TECHNICAL FIELD

This disclosure relates generally to a cooling system.

BACKGROUND

Cooling systems cycle refrigerant to cool various spaces.

SUMMARY

Cooling systems cycle refrigerant to cool various spaces. For example, in some industrial facilities, cooling systems cycle a primary refrigerant that cools secondary refrigerants. The secondary refrigerants are then cycled to cool different parts of the industrial facility (e.g., different industrial and/or manufacturing processes). These systems typically include a compressor to compress the primary refrigerant and a high side heat exchanger that removes heat from the compressed primary refrigerant. When the compressor compresses the primary refrigerant, oil that coats certain components of the compressor may mix with and be discharged with the primary refrigerant.

Depending on the nature of the primary refrigerant, the cooling system may be able to move the oil along with the primary refrigerant through the cooling system such that the oil is eventually cycled back to the compressor. However, when certain primary refrigerants (e.g., carbon dioxide) are used, the oil may get stuck in a portion of the cooling system (e.g., at a low side heat exchanger). As a result, the compressor(s) in the system begin losing oil, which eventually leads to breakdown or failure. Additionally, the components in which the oil gets stuck may also become less efficient as the oil builds in these components.

This disclosure contemplates unconventional cooling systems that drain 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 systems operate 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. In this manner, oil in a low side heat exchanger is returned to a compressor. Certain embodiments of the cooling system are described below.

According to an embodiment, a system includes a flash tank, a first low side heat exchanger, an accumulator, a first compressor, a second compressor, an oil reservoir, a first valve, a second valve, and a third valve. The flash tank stores a primary refrigerant. During a first mode of operation, the first and second valves are closed, the third valve is open, the first low side heat exchanger uses primary refrigerant from the flash tank to cool a secondary refrigerant, the accumulator receives primary refrigerant from the first low side heat exchanger, the first compressor compresses primary refrigerant from the accumulator, and the second compressor compresses primary refrigerant from the first compressor. During a second mode of operation, the first valve is open and directs primary refrigerant from the first low side heat exchanger and an oil from the first low side heat exchanger to a vessel, the second valve is closed, and the third valve is open and directs primary refrigerant from the vessel to the accumulator. During a third mode of operation, the first and third valves are closed and the second valve is open and directs primary refrigerant from the second compressor to the vessel. The primary refrigerant from the second compressor pushes the oil in the vessel to the oil reservoir.

According to another embodiment, a method includes storing, by a flash tank, a primary refrigerant. During a first mode of operation, the method includes closing a first valve and a second valve, opening a third valve, using, by a first low side heat exchanger, primary refrigerant from the flash tank to cool a secondary refrigerant, receiving, by an accumulator, primary refrigerant from the first low side heat exchanger, compressing, by a first compressor, primary refrigerant from the accumulator, and compressing, by a second compressor, primary refrigerant from the first compressor. During a second mode of operation, the method includes opening the first valve, directing, by the first valve, primary refrigerant from the first low side heat exchanger and an oil from the first low side heat exchanger to a vessel, closing the second valve, opening the third valve, and directing, by the third valve, primary refrigerant from the vessel to the accumulator. During a third mode of operation, the method includes closing the first and third valves, opening the second valve, directing, by the second valve, primary refrigerant from the second compressor to the vessel, and pushing, by the primary refrigerant from the second compressor, the oil in the vessel to an oil reservoir.

According to yet another embodiment, a system includes a high side heat exchanger, a flash tank, a first low side heat exchanger, an accumulator, a first compressor, a second compressor, an oil reservoir, a first valve, a second valve, and a third valve. The high side heat exchanger removes heat from a primary refrigerant. The flash tank stores the primary refrigerant. During a first mode of operation, the first and second valves are closed, the third valve is open, the first low side heat exchanger uses primary refrigerant from the flash tank to cool a secondary refrigerant, the accumulator receives primary refrigerant from the first low side heat exchanger, the first compressor compresses primary refrigerant from the accumulator, and the second compressor compresses primary refrigerant from the first compressor. During a second mode of operation, the first valve is open and directs primary refrigerant from the first low side heat exchanger and an oil from the first low side heat exchanger to a vessel, the second valve is closed, and the third valve is open and directs primary refrigerant from the vessel to the accumulator. During a third mode of operation, the first and third valves are closed and the second valve is open and directs primary refrigerant from the second compressor to the vessel. The primary refrigerant from the second compressor pushes the oil in the vessel to the oil reservoir.

