The present invention relates to a vapour compression system of a kind which comprises an ejector. The vapour compression system according to the invention is capable of ensuring efficient operation of the ejector, regardless of the ambient temperature.

BACKGROUND OF THE INVENTION

In some vapour compression systems an ejector is arranged in a refrigerant path, at a position downstream relative to a heat rejecting heat exchanger. Thereby refrigerant leaving the heat rejecting heat exchanger is supplied to a primary inlet of the ejector. Refrigerant leaving an evaporator of the vapour compression system may be supplied to a secondary inlet of the ejector.

An ejector is a type of pump which uses the Venturi effect to increase the pressure energy of fluid at a secondary inlet (or suction inlet) of the ejector by means of a motive fluid supplied to a primary inlet (or motive inlet) of the ejector. Thereby, arranging an ejector in the refrigerant path as described will cause the refrigerant to perform work, and thereby the power consumption of the vapour compression system is reduced as compared to the situation where no ejector is provided . It is desirable to allow as large a portion as possible of the refrigerant leaving the evaporator to be supplied to the secondary inlet of the ejector.

An outlet of the ejector is normally connected to a receiver, in which liquid refrigerant is separated from gaseous refrigerant. The liquid part of the refrigerant is supplied to the evaporator, via an expansion device. The gaseous part of the refrigerant may be supplied to a compressor. Thereby the gaseous part of the refrigerant is not subjected to the pressure drop introduced by the expansion device, and the work required in order to compress the refrigerant can therefore be reduced. When the ambient temperature is high, such as during the summer period, the temperature as well as the pressure of the refrigerant leaving the heat rejecting heat exchanger is relatively high. In this case the ejector performs well, and it is advantageous to supply all of the refrigerant leaving the evaporator to the secondary inlet of the ejector, and to supply gaseous refrigerant to the compressors from the receiver only. When the vapour compression system is operated in this manner, it is sometimes referred to as 'summer mode'. On the other hand, when the ambient temperature is low, such as during the winter period, the temperature as well as the pressure of the refrigerant leaving the heat rejecting heat exchanger is relatively low. In this case the ejector is not performing well, and it is advantageous to supply the refrigerant leaving the evaporator to the compressors, instead of to the secondary inlet of the ejector. When the vapour compression system is operated in this manner, it is sometimes referred to as 'winter mode'.

When the ambient temperature changes from a temperature regime which may be regarded as corresponding to 'summer mode' operating conditions to a temperature regime which may be regarded as corresponding to 'winter mode' operating conditions, or vice versa, it is desirable to be able to ensure that the vapour compression system is also switched from operating in the 'summer mode' to operating in the 'winter mode', or vice versa.

US 2012/0167601 Al discloses an ejector cycle. A heat rejecting heat exchanger is coupled to a compressor to receive compressed refrigerant. An ejector has a primary inlet coupled to the heat rejecting heat exchanger, a secondary inlet and an outlet. A separator has an inlet coupled to the outlet of the ejector, a gas outlet and a liquid outlet. The system can be switched between first and second modes. In the first mode refrigerant leaving the heat absorbing heat exchanger is supplied to the secondary inlet of the ejector. In the second mode refrigerant leaving the heat absorbing heat exchanger is supplied to the compressor.

DESCRIPTION OF THE INVENTION It is an object of embodiments of the invention to provide a vapour compression system comprising an ejector, in which efficient operation of the ejector is ensured, regardless of the ambient temperature.

The invention provides a 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, an outlet of the heat rejecting heat exchanger being connected to a primary inlet of the ejector and an outlet of the ejector being connected to the receiver, wherein the vapour compression system further comprises a non-return valve arranged in the refrigerant path which interconnects an outlet of the evaporator and an inlet of the compressor unit, in such a manner that a refrigerant flow from the outlet of the evaporator towards the inlet of the compressor unit is allowed, while a fluid flow from the inlet of the compressor unit towards the outlet of the evaporator is prevented, wherein the outlet of the evaporator is connected to a secondary inlet of the ejector and to the inlet of the compressor unit, via the non-return valve, and wherein a gaseous outlet of the receiver is connected to a part of the refrigerant path which interconnects the non-return valve and the inlet of the compressor unit.

