Thermal conductivity of natural materials used for thermal insulation

Abstract

The possibility to determine the thermal conductivity of construction materials outside the laboratory conditions is useful for professional practice mainly for control and inspection activities on real existing buildings. This paper describes the method and results of measurements focused on different natural thermal insulations based on agricultural products as strawboard panel Solomit and thermal insulating material from hemp, which are used mainly for improvement of the thermal properties of buildings. The measuring principle was based on the dynamic unsteady method. The measurement consists in the analysis of a thermal response of the tested material to heat flux pulses. Thermal conductivity of Solomit straw board panels with the longitudinal alignment of stalks to the direction of heat flux was 0.089 W•m•K-1 and with the transversal alignment of stalks 0.066 W•m•K-1. Results of the measurement confirmed that the thermal conductivity of the straw boards depends on the orientation of the stalk material. If the heat flux is directed in a direction perpendicular to the blades the thermal conductivity is lower than that in the direction along the stalks. The thermal conductivity of the natural insulation material manufactured from hemp was from 0.041 to 0.046 W•m•K-1. Crushing of the stalk structure before the production of building materials of vegetable origin enables the subsequent production of panels with constant thermal insulation properties. By deformation of the thermal insulating material not only its density is changed, but also the thermal conductivity. Solomit straw board panels used during sixty years historically demonstrated the reasonable use of this material in lightweight constructions for agriculture and other purposes.