From the Lab Scale to the Construction Site Scale: Properties of Hemp Thermal Insulation

Abstract

Integrate bio-resources in construction materials is a key to reduce the environmental impact of the building industry. The hemp, as local and annually renewable plant resource, proves to be particularly suitable. The study presented in this article is a part of the “INNOFIB” ADEME project. The objective of this project is to develop an innovative industrial process of functionalisation of hemp fibre by dry process. The resulting product will be usable as thermal insulation material. The thermal properties of such material applied by blowing appear to be directly linked to the bulk density. One challenge of this project is to identify the hemp fibre morphology that leads to the best thermal performances. Several refined fibres shaped using various industrial processes, and reference insulating materials, are subjected to characterisation tests. Laboratory protocols, adapted to be applied to fibrous materials, evaluate the morphology, physical and thermal properties of bulk fibres: shape, length average fibre diameter, density, and thermal conductivity. Interestingly, for such bulk fibre materials, the thermal conductivity appears as a decreasing function of the density for the lowest densities. The thermal conductivity calculated with a predictive model including conduction and radiation is compared to the experimental data. The obtained results guide the selection of the best industrial process for the fibre preparation. The selected solution is then applied in the attic of a house used as demonstrator. Temperature and heat flux sensors are placed to record the data in real conditions. The on-site measurements are used to check the compliance of the effective thermal performances.