A METHOD FOR CONTROLLING A VALVE ARRANGEMENT IN A VAPOUR COMPRESSION SYSTEM

Abstract

A method for controlling a valve arrangement (12), e.g. in the form of a three way valve, in a vapour compression system (1) is disclosed, the vapour compression system (1) comprising an ejector (6). The valve arrangement (12) is arranged to supply refrigerant to a compressor unit (2) from the gaseous outlet (11) of a receiver (7) and/or from the outlet of an evaporator (9). The vapour compression system (1) may be operated in a first mode of operation (summer mode) or in a second mode of operation (winter mode). When operated in the second mode of operation, it is determined whether or not conditions for operating the vapour compression system (1) in the first mode of operation are prevailing. If this is the case, the valve arrangement (12) is actively switched to the first mode of operation by closing a first inlet (13) towards the evaporator (7) and fully opening a second inlet (14) towards the receiver (7).

Claims

1. A method for controlling a valve arrangement in a vapour compression system, the vapour compression system comprising a compressor unit comprising one or more compressors, a heat rejecting heat exchanger, an ejector, a receiver, an expansion device and an evaporator arranged in a refrigerant path, wherein an outlet of the heat rejecting heat exchanger is connected to a primary inlet of the ejector, an outlet of the ejector is connected to the receiver, an outlet of the evaporator is connected to a secondary inlet of the ejector and to a first inlet of the valve arrangement, a gaseous outlet of the receiver is connected to a second inlet of the valve arrangement, and an outlet of the valve arrangement is connected to an inlet of the compressor unit, the valve arrangement thereby being arranged to supply refrigerant to the compressor unit from the gaseous outlet of the receiver and/or from the outlet of the evaporator, the method comprising the steps of: defining a first mode of operation of the vapour compression system, in which the valve arrangement is operated to keep the first inlet of the valve arrangement closed and to keep the second inlet of the valve arrangement open, defining a second mode of operation of the vapour compression system, in which the valve arrangement is operated to keep the first inlet of the valve arrangement open and to operate the second inlet of the valve arrangement to bypass vapour in order to maintain a pressure level in the receiver, in the case that the vapour compression system is operated in the second mode of operation: determining whether or not conditions for operating the vapour compression system in the first mode of operation are prevailing, and in the case that conditions for operating the vapour compression system in the first mode of operating are prevailing, actively closing the first inlet of the valve arrangement and fully opening the second inlet of the valve arrangement.

2. The method according to claim 1, wherein the step of determining whether or not conditions for operating the vapour compression system in the first mode of operation are prevailing comprises the steps of: determining a distribution of refrigerant supplied to the valve arrangement, including determining how large a portion of the refrigerant being supplied from the outlet of the valve arrangement to the compressor unit is received in the valve arrangement via the first inlet, and how large a portion is received via the second inlet, and determining that conditions for operating the vapour compression system in the first mode of operation are prevailing if the portion of refrigerant received via the second inlet of the valve arrangement exceeds a predefined percentage of the refrigerant supplied from the outlet of the valve arrangement to the inlet of the compressor unit, said predefined percentage being at least 70%.

3. The method according to claim 2, wherein the step of determining a distribution of refrigerant supplied to the valve arrangement comprises measuring a temperature of refrigerant entering the valve arrangement via the first inlet, a temperature of refrigerant entering the valve arrangement via the second inlet, and a temperature of refrigerant leaving the valve arrangement via the outlet, and comparing the measured temperatures.

4. The method according to claim 2, wherein the step of determining a distribution of refrigerant supplied to the valve arrangement comprises determining an opening degree of the second inlet of the valve arrangement.

5. The method according to claim 2, wherein the step of determining a distribution of refrigerant supplied to the valve arrangement comprises the step of determining a flow direction of refrigerant at the first inlet of the valve arrangement.

6. The method according to claim 5, wherein the step of determining a flow direction of refrigerant at the first inlet of the valve arrangement comprises the steps of: modulating an opening degree of the first inlet of the valve arrangement, and measuring changes in a pressure of refrigerant at the first inlet of the valve arrangement in response to the modulation of the opening degree of the first inlet of the valve arrangement.

7. The method according to claim 1, wherein the step of determining whether or not conditions for operating the vapour compression system in the first mode of operation are prevailing comprises the steps of: measuring a parameter of the vapour compression system, where an enthalpy of refrigerant leaving the heat rejecting heat exchanger can be derived from the measured parameter, and determining that conditions for operating the vapour compression system in the first mode of operation are prevailing if the measured parameter exceeds a predefined threshold value.

