Thermodynamic mechanism of high energy performance of air source heat pump with coupled liquid-storage to gas-liquid separator

•Transient loss and defrosting loss of the air source heat pump system coupled with the liquid storage gas–liquid separator were identified.•A semi theoretical model based on experimental data for energy efficiency evaluation of air source heat pump system coupled with liquid storage gas–liquid separator was proposed.•Evaluated energy efficiency of the air source heat pump coupled with the liquid storage gas–liquid separator was higher than that of the traditional air source heat pump.•Path of energy efficiency improvement of air source heat pump system coupled with liquid storage gas–liquid separator was proposed.