Based on the theoretical analysis on the working process of an air-source heat pump water heater with liquid injection in suction vapor

the relations between liquid injection ratio and heat pump performance parameters were established. An experiment was conducted under different conditions to investigate the influence of liquid injection on the performance of heat pump water heater. The predictions were verified with the experimental data. The results show that liquid injection could reduce the compressor discharge temperature

but it also reduced the heat capacity and heat coefficient and increase power input of the heat pump water heater. The highest injection ratio should be controlled below 5%. In addition

when the ambient temperature was below 20 ℃

liquid injection could reduce the compressor discharge temperature by above 10 ℃

while the decrease of the heat capacity

the increase of the power input and the decrease of the heat coefficient was less than 5%

1.5%

and 7%

respectively.