## 1 Introduction
### Digital Twins and Building Conservation  
The evolution of technology is enabling a more efficient use of data collected from sensors. The establishment of the field of building performance simulations as a predictive tool is making it possible to better predict what is going to happen in the future and what corrective measures should be adopted to avoid damage to precious artefacts. It is possible to trace the development in the field of simulation and its relationship to data collection from buildings from the 1960s, confirming its value for decision making in the different phases of a building's lifecycle [69]. Among the new tools developed for the preventive maintenance of heritage are digital twins (DTs), which are virtual representations designed to accurately reflect a physical object. DTs can assist in the preventative maintenance process by allowing adjustments to be made based on simulations that draw on monitoring data. This technology is now being implemented in the management of buildings. DTs can be part of preventative maintenance plans (PMPs) developed for asset management and are often based on models developed with HBIM technologies. This makes it possible to generate dynamic models that enable changes in the decision-making process once the data collected by the physical twin have been analysed.  
DTs have begun to be applied in heritage buildings and historic sites by way of case study research. This has demonstrated that the use of data from sensors and digital twins can help to safeguard the integrity of heritage assets by acting in a preventative way [70]. Digital technologies offer many opportunities for creating a virtual replica of heritage objects, from which it is possible to explore scenarios and hence adopt an informed approach to the preservation and protection of heritage. With these tools, qualitative and quantitative indicators of the current condition of heritage can be defined and validated in an interdisciplinary framework [71].  
The first experiences in the development of DTs have their origin in purely geometric representations that were born from LIDAR and that allowed for a better experience of the protected building while guaranteeing it was not deteriorated by visits [72]. However, it has been shown that a DT applied to HBIM allows access to different layers of information to properly document the building and directly involve the owner in the process of preserving the historical legacy [73]. There are experiences in the use of DTs for heritage conservation with the aim of improving interior conditions in historic buildings. In these investigations, through HBIM, it has been possible to develop computational fluid dynamics (CFD) to evaluate the amount of ventilation needed and reduce the equipment needed to condition a historic site [26]. At the same time, the use of DTs supported by HBIM strategies has made it possible to integrate both technologies into a decision support system based on artificial intelligence (in this case machine learning techniques) for the management of museum collections in historical architectures [74]. There are also experiences in the use of DTs for the conservation of cultural artefacts [75].