Method for controlling a vapour compression system in a flooded state

Abstract

A vapour compression system (1) includes an ejector (6) and a liquid separating device (10) arranged in a suction line. At least one evaporator (9) is allowed to be operated in a flooded state. A flow rate of refrigerant from the liquid separating device (10) to the secondary inlet (15) of the ejector (6) is detected, and it is determined whether or not the flow rate is sufficient to remove liquid refrigerant produced by the evaporator(s) (9) from the liquid separating device (10). In the case that it is determined that the flow rate of refrigerant from the liquid separating device (10) to the secondary inlet (15) of the ejector (6) is insufficient to remove liquid refrigerant produced by the evaporator(s) (9), the flow rate of refrigerant from the liquid separating device (10) to the secondary inlet (15) of the ejector (6) is increased, and/or a flow rate of liquid refrigerant from the evaporator(s) (9) to the liquid separating device (10) is decreased.

Claims

1. A method for controlling a vapour compression system, the vapour compression system comprising a compressor unit, a heat rejecting heat exchanger, an ejector, a receiver, at least one expansion device and at least one evaporator arranged in a refrigerant path, the vapour compression system further comprising a liquid separating device arranged in a suction line of the of vapour compression system, the liquid separating device comprising a gaseous outlet connected to the inlet of the compressor unit and a liquid outlet connected to a secondary inlet of the ejector, the method comprising the steps of: allowing at least one evaporator to be operated in a flooded state, detecting a flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector, and determining whether or not the flow rate is sufficient to remove liquid refrigerant produced by the evaporator(s) being allowed to be operated in a flooded state from the liquid separating device, and in the case that it is determined that the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector is insufficient to remove liquid refrigerant produced by the evaporator(s) being allowed to be operated in a flooded state from the liquid separating device, increasing the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector, and/or decreasing a flow rate of liquid refrigerant from the evaporator(s) to the liquid separating device.

2. The method according to claim 1, wherein the step of increasing the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector comprises reducing a pressure prevailing inside the receiver.

3. The method according to claim 2, wherein the step of increasing the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector comprises increasing a pressure of refrigerant leaving the heat rejecting heat exchanger and entering a primary inlet of the ejector.

4. The method according to claim 2, wherein the step of reducing the flow rate of liquid refrigerant from the evaporator(s) to the liquid separating device comprises preventing at least some of the evaporator(s) from being operated in a flooded state.

5. The method according to claim 2, wherein the step of reducing the flow rate of liquid refrigerant from the evaporator(s) to the liquid separating device comprises decreasing a pressure prevailing in the suction line of the vapour compression system.

6. The method according to claim 2, wherein the step of detecting the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector comprises measuring the flow rate by means of a flow switch and/or a flow sensor.

7. The method according to claim 2, wherein the step of determining whether or not the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector is sufficient to remove liquid refrigerant produced by the evaporator(s) being allowed to be operated in a flooded state from the liquid separating device comprises measuring a temperature of refrigerant in the suction line.

8. The method according to claim 1, wherein the step of increasing the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector comprises increasing a pressure of refrigerant leaving the heat rejecting heat exchanger and entering a primary inlet of the ejector.

9. The method according to claim 8, wherein the step of reducing the flow rate of liquid refrigerant from the evaporator(s) to the liquid separating device comprises preventing at least some of the evaporator(s) from being operated in a flooded state.

10. The method according to claim 8, wherein the step of reducing the flow rate of liquid refrigerant from the evaporator(s) to the liquid separating device comprises decreasing a pressure prevailing in the suction line of the vapour compression system.

11. The method according to claim 8, wherein the step of detecting the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector comprises measuring the flow rate by means of a flow switch and/or a flow sensor.

12. The method according to claim 8, wherein the step of determining whether or not the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector is sufficient to remove liquid refrigerant produced by the evaporator(s) being allowed to be operated in a flooded state from the liquid separating device comprises measuring a temperature of refrigerant in the suction line.

13. The method according to claim 1, wherein the step of reducing the flow rate of liquid refrigerant from the evaporator(s) to the liquid separating device comprises preventing at least some of the evaporator(s) from being operated in a flooded state.

14. The method according to claim 13, wherein the step of reducing the flow rate of liquid refrigerant from the evaporator(s) to the liquid separating device comprises decreasing a pressure prevailing in the suction line of the vapour compression system.

15. The method according to claim 13, wherein the step of detecting the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector comprises measuring the flow rate by means of a flow switch and/or a flow sensor.

16. The method according to claim 1, wherein the step of reducing the flow rate of liquid refrigerant from the evaporator(s) to the liquid separating device comprises decreasing a pressure prevailing in the suction line of the vapour compression system.

17. The method according to claim 16, wherein the step of detecting the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector comprises measuring the flow rate by means of a flow switch and/or a flow sensor.

18. The method according to claim 1, wherein the step of detecting the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector comprises measuring the flow rate by means of a flow switch and/or a flow sensor.