8. The method according to claim 1, wherein the valve arrangement is or comprises a three way valve.

9. The method according to claim 1, wherein the vapour compression system further comprises a high pressure valve interconnecting an outlet of the heat rejecting heat exchanger and an inlet of the receiver, the high pressure valve being arranged in parallel to the ejector, and wherein refrigerant leaving the heat rejecting heat exchanger is divided into a flow passing through the high pressure valve and a flow passing through the ejector, via the primary inlet of the ejector.

10. The method according to claim 1, wherein the vapour compression system is arranged to have a transcritical refrigerant flowing in the refrigerant path.

11. The method according to claim 1, wherein the heat rejecting heat exchanger is a gas cooler.

12. The method according to claim 3, wherein the step of determining a distribution of refrigerant supplied to the valve arrangement comprises determining an opening degree of the second inlet of the valve arrangement.

13. The method according to claim 3, wherein the step of determining a distribution of refrigerant supplied to the valve arrangement comprises the step of determining a flow direction of refrigerant at the first inlet of the valve arrangement.

14. The method according to claim 4, wherein the step of determining a distribution of refrigerant supplied to the valve arrangement comprises the step of determining a flow direction of refrigerant at the first inlet of the valve arrangement.

15. The method according to claim 2, wherein the valve arrangement is or comprises a three way valve.

16. The method according to claim 3, wherein the valve arrangement is or comprises a three way valve.

17. The method according to claim 4, wherein the valve arrangement is or comprises a three way valve.

18. The method according to claim 5, wherein the valve arrangement is or comprises a three way valve.

19. The method according to claim 6, wherein the valve arrangement is or comprises a three way valve.

20. The method according to claim 7, wherein the valve arrangement is or comprises a three way valve.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0069] The invention will now be described in further detail with reference to the accompanying drawing in which

[0070] FIG. 1 is a diagrammatic view of a vapour compression system being controlled using a method according to an embodiment of the invention.

DETAILED DESCRIPTION

[0071] FIG. 1 is a diagrammatic view of a vapour compression system 1 being controlled using a method according to an embodiment of the invention. The vapour compression system 1 comprises a compressor unit 2, comprising a number of compressors 3, two of which are shown, a heat rejecting heat exchanger 4, a high pressure valve 5, an ejector 6, a receiver 7, an expansion device 8, in the form of an expansion valve, and an evaporator 9 arranged in a refrigerant path. The receiver 7 comprises a liquid outlet 10 and a gaseous outlet 11. The liquid outlet 10 is connected to the expansion device 8, i.e. the liquid part of the refrigerant in the receiver 7 is supplied to the evaporator 9, via the expansion device 8.

[0072] A three way valve 12 is mounted in the refrigerant path with a first inlet 13 connected to an outlet of the evaporator 9, a second inlet 14 connected to the gaseous outlet 11 of the receiver 7, and an outlet 15 connected to the compressors 3 of the compressor unit 2. Accordingly, the three way valve 12 controls the supply of refrigerant to the compressor unit 2, via the outlet 15, from the outlet of the evaporator 9, via the first inlet 13, and from the gaseous outlet 11 of the receiver 7, via the second inlet 14, respectively.

[0073] Refrigerant leaving the heat rejecting heat exchanger 4 is divided between the high pressure valve 5 and a primary inlet 16 of the ejector 6, in such a manner that some of the refrigerant may pass through the high pressure valve 5, and at least some of the refrigerant passes through the ejector 6, via the primary inlet 16, before being supplied to the receiver 7.

[0074] A secondary inlet 17 of the ejector 6 is connected to the outlet of the evaporator 9. Thus, refrigerant leaving the evaporator 9 can either be supplied to the secondary inlet 17 of the ejector 6, or to the first inlet 13 of the three way valve 12.

[0075] The vapour compression system 1 of FIG. 1 may be operated in the following manner. Refrigerant is compressed by the compressors 3 of the compressor unit 2 before being supplied to the heat rejecting heat exchanger 4. In the heat rejecting heat exchanger 4 heat exchange takes place between the refrigerant and the ambient, in such a manner that heat is rejected from the refrigerant flowing through the heat rejecting heat exchanger 4.

[0076] The refrigerant leaving the heat rejecting heat exchanger 4 is supplied to one or both of the high pressure valve 5 and the primary inlet 16 of the ejector 6, as described above, where the refrigerant undergoes expansion before being supplied to the receiver 7.

[0077] 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 expansion device 8, via the liquid outlet 10. The expansion device 8 expands the refrigerant before it is supplied to the evaporator 9. The refrigerant being supplied to the evaporator 9 is in a mixed liquid and gaseous state.

