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Heat Island Effect

Conference Call/Webcast Presentations, January 2005

Heat Island Reduction Initiative (HIRI) Graphic Depicting Heat Island Curve and HIRI Logo




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Urban Form and Climate

Presentations by Gerald Mills - University College Dublin

Gerald Mills, a Professor of Geography at University College Dublin, joined the call for a presentation on the relationship between urban form, function, and climate. He began by noting that urban areas create distinctive climates due to factors including: (1) Physical form and composition, (2) Urban activities that alter the atmospheric composition by emitting waste heat and materials. Dr. Mills then said that these aspects of cities can be modified with adequate consideration of technology innovation, design change, and behavior modification. As a result, there is great demand for stronger linkages between urban climatologists, planners, and designers.

Dr. Mills also pointed out the relationship between the magnitude of an urban heat island and the physical structure of the settlement, which is largely determined by city-scale transportation planning. A policy prescription following from this observation is that "sustainable" cities can be achieved through mixed, high-density land-use that reduces travel demand.

Dr. Mills presented results suggesting a clear relationship between population density and automobile fuel consumption. He also showed data indicating that smaller settlements consume less energy and generate less waste.

Dr. Mills noted that a potential problem with implementing the "sustainable" strategy of increasing urban density to decrease energy use and accrue additional environmental benefits is that as buildings of similar height move closer to each other, air flow between and around buildings is reduced. Thus, air mixes much less between buildings - such as in street canyons between tall buildings - and instead air passes over the tops of the buildings. This phenomenon, ironically, means that although there may be fewer emissions due to less vehicle traffic, the emission concentrations between buildings may be higher, due to the lack of air flow and mixing. Thus, compact, high density urban developments must consciously incorporate surface roughness - diverse building heights and potentially orientations - into their design. This will increase air flow between buildings resulting in better street level air quality compared to developments that have buildings of the same height and orientation that are built closely together.

To conclude his presentation, Dr. Mills described the key take-aways from his research. One is that establishing relationships between measures of urban form and activity is necessary to link urban planning decisions to urban climate effects. Another is that this scenario illustrates the potential pitfalls of implementing measures based on a single perspective. In particular, it illustrates the importance of good design at the building group scale to ensure that decisions at the settlement scale do not have unintended micro-scale consequences.

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NY's Surface Heat Island

Presentation by Dr. Bill Solecki and Jennifer Cox, PhD Candidate - Hunter College

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Chicago's Energy Conservation Code

Presentation by Brendan Daley, Legislative Liaison, Chicago Department of Environment

Brendan Daley of Chicago's Department of Environment (DoE) joined the call to provide an update on Chicago's Energy Conservation Code, specifically the inclusion of cool roofs. This provision addresses the city's explicit goal of reducing the urban heat island effect through the mandatory use of cool roofs on new and renovated buildings roofs. Mr. Daley said the measure is consistent with Chicago's goal of becoming one of the greenest cities in the country.

The presentation focused on general background with respect to code implementation and on current code requirements.

Mr. Daley began his presentation with the history of the city's building code. He discussed how the department collaborated with the city's building team to draft an energy efficiency code based on the International Energy Efficiency Code, presenting it to the City Council in September 2002. The final code was passed by City Council in 2003 (with the exception of reflectivity requirements for medium sloped roofs, which were added in 2004).

Mr. Daley then raised some general concerns that arose during debate about standard setting of the cool roof portion of the code. One was the availability of colored asphalt shingles, which make up approximately 85% of the city's roof stock. Another concern raised by unions and asphalt shingle manufacturers was that the code would adversely affect their market share. They disputed research about the benefits of the code, especially the building-level savings being attributed to the modification.

After working through these issues, the code was eventually adopted with the following requirements for low sloped roofs (defined as those with a slope between 0" rise over 12" run and 2" rise over 12"):

  • 0.25 reflectivity on roofs installed prior to and including 12/31/08
  • ENERGY STAR reflectivity on roofs installed after 12/31/08

For medium sloped roofs (defined as those with a slope between 2" rise over 12" run and 5" rise over 12" run) the requirements are:

  • 0.15 reflectivity for roofs on buildings built after 1/1/05 (new construction)
  • Multiple sloped roofs are subject to this requirement if the majority of the roof is medium sloped

Mr. Daley also noted that the code requires that reflectivity be verified. The Department of Construction and Permits issues the applicable permits and requires the architect of record to certify that the roofing materials for each project meet these requirements. As a technical resource, DoE maintains a Web site with a list of asphalt shingles that meet the 0.15 reflectivity specification.

The methods used to evaluate code compliance – as described in the amendment – are American Society of Testing and Materials (ASTM) E903, ASTM E 1918, or, alternatively, testing with a portable reflectometer at near ambient conditions.

Mr. Daley said that in addition to cool roofs, the code offers exemptions to accommodate green roofs and solar panels. The code language says, "The portion of the roof that is covered by a... rooftop garden, or a green roof, is exempted from the requirements of this section," and that, "An area including and adjacent to rooftop photovoltaic and solar thermal equipment, totaling not more than three times the area that is covered with such equipment, may be exempted from the requirements of this section."

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Call Participants:

Hashem Akbari, LBNL

Jennifer Atwood, TreeUtah

Drew Ballensky, Duro-last Roofing

Ryan Bell, ICLEI

David Brosch, Baltimore WAP

Nancy Bragado, San Diego

Pamela Berger, City of Houston

Marion Clark, MD National Capital Park
and Planning Commission

David Cole, EPA OAQPS

Jennifer Cox, Regional Plan Association -NYC

Brendan Daley, Chicago

Leila A. DeMaree, City of Gilbert

Kathy Diehl, EPA R9

Pat Duff, Arbortender

Maury Estes, NASA

Kevin Foley, Sarnafil

Mike Gonzales, San Diego

Rosalie Green, EPA

Griggs, Atlanta

John Hadalski, Philadelphia

Gretchen Hardison, LA

Gordon Heisler, USDA FS

David Hitchcock, HARC
Stephen Keach, PQA

Gordon Kenna, City of Atlanta

Mardi Klevs, EPA R5

Eugenia Kalnay, U of MD

Michelle Knapik, City of Philadelphia

Carole J. Lenz, Houston

Ed Linky, EPA R2

Megan Lewis, APA

Fredda Lippes, City of Philadelphia

Jeff Luvall, NASA

Gary NcNeil, EPA

Michael Menelli, EPA

Darlene Messina, City of Philadelphia

Gerald Mills, Univ. of Dublin

Linda Pratt, City of San Diego

Pepper Provenzano, TreeLink

Dale Quattrochi, NASA

Liz Robinson, Energy Coordinating Agency

Jim Scapellato, ACPA

Bill Solecki, Hunter College

John Sullivan, PCA

Harold Taft, AL Forestry Commission

Eva Wong, EPA

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