The paper presents some results of a project that has been aimed at developing an event–driven user-centric middleware for the monitoring and management of energy consumption in already existing public buildings. One of the strengths of the designed system is that it allows an easy integration of heterogeneous technologies and their hardware independent interoperability. This is a feature of great importance for existing buildings, where already existing controls could be integrated with new technologies to enhance the energy efficiency of a building. The functionality of the system has been tested in a number of representative spaces of already existing public buildings where the already installed HVAC and lighting services have been equipped with monitoring and actuating systems designed and implemented using commercial off-the shelf wired and wireless devices. The paper focuses on the energy aspects, which have been obtained by applying the designed system to monitor and control the electric lighting fixtures of different office spaces. The outcomes obtained from the monitored data have shown some significant differences from the expected and previously estimated energy saving results, and the paper offers some possible explanations. Some criticalities, in part related to the characteristics of the commercial off—the shelf adopted devices and in part to the difficulties encountered in monitoring and analysing the huge number of recorded data, are outlined.