According to an embodiment, a system includes a flash tank, a first low side heat exchanger, a first accumulator, a first compressor, a second accumulator, a second compressor, a first valve, a second valve, and a third valve. The flash tank stores a primary refrigerant. During a first mode of operation, the first and second valves are closed, the third valve is open, the first low side heat exchanger uses primary refrigerant from the flash tank to cool a secondary refrigerant, the first accumulator receives primary refrigerant from the first low side heat exchanger, the first compressor compresses primary refrigerant from the first accumulator, the second accumulator receives primary refrigerant from the first compressor, and the second compressor compresses primary refrigerant from the second accumulator. During a second mode of operation, the first valve is open and directs primary refrigerant from the first low side heat exchanger and an oil from the first low side heat exchanger to a vessel, the second valve is closed, and the third valve is open and directs primary refrigerant from the vessel to the first accumulator. During a third mode of operation, the first and third valves are closed and the second valve is open and directs primary refrigerant from the second compressor to the vessel. The primary refrigerant from the second compressor pushes the oil in the vessel to the second accumulator.

According to another embodiment, a method includes storing, by a flash tank, a primary refrigerant. During a first mode of operation, the method includes closing a first valve and a second valve, opening a third valve, using, by a first low side heat exchanger, primary refrigerant from the flash tank to cool a secondary refrigerant, receiving, by a first accumulator, primary refrigerant from the first low side heat exchanger, compressing, by a first compressor, primary refrigerant from the first accumulator, receiving, by a second accumulator, primary refrigerant from the first compressor, and compressing by a second compressor, primary refrigerant from the second accumulator. During a second mode of operation, the method includes opening the first valve, directing, by the first valve, primary refrigerant from the first low side heat exchanger and an oil from the first low side heat exchanger to a vessel, closing the second valve, opening the third valve, and directing, by the third valve, primary refrigerant from the vessel to the first accumulator. During a third mode of operation, the method includes closing the first and third valves, opening the second valve, directing, by the second valve, primary refrigerant from the second compressor to the vessel, and pushing, by the primary refrigerant from the second compressor, the oil in the vessel to the second accumulator.

According to yet another embodiment, a system includes a high side heat exchanger, a flash tank, a first low side heat exchanger, a first accumulator, a first compressor, a second accumulator, a second compressor, a first valve, a second valve, and a third valve. The high side heat exchanger removes heat from a primary refrigerant. The flash tank stores the primary refrigerant. During a first mode of operation, the first and second valves are closed, the third valve is open, the first low side heat exchanger uses primary refrigerant from the flash tank to cool a secondary refrigerant, the first accumulator receives primary refrigerant from the first low side heat exchanger, the first compressor compresses primary refrigerant from the first accumulator, the second accumulator receives primary refrigerant from the first compressor, and the second compressor compresses primary refrigerant from the second accumulator. During a second mode of operation, the first valve is open and directs primary refrigerant from the first low side heat exchanger and an oil from the first low side heat exchanger to a vessel, the second valve is closed, and the third valve is open and directs primary refrigerant from the vessel to the first accumulator. During a third mode of operation, the first and third valves are closed and the second valve is open and directs primary refrigerant from the second compressor to the vessel. The primary refrigerant from the second compressor pushes the oil in the vessel to the second accumulator.

Certain embodiments provide one or more technical advantages. For example, an embodiment allows oil to be drained from a low side heat exchanger and returned to a compressor, which may improve the efficiency of the low side heat exchanger and the lifespan of the compressor. Certain embodiments may include none, some, or all of the above technical advantages. One or more other technical advantages may be readily apparent to one skilled in the art from the figures, descriptions, and claims included herein.

