Chatham House Associate Fellow and chartered member of the Royal Institute of British Architects (RIBA), Karim Elgendy explores the role of buildings in the race to net zero cities.
Keeping cities cool as the planet warms
Wuhan is experiencing a silver-lining as the dark clouds of 2020 make way for something new. For the city’s 11 million residents exposed to searing summer temperatures, respite is coming in the form of large fabric ‘clouds’ that promise to shield them from the blazing sun. By capturing breezes and air movements the ‘clouds’ gently fan passers-by.
Designed by HDA, a Parisian architectural practice that’s also behind Miami’s Climate Ribbon, which uses similar structures to naturally regulate the temperature of urban spaces, the ‘clouds’ are one of several novel ways that architects, entrepreneurs and scientists are exploring to keep cities cool – without ramping up climate-polluting air-conditioning units.
Already basking in warmer temperatures than the surrounding countryside, cities are suffering from record-breaking highs that residents are often ill-equipped to handle. The last decade has been the hottest on record and as millions more swarm to urban jungles, city temperatures will keep rising. And ironically air-conditioning is a big part of the problem by using climate-polluting coolants and pumping warm air right back into the atmosphere.
While manufacturers release more energy-efficient designs, the reality is that even the most efficient air-conditioning drives global warming, says Ellen Dobbs, International Development Manager at climate charity Ashden. Globally, air conditioners and electric fans already account for about a fifth of the total electricity used in buildings today. The International Energy Agency estimates that global energy demand from air-conditioners will triple by 2050.
“Rising temperatures create significant challenges for urban centers, where extreme temperatures are often exacerbated by the urban heat island effect,” says Jessica Brown, Executive Director of the Kigali Cooling Efficiency Program at the ClimateWorks Foundation. “Cooler cities lead to positive impacts on human health, air quality, economic productivity, public safety, energy savings and quality of life.” Simply, when we’re hot, we’re less productive and economies suffer.”
This highlights the disparity between developed and developing countries, with the world’s 30 hottest cities all located in less economically developed regions. “The extreme heat threat is greatest for the one billion people in poorer countries who have no access to reliable cooling,” says Dobbs. But the need for efficient, low-carbon cooling solutions is required in developing and developed countries alike, since developed countries already have a high saturation of air-conditioning units and refrigerators.
While cooling sector emissions are already substantial in developed countries, rapid growth is expected in developing countries over the next few decades, says Axum Teferra from ClimateWorks Foundation. In India, there are currently 27 million room air-conditioning units installed, and that number is projected to grow to 1 billion by 2050, she says. But the cost of newer, more efficient appliances isn’t feasible for many low-income households, so other solutions are needed.
Cooling by Design
To create the innovative cooling clouds in Wuhan, HAD is working with a wind tunnel laboratory. The project will see them design a series of canopies next to the Buddhist temple of Guiyan, that provide shading and naturally help to ventilate the streets. “My client told me in Miami that the public street was 6-degrees cooler,” HAD Founder Hugh Dutton says of the Climate Ribbon. “Looking to nature and being sensitive to her forces and the environment” is pivotal in design.
Many cities across the world align to Dutton’s thinking, looking to trees, plants and green spaces to keep residents cool. In Singapore, any greenery lost on the ground has to be replaced with greenery in the sky. Barcelona is promoting the transformation of roofs into gardens and London plans to become zero-carbon and at least 50 percent green by 2050 through measures that include planting more trees along streets. Cities from Beijing to Stuttgart are building green ‘ventilation corridors’ that decrease air pollution and alleviate heat.
“The Colombian city of Medellin has lowered temperatures by 2 to 3ºC with its Green Corridors urban planting projects,” Dobbs says. Some 30 green corridors of trees, plants and bushes were planted, transforming derelict parts of the city into green oases. “We need to invest in sustainable alternatives to air-conditioning – like buildings that make smart-use of shading and ventilation and cooling our streets with trees and water.”
Alternative Building Materials
US-based startup, SkyCool, is innovating with alternative building materials. The company has developed a panel and optical film that reflects sunlight and emits heat back into the sky during the hottest hours of the day. The panels can be used to make existing refrigeration and air-conditioning systems more efficient or replace air-conditioning units altogether. When connected to air-conditioning units they can create energy savings of 30 to 40 percent. Already SkyCool has worked with Engie Group and Microsoft. Longer-term, it plans to develop its technology for the residential cooling market.
And simply painting roofs with a reflective white coating is another effective way of keeping internal building temperatures down, particularly in developing regions. It’s also low-cost, as well as quick and easy to implement. A cool roofs project at an Indonesian industrial building has seen indoor temperatures slide by 10.7ºC.
Keeping urban jungles cool bolsters economies can also saves lives. The Ahmedabad Heat Action Plan in India which implements measures including planting trees and painting roofs, saves over 1,000 lives-a-year. “There’s an assumption that air-conditioning must be the cooling solution in all buildings and a large air-conditioning industry is pushing that approach,” Dobbs says. But low-carbon solutions can be really effective. “There are huge opportunities everywhere.”
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