Thermal characterization of homogeneous walls using inverse method

Current environmental concerns have promoted efforts to reduce the consumption of energy. In moving towards improving existing buildings, the study of the thermal behaviour of a wall is not easy because its actual thermophysical properties are not well-known. These parameters are nevertheless fundamental for the economic optimisation of building refurbishment or for the verification of their performance in situ. It is thus important to be able to characterize existing building walls. The objective of our study was to develop a method to thermally characterize a wall adapted to in situ applications based on an active approach. The principle of identification consists of thermally examining an access surface by applying a heat flux and studying the response in terms of the temperature recorded by infrared thermography on the opposite surface. Based on signals of flux and of temperatures measured at the edges of the wall, the thermophysical properties (thermal conductivity and volumetric heat) of the wall are estimated by inverse method. The method was applied first to a homogeneous gypsum-tile panel in laboratory. The results were compared to reference values obtained from a classical procedure. Then, the method has been implemented in situ on a homogeneous reinforced concrete shell.