Integrated Air-Conditioning Circuit and CO2 Refrigeration System Incorporating Same

Abstract

The present invention relates to an integrated air-conditioning (A/C) circuit for a Carbon Dioxide (CO2) refrigeration system having a CO2 based refrigerant circuit including a high pressure refrigerant cooling heat exchanger that passes refrigerant received at a high pressure in heat exchange relationship with a cooling medium. The A/C circuit is nested within the CO2 refrigeration system and includes a means of directing discharge from an outlet line of the refrigerant cooling heat exchanger into the nested air-conditioning circuit. The A/C circuit further includes a means of reducing the pressure of the refrigerant directed from the outlet line of the refrigerant cooling heat exchanger, and a refrigerant heating heat exchanger for receiving the refrigerant having a reduced pressure and passing the refrigerant in heat exchange relationship with a heating medium to generate chilled fluid.

Claims

1. An integrated air-conditioning (A/C) circuit for a Carbon Dioxide (CO.sub.2) refrigeration system having a CO.sub.2 based refrigerant circuit including a high pressure refrigerant cooling heat exchanger that passes refrigerant received at a high pressure in heat exchange relationship with a cooling medium, wherein the A/C circuit is nested within the CO.sub.2 refrigeration system and includes: a means of directing discharge from an outlet line of the refrigerant cooling heat exchanger into the nested air-conditioning circuit, a means of reducing the pressure of the refrigerant directed from the outlet line of the refrigerant cooling heat exchanger, and a refrigerant heating heat exchanger for receiving the refrigerant having a reduced pressure and passing the refrigerant in heat exchange relationship with a heating medium to generate chilled fluid.

2. An integrated air-conditioning circuit according to claim 1, further including: a means of re-compressing the refrigerant from the refrigerant heating heat exchanger before passing the refrigerant to an inlet line of the refrigerant cooling heat exchanger.

3. An integrated air-conditioning circuit according to claim 1, wherein the chilled fluid is chilled water generated when the refrigerant heating heat exchanger is a CO.sub.2:H.sub.2O heat exchanger.

4. An integrated air-conditioning circuit according to claim 1, wherein the chilled fluid chilled air generated when the refrigerant heating heat exchanger is a CO.sub.2 ambient air heat exchanger.

5. An integrated air-conditioning circuit according to claim 1, wherein the means of reducing the pressure of the refrigerant is an expansion valve located upstream of the refrigerant heating heat exchanger which expands the refrigerant directly into the refrigerant heating heat exchanger.

6. An integrated air-conditioning circuit according to claim 1, wherein the means of re-compressing the refrigerant from the refrigerant heating heat exchanger before passing the refrigerant back to the inlet line of the refrigerant cooling heat exchanger is one or more refrigerant compression devices.

7. An integrated air-conditioning circuit according to claim 6, wherein the one or more refrigerant compression devices are one or more dedicated A/C compressors located downstream of the refrigerant heating heat exchanger operating at approximately 5 to 7 degrees Celsius.

8. An integrated air-conditioning circuit according to claim 1, further including: a means of pumping the generated chilled fluid to an A/C chilled fluid handling evaporator for the purpose of utilising the chilled fluid for air-conditioning.

9. An integrated air-conditioning circuit according to claim 1, wherein in addition to including a high-pressure refrigerant cooling heat exchanger, the CO.sub.2 based refrigerant circuit further includes: one or more refrigerant compression devices located upstream of the refrigerant cooling heat exchanger, a refrigerant heating heat exchanger for passing refrigerant at a low pressure in heat exchange relationship with a heating medium, and an expansion device disposed in the CO.sub.2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said refrigerant heating heat exchanger.

