Abstract: The electrical distribution networks overload, caused by a massive use of heating and air-conditioning systems in peak hour, has made load shedding the only means of recourse to protect the network from total collapse. This problem can be attenuated by energy storage produced at off peak hour by incorporating some phase change materials in the envelope of the building. To evaluate the impact of such a material used as wallboard on thermal comfort, a numeric model based on the thermal balances of the building is elaborated and solved using an explicit diagram of finite differences. The use of the model, after validation, for the simulation of a building in extreme conditions alloys the confirmation of the possibility of shifting part of the electrical consumption from peak hour to off peak hour.