A Solar Heated Kiln for Drying New Zealand Hardwoods

The design of a simple greenhouse-type solar kiln for drying New Zealand hardwoods is described. Special features include split construction to ease loading and automatic venting with cheap humidity sensors to give control over drying conditions. The results of two kiln trials are presented, in which 25 mm thick boards of red beech and silver beech were dried. Drying times were approximately halved compared with the air drying times for these species reported by other workers. The wet-bulb depression, a measure of the driving force for drying, was doubled in the solar kiln compared with open-air drying. An analysis of the economic viability of the solar kiln compared to air drying showed that the annual cost of drying in the solar kiln is 45% greater than the air-drying operation if open-air drying takes twice as long as drying in the solar kiln, but is 7% less than open-air drying when this is six times slower.