The invention provides a vapour compression system. In the present context the term 'vapour compression system' should be interpreted to mean any system in which a flow of fluid medium, such as refrigerant, circulates and is alternatingly compressed and expanded, thereby providing either refrigeration or heating of a volume. Thus, the vapour compression system may be a refrigeration system, an air condition system, a heat pump etc.

The vapour compression system may be operated in the following manner. Refrigerant flowing in the refrigerant path is compressed by means of the compressors in the compressor unit, and the compressed refrigerant is supplied to the heat rejecting heat exchanger. In the heat rejecting heat exchanger heat exchange takes place between the refrigerant flowing through the heat rejecting heat exchanger and the ambient, in such a manner that heat is rejected from the refrigerant to the ambient. In the case that the heat rejecting heat exchanger is in the form of a condenser, the refrigerant is at least partly condensed, and in the case that the heat rejecting heat exchanger is in the form of a gas cooler, the refrigerant is cooled, but remains in the gaseous phase.

The refrigerant leaving the heat rejecting heat exchanger is supplied to a primary inlet of the ejector, where the refrigerant undergoes expansion before being supplied to the receiver. In the receiver the refrigerant is separated into a liquid part and a gaseous part. The liquid part of the refrigerant is supplied to the expansion device, via the liquid outlet. The expansion device expands the refrigerant before it is supplied to the evaporator. The refrigerant being supplied to the evaporator is in a mixed liquid and gaseous state. The gaseous part of the refrigerant in the receiver is supplied to a refrigerant path

interconnecting the non-return valve and an inlet of the compressor unit, i.e. it is supplied to the inlet of the compressor unit.

In the evaporator, 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. The refrigerant leaving the evaporator is supplied to the inlet of the compressor unit, via the non-return valve, and/or to the secondary inlet of the ejector.

Accordingly, refrigerant circulating the refrigerant path is alternatingly compressed by the compressor(s) of the compressor unit and expanded by the expansion device, while heat exchange takes place at the heat rejecting heat exchanger and at the evaporator, thereby providing heating or cooling.

The non-return valve is arranged to allow refrigerant flow from the outlet of the evaporator towards the inlet of the compressor unit, but to prevent refrigerant flow from the inlet of the compressor unit towards the outlet of the evaporator. Accordingly, refrigerant leaving the evaporator is allowed to reach the inlet of the compressor unit, via the non-return valve. However, a reverse flow of refrigerant from the inlet of the compressor unit, towards the outlet of the evaporator is prevented by the non-return valve.

The non-return valve could, e.g.. be of a passive kind or of an actively controlled kind. A passive valve could, e.g., be a simple check valve, or of a type comprising a resilient valve member pressed against another valve member in the closed position. Alternatively or additionally, the passive valve could be of a spring biased type. An actively controlled valve could, e.g., rely on mechanical valve switching or it could rely on electromagnetic switching.

The outlet of the evaporator is connected to a secondary inlet of the ejector and to the inlet of the compressor unit, via the non-return valve. Accordingly, refrigerant leaving the evaporator is supplied to the secondary inlet of the ejector and/or to the inlet of the compressor unit, via the non-return valve. Thus, all of the refrigerant leaving the evaporator may be supplied to the secondary inlet of the ejector. As an alternative, all of the refrigerant leaving the evaporator may be supplied to the inlet of the compressor unit, via the non- return valve. As another alternative, some of the refrigerant leaving the evaporator may be supplied to the secondary inlet of the ejector, and some of the refrigerant leaving the evaporator may be supplied to the inlet of the compressor unit, via the non-return valve.

A gaseous outlet of the receiver is connected to a part of the refrigerant path which interconnects the non-return valve and the inlet of the compressor unit. Accordingly, gaseous refrigerant from the receiver can be supplied directly to the inlet of the compressor unit.