10. An integrated air-conditioning circuit according to claim 9, wherein the refrigeration system further includes: a flash tank receiver disposed in the CO.sub.2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said expansion device, at least one ejector disposed in the CO.sub.2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said flash tank receiver, a three-way valve disposed at an entry side of the one or more refrigerant compression devices, and a controller operable to switch the mode of operation of the refrigeration system, from: a baseline mode in which the flash tank receiver receives refrigerant exclusively from the refrigerant cooling heat exchanger, and vapour refrigerant from the flash tank receiver is caused to pass through a first refrigerant line from the flash tank receiver to the refrigerant compression device such that refrigerant passing from the refrigerant heating heat exchanger of the refrigerant circuit to the refrigerant compression device is mixed with said vapour refrigerant from the flash tank, the flash gas receiver having associated therewith a flash gas bypass valve to manage flash gas as it accumulates in the flash gas receiver, to: a parallel compression mode in which the flash gas bypass valve is closed and vapour refrigerant from the flash tank receiver is caused to pass through a second refrigerant line to one or more second refrigerant compression devices that operate in parallel with the one or more refrigerant compression devices, the one or more second refrigerant compression devices managing the flash gas as it accumulates in the flash gas receiver by recompressing and discharging same to the inlet line of the refrigerant cooling heat exchanger, and subsequently to: an ejector mode in which the three-way valve disposed at an entry side of the one or more refrigerant compression devices is operated to cause vapour refrigerant from the flash tank receiver to, in addition to passing through the second refrigerant line to the one or more second refrigerant compression devices, pass through a third refrigerant line from the flash tank receiver to the one or more refrigerant compression devices, wherein refrigerant from the refrigerant heating heat exchanger of the refrigerant circuit is diverted through a fourth refrigerant line to the at least one ejector where the refrigerant is mixed with refrigerant from the refrigerant cooling heat exchanger, the flash tank receiver thereby receiving a mix of refrigerants from the refrigerant heating heat exchanger and the refrigerant cooling heat exchanger.

11. An integrated air-conditioning circuit according to claim 9, wherein the refrigeration system further includes: a flash tank receiver disposed in the CO.sub.2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said expansion device, at least one ejector disposed in the CO.sub.2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said flash tank receiver, a three-way valve disposed at an entry side of the one or more refrigerant compression devices and operable to switch the mode of operation of the refrigeration system between: a first mode in which the flash tank receiver receives refrigerant exclusively from the refrigerant cooling heat exchanger such that vapour refrigerant from the flash tank receiver is caused to pass through a first refrigerant line from the flash tank receiver to the one or more refrigerant compression devices with refrigerant passing from the refrigerant heating heat exchanger of the refrigerant circuit to the one or more refrigerant compression devices mixed with said vapour refrigerant from the flash tank, and a second mode in which the vapour refrigerant from the flash tank receiver is caused to pass through a second refrigerant line from the flash tank receiver to the one or more refrigerant compression devices such that the one or more refrigerant compression devices are supplied refrigerant exclusively from the flash gas receiver, wherein refrigerant from the refrigerant heating heat exchanger of the refrigerant circuit is diverted through a third refrigerant line to the at least one ejector with the refrigerant mixed with refrigerant from the refrigerant cooling heat exchanger, the flash tank receiver thereby receiving a mixture of refrigerants from the refrigerant heating heat exchanger and the refrigerant cooling heat exchanger, and a controller operatively associated with the three-way valve, the controller operable to cause the refrigeration system to transition directly from the first to the second mode of operation when a particular condition has been detected.

