Heat-storage capacity and moisture gradient of wood-shaving insulation panels for building use

The thermal diffusivity of insulation panels consisting of wood shavings is smaller than that of the glass-wool panels that are commonly used in buildings as insulation material. In the present study, the heat-storage capacity of wood-shaving insulation panels was compared with that of glass-wool panels, focusing on daily changes in room temperature in winter. The moisture gradient of wood-shaving insulation panels was also examined with respect to the avoidance of dew condensation. The panels were installed in two different rooms, with the same structure and thermal resistance, of a small one-story house (18 squarem) built in Morioka, Japan. The rooms were heated for 12 hours a day (0-12pm, 20degC) by an air conditioner, and the surface and air temperatures of the two rooms were compared. Minimum room temperatures in the early morning were found to be 2degC higher in the room with wood-shaving insulation panels. This was due to the fact that room surface temperatures were 0.6-1.6degC higher, since the thermal diffusivity of the wood-shaving insulation panels is half that of the glass wool panels. However, the amount of heating energy required was 4% greater in the room insulated with the wood-shaving panels due to a 30% greater heat mass. During one-week of continuous room heating in the dead of winter, a large moisture and temperature gradient developed throughout the thickness of the wood-shaving insulation panel. When the temperature gradient reached 20degC, the moisture content was 24% at the lowest-temperature surface and 5% at the highest temperature surface. However, dew condensation was not observed. Measurement of heat-flow in the presence of this moisture gradient revealed that the thermal conductivity of the wood-shaving insulation panel did not change. Moreover, the moisture gradient disappeared within a couple of days following the disappearance of the temperature gradient, suggesting that moisture permeability is great inside the wood-shaving panel.