Low Energy Building Materials Suitable for Bhutanese Architecture - Wood Wool Slab

Abstract: Rammed earth is commonly used to construct traditional Bhutanese buildings. In colder areas, the thermal performance of these buildings is poor leading to the easy ingress of cold air demanding more heating energy to make a comfortable indoor climate. Modern insulation materials are not common in Bhutan due to the lack of knowledge on the advantage of thermal insulating materials, the unavailability of local insulating materials, and the cost associated with them. The construction in urban areas is dominated by modern building materials such as concrete and bricks nevertheless rural areas prefer the use of local materials. To improve the indoor environment, new bio-based building insulating material called wood wool slab was introduced. As a pilot project, the Bhutanese blue pine was used as the main raw material to manufacture wood wool, and cement was used as a binder to prepare wood wool slabs in two different methods. Three different specimen was made and tested in civil engineering laboratory for the bending strength test, among which specimen 3 stands the highest bending force 584 N at a displacement of approximately 11 mm whereas specimen 1 and specimen 2 resist a force of nearly 300 N. Thermal conductivity test was also performed in physics laboratory by Hot Disk (TPS 2500S), however, the test was unsuccessful due to uneven surface of the specimen that provides defective results. In the performed simulations, the value from the Swedish wood wool slab results was used to compare the thermal performance and energy performance in unheated cases, 2 kW cases, and 10 kW cases. The comparison was made with rammed earth and burnt bricks. The highest energy consumption in a year was 24123 kWh in rammed earth buildings, followed by burnt bricks with 17922 kWh and the lowest was 6576 kWh for wood wool slab buildings. Accordingly, the thermal performance of these three building materials was compared in an unheated case. The wood wool slab has shown better performance which means that it can retain heat for a longer duration. This result indicates that the wood wool slab can be a good alternative for the Bhutanese construction industry to make buildings thermally comfortable and energy-efficient.