# Interoperability between Building Information Modelling (BIM) and Building Energy Model (BEM)
## 1 Introduction  
The challenge of designing a high-performance building demands better data exchange between the building information modelling (BIM) and building energy model (BEM). The building sector is responsible for 40% of the energy consumption in Europe, in which the building envelope is the main constructive element, in terms of its impact on the building's energy consumption [1]. The European Union has submitted a set of directives to eliminate inefficient buildings, through the Energy Performance of Buildings Directive (EPBD) [2, 3], which is the leading legislative and policy instrument. This directive focuses on the building sector (i.e., new and existing constructions) and determines that the existing ones must be nearly zero energy buildings (NZEBs) by 2050 [4]. The NZEB standard is valuable for the environment, as well as for the end-users of the building, asenergy savings also reduce costs [5]. In this framework, there has been a growing interest in energy modelling studies, in order to understand how to optimise energy consumption in buildings [6]. In this context, on the 28 October 2020, the Sustainable Places 2020 virtual conference took place, where nine EU-funded research projects showed their work and exposed some innovative solutions advanced in their projects. All of them highlighted the challenges that the industry continues to face under the digital transformation [7]. Recently, the construction sector has been identified as the poorest in Europe, in terms of productivity, as there exist many difficulties in this sector to integrate digital innovations [8]. Over the last two decades, BIM has been used in the construction sector, with the focus to improve collaboration between different stakeholders [9], facilitate the fast creation of different designs, and to decrease its inefficiencies on-site and among the project disciplines [10]. It has also become the core of the cyber-physical system and a great tool to improve the energy efficiency concept in building design, once it is able to improve the quality and performance of the construction life-cycle under the industry 4.0 paradigm [11]. At present, BIM is crucial for bridging the gap between digitalisation and the construction field. The digital information management tools offered by BIM make it possible to optimise and better control constructive processes, from the design stage to the management of the building's life-cycle and maintenance [12]. BEMs are the basis of energy performance certificates (EPCs) and assessments. Both EPCs and assessments should be user-friendly, profitable, and more reliable, in order to give investors confidence in the energy efficiency sector. Then, the certification processes and BEMs should achieve these requirements [13]. In addition, BEMs can be organized into three categories: Physics-based models (white-box) [14], pure data-driven or statistical models (black-box) [15], and hybrid models (grey-box) [16]. In this paper, white-box models were considered, as they enable the definition of all the elements that influence the building's energy behaviour (e.g., the weather, internal loads, construction) [17; 18] and, therefore, have a clear connection with BIM components. Although heating ventilation air conditioning (HVAC) systems are also important to the energy analysis, they were not considered in this study. Furthermore, interoperability between BIM and BEM could be a step forward in reducing costs and saving model re-creation time during the design phase. BIM has the potential to streamline the production of energy models, by storing important data such as building geometry, construction typology, and thermal properties [19], as well as enabling the iteration of efficient designs in a shared environment [20]. In addition, BEMs are key elements in understanding how to reduce energy consumption and how to improve it [21]. Furthermore, BEM tools and measures can carry out energy simulations, analyse energy needs, and improve the project design [22].