R404A has been widely used in refrigeration systems. However, since R404A has high GWP it will be regulated by 2020 in EU. R449A is one of the alternative refrigerants. In previous studies, a refrigeration system using R449A showed slightly lower cooling capacity and higher COP compared to that using R404A. However, it shows high compressor discharge temperature. The high compressor discharge temperatures can degrade the system reliability. Therefore, it is very important for a refrigeration system using R449A to obtain enough cooling capacity and to decrease high discharge temperature. However, studies concerned with increasing the performance of the refrigeration system using R449A are very limited. The flash tank vapor injection is one of the methods to enhance the performance of the refrigeration system using R449A. In the flash tank vapor injection cycle, the compressor discharge temperature decreased by the inter-cooling effect of the vapor injected to the compressor, and the cooling capacity improved by the flash tank.
In this study, a flash tank vapor injection refrigeration system using R449A is experimentally investigated in AHRI 1251 condition, which is a refrigeration system standard in United States of America. In this condition, the refrigeration system is evaluated using COP and annual walk-in energy factor (AWEF). The flash tank vapor injection cycle is superior to the single stage refrigeration cycle according to the compressor reliability at hot weather conditions. However, the COP and AWEF of the flash tank vapor injection cycle are lower than that of the single stage refrigeration cycle. The discharge temperature of the flash tank vapor injection cycle is lower than that of the single stage refrigeration cycle at A condition due to compressor cooling by the injected refrigerant. The flash tank vapor injection is not good for the COP and AWEF. However, it can decrease the compressor discharge temperature effectively and increase the cooling capacity.