In November 2007 the community of Tanana installed two cordwood boilers to heat a washeteria with a system similar to one operating in Dot Lake since the late 1990s. Cordwood is burned to heat a large reservoir of water. Wood is burned with 75.4% efficiency at a high temperature for about two hours, twice a day. The water stores the heat and circulates it to the washeteria and other buildings as needed.
The Tanana project represents an efficient method of burning wood. Other boiler systems are now being developed to operate at high efficiency. Compared to the low-efficiency OWBs (Outdoor Wood Boilers), these boilers use half the wood fuel. Many communities could benefit from these systems. They are heat-only systems and have not yet been integrated into CHP systems capable of generating power.
- System: Two (2) 1850 gallon hot water boilers, 425,000 Btu/hr each
- Manufacturer: Garn, Minnesota
- Fuel: cordwood substitutes for 9,000 gallons diesel per year (250 gals/day)
- Wood fuel (spruce) at $225/cord is equivalent to diesel at $2/gallon
- Schedule: installed November 2007
- Budget: $170,000 including photovoltaic solar panels on roof of Washeteria
Data and Analysis
Assuming 72 cords/yr are necessary to displace 9,000 gal/yr of diesel, increased labor costs of $1,100/yr over the existing oil system, $850/yr for power and other wood system O&M, $225/cord of spruce, and $5.00/gal for heating fuel, annual savings are approximately $26,700/yr. Therefore the simple payback on the initial system cost is $170,000/$26,700; approximately 6.5 years.