Digital twin technology connects a physical entity with its virtual model in real-time, thanks to its comprehensive and sophisticated capabilities. Using this technology, various functions can be realized, including simulation, integration, testing, monitoring, and maintenance. Using accurate and detailed virtual models, they monitor device status, predict their future behavior, and even explore a wide range of operational strategies. This allows for a deeper understanding of real-world systems and optimization. Digital twin technology was first used by NASA in the Apollo space program in 2002. As a result of these innovations, NASA built replicas and models of the spacecraft systems on the ground (e.g., a digital twin) to efficiently manage and maintain spacecrafts far out in space. This innovation served as the basis for the development of digital twin technology. After Michael Grieves of the University of Michigan made a public presentation introducing the idea of the digital twin in 2003 ^[1].

Since the beginning of the 21st century, information technology has rapidly developed, especially with the emergence of a new generation of information technologies, including the Internet of Things (IoT), cloud computing, big data analytics, artificial intelligence (AI), and many others. Digitalization has significantly accelerated ^[2]. As a result of this development, digital twin technology has increasingly been used in various fields. Several fields have been transformed by integrating the physical and virtual worlds, making digitization a driving force of innovation. Various applications of digital twins have been found in areas such as smart cities, healthcare, agriculture, transportation, automotive, aerospace, manufacturing, energy, electricity, and other fields. Manufacturing companies can use digital twins to improve product quality, reduce production costs, increase delivery speed, and predict bottlenecks during the production process to accelerate the launch of new products ^[3]. An urban planner may use digital twin technology to simulate the infrastructure and operations of a city to provide planning and decision-making advice. Digital twins can be used in the energy sector to simulate and analyze energy demand, for example, to test various lighting designs in various application scenarios through computer simulation to choose the most appropriate one ^[4].

A digital twin technology in architecture allows real-time connectivity between an actual building and its virtual counterpart. Further to this subject, an effective assessment of unanticipated or unpredictable aspects of a building can be accomplished. Furthermore, it contributes significantly to streamlining building workflows, reducing maintenance costs, improving building user engagement, and integrating a variety of building information technologies into the building operations ^[5]. Digital twin technology has significantly improved the construction project implementation process, including reducing the time to completion and lowering the budget. Many emerging fields will benefit from this, including the design and construction of smart buildings, where using this technology can reduce the cost and time of building a building, enhance collaboration and productivity, improve the efficiency of utilizing existing buildings, and improve safety and sustainability ^[6]. In addition, digital twin technology can help achieve some previously unreachable building goals. Additionally, digital twin technology can help meet previously unattainable goals in the construction industry. As an example, this technology can help develop more effective maintenance strategies by providing real-time information on the status of systems or equipment. The construction industry could achieve this by performing preventive maintenance and improving facility management efficiency. In urban planning, digital twin technology may provide researchers and planners with more information regarding the growth of cities or help predict the effectiveness of using urban facilities. Though digital twin technology offers significant potential, several challenges remain to overcome, including data processing on a large scale, data security and privacy, cost control, technical limitations, and seamless integration of the physical and digital worlds. Several additional challenges and complexity arise in the architectural field, particularly in data collection and processing, real-time monitoring, data updates, data access, personalization of user interface design, cybersecurity, and integration with intelligent solutions ^[7]. Professionals in related industries are actively engaged in research and development to overcome these challenges. As a result of these initiatives, several industry leaders have made significant investments in digital twin technology. At the same time, the increased attention and increasing number of publications have led to a strong impetus for advancing the technology ^[8]. The application of digital twin technology has achieved significant growth in recent years, a trend closely related to the rapid development of Industry 4.0. Along with providing a wide array of application scenarios, the development of Industry 4.0 also provides the necessary support for the technology’s development. With the continuous development of Industry 4.0, digital twin technology has more significant potential for solving current problems and advancing the industry further.

The application of digital twin technology has contributed positively to this. The industrial process sector accounts for 35.2% of global CO₂ equivalent emissions, and 69% of these are directly related to industrial energy use, highlighting the need for immediate action to reduce industrial energy consumption and emissions. Digital twin technology has great potential to provide the best physical solution to support plant operations and asset management to effectively address the energy emissions challenge ^[9].

Digital twin technology has become increasingly crucial for managing buildings’ energy consumption in recent years. This innovative technology allows managers to monitor the energy usage of building facilities, including lighting, plug loads (already accounting for 33% of total energy use in commercial buildings, ^[10] and HVAC systems. In this way, they can understand and optimize building energy consumption patterns in detail. It is worth mentioning that the commercial and office sector accounts for 71% of total global energy consumption, of which at least 18% is used for lighting, accounting for 20% of global energy consumption ^[11].

