The principle and various system types for implementing refrigerant injection technology

such as the liquid injection cycle

subcooler vapor injection cycle

and flash tank vapor injection cycle

are introduced to optimize the performance of air source heat pumps operating under low-temperature and high-temperature conditions. A summary of research conducted in line with the various refrigerant injection technologies aimed at improving the system performance and related structural and operational parameter optimizations

both on the systemand component level

was provided herein. Moreover

experiment and simulation studies on alternative refrigerant on R32

R410A

R417A

R1234yf

and R290/R600a for various types of system with refrigerant injection technology were also reviewed. The progress of research for compressors’ structural improvement was additionally covered

involving those of scroll and rotary compressors. A commonly agreed point in vapor injection technology is its ability to enhance the heating performance of air source heat pump operating at low temperatures. Nowadays

an increasing number of researches are focusing on how new forms of system with refrigerant injection technology can improve the heating performance of heat pumps. However

seldom deal on enhancing the cooling performance operation at high temperatures can be found. Finally

in terms of the development situations and difficulties encountered in implementing refrigerant injection technology

the research and development directions of refrigerant injection technology are envisioned.