Heat Island Group (Lawrence Berkeley National Laboratory)

The Heat Island Group is a research group within the Energy Technologies Area of Lawrence Berkeley National Laboratory (LBNL), a US Department of Energy national laboratory in Berkeley, California. It studies how surfaces such as roofs and pavements affect building energy use, urban temperatures and air quality, and it is one of the best-known sources of research on cool roofs.

Research topics

• Cool roofs: measuring how solar reflectance and thermal emittance affect roof temperatures and building energy use.
• Cool colours: pigments that reflect near-infrared sunlight while appearing dark, allowing cooler tile, shingle and metal products in traditional colours.
• Urban heat islands: modelling how citywide changes in surface reflectance affect air temperature.
• Cool pavements and other urban surfaces.
• Aging and soiling: how reflectance declines with dirt and weather, and how to measure aged values.

Findings often cited

The group's public materials report that, on a typical summer afternoon, a clean white roof reflecting 80 percent of sunlight stays about 31 °C (55 °F) cooler than a grey roof reflecting 20 percent, and that a black roof was measured about 30 °C (54 °F) warmer than a white one. Its research also concluded that winter heating penalties from cool roofs are usually small compared with summer cooling savings across most of the United States.

Widely cited studies by Hashem Akbari and colleagues, published in 2009 and 2012, estimated the global cooling effect of increasing roof and pavement reflectance, expressed as equivalent offsets of greenhouse gas emissions (24 gigatonnes for whitening urban flat roofs in warm climates in the 2009 study).

Influence

Its online resources explain cool roof science for homeowners, builders and policymakers.