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.

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, an oil return pipe that returns the oil discharged by the high-stage compressor to the low-stage compressor, and an oil discharge pipe that discharges the oil in the low-stage compressor. The low-stage compressor includes a compression part that compresses the refrigerant, a motor that drives the compression part, and a container that houses the compression part and the motor. The container forms a high-pressure space storing compressed refrigerant. Inside of the oil return pipe and inside of the oil discharge pipe are connected to the high-pressure 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.

An air conditioning apparatus is provided that may include an outdoor unit including a compressor and an outdoor heat exchanger and through which a refrigerant is circulated, an indoor unit through which a fluid, such as water is circulated, and at least one heat exchange device including a heat exchanger in which the refrigerant and the fluid are heat-exchanged with each other. The at least one heat exchange device may include a high-pressure guide tube that extends from a high-pressure gas tube of the outdoor unit so as to be connected to a first side of the heat exchanger, a low-pressure guide tube that extends from a low-pressure gas tube of the outdoor unit so as to be combined with the high-pressure guide tube, a liquid guide tube that extends from a liquid tube of the outdoor unit so as to be connected to a second side of the heat exchanger, and a solenoid valve installed in the high-pressure guide tube or the low-pressure guide tube to perform an opening and closing operation so as to allow the refrigerant to flow in a first direction. The high-pressure gas tube and the low-pressure gas tube may be connected to each other by a single gas tube, and when the indoor unit performs a cooling operation or a heating operation, flow of refrigerant in the first direction may be blocked in a state in which power is applied to the solenoid valve.

A circulation system of an air conditioner, an air conditioner, and an air conditioner control method. The circulation system of the air conditioner includes a compressor, a first heat exchanger, a second heat exchanger, and a gas-liquid separation assembly. The gas-liquid separation assembly, together with the compressor, the first heat exchanger, and the second heat exchanger, forms a loop; the gas-liquid separation assembly includes two or more gas-liquid separators which are connected in series; the gas-liquid separation assembly is configured to perform gas-liquid separation for refrigerant. Further, two or more-staged gas-liquid separation can be performed for the refrigerant flowing back to the compressor, so that a problem that return oil containing liquid in the compressor can be effectively solved.

A flow path switching mechanism (70) includes first to fourth flow paths (71, 72, 73, 74) and opening and closing mechanisms (V1, V2, V3, V4, 75, 76) that can each open and close a corresponding one of the flow paths (71, 72, 73, 74). A first connection point (C1) connecting an inflow portion of the first flow path (71) and an inflow portion of the second flow path (72) is connected to a discharge portion of a compression unit (30). A second connection point (C2) connecting an outflow portion of the first flow path (71) and an inflow portion of the third flow path (73) is connected to a gas-side end of a heat source heat exchanger (22). A third connection point (C3) connecting an outflow portion of the second flow path (72) and an inflow portion of the fourth flow path (74) is connected to a gas-side end of a second utilization heat exchanger (85, 93). A fourth connection point (C4) connecting an outflow portion of the third flow path (73) and an outflow portion of the fourth flow path (74), and a gas-side end of a first utilization heat exchanger (83) are connected to a suction portion of the compression unit (30).

Systems and methods for controlled subcooling of working fluid in a heating, ventilation, air conditioning and refrigeration (HVACR) system through a suction line heat exchanger are disclosed. The suction line heat exchanger may receive a first fluid flow travelling to a suction of the compressor in the HVACR system and second flow of working fluid that is travelling from a heat exchanger receiving the discharge of the compressor to an expansion device. Superheating of the first working fluid may be determined based on temperature measurements prior to and following the suction line heat exchanger. The superheating may be used to control the quantity of the second flow of working fluid introduced into the suction line heat exchanger, for example to maintain superheat that is below a threshold value. These systems may include chillers and heat pump systems, and methods may be applied to chillers or heat pump systems.

A heating and cooling system includes a heat exchange section to transfer heat between refrigerant and air in both a heating mode and a cooling mode. The heat exchange section includes at least two refrigerant passes. Refrigerant is circuited through the refrigerant passes in the same direction in both the heating mode and the cooling mode, so that the overall flow orientation between the refrigerant passes and the air is a counter-flow orientation in both the heating mode and the cooling mode.

A refrigeration cycle apparatus includes a heat exchanger, and a flow switching circuit configured to switch the heat exchanger to act as any one of an evaporator and a condenser, the flow switching circuit is configured to allow refrigerant to flow into the heat exchanger in the same direction both in a case where the heat exchanger acts as an evaporator and in a case where the heat exchanger acts as a condenser, the heat exchanger includes a path switching circuit including a plurality of paths, and the path switching circuit is configured to switch an order of the plurality of paths through which refrigerant flows between an order of the plurality of paths in the case where the heat exchanger acts as an evaporator and another order of the plurality of paths in the case where the heat exchanger acts as a condenser.

A second flow path switching apparatus includes a first distribution apparatus configured to distribute refrigerant to a plurality of refrigerant paths in a first heat exchange portion, a second distribution apparatus configured to distribute refrigerant to the plurality of refrigerant paths in the first heat exchange portion and a second heat exchange portion, and a switch portion configured to switch connection of a refrigerant inlet of a first heat exchange apparatus to the first distribution apparatus or to the second distribution apparatus and switch whether refrigerant which flows out of a refrigerant outlet of the first heat exchange portion is allowed to pass through the second heat exchange portion or to merge with refrigerant which flows out of a refrigerant outlet of the second heat exchange portion in accordance with whether an order of circulation of the refrigerant is a first order (cooling) or a second order (heating).