Abstract
This study evaluates the performance of an R744/R404A cascade refrigeration system (CRS) with internal heat exchangers (IHE) in supermarkets. R744 is used as the refrigerant in a low-temperature cycle, and R404A is used as the refrigerant in a high-temperature cycle. In previous studies, there are many studies including theoretical performance analysis of the CRS. However, experimental studies on the CRS are lacking, and experimental research on the R744/R404A system with an IHE is scarce. Therefore, this study provides basic data for optimal refrigeration system design by experimentally evaluating the results of modifying various parameters. The operating parameters considered in this study include subcooling and superheating, condensing and evaporating temperature, cascade evaporation temperature, and IHE efficiency in the R744 low- and R404A high-temperature cycle. The main results are summarized as follows: (1) By applying the results of this study, energy efficiency is achieved by optimizing the overall coefficient of performance (COP) of the CRS, and the refrigerant charge of the R404A cycle is minimized and economic efficiency is also obtained, enabling operation and maintenance as an environment-friendly system. (2) When designing the CRS, finding the cascade evaporation temperature that has the optimum and maximum COP according to the refrigerant combination should be considered with the highest priority.
Highlights
In the field of supermarket refrigeration technology, the hydrofluorocarbon (HFC)refrigerant R404A has been widely adopted as an alternative to R22 refrigerant [1]
R744 (CO2) refrigerants are predominantly applied to the low-temperature side of the cascade refrigeration system (CRS), with R290, R717, and R404A refrigerants predominantly applied to the high-temperature side [3]
After operating the R404A refrigeration cycle, when the R744 condensation pressure drops to a certain pressure, the R744 compressor is turned on, and the low-temperature expansion valve and inverter frequency are adjusted for the R744 compressor to control the evaporation temperature and mass flow rate of the CRS
Summary
In the field of supermarket refrigeration technology, the hydrofluorocarbon (HFC)refrigerant R404A has been widely adopted as an alternative to R22 refrigerant [1]. In the field of supermarket refrigeration technology, the hydrofluorocarbon (HFC). The R744/R404A CRS has a 25% higher coefficient of performance (COP) than single-stage compression refrigerators using only R404A [2]. R744 (CO2) refrigerants are predominantly applied to the low-temperature side of the CRS, with R290 (propane), R717 (ammonia), and R404A refrigerants predominantly applied to the high-temperature side [3]. Despite its high global warming potential (GWP), R404A is considered a safe high-temperature refrigerant for supermarket CRSs [5] because R404A is classified into the. A1 group by the ASHRAE 34 safety group [6]. It can still be used in countries such as developing countries despite its high GWP. Developed countries recommend using R448A and R449A as replacement refrigerants for R404A because they are not available in the near future or present
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