## 3 Results
### Hybrid Compression/Absorption Chiller  
Figure 3 shows the results of the cooling supplied to the conditioned space by the absorption system, \(\dot{Q}_{ae}\), and by the compression system coupled to the Stirling engine, \(\dot{Q}_{ce}\), considering the operating range of the refrigeration systems, from \(x_{a}=0\) to \(x_{a}=1\). It also shows the heat required in the generator of the absorption system, \(\dot{Q}_{g}\), and that required in the hot source of the Stirling engine, \(\dot{Q}_{HS}\), that moves the compression refrigeration system. In the figure, it can be seen that the heat demanded by the two cooling systems is equal when \(x_{a}=0.5\). When the absorption system is not operated (\(x_{a}=0\)), the compression system provides 100% of the cooling demand, while when the absorption system operates at 100% (\(x_{a}=1\)), the compression system does not operate. The heat demanded by each refrigeration system for its operation changes in a different way. The heat demanded by the generator of the absorption system is greater than the cooling power produced by approximately 13% and 16% at 28 and 37 \({}^{\circ}\)C, respectively, of condensation temperature. On the other hand, the heat required by the Stirling engine to feed the compression refrigeration system is greater than the cooling power produced by approximately 2.9% and 27.9% at 28 and 37 \({}^{\circ}\)C, respectively, if the heat engine operates with an efficiency of 0.1. However, if this heat engine operates with an efficiency of 0.3, the heat required as input by the Stirling engine is less than the cooling power produced, up to 66.6 and 53.4% at 28 and 37 \({}^{\circ}\)C in the condenser, respectively. This means that, if the conditioned space is required to be cooled only by the absorption system, approximately 16% more heat is required in the supply to this system. Whereas, if the cooling occurs only with the compression system coupled to the Stirling engine, the heat required by the system may be less than the cooling produced (up to 53.8% if the engine operates with an efficiency of 0.3 and 37 \({}^{\circ}\)C at the condenser). This is due to the good performance of the compression system. The power ratio of the compressor to the pump of the compression and absorption system, respectively, is shown in Figure 4, for the entire operating range of the chiller, from \(x_{a}=0\) to \(x_{a}=1\). When the absorption system operates at 5% (\(x_{a}=0.05\)), the power ratio is approximately 560, with \(T_{\rm c}=30\)\({}^{\circ}\)C and \(T_{e}=5\)\({}^{\circ}\)C. At the same temperature in the condenser and \(T_{e}=15\)\({}^{\circ}\)C, the power ratio is approximately 490. This is due to the minimal power required by the pump of the absorption system and because the cooling required in the conditioned space is supplied almost entirely by the compression system. This power ratio decreases from about 130 to 30 in the range from \(x_{a}=0.2\) to \(x_{a}=0.45\). The power ratio is reduced to approximately 5, when the absorption system operates at approximately 95%. According to this figure, it is recommended to operate the hybrid cooler from \(x_{a}=0.2\) to \(x_{a}=1\). Figure 5 shows the relationship between the useful heat generated by the solar concentrator and the cooling power produced by the hybrid cooler throughout the entire operating range of the system, from \(x_{a}=0\) to \(x_{a}=1\). From the figure, it can be seen that if the efficiency of the Stirling engine is 0.1, the heat supplied to the global system is greater than the cooling power produced (\(r_{q}>1\)). This means that more heat is supplied than cold is produced. Whereas, if the efficiency of the heat engine is 0.2 and 0.3, the heat supplied to the global system is less than the cooling power produced in the operating range from \(x_{a}=0\) to \(x_{a}=0.65\) and \(x_{a}=0.8\), respectively. After these values, in all cases of efficiency and condensation temperature analyzed in this work, the heat supplied to the hybrid system is greater than the cooling power produced.