One System in Focus: Wood Chip Heating at U-32

This article was written by senior Charlie Haynes

 

Each week in the winter tractor trailer trucks arrive at U-32 High School in Montpelier, Vermont. The doors of the trailer swing open, revealing 30 tons of wood chips. The trailer floor is broken into 3 sections that work together, sliding back and forth to “walk” the chips out of the trailer and into a concrete and steel pit. The pit holds 70 tons of wood chips, and feeds the heating system. In the last three years, U-32 has burned on average 960.58 tons of wood chips each winter. 

 

 

A question arises with this system: How sustainable is wood chip heating for Vermont’s schools?  

 

Not everyone is convinced wood chips are the way to go. William Schlesinger is a biochemist, and member of the US Environmental Protection Agency Advisory Board. “When you cut down existing trees and burn them, you immediately put carbon dioxide in the air,” he said in an article in The Guardian. “None of the companies can guarantee they can regrow untouched forest to capture the same amount of carbon released.”  

 

Despite this, biomass heating still does work for climate change, says Andrea Colnes from the New England Forestry Foundation. “There is a strong alignment between doing really good forestry, and the need for markets for that low-quality wood, that can help pay for that forest management over time.” Colnes said in a Maine Public article. “So they really do fit together.”  

 

The sustainability depends on how easily they can be supplied, and the process for sourcing them.  

 

This past winter the school only burned 820 tons of wood chips, because there was a period of time when their usual supplier was unable to consistently supply wood chips, according to Chris O’Brien, Director of Facilities for the district.  

 

The school’s usual supplier is Limlaw Chipping & Land Clearing, Inc. The owner, Bruce Limlaw, said that he had not had significant issues with supplying wood chips this winter, and that U-32 school had switched to getting their wood chips from Cousineau Forest Products. In the interview, Limlaw did say that there had been troubles with “the green people, such as people who don’t want the trees cut.”

 

According to Jim Donelly of Cousineau Forest Products, the school’s current supplier,, the wood chips burned at U-32 are all sustainably harvested, as a byproduct from logging operations. He said once trees are harvested, they are sectioned into thirds. The bottom section is the saw log, long and straight enough to be used for lumber. The middle part is pulp wood, used for firewood, or making wood pallets. Lastly, the top third, which is considered biomass, is either turned into wood chips, or left to decay and return to the earth.  

 

Wood chip heating is still tied to oil in a couple ways.

 

Despite the wood chip boiler, U32 still burns approximately 15,000 gallons of heating oil yearly as well. This is backup heat, but also responsible for hot water production. Oil is also used to produce the wood chips, as all the logging equipment is petroleum powered.  

 

#2 Fuel Oil (typical heating oil) is currently $5.97 a gallon as of May 2022, compared to $2.64 in May 2021, according to the State of Vermont Public Service. According to Jim Donelly of Cousineau Forest Products, there has been little change in the price of lower grade wood chips so far. The high oil prices will raise wood chip prices, he said, but “luckily the price of chips will stay well below the cost of other fuels for heating by comparison.”  

 

The future of heating at U-32 is pretty certain right now, as the wood chip boiler at U-32 is just over 20 years old, but according to Matt Colburn of Messersmith (the company who made the system), it isn’t even half way through its life. The boilers they make are highly serviceable, and “as long as the systems are cared for and maintained they will last over 50 years.”  

 

 

Inside the pit a small auger slides from the front to the back wall, and pulls the wood chips onto a small conveyor belt to the hopper, a box roughly 2’ by 2’ by 3’ with two sensors on opposite sides. Once the chips pile up and block the sensor’s line of view, it stops calling for chips.  At full operating speed, this occurs every few minutes.  

 

From this hopper, two very small augurs pull the wood chips into the firebox, where they are burned and turned into heat to keep the school 200,000 sq feet warm all winter long.  

 

Once all those wood chips are burned, Bob Weinstein, a member of the maintenance staff, puts on a full fire retardant suit daily to clean what is left out. With his metal shovel, he shovels the ash out and into metal trash cans.  A few times a winter the system is completely shut down for cleaning. After these complete shut downs Weinstein shovels wood chips into the boiler, and lights them by hand to start the boiler once again.  

 

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