Experimental research on the indoor environment control of natural insulation materials: Carbonized rice hull and straw bales

The purpose of this research was to assess the performance of straw bales and carbonized rice hulls when used as natural insulation to regulate the indoor environment. Toward that end, specimens of straw bales and carbonized rice hulls were tested in the Korea Conformity Laboratories. Based on the results, real-scale mockup rooms insulated with these natural materials were constructed for cost analysis and performance evaluation. The cost analysis results showed that carbonized rice hulls are relatively cost effective and economically feasible. The thermal conductivity of carbonized rice hulls is lower than that of straw bales, and no difference in thermal performance was shown in relation to the different construction method used for each material. With regard to humidity, both mockup rooms built with each of the natural materials exhibited stable variations compared to the outside weather, and both materials sustained a general humidity within a comfortable 40-60% range. The straw bales mockup room was shown to produce a higher CO₂ emission possibly due to the bio-metabolism (anaerobic fermentation), suggesting that this material should be used with caution. Carbonized rice hulls were proven to be a good natural insulation material and a good regulator of indoor humidity and would not yield CO₂ due to bio-metabolism.