In the context of more and more efficient building research, as passive house or Energy plus building, the occupants have become a central actor of building system. In order to integrate them in the design phase of a building, it is proposed to complete the classical definition of “energy efficiency” with the concept of “usage energy efficiency”. This concept integrates the notion of satisfaction and energy consumption which are summarized in a compromise decision plane. The research work is ilustrated thanks to a real platform, where the proposed tool has been applied to a heating system. It appears that this tool, used as a decision support in the design phase, could both improve the integration of user in building system and reduce energy consumption.