March 9, 2012
New York's White Roofs Prove They're Cool: A new study quantifies the true beauty of white roofs -- dramatically cooler surfaces that reduce discomfort, cooling costs, and a tad of global warming. (Sam Kornell, 3/08/12, Miller-McCune)
Miller-McCune has in the past reported on the curious phenomenon scientists refer to as the "urban heat island effect," in which cities -- dark jungles of asphalt, metal, and concrete -- turn into heat reservoirs, soaking up the warmth of the sun. By failing to reflect solar radiation back into the atmosphere, they can end up more than 5 degrees warmer than surrounding areas.
Last summer, on the most sweltering day in New York -- July 22, 2011 -- the researchers discovered that a white-surfaced roof was 43 percent cooler than a typical black counterpart (which reached up to 170 degrees Fahrenheit). Not coincidentally, July 22 set a city record for electricity use, as miserable citizens twisted the dials of their air conditioners to "high."
In 2007, NYC Mayor Michael Bloomberg signed into a law a program to reduce the city's greenhouse emissions by 30 percent by 2030. According to the authors of the study, increasing the city's "albedo" -- the degree to which it reflects solar radiation -- by brightening its surfaces is one of the quickest, cheapest, and most effective ways to achieve significant reductions.
The study compared the benefits of two methods of increasing reflectivity. Professionally installed white membrane coverings, which cost about $15 to $28 per square foot, were found to be more durable, but for 50 cents a square foot, the job could be done with white acrylic paint, with repainting expected every two years. This second, DIY method is being promoted by the city's CoolRoofs program as a highly cost-effective way to cool the city and reduce its greenhouse gas emissions by lowering energy demand during hot summer months.
Posted by Orrin Judd at March 9, 2012 5:58 AM