Air-conditioning apparatus

Abstract

An air-conditioning apparatus includes a refrigerant circuit in which a compressor, an indoor heat exchanger, a first expansion device, an outdoor heat exchanger, and a flow switching device are sequentially connected to each other; a hot gas bypass pipe coupling a discharge port of the compressor and the flow switching device to each other; and a controller. The outdoor heat exchanger includes an upper heat exchanger and a lower heat exchanger having passages in parallel with each other. The outdoor heat exchanger includes a plurality of hairpin pipes, which are part of a heat transfer pipe. When the upper heat exchanger is defrosted, all hairpin pipes that are located at a lowermost step of the upper heat exchanger are used as refrigerant inlets. When the lower heat exchanger is defrosted, all hairpin pipes that are located at an uppermost step of the lower heat exchanger are used as refrigerant inlets.

1 . An air-conditioning apparatus comprising:
 a refrigerant circuit in which a compressor, an indoor heat exchanger, a first expansion device, an outdoor heat exchanger, and a flow switching device are sequentially connected to each other by pipes and through which refrigerant circulates, the compressor being configured to compress and discharge the refrigerant, the indoor heat exchanger being configured to allow the refrigerant to exchange heat with indoor air, the first expansion device being configured to reduce pressure of the refrigerant, the outdoor heat exchanger including an upper heat exchanger and a lower heat exchanger having passages in parallel with each other and being configured to allow the refrigerant to exchange heat with outdoor air, the flow switching device being configured to switch flows of the refrigerant toward the upper heat exchanger and the lower heat exchanger;   a hot gas bypass pipe coupling a discharge port of the compressor and the flow switching device to each other; and   a controller configured to perform a heating-defrosting operation for alternately defrosting the upper heat exchanger and the lower heat exchanger while performing a normal heating operation,   the outdoor heat exchanger including a plurality of hairpin pipes, which are part of a heat transfer pipe,   when the upper heat exchanger is defrosted,   among the plurality of hairpin pipes, all hairpin pipes located at a lowermost step of the upper heat exchanger being used as refrigerant inlets,   when the lower heat exchanger is defrosted,   among the plurality of hairpin pipes, all hairpin pipes located at an uppermost step of the lower heat exchanger being used as refrigerant inlets.   
     
     
         2 . The air-conditioning apparatus of  claim 1 , further comprising:
 a second expansion device provided at the hot gas bypass pipe;   a first boundary-temperature detection device configured to directly or indirectly detect a temperature at the hairpin pipes located at the lowermost step of the upper heat exchanger; and   a second boundary-temperature detection device configured to directly or indirectly detect a temperature at the hairpin pipes located at the uppermost step of the lower heat exchanger,   wherein the controller is configured to control, based on the temperature detected by the first boundary-temperature detection device and the temperature detected by the second boundary-temperature detection device, the second expansion device such that both the temperature at the hairpin pipes located at the lowermost step of the upper heat exchanger and the temperature at the hairpin pipes located at the uppermost step of the lower heat exchanger are higher than 0 degrees C. during the heating-defrosting operation.