This paper explores the integration of digital twin technology for enhanced fault diagnosis in smart buildings, aiming to optimize energy performance. Indeed, the emergence of digital twins represents a significant advance in this field, as they enable the monitoring and regulation of the various systems as heating, ventilation and air conditioning (HVAC). They can also analyze the data generated by such systems to detect possible faults, and even make predictions to anticipate potential problems. Nevertheless, managing the interoperability of heterogeneous data remains a challenge to achieve an operational and efficient digital twin. Taking the fault detection and diagnosis (FDD) process for building HVAC systems as the case, this paper details a global digital framework in terms of data management, service supporting and user interface.