Sep. 20--NEW HAVEN -- Looking a little like a 19th century Vermont barn, the newest building on the Yale University campus is attracting international attention because it's one of the most environmentally friendly buildings of its type in the world.

Kroon Hall, around the corner from the Peabody Museum, is the new home of the Yale School of Forestry and Environmental Studies.

It gets electricity from the sun. Geothermal energy provides heat and air conditioning. Rainwater from the roof and grounds is used to run the commodes. Solar panels heat the water. In the winter, heat exchangers pull heat energy from warm exhaust air to aid the heating system.

Experts say that it uses about half the electricity than what would be expected for a building its size, and the photovoltaic array on the roof supply one-fourth of the remaining electrical load.

The structure is heated and cooled entirely with geothermal energy -- there's no backup furnace or air conditioning system -- or even a water heater for that matter.

Kroon is designed so it won't require much heating and cooling in the first place. Its east-west orientation maximizes solar heating in the winter, and the 23-degree tilt of the exterior slats deflect the sun's rays when it's high in the sky in the summer months. The massive concrete superstructure -- there's no steel skeleton -- acts as a huge heat sink. This "thermal mass" absorbs heart during the summer months, which slowly radiates

back into the structure during the winter.

Built into a hillside, the first floor is partly underground, further reducing energy demand. Green lights throughout Kroon warn occupants that it's a "green day," meaning that the temperature outdoors is comfortable, the ventilation system has shut down to save energy, and people should open windows if they want fresh air.

"Everybody takes responsibility for their own environment," said David DeFusco, spokesman for the school.

The ventilation system, when it does operate, sends heated or cooled air through plenums under the floor, rather than ductwork in the ceiling. This air emerges through round vents in the floor than can be manually opened and closed.

"We're pushing the envelope on our mechanical system," said Davis Spaulding, a senior engineer with Yale's Office of Facilities. "We fully expect it will take a year to fine tune it. But other than that, it's been a terrific building."

He said that Kroon's soaring spaces are designed to work with the HVAC, or heating, ventilation and air conditioning, system, not against it. "We have what's called a displacement air system," he said.