Losing Ground

Installing reflective pavement is supposed to cool down cities and cut energy use. But these materials also reflect light into the windows of nearby buildings and heat them up, which could prompt people to use even more energy for air-conditioning.

Some cities already use reflective roofs, which lower the amount of heat absorbed by buildings. So people “now propose that reflective pavements should be the next step,” researchers write in Urban Climate. But past studies suggest this might not be a good idea. Consider the opposite case: One study found that in San Diego, installing artificial turf — a highly non-reflective material — could cut a nearby building’s energy use by making less sunlight bounce toward it.

Using a model, the study authors simulated how reflective pavements would affect four-story office buildings with windows in Phoenix, Arizona. The more reflective the ground was, the more cooling those buildings required. If the pavement’s albedo — a measure of a surface’s reflectivity — rose from 0.1 to 0.5, the annual energy needed for cooling increased as much as 11 percent.

City planners could still use reflective pavement on roads far away from buildings, the researchers note. But for areas with offices similar to the ones modelled in the study, they write, “reflective pavements should be considered with caution.” Roberta Kwok | 9 November 2012

Source: Yaghoobian, N. and J. Kleissl. 2012. Effect of reflective pavements on building energy use. Urban Climate doi: 10.1016/j.uclim.2012.09.002.

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