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A meeting of the minds when NYC °CoolRoofs visits PPPL

The cool roof at PPPL was downright chilly when two representatives from New York City Mayor Michael Bloomberg’s NYC °CoolRoofs program came to visit the Laboratory recently. But the meeting itself was warm and could lead to a partnership between the city group, PPPL and Princeton.

Geraldine Sweeney and Wendy Dessy, who are both involved with the NYC °CoolRoofs program, got a frosty firsthand view during the Jan. 18 meeting of the rooftop of PPPL’s Lyman Spitzer building, which is divided into a section covered by a cool white membrane a black membrane. They also were able to view one of the five weather stations that will measure how the different roofs save energy in varying temperatures and weather conditions.

Dessy said she read about PPPL’s cool roofs program on the Web and already knew something about PPPL because her son, Jay, who was also at the meeting, is a freshman at Princeton. “I was excited to learn about Princeton’s research efforts surrounding cool roofs and to have the opportunity of further brainstorming how we could benefit from each other’s work,” said Dessy.

NYC °CoolRoofs has an army of volunteers who coat dark rooftops with reflective white paint to help them reduce energy, cooling costs and carbon emissions. The program supports New York City’s goal of reducing greenhouse gas emissions 30 percent by 2030.

Program has coated 3.6 million square feet of rooftops 

 More than 4,000 volunteers have coated 3.6 million square feet of rooftops on 415 buildings in the organization’s first three years.  The group targets areas that have been identified as “hot spots,” where the urban heat island effect is the worst. They have strict criteria for what types of buildings they can coat and they only work with buildings owned by non-profit organizations in areas that are easily accessible to volunteers. NYC °CoolRoofs also encourages building owners to cool their own roofs, and provides a “Cool It Yourself” toolkit on their website.

 Geraldine Sweeney, chief strategy advisor in the Mayor’s Office of Operations, said converting black roofs to white cool roofs is important because it combats the urban heat island effect, which causes New York City to be five to seven degrees warmer than surrounding areas because of the vast number of roads and buildings made of asphalt and concrete that absorb heat.  “Our goal is to coat 1 million-square-feet of rooftop per year,” Sweeney told the group at the meeting. “The program provides benefits and savings to the building owner and has proved to be an effective way to help combat the urban heat island effect.”

 Sweeney helped start the CoolRoofs program, which was launched in September 2009 in Long Island City at a press conference with Mayor Bloomberg and former Vice President Al Gore. Dessy, the partnership manager for NYC Service, an organization that connects volunteers with service projects like Cool Roofs, works closely with the project to raise funds from companies and coordinate volunteers. The program is a collaboration between NYC Service and the Department of Buildings.

Sharing research results

PPPL Deputy Director for Operations Adam Cohen, who gave Sweeney and Dessy a tour of PPPL’s laboratory and fusion activities, described the meeting as “very positive.” “It was great that they made the trek out here,” he said. “We showed them our cool roof activities and results and gave them some ideas that could be applied to their program.”

The pilot program for NYC °CoolRoofs was monitored by Columbia University’s Center for Climate Research, which collected data on three white “cool roofs,” including one on the Museum of Modern Art Queens in Long Island City, and found there was a 42 degree Fahrenheit difference between white and black roofs during the day in the summer.

 NYC °CoolRoofs was one of the first large-scale cool roof programs in the country and is possibly one of the largest in the world, Sweeney said. As a pioneer of the cool roofs concept, New York City is a charter member of the 100 Cool Cities an initiative of the Global Cool Cities Alliance, which aims to install cool roofs and pavements in the 100 largest cities in the world from Mumbai to Chicago, to combat climate change.

 The CoolRoofs program is interested in researching the effects of its program on a larger scale, Sweeney said. “The data collected shows a dramatic decrease in temperature from a black rooftop to a white rooftop, and we’re studying the associated environmental benefits. By continuing to expand this program out on a citywide scale could have a tremendous impact on the environment in the years to come.”

Interest in a model to predict the energy efficiency of roofs

Sweeney and Dessy are particularly interested in the model being developed by Elie Bou-Zeid, a professor of civil and environmental engineering at Princeton University. Bou-Zeid, the lead researcher on the project at Princeton, is designing a way to predict the most energy-efficient roof for our regional climate and others. The model uses precise information from the PPPL sensors and weather stations and data on PPPL’s energy consumption for heating and air conditioning from its automatic building systems.

NYC °CoolRoofs has a strong interest in further quantifying the benefits of cool roofs, Bou-Zeid said. “They’ve been going out and painting these roofs white. What they’re interested in at this point is whether our measurements and models can help them confirm and quantify the impacts of their program,” Bou-Zeid explained. “They’re interested in what kinds of roofs would give them the most benefits if they paint them white.”

Bou-Zeid said he would share his exact findings with the NYC °CoolRoofs team once he has completed the project over the next couple of months. But the data already show that there is a dramatic temperature difference between white roofs and black roofs in the summer. When temperatures were in the 90s during the third week of August last summer, for example, the temperature on the cool roof was between 90 to 100 degrees Fahrenheit, while the temperature on the black roof was 130 to 170 degrees. This temperature decrease could reduce the need for air conditioners, lower electric bills and reduce energy consumption and greenhouse gas emissions. However, Bou-Zeid’s research also shows that there is much less difference in energy consumption between white and black roofs when a roof is well insulated.

Applying research to New York City

CoolRoofs would like to see how the research at PPPL could apply to buildings in New York. “One of the things we could look at is how well a roof is insulated and how do you apply that to a large-scale environment like New York City,” Sweeney said.

 NYC °CoolRoofs has been collecting information from building owners on energy bills before and after their roofs were converted to cool roofs. Keith Rule, a senior project engineer at PPPL, and Bou-Zeid may help them analyze that information by supporting a research project by a summer intern.

 “I personally think all of this contributes to the validity and importance of the program and as your team pointed out, there are different benefits to different environments doing this,” Dessy said.

The researchers at PPPL and Princeton also pointed out at the meeting that the type of air conditioner a building uses could theoretically be another factor in determining how effective the cool roofs are.  A rooftop air conditioner on a cool roof could potentially save more energy than a window air conditioner because the cool roof would not only cool the surrounding roof, it may also cool the air being taken in by the air conditioner and circulated in the building.  Rule and Bou-Zeid said they would be interested in doing the research to determine whether that theory is true.

Rule and Bou-Zeid also discussed the possibility of getting Google, which has previously provided funding to NYC° CoolRoofs, to use Google Earth to collaborate with the group on their research. Dessy has worked with Google in the past and they have shown an interest in aiding and helping to fund environmental issues. They are particularly interested in analyzing the effectiveness of cool roofs by finding out what percentage of roofs in the city are white versus black and what percentages of these areas are asphalt and concrete.  The research could also perhaps include finding out what percentage of buildings have rooftop air conditioners.

Rule said PPPL is happy to play a role in supporting NYC° CoolRoofs.  “This is part of our mission to do science education and outreach,” said Rule “so when we have tangible information that could be shared and when you can continue collaborating with Princeton University professors, we all benefit.”

For more information on the NYC Cool Roofs project, please visit: www.nyc.gov/coolroofs

U.S. Department of Energy
Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.

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