In this article, ways for improving the energetic performance of buildings are investigated. A state of the art leads to the introduction of a performance indicator expressed in kWh/m2/yr. To improve the value of this indicator, a processor-based prototype of a real-time data-acquisition and monitoring system is developed in collaboration with two industrial companies. The set of measurements and corresponding sensors that are necessary to compute the value of the indicator while being consistent with the natural segmentation of energy consumption, is listed, thanks to the representation of the building using a systemic approach. Control algorithms are tested in simulation to improve renewable energy consumption while reducing fossil energy dependence, which are deemed to be applicable in practice using the proposed electronics. Simulations concerning the control and optimization of the power applied to two warmers in a room show large potential for fossil energy consumption reduction.