The back wing of Plainfield Elementary School was built in 1989, too late to be influenced by the energy crisis of the 1970s.

Special education teacher Laura Spratt said that when the old ventilation system was turned on, teachers would have to raise their voices to be heard and papers would blow off students' desks.

But since a “deep energy retrofit” of the 9,000-square-foot wing, the heating has gone quiet.

“It's easier to teach kids if the environment isn't oppressive,” Spratt said at the end of a school day last week.

As important as a good environment for learning can be, saving money is also essential, especially as energy costs rise. The renovation, completed last summer, is expected to slash the cost of heating and lighting the school's wing by 90 percent, said Bill Knight, the school's facilities manager and a member of its facilities committee.

“My suspicion is that it's actually going to be better than that,” said Knight, a graduate of Cornell University's engineering school who has worked in construction since his college days.

According to research by the facilities committee, no school has done an energy retrofit as thorough as Plainfield's. The work of the committee, which started to improve the school's efficiency in 2003, has influenced Kimball Union Academy, which is using some of the same measures in a major renovation of Miller Bicentennial Hall.

At Plainfield Elementary, the renovation included exchanging all of the lighting, substituting brighter “daylight” bulbs that use 23 watts apiece for old bulbs that used 42 watts each. The classroom lights are fitted with occupancy sensors that turn the lights off when the rooms are empty. Although the wing was switched to an electric “air source heat pump” heating system, its electricity usage is down from 240,000 kilowatt hours to around 150,000 kilowatt hours, Knight said.

The air source heat pump is a technology widely used elsewhere in the world, but it's just catching on in the United States. A brief description of how it works doesn't seem to make much sense -- it draws warmth from the outside air and pumps it into the building. The heat pumps will almost completely replace the old system, which runs on heating oil. The school still has its furnace, but it shouldn't have to run more than a few days each winter. The system can also provide air conditioning in the summer.

In addition, hanging from the ceiling in each classroom is a long tube attached to a heat-recovery ventilator. When the ventilation kicks on to bring fresh air into the room, the cold outside air is warmed up by the outgoing air.

“We don't need to heat that air as much as we would otherwise,” Knight said. In addition, the ventilation system kicks on only when the amount of exhaled carbon dioxide reaches a certain level.

The efficient heaters are warming a much more heavily insulated building. New windows, walls that now carry 6½ inches of foam insulation, added insulation on the roof and the foundation and a tightly sealed building make the building much easier to heat.

“We've used about five bucks to heat this area up to Thanksgiving,” Knight said of the renovated wing. The savings were “incredible enough that we all had to have a conversation about whether it was right,” he added. As part of its energy efficiency drive, the school has added meters to measure energy use wherever possible.

The energy retrofit was part of an otherwise routine renovation project to replace the wing's deteriorating siding and windows, which “had completely failed,” Knight said. When the building was put up, there was almost no attention paid to energy efficiency. Voters tend to approve school construction projects solely on the bottom line, but schools can cost less in the long run when they spend more upfront on energy efficiency, Knight said.

The school district spent $330,000 on the renovation as a 10-year bond. The reduced energy consumption offsets about half the cost, Knight said.

And the school's work will continue; it has received a grant of nearly $275,000 from New Hampshire's Office of Energy and Planning to do the same type of renovation on the original 1973 school building.

The efficiency effort has been led by Plainfield residents and built by local contractors under Knight's supervision. Some of the people who have served on the Plainfield Facilities Committee also have an influence on Kimball Union Academy, notably Allan Ferguson, a retired executive who sits on the facilities committee as well as KUA's board.

As a result, the private college preparatory school in Meriden has been reducing energy consumption by 7 percent a year for the past three years, said James Gray, the school's chief operating officer and chief financial officer.

The renovation of Miller Hall, an under-used brick building constructed 60 years ago, uses many of the same principles put in place at Plainfield Elementary, including more efficient lighting, air source heat pumps, heavy insulation, tight sealing against air infiltration and a carbon-dioxide sensing ventilation system. While electricity usage will remain roughly the same -- in part because the building was lightly used before the renovation -- the school won't have to burn the 13,000 gallons of fuel oil needed to heat the building last winter.

“The only time the oil will come on is when we get to minus five to minus 10,” a couple of days a winter, he estimated. The school will also have an engineer verify that all of the new systems are working as they should.

The completed section of the renovation includes 14 new classrooms and offices for the English, history and world language departments.

The second phase of the renovation, planned for next summer, will include turning a dining hall into a library and building three more classrooms. A third phase would add a new learning center and additional classrooms.

The renovated building is a big step toward longer-term goals. KUA has committed itself to being carbon neutral in 20 years, Gray said. All future building upgrades are likely to go through an energy-efficiency process, as Miller Hall did, he added.

All the work the schools are doing today is meant to insulate them, no pun intended, against future oil price shocks.

“Oil will go back to $150 a barrel, and it may go to $300 for all I know,” Gray said. “If we don't do what we can today to minimize energy consumption, it's just going to eat our lunch later.”

Alex Hanson can be reached at ahanson@vnews.com or 603-727-3219.