New photonic membranes that reflect solar radiation could help reduce extreme temperatures in our cities
A revolutionary demonstration project – inspired by research on photonic membranes from Stanford University – was on display in the centre of Paris during September as part of the initiatives for the UN Climate Change Summit COP 21.
Scientists, engineers and designers from Transsolar, an international climate engineering firm, and Carlo Ratti Associati, a design and innovation consultancy founded by Massachusetts Institute of Technology professor Carlo Ratti, have presented a demonstration project that looks at how to reverse climate change in cities. Inspired by cutting edge nanotech research from Stanford University, the team exhibited new photonic membranes that reflect solar radiation could help reduce extreme temperatures in our cities, at zero energy cost and zero water demand. The demonstrator, developed with the Mairie de Paris, was part of a series of events under the banner of “Paris Climat 2015” and the United Nations Framework on Climate Change’s Conference of Parties (COP21), to be held in Paris later this year.
“Since primary school, we’ve all studied how greenhouses (sometimes also called hot-houses) work: they are enclosures that let in the sun’s short wave radiation, while trapping long wave radiation. As a result, temperatures increase. Now imagine doing exactly the opposite: finding a material that would reflect incoming short wave radiation from the sun, while letting the earth radiate to outer space. The result would be a net cooling of the city – something we could call a cool-house,” says Carlo Ratti, founder of Carlo Ratti Associati and professor at the Massachusetts Institute of Technology. Theoretically, if one were able to cover a large urban area in an optimized material we could reach temperatures below zero even during the summer. In reality, today’s membranes can achieve decreases in temperature of several degrees.
“The demonstration project in Paris explored different types of membranes and used advanced computer simulations to evaluate what the overall effect would be in Paris,” explains Thomas Auer, managing director of Transsolar and professor at the Technical University of Munich. “The principle is nothing new: green canopies in cities are very effective and have been used to a similar effect for centuries. However, in the coming years, new synthetic membranes will open up unprecedented opportunities.” While cooling at zero energy cost may seem an impossible idea, it turns out that there is a way of achieving this by harnessing a renewable “resource" that we may not realise we have access to: the extreme low temperature of the universe. Researchers at Stanford University in California, USA, have shown that a special kind of ‘photonic’ material or surface can be designed to reflect nearly all incoming sunlight while also sending its heat to the sky, and thus the cold of space, as infrared light. This sky-facing surface can thus stay 5-10°C below air temperature entirely on its own, even under direct sunlight, and thus provide more than just shade: it could be a source of cooling for tomorrow’s buildings that requires no electricity or water. Suddenly, Paris feels more like Stockholm or Reykjavik.
“In 1960, the great American inventor Buckminster Fuller proposed to cover midtown Manhattan with a giant greenhouse, in order to mitigate its cold winters,” comments Emma Greer, project manager at Carlo Ratti Associati. “Fifty years down the line, our planet is grappling with the opposite issue – overheating – but some of the solutions might be similar.” Extreme weather patterns brought about by global warming, such as the infamous heat wave of 2003, represent a direct threat to our cities. With temperatures on the rise, uncomfortable urban climates discourage people from living and walking outside air-conditioned buildings. This also leads to more inside conditioned spaces and higher energy demand for air conditioning in buildings that have traditionally not needed it. The challenge at hand is to develop climate remediation solutions that ensure ubiquitous comfort. As an example, if one were to wrap Paris’s Ile de la Cite with a photonic membrane, its temperature would be 5-10 degrees lower. “Such an intervention might not be practical – but covering courtyards and public plazas might be a feasible option,” adds Greer.
For more information visit: www.cool-paris.fr
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