12. An integrated air-conditioning circuit according to claim 9, wherein the refrigeration system further includes: a flash tank receiver disposed in the CO.sub.2 based refrigerant circuit downstream from said refrigerant cooling heat exchanger, the flash tank receiver having associated therewith a flash gas bypass valve, at least one liquid ejector disposed in the CO.sub.2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said flash tank receiver, and a suction accumulator disposed in the refrigerant circuit downstream of the refrigerant heating heat exchanger of the refrigerant circuit to capture any liquid refrigerant from the refrigerant heating heat exchanger of the refrigerant circuit, wherein the mode of operation of the refrigeration system is configured to be switched between: a first mode of operation in which the flash tank receiver receives refrigerant exclusively from the refrigerant cooling heat exchanger such that vapour refrigerant from the flash tank receiver is caused to pass through a refrigerant line from the flash tank receiver to the one or more refrigerant compression devices with refrigerant passing from the refrigerant heating heat exchanger of the refrigerant circuit to the one or more refrigerant compression devices mixed with said vapour refrigerant from the flash tank, and a second mode of operation wherein the at least one liquid ejector is operated to entrain a portion of liquid refrigerant recovered from the suction accumulator and to re-inject said liquid back into the flash tank receiver, where the flash gas bypass valve is configured to manage flash gas build-up in the receiver, and a controller operatively associated with the three-way valve, the controller operable to cause the refrigeration system to transition directly from the first to the second mode of operation when a particular condition has been detected.

13. An integrated air-conditioning circuit according to claim 11, wherein the controller is configured to automatically activate or schedule the transition from the first to the second mode of operation upon determining the particular condition which includes one or more of: dry-bulb ambient temperature increasing from a first temperature below approximately 25 degrees Celsius to a second temperature equal to or greater than approximately 25 degrees Celsius, and a temperature at a discharge of the refrigerant cooling heat exchanger increasing from a first temperature below approximately 27 degrees Celsius to a second temperature equal to or greater than approximately 27 degrees Celsius.

14. An integrated air-conditioning circuit according to claim 10, wherein the refrigeration system further includes a second refrigerant heating heat exchanger arranged in parallel with the refrigerant heating heat exchanger with an associated expansion device, and associated with a second expansion device, the second refrigerant heating heat exchanger also configured to pass refrigerant at a low pressure in heat exchange relationship with a heating medium, the refrigerant heating heat exchanger configured to output MT refrigerant, and the second refrigerant heating heat exchanger configured to output low temperature (LT) refrigerant.

15. An integrated air-conditioning circuit according to claim 10, wherein the integrated air-conditioning circuit is operated when an associated store requires temperature and/or humidity adjustment, including at any time during said different modes of operation.

16. A Carbon Dioxide (CO.sub.2) refrigeration system including an integrated air-conditioning circuit according to claim 1.

17. A Carbon Dioxide (CO.sub.2) refrigeration system including: a CO.sub.2 based refrigerant circuit including: a high-pressure refrigerant cooling heat exchanger that passes refrigerant received at a high pressure in heat exchange relationship with a cooling medium, one or more refrigerant compression devices located upstream of the refrigerant cooling heat exchanger, a refrigerant heating heat exchanger for passing refrigerant at a low pressure in heat exchange relationship with a heating medium, and an expansion device disposed downstream of said refrigerant cooling heat exchanger and upstream of said refrigerant heating heat exchanger, a flash tank receiver disposed in the CO.sub.2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said expansion device, at least one ejector disposed in the CO.sub.2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said flash tank receiver, a three-way valve disposed at an entry side of the one or more refrigerant compression devices, and a controller operable to switch the mode of operation of the refrigeration system, from: a baseline mode in which the flash tank receiver receives refrigerant exclusively from the refrigerant cooling heat exchanger, and vapour refrigerant from the flash tank receiver is caused to pass through a first refrigerant line from the flash tank receiver to the refrigerant compression device such that refrigerant passing from the refrigerant heating heat exchanger of the refrigerant circuit to the refrigerant compression device is mixed with said vapour refrigerant from the flash tank, the flash gas receiver having associated therewith a flash gas bypass valve to manage flash gas as it accumulates in the flash gas receiver, to: a parallel compression mode in which the flash gas bypass valve is closed and vapour refrigerant from the flash tank receiver is caused to pass through a second refrigerant line to one or more second refrigerant compression devices that operate in parallel with the one or more refrigerant compression devices, the one or more second refrigerant compression devices managing the flash gas as it accumulates in the flash gas receiver by recompressing and discharging same to the inlet line of the refrigerant cooling heat exchanger, and subsequently to: an ejector mode in which the three-way valve disposed at an entry side of the one or more refrigerant compression devices is operated to cause vapour refrigerant from the flash tank receiver to, in addition to passing through the second refrigerant line to the one or more second refrigerant compression devices, pass through a third refrigerant line from the flash tank receiver to the one or more refrigerant compression devices, wherein refrigerant from the refrigerant heating heat exchanger of the refrigerant circuit is diverted through a fourth refrigerant line to the at least one ejector where the refrigerant is mixed with refrigerant from the refrigerant cooling heat exchanger, the flash tank receiver thereby receiving a mix of refrigerants from the refrigerant heating heat exchanger and the refrigerant cooling heat exchanger, and an integrated A/C circuit, including: a means of directing discharge from an outlet line of the refrigerant cooling heat exchanger into the integrated air-conditioning circuit, a means of reducing the pressure of the refrigerant directed from the outlet line of the refrigerant cooling heat exchanger, a second refrigerant heating heat exchanger for receiving the refrigerant of reduced pressure and passing the refrigerant in heat exchange relationship with a heating medium to generate chilled fluid, and a means of re-compressing the refrigerant from the second refrigerant heating heat exchanger before passing the refrigerant to an inlet line of the refrigerant cooling heat exchanger.

