A steady-state simulation model of vapor injection heat pump systems with flash tank is developed. In the model

the vapor-injected compressor model is developed by establishing the theory-based explicit equations; the heat exchanger model is established using multi-zone method to reflect the characteristics of each phase zone; and a system iteration algorithm based on sequential module method is developed to solve the component models. The validation results show that

for the compressor model

the deviations of the mass flow rate and input power are within ±7% and ±5%

respectively; for the heat exchanger model

the deviations of the heat capacity and pressure drop are within ±3% and ±4%

respectively. Compared to the traditional heat pump system

the heat capacity is increased by 18.9% when the outdoor temperature is -20℃.