Green Roof Advantage
 

Source: Energy Emissivity Analysis of GSU Rooftops, 1998

During the 8-week GSU project, in situ measurements of the surface temperature of twenty building rooftops were taken with an infrared thermometer in June and compared with the remotely sensed data set of May 1997. Four basic roof systems were studied, tar and gravel, asphalt and gravel, modified bitumen, and EPDM-B. The initial results of the study do not generally indicate significant differences between surface temperatures and the four roof systems. However, the black EPDM-B without a river rock covering was significantly hotter, approximately 25 degrees Fahrenheit, than the EPDM-B with river rock (8). Examples of the EPDM-B roof cover is provided in (figure 4).

The most interesting result was a strong correlation between older gravel surfaced coal tar pitch roofs and higher surface temperatures. The gravel-surfaced coal tar pitch roof is common in commercial areas throughout the United States. As the roof deteriorates through exposure to sunlight and weather, the flow of bitumen allows gravel to become more embedded, exposing the dark colored bitumen to greater solar loading (9) This causes the roof surface to become hotter as shown in (figure 5).

Source: Energy Emissivity Analysis of GSU Rooftops, 1998

It has been suggested that the study could be expanded to include white thermal plastics, white-coated membranes, and metal roofs to provide a more comprehensive analysis of the majority of roofing types present within the Atlanta metropolitan area. More study on the role of insulation and roof surface temperatures is also desirable to correctly interpret results.

A CD-ROM with all flight lines georeferenced in a variety of image file formats has been developed. The georeferenced datasets on CD-ROM has been provided to the Atlanta Regional Commission (ARC) and Georgia Tech Geographic Information System laboratory. Thermal color wall size work maps of three flight lines over the heart of the Atlanta Central Business District and surrounding area have been developed to identify "hot spots" and other areas for further study. The maps are approximately 2.5 feet in width and 5 feet in length.

As we have worked in Atlanta, it has become apparent that a local presence would significantly facilitate ongoing efforts to share data with planners, decision-makers, and others. Also, to enable these end users to effectively utilize research results in new policies or the daily conduct of business.

Conclusions and Future Plans

• A significant number of key stakeholders are interested in the urban heat island research project and in finding ways to mitigate the heat island and improve the quality of the Metropolitan Atlanta environment.
• Establishing a local presence is essential to maintaining the interest of key stakeholders and in the ultimate use of project results for the benefit of the community.
• Leveraging resources to engage more students and faculty in the project is needed to address a reasonable portion of the applied research needs identified.
• Effective data transfer to high end users such as the ARC and Georgia Tech GIS unit remains a challenge, particularly in providing data in a "standard" format that can be ingested by different computer hardware and software.

Planned Activities for 1999.

• Check and refine georeferencing of all flight lines.
• Provide wall size thermal color work maps of additional flight lines as needed.
• Determine an appropriate classification scheme and produce a preliminary land cover classification for the study area.
• Engage faculty and students in the project for research support as possible by externally funded research and education programs.
• Begin to perform analyses of thermal responses by land cover types.
• Keep the application working group updated and assist them with keeping key stakeholders engaged in developing and implementing urban heat island reduction plans.
• Write collaborative proposals to pursue applied research objectives.
• Publication of the results from Project ATLANTA in the open refereed literature.

Salt Lake City Cool Communities Program

Population, urban expansion and commercial development are on the rise in metropolitan Salt Lake City. In the last six years alone, Utah has experienced an unprecedented economic boom, attracting large numbers of residents from other states. Current Salt Lake metropolitan projections show a sixty-five percent surge in population, up to 1.3 million residents along the Wasatch Front by 2020. This, coupled with a consistently growing residential population, has resulted in tremendous urban expansion and development.

As a result of Salt Lake City’s unique geographical conditions, with the Wasatch Mountains bordering the east and the Oquirrh Mountains and Great Salt Lake bordering the west, the Wasatch Front area experiences unique air quality conditions that result in high levels of ground level ozone in the summer, precipitated by criteria pollutants such as NOx and VOC’s, and an unsightly and hazardous inversion in the winter. In fact, the new EPA standard for ground layer ozone which measures ozone over an eight-hour period and considers the air dangerously polluted when ozone concentration exceed .08 parts per million, was exceeded 68 times on 21 days across the state last summer. (10)

Emerging development and urban growth currently underway in Salt Lake City cause energy, air quality and environmental problems that could adversely affect the people and children that live and work in this uniquely situated city. Planners, developers, community leaders and the public at large in the Salt Lake City area need reliable and practical information and support to implement strategies in their neighborhoods that reduce energy consumption, improve air and water quality, manage storm water runoff, provide habitat for urban wildlife and improve the overall comfort, livability and economic vitality of their urban neighborhoods.

Cool Communities is a collaborative federal and local program designed to implement practical strategies that reduce peak load electrical consumption, mitigate the development of urban heat islands and directly improve air quality. These strategies include 1) the use of "cool" roof and street surfaces that are light-colored and reflect incoming solar radiation as opposed to absorbing and emitting it back into the environment, thereby reducing surface and ambient air temperatures, and 2) the use of strategically planted, drought tolerant deciduous and coniferous trees, shrubs and ground covers that evaporate cool water vapor into the air while directly shading and protecting buildings, streets, and parking lots.

Salt Lake City became a Cool Communities pilot in November, 1995. Its primary local partners include the Utah Office of Energy Services and Tree Utah. The program is operated through a broad based steering committee with members from a variety of professional fields, including architecture, landscape architecture, private industry, government, non-profit and educational. Steering Committee members participate in four working committees. These are: Research and Technical Committee, Planning and Policy Committee, Implementation Committee, and the Outreach and Education Committee.

In terms of air quality improvements, Cool Communities’ strategies reduce electrical demand associated with air conditioning because the program seeks to mitigate urban heat islands, a prime source of heat in cities. Overall, these reductions result in less cooling energy demand by regional power plants, reducing the pollution associated with the burning of fossil fuel. Another main component of Cool Communities is the use of trees and vegetation in the urban environment. Urban trees directly sequester CO2, as well as PM(10) and other airborne particulate. Cool Communities goals also include strategies that reduce citizen dependency on the automobile. For example, narrow streets, tree-lined sidewalks, bicycle paths, and downtown public transportation provide citizens with pedestrian friendly and "green" urban surroundings. These activities directly reduce automobile emissions, which include NOx and CO2. With a de-emphasis on the automobile, less expansive, heat producing parking areas are needed, thereby reducing evaporative losses of VOC’s from vehicular gas tanks. Also, parking areas that include trees and light-colored surfaces produce cooler temperatures, resulting in reduced need for automobile air conditioning, another air quality concern.

In terms of energy consumption, there is potential for Cool Communities to significantly save energy. The combined use of strategically planted shade trees and other vegetation with the use of light-colored, highly reflective building and street surfaces have demonstrated impressive reductions in energy consumption. For example, computer simulations generated by Lawrence Berkeley National Laboratory, demonstrate that the effect of planting three trees around a typical house can save 18 - 44% of peak electrical power, and up to 53% of the total annual cooling electricity use. LBNL also estimates that a typical house with an albedo (reflectivity level) of 90% consumed 60% less energy, had a 35% lower peak electrical power demand, and experienced 44% fewer cooling hours. Furthermore, the U.S. Department of Energy predicts that if all the nation’s roads and buildings were changed from black to light-colored, reflective surfaces, approximately $4 billion a year could be saved annually in air conditioning bills and smog could be reduced by 10%.