As a result, the annual energy use of an office building is influenced by many factors, including location, equipment uses, hours of operation, HVAC systems, and lighting technology, which makes improving the energy efficiency of lighting systems, while ensuring lighting quality and illumination, a key area for green building energy efficiency research ^[12].

In addition, digital twin technology can simulate the operating state of devices and systems to optimize their operation in real time, thus improving energy efficiency. This feature makes the digital twin powerful technical support for energy-saving efforts. In addition, the predictive maintenance function of digital twins can anticipate and deal with possible equipment problems in advance, avoiding energy waste due to equipment failure and thus saving maintenance and repair costs.

Digital twin technology can simulate the energy performance of different design options during the planning, design, and construction phases of a building, providing designers with a basis for making more energy-efficient decisions. It can also generate comprehensive energy usage reports and forecasts, which provide an important reference for developing energy management strategies. For example, during the construction phase, the digital twin can simulate the characteristics of utilities to enhance the operation, maintenance, and lifetime of facilities, and combine real-time data such as building information and building automation systems to accurately reflect the actual performance and energy consumption of the building ^[13].

Combined with an intelligent building management system, digital twin (DT) technology automates a building’s energy use, thereby achieving energy savings and reducing carbon emissions. At the same time, DT technology helps reduce operating costs by improving energy efficiency and reducing maintenance costs, which in turn improves the economic efficiency of buildings. In addition, the advantages of DT technology are reflected in ensuring low-carbon production, mitigating the impact of economic activities on carbon emissions, testing energy strategies online, monitoring abnormal energy consumption, and warning of high-emission behaviour. Together, these benefits and applications highlight the key role of DT technology in driving environmental goals and improving energy efficiency ^[14].

Overall, the role of the digital twin in building energy management is indispensable. It not only helps us understand and manage the energy use of buildings in greater depth, driving energy efficiency, and environmental goals but also significantly improves the economic efficiency of buildings.

3. Building Information Modelling (BIM)

Building Information Modelling (BIM) was first proposed in the 1970s as a digital representation of the physical and functional characteristics, including various building data and information, and used throughout the life cycle of the buildings ^[15]. The initial application of BIM in new construction is mainly about design, visualization, coordination, and throughout project management phases ^[16]. Since BIM includes all the information of the structure, it is multidimensional from its nature, and each subset containing different information can be called a dimension. BIM can be mainly divided into eight dimensions, which are object model, time, cost, operation, sustainability, and safety ^[17]. In simple terms, BIM can be both a technology and a process; it provides a visual platform for stakeholders to better collaborate and communicate throughout a project. For traditional project collaboration, project documents, and technical drawings are manually passed between stakeholders, and subjective interpretation can easily lead to misinterpretation during information transformation, negatively affecting collaboration efficiency. However, the application of BIM enables stakeholders to communicate and share information through a database with a visualized model. The information-sharing process allows real-time remote communication, supported by cloud computing, significantly increasing collaboration flexibility ^[18]. Graphical models enable stakeholders to reach a consensus on decisions early in the project life cycle, significantly reducing project costs and improving project quality ^[19]. For example, converting 2D technical drawings into 3D for sharing between design and construction teams can quickly gain a common understanding of expected deliverables. Digital transformation drives the energy sector through the Fourth Industrial Revolution, and BIM is expected to be the core of the “digital twin” for actual buildings [20,21]^[20][21]. The application of various digital technologies such as smart meters, advanced control systems, artificial intelligence, and deep learning algorithms positively impact the management of global energy systems, and these new methods of combining different technologies and software with BIM are called Integrated Building Information Modelling (iBIM) ^[22] BIM has been proven to comprehensively shape digital twins when combined with methods and tools such as Augmented Reality (AR), the Internet of Things (IoT), and Big Data [23,24]^[23][24]. Building Information Modelling (BIM) has also emerged as a potential solution to improve energy efficiency. Digital representations of construction processes through BIM platforms can facilitate information exchange and interoperability in digital formats. The application of digitalization and BIM can significantly improve the overall efficiency of the energy system, as well as the collaboration, flexibility, and information update throughout the building life cycle. Combining BIM with Building Energy Modelling (BEM) can save energy and costs ^[25].

