# Analysis, Evaluation and Simulation of Railway
## Materials and Methods
### Hotel Power (Hotel Loads)  
In railway systems, the electrical load in the passenger units or coaches (i.e., load of lights, ventilation, heating and air conditioning, information screens, opening and closing of doors, loads in restaurant cars, etc., are referred to as \"hotel load\" or \"hotel power\"). UIC estimates that the amount of energy needed for hotel loads range from 10-15% and in some cases (SBB-CFF-FFS, Swiss Railways [44]) up to nearly 40-50% of the total energy consumption of the train [2]. Hotel loads can be directly supplied by the locomotive (e.g., Locomotive S-334) which involves a reduction of traction effort (see Figure 5a), can be feed from overhead lines through converters in coaches or, in some cases (e.g., Talgo IV coaches), trains are fed from power cars (1 or 2 cars) placed at the ends of the rake. Each power car is installed with one, or several DG sets generating 3-phase (4 wire) power supply at 3 kV DC or 380 Volts 50 Hz. Power is transmitted to entire rake through two cable feeders, running through the whole length of the train. In \"conventional\" intercity trains in Spain (mainly in the period 1990-2010), this electric power supply is tapped at each coach (e.g., Eurofima standard coaches) through 45 kVA DC/AC converters from 3 kV DC supply. Main characteristics are given in Table 4. These characteristics allow foreseeing some ratios of power demand, due to the occupation of passenger trains with respect to average power needed for traction purposes. As it has been stated before, some railway operators report high hotel loads in some trains. For this reason, SBB actually develops a Demand Response (DR) initiative based on the control of head points and heaters in train coaches [45]. This load control, according to SBB pilot reports, happens without affecting the performance of the heating system. This DR policy is well known in conventional power systems in residential and commercial segments [46]. Potential loads of interest are Water Heater (WH) [47] and Heat Ventilation and Air Conditioning Loads (HVAC) [48], due to the thermal inertia (storage) in walls (HVAC) or water tanks (WH), because of the specific heat of building envelope materials or water (WH). This kind of thermal storage covers energy supply to maintain the service (temperature), while power is switched-off. The construction of train vehicles is especially based on steel (c = 477 J/kgK), and aluminum (c = 896 J/kgK) and this represents a valuable capacity for heat storage, with a similar potential to bricks in buildings' envelope. There are several possibilities to model HVAC systems and their environment (vehicle or building envelope): A white box, grey box, and black box. Some references in the literature classify these models in physics-based, grey box, and data-driven [49]. According to some experiences, the same principles can be applied to thermal models of HVAC systems for rail vehicles [50]. The first alternative is white box models. Thermal design software, such as EnergyPlus, E_Quest [51], or Modelica, are considered as white box approaches, but they have some drawbacks. This approach is too complex (a high cost for computation time and resources) to evaluate demand response (EnergyPlus works with high order \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Series** & \begin{tabular}{c} **Converter (3** \\ **kVDC-380 VAC**) \\ \end{tabular} & \
\begin{tabular}{c} **HVAC** \\ **HVAC** \\ **(Resistors)** \\ \end{tabular} &
\begin{tabular}{c} **Heat** \\ **Loads/Passenger** \\ \end{tabular} \\ \hline
9000 & 45 kVA & \
\begin{tabular}{c} 3000 kcal/h \\ 22 kW \\ \end{tabular} & 11 kW & 1400 W & 510 W \\ \hline B-10000 & 45 kVA &
\begin{tabular}{c} 3000 kcal/h \\ 22 kW \\ \end{tabular} & 14.5 kW & 590 W & 562 W \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Hotel loads for 9000/10000 RENFE coaches 1.  
state-space models, e.g., model order around 30-40). Besides, the identification and evaluation of every necessary parameter are time consuming (and consequently, it is difficult to identify them).