19. The method according to claim 1, wherein the step of determining whether or not the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector is sufficient to remove liquid refrigerant produced by the evaporator(s) being allowed to be operated in a flooded state from the liquid separating device comprises measuring a temperature of refrigerant in the suction line.

20. The method according to claim 1, wherein the step of determining whether or not the flow rate of refrigerant from the liquid separating device to the secondary inlet of the ejector is sufficient to remove liquid refrigerant produced by the evaporator(s) being allowed to be operated in a flooded state from the liquid separating device is performed on the basis of characteristics of the ejector.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described with reference to the accompanying drawings in which

(2) FIG. 1 is a diagrammatic view of a vapour compression system being controlled in accordance with a method according to a first embodiment of the invention,

(3) FIG. 2 is a diagrammatic view of a vapour compression system being controlled in accordance with a method according to a second embodiment of the invention,

(4) FIG. 3 is a diagrammatic view of a vapour compression system being controlled in accordance with a method according to a third embodiment of the invention, and

(5) FIG. 4 is a diagrammatic view of a vapour compression system being controlled in accordance with a method according to a fourth embodiment of the invention.

DETAILED DESCRIPTION

(6) FIG. 1 is a diagrammatic view of a vapour compression system 1 being controlled in accordance with a method according to a first embodiment of the invention. The vapour compression system 1 comprises a compressor unit 2 comprising a number of compressors 3, 4, three of which are shown, a heat rejecting heat exchanger 5, an ejector 6, a receiver 7, an expansion device 8, in the form of an expansion valve, an evaporator 9, and a liquid separating device 10, arranged in a refrigerant path.

(7) Two of the shown compressors 3 are connected to a gaseous outlet 11 of the liquid separating device 10. Accordingly, gaseous refrigerant leaving the evaporator 9 can be supplied to these compressors 3, via the liquid separating device 10. The third compressor 4 is connected to a gaseous outlet 12 of the receiver 7. Accordingly, gaseous refrigerant can be supplied directly from the receiver 7 to this compressor 4.

(8) Refrigerant flowing in the refrigerant path is compressed by the compressors 3, 4 of the compressor unit 2. The compressed refrigerant is supplied to the heat rejecting heat exchanger 5, where heat exchange takes place in such a manner that heat is rejected from the refrigerant.

(9) The refrigerant leaving the heat rejecting heat exchanger 5 is supplied to a primary inlet 13 of the ejector 6, before being supplied to the receiver 7. When passing through the ejector 6 the refrigerant undergoes expansion. Thereby the pressure of the refrigerant is reduced, and the refrigerant being supplied to the receiver 7 is in a mixed liquid and gaseous state.

(10) In the receiver 7 the refrigerant is separated into a liquid part and a gaseous part. The liquid part of the refrigerant is supplied to the evaporator 9, via a liquid outlet 14 of the receiver 7 and the expansion device 8. In the evaporator 9, the liquid part of the refrigerant is at least partly evaporated, while heat exchange takes place in such a manner that heat is absorbed by the refrigerant.

(11) The evaporator 9 is allowed to be operated in a flooded state, i.e. in such a manner that liquid refrigerant is present along the entire length of the evaporator 9. Thereby some of the refrigerant passing through the evaporator 9 and entering the suction line may be in a liquid state.

(12) The refrigerant leaving the evaporator 9 is received in the liquid separating device 10, where the refrigerant is separated into a liquid part and a gaseous part. The liquid part of the refrigerant is supplied to a secondary inlet 15 of the ejector 6, via a liquid outlet 16 of the liquid separating device 10. At least some of the gaseous refrigerant may be supplied to the compressors 3 of the compressor unit 2 via the gaseous outlet 11 of the liquid separating device 10. However, it is not ruled out that at least some of the gaseous refrigerant is supplied to the secondary inlet 15 of the ejector 6, via the liquid outlet 16 of the liquid separating device 10.

(13) Accordingly, the liquid separating device 10 ensures that any liquid refrigerant which passes through the evaporator 9 is prevented from reaching the compressors 3, 4 of the compressor unit 2. Instead such liquid refrigerant is supplied to the secondary inlet 15 of the ejector 6.

(14) The gaseous part of the refrigerant in the receiver 7 may be supplied to the compressor 4. Furthermore, some of the gaseous refrigerant in the receiver 7 may be supplied to compressors 3, via a bypass valve 17. Opening the bypass valve 17 increases the compressor capacity being available for compressing refrigerant received from the gaseous outlet 12 of the receiver 7.

(15) According to the method of the invention, a flow rate of refrigerant from the liquid separating device 10 to the secondary inlet 15 of the ejector 6 is detected. It is further determined whether or not the flow rate is sufficient to remove the liquid refrigerant which is allowed to pass through the evaporator 9 and enter the liquid separating device 10.

