Con Edison ‘Cool’ Roofs Reduce Energy Costs

by | May 5, 2010

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Con Edison’s green and white roofs atop of its training and conference center in Long Island City help prevent energy losses, provide other environmental benefits, and reduce heating and cooling costs, compared to traditional dark roofs, according to research from Columbia University.

A key finding of the study (PDF) shows that the green roof, consisting of 21,000 plants, on The Learning Center reduces summer heat gains by up to 84 percent and winter heat losses by up to 37 percent, compared to a black roof. The white roof reduces summer heat gains by up to 67 percent. NWC says these figures represent only the reduced amount of heat flowing through the roof, not a building’s energy consumption.

This translates into an estimated annual cost savings of $330 to $350 for heating and $225 for cooling, according to the study.

The green and white roofs also prevent “heat island effect,” where dark roofs absorb sunlight during the day and radiate heat back into the atmosphere at night, say researchers.

Con Edison has installed nearly 250,000 square feet of white roofing, including on its Manhattan headquarters, and has plans for at least another 220,000 square feet by the end of 2010.

The energy provider commissioned a study by Columbia scientists to measure temperatures and other data on the green, white and dark sections of the training center’s roof. The goal was to determine the environmental and energy-consumption performance of each type of roof as well as the cost-benefit estimates for energy conservation.

While green roofs are more energy efficient and offer benefits such as water runoff control and noise reduction, it is more expensive than a white roof, according to the study.

During the next phase of the study, researchers will measure the quantity and quality of the water runoff from the green roof and compare it to the control roofs. Excess storm water runoff in urban areas leads to combined-sewage-overflows that pollute surrounding waterways, according to researchers.

Similarly, the University of Oklahoma National Weather Center (NWC) plans to evaluate its recently installed Experimental Green Roof as potential contributors to green urban development.

The green roof, located on NWC’s sixth-floor outdoor classroom, comprises 1,280 square feet and consists of 160 planted green roof trays. NWC says vegetative or green roof systems cool structures during the summer months, and reduce annual storm-water runoff as well as pollutants in the storm-water effluent.

The state’s first experimental university vegetative roof system will be evaluated for energy and water efficiency and water quality. As part of the primary evaluation, researchers will study plant performance, changes in the radiation balance, cooling efficiency for various climate conditions and impacts on building day lighting.

A second phase of the project is scheduled to begin later this year and will add 220 square feet to the existing green roof. The roof will remain at NWC for up to three years for investigation.

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