A cooling system drains oil from low side heat exchangers to vessels and then uses compressed refrigerant to push the oil in the vessels back towards a compressor. Generally, the cooling system operates in three different modes of operation: a normal mode, an oil drain mode, and an oil return mode. During the normal mode, a primary refrigerant is cycled to cool one or more secondary refrigerants. As the primary refrigerant is cycled, oil from a compressor may mix with the primary refrigerant and become stuck in a low side heat exchanger. During the oil drain mode, the oil in the low side heat exchanger is allowed to drain into a vessel. During the oil return mode, compressed refrigerant is directed to the vessel to push the oil in the vessel back towards a compressor.

A refrigeration cycle apparatus includes: a refrigerant circuit; an oil reservoir; a first pipe that connects the oil separator and the oil reservoir, the first pipe being configured to send the refrigeration oil separated by the oil separator to the oil reservoir; a first valve provided at the first pipe; a second pipe that connects the oil reservoir and a suction side of the compressor; a second valve provided at the second pipe; a third pipe that connects the oil reservoir and the suction side of the compressor at a position lower than a position at which the second pipe is connected to the oil reservoir; and a third valve provided at the third pipe. The first to third valves are closed in a non-operational period of the compressor.

A technique that allows a plurality of series-connected compressors in a refrigerant circuit to have equal amounts of oil in a more versatile manner is provided. A compression apparatus according to an embodiment in the disclosure includes series-connected compressors 10, 20 in a refrigerant circuit 1 that is to circulate a refrigerant; an oil separator 30 is provided in a discharge passage 50 of the compressor 10 of the compressors 10, 20, and separates oil from the refrigerant discharged from the compressor 10 and causes the refrigerant separated from the oil to flow downstream (intake passage 80); an oil return passage 70 returns the oil separated by the oil separator 30 to the compressor 10 neighboring upstream; an oil discharge outlet 10A is provided in the compressor 10; and an oil discharge passage 60 connects the oil discharge outlet 10A to an inlet of the oil separator 30.

A refrigerant circuit includes a compressor, a high-pressure side heat exchanger, a decompressor, and a low-pressure side heat exchanger, which are annularly interconnected by a refrigerant pipe, and is configured to circulate refrigerant. The refrigerant circuit performs an oil recovery operation based on an operation history of the compressor ring a normal operation of the refrigerant circuit and an amount of oil in the compressor detected by an oil depletion sensor.

A cooling system uses P-traps to address the oil return issues that result from a vertical separation between a compressor and a heat exchanger. Generally, the vertical piping that carries the refrigerant from the compressor to the heat exchanger includes P-traps installed at various heights to capture oil in the refrigerant and to prevent that oil from flowing back to the compressor. T-connections are coupled to the P-traps to allow the oil to drain out of the P-traps. The oil may then be collected and returned to the compressor.

This refrigeration apparatus (1) includes a main refrigerant circuit (2) including a positive displacement compressor (4), a condenser (6), an expansion valve (8), and an evaporator (10), through which a refrigerant circulates successively in a closed loop circulation, and a lubrication refrigerant line (18) connected to the main refrigerant circuit (2) between the condenser (6) and the expansion valve (8) or to the condenser (6), in which circulates a portion of the refrigerant of the main refrigerant circuit (2) and connected to the compressor (4) for lubrication of said compressor (4) with the refrigerant. The refrigeration apparatus includes a lubrication refrigerant tank (20) connected to the lubrication refrigerant line (18) upstream the compressor (4), the lubrication tank (20) being configured to store liquid refrigerant for lubrication of the compressor (4) and the lubrication refrigerant tank (20) comprises means (32, 34; 38, 40) to cool down the refrigerant.

Provided is a refrigeration apparatus capable of appropriately supplying oil separated by oil separators to compressors according to the situation. The refrigeration apparatus includes N refrigeration units each including a compressor, an oil separator, an oil return pipe, and a heat dissipation heat exchanger; N pressure reducing valves each connected to the heat dissipation heat exchanger of a corresponding one of the N refrigeration units; and an oil return control mechanism that controls a return destination of the oil separated by the oil separators of the N refrigeration units. The oil return control mechanism includes an oil supply pipe that connects the oil return pipes of the N refrigeration units to each other, and a flow control mechanism, which controls a flowing condition of oil in the oil supply pipe, disposed in the oil supply pipe.

Provided is a refrigeration apparatus capable of appropriately supplying oil separated by oil separators to compressors according to the situation. The refrigeration apparatus includes refrigeration units each including a compressor, an oil separator, an oil return pipe, and a heat dissipation heat exchanger; a pressure reducing valve connected to the heat dissipation heat exchangers; and an oil return control mechanism controlling a return destination of the oil separated by the oil separators. The oil return control mechanism includes an oil supply pipe connecting the oil return pipes; a flow control mechanism, controlling a flowing condition of oil in the oil supply pipe, disposed in the oil supply pipe; and an ejection control mechanism, controlling an ejection condition of oil ejected from the oil separator, disposed in each oil return pipe at a position closer to the oil separator than a connection position with the oil supply pipe is.

A multi-air conditioner for heating/cooling operations, including at least one indoor unit for heating/cooling operations including an indoor heat exchanger; and an outdoor unit for heating/cooling operations including a compressor, an outdoor heat exchanger, and a switching unit configured to be disposed in a discharge side of the compressor to switch a flow of refrigerant. The outdoor unit includes a receiver that selectively stores refrigerant or oil according to a cooling or heating operation mode and provides the stored refrigerant or oil to the compressor. Accordingly, in the accumulator of the multi-air conditioner using the receiver, the receiver which is not used in the heating mode may be converted and used for oil storage, thereby preventing oil burnout without adding structure.

A system for measuring oil circulation ratio in a vapor-compression refrigeration system (VCRS) is provided. The system may include an oil separator configured to receive the refrigerant and oil flow from the low-pressure line of the VCRS and output a oil flow and a refrigerant flow. The system may further include an oil collector configured to receive the separated oil flow provided by the oil separator. A valve may control an oil flow from the oil collector to the low-pressure line. A level sensor may measure oil level in the oil collector. The system may close, in response to the oil being at or less than a first level, the valve to collect oil in the oil collector. The system may open, in response to the oil being at or greater than a second level, the valve to release oil from the oil collector to the low-pressure line.