Energy consumption is a worldwide concern and improving insulation is a way to save energy in buildings. In Algeria about 42.7% of the total energy is consumed by residential sector. This study investigates the thermal behaviour of external walls used in buildings located in a chosen Algerian city under real climatic conditions. The transient heat conduction through a composite wall made of 3 or 5 parallel layers of different materials and thicknesses was numerically resolved. The equations system resolution was carried out by the finite differences method according to the Crank-Nicolson scheme. The outdoor temperature and the solar heat flux were approximated using analytic expressions, and were used as boundary conditions in the developed FORTRAN program. Simulations were performed for materials used in actual building constructions in Batna city as well as for materials proposed to improve insulation and an approach to define the costs of studied cases was developed. The results show that the actual way of construction gives poor thermal insulation. We proposed several technical solutions for new constructions as well as for the existing buildings to improve energy efficiency at lower costs.

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In this work a numerical study of the thermal behavior of a multilayer building wall (3 and 5 layers) is presented. The external side of the wall is subjected to the local atmospheric conditions of Algeria. The finite differences method is used to solve the transient heat transfer equations through the building wall, which is submitted to a solar heat flux, and a convective heat transfer with the environment. A sinusoidal forms of the external temperature and the solar flux were used to approach the measured data of Ouargla city (Algeria) (attitude 31°57' N, longitude: 5° 20'E, altitude 123-315 m), during the summer and winter seasons. An economic study is presented and a solution for a good thermal insulation at a lower cost is proposed.

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