Cooling system with oil return to accumulator

Patent metadata

Field	Value
Publication number	US-11933527-B2
Application number	US-202016803306-A
Country	US
Kind code	B2
Filing date	Feb 27, 2020
Priority date	Feb 27, 2020
Publication date	Mar 19, 2024
Grant date	Mar 19, 2024

Abstract

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.

First claim

What is claimed is:

1. A system comprising:
a flash tank configured to store a primary refrigerant;
a first low side heat exchanger;
an accumulator disposed downstream of the first low side heat exchanger, wherein the accumulator comprises a U-shaped pipe having an end configured to receive the primary refrigerant, and wherein the U-shaped pipe comprises a hole located towards a bottom of the accumulator;
a first compressor;
a second compressor disposed downstream of the first compressor;
a first valve associated with the first low side heat exchanger and is disposed upstream of the accumulator in parallel with the first low side heat exchanger;
a first cooling system fluidly coupled to the first low side heat exchanger; and
a second valve associated with the first low side heat exchanger and is disposed between a discharge side of the first valve and a suction side of a first vessel, wherein the first vessel is disposed between the first valve and the accumulator, wherein the second valve is configured to direct primary refrigerant discharged from the first compressor to the first vessel,
wherein during a first mode of operation:
the first and second valves are closed;
the first low side heat exchanger is configured to use the primary refrigerant from the flash tank to cool a secondary refrigerant;
the accumulator is configured to receive the primary refrigerant from the first low side heat exchanger;
the first cooling system is configured to receive the cooled secondary refrigerant;
the first compressor is configured to compress the primary refrigerant from the accumulator; and
the second compressor is configured to compress the primary refrigerant from the first compressor,

wherein during a second mode of operation:
the first valve is open and configured to direct the primary refrigerant from the first low side heat exchanger and an oil from the first low side heat exchanger to the first vessel; and
the second valve is closed,

wherein during a third mode of operation:
the first valve is closed; and
the second valve is open and directs the primary refrigerant from the first compressor to the first vessel, wherein the primary refrigerant from the first compressor pushes the oil in the first vessel to the accumulator, and wherein the oil collected at the bottom of the accumulator is sucked through the hole in the U-shaped pipe and directed to the first compressor.

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, the system transitions from the first mode of operation to the second mode of operation when a difference between the temperature detected by the first sensor and the temperature detected by the second sensor exceeds a threshold.

3. The system of claim 1 , further comprising a check valve that directs primary refrigerant from the first low side heat exchanger to the 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 third valve; and
a fourth valve, during the first, second, and third modes of operation:
the third and fourth valves are closed;
the second low side heat exchanger uses primary refrigerant from the flash tank to cool a tertiary refrigerant; and
the accumulator receives primary refrigerant from the second low side heat exchanger.

5. The system of claim 1 , wherein during the third mode of operation, the second valve receives primary refrigerant directly from the first compressor.

6. The system of claim 1 , further comprising a sensor configured to detect a level of the oil, the system transitions from the first mode of operation to the second mode of operation when the detected level falls below a threshold.

7. The system of claim 4 , further comprising a second vessel disposed between the third valve and the accumulator.

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;
using, by a first low side heat exchanger, primary refrigerant from the flash tank to cool a secondary refrigerant, wherein both the first valve and the second valve are each associated with the first low side heat exchanger;
receiving, by an accumulator disposed downstream of the first low side heat exchanger, primary refrigerant from the first low side heat exchanger, wherein the accumulator comprises a U-shaped pipe having an end configured to receive the primary refrigerant, and wherein the U-shaped pipe comprises a hole located towards a bottom of the accumulator;
receiving, by a first cooling system fluidly coupled to the first low side heat exchanger, the cooled secondary refrigerant;
compressing, by a first compressor, primary refrigerant from the accumulator; and
compressing, by a second compressor disposed downstream of the first compressor, primary refrigerant from the first compressor,

during a second mode of operation:
opening the first valve, wherein the first valve is disposed upstream of the accumulator in parallel with the first low side heat exchanger;
closing the second valve, wherein the second valve is disposed between a discharge side of the first valve and a suction side of a first vessel, wherein the first vessel is disposed between the first valve and the accumulator; and
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 the first vessel; and

during a third mode of operation:
closing the first valve;
opening the second valve;
directing, by the second valve, primary refrigerant from the first compressor to the first vessel; and
pushing, by the primary refrigerant from the first compressor, the oil in the first vessel to the accumulator and wherein the oil collected at the bottom of the accumulator is sucked through the hole in the U-shaped pipe and directed to the first compressor.

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; and
transitioning from the first mode of operation to the second mode of operation when a difference between the temperature detected by the first sensor and the temperature detected by the second sensor exceeds a threshold.

10. The method of claim 8 , further comprising directing, by a check valve, primary refrigerant from the first low side heat exchanger to the accumulator when a pressure of the primary refrigerant exceeds a threshold.

11. The method of claim 8 , further comprising, during the first, second, and third modes of operation:
closing a third valve and a fourth valve;
using, by a second low side heat exchanger, primary refrigerant from the flash tank to cool a tertiary refrigerant; and
receiving, by the accumulator, primary refrigerant from the second low side heat exchanger.

12. The method of claim 8 , further comprising, during the third mode of operation, the second valve receives primary refrigerant directly from the first compressor.

13. The method of claim 8 , further comprising:
detecting, by a sensor, a level of the oil; and
transitioning from the first mode of operation to the second mode of operation when the detected level falls below a threshold.

14. The method of claim 11 , wherein a second vessel is disposed between the

Assignees

• Heatcraft Refrigeration Products Llc

Inventors

• Zha Shitong

Classifications

• F25B43/02 Primary

  for separating lubricants from the refrigerant · CPC title

• F25B41/20

  Disposition of valves, e.g. of on-off valves or flow control valves (expansion valves F25B41/31) · CPC title

• F25B43/006

  Accumulators · CPC title

• F25B2500/04

  Clogging · CPC title

• F25B2600/2519

  On-off valves · CPC title