However, since the non-return valve is arranged to prevent a fluid flow from the inlet of the compressor unit towards the outlet of the evaporator, refrigerant from the gaseous outlet of the receiver is only allowed to flow towards the inlet of the compressor unit, and a reverse flow towards the outlet of the evaporator is prevented. Additionally, if the pressure prevailing in the refrigerant path between the non-return valve and the inlet of the compressor unit is higher than the pressure prevailing in the refrigerant path between the evaporator and the non-return valve, no net refrigerant flow, through the non-return valve, is expected from the outlet of the evaporator towards the inlet of the compressor unit, due to the pressure difference. In this case no or only a limited amount of refrigerant from the outlet of the evaporator will flow to the inlet of the compressor unit. In this case the vapour compression system may be regarded as operating in accordance with a 'summer mode'. Furthermore, the non-return valve automatically ensures that this is obtained. On the other hand, if the pressure prevailing in the refrigerant path between the non-return valve and the inlet of the compressor unit is lower than the pressure prevailing in the refrigerant path between the evaporator and the non-return valve, a net refrigerant flow, through the non-return valve, is expected from the outlet of the evaporator towards the inlet of the compressor unit. Accordingly, the vapour compression system may be regarded as operating in accordance with a 'winter mode' in this case, and this is automatically ensured by the non-return valve.

An ejector present in the vapour compression system according to the invention has two inlets, as described above. A primary inlet (or motive inlet) connected to the outlet of the heat rejecting heat exchanger and a secondary inlet (or suction inlet) connected to the outlet of the evaporator. The ability to suck refrigerant from the secondary inlet depends on the pressure at the primary inlet. The pressure at the primary inlet of the ejector depends proportionally on the ambient temperature, which is relatively low during the winter season, and relatively high during the summer season . Thus, the ejector might not be able to suck in all refrigerant from the outlet of the evaporator during winter time in which case some refrigerant must be allowed to flow from the outlet of the evaporator to the inlet of the compressor unit.

When the ambient temperature is relatively low, so is the pressure prevailing at the gaseous outlet of the receiver as described above. However, although the pressure prevailing at the gaseous outlet of the receiver is relatively low compared to a situation in which ambient temperatures are relatively high, it might not be lower than the pressure prevailing at the outlet of the evaporator. In this case, only refrigerant from the gaseous outlet of the receiver is allowed to flow to the inlet of the compressor unit. As described above, during winter time the ejector might not be able to suck in all refrigerant from the outlet of the evaporator, in which case, refrigerant from the outlet of the evaporator should be allowed to pass the non- return valve and reach the inlet of the compressor unit.

In summary, the vapour compression system according to the invention is switched, due to pressure changes, and due to the non-return valve, between operating according to a 'summer mode' and according to a 'winter mode' as appropriate. The vapour compression system may further comprise a control valve arranged between the gaseous outlet of the receiver and the part of the refrigerant path which interconnects the non-return valve and the inlet of the compressor unit. According to this embodiment, the refrigerant flow from the gaseous outlet of the receiver towards the inlet of the compressor unit is controlled by means of the control valve.

The control valve may be of a kind which defines a variable opening degree. In this case the opening degree of the control valve, and thereby the mass flow of refrigerant from the gaseous outlet of the receiver towards the inlet of the compressor unit, can be adjusted between a fully closed position, defining a zero mass flow, and a fully open position, defining a maximum mass flow. The opening degree may be continuously variable or stepwise variable.

As an alternative, the control valve may be switchable between a fully closed position and a fully open position. In this case an effective opening degree of the control valve may be obtained by varying durations of open and closed periods in a manner which is known per se. Since the control valve controls the mass flow of refrigerant from the gaseous outlet of the receiver to the part of the refrigerant path which interconnects the non-return valve and the inlet of the compressor unit, the control valve can also be used for controlling the pressure in this part of the refrigerant path. Accordingly, the control valve can also be used for controlling the refrigerant flow from the outlet of the evaporator towards the secondary inlet of the ejector and the inlet of the compressor unit, respectively, as described above.

In summary, according to this embodiment, the vapour compression system can be switched, selectively, between operating according to a 'summer mode' and according to a 'winter mode' solely by appropriately controlling the control valve.

