Resource Efficient Wood Drying Kilns
by Stephen C. Taylor
January 13, 1999
Vermont Family Forests (VFF) is an organization of woodland owners seeking to "cultivate local family forests for economic and social benefits while protecting the ecological integrity of the forest community as a whole". In 1997, VFF conducted a survey of wood product manufacturers in western Vermont, identifying a lack of wood-drying facilities as a substantial limitation to the utilization of lumber from local sources.
Timber owners and wood product manufacturers can add substantial value to their resources by drying their own lumber. To promote the establishment of accessible wood drying facilities in the VFF area, this report provides an overview of kiln designs, processes, operational aspects, and economic considerations.
The research emphasizes energy efficiency for two reasons: First, kiln drying is energy intensive, and the cost of energy can account for as much as 50% of the total cost of production. Second, just as the environmental impacts of forest management and harvesting must be addressed in a sustainable forest system, so too must the impact of energy ( in processing) be considered.
The results of the research indicate that solar drying, while limited to 3 seasons in Vermont, is generally feasible and may be cost effective in comparison to traditional kiln designs. An economic analysis of solar, dehumidification, and traditional kiln designs indicates very similar life-cycle cost of production, but widely varying production capabilities. For any given operation, a wide variety of factors will affect the choice of a specific kiln design. Such factors include the desired production volume, availability of existing infrastructure for lumber handling, diversity of products and other 'value-adding' processes, marketing plan, access to raw materials, and retail operations.
The report also states: Before most hardwoods can be processed into furniture or other wood products, it is necessary to remove nearly
one quart of water per board foot of lumber.
Although the low operating temperature in solar kilns slows the process, it also offers several distinct benefits. First, the risk of degrade is substantially reduced because the water removal is slower, and because the moisture gradient in each board is typically "relaxed" each night as a result of "diurnal cycling". Second,
the requirement for monitoring and adjustment is generally much lower with solar kilns. This translates into low labor costs and ease of operation, making solar kilns particularly attractive for less experienced operators.