18 May 2017
Lumber is used primarily as building material. Since freshly cut down lumber contains a large amount of water, it is necessary to dry it to constant moisture content for high quality. Currently, artificial drying method as typified by steam drying system has become the mainstream of lumber drying in Japan, but the existing system takes high equipment and energy costs. The aim of this study was to reduce energy cost and to save primary energy for lumber drying system by applying an industrial heat pump as a substitute heat source equipment. We built a prototype lumber drying system with a solar thermal collector, a water-circulation type heat pump and a waste heat recovery heat exchanger. This system had a 20m3 drying room about equal to an existing steam drying system with a heavy oil-fired boiler. As a result of experimental study, this system can reduce primary energy consumption by 56%, CO2 emissions by 54% and energy cost by 60%, compared to the steam drying system, keeping the kiln-dried lumber quality high. In addition, we evaluated the energy performance of this system and obtained some design guides for commercialization of this system.