Book Description

The lumber solar dryer is a wood-framed structure covered with thin transparent materials that permit transmission of shortwave solar energy. Baffled fans provide air circulation. Air exchange is regulated using adjustable vents and mist sprayers permit some additional control of relative humidity. At Rio Piedras-San Juan, temperature, relative humidity, and solar radiation are fairly uniform throughout the year, being slightly more favorable for rapid lumber drying during february-march. Solar and air drying time of seven charges of Honduras mahogany of varying thicknesses and one mixed charge of 11 hardwood species has been determined. From an initial green moisture content of 50 percent, l-inch mahogany can be solar dried to a final moisture content of 12 percent in 18 days, 1-1/4-inch requires 25 days, and 2-inch stock about 41 days. The mixed hardwoods (1-1/4-inch), ranging in basic specific gravity from 0.48 to 0.82 required 43 days to solar-dry from an average green moisture content of 60 percent to a final average moisture content of 12 percent. At the end of the runs, moisture content of sample boards usually ranged +- 2 percent from this mean. A 48-hour mist spray conditioning treatment is adequate to remove severe casehardening. A moisture content of 15 percent can be reached in the solar dryer in one-half to one-fourth the time required for air drying. Nevertheless, warping and checking in the solar-dried lumber are no more severe than in matched air-dried material.