A refrigerant cycle apparatus includes a main refrigerant circuit, a bypass circuit, and a controller. The main refrigerant circuit includes a compressor, a heat source-side heat exchanger, a heat source-side expansion valve, and a utilization-side heat exchanger. The controller performs a second operation of opening a hot gas bypass valve in a state in which the compressor is driven before performing a first operation in which the heat source-side heat exchanger serves as a heat absorber for the refrigerant and the utilization-side heat exchanger serves as a radiator for the refrigerant. In the first operation or the second operation, when a difference between a pressure of the refrigerant on the discharge side of the compressor and a pressure of the refrigerant on the suction side of the compressor becomes larger than a first predetermined value, the controller decreases the number of revolutions of the compressor.

A refrigeration cycle apparatus includes a hot water tank, a heat source for heating water in the hot water tank, and a refrigeration cycle circuit that includes an indoor heat exchanger, a heat-source heat exchanger, and a water heat exchanger. The indoor heat exchanger may operate as a condenser. When an outside temperature is greater than a specified temperature, the refrigeration cycle apparatus operates in a first state in which the heat-source heat exchanger operates as an evaporator and the water heat exchanger does not operate. When the outside temperature is less than the specified temperature, the refrigeration cycle apparatus operates in a second state in which the water heat exchanger operates as an evaporator and refrigerant therein absorbs heat from water in the hot water tank heated by the heat source and the heat-source heat exchanger does not operate.

A refrigeration cycle apparatus includes a heat source unit configured to supply refrigerant, a first distribution unit and a second distribution unit respectively connected to the heat source unit, and a distribution pipe located between the heat source unit and the first distribution unit and the second distribution unit for distributing the refrigerant flowing from the heat source unit into the first distribution unit and the second distribution unit. Further, the first distribution unit and the second distribution unit individually include a heat exchanger configured to serve as a condenser. Further, if the refrigerant flowing through the distribution pipe is unevenly distributed into the first distribution unit and the second distribution unit, a degree of subcooling at an outlet of the heat exchanger of one of the first distribution unit and the second distribution unit of which the distributed refrigerant is of high quality is increased.

A multistage compression system uses refrigerant and oil. The multistage compression system includes a low-stage compressor that compresses the refrigerant, a high-stage compressor that further compresses the refrigerant compressed by the low-stage compressor, refrigerant pipes that-introduce the refrigerant compressed and discharged by the low-stage compressor into a suction part of the high-stage compressor, a pressure reducing element disposed between the refrigerant pipes, an accumulator disposed between the refrigerant pipes at a downstream side of the pressure reducing element and at an upstream side of the high-stage compressor, and an oil discharge pipe. The oil discharge pipe discharges the oil in the low-stage compressor. The oil discharge pipe connects the low-stage compressor and a portion of the refrigerant pipes. The portion of the refrigerant pipes is on a downstream side of the pressure reducing element and an upstream side of the accumulator.

A multistage compression system uses refrigerant and oil. The multistage compression system includes a low-stage compressor that compresses the refrigerant, a high-stage compressor that further compresses the refrigerant compressed by the low-stage compressor, refrigerant pipes that introduce the refrigerant compressed and discharged by the low-stage compressor into a suction part of the high-stage compressor, an intercooler, and an oil discharge pipe. The intercooler cools the refrigerant discharged by the low-stage compressor before the refrigerant is sucked into the high-stage compressor. The intercooler is disposed between the refrigerant pipes. The oil discharge pipe discharges the oil in the low-stage compressor. The oil discharge pipe connects the low-stage compressor and a portion of the refrigerant pipes. The portion of the refrigerant pipes is on an upstream side of the intercooler.

Disclosed is a four-way valve including a housing having a refrigerant filling chamber formed therein, a high pressure pipe hole formed on a bottom surface of the housing and coupled to a high pressure pipe through which refrigerant discharged from the compressor flows, a first pipe hole formed on an upper surface of the housing and coupled to a first pipe extending to a first heat exchanger, a second pipe hole formed on the upper surface of the housing and coupled to a second pipe extending to a second heat exchanger, a low pressure pipe hole formed on the upper surface of the housing and configured to allow the refrigerant to be collected to the compressor, and a switching guide configured to rotate to allow the low pressure pipe hole to selectively communicate with the first pipe hole or the second pipe hole.

A multi-split system and a liquid return prevention control method thereof during defrosting of the multi-split system. The method includes the following steps: when the multi-split system is in heating operation, detecting gas exhaust pressure (PC), gas return pressure (PE) and gas exhaust temperature (TP) of a compressor in real time; if an outdoor unit receives a defrosting instruction, sending a defrosting signal to a diverter and heating indoor units in multiple indoor units, controlling, by means of the diverter, a throttling element (EXV2) to close before first reversing of a four-way valve and last for a pre-set time, so as to reduce the amount of a refrigerant returned to the outdoor unit; and regulating the opening of the throttling element (EXV2) according to the gas exhaust pressure (PC), gas return pressure (PE) and gas exhaust temperature (TP) during defrosting operation of the multi-split system, so that the risk of liquid return occurred to the compressor during a defrosting process, and the safety and reliability of the system are greatly improved.

A method of conditioning air includes controlling a secondary refrigerant flow control valve to select between a first mode in which refrigerant flows from a discharge line to a main refrigerant flow control valve, and a second mode in which refrigerant flows from the discharge line to a gas reheat heat exchanger and then flows to the main refrigerant flow control valve. A heat transfer medium flow control valve is controlled to adjust the flow of the heat transfer medium into a heat source side heat exchanger. The heat transfer medium flow control valve allows the heat transfer medium to flow to the heat source side heat exchanger when the secondary refrigerant flow control valve is in the first mode, and adjusts the flow of the heat transfer medium to the heat source side heat exchanger when the secondary refrigerant flow control valve is in the second mode.

An air conditioner includes: a heat-source-side unit including a heat-source-side heat exchanger; a use-side unit, in a space to be air conditioned, including a use-side heat exchanger and a use-side fan that supplies air to the use-side heat exchanger; and a connection pipe that connects the heat-source-side unit to the use-side unit. The air conditioner performs air-conditioning of the space by circulating refrigerant in a refrigerant circuit including: the heat-source-side heat exchanger; the use-side heat exchanger; and the connection pipe. The refrigerant circuit further includes: a first pipe made of a first metal material; a second pipe made of a second metal material; and a connecting portion between the first pipe and the second pipe. The connecting portion is in an unventilated space.

An air conditioning apparatus may include an outdoor unit through which a first fluid, such as refrigerant circulates, an indoor unit through which a second fluid, such as water circulates, a heat exchange device which is configured to connect the outdoor unit to the indoor unit and in which the first fluid and the second fluid are heat-exchanged with each other, a first inner tube which is configured to connect the outdoor unit to the heat exchange device and through which the first fluid at high-pressure flows, a second inner tube which is configured to connect the outdoor unit to the heat exchange device and through which the first fluid at low-pressure flows, and a third inner tube which is configured to connect the outdoor unit to the heat exchange device and through which the first fluid in liquid form flows. The heat exchange device may include a bypass tube configured to bypass the second inner tube and a flow control valve provided in the bypass tube.