## 3 Research Project Stages  
This paper presents some stages of an ongoing research project. The aim of the research project is to define a Building Management Systems (BMS) based on an occupancy-oriented Digital Twin (DT), evolving from and enriching the Building Information Model (BIM) and integrating occupancy levels and additional relevant data from Post-Occupancy Evaluations (POEs). The expected results of the research project are: monitoring occupancy and defining building occupancy patterns, optimizing current O&M management, building space use and organization, cleaning activities, and, as possible future implementations, applying Smart Contract to cleaning and maintenance services and extending the IoT network with other kind of sensors for safety and quality control. The research project stages are presented in Figure 1.  
The first two stages, \"definition of BIM guidelines\" and \"BIM model creation\", have been previously analyzed in a publication by [PERSON] et al. [75]. \"Preliminary analyses\", \"system installation\", and \"test campaigns\" are presented in this paper, as they are critical to provide the foundations upon which the occupancy-oriented DT should be based. The \"occupancy-oriented DT\" set of activities is currently under development. In future steps of the research, collected data will be analyzed to identify occupancy patterns of the building spaces, and evaluate current management of spaces in terms of people permanence and cleaning frequency. In addition, benchmarks to evaluate optimization strategies will be defined together with the subjects in charge of O&M in the case study building, a fundamental step to evaluate advantages and results of the methodology [76]. The defined occupancy-oriented DT will be the base for the subsequent phase, i.e., \"FM scenario definition and optimization\", that will allow the optimization of cleaning activities and contracts that are currently based on the building floor areas, and to reach a better organization and planning of space usage. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sensor Type** & **Main Aspects** & **Pros** & **Cons** \\ \hline \multirow{3}{*}{Camera-based sensors [25, 26]} & \multirow{3}{*}{Average accuracy of 97\%} & High accuracy & Users detection only within \\  & & Security and safety & field-of-view \\  & & applications & Privacy issues and \\  & & & Hawthorne effect \\ \hline CO2 concentration change sensors & \multirow{3}{*}{Average accuracy of 94\%} & Often used in buildings & Less reliable than other type \\  [25, 26, 66] & & No privacy issues & of sensors \\ \hline \multirow{3}{*}{Visual light and infrared (PIR) technologies [9, 16, 67]} & High accuracy of 97\% & \multirow{3}{*}{High accuracy} & Issues in detecting \\  & (unoccupied–occupied & & stationary occupants \\   technologies & scenarios) & & Users’ presence/absence \\  [9, 16, 67, 68] & Accuracy 93\% (stationary and & \multirow{3}{*}{No privacy issues} & detection only within the \\  & & moving occupants) & field-of-view \\ \hline \multirow{3}{*}{Radio frequency identification (RFID) sensors [9, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73,Figure 1 also provides \"possible future implementations\" of the research project. The integration of other kinds of sensors, such as \"sensors for safety (man down) and quality control\" will allow the monitoring and optimization of different aspects of the building management, resulting in a complete report of building conditions and indoor environmental quality. In addition, a possible future implementation of the system will be the definition of \"smart contracts for facility management and cleaning activities\" that would be based on the actual need of cleaning defined in previous stages.