An additive heat transfer unit (AHTU) can be part of or added to an air source heat pump HVAC system. The heat pump system can include a compressor, an expansion valve, first and second air source heat exchangers, and a reversing valve. The system can have a cooling mode and a heating mode, such that in the cooling mode the first air source heat exchanger functions as an evaporator and the second air source heat exchanger functions as a condenser, this being reversed in the heating mode. The AHTU can include a liquid source heat exchanger that can be used to increase the efficiency of the system.

An air conditioner may include a plurality of indoor units and a plurality of outdoor units connected to the plurality of indoor units. Each of the plurality of outdoor units may include a plurality of outdoor heat exchangers. Each of the outdoor heat exchangers may include a plurality of heat exchanger parts. When a defrosting operation condition is satisfied during a heating operation, indicating that a defrosting operation should be performed the plurality of heat exchanger parts of the plurality of outdoor heat exchangers may successively perform the defrosting operation.

A multi-type air conditioner is provided that includes an outdoor unit having a liquid pipe through which a liquid refrigerant flows, and a gas pipe through which a gas refrigerant flows; a plurality of indoor units including a first indoor unit and a second indoor unit each connected to the liquid pipe and the gas pipe to circulate a refrigerant; a gas pipe connecting tube connecting the gas pipe and the plurality of indoor units so that a gas refrigerant flows therethrough; and a liquid pipe connecting tube connecting the liquid pipe and the plurality of indoor units so that a liquid refrigerant flows therethrough.

An outdoor expansion valve is provided for a liquid side pipe of an outdoor circuit. The outdoor circuit is provided with a liquid side bypass pipe that allows the liquid side pipe to communicate with a suction side of a compressor. Receiving a signal indicating that a refrigerant has leaked from an indoor circuit, an outdoor controller executes a refrigerant recovery control operation of operating the compressor with a liquid side control valve closed, and executes a valve control operation of opening a liquid side bypass valve of the liquid side bypass pipe in the refrigerant recovery control operation. As a result, the refrigerant can be recovered from an utilization-side circuit to a heat-source-side circuit while avoiding damage to the compressor, and the amount of refrigerant leaking from the utilization-side circuit can be reduced.

Provided is a multi-type air conditioner, including: an outdoor unit having a liquid pipe through which a liquid refrigerant flows, and a gas pipe through which a gas refrigerant flows; a plurality of indoor units comprising a first indoor unit and a second indoor unit each connected to the liquid pipe and the gas pipe to circulate a refrigerant; a gas pipe connecting tube connecting the gas pipe and the plurality of indoor units so that a gas refrigerant flows therethrough; and a liquid pipe connecting tube connecting the liquid pipe and the plurality of indoor units so that a liquid refrigerant flows therethrough. The first indoor unit may include: a first indoor heat exchanger comprising a first heat exchanger configured to perform heat exchange between indoor air and a refrigerant, and a second heat exchanger configured to perform heat exchange between indoor air and a refrigerant and arranged in a stacked fashion with the first heat exchanger; a first indoor fan configured to blow air to the first heat exchanger and the second heat exchanger; a first liquid branch pipe connecting the liquid pipe connecting tube and the first heat exchanger so that a refrigerant flows therethrough; a first gas branch pipe connecting the gas pipe connecting tube and the second heat exchanger so that a refrigerant flows therethrough; a first heat exchanger connecting pipe connected to the first heat exchanger so that a refrigerant flows therethrough; a second heat exchanger connecting pipe connected to the second heat exchanger so that a refrigerant flows therethrough; a return pipe having one side connected to the first gas branch pipe and the other side connected to the first heat exchanger connecting pipe and the second heat exchanger connecting pipe; a first indoor expansion valve disposed at the second heat exchanger connecting pipe, wherein an opening amount of the first indoor expansion valve is adjusted in response to an input signal from a controller to selectively expand a flowing refrigerant; and a first expansion valve disposed in the return pipe, wherein an opening amount of the first expansion valve is adjusted in response to an input signal from the controller to selectively expand a flowing refrigerant.

Since the multi-type air conditioner according to the present disclosure can operate the first heat exchanger as a condenser and the second heat exchanger as an evaporator among the indoor heat exchangers, it is possible to constantly operate the dehumidifying mode while maintaining a room temperature within a predetermined range.

An outdoor expansion valve is provided for a liquid side pipe of an outdoor circuit. The outdoor circuit is provided with a liquid side bypass pipe that allows the liquid side pipe to communicate with a suction side of a compressor. Receiving a signal indicating that a refrigerant has leaked from an indoor circuit, an outdoor controller executes a refrigerant recovery control operation of operating the compressor with a liquid side control valve closed, and executes a valve control operation of opening a liquid side bypass valve of the liquid side bypass pipe in the refrigerant recovery control operation. As a result, the refrigerant can be recovered from an utilization-side circuit to a heat-source-side circuit while avoiding damage to the compressor, and the amount of refrigerant leaking from the utilization-side circuit can be reduced.