From the day it opened, the waterfront headquarters of the Chesapeake Bay Foundation was expected to consume 51.2 percent less energy than a conventional office building the same size.

Now that the building has been in operation for nearly two years, it actually has exceeded those expectations - consuming 52.5 percent less energy than a conventional building, according to monitoring by the National Renewable Energy Laboratory, part of the U.S. Department of Energy.

It's also showing ways to improve the next generation of "green buildings" - structures designed to be environmentally sound and ecologically sensitive.

"It's better than we expected," said Mary Tod Winchester, vice president of administration and operations for the Chesapeake Bay Foundation.

"We're very happy" with the results, said Greg Mella, project architect for the lead design firm, the SmithGroup.

In the world of green architecture, where expectations are so high to begin with, "it's really wonderful" to meet or exceed them, Mella said. "Typically, buildings rarely perform as well as engineering design assumptions. This proves you can design a green building, and it will operate as expected."

The three-story, $7.2 million structure, known as the Philip Merrill Environmental Center, opened in late November 2000 as headquarters for the Chesapeake Bay Foundation, an environmental advocacy and education organization with about 100,000 members and a staff of 80.

Set on the shore of the Chesapeake Bay, in the Annapolis community of Bay Ridge, the 32,000-square-foot building was designed to accommodate employees consolidated from four locations and serve as a setting for environmental education and training of volunteers. Given the organization's mission of protecting the bay, directors wanted a structure that would set a high standard for eco-friendly design.

The SmithGroup, working with environmental consultant Janet Harrison of Annapolis, designed a building in which ecologically sound principles are integrated with other architectural features from the start, not added at the last minute. There's nothing so esoteric or unusual about the building that others couldn't incorporate its ideas into their offices as well.

The building rises from the foundation of the old Bay Ridge Inn. From a distance, it appears to be part farm building, part office. There is a sharp contrast between the land side, which is closed up with metal and masonry walls and accentuated by three large cisterns near the entrance, and the water side, which opens to the sun and the bay. The roof is sloped to catch rainwater, which is recycled for use by the building's occupants.

One wing juts out on the water side, containing a conference center that can be used when the rest of the building is closed. On the south side is a wall of glass, partly shielded by wooden beams and trusses that support the building, and sun-shades made from recycled pickle barrels. An upper level holds a row of photovoltaic panels that help generate part of the building's electricity, while decks and ramps offer sweeping views of the bay.

Inside, the high-ceilinged work spaces are filled with natural light. The staff opted to work in an open plan layout, rather than private offices, because it's more energy-efficient. The only concessions to private offices are separate rooms for the human resources and accounting departments, where employees needed extra privacy and security.

The technology is "state of the green," including lights that automatically turn on and off, triggered by heat and motion sensors, and signals that notify employees when outdoor temperature and humidity conditions permit opening the windows for natural ventilation.

Practically every material in the building was selected because it's environmentally correct, from the bamboo floor in the lobby, to the cork tiles finished with beeswax on other floor surfaces, to ceiling tiles made of recycled paper.

Designers used a variety of low-tech solutions as well. The flushless toilets, for example, are nothing more than an updated version of the old-style privy. Waste from the toilets drops down to a first-level compost heap, which is intended to produce a form of mulch to fertilize the grounds.

Dedicated Nov. 14, 2000, the Merrill Center has been called "the nation's greenest office building" after becoming the first to receive the highest rating for Leadership in Environmental Engineering and Design (LEED) from the U.S. Green Building Council in 2000. It was named one of the Top Ten Green Projects for 2001 by the American Institute of Architects, and a 2001 winner of the BusinessWeek/Architectural Record Awards honoring projects demonstrating that "good design is good business."

The National Renewable Energy Laboratory began monitoring the building in early 2001. The 52.5 percent figure covers the period from May 2001 to May 2002.

Mella and Winchester said the foundation originally expected to be able to rely on natural ventilation 9 percent to 10 percent of the time, but it has been able to rely on it more than 33 percent of the time. In addition, they said, planners expected that the staff would use 1,200 gallons of water a day but, largely because of the flushless toilets, it has used just 90 gallons a day - and 60 gallons of that is stored rainwater. Also, the solar heating system has been so effective that the building has never run out of hot water, even in winter.

Asked if the foundation would have done anything differently, Winchester said the directors have concluded that building engineers may have been overly cautious when designing mechanical systems, and that certain pumps, ducts and other elements didn't need to be as large as they are, based on the amount of energy consumed so far.

Had the foundation known that before construction began, she said, it might have been able to make a smaller initial investment for heating, ventilation and air conditioning. But now that the systems are in place, she said, it's not a problem.

"When you're a pioneer, you don't know," Winchester said. "You do what you think is going to work. We had some of the best minds in the industry working on this."

The findings about energy consumption indicate that the same building could be constructed for less today, using what operators know now, and that bodes well for future projects, said Harrison, the environmental consultant.

"There's a certain skepticism that many people have about green buildings," she said. "If they perform better than expected, in the future, engineers won't feel they have to be so cautious about the mechanical systems. They won't install so many redundant backup systems. This is where you're going to get real savings."

The SmithGroup and Harrison are at work on a second green building in Maryland, a 58,000-square-foot academic building for St. Mary's College. When a team collaborates more than once, members can build on what they learned from previous projects, Harrison said.

Meanwhile, the Chesapeake Bay Foundation will continue to seek ways to make the building operate more efficiently. "We envision this building as a laboratory, constantly testing out new technology," Mella said.

While it works to get even greener, the foundation doesn't want to act alone.

"We're setting an example," Winchester said. "We'd like to think that what we have done, in five years, will become the norm. The whole idea is to get people to do what we're doing, because that is what is going to make the difference."