# Energy Optimization in Hotels: Strategies for Efficiency in Hot Water Systems
## 4 Results and Discussion
### Results of the Thermodynamic Evaluation  
It is assumed that the operating conditions are steady-state, which implies that the mass flow rate of water in the primary hot water circuit (PHWC) remains constant under all circumstances. Based on the operating regimes established for the chillers and the input variables to the thermodynamic model, as detailed in Figure 7, several key operating parameters of the system are obtained and presented in Table 1.  
To evaluate the system's operating conditions, two working regimes are analyzed:  
* Nominal regime:pressure of 1.7 bar (\(-10\)\({}^{\circ}\)C) and 12.2 bar (46 \({}^{\circ}\)C), with corresponding evaporation and condensation temperatures; for the chilled water circuit, supply and return temperatures of 8 \({}^{\circ}\)C and 11 \({}^{\circ}\)C, respectively;
* Part-load regime:pressure of 1.5 bar (\(-7\)\({}^{\circ}\)C) and 11 bar (43 \({}^{\circ}\)C), with corresponding evaporation and condensation temperatures; for the chilled water circuit, supply and return temperatures of 8.5 \({}^{\circ}\)C and 12 \({}^{\circ}\)C, respectively. From the above table, it can be concluded that, when the chillers operate at partial load, the refrigerant temperature at the compressor outlet reaches values of 59.18 \({}^{\circ}\)C and 60.67 \({}^{\circ}\)C, respectively. In turn, the water temperature at the recuperator outlet is 55.11 \({}^{\circ}\)C and 56.11 \({}^{\circ}\)C. These values are insufficient to guarantee an adequate water temperature in the primary DHW circuit, which must be between 60 and 65 \({}^{\circ}\)C to comply with the technical requirements established by the standards. Figure 6: Hotel consumption data: (**a**) daily profile of domestic hot water consumption typical of a winter day; (**b**) hotel occupancy during the year. Under these conditions, heat recovery ranges between 8.09% and 17.86% for each chiller, respectively. These results indicate that, in reduced load situations, the current operating parameters do not ensure efficient operation, as the heat recovery is below its nominal value. The same is true for the coefficient of performance (COP), which is also negatively affected. It is observed that, when the operating conditions of the system do not coincide with those of maximum demand for which it was designed, the water temperature in the heat recovery system moves away from the desired values. This is because, regardless of the load regime, the design and operating parameters, such as the flows in the hot water circuits and the temperature of the inlet water to the recuperator, remain constant. Although the design parameters cannot be changed without replacing the heat exchanger, it is possible to adjust the working flows in the recovery circuit. Therefore, the option of varying the water flow in the primary DHW circuit to reach temperatures above 60 \({}^{\circ}\)C is considered. By reducing the flow rate in the heat recovery unit, an increase in temperature is achieved (see Figure 7). A balance can be established between the flow rate that maximizes the temperature in the DHW circuit and the heat exchange required to ensure that the domestic hot water supply temperature reaches 55 \({}^{\circ}\)C.  
In the optimization process using genetic algorithms (GA), a heuristic method designed to identify the optimal values of the key decision variables considered in the analysis was implemented. Through multiple iterations, the GA progressively refine the solutions, converging towards the values closest to the global optimum of the objective function. An illustrative example of GA convergence is presented in Figure 8.  
As a result of the optimization procedure, new mass flow values in the primary and secondary hot water circuits are obtained: \(\textit{ht}_{cp}=1.19\) kg/s and \(\textit{ht}_{cs}=1.77\) kg/s, respectively. For these new flow rates, temperature behavior in the hot water circuits is stabilized, and the domestic hot water (DHW) demand of the hotel is met.