Fuel and material utilization of a waste shiitake (Lentinula edodes) mushroom bed derived from hardwood chips II thermal conductivity of compression-dried waste mushroom beds

Abstract

This study investigated using waste mushroom beds as insulation material and applied compression-drying to eliminate the coarse voids that are unfavorable for insulation. The relationship between air-dry density and thermal conductivity was investigated. The mean air-dry density of the uncompacted waste mushroom beds was approximately 200 kg/m3, which increased to approximately 550 kg/m3 after four levels of compression-drying. A linear relationship was recognized between the air-dry density and thermal conductivity of the waste mushroom bed. Comparing this relationship to those of wood and mat-formed wood-based panels showed that the thermal conductivity of a waste mushroom bed is similar to that of wood at low densities and mat-formed wood-based panels at high densities. Furthermore, the thermal conductivity of heat bridges was estimated using a series–parallel heat-flow model for voids and substances, and the substance thermal conductivity was in the order of wood (0.218 W/mK), waste mushroom bed (0.288 W/mK), and mycelium (0.368 W/mK). The same heat-flow model was applied to a waste mushroom bed to obtain the substance thermal conductivity along the heat-flow direction. The results show that the waste mushroom bed substance also has an anisotropic thermal conductivity.