## 3 Supermarket Refrigeration System  
In this study, the measurement data from an indirect supermarket refrigeration system, as shown in Figure 2 (installed in 2005 in Sodertalje, Sweden), were used to compare the performance of the two refrigerants. Each supermarket refrigeration system consists of three parallel circuits to provide the required cooling capacities at low temperature (\(-35\)\({}^{\circ}\)C to \(-25\)\({}^{\circ}\)C) and medium temperature (\(-9\)\({}^{\circ}\)C to \(-5\)\({}^{\circ}\)C). A simplified diagram of the cooling systems is shown in Figure 3. As can be seen, the refrigeration system delivers cooling to the secondary refrigeration circuits working with CO\({}_{2}\) and propylene glycol/water mixture (38/62 per volume) in LT and MT circuits, respectively, and the secondary fluid distributes this further to cabinets to cool the products in them. The heat rejected from the connected cabinets is transferred to a dry cooler through a secondary fluid circuit and then is rejected to the ambient. In this study, the analyzed refrigeration system is one of the three refrigeration loops combined in parallel in the cooling system. The schematic of the supermarket refrigeration systems used in LT and MT applications is presented in Figure 4.  
Figure 1: Comparison between the main properties of R404A and R449A. Figure 4: Schematic of the supermarket refrigeration system: (**a**) LT and (**b**) MT circuits. Figure 3: A simplified drawing of the cooling system. Figure 2: Supermarket refrigeration system used in this study. Table 1 represents the details of the components of the refrigeration systems used in this study. Both systems are based on semi-hermetic reciprocating compressors (higher capacity for the MT circuit) and plate heat exchangers. The performance of the two refrigeration circuits using R404A and R449A was monitored and measured for 172 days, and the data at steady-state conditions were selected for this study. The refrigerant charge amount was 12.0 kg for R404A, and it was 12.5 kg when R449A was retrofitted into the supermarket refrigeration system. An electronic expansion valve was adjusted to obtain the correct superheating temperature, and the POE lubricant substitution was performed according to the manufacturer recommendation when retrofitting the refrigerant. The adjustment of the electronic expansion device and the amount of refrigerant charge provided approximately comparable superheating and subcooling degrees. In the LT circuit, the middle evaporating temperature (calculated as the sum of 1/3 of the dew point temperature and 2/3 of the bubble temperature at the evaporating pressure) varied between \(-40\)\({}^{\circ}\)C and \(-31\)\({}^{\circ}\)C for both R449A and R404A systems. The middle condensing temperature (vapor quality 0.5) was slightly higher in the R404A system (between 21 \({}^{\circ}\)C and 47 \({}^{\circ}\)C) than that of the R449A (between 13 \({}^{\circ}\)C and 43 \({}^{\circ}\)C). The subcooling degree was observed to be \(17+-7\) K for the R404A system, while most of the measured subcooling temperature was \(29+-6\) K for the R449A. On average, the R449A system operated at higher subcooling temperature than the system using R404A at LT application. Both R404A and R449A systems operated with comparable superheating degrees, varying between 8 K and 11 K.  
During the MT system operation, it was observed that the majority of the measured values for the subcooling and superheating temperatures were 3 \(\pm\) 2 and 7 \(\pm\) 2 K, respectively. The measured superheating and subcooling temperatures were slightly lower, 1.5 K on average, for when R449A was used as the working refrigerant compared to when the system operated with R404A. A wide range of middle condensing and middle evaporating temperatures was observed when the medium temperature cooling system operated with R404A and R449A. The system operated with slightly higher middle evaporating and middle condensing temperature with R404A compared to R449A.