September 8, 2014

Got Heat? Get Wood

At this time of year, the days begin to feel cooler even with the deceptive summer weather that seems to linger. Fall is just around the corner and that often brings up the thought of winter, which many people try to avoid thinking about. For me, fall makes me think about heating, specifically wood heat. Most people who heat with wood have already cut, stacked and stored it for the upcoming heating season prompting me to think we are not much different from the squirrels that gather nuts and seeds for their winter needs.

Last fall Squam Lakes Natural Science Center started planning for its future energy use that’s a bit different. We converted our heating units for four buildings from fossil fuel to wood. Why? There were many reasons that helped us to make this decision but two stood out. First the cost of natural gas and heating oil has fluctuated over the years making it difficult to project a budget for our yearly heating needs. The second reason was that we wanted to find a source of fuel that was “local” and renewable. These reasons led us to the solution to heat with wood, not a wood stove, not a wood furnace, but a dual stage wood gasification boiler. These units are sometimes confused with outdoor wood furnaces but there are significant differences between them.

One concern people have with a wood furnace is the smoke particulates released into the air that affect air quality in the area. This happens because the fire is regulated by a draft fan that controls the burn rate of the wood depending on the heat demand from the building, which causes the fire to vary between a full burn and smoldering. Outdoor wood furnaces operate at relatively low temperatures resulting in inefficient combustion causing energy to go up the chimney as smoke.

Dual stage wood gasification boilers are constructed and operate differently. There are two burn chambers. In the first chamber the fire burns at a relatively low temperature and low oxygen level. This forces organic gases from the wood into the secondary combustion chamber where super-heated oxygen-rich air is introduced. This allows burning of gasses at very high temperatures, resulting in low particulate emissions because of an almost complete combustion of fuel. During the first 20 minutes of operation of our dual stage wood gasification boilers the only visible emission is steam. After the units reach their optimum burn temperature the steam dissipates and there are no visible emissions.

The heat generated from our wood gasification units is transferred and stored in two water “jackets” that surround the boilers and hold 5400 gallons of water. These act like batteries, storing heat until it is needed by one of the five buildings. Then the heat is transferred across a heat exchanger to insulated pipes that run underground to deliver the heat to each building. Cooler water returns from the building through other insulated underground pipes where it is “recharged” by the boilers.

This process is exciting for us because the wood gasification units will replace five oil or propane furnaces and reduce our reliance on fossil fuels. Our wood travels a distance of less than ten miles from standing tree to log at the boiler. The ash produced during the gasification process will be used as an amendment for composting. We also expect to lower our heating fuel bill, but the amount saved will depend on how effectively we manage the heating process. Conservatively we expect to reduce heating costs by 50%. This process also provides us a direct link to our fuel, through cutting, stacking, and burning, making us more aware of how much is used and where it comes from. Finally, this project allows us to broaden our scope of opening a window to the natural world to include physical examples of how our actions impact the world around us.

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