Wednesday, July 29, 2009

Cooling the Planet with White Roofs


Some energy solutions are complicated. Others are amazingly simple. Among the simplest is a trend that has developed in California to use heat reflective properties of white surfaces to save energy. Homeowners and businesses are installing roof coverings made of a shiny plasticized material that can reduce air-conditioning costs by 20 percent or more during sunny weather, as reported by Felecity Barringer in a New York Times article, White Roofs Catch On as Energy Cost Cutters.

As shown in the photo (by J. Emilio Flores), a Chino, CA discount store relies on a combination of solar panels and white roof covering to minimize energy requirements.

This approach is validated by historical precedents dating back centuries.

The physics behind cool roofs is simple. Solar energy delivers both light and heat, and the heat from sunlight is readily absorbed by dark colors. (An asphalt roof in New York can rise to 180 degrees on a hot summer day.) Lighter colors, however, reflect back a sizable fraction of the radiation, helping to keep a building — and, more broadly, the city and Earth — cooler. They also re-emit some of the heat they absorb.

Unlike high-technology solutions to reducing energy use, like light-emitting diodes in lamp fixtures, white roofs have a long and humble history. Houses in hot climates have been whitewashed for centuries.

It's going to take a multitude of techniques, as well as substantial lifestyle changes, to cope with climate disruption threats, but something as simple as a white roof isn't a bad place to get started.