The control valve may be arranged to be controlled on the basis of a pressure prevailing in the receiver. According to this embodiment, the pressure prevailing inside the receiver is measured, and the measured pressure is used as a control parameter for the control valve. For instance, if the pressure prevailing inside the receiver increases, the opening degree of the control valve may be increased, and if the pressure prevailing inside the receiver decreases, the opening degree of the control valve may be decreased. As an alternative, the control valve may be arranged to be controlled on the basis of a pressure difference between the pressure prevailing in the receiver and the pressure prevailing in the evaporator. According to this embodiment, the pressure prevailing inside the receiver and the pressure prevailing inside the evaporator are measured, and the measured pressure difference is used as a control parameter for the control valve. For instance, if the pressure prevailing inside the receiver increases relatively to the pressure prevailing in the evaporator, the opening degree of the control valve may be increased, and if the pressure prevailing inside the receiver decreases relative to the pressure prevailing in the evaporator, the opening degree of the control valve may be decreased.

As another alternative, another suitable control parameter may be used for controlling the control valve.

As yet another alternative, the vapour compression system may not include a control valve. In this case the vapour compression system may be operated in the following manner. When the ambient temperature is relatively high, such as during the summer period, the pressure in the receiver must be expected to be relatively high. Thereby the pressure prevailing at the gaseous outlet of the receiver is also relatively high . Furthermore, since there, in this case, is no control valve arranged between the gaseous outlet of the receiver and the part of the refrigerant path which interconnects non-return valve and the inlet of the compressor unit, a relatively high pressure will also prevail in this part of the refrigerant path. This will most likely result in a relatively high pressure prevailing in the part of the refrigerant path interconnecting the non-return valve and the inlet of the compressor unit as compared to the pressure prevailing in the part of the refrigerant path interconnecting the outlet of the evaporator and the non-return valve. Due to this pressure difference, refrigerant from the outlet of the evaporator will primarily or only flow to the secondary inlet of the ejector. Thus, the vapour compression system is automatically operated according to a 'summer mode' in this case.

On the other hand, when the ambient temperature is relatively low, such as during winter time, the pressure in the receiver, and thereby the pressure prevailing at the gaseous outlet of the receiver and in the part of the refrigerant path interconnecting the non-return valve and the inlet of the compressor unit must be expected to be relatively low. When the pressure prevailing in the part of the refrigerant path interconnecting the outlet of the evaporator and the non-return valve is higher than the pressure prevailing in the part of the refrigerant path interconnecting the non-return valve and the inlet of the compressor unit, the non-return valve allows refrigerant to flow from the outlet of the evaporator to the inlet of the compressor unit. Thus, it is automatically obtained that the vapour compression system is operated according to a 'winter mode' in this case.

The non-return valve may further be arranged to close, thereby preventing a refrigerant flow from the inlet of the compressor unit towards the outlet of the evaporator, in the case that a pressure prevailing in the part of the refrigerant path which interconnects the non-return valve and the inlet of the compressor unit exceeds a pressure prevailing in a part of the refrigerant path which interconnects the outlet of the evaporator and the non-return valve.

Accordingly, when the pressure prevailing in the refrigerant path interconnecting the nonreturn valve and the inlet of the compressor unit exceeds the pressure prevailing in the refrigerant path interconnecting the outlet of the evaporator and the non-return valve, the non-return valve may be closed, which prevents a reverse flow towards the outlet of the evaporator.

The non-return valve may further be arranged to prevent a refrigerant flow from the outlet of the evaporator towards the inlet of the compressor unit, in the case that a pressure prevailing in the part of the refrigerant path which interconnects the non-return valve and the inlet of the compressor unit exceeds a pressure prevailing in a part of the refrigerant path which interconnects the outlet of the evaporator and the non-return valve.

