## 3 BIM and DTs--Latest Development Trends and Challenges
### Standards, Requirements, and Approaches
#### 4.1.1. BACS and Energy Efficiency Performance  
The rapid development of BACS technology over the past two decades has resulted in the need to systematize not only communication and data transmission standards but also the automation functions themselves along with the principles of their functional integration. In the first decade of the 2000s, the EN 15232 standard entitled \"Energy performance of buildings--Impact of Building Automation, Controls and Building Management\" was developed, which was updated several times. The latest version from 2017 [14] introduces four categories of BACS, marked with letters from A to D depending on their impact on a building's energy efficiency, as shown in Figure 5[8; 101]. It is crucial to note that these categories differ from the energy efficiency classes of entire buildings as defined in the EN ISO 52003 standard [102]. As shown in [103], the standard can be used already at the design and prototype stage. The simplified list of control functions with a basic indicator calculation method could be used for buildings without detailed information related to BACS and TBM concepts. This allows for the optimization and evaluation of different design and functional variants. At the construction stage, the building can be used to identify areas where energy consumption can be additionally reduced. On this basis, integrators could consider various variants of temperature and lighting, considering daylight availability, occupancy factors, etc. However, as indicated in [104], there is a gap between the assumptions of EN 15232:2017  
Figure 5: Categories of building automation systems from EN 15232:2017.  
and the actual performance of BACS. The standard suggests that the higher the level of automation, the greater the energy savings, but the practice shows that users can circumvent these systems to meet their needs, for example, by blocking light or presence sensors [5; 105]. Users may not be aware of the impact of their actions on energy consumption. Therefore, it is important to raise awareness and educate both professionals and ordinary household members. Moreover, case studies for different kinds of buildings are very important and useful, considering not only various use scenarios but also different geographical locations of buildings. This represents a clear application area for BIM during the design and construction phases, as well as for DTs during the operation of buildings with BACS and BMS. In 2021, the EN 15232 standard was replaced by the EN ISO 52120 standard [15], which introduced minor changes and sanctioned the significance of the TBM function in BACS systems and advanced BMS scenarios, particularly in the context of active monitoring and management platforms of local energy networks--microgrids. The EN ISO 52120 standard applies to the energy performance of buildings with the BACS and TBM functions. According to [106; 107], it raises awareness of the benefits and requirements of building automation for energy efficiency in buildings. Moreover, it defines building readiness levels for integration with smart grid systems and provides methods for verifying the potential of BACS functions and installations in the area of improving the energy efficiency of buildings, as illustrated in Figure 6.  
The standard defines and describes three verification methods, along with performance indicators, for the calculation and comparison methods. All of these methods have the potential to utilize BIM and DT tools in both the design and verification procedures of BACS and BMS installations. Although the standard considers a multitude of factors affecting the energy efficiency of buildings, there are some key elements that are overlooked. The most crucial aspects are stated by [PERSON] et al. in their paper [13]. The system presented by the authors considers and analyzes the load on the building, user behavior, climatic conditions, and maintained temperatures, adapting the operation of the systems to adjust energy consumption to these parameters.