Energy performance and thickness optimization of hemp wool insulation and air cavity layers integrated in Moroccan building walls’

Interest in the use of bio-based materials for thermal insulation of buildings has been increasing in recent years. Indeed, the integration of these materials into building envelopes will simultaneously reduce energy use and greenhouse gas (GHG) emission rates. In this context, the thermal performance of bio-based insulation materials is studied and compared to that of conventional insulation materials. However, the majority of these studies, concentrated especially in Europe, lack economic analysis. Cultivated for centuries in Morocco, the use of hemp in the building industry is very limited. The aim of this study is to assess the use of hemp as insulation material for Moroccan external building walls located in Meknes, a city characterized by the Mediterranean climate Csa. Firstly, time lag and decrement factor are investigated in order to assess the dynamic thermal behavior of an external multilayer wall insulated with hemp wool. Afterwards, based on a life cycle cost analysis (LCCA), optimum hemp wool thickness, energy savings and payback period are determined for an analysis period of 20 years. Using a computer program developed in Matlab, an implicit finite difference method is applied to solve the 1D heat equation and investigations are carried out for different wall orientations. It was found that highest optimum insulation thicknesses are provided by east and west orientations (5 cm) followed by the southern and the northern ones (4 and 3 cm, respectively). In addition, an air gap layer is introduced to the optimal insulated multilayer wall, and a third investigation is conducted. The optimal air gap thickness is determined based on the analysis of various thermal parameters such as Prandtl, Rayleigh and Nusselt numbers, conduction, convection and radiation heat transfer rates. For all wall orientations, optimum air gap thickness was found equal to 1.3 cm. Annual GHG emissions were also calculated and it was found that they can be decreased by about 71% with the use of optimum thicknesses of hemp wool and air cavity insulations. Finally, a comparative study with the recommendations set by the Moroccan thermal regulation is conducted. The findings showed that our investigated configuration would be more efficient from thermal, economical and environmental points of view.