When the pressure prevailing in the part of the refrigerant path which interconnects the nonreturn valve and the inlet of the compressor unit exceeds the pressure prevailing in the part of the refrigerant path which interconnects the outlet of the evaporator and the non-return valve, the non-return valve may be closed, in the manner described above. In this case, no refrigerant flow is allowed to flow across the non-return valve. Consequently, all refrigerant from the outlet of the evaporator flows to the secondary inlet of the ejector, and it is efficiently prevented that refrigerant flows from the outlet of the evaporator towards the inlet of the compressor unit, via the non-return valve. As described above, this is, e.g ., the case when the ambient temperature is relatively high and the system is operated according to a 'summer mode'. It is noted that the refrigerant is unlikely to flow from a part of the refrigerant path with a relatively low prevailing pressure to a part of the refrigerant path with a relatively high prevailing pressure. Accordingly, when the pressure prevailing in the part of the refrigerant path which interconnects the non-return valve and the inlet of the compressor unit is higher than the pressure prevailing in the part of the refrigerant path which interconnects the outlet of the evaporator and the non-return valve, refrigerant will not flow from the outlet of the evaporator towards the inlet of the compressor unit, via the non-return valve, even if the non-return valve is not closed. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in further detail with reference to the accompanying drawing in which Fig. 1 is a diagrammatic view of a vapour compression system according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Fig. 1 is a diagrammatic view of a vapour compression system 1 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, an ejector 5, a receiver 6, an expansion device 7, in the form of an expansion valve, and an evaporator 8 arranged in a refrigerant path. The vapour compression system 1 further comprises a non-return valve 9 and a control valve 10. The receiver 6 is arranged to separate refrigerant into a liquid part and a gaseous part, and the receiver 6 comprises a liquid outlet 11 and a gaseous outlet 12. The liquid outlet 11 is connected to the expansion device 7, i.e. the liquid part of the refrigerant in the receiver 6 is supplied to the evaporator 8, via the expansion device 7.

The vapour compression system 1 of Fig. 1 may be operated in the following manner.

Refrigerant flowing in the refrigerant path is compressed by means of the compressors 3 of the compressor unit 2, and the compressed refrigerant is supplied to the heat rejecting heat exchanger 4. In the heat rejecting heat exchanger 4 heat exchange takes place between the refrigerant flowing through the heat rejecting heat exchanger 4 and the ambient, in such a manner that heat is rejected from the refrigerant to the ambient. In the case that the heat rejecting heat exchanger 4 is in the form of a condenser, the refrigerant is at least partly condensed, and in the case that the heat rejecting heat exchanger 4 is in the form of a gas cooler, the refrigerant is cooled, but remains in the gaseous phase.

The refrigerant leaving the heat rejecting heat exchanger 4 is supplied to a primary inlet 13 of the ejector 5, where the refrigerant undergoes expansion before being supplied to the receiver 6.

In the receiver 6 the refrigerant is separated into a liquid part and a gaseous part. The liquid part of the refrigerant is supplied to the expansion device 7, via the liquid outlet 11. The expansion device 7 expands the refrigerant before it is supplied to the evaporator 8. The refrigerant being supplied to the evaporator 8 is in a mixed liquid and gaseous state. The gaseous part of the refrigerant in the receiver 6 is supplied to an inlet 13 of the control valve 10. From an outlet 14 of the control valve 10, refrigerant is supplied to a part of the refrigerant path interconnecting the non-return valve 9 and an inlet 15 of the compressor unit 2. Thereby a refrigerant flow from the gaseous outlet 12 of the receiver 6 towards the part of the refrigerant path interconnecting the non-return valve 9 and the inlet 15 of the compressor unit 2 is controlled by means of the control valve 10.

In the evaporator 8 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 8. The refrigerant leaving the evaporator 8 is supplied to the non-return valve 9 and/or to a secondary inlet 16 of the ejector 5.

Two refrigerant paths lead to the inlet 15 of the compressor unit 2. Refrigerant can be delivered from the evaporator 8, via the non-return valve 9, and/or from the gaseous outlet 12 of the receiver 6, passing through the control valve 10. If the pressure prevailing at the outlet 14 of the control valve 10 is higher than the pressure prevailing at the outlet 17 of the evaporator 8, the non-return 9 valve is closed. In this case, all the refrigerant at the inlet 15 of the compressor unit 2 is supplied from the gaseous outlet 12 of the receiver 6. The pressure prevailing in the refrigerant path interconnecting the non-return valve 9 and the inlet 15 of the compressor unit 2 relative to the pressure prevailing in the refrigerant path interconnecting the outlet 17 of the evaporator 8 depends on the pressure prevailing in the receiver 6 and to which extent the control valve 10 allows a flow across it. As described above, the refrigerant flow across the non-return valve 9 is determined by the pressures prevailing on either side of it. Then the flow across the non-return valve 9 and thus switching between operation according to a summer mode or a winter mode can be simply achieved by controlling the control valve 10 in an appropriate manner.