This study aspires to introduce a comprehensive framework for the operational assessment of buildings energy performance, with the use of advanced tools and practices for building digitization. For the purpose of this study, a relevant set of operational indicators was employed, with the purpose to provide information, both to the landlords and the tenants, related to the actual energy performance of the building. The novelty of this study relies on the fact that for the extraction of the operational rating, a digital twin environment was used, employing smart sensors, real time measurements and a BIM environment. Within this study, the proposed concepts are demonstrated in a case study building of mixed used. This study aims to shed light to the development of practices for the remote and smart real time energy assessment of building units.