## 1 Introduction
### Background  
The term conservation refers to the definition agreed at the XXV ICOM General Assembly in Shanghai in November 2009: \"all those measures and actions that aim to avoid or minimise future deterioration or loss. They are carried out on the context or area surrounding the property, or more frequently on a group of goods regardless of their age or condition. These measures and actions are indirect, as they do not interfere with the materials and structures of the goods. They do not, therefore, change their appearance.\" [19]. The conservation of heritage buildings that contain works of art requires stable conditions of humidity, temperature, and CO\({}_{2}\) concentrations. This may be difficult to achieve without the help of mechanical conditioning systems, which consume energy and may have a high impact in the building architecture and its protected assets. The importance of data monitoring and collection for the control of internal environmental conditions hasbeen demonstrated [20], and more recently, the value of generating digital repositories in which to host data to inform decision-making processes has been proven [21; 22; 23; 24]. There is a general agreement that the conditions for the conservation of heritage assets should be set between 18 \({}^{\circ}\)C and 22 \({}^{\circ}\)C, between 45% and 65% relative humidity, and below 500 ppm for CO\({}_{2}\) concentration [25; 26; 27]. The concentration of CO\({}_{2}\) begins to affect people from 1000 ppm and is deemed to be uncomfortable from 1500 ppm [28]. Preventive maintenance plans (PMPs) provide the motivation to collect building performance data, from which it is possible to evaluate the current conditions within buildings, and the stress to which they are subjected. PMPs allow the design of conservation strategies to ensure targeted maintenance of artefacts and they can also contribute to the wellbeing of the people who use the building because the internal environment is better controlled [29]. To support PMPs, the use of strategies based on heritage building information modelling (HBIM) allows centralisation of information that, applied to historic buildings, becomes repositories where geometric, constructive, and historical information can be collected, facilitating collaborative work and the exchange of coordinated information between multidisciplinary teams [30; 31; 32; 33]. This strategy supports what was stated in the Amsterdam Congress held in 1975, where it was agreed that architectures and historical sites require more prudent tools and operational practices to guide each intervention on cultural heritage from a global point of view [34]. From these centralised repositories it is possible to develop digital twins (DTs) that allow simulations to be prepared to support maintenance strategies. These simulations are traditionally focused on energy and environmental improvements [35], but also allow, among other actions, researchers to evaluate the influence of people on the use of buildings as one of the contradictory factors in the process of heritage conservation. Appropriate use of a building contributes to its conservation, but, at the same time, large visitor numbers can generate conditions that result in the deterioration of the cultural assets that compose it. Cultural tourism monopolises general attention because it has the effect of re-valuing heritage. In particular, the income generated from cultural tourism boosts the local and national economy. However, tourism can also be harmful if a coherent policy is not followed. Thus, it is necessary to establish protocols that address the establishment of a balance between marketing and visitor planning, and the conservation and maintenance of the heritage asset. This can be achieved by taking measures aimed at preventive conservation in preference to active conservation, since it is preferable to conserve rather than restore or renovate [36].