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The cascade refrigeration systems (CRS) used in hypermarkets and supermarkets, which are used by many people, have been employing R744 for the low-temperature cycle (LTC) and R404A for the high-temperature cycle (HTC) due to environmental and public safety issues. However, the use of R404A is limited due to its high GWP, and therefore research on alternative refrigerants is necessary. Nevertheless, there is no detailed study in the literature that compares and analyzes the three refrigerants for practical design by applying R744 for LTC and R404A, R448A, and R449A for HTC in CRS. Therefore, this study aims to provide data for the practical detailed design of an alternative system to R744/R404A CRS. Under standard conditions, we analyzed how the exergy destruction rate (EDR) and exergy efficiency (EE) of the system and the EDR of each component change when the important factors affecting CRS (degree of superheating (DSH), degree of subcooling (DSC), and internal heat exchanger (IHX) efficiency of HTC, DSH of LTC, condensation temperature (CT), evaporation temperature (ET), cascade evaporation temperature (CET), and temperature difference of CHX) are varied over a wide range. The main conclusions are as follows. (1) Under the given constant conditions, the smallest change in system EDR based on R448A is DSH of HTC (decreased by 0.07–0.1 kW), followed by IHX of HTC (decreased by 0.12–0.3 kW), DSH of LTC (increased by 0.19–0.25 kW), DSC of HTC (decreased by 0.59–0.69 kW), temperature difference of CHX (increased by 1.57–1.83 kW), CET (decreased and then increased by 0.67–4.43 kW), CT (increased by 1.49–3.9 kW), ET (decreased by 2.39–4.61 kW). (2) The highest change rate of system EE based on R448A is CET (increased and then decreased by 1.38–8.28%), followed by temperature difference of CHX (decreased by 2.96–3.16%), ET (increased and then decreased by 0.63–2.75%), DSC of HTC (increased by 1.26–1.34%), CT (increased and then decreased by 0.24–1.12%), IHX of HTC (increased by 0.11–1.02%), DSH of LTC (decreased by 0.35–0.49%), and DSH of HTC (increased by 0.14–0.19%). [ABSTRACT FROM AUTHOR]

The R744/R404A cascade refrigeration system (CRS) has been widely used in supermarkets and hypermarkets, but due to the refrigerant regulation of R404A, research on alternative refrigerants is necessary. In addition, although there have been quite a few studies on R448A and R449A, which are well-known alternatives to R404A, few studies have analyzed the performance coefficients of the three refrigerants, and the studies that have analyzed them are not based on enough variables. Therefore, we aimed to understand the performance characteristics of CRS combined with an internal heat exchanger (IHX) by applying R744 for the low-temperature cycle (LTC) and R404A, R448A, and R449A for the high-temperature cycle (HTC). The analysis method was to analyze the coefficient of performance (COP) and mass flow rate (MFR) of the three refrigerants according to the degree of subcooling (DSC) and degree of superheating (DSH), IHX efficiency, temperature difference in the cascade heat exchanger (CHX), condensation temperature (CT), evaporation temperature (ET), and cascade evaporation temperature (CET). The purpose of this study is to compare R448A and R449A, alternative refrigerants to R404A, in an R744/R404A CRS, with R404A to provide sufficient data for optimal CRS design. The comparison results are as follows: (1) Compared with R404A, the MFR of R448A and R449A are 67.27–77.6% and 70.05–80.80%, respectively, under the same conditions. Therefore, R448A and R449A are economically favorable because they have less refrigerant charge than R404A, and R448A is more favorable than R449A. (2) The R744/R448A CRS is stable and performs better than the R744/R449A CRS in places with large changes in the surrounding environment. [ABSTRACT FROM AUTHOR]

Although the R404A indirect refrigeration system (IRS) with an internal heat exchanger (IHX) and R744 as the secondary fluid has potential applications in supermarkets and hypermarkets, the exergy characteristics of this IRS have not been extensively investigated. In this study, the factors affecting the R744 exergy characteristics (degree of subcooling (DSB) and degree of superheating (DSP) of the R404A cycle, DSP of the R744 cycle, condensation temperature (CT) and cascade evaporation temperature (CET), and IHX efficiency) were experimentally evaluated to obtain basic data for the design of R404A IRS with R744 as the optimal secondary fluid. The main results can be summarized as follows: (1) Under given conditions, the smallest change in the system exergy destruction rate (EDR) according to the change in each parameter is the DSP of the R744 cycle (0.3–1%), followed by the DSB of the R404A cycle (6.1–8.8%), the IHX efficiency of the R404A cycle (3.8–14.3%), the DSP of the R404A cycle (11.7–15.9%), the CET (29.4–41.9%), and the CT (35–47%). (2) Also, in terms of the exergy efficiency of system (EES), the largest value was obtained for the DSP of the R404A cycle (2.4–12.7%), followed by the IHX efficiency of the R404A cycle (3–10.2%), the CET (2.2–8.7%), the CT (4–6.9%), the DSB of the R404A cycle (2.7–6.2%), and the DSP of the R744 cycle (0.04–1.2%). (3) In order to lower the system EDR, DSP, DSB, and IHX efficiency of the R404A cycle, the CET must be increased to the maximum, and to lower the DSP of the R744 cycle, the CT must be reduced to the minimum. [ABSTRACT FROM AUTHOR]

In this study, the performance characteristics of an R404A indirect refrigeration system (IRS) applied to an internal heat exchanger (IHX) is evaluated for supermarkets and hypermarkets. In a direct expansion system, R404A is the primary refrigerant and R744, a brine, is the secondary fluid. While there are abundant studies analyzing the theoretical performance of IRS, experimental research on IRS is lacking, and there are no papers that address the results of changes in the IHX in detail. In this study, the results achieved by modifying various parameters are experimentally evaluated to provide fundamental data for designing the optimal IRS. In the main results, looking at the trend of the increase in IHX efficiency, the change is very minimal when the efficiency is above 50%, so it is ideal to apply an IHX efficiency of about 50% considering economics and COP, etc. Applying the results in this study enables the operation and maintenance of IRSs as an eco-friendly system by achieving energy efficiency through optimizing the system coefficient of performance and securing economic feasibility by minimizing the R404A charging amount of the refrigeration cycle. To serve supermarkets and hypermarkets, R744 as a secondary fluid may help to realize an ecologically friendly, compact IRS system with a high heat transfer coefficient that can operate at low temperatures (−35 to 5 °C). [ABSTRACT FROM AUTHOR]

In this paper, R404 refrigeration system is evaluated to understand the exergy characteristics of an indirect refrigeration system for R404A that adopted CO2 as a secondary refrigerant. This provides basic data for the optimal design of indirect refrigeration system for the R404A. The results are summarized as follows. It was confirmed that the system's exergy loss increased as the R404A condensation temperature, the CO2 cooler temperature difference, and the CO2 mass flow rate increased under a fixed experimental condition. However, the system's exergy loss decreased as the CO2 evaporation temperature increased. It was also found that the exergy loss of the R404A refrigeration system was higher than that of the CO2 secondary refrigerant system. It was also confirmed that total exergy loss of the R404A refrigeration system and the indirect refrigeration system tended to be inversely related to the coefficient of performance. Regardless of any experimental conditions, the exergy loss rate of components was the largest in the compressor, followed by the R404A condenser, the expansion valve, the internal heat exchanger, the CO2 cooler, the CO2 evaporator and the pump. Therefore, in conclusion, it is necessary to reduce exergy loss in the compressor and the R404A condenser to improve the overall performance of this system. [ABSTRACT FROM AUTHOR]