4. Digital Twin

The development of this technology can be traced back to the 1960s when NASA devised “digital twins” to assess failures in the Apollo missions. The same physical spacecraft was built to simulate and study the different conditions the spacecraft would face in space. Later, David Gelernter proposed the idea of Digital Twin technology in 1991. Subsequently, Michael Grieves proposed the concept of Digital Twin Software in 2002; this was the first time to apply software to the manufacturing industry. In 2010, NASA defined the concept of the Digital Twin in detail, becoming an essential part of the aerospace field ^[4]. In 2002, NASA’s Greaves and Vickers introduced the concept of digital twins for the product lifecycle management (PLM) ^[26]. Broadly defined as “a digital twin is a dynamic, self-evolving digital/virtual model that represents the state of a real-life object and its physical twin. A digital twin is created by exchanging real-time data and preserving historical data realized”. However, for a long time, the ‘digital twin’ has been just a concept without any suitable technical means to support its application. With the advent of Industry 4.0, digital technologies are developing rapidly and promoting digital transformation in various industries. The transformation also promotes the development and application of digital twin technology. Digital twins are widely used in manufacturing, construction, medical care, urban planning, energy, agriculture, and other fields to optimize production, design, maintenance, and monitoring, improve efficiency and sustainability, and manage and optimize entities, processes and systems to achieve Increased efficiency, reduced costs and increased sustainability ^[27]. For the construction industry, a digital twin is defined as “a real-time representation of a fully or partially completed and developed building or structure to represent the state and characteristics of the building or structure it reflects” ^[28]. Thus, it enables seamless synchronization and monitoring of energy systems through computerized and virtual world simulations based on data, information, and consumer behavior. 3D modelling, digital prototyping, and system simulation are all products based on the digital twin concept ^[28]. As mentioned before, the digital twin (DT) aims to gain insight and predict the performance of a physical product, process, or infrastructure through a virtual model. A digital twin consists of a physical system, a virtual model, and the data network between the two ^[4]. Digital twins are used to improve physical entities’ performance by using virtual models’ computational tools. Real-time data from physical entities is used to inform the development of virtual model parameters, boundary conditions, and dynamics. This results in a more realistic representation of the actual entity being modelled ^[26]. The digital twin is a digital version of a physical entity with the principle of establishing a digital model by collecting data on physical entities, processes or systems, and interacting and collaborating with physical entities in real time to achieve optimization and improvement. Therefore, to make digital twin become practical, there is a need for an integrated analysis system ^[11]. Digital Twin can predict potential problems in real time by monitoring physical entities and providing feedback to aid decision-making and improvement, optimize design management processes, reduce costs, and promote sustainability ^[29]. Due to these characteristics, digital twins were introduced into the construction industry and combined with BIM based on CAD, SolidWorks, Revit, etc., to create an integrated construction management process covering the entire building life cycle ^[29]. Digital twin technology is at the heart of building energy efficiency. Electricity, heating, and air conditioning (HVAC systems) account for a large percentage of total building expenditures. Through the application of digital twin technology, it is possible to simulate the energy performance of buildings and predict their energy consumption patterns to control and reduce energy consumption and improve the energy efficiency of buildings. This will positively impact reducing energy waste and lowering the total cost of ownership of the building. Managing the costs, benefits and risks associated with the energy transition is essential to achieving sustainability. Within the Sustainable Development Goals (SDGs) framework, the development of sustainable, affordable, reliable, and innovative energy systems and services has become an important issue. Digitalization and digital twin technologies can help drive energy sector sustainability and the transformation and upgrading of energy systems.

5. From BIM to Digital Twin

As mentioned before, Industry 4.0 technologies have significantly impacted the construction industry. Building Information Modelling (BIM) has been widely adopted and continuously improved recently. Integrating building component information into building models through parametric modelling extends the 3D model of real-world projects. The process and framework of BIM are used to establish a clear project vision in the early stages of the project design ^[30]. As for three critical areas of technology, safety and management, BIM has been proven to assist in realizing digital twins (DT), significantly improving the prediction, management and monitoring of project quality and performance ^[31]. The integration of BIM and DT is based on the BIM model to create a virtual replica of a building or facility, combined with other software to fully simulate the physical environment of the building entity to create a Digital Twin ^[32]. In simple terms, in construction, a digital twin can be considered an iterative and upgraded version that includes BIM. Digital Twin is dynamic, and its real-time nature allows the project to be optimized and adjusted during the construction and implementation phase, realizing the synchronization of the real and virtual models in the platform. This integration combines the advantages of BIM and digital twins, enabling stakeholders to increase process visibility, efficient information transfer and communication based on real-time data synchronized to the digital twin. DTs provide insight into the lifetime and characteristics of individual products and can optimize their sustainability, helping to improve future product generations ^[33]. While current federated technologies are still limited by data transparency, concurrent viewing and editing of a single federated model, and controlled coordination of information access, ^[31] applications of BIM and digital twins are expected to play a vital role in smart building management.