18. A Carbon Dioxide (CO.sub.2) refrigeration system including: a CO.sub.2 based refrigerant circuit including: a high-pressure refrigerant cooling heat exchanger that passes refrigerant received at a high pressure in heat exchange relationship with a cooling medium, one or more refrigerant compression devices located upstream of the refrigerant cooling heat exchanger, a refrigerant heating heat exchanger for passing refrigerant at a low pressure in heat exchange relationship with a heating medium, and an expansion device disposed downstream of said refrigerant cooling heat exchanger and upstream of said refrigerant heating heat exchanger, a flash tank receiver disposed in the CO.sub.2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said expansion device, at least one ejector disposed in the CO.sub.2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said flash tank receiver, a three-way valve disposed at an entry side of the one or more refrigerant compression devices and operable to switch the mode of operation of the refrigeration system between: a first mode in which the flash tank receiver receives refrigerant exclusively from the refrigerant cooling heat exchanger such that vapour refrigerant from the flash tank receiver is caused to pass through a first refrigerant line from the flash tank receiver to the one or more refrigerant compression devices with refrigerant passing from the refrigerant heating heat exchanger of the refrigerant circuit to the one or more refrigerant compression devices mixed with said vapour refrigerant from the flash tank, and a second mode in which the vapour refrigerant from the flash tank receiver is caused to pass through a second refrigerant line from the flash tank receiver to the one or more refrigerant compression devices such that the one or more refrigerant compression devices are supplied refrigerant exclusively from the flash gas receiver, wherein refrigerant from the refrigerant heating heat exchanger of the refrigerant circuit is diverted through a third refrigerant line to the at least one ejector with the refrigerant mixed with refrigerant from the refrigerant cooling heat exchanger, the flash tank receiver thereby receiving a mixture of refrigerants from the refrigerant heating heat exchanger and the refrigerant cooling heat exchanger, and a controller operatively associated with the three-way valve, the controller operable to cause the refrigeration system to transition directly from the first to the second mode of operation when a particular condition has been detected, and an integrated A/C circuit, including: a means of directing discharge from an outlet line of the refrigerant cooling heat exchanger into the integrated air-conditioning circuit, a means of reducing the pressure of the refrigerant directed from the outlet line of the refrigerant cooling heat exchanger, a second refrigerant heating heat exchanger for receiving the refrigerant of reduced pressure and passing the refrigerant in heat exchange relationship with a heating medium to generate chilled fluid, and a means of re-compressing the refrigerant from the second refrigerant heating heat exchanger before passing the refrigerant to an inlet line of the refrigerant cooling heat exchanger.

