade that not only looks unusual.
“We use evaporative cooling by pouring water on clay pots and letting it circulate. The air flows through these pots, which are shaped like cylindrical hollow tubes, cooling the space and coming out again without releasing any heat. Our system brings indoor temperatures to 28 degrees with low power consumption,” explains Siripurapu.
Further plus points: The life cycle analysis of all processes and materials is more advantageous compared to conventional air conditioning systems. In addition, the façade elements can be manufactured by local craftsmen.
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A Pakistani company, on the other hand, relies on cold from the depths: GeoAirCon uses the stable temperatures of 20 to 22 degrees that prevail at a depth of three to four meters to geothermally cool households: water circulates in a system of underground pipes and thus cools down naturally. Pumped back to the surface, the cool water can cool rooms down to 28 degrees – at outside temperatures of 40 degrees – and, according to GeoAirCon, requires 70 percent less energy than conventional air conditioning systems. The “low-cost heat exchanger” costs an average of 500 dollars and, thanks to an optional vertical construction, can also be implemented in densely populated areas.  

And the multi-award-winning Austria Pavilion at the EXPO 2020 in Dubai, which has just come to an end, also used natural temperature regulation. That from Querkraft Architects The building created has 38 open-topped concrete cones that catch the wind and ensure air circulation. 

Heat Expo 2020 Dubai
Nice and cool: The Austria Pavilion at EXPO 2020
Heat Expo Austria

So-called wind catchers are an architectural element that has been used in the region for centuries and that is now being remembered more often in the discussion about emission-free cooling. In addition to the towers, the architects also used cooling clay coatings, plants and a water mist system. The pavilion is said to use 70 percent less energy than comparable, air-conditioned buildings. 

Cooling as a service

The search for sustainable cooling is not just about people. Cold is also often a must for the shelf life of food and medical products (see also corporAID article "Uneaten".) But what to do if small farmers and traders don't have the money for refrigerators or they can only operate their devices with diesel oil because they live far away from a power grid? The answer could be "Cooling as a service": With this business model, people only pay for the use of a cooling device. The provider remains the owner and takes over its installation and maintenance. 

Solar freeze is revolutionizing refrigerated storage in Kenya in this way: The company sets up walk-in refrigerated containers that are operated with environmentally friendly solar energy. Farmers can store their tomatoes and mangoes in it and pay 40 cents per crate per day - and, as is very common in Kenya, they can do it very easily via mobile phone.

Auch Koolboks in Nigeria offers retailers refrigeration services on a pay-as-you-go model. In the course of the pandemic, the company has also added vaccination refrigerators for the correct storage of vaccines to its range.

Koolboks
Life is cool! says Koolboks. The company provides refrigerators in Nigeria on a pay-as-you-go model.

More and more companies from India to Africa are thus improving access to an important service and at the same time spreading more climate-friendly cooling technologies. A cool future is almost inevitable.

Photos: cBalance, Purdue University/Jared Pike, Jasón Sosa Gomez/Échale, Econsult/Ashden, CoolAnt, Idora Baharudin, Expo Austria, Dani Eid/EXPO 2020, Base/Koolboks