In the current context of thermal improvement in the building sector, research of new solutions to integrate to the retrofitting process is an essential step in the way of saving energy. With the purpose of maintaining or improving the summer comfort after a retrofitting in a residential building, Phase Change Materials (PCM) could be used to bring enough inertia to use the freshness of night for cooling during the warmest hour in the day. Passive solutions of PCM integration have demonstrated their limited benefits. Using PCM in the way proposed in this article goes through the design of a PCM/air system able to store latent heat. This unit is coupled to the ventilation system to ensure that the heat transfers between the ventilated air and the PCM stock are forced convection and then higher than the ones with natural convection. The fusion and solidification temperature for the PCM needs to be carefully chosen to allow the latent heat storage. To analyze the behavior of such a system in a retrofitted house with the climate of 4 different French cities, simulations in different configurations have been carried out. According to these climates, we analyze the necessary conditions for the improvement of efficiency of PCM use. Also, the appropriate PCM melting temperature range is defined with corresponding existing PCM characteristics. After, optimal thickness is obtained considering the diurnal temperature evolutions. The TRNSYS software runs the modeled house, coupled with Matlab for the PCM/air system model. The number of units of such a system can be changed and adapted to the different climates. Results are expressed in terms of percentage of the time when the indoor operative temperature reaches a certain level. Comparisons are made with classical systems without PCM. (C) 2014 Elsevier Ltd. All rights reserved.