## 3 Results  
### Belt Drive as the Transmission Unit  
When a belt drive was used as the transmission unit for the coupling of expander and compressor, both the ORC and VCC could be operated at their optimum conditions simultaneously. In this case, the transmission ratio could be adjusted by changing the diameters of two pulleys.  
As the refrigeration cycle was powered by the ORC expander, the variation of the ORC power output had a great effect on the performance of the refrigeration cycle. Figure 5 presents the comparison of ORC power output among the four different working fluids. The figure shows that for R1233 zd and R1234 zez, the power output firstly increases and then decreases after reaching its peak value roughly at 340o kPa. This is because enthalpy change across the expander increased as the evaporation pressure increases. However, the mass flow rate of working fluid decreases as the ORC evaporation pressure increases. As a result, the different variation trends of these two parameters lead to an optimal power output when the ORC was operated nearly at the critical pressure. For the working fluids with lower critical temperatures, such as R245 fa and R245 ca, the maximum cooling capacity appeares at a higher evaporation pressure, whereas it appeares at a lower evaporation pressure for the working fluids with lower critical temperatures, namely, R1233 zd and R1234 zez. Furthermore, it can be observed that R1233 zd and R245 ca have a higher power output in comparison with R1234 zez and R245 fa.  
In this system, the power generated in the ORC expander was consumed by the VCC compressor. Hence, the sole useful energy output of the whole system was the cooling generated in the VCC. Figure 6 shows the variation of cooling capacity and \(EER\) with evaporation pressure. The cooling capacity has a similar variation trend with that of the ORC power output, as shown in Figure 5. This is because the power consumed by the VCC compressor is equal to that generated by the ORC expander. For a given condensation temperature, the power input into the VCC decides the mass flow rate of the refrigerant in the VCC. In other words, the cooling capacity is decided by the power input of the VCC.  
Figure 6 also indicates that the \(EER\) decreases with the ORC evaporation pressure. According to Equation (32), \(EER\) is defined as the cooling capacity of evaporation in the VCC to the power generated by the ORC. As the ORC evaporation pressure increases, more power is supplied to the VCC subsystem, and the cooling capacity of the evaporator also increases because of the increasing refrigerant flow in VCC. This can be attributed to the fact that the power consumed by the compressor increased, although the cooling capacity also rises. The growth rate of the cooling capacity is not comparable to that of the compressor power, resulting in a smaller \(EER\).  
Figure 5: Effects of ORC evaporation pressure on ORC power output for different working fluids.  
Figure 7 shows the variation of exergy efficiency when the ORC is operated under different evaporation pressures. In this system, the exergy output refers to the cooling exergy of the evaporator in the VCC, and the exergy input consists of the heat exergy of the evaporator in the ORC and the pump power. At the same evaporation temperature, the variation trend of exergy efficiency in Figure 6 is similar to that of the cooling capacity. This is because the exergy output of cooling is linearly correlated to the cooling capacity at a given VCC evaporation temperature. Furthermore, a higher ORC evaporation pressure leads to a better temperature match between the organic working fluid and the exhaust gas, and the exergy destruction per mass unit decreases.