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Solution of the Month:

Seeing Forest and Trees

A biomass heating facility makes use of wood chips while blending into the landscape.

By David Sokol
January 2013
Photo © David Sundberg/Esto

Move over, mulch, wood chips are gaining ground as a renewable fuel source. According to the U.S. Department of Energy’s Energy Efficiency and Renewable Energy division, today biomass surpasses hydropower to represent more than half of all renewable energy used in America. Wood chips—usually waste from the manufacturing of paper, lumber, and other products—are the most popular form of biomass.

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Whereas money-conscious consumers may choose wood chips for proximity and local abundance, sustainability advocates are embracing them to divert landfill and lower emissions. Burning the material produces less sulfur dioxide than other fuels, for instance. Moreover, the practice is considered carbon-neutral, because it releases only the carbon sequestered during tree growth—not to mention that sustainably managed sources of wood chips replant trees in order to capture that carbon yet again.

One wood-chip champion is The Hotchkiss School located in Lakeville, Connecticut. The independent boarding school for approximately 600 high schoolers from the U.S. and abroad carries out extensive green programs that range from removal of invasive plant species to employing regenerative agricultural techniques on the academic farm. “Our environmental initiatives are aimed at encouraging students to focus on a solution-oriented, regenerative approach to the complex ecological issues of our time,” Joshua Hahn, assistant head of Hotchkiss and its director of environmental initiatives, says of the school’s overall approach to sustainability.

“Growing food, producing energy, building soil, sequestering carbon—these are all actions we as an institution can model so there is not a disconnect between the way we teach and the way we live on campus.”

As part of a pledge to be carbon neutral by 2020, Hotchkiss has purchased wind power to supply 34 percent of campus electrical demand. It also recently completed a biomass facility to replace a steam plant housing 18-year-old oil-fired boilers. The new building, designed by Centerbrook Architects and Planners, will be only the third power plant in the United States to earn LEED certification. It is currently targeting a Silver rating.

The 16,500-square-foot central heating facility sits on the edge of campus—on the far side of the golf course—so that deliveries of wood chips take place without disrupting pedestrian traffic. From this distance, students may not even recognize the campus addition. The Centerbrook design team gave the low-slung, engineered wood structure an undulating roof that Centerbrook partner Jefferson Riley calls both a showcase of Hotchkiss’ principles and a “sensitive but notable disappearing act as it merges into the landscape.” The serpentine top is planted with sedum, and whatever rainfall this extensive green roof does not capture is channeled into new bioswales that recharge existing wetlands.

In the spirit of a showcase and at the request of the client, Centerbrook designed educational experiences into the biomass central heating facility. The building’s own laminated-wood structure and its two Messersmith biomass boilers stand in plain sight, which students and other visitors will see from a mezzanine hugging the perimeter of the interior. This area will also include interpretive exhibits, wall-mounted charts and maps, and a series of interactive consoles tracking the boilers’ activity.

Their performance should be impressive. Because the Messersmith biomass boilers create steam heat at a low pressure, they enjoy a burn efficiency rate of as much as 82 percent. Trucks will dump 5,400 tons of wood chips annually in one of four delivery bays; Hotchkiss officials are calculating two deliveries per day in winter, and complete inactivity in summer.

Even when students are not witnessing the biomass facility in action, they will be interacting with it. During peak operation in wintertime, the heating facility should produce two barrels of ash each week. The ash will then relay to the Hotchkiss farm, where it will be used as fertilizer. Partnering the heating plant and local farm reinforces the interconnectedness concept of ecological thinking that is being taught to students.

Thanks to an electrostatic precipitator, which Messersmith sourced from the German company Weis Environmental, most particulate matter will be removed from the boiler exhaust gas (flue gas) in the form of ash. Only particulates measuring less than 0.03 microns in diameter will be disbursed to prevailing winds via the facility’s 48-foot-tall chimney.

Locally sourced wood chips from sustainably managed forests will replace approximately 150,000 gallons of fuel oil per year. In addition to particulate control, the new steam supply will cut sulfur dioxide emissions by more than 90 percent and reduce carbon footprint by as much as 45 percent over the old way of doing things. Expenses come down, too. Assuming $2.50 per gallon of heating oil, biomass will save the school a minimum of $522,000 annually, a 62 percent reduction.

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