Cooling system with oil return to accumulator
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.
1. A system comprising:
a flash tank configured to store a primary refrigerant;
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, wherein during a first mode of operation:
the first, second, and third valves are closed;
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 and third valves are closed; and
the second valve is open and directs primary refrigerant from the second compressor to a vessel, the primary refrigerant from the second compressor pushes the oil in the vessel to the second accumulator.
2. The system of claim 1 , further comprising:
a first sensor configured to detect a temperature of the primary refrigerant in the first low side heat exchanger; and
a second sensor configured to detect a temperature of the secondary refrigerant.
3. The system of claim 1 , further comprising a check valve that directs primary refrigerant from the first low side heat exchanger to the first accumulator when a pressure of the primary refrigerant exceeds a threshold.
4. The system of claim 1 , further comprising:
a second low side heat exchanger;
a fourth valve;
a fifth valve; and
a sixth valve, wherein during the first and second modes of operation:
the fourth and fifth valves are closed;
the sixth valve is open;
the second low side heat exchanger uses primary refrigerant from the flash tank to cool a tertiary refrigerant; and
the first accumulator receives primary refrigerant from the second low side heat exchanger.
5. The system of claim 1 , wherein during the second mode of operation, the second accumulator directs the oil in the second accumulator to the second compressor.
6. The system of claim 1 , further comprising a sensor configured to detect a level of the oil in an oil reservoir.
7. The system of claim 1 , wherein the vessel comprises a coil.
8. A method comprising:
storing, by a flash tank, a primary refrigerant;
during a first mode of operation:
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:
closing the first and third valves;
opening the second valve;
directing, by the second valve, primary refrigerant from the second compressor to a vessel; and
pushing, by the primary refrigerant from the second compressor, the oil in the vessel to the second accumulator.
9. The method of claim 8 , further comprising:
detecting, by a first sensor, a temperature of the primary refrigerant in the first low side heat exchanger;
detecting, by a second sensor, a temperature of the secondary refrigerant.
10. The method of claim 8 , further comprising directing, by a check valve, primary refrigerant from the first low side heat exchanger to the first accumulator when a pressure of the primary refrigerant exceeds a threshold.
11. The method of claim 8 , further comprising, during the first and second modes of operation:
closing a fourth valve and a fifth valve;
opening a sixth valve;
using, by a second low side heat exchanger, primary refrigerant from the flash tank to cool a tertiary refrigerant; and
receiving, by the first accumulator, primary refrigerant from the second low side heat exchanger.
12. The method of claim 8 , further comprising, during the second mode of operation, directing, by the second accumulator, the oil in the second accumulator to the second compressor.
13. The method of claim 8 , further comprising:
detecting, by a sensor, a level of the oil in an oil reservoir.
14. The method of claim 8 , wherein the vessel comprises a coil.
15. A system comprising:
a high side heat exchanger configured to remove heat from a primary refrigerant;
a flash tank configured to store the primary refrigerant;
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, wherein 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 and third valves are closed; and
the second valve is open and directs primary refrigerant from the second compressor to a vessel, the primary refrigerant from the second compressor pushes the oil in the vessel to the second accumulator.
16. The system of claim 15 , further comprising:
a first sensor configured to detect a temperature of the primary refrigerant in the first low side heat exchanger; and
a second sensor configured to detect a temperature of the secondary refrigerant.
17. The system of claim 15 , further comprising a check valve that directs primary refrigerant from the first low side heat exchanger to the first accumulator when a pressure of the primary refrigerant exceeds a threshold.
18. The system of claim 15 , further comprising:
a second low side heat exchanger;
a fourth valve;
a fifth valve; and
a sixth valve, wherein during the first and second modes of operation:
the fourth and fifth valves are closed;
the sixth valve is open;
the second low side heat exchanger uses primary refrigerant from the flash tank to cool a tertiary refrigerant; and
the first accumulator receives primary refrigerant from the second low side heat exchanger.
19. The system of claim 15 , wherein during the second mode of operation, the second accumulator directs the oil in the second accumulator to the second compressor.
20. The system of claim 15 , further comprising a sensor configured to detect a level of the oil in an oil reservoir.