The Secretary for the Department of Energy, Steven Chu backed an idea to whitewash roofs and highways. It is claimed that whitening the world's roofs and roads would have the same effect on global warming as removing all the world's cars for 11 years.
CNN reported that a white roof has three benefits:
- It keeps buildings cooler, reducing the amount of energy required for air conditioning.
- It reduces the so-call "heat island" effect, the heating up of entire urban areas which then causes other buildings in the vicinity to heat up, whether they are in direct contact with the sun or not.
- A white roof or road will actually reflect the sun's rays back into space, keeping the atmosphere cooler.
The science is nicely summarized:
The science behind this is solution is also simple. When a person paints their roof white they are increasing reflectivity (albedo) of the light coming from the sun. Historically, builders have not considered albedo. Low albedo (dark) surfaces convert visible sunlight to vibrations of their molecules (heat). This is heat is then re-radiated upward as infrared waves, giving it a second chance at being absorbed as greenhouse gas. By painting your roof white your cause this process to be greatly reduced, which in turn reduces the heat and infrared
energy produced. This in turns keeps structures and areas cooler causing less energy to be expended in cooling. [A noted scientist in the field of renewables] believes that, "local/global warming is needlessly accentuated, at any level of greenhouse-gas concentration. Correcting this has immediate effect & climate benefit."
The Anaheim Hilton estimated that it saved $300,000 by installing a $150,000 tinted topcoat filled with tiny hollow glass balls that deflect heat, layered over a waterproof undercoat made of recycled rubber. The LA Times reported that the white coating deflects nearly 85% of the heat that hits it, reducing the surface temperature by as much as 50 degrees, reducing the energy needed to cool the hotel's interior, cutting air-conditioning costs and cutting carbon emissions.
The Energy Department said a white roof can knock 10% to 20% off a building's electric bill. To that end, it is encouraging anyone replacing or building a roof to take advantage of $2 billion in tax credits available under the stimulus plan.
But a white roof may not be best for all roofs in all locations. Others have noted that there may be a "winter penalty" when cool roofs are installed in northern climates. Manufacturers of traditional black roofs have stated that in cooler climates, the major goal of energy savings will be to reduce heating costs and that may best be achieved with a ballasted roof because the ballast retains the sun’s heat energy during colder months.
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