An outdoor unit, connected with indoor units by pipes to constitute a refrigerant circuit, includes a compressor configured to compress and discharge refrigerant, a plurality of parallel heat exchangers configured to allow heat exchange between air and the refrigerant, a first defrosting pipe serving as a flow path for branching a part of the refrigerant discharged by the compressor and allowing the refrigerant to flow into the parallel heat exchanger to be defrosted for defrosting, a first expansion device configured to decompress the refrigerant passing through the first defrosting pipe, a second expansion device configured to adjust the pressure of the refrigerant that passed through the parallel heat exchanger to be defrosted, and a controller configured to control the second expansion device such that the pressure of the refrigerant that passed through the parallel heat exchanger to be defrosted falls within a predetermined range.

An air-conditioning apparatus includes a main circuit in which a compressor, an indoor heat exchanger, a first flow control device, and a plurality of parallel heat exchangers connected in parallel to each other are sequentially connected via a pipe to allow refrigerant to circulate, a first defrost pipe that branches a part of the refrigerant discharged from the compressor and allows the refrigerant to flow into the parallel heat exchanger to be defrosted among the plurality of parallel heat exchangers, a expansion device provided in the first defrost pipe and configured to depressurize the refrigerant discharged from the compressor, and a connection switching device that allows the refrigerant flowing out of the parallel heat exchanger to be defrosted to flow into the main circuit at a position upstream of the parallel heat exchangers other than the parallel heat exchanger subject to defrosting.

A heat pump system for conditioning regeneration air from a space is provided. The heat pump system is operable in a winter mode and/or a summer mode, and may be selectively operated in a defrost mode or cycle. During a defrost mode, hot refrigerant may be used to directly and sequentially defrost the regeneration air heat exchanger. A compressor may be configured to be overdriven during a defrost cycle.

An air-conditioning apparatus includes a refrigerant circuit and a controller. The refrigerant circuit includes a main circuit and a bypass circuit. The bypass circuit is connected, by a pipe, to each of a plurality of parallel outdoor heat exchangers via a defrosting refrigerant pressure-reducing device, a defrosting flow passage switching device, and a backflow prevention device. The controller switches a flow passage for use in introduction of refrigerant using the defrosting flow passage switching device, to select one of the plurality of parallel outdoor heat exchangers as a defrosting target to be defrosted; and supplies defrosting refrigerant whose pressure is reduced by the defrosting refrigerant pressure-reducing device to the selected one of the plurality of parallel outdoor heat exchangers.

An improved refrigeration cycle defrosting system and method is disclosed. The device uses operation of a compressor to supply heat for the defrosting process without relying on deviation of a hot refrigerant gas from the compressor outlet or any other heating device.

Even in the case of a large outdoor heat exchanger (24), it is possible to completely remove frost without reducing the defrosting effect. Provided are: a distributor (25) installed between the outdoor heat exchanger (24) and an expansion valve (26); a plurality of distribution pipes (252) of which one end is connected to the distributor (25) and of which the other end is connected to a plurality of heat transfer pipes (241) of the outdoor heat exchanger (24); and a bypass pipe (30) of which one end is connected to a compressor (23) and diverges on the way, and simultaneously of which the respective plurality of other ends are connected to a connection part between the distribution pipe (252) and the heat transfer pipe (241) or in the vicinity thereof.

An alternating type heat pump has first to third rows of outdoor unit coils adapted to selectively perform the functions of an evaporator and a condenser in accordance with the outdoor conditions and the load variations, thereby improving the performance of the heat pump, and is capable of allowing the first to third rows of outdoor unit coils to be operated as a condenser in an alternating manner under the conditions where frost on the outdoor unit coils may be formed especially in winter seasons, thereby basically preventing the conditions on which the frost is formed.

An air conditioner operable even in a low-load cooling or heating mode is provided. The air conditioner may include a compressor that compresses a refrigerant, a main outdoor heat exchanger that condenses the refrigerant in a cooling mode and that evaporates the refrigerant in a heating mode, an indoor heat exchanger that evaporates the refrigerant in the cooling mode while condensing the refrigerant in the heating mode, a switch that guides the refrigerant discharged from the compressor to the main outdoor heat exchanger in the cooling mode and that guides the refrigerant discharged from the compressor to the indoor heat exchanger in the heating mode, and a sub outdoor heat exchanger that evaporates a portion of the refrigerant condensed in the main outdoor heat exchanger in a low-load cooling mode and that condenses a portion of the refrigerant discharged from the compressor in a low-load heating mode.

An improved refrigeration cycle defrosting system and method is disclosed. The device uses operation of a compressor to supply heat for the defrosting process without relying on deviation of a hot refrigerant gas from the compressor outlet or any other heating device.

An air conditioner, and a control method, including a compressor to compress a refrigerant; an outdoor heat exchanger; a first four-way valve between a discharge port of the compressor and an upper inlet of the outdoor heat exchanger; a second four-way valve between the discharge port of the compressor and a lower inlet of the outdoor heat exchanger; and a controller electrically connected to the compressor and the first four-way valve and the second four-way valve to control the first and second four-way valves to perform a first defrosting operation which defrosts an upper and a lower portion of the outdoor heat exchanger during a heating operation, and control the first and second four-way valves to perform a second defrosting operation which operates the upper portion as an evaporator, and operates the lower portion as a condenser, based on a detected need for additional defrosting of the lower portion.