Refrigerant migration during startup of a split air conditioner in heating mode

•Refrigerant migration during startup of air conditioner was studied in heating mode.•Refrigerant migration after shutdown causes the condenser lack of refrigerant.•Control methods are proposed to improve startup heating performance.•Increasing the refrigerant mass in the condenser can supply warm air more rapidly. During winters, room air conditioners are generally expected to supply occupants with hot air rapidly following startup. In this study, the refrigerant migration characteristics during startup of a split air conditioner were experimentally investigated in heating mode. The transient refrigerant distribution inside main components was measured by using the quick-closing valve technique. The high and low side pressures and temperatures of the system were also investigated under the given operating conditions. All experiments were carried out in psychrometric rooms. On this basis, two control methods during the startup and shutdown process were proposed and tested. It was verified that increasing the refrigerant mass in the condenser prior to restarting can benefit the establishment of high pressure and supply occupants with air at a comfortable temperature more rapidly.