At Dallas/Fort Worth Airport, the lights are controlled by sensors that measure sunlight. They dim immediately when it's sunny and brighten when a passing cloud blocks the sun.
At a new middle school in Washington, D.C., the air conditioner shuts off when a window is open.
A wall of windows at a University of Pennsylvania engineering building has built-in blinds adjusted by a computer program that tracks the sun's path.
Buildings are getting smarter -- and the next generation of building materials is expected to do even more.
Windows could trap the sun's energy to heat hot water. Sensors that measure the carbon dioxide exhaled by people in a room could determine whether the air conditioning needs to be turned up.
"More potential products have been invented in the last 15 years than in the entire prior history of architecture," says Philadelphia architect Stephen Kieran. "We're only beginning to tap the potential of those materials."
The new materials and technology are being used in a wave of buildings designed to save as much energy as possible. They range from old ideas, like "green roofs," where a layer of plants on a roof helps the building retain heat in winter and stay cool in summer, and new ideas, like special coating for windows that lets light in but keeps heat out.
Most commercial buildings in the United States still lack the most rudimentary technology, such as timers for lights, but the idea of buildings that use technology to save energy got a boost from the 2000 energy crisis, when California experienced blackouts and electricity prices rose.
That year, the U.S. Green Building Council launched a program to accredit building professionals in environmental design. Interest in the program, called LEED, for Leadership in Energy and Environmental Design, has skyrocketed. Since 2000, about 19,000 people have been accredited, 9,000 in the last month alone.
About 4 percent of new commercial construction is now completed under LEED guidelines, said Taryn Holowka, a spokeswoman for the Green Building Council.
Still, relatively cheap energy costs in the United States mean most building owners remain unconcerned with efficiency, said Srinivas Katipamula, a research engineer at Pacific Northwest National Laboratory. Of the roughly 4.7 million commercial buildings in the United States, only 10 percent have energy management systems or time clocks that turn lights on or off based on the time of day, he said.
Carlton Brown, chief operating officer of building developer Full Spectrum, is finishing a smart, green 128-unit condo project in New York City's Harlem neighborhood that took more than five years to get off the ground.
"We were talking about a green building and a smart building and people were not really interested," he said. Full Spectrum is finishing the project, which includes wireless broadband in every unit and washing machines that can be reserved via Internet.
Interest in smart, energy-efficient buildings is growing, especially among those who manage large facilities, such as airports, and buildings that traditionally use lots of energy, such as laboratories.
That's because "the operating costs of a building in its lifetime can be hundreds of times more expensive than the building was in the first place," said Doug Lockhart, who until recently worked as energy manager for Lawrence Berkeley National Laboratory.
A new building at the Natural Energy Laboratory of Hawaii will be a "net zero energy building," using no energy from the electric grid. The building will be cooled with piped-in 43 degrees Fahrenheit sea water and the condensation on the pipes will be used for irrigation.
New systems use energy when it's cheapest.
The Dallas/Fort Worth Airport installed a 6 million gallon thermal storage tank that lets the airport chill air conditioner coolant in the middle of the night, when energy is cheapest, for use during the day, when energy is more expensive. This has cut cooling costs by 91 percent during periods of peak electrical demand.
"This saves real money while we use less resources and pollute less," said Jim Crites, executive vice president of operations at the airport.
Gray water systems, which recycle water from sinks and showers, were once largely the province of hippies.
But President Bush's ranch in Crawford, Texas, has such systems, as will The Bank of America Tower at One Bryant Park in New York, a 54-story building being developed by the Durst Organization.