A phase-change material (PCM) is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy. Heat is absorbed or released when the material changes from solid to liquid and vice versa; thus, PCMs are classified as latent heat storage (LHS) units.

The work presented in this paper is related to the study of a passive solar system applied in facades with Trombe wall. In particular it was evaluated the effect of the incorporation of phase changing materials (PCM's) was assessed using namely PCM based on paraffin and another one based on octadecane. For this purpose, firstly an experimental campaign conducted at Bragança Polytechnic Institute was performed in order to evaluate the blending mode of all the constituents of the mortar, the content of PCM to incorporate in the mortar as well as the involved water quantity, including mechanical characterization of the mortar with and without PCM. The second part was devoted to the study of tests models using cement mortar and an appropriate geometry, by exposure to atmospheric thermal action. With data acquisition equipment it was possible to obtain temperature records and thermal conductivity of the main facade elements in 10 to 10 minutes intervals and so it was possible to establish a comparison between the tested models. Main conclusions of this work are that the incorporation of PCM's into thermal mortars can bring benefits in terms of thermal comfort, greater efficiency and sustainability to buildings, as well as improve the efficiency of Trombe wall building system.