# Transcritical R744 Supermarket Refrigeration System Integrated with a Heat-Driven Ejector Chiller
## 3 Results and Discussion
### Impact of Operating the Proposed System at the Optimal Conditions of the Conventional R744 Systems  
Adoption of new technology is always challenging due to the complex nature of its circuitry, which gives rise to the need to develop a new set of controllers, which may increase the investment cost. This section evaluates the suitability of the existing high-pressure controllers for use in the proposed system. The R744 refrigeration system integrated with the R717-based HEC was operated at the optimum high-side pressure of the PC system. The results are depicted in Figure 14. Below 32 \({}^{\circ}\)C ambient temperature, the penalty on the COP of the proposed system was found to be below 1%. However, as the ambient temperature increased, the deviation was found to rise from 1.5% at 33 \({}^{\circ}\)C to 5.9% at 43 \({}^{\circ}\)C. This was attributed to the fact that below 32 \({}^{\circ}\)C, the difference in the optimal high-side pressure (Figure 15) between the proposed and the PC system was relatively lower (<2.5%), while the same was found to increase by 9.9% at 43 \({}^{\circ}\)C ambient temperature. Operating the system at a GC pressure lower than the optimum reduced the quantity of heat extracted from the R744 in the generator (Figure 16), which further reduced the cooling capacity of the HEC and hence the degree of subcooling achieved was relatively lower (Figure 17). As a result, operating the proposed system at the optimal pressure of the PC system resulted in higher flash vapor generation in the liquid receiver, which increased the power consumption significantly. The performance of the proposed system was found to be highly sensitive to the operating GC pressure. At 29 \({}^{\circ}\)C ambient temperature, a 2% shift from the optimal pressure reduced the generator heat input by 2.8% and the degree of subcooling by 23%. However, it was interesting to observe that the penalty on the COP was relatively less when the proposed system was operated at the optimum pressure of the CB system (Figure 14). Since the optimum high-side pressure for the CB system was higher compared to that of the PC system (Figure 15), the heat extraction in the generator was relatively higher (Figure 16), which led to higher heat extraction in the subcooler (Figure 17). As a result, the use of the high-pressure controllers of the CB system was found to impose a lower penalty on the system performance compared to the controllers of the PC system. The R744 system integrated with the R718-based HEC also showed a similar trend (Figure 14). However, the penalty with R718 was significantly higher compared to the R717-based HEC. As observed from the previous analysis, the cooling capacity of the R718 system ranged from 2.2 kW to 17.98 kW when operated at its optimal conditions (Figure 9). However, use of the existing high-pressure controllers of the CB and the PC system further reduced its cooling capacity due to operation at relatively lower GC pressure (Figures 8 and 15). Shift from the optimal operating conditions also led to performance depreciation of the R600a-based HEC. However, the penalty imposed with R600a was significantly lower compared to R718.  
Figure 14: Performance depreciation due to use of existing optimal high-pressure strategy.  
Figure 15: Comparison of the optimum gas-cooler pressure.  
Figure 16: Impact on the waste heat utilization due to shift from optimum operation.  
Figure 17: Percentage reduction in the subcooling potential due to shift from optimum operation.