[0078] In the evaporator 9 the liquid part of the refrigerant is at least partly evaporated, while heat exchange takes place between the refrigerant and the ambient in such a manner that heat is absorbed by the refrigerant flowing through the evaporator 9. The refrigerant leaving the evaporator 9 is either supplied to the compressor unit 2, via the first inlet 13 of the three way valve 12, or to the secondary inlet 17 of the ejector 6, where the pressure of the refrigerant is increased due to work performed by the refrigerant received at the primary inlet 16 of the ejector 6 from the heat rejecting heat exchanger 4.

[0079] The gaseous part of the refrigerant in the receiver 7 is supplied to the compressor unit 2, via the second inlet 14 of the three way valve 12. Thereby the gaseous part of the refrigerant does not undergo the expansion introduced by the expansion device 8, and the work required by the compressors 3 of the compressor unit 2 in order to compress the refrigerant is thereby reduced.

[0080] The vapour compression system 1 of FIG. 1 may be operated in a first mode of operation or in a second mode of operation. The three way valve 12 can be controlled in such a manner that it determines whether the vapour compression system 1 is operated in the first mode of operation or in the second mode of operation.

[0081] In the first mode of operation the first inlet 13 of the three way valve 12 is kept closed, and the second inlet 14 of the three way valve 12 is kept open. Thereby, the three way valve 12 ensures that refrigerant is supplied from the gaseous outlet 11 of the receiver 7 to the compressors 3 of the compressor unit 2, via the second inlet 14 of the three way valve 12. Furthermore, the three way valve 12 ensures that refrigerant leaving the evaporator 9 is not allowed to reach the compressors 3 of the compressor unit 2, since the first inlet 13 of the three way valve 12 is closed. Instead, all of the refrigerant leaving the evaporator 9 is supplied to the secondary inlet 17 of the ejector 6. Thus, in the first mode of operation the ejector 6 performs well, and this situation corresponds to a ‘summer mode’ as described above.

[0082] In the second mode of operation the first inlet 13 of the three way valve 12 is kept open, and the second inlet 14 of the three way valve 12 is arranged to bypass vapour in order to maintain a pressure level in the receiver 7. Thereby, the three way valve 12 allows refrigerant leaving the evaporator 9 to be supplied to the compressors 3 of the compressor unit 2, via the first inlet 13 of the three way valve 12. The second inlet 14 of the three way valve 12 is normally closed, but will open in the case that the pressure inside the receiver 7 increases above a maximum threshold value. Accordingly, the second inlet 14 of the three way valve 12 in this case operates as a bypass valve. This situation corresponds to a ‘winter mode’ as described above.

[0083] When the vapour compression system 1 is operated in the second mode of operation, it may be operated in the following manner.

[0084] Initially it is determined whether or not conditions for operating the vapour compression system 1 in the first mode of operation are prevailing. This may simply include measuring the outside temperature, and if this is sufficiently high it is determined that it will be beneficial to operate the vapour compression system 1 in the first mode of operation, i.e. in the ‘summer mode’.

[0085] As an alternative, the temperatures of refrigerant at the first inlet 13 of the three way valve 12, at the second inlet 14 of the three way valve 12, and at the outlet 15 of the three way valve 12 may be measured, and the measured temperatures may be compared. Based on the comparison, it may be determined how large a portion of the refrigerant being supplied to the compressor unit 2 originates from the first inlet 13 of the three way valve 12, and how large a portion originates from the second inlet 14 of the three way valve 12. Alternatively or additionally, a flow direction of the refrigerant at the first inlet 13 of the three way valve 12 may be determined, based on the comparison of the measured temperatures, as described above.

[0086] As another alternative, the flow direction of refrigerant at the first inlet 13 of the three way valve 12 may be determined by modulating an opening degree of the first inlet 13 of the three way valve 12, and monitoring a pressure of the refrigerant at the first inlet 13 of the three way valve 12. This has also been described above.

[0087] In the case that it is determined that conditions for operating the vapour compression system 1 in the first mode of operation, the first inlet 13 of the three way valve 12 is actively closed, and the second inlet 14 of the three way valve 12 is fully opened. Thereby the three way valve 12 is actively moved into a state where refrigerant leaving the evaporator 9 is prevented from being supplied to the compressors 3 of the compressor unit 2, but is instead supplied to the secondary inlet 17 of the ejector 6. Furthermore, it is ensured that gaseous refrigerant is supplied from the gaseous outlet 11 of the receiver 7 to the compressors 3 of the compressor unit 2 to a maximum extent, since the second inlet 14 of the three way valve 12 is fully open. Accordingly, the three way valve 12 is actively moved to a state which causes the vapour compression system 1 to be operated in the first mode of operation, when the right conditions are present.

[0088] 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.