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In Every Season, White is the New Green
Want an effective tool to fight global warming? Try a can of paint.
As the director of facilities at Radford University can tell you, the most powerful and elegant form of solar power is simple passive solar. This is true both in the case of trapping the sun’s heat and for its inverse, deflecting it. Dark-colored roofs act as solar collectors, which in most circumstances has the net effect of wasting energy. The heat trapped by dark roofs causes increased cooling energy use, higher peak electricity demand, and increased air pollution due to the heat island effect.
Although it is true that a dark roof soaks up heat in winter as well as summer (and therefore can save a bit on heating), a white roof is a net energy saver even in the northernmost parts of the United States. There are several reasons for this: During winter the sun is lower to the horizon and does not hit roofs for as many hours of the day or as directly and intensely as it does in the summer; therefore, the overall solar collection is far less. White roofs also retain snow cover, an excellent insulating material, better than dark ones.
Most importantly, because heat rises, the heat gain on a dark roof in winter stays at the top of a building (rather than heating the structure) before disseminating into the surrounding atmosphere. It is precisely this cycle of heat capture and loss that creates “heat islands” in metropolitan areas, a major contributor to global warming.
White reflective membranes or coated roofs last longer (because the intensity of the heat breaks down dark roofing materials faster), create cost savings, and lower a building’s carbon footprint. The degree of efficiency achieved simply by using this technique is astounding. A white roof typically only increases 10-25 degrees F above the air temperature, even on the sunniest of days. To illustrate the comparison between white roofs and dark roofs: On a clear, sunny summer day when the air temperature is 90 degrees Fahrenheit, a typical white roof might reach approximately 110 degrees. An aluminum roof would be hotter, at 140 degrees, while a standard black, single ply roof will heat up to 190 degrees or more.
According to physicist Hashem Akbari of the Lawrence Berkeley National Laboratory, a 1,000-square-foot “cool” roof offsets ten metric tons of carbon dioxide emissions in the atmosphere. If a hundred major urban areas in temperate and tropical regions switched to reflective materials for their roofs and pavements, it would offset roughly 44 metric gigatons of greenhouse gases-equal to ten years of emissions growth. Akbari and his colleagues are proposing an international campaign to the UN to organize all the large cities in these regions to develop white roof installation programs.
“I call it win-win-win,” Akbari said. “First, a cooler environment not only saves energy but improves comfort. Second, cooling a city by a few degrees dramatically reduces smog. And the third win is offsetting global warming.”
There are many ways to get a roof white. A simple coat of white paint creates remarkable efficiency. For an even greater degree of reflectivity, white roofs can be made from inherently cool roofing materials, such as white vinyl or roof coating. Two new roof coatings on the market made by HyperSeal, Inc, contain glass microspheres that increase both insulating and reflective properties.
Harvard Divinity School, Depauw University, Valparaiso University, Mount Wachusett College, Thomas More College, University of Florida, and University of California, Santa Barbara are among the many educational institutions that have started to integrate white roof technology into their campus structures. Many of them have already won environmental awards for their buildings.
The athletic arena at Radford University, however, takes the cake. Sporting the first roof of its kind, the top of the Dedmon Center features a fabric membrane with nanotechnology insulation. At only two inches thick, the composite fabric system has an insulation value of R-12. It also allows a moderate amount of natural light to pass through the membrane, reducing the need for artificial lighting during the day. This fusion of aesthetics, conservation, and technology is an elegant response to the increasing awareness of energy waste.
Photo courtesy of Mount Wachusett College.
To Slow Global Warming, Install White Roofs: Los Angeles Times
Universities, EPA Work to Cool Heat Islands: ClimateEdu