## 4 Discussion  
When creating simplified models of the energy hub components, we need to consider the technical structure of the system and, based on the data obtained, determine the necessary and sufficient parameters of the model elements depending on the objective function implemented by the simulation model. The generally accepted assumptions suggest that the energy hub consists of converters, storage devices, and energy transmission systems [39; 40]. Energy conversion systems are represented by the following systems, devices, and structure:  
* Systems that change the characteristics of an energy channel without converting one type of energy into another (transformers, heat exchangers);
* Systems that convert one type of energy into another, i.e., energy conversion systems: electric heating devices, gas turbines, and others. * Energy storage systems are as follows:
* Electric energy storage devices (electrochemical, pneumatic, pumped, and kinetic);
* Thermal energy storage devices (tanks and others);
* Gas storage facilities. * Energy transmission systems include the following points:
* Power transmission lines;
* Heat networks;
* Gas supply structure. When modeling a real-world multi-energy system, one should consider the feasibility of its technical implementation and the need to factor in its structure in the simulation model [2]. The flow diagram of the simulation model can be represented as shown in Figure 7.  
Figure 7 shows a flow diagram for the three most common energy supply channels. This approach, however, can be employed to simulate the systems containing an arbitrary number of energy supply channels. The specific implementation of this flow diagram depends on the software implementation of the simulation systems. Thus, the simulation model of a multi-energy system that implements the integrated approach can be represented as follows (Figure 8). The models designed based on the above principles include the following models:  
* A simulation model of a multi-energy system for two energy (electrical and thermal) supply channels;
* A model of converters of electrical energy into thermal energy;
* A model of the electrical and thermal energy storage systems. The simulation model considers the joint operation of the energy supply system for all channels, given their mutual influence. When building a model, the objective function is to determine the energy losses in all the main components of the energy hub. The developed model makes it possible to study the mutual influence of various energy supply channels on each other, to determine the energy losses in all the main elements of the energy supply system under various operating conditions, and factor in the functioning of the storage systems when accumulating and supplying energy. The computational experiment involved examining the operating conditions of the electrical energy storage device in the charge and discharge modes with the consumer load varying in a wide range and determining the total energy and energy losses at the power supply channel input. The simulation results for charging and discharging the energy storage device are shown in Figure 9.  
The analysis of the obtained results makes it possible to estimate the region of minimum energy losses in the components of the energy hub for various operating conditions in the power supply channel and storage systems. The non-linearity of changes in losses is due to the non-linearity of the efficiency of devices depending on the load. The non-linearity of the obtained characteristics is explained by the curve of the change in the efficiency of the transformer along the power supply channel and the characteristics of the charge and discharge of the energy storage. Figure 7: Flow diagram of a simulation model of a multi-energy system for three energy supply channels.