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Of biomass and green roofs: US school slashes winter energy bill


May 1, 2013

The Hotchkiss School's new biomass building (Photo: Centerbrook)

The Hotchkiss School's new biomass building (Photo: Centerbrook)

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A US school has cut a six-figure sum from its winter energy bill by replacing its oil-burning boiler with woodchip biomass ones. The switch has reduced the school's carbon footprint by between 35 and 45 percent. The boilers are housed in a brand new green-roofed building which has become only the third LEED-certified power facility in the US.

Unlike the oil-fired boiler they have replaced, the biomass burners combust locally-sourced woodchip, which, though not a wholly clean source of energy, is cleaner than using oil. An electrostatic precipitator removes 95 percent of particulates from emissions before entering the atmosphere.

Because the woodchip comes from FSC-certified forests, it's effectively a renewable source of energy as the forests are managed to maintain their stock. The International Panel on Climate Change goes so far as to argue that appropriately sourced woodchip is a carbon neutral fuel for this very reason. The carbon lost to the atmosphere when the woodchip is burned is gradually put back as replacement trees grow.

There are green roofs and there are green roofs. The former, best written in the sort of quotation marks that express dubiousness, are often little more than a thin shrubbery planted apologetically in the corner of a roof terrace. The latter are almost lush undulating meadows in comparison, and create the impression that the building has been slipped into the landscape like a letter into an envelope – when viewed from a favorable angle at least. It's firmly in this category that the new biomass building at the Hotchkiss School in Connecticut belongs.

The The 48-foot chimney stands out from all angles, mind (Photo: Centerbrook)

As one should expect from a green roof, this one serves more than aesthetic purposes. Bioswales, specially designed sloping channels, combine with rain gardens to slow and filter rainwater before it enters the ground.

Expected to be awarded a Silver certificate, the building is only the third power facility to achieve a LEED rating in the US. Though not the most exacting building standard, LEED nevertheless nudges buildings in environmentally-friendly directions. Here, water-saving faucets, local and recycled building materials and energy-efficient lighting and ventilation all feature in the design by the building's architect, Centerbrook.

The Hotchkiss School reports that between mid-October and the end of December, nearly half of the system's winter operating period, the school slashed more than US$350,000 from its energy bill.

Sources: Centerbrook, the Hotchkiss School, via Arch Daily

About the Author
James Holloway James lives in East London where he punctuates endless tea drinking with freelance writing and meteorological angst. Unlocking Every Extend Extra Extreme’s “Master of Extreme” achievement was the fourth proudest moment of his life. All articles by James Holloway

I keep wondering why public facilities don't make use of green technologies more frequently

Racqia Dvorak

More good would have been done by replacing the boilers with water cooled diesel engines driving electrical generators.


Hmm, sounds great, but what is the extra cost to build the school versus traditional building methods? What subsidies are they receiving?

Usually projects like this have horrible payback periods and that's why public and private facilities don't use "green" technologies.

Jason Holman

Racqia, because of people like Slowburn

Bill Bennett

You could use Stirling cycle powered generators and still dump the heat into the boilers.


I would guess the payback period is fairly short if they're recovering 350 grand in half a heating season in New England! I don't know what the additional upkeep costs are on a green roof in a temperate climate with a deep winter. These things are catching on faster in tropical and sub-tropical climates where they reduce air conditioning costs significantly and there is no frost to worry about.


A local workable solution, without the nearby mill to provide the wood chips then what. would other schools cut down trees just to make chips? But if this burns truly waste product, bark then OK. Otherwise even sawdust is used to make products like MDF. My concern is people get the impression this could be done for all schools. Same as showing an article about the College of Southern Idaho and how most of heating is from geothermal. It only works because the college sits over an area with high geothermal activity.

Tom Swift

I think it would probably be greener for the wood chips to be spread on the ground to provide the nutrients for the next generation of trees.

re; Tom Swift

There are some trees that their only commercial value is in their fuel value.


Dvorak, what you mean is that you wonder why you don't hear about it more often. Around the country, many facilities are slowly "greening their footprint" but it's a slow process with a lot of upfront investment, so usually only something that happens in new developments by someone with the money to put down and the intention of staying long enough to see the payoff. Often tearing down an old building is less green (and more costly) than reusing it, despite it's limitations, so developers and designers also often think about that and work to slowly convert buildings rather than leveling an area and redoing it. Finally, with slow growth, people are hesitant to invest, so even if a higher portion of the new buildings going up are "green", the total number of new buildings has slowed, and several large investments have gone under.


where's the passive solar that goes with it?


350k saved, to heat a building that size. damn somethings not right with this picture.


re; frogola

That building is just the shack holding the boilers. The hot water/steam is used elsewhere.

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