## 5 Results and Discussion
### LT Application  
The agreement between the experimental and ANN modelling results for the energetic performance parameters, including the COP, the cooling capacity, and the compressor discharge temperature, is shown in Figure 6. The vertical axis represents the ANN modelling results, while the horizontal axis shows the experimental values. In each graph, a straight line indicating a perfect prediction and a \(\pm\)10% error band was used to evaluate the modelling accuracy. Note that for all graphics in Figure 6, the comparisons were made using the values for both R404A and R449A without distinction. As can be seen, most of the points are within the \(\pm\)10% error band, indicating an outstanding accuracy of the model. The results demonstrate that the ANN model predicted the energy parameters of the supermarket refrigeration system with high accuracy despite wide ranges of operating conditions.  
Figure 6: \(Cont.\)  
Figure 7 represents the field measurement results of the supermarket refrigeration system for R404A and R449A at the LT application. According to the experimental results, the supermarket refrigeration system exhibited a better performance when operating with R449A than R404A. It is observed that at a constant middle condensing temperature of 30 \({}^{\circ}\)C, the cooling capacity increases when using R449A as a substitution to R404A. It is important to note that the supermarket refrigeration system operated with comparable superheating temperatures for R404A and R449A refrigerants at LT case. However, the system experienced different ranges of subcooling temperatures with these two refrigerants. It was observed that the subcooling temperature for R449A is remarkably higher than that of R404A. Over the range of operating conditions, the subcooling temperature for the system using R449A was 12 K higher than that of R404A. The higher cooling capacity of the MT surpasses cabinet thermal requirements, so this excess is used for a higher subcooling in the R449A LT circuit. Then, the positive effect of subcooling temperature can explain the higher COP and cooling capacity values for the system using R449A compared to R404A. It is also observed that the system using R449A has a higher discharge temperature than R404A. For both refrigerants, the maximum average observed discharge temperature (86 \({}^{\circ}\)C) is still within the safe limit recommended by the compressor manufacturer and does not affect the compressor lifetime and oil lubricating properties.  
Figure 6: Validation of the (**a**) COP, (**b**) cooling capacity, and (**c**) discharge temperature at low temperature application.  
Figure 7: _Cont._  
As mentioned above, the difference in the subcooling temperature of the two refrigerants can affect the performance of the system. To better judge the influence of R449A as a substitution to R404A, the ANN model is employed to compare R404A and R449A under the same operating conditions.  
The predicted results of the energy parameters of the supermarket refrigeration system under the same operating conditions at different possible evaporating temperatures is shown in Figure 8. According to the predicted results, the supermarket refrigeration system using R449A exhibited a better energy performance as it has a higher COP than R404A at different middle evaporating temperatures. However, the cooling capacity was found to be comparable for R404A and R449A. The COP of the system using R449A was predicted to be higher by 10%, on average, than R404A over the middle evaporating temperature range. The modelling results also confirmed that the discharge temperature for R449A is higher than R404A under the same operating conditions, about 10 K on average.  
Figure 8: \(Cont.\)  
Figure 7: Experimental values for (**a**) COP, (**b**) cooling capacity, and (**c**) discharge temperature of the supermarket refrigeration system at LT application.