The results obtained showed that RE170 and R510A have similar saturation vapour pressure characteristics and thermophysical properties with R134a. The Energy performance of both R510A and RE170 was better than that of R134a. The average COPs of R510A and RE170 are higher than that of R134a by 20.7 and 13.1%, respectively. The lowest discharge temperature and energy consumption, and highest COP of the system were obtained using R510A. Generally, R510A and RE170 performed better than R134a; their energy consumptions are 20.4 and 14.1% less than that of R134a, respectively. Therefore, they can be used as drop-in substitutes in the existing R134a refrigeration systems.