April 9, 2019


Cool roofs reduce urban heat; green ones, not so much (Cosmos, 4/09/19)

The term "cool roof" denotes one that reflects sunlight, thereby reducing local temperatures. This can be achieved by a simple low-tech fix - painting it a lighter colour. The effect is cumulative: the more cool roofs, the greater the albedo, and thus the more solar radiation reflected rather than absorbed.

This can potentially reduce urban temperatures, the researchers say, and may also lower building energy consumption for cooling, both of which are projected to increase in future due to a combination of rising temperature and increasing incomes.

The researchers found that over a summer season, the difference between simulated urban and rural temperature was 1.1 degrees Celsius on average, and 1.8  degrees when including only night times. The maximum difference was nine degrees.

"Our results suggest that the UHI contributes up to 40% of heat-related mortality over the summer period and that cool roofs implemented across the whole city [of Birmingham] could potentially offset 18% of seasonal heat-related mortality associated with the UHI," the researchers conclude.

The figure corresponds to 7% of the total heat-related mortality recorded during the study period.

During heatwaves, modelling suggested that cool roofs could reduce city-centre daytime air temperature by 0.5 degrees on average, up to a maximum of about three  degrees.

The researchers say cool roofs reduced average UHI intensity by about 23%, and reduced heat-related mortality associated with the UHI by about 25%, during a heatwave. They also found that temperature reductions varied according to the type of buildings on which cool roofs were applied.

Targeting only commercial and industrial buildings contributed more than half of the reduction for heatwave periods.

"Our modelling suggested that modifying half of all industrial/commercial urban buildings could have the same impact as modifying all high-intensity residential buildings in the West Midlands," the researchers note.

Posted by at April 9, 2019 4:28 AM