## 4 Results and Discussion
### Combined ORC-Single Evaporator VCR Cycle Results  
Figure 3 represents effect of evaporator temperature on \(\mathrm{COP_{sys}}\), \(\mathrm{\eta_{ex,sys}}\), and \(\mathrm{\dot{m}_{total}}\). Increase in evaporator temperature leads to a rise in coefficient of performance of system. As the evaporator temperature increases, compressor power decreases, and thus leading to an increase in \(\mathrm{COP_{VCR}}\). For this reason, \(\mathrm{COP_{sys}}\) increases as well according to Figure 3a. Increase in evaporator temperature has a negative effect on exergy efficiency of system according to Figure 3b. Exergy transferred with heat in evaporator decreases as a result of increase in evaporator temperature. This situation effects \(\mathrm{\eta_{ex,VCR}}\) negatively, thereby reducing \(\mathrm{\eta_{ex,sys}}\). Figure 3c states that, increase in evaporator temperature causes a decrease in total mass flow rate. Because of the fact that compressor power decreases with increasing evaporator temperature, turbine power decreases as well. Decrease in turbine power causes decline in \(\mathrm{\dot{m}_{ORC}}\). Therefore, total mass flow rate of combined system decreases too. It can be detected from Figure 3 that R600a achieves the best \(\mathrm{COP_{sys}}\) and \(\mathrm{\eta_{ex,sys}}\) and can be labelled as the most efficient working fluid. Figure 4 shows influence of temperature of condenser in VCR cycle on system performance. As condenser temperature rises from 30 \({}^{\circ}\)C to 50 \({}^{\circ}\)C, condenser pressure and exit enthalpy of compressor increase. For this reason, compressor power increases and \(\mathrm{COP_{VCR}}\) is negatively affected. This situation causes fall in \(\mathrm{COP_{sys}}\) and can be seen from Figure 4a. \(\mathrm{\eta_{ex,sys}}\) declines with increase in condenser temperature as presented in Figure 4b. The reason is increase of compressor power and thus decrease in exergy efficiency of refrigeration cycle. If \(\mathrm{\eta_{ex,VCR}}\) declines, \(\mathrm{\eta_{ex,sys}}\) decreases as well according to Equation (10). Figure 4c represents that increase in condenser temperature leads to rise in \(\mathrm{\dot{m}_{total}}\). Since compressor power increases as a result of increasing condenser temperature, \(\mathrm{\dot{m}_{VCR}}\) increases. Turbine power is also positively affected from this condition because compressor is directly connected to turbine. As a result, \(\mathrm{\dot{m}_{ORC}}\) rises as well. For these reasons, total mass flow rate of combined system increases. R227 ea shows maximum mass flow rate since it has the highest molecular mass. Figure 3: Effect of \(\rm T_{evap}\) on \(\rm COP_{sys}\) (**a**), \(\rm\eta_{ex,sys}\) (**b**), and \(\rm\dot{m}_{total}\) (**c**) in combined ORC-single evaporator VCR cycle. Figure 4: Influence of \(\rm T_{cond,VCR}\) on \(\rm COP_{sys}\) (**a**), \(\rm\tau_{lex,sys}\) (**b**), and \(\rm\dot{m}_{total}\) (**c**) in combined ORC-single evaporator VCR cycle. Figure 5 depicts impact of compressor isentropic efficiency on system performance. Change of isentropic efficiency from 0.65 to 0.85 increases \(\text{COPsys}\) as can be seen from Figure 5a. Compressor power decreases with increasing isentropic efficiency. So, \(\text{COPVCR}\) and, consequently, \(\text{COPVsys}\) rise. Decline in compressor power increases exergy efficiency of refrigeration cycle and thereby increasing \(\eta_{\text{ex,sys}}\) for all fluids as given in Figure 5b. Figure 6 indicates how system performance is affected by boiler temperature. The effect of boiler temperature on \(\text{COPVsys}\) is exhibited in Figure 6a. It can be observed from figure that increase of boiler temperature from 60 \({}^{\circ}\)C to 100 \({}^{\circ}\)C effects positively coefficient of performance of combined system. Turbine inlet enthalpy rises with increasing boiler temperature. To satisfy constant compressor and turbine power, \(\dot{\text{m}}_{\text{ORC}}\) must decrease. For this reason, heat input to boiler decreases and \(\eta_{\text{ORC}}\) increases according to Equation (4).