## 3 Results
### Sharing a Common Shaft  
In this section, the case where the expander and compressor shared a common shaft is studied, wherein the transmission ratio was 1. The marine engine is operated under 100% MCR. From the above analysis, R245 ca and R1233 zd show comparable performance. R1233 zd is selected as the ORC working fluid because it is more environmentally friendly than R245 ca. The ORC condensation temperatures  
Figure 6: Effect of ORC evaporation pressure on cooling capacity and energy efficiency ratio for different working fluids. Figure 7: Effect of ORC evaporation pressure on exergy efficiency of combined cycle. are set as 308 K by using sea water as the heat sink. In this system, the pressure difference across the expander is equal to that across the compressor (\(P_{3}\)-\(P_{4}\) = \(P_{S}\)-\(P_{7}\)). Figure 8 shows the variation of cooling capacity under different VCC evaporation temperatures. It can be seen that the cooling capacity decreases with ORC evaporation pressure and increased with the cold air temperature. With the increase of the ORC evaporation pressure, the VCC condensation pressure is enhanced for a fixed PPTD and a constant heat sink, resulting in a higher discharged temperature. The enthalpy difference across the compressor outlet and inlet become greater. Consequently, the cooling capacity of the VCC evaporator is reduced because of the decreasing flow rate of the VCC refrigerant. The calculated \(EER\) of cooling strongly depends on the operating conditions, especially absolute temperature and the temperature difference between the heat sink and the target refrigeration temperature. Figure 9 illustrates that the \(EER\) of cooling decreases with ORC evaporation pressure. For a given heat sink temperature, the VCC condensation pressure and temperature rise when the ORC evaporation pressure is increased. In that case, the temperature lift of the refrigerant between the condenser and the evaporator is enhanced, resulting in a decreased \(EER\). In this system, both ORC and VCC used sea water as the heat sink. The effect of condensation temperature on the performance of both the ORC power cycle and the VCC refrigeration cycle was analysed. The condensation temperatures in both subsystems were assumed to be the same, as they both used the same heat sink. The curves in Figure 10 present an ascending trend as the condensation temperature increases. By sharing a common shaft, the pressure difference between the ORC expander inlet and outlet is equal to that between the compressor outlet and inlet, which can be expressed as \(P_{3}\)-\(P_{4}\) = \(P_{S}\)-\(P_{7}\). The variation of ORC condensation temperature influences the ORC and VCC. When the ORC is operated at the same evaporation pressure, the pressure difference across the expander is reduced if the condensation temperature is increased. As a result, the VCC evaporation pressure \(P_{7}\) was decreases, as the VCC expander outlet pressure \(P_{S}\) increases with the VCC condensation temperature, explaining why the evaporation temperature increased with the condensation temperature. From Figure 10, it can be concluded that the ORC subsystem should be operated at a higher evaporation pressure to achieve a lower required refrigeration temperature. Figure 11 shows the variation of the cooling capacity with variable condensation temperatures. It can be observed that the cooling capacity increases with rising condensation temperature. For the ORC subsystem, the expander could generate less power output to drive the VCC compressor. In the VCC subsystem, the power consumed by per unit mass refrigerant in the VCC is reduced because the  
Figure 8: Effect of ORC evaporation pressure on cooling capacity for the case of sharing a common shaft. pressure difference across the compressor decreases with the increase of condensation temperature, as mentioned above. The enthalpy difference of the refrigerant at the compressor outlet and inlet decreases as well, leading to a larger mass flow rate of refrigerant.