(16) If the flow rate is insufficient to remove the liquid refrigerant produced by the evaporator 9, then liquid refrigerant will accumulate in the liquid separating device 10, eventually resulting in liquid refrigerant flowing towards the compressor unit 2, via the gaseous outlet 11 of the liquid separating device 10. This is undesirable, since it may cause damage to the compressors 3, 4.

(17) Therefore, when it is determined that the flow rate is insufficient to remove the liquid refrigerant produced by the evaporator 9, the flow rate of refrigerant from the liquid separating device 10 to the secondary inlet 15 of the ejector 6 is increased, and/or a flow rate of liquid refrigerant from the evaporator 9 to the liquid separating device 10 is decreased. Thereby it is ensured that the flow rate of refrigerant from the liquid separating device 10 to the secondary inlet 15 of the ejector 6 is sufficient to remove the liquid refrigerant produced by the evaporator 9, and accumulation of liquid refrigerant in the liquid separating device 10 is avoided.

(18) The flow rate of refrigerant from the liquid separating device 10 to the secondary inlet 15 of the ejector 6 could, e.g., be increased by decreasing a pressure prevailing inside the receiver 7 and/or by increasing a pressure of refrigerant leaving the heat rejecting heat exchanger 5 and entering the primary inlet 13 of the ejector 6. This has been described in detail above.

(19) The flow rate of liquid refrigerant from the evaporator 9 to the liquid separating device 10 could, e.g., be decreased by preventing the evaporator 9 from operating in a flooded state or by decreasing a pressure prevailing in the suction line. This has been described in detail above.

(20) FIG. 2 is a diagrammatic view of a vapour compression system 1 being controlled in accordance with a method according to a second embodiment of the invention. The vapour compression system 1 of FIG. 2 is very similar to the vapour compression system 1 of FIG. 1, and it will therefore not be described in detail here.

(21) In the vapour compression system 1 of FIG. 2, a flow sensor 18 is arranged in the part of the refrigerant path which interconnects the liquid outlet 16 of the liquid separating device 10 and the secondary inlet 15 of the ejector 6. The flow sensor 18 is used for detecting the flow rate of refrigerant from the liquid separating device 10 to the secondary inlet 15 of the ejector 6. Furthermore, a flow switch could be arranged in this part of the refrigerant path, or the flow sensor 18 could be replaced by a flow switch.

(22) FIG. 3 is a diagrammatic view of a vapour compression system 1 being controlled in accordance with a method according to a third embodiment of the invention. The vapour compression system 1 of FIG. 3 is very similar to the vapour compression systems 1 of FIGS. 1 and 2, and it will therefore not be described in detail here.

(23) In the vapour compression system 1 of FIG. 3, only two compressors 3 are shown in the compressor unit 2. Both of the compressors 3 are connected to the gaseous outlet 11 of the liquid separating device 10. Accordingly, gaseous refrigerant from the receiver 7 can only be supplied to the compressor unit 2 via the bypass valve 17.

(24) FIG. 4 is a diagrammatic view of a vapour compression system 1 being controlled in accordance with a method according to a fourth embodiment of the invention. The vapour compression system 1 of FIG. 4 is very similar to the vapour compression systems 1 of FIGS. 1-3, and it will therefore not be described in detail here.

(25) In the compressor unit 2 of the vapour compression system 1 of FIG. 4, one compressor 3 is shown as being connected to the gaseous outlet 11 of the liquid separating device 10 and one compressor 4 is shown as being connected to the gaseous outlet 12 of the receiver 7. A third compressor 19 is shown as being provided with a three way valve 20 which allows the compressor 19 to be selectively connected to the gaseous outlet 11 of the liquid separating device 10 or to the gaseous outlet 12 of the receiver 7. Thereby some of the compressor capacity of the compressor unit 2 can be shifted between main compressor capacity, i.e. when the compressor 19 is connected to the gaseous outlet 11 of the liquid separating device 10, and receiver compressor capacity, i.e. when the compressor 19 is connected to the gaseous outlet 12 of the receiver 7. Thereby it is possible to adjust the pressure prevailing inside the receiver 7, and thereby the flow rate of refrigerant from the liquid separating device 10 to the secondary inlet 15 of the ejector 6, by operating the three way valve 20, thereby increasing or decreasing the amount of compressor capacity being available for compressing refrigerant received from the gaseous outlet 12 of the receiver 7.

(26) Furthermore, the vapour compression system 1 of FIG. 4 comprises three expansion devices 8a, 8b, 8c and three evaporators 9a, 9b, 9c, arranged fluidly in parallel in the refrigerant path. Each of the expansion devices 8a, 8b, 8c is arranged to control a flow of refrigerant to one of the evaporators 9a, 9b, 9c.

(27) When controlling the vapour compression system 1 of FIG. 4, all of the evaporators 9a, 9b, 9c may be allowed to be operated in a flooded state, or only some of the evaporators 9a, 9b, 9c may be allowed to be operated in a flooded state.

(28) While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.