Performance improvement using subcooling on freezer with R22 and R290 as refrigerant for various ambient temperatures

Abstract

Vapor compression refrigeration cycle (VCRC) is widely used in freezers. In a simple cycle of the VCRC, refrigerant in the condenser exit is at liquid saturated line. If the refrigerant temperature in the condenser exit is further cooled to the subcooled region results in an increase in the cooling capacity due to low vapor quality of refrigerant entering the evaporator. The lower the refrigerant quality entering the evaporator, the higher the cooling capacity on the evaporator. The increase in the cooling capacity enhances the freezer performance. Subcooling uses liquid suction heat exchanger (LSHX) is applied to transfer heat from the exit of the condenser (liquid line) to the suction of the compressor. Because the temperature of liquid line is higher than that of the suction line, heat flows from liquid line to the suction line, results in the decrease in temperature of the exit of the condenser and the increase in the suction temperature (superheating). Consequently, the use of the LSHX is always followed by superheating on the suction of the compressor. The superheating causes an increase in the input power. As a result, subcooling using the LSHX is not always followed by the increase in the coefficient of performance (COP) of the freezer, depending on the type of refrigerant used. Refrigerant of R22 is widely used as refrigerant in the freezers. Because R22 has a high global warming potential (GWP), the near future this refrigerant must be phased out. Refrigerant of R290 (propane) is recommended as a substitute refrigerant for R22. The R290 is a natural refrigerant, abundant and relatively cheaper than that of R22. This paper investigates the use of LSHX subcooling in freezer with the evaporating temperature of -20 °C for various ambient temperatures, viz., 30, 35 and 40 °C using R22 and R290 as working fluids. It is well known that the COP of the freezer decreases with an increase in the ambient temperature. As a result, the use of the LSHX subcooler is expected to enhance the COP of the freezer for the higher ambient temperatures. There are three parameters, viz., the cooling capacity, the discharge temperature and COP improvement will be investigated in the present study. Numerical results showed that the increase in subcooling and ambient temperature increase the cooling capacity and COP improvements. In addition, the cooling capacity and COP improvements of R290 using the subcooling of LSHX were higher than that of R22 for all ambient temperatures. Also, the increase in degree of subcooling enhanced the cooling capacity and COP improvements. For R22, at the ambient temperature above 35 °C is not recommended using LSHX subcooling in freezers, because it will increase the discharge temperature above 90 °C. However, the use of LSHX subcooling is recommended for all ambient temperatures in freezer using R290, because the discharge temperature on the freezer is still below 80 °C.