# Designing a Conceptual Digital Twin Architecture for High-Temperature Heat Upgrade Systems
## 5 Discussion  
### Digital Twin Iteration Process  
Developing a digital twin in parallel with the create and build cycles of the physical system raises additional challenges, particularly due to the absence of a bidirectional connection with the physical system during early stages, since data is the driving element of the DT [47]. To classify different degrees of data integration and automation level of the bidirectional communication, authors of [48] introduce three types of DT, from simplest to most complex one: digital model, digital shadow, and digital twin. These three DT levels can be used as key steps in an iterative development process of DT. This process is close to what the DT throughout the product lifecycle was envision in [49] where only two types of DT are used: DT prototype and DT instance. Similarly, from a DT-based product design perspective, this process consists of conceptual design, detailed design and virtual verification [13].  
The first step is represented by creating a digital model of the desired physical system, including mathematical modelling, 3D environmental representation, and computer-aided  
Figure 8: Information flow modeling—physical processes and data perspective.  
design (CAD). The digital model is used in simulations allowing for virtual analysis of the physical system potential. At the same time, it supports evaluation of control systems and workflow designs, providing valuable insights during the initial phases. For our DT architecture, to instantiate a digital model would mean creating the Simulation component of Services layer, coupled with the Visual Tools layer and most of the components of Processed data layer, as seen in Figure 9a.  
During the build phase of the physical model, the physical-to-virtual connection becomes operational, allowing real-world data to be collected and integrated into the digital model. This synchronization enables real-time monitoring and analysis of the physical system, allowing the refinement of AI algorithms and updates to the digital model for increased accuracy. In addition to the architectural components of a digital model, Physical and Hardware Control Units layers are now available. Instantiating the Real Time Data component from Processed Data layer, AI Prediction and Optimization services completes this step, transforming the digital model into a digital shadow. The required digital shadow components can be seen in Figure 9b.  
The final stage Is achieved when the virtual-to-physical connection is established, completing the real-time bidirectional link though the Control HUB and Remote Config modules. This feedback loop connection upgrades the digital shadow to a fully functional digital twin, enabling it to interact with and directly control the physical system. The real-time feedback loop ensures continuous optimization and operational alignment between the digital and physical counterparts as described in Section 3. All the DT components can be seen in Figure 1.  
Figure 9: (**a**) Proposed DT architecture instantiation for the digital model; (**b**) proposed DT architecture instantiation for the digital shadow.