Faced with rising energy costs, building owners and managers are discovering that light-colored, reflective roofs can play a critical role in cutting energy consumption. The State of California agrees, and has become the first state to offer cash rebates for the replacement of dark roofs with highly reflective surfaces.
The incentives, offered through the California Energy Commission (CEC) Cool Roof Retrofit Program, apply to low-slope roofs on nonresidential or multifamily buildings that are mechanically cooled in the summer. The program offers financial incentives to replace dark roofs that reflect less than 30 percent of sunlight with nonmetallic roofs that reflect at least 65 percent of sunlight.
While the incentives save money up front, the most significant savings come in reduced energy consumption over years of use. According to the CEC, cool roofs reduce peak electricity demand, reduce cooling energy use, improve building comfort, reduce the 'heat island' effect and even reduce air pollution. When the temperature outdoors reaches 90 F, the temperature on a black roof can be as high as 160 F, according to The Heat Island Group at the University of California, Berkeley. Some of that heat is transferred inside to the occupants of the building, resulting in higher utility costs for air conditioning to keep the occupants comfortable.
Greg Zoll, senior superintendent at the University of California, Los Angeles, is taking advantage of the incentive program to cover a dark built-up roof on the Young Research Library with a white vinyl membrane. The incentive itself will save the university about $8,000 on the project -- money that Zoll says will be invested in improving the R-value of the building's insulation.
The real savings, though, will come over time. Zoll says the university has installed a number of reflective roofing membranes on other buildings on campus in the last five years, and it is saving 20 percent to 30 percent in energy costs by combining the reflective roof with increased R-value insulation. During the peak air-conditioning season, he figures the university saves an average of about $10,000 a year in energy costs. 'These roofing systems are designed to last 30 years, so multiply that out over the roof's lifecycle,' he adds, for the true savings.
Studies prove energy savings
Additional studies by the Florida Solar Energy Center and the U.S. Environmental Protection Agency (EPA) confirm that reflective roofs made of polyvinyl chloride (PVC or vinyl) membranes or other single-ply materials can reduce utility costs of air conditioning by as much as 50 percent. And cooling demand in the peak hours -- the most costly -- can be reduced by 10 percent to 15 percent, reducing demand on the grid. According to the EPA, $40 billion is spent annually in the United States to air condition buildings -- about one-sixth of all electricity generated in the United States each year.
In a recent study sponsored by the EPA and the U.S. Department of Energy (DOE) scientists at the Lawrence Berkeley National Laboratory measured and documented summertime air-conditioning energy savings and power demand reduction from a large retail store in Austin, Texas. The store was retrofitted with a reflective vinyl roof membrane manufactured by Sarnafil Inc. Temperatures were monitored with the original black rubber roofing membrane from August 1999 to April 2000. In May 2000, the roof was replaced with a white thermoplastic membrane, and monitoring continued from late May through the summer of 2000.
The results: The average daily summertime temperature on the surface of the black roof was 168 F, but only 125 F on the white vinyl roof. Measured at the plenum between the roof and the ceiling, average temperatures were reduced from 101 F to 95 F.
The study concluded that installation of the white vinyl roof would save the building's owners about 63 megawatt hours of energy consumption per year, with annual energy- and peak-demand savings of about $7,200. They conservatively extrapolated this over a 13-year expected life for the roof and concluded that the present value of future energy savings would range from $62,000 to $71,000.
The study points out that that the magnitude of energy savings will vary depending upon the building type, level of roof insulation, ventilation rate between roof and ceiling, size and efficiency of the air-conditioning system and, of course, roof solar reflectance.
Source: The Vinyl Institute, Arlington, Va.