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Cool roofs, cool research 

By Russ Cooper

In the deep freeze of winter, it may seem a bit odd to be talking about bringing the temperature of the city down, but for engineering professor Hashem Akbari, it’s more than a hot topic.

Akbari, who joined Concordia in June 2009 as Building, Civil and Environmental Professor and a future Hydro-Quebec Research Chair, is studying the urban heat island; the phenomenon whereby a metropolis is usually significantly warmer than its rural surroundings. In an attempt to address the energy used to cool cities around the world during hot weather, he’s developing light reflective materials for roofs and pavements.

This simple idea, says Akbari, can potentially delay the effects of global warming.
Here’s how: Generally, pavements and roofs in urban environments are dark and absorb 80 to 90% of sunlight; this, obviously, keeps heat in the city. Those same surfaces covered with his reflective materials (white for roofs, lighter colours for pavements) will absorb only 30 to 65%.

By decreasing absorption of roofs by 25% and pavements by 15%, the overall temperature of a city can be reduced by two to three degrees Celsius. Ipso facto, energy requirements for cooling during summer are reduced.

Together, pavements and roofs comprise over 60% of urban surfaces. Akbari states 10 sq m of white roof replacing a dark roof can offset one tonne of CO₂. In other words, the temperature reduction due to radiation not being absorbed by the earth is equal to the increase in temperature caused by one tonne of CO₂ in the atmosphere, effectively balancing any change.

That means if we resurfaced the 60% of the island of Montreal’s 500 sq km comprised of pavements and roofs with reflective materials, our city alone could offset over 12 million tonnes of CO₂.

He admits it may be more useful in hot regions – those without snow to cover roofs and roads – but efforts in even the coldest climates even would positively contribute to the overall effect. “If major cities around the world adopt the technology, we’d be well on our way to making a very significant dent in rising temperatures,” he says. Akbari estimates that permanently retrofitting urban roofs and pavements in the tropical and temperate regions of the world would create a one-time offset of 44 billion tonnes of emitted CO₂.

Before joining Concordia, Akbari spent 26 years at the Environmental Energy Technologies Division at Lawrence Berkeley National Laboratory (LBNL) at the University of California, Berkeley. Since Sept. 2008, Akbari has been leading an international campaign to develop regional programs to install reflective roofs and pavements in the 100 largest cities of the world. Steve Chu, currently U.S. Secretary of Energy and former LBNL director, strongly supports the technology, repeatedly bringing it to the attention of the media and policy makers.

Akbari sees enormous potential in Concordia’s dedication to innovation of sustainable energy and methods. “The energy utilization per Canadian is twice that of Californians,” he says. “There’s a lot of room for improvement here. It’s one of the reasons I decided to come to Canada and Concordia.”

Currently, he is helping to organize the next meeting of the European Union Cool Roof Council for rating and labelling the optical properties of roofing surfaces in Europe to be held in La Rochelle, France on Feb. 2 and 3, 2010. Akbari is also a member of the board of the Oakland-based Cool Roof Rating Council (CRRC), an organization he helped to establish in 1998.