"There is a huge potential for savings by using roofing material that doesn't absorb heat and transmit it into a building," said Bill Miller, a researcher in ORNL's Energy Division. "What we're doing is developing procedures that are non-biased and allow a consumer to determine the advantages of using a highly reflective roofing material when re-roofing an existing building or during construction of a new building.".
While the "cool roof" is a simple concept, testing under highly variable conditions can affect results and cause confusion in the roofing industry and among regulators and consumers who do not know how to evaluate marketing claims. Using ORNL's Building Technology Center, researchers hope to quantify the long-term energy and durability benefits of highly reflective roofing materials. Researchers also plan to develop and promote a fair and credible procedure to help consumers choose a roofing material.
In this project, researchers are using side-by-side comparisons of products under the same climatic conditions to evaluate roofing material with varying degrees of reflectivity. Two three-year studies are focusing on 18 different single-ply membranes, 11 different bare and painted metal roofs and two photovoltaic systems. Researchers are also studying 24 different roof coatings, so the center covers the entire range of cool roofing membranes, metal roofs and roof coatings available on the market.
Consumer decision guidelines will be based upon these extensive test results.
Researchers know that roofs with high initial solar reflectance degrade with time as dirt accumulation affects the surface. Add to that the effect on roofs of different climates throughout the United States and the job of predicting reflectivity and subsequent energy savings becomes complicated, Miller said.
DOE and ORNL hope to increase the use of reflective roofing in areas of the nation where it can benefit consumers. In the Southeast and other states with hot climates, consumers could save up to 40 percent on their electric bills during months they use air conditioning.
"We want to support the roofing industry in accelerating market penetration of cool roof materials," Miller said. "By helping the industry, we can help DOE in one of its missions, which is to ensure that the industry remains competitive in a global market."
Another goal is to increase energy efficiency, which decreases the burning of fossil fuels and decreases the emission of greenhouse gases. It also reduces demand for foreign oil.
In colder climates, however, studies have shown that summer decreases in the use of electricity to cool buildings with highly reflective roofs may be offset by winter increases in heating costs. Cities cited in the study were Chicago and Philadelphia.
"Similarly, highly reflective roofs may not be the best option for urban areas because the reflected sunlight can affect surrounding buildings," Miller said. "But in those instances, rather than reflect or transmit the sun's energy, why not absorb the energy and convert it into electricity using solid-state conversions of heat to electricity?" .
While other research facilities around the country are also performing studies on roofing materials, ORNL is uniquely positioned in that companies and trade associations representing about 80 percent of the roofing industry work with researchers at the Building Technology Center, which is a national users facility.
"By working with the industry, we are developing procedures to help in the design of roofs that will be more energy-efficient and will ultimately save consumers money," Miller said.
DOE and ORNL also will assist the Environmental Protection Agency in applying the Energy Star Roof Products Program to help consumers quickly identify energy-efficient, cost-effective roofing. Products that bear the EPA Energy Star label save energy and help prevent air pollution.
The Building Technology Center's location in East Tennessee, which experiences diverse weather conditions representative of many locations around the nation, also makes it especially useful for evaluation purposes.
The research is funded by the roofing industry and DOE. ORNL is a DOE multiprogram research facility managed by Lockheed Martin Energy Research Corporation.