## 3 Results
### Solar Collector for Hybrid Chiller
In the figure, the solar concentrator efficiency is in the range from 0.33 to 0.75. COP of the absorption system is 0.85, while COP of the compression system is 11, when \(T_{h}=200\)\({}^{\circ}\)C, \(T_{e}=10\)\({}^{\circ}\)C and \(T_{c}=28\)\({}^{\circ}\)C.  
The COP of the cooling systems and the collector efficiency are shown in Figure 11 as a function of \(T_{h}\). In the figure, it can be seen that when \(T_{e}=5\)\({}^{\circ}\)C and \(T_{c}=37\)\({}^{\circ}\)C, the COP\({}_{\rm ar}\) increases from 0.27 to 0.78 approximately. However, when \(T_{e}=10\)\({}^{\circ}\)C and \(T_{c}=28\)\({}^{\circ}\)C, the change in COP\({}_{\rm ar}\) is negligible. The change in COP\({}_{\rm cr}\) is only appreciated with respect to \(T_{c}\). Finally, the efficiency of the collector decreases as the collector temperature increases, as can be seen in the figure on the right side. Figure 10: Efficiency of the solar collector and cooling systems, with respect to radiation in the solar concentrator. Figure 9: Efficiency of the solar concentrator with respect to \((T_{i}-T_{o})/I\) at 3 hot spot temperatures. The energy savings of the proposed hybrid chiller were determined in comparison to a commercial air conditioning equipment of 0.75 tons of refrigeration (2636 kW) [32]. The cooling capacity of the hybrid system is 2.72 kW (0.47 kW in the absorption evaporator and 2.25 kW in the compression evaporator). The electricity consumption of the compressor was 0.85 kW, taken from [32], while the electricity consumption of the solution pump was \(P_{E}\) = 0.032 kW, obtained from Figure 5, at the maximum recommended operating value of the absorption system, \(x_{a}\) = 0.4, with \(T_{c}\) = 37 \({}^{\circ}\)C and \(T_{c}\) = 15 \({}^{\circ}\)C (\(P_{\rm E}\) = \(P_{p}\)/\(\eta_{p}\) = 0.028/0.85). The cost of electricity in American dollars ($) per kWh in Mexico was taken from [33]. The energy savings of the proposed chiller, shown in Figure 12, were determined considering an operating period of 8 h per day, as recommended in [34], during 365 days per year. In Figure 12, it can be seen that electricity consumption of the conventional system is 26.6 times the consumption of the hybrid system. In cumulative values, with this difference in annual consumption, the energy savings with the proposed system is close to 60 MWh at the end of the equipment's useful life, 25 years.  
The cost of operating the systems is shown in Figure 13. The initial cost of the proposed system was $3400 ($2000 absorption system, $800 Stirling engine and $600 solar collector). It can be seen from the figure that the operating cost of the conventional system is 26.6 times greater than that of the proposed system. Considering the cost of investment for the proposed system as negative and cumulative values, it can be seen that the recovery of the investment occurs in year 9. From that  
Figure 11: Efficiency of the solar collector and cooling systems, with respect to radiation in the solar concentrator.  
Figure 12: Energy savings caused by the proposed system.  
moment, an economic saving of $5300 can be achieved at the end of the useful life of the proposed system, 25 years.