Between the uncertain cost of transporting fuel and an unstable economy, wood is an increasingly important alternative source of energy in Alaska. In many communities, fuel wood is readily available making this choice even more attractive. Researchers with the U.S. Forest Service have looked at the feasibility of using cordwood energy systems for heating small Alaskan communities.
The Forest Service investigators reviewed the feasibility of using high-efficiency cordwood heating systems based on the factors based on the factors described below. These heating installations can use a variety of biomass forms like cordwood, wood pellets and sawmill slabs. Cordwood energy systems are relatively low in their cost for installation and as the cost of fossil fuels increase, they become even more economical to operate. Use of these systems in small communities would be based on the sustainable harvest of small volumes of wood from nearby forests each year. Cordwood harvests could provide additional opportunities for the local cash economy and improve forest health through proper forest management.
A PDF copy of Nicholls and Miles report from the Pacific Northwest Research Station can be viewed here.
Practical Considerations Cordwood Energy Systems
Investigators looked at a number of factors that would effect the economic operation of a high-efficiency cordwood energy system:
- Wood Fuel Source – A community needs a nearby source of cordwood that can be harvested on a sustainable basis. A small village would require access to about 25 acres of forested land to gather 250 cords of wood each year. Fuel harvest could fit into local hazard reduction in the wildland-urban interface.
- Drying the Cordwood – More heat energy is recovered from cordwood that is properly dried. In many parts of Alaska, air-drying of cordwood could be accomplished during the summer season. Splitting the firewood greatly lowers drying times.
- Cordwood Size – Firewood is measured in volume and the standard unit of measure is a cord. A cord is stack of firewood that measures 4ft by 4ft by 8ft comprising a total volume of 128 cubic feet. Actual volume in cord can vary greatly depending on the size of the firewood and how it’s stacked. Knowing the actual volume of a delivered cord of firewood is important in evaluating the cost/benefit ratio of a proposed heating installation.
- Wood Fuel Costs – The cost of firewood varies greatly across Alaska, from less than $100 per cord to over $250. Having a viable established local cordwood market is an important factor for someone thinking about installing a cordwood heating system.
- Wood Fuel Sizing – The firebox of the cordwood heating system needs to be large enough to be loaded efficiently. Firewood must be cut to a length appropriate for the intended boiler.
- Heating Value of Various Wood Species – The heating value of wood is based on its weight per cubic foot or density. The density of wood varies between species of trees. The report mentions for instance that Cottonwood is less dense than Yellow Cedar. Knowing the density of the firewood used plays into the amount of energy produced by a cordwood heating system.
- Cordwood Heating System Sizing – The output or capacity of the heating system needs to be matched to the size or heating demand of the community. These systems are not efficient replacements for small systems that use less than 500 gallons of fuel a year. Larger systems will not save a community money unless they can be sheltered, use low-cost cordwood, enjoy low labor costs, and piping between buildings is minimal.
Reference: Nicholls, D. and Miles, T. (2009) Cordwood energy systems for community heating in Alaska–an overview. General Technical Reports PNW-GTR-783. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 17 p.
This article was first seen at Suite101.com Copyright © 2013 by Alan Sorum