19. A Carbon Dioxide (CO.sub.2) refrigeration system including: a CO.sub.2 based refrigerant circuit including: a high-pressure refrigerant cooling heat exchanger that passes refrigerant received at a high pressure in heat exchange relationship with a cooling medium, one or more refrigerant compression devices located upstream of the refrigerant cooling heat exchanger, a refrigerant heating heat exchanger for passing refrigerant at a low pressure in heat exchange relationship with a heating medium, and an expansion device disposed downstream of said refrigerant cooling heat exchanger and upstream of said refrigerant heating heat exchanger, a flash tank receiver disposed in the CO.sub.2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger, the flash tank receiver having associated therewith a flash gas bypass valve, at least one liquid ejector disposed in the CO.sub.2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said flash tank receiver, and a suction accumulator disposed in the refrigerant circuit downstream of the refrigerant heating heat exchanger of the refrigerant circuit to capture any liquid refrigerant from the refrigerant heating heat exchanger of the refrigerant circuit, wherein the mode of operation of the refrigeration system is configured to be switched between: a first mode of operation in which the flash tank receiver receives refrigerant exclusively from the refrigerant cooling heat exchanger such that vapour refrigerant from the flash tank receiver is caused to pass through a refrigerant line from the flash tank receiver to the one or more refrigerant compression devices with refrigerant passing from the refrigerant heating heat exchanger of the refrigerant circuit to the one or more refrigerant compression devices mixed with said vapour refrigerant from the flash tank, and a second mode of operation wherein the at least one liquid ejector is operated to entrain a portion of liquid refrigerant recovered from the suction accumulator and to re-inject said liquid back into the flash tank receiver, where the flash gas bypass valve is configured to manage flash gas build-up in the receiver, with a controller operable to cause the refrigeration system to transition directly from the first to the second mode of operation when a particular condition has been detected, and an integrated A/C circuit, including: a means of directing discharge from an outlet line of the refrigerant cooling heat exchanger into the integrated air-conditioning circuit, a means of reducing the pressure of the refrigerant directed from the outlet line of the refrigerant cooling heat exchanger, a second refrigerant heating heat exchanger for receiving the refrigerant of reduced pressure and passing the refrigerant in heat exchange relationship with a heating medium to generate chilled fluid, and a means of re-compressing the refrigerant from the second refrigerant heating heat exchanger before passing the refrigerant to an inlet line of the refrigerant cooling heat exchanger.

20. An integrated air-conditioning circuit according to claim 12, wherein the controller is configured to automatically activate or schedule the transition from the first to the second mode of operation upon determining the particular condition which includes one or more of: dry-bulb ambient temperature increasing from a first temperature below approximately 25 degrees Celsius to a second temperature equal to or greater than approximately 25 degrees Celsius, and a temperature at a discharge of the refrigerant cooling heat exchanger increasing from a first temperature below approximately 27 degrees Celsius to a second temperature equal to or greater than approximately 27 degrees Celsius.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Features of the present disclosure are illustrated by way of example and not limited in the following Figure(s), in which like numerals indicate like elements, in which:

[0045] FIG. 1 illustrates a prior art Carbon Dioxide (CO.sub.2) refrigeration system operating in ejector mode.

[0046] FIG. 2 illustrates a CO.sub.2 refrigeration system including an integrated air-conditioning (A/C) circuit configured in accordance with an embodiment of the present invention.

[0047] FIG. 3 illustrates an enlarged view of section 100a of the refrigeration system and integrated A/C circuit of FIG. 2.

[0048] FIG. 4 illustrates an enlarged view of section 100b of the refrigeration system and integrated A/C circuit of FIG. 2.

[0049] FIG. 5 illustrates an enlarged view of section 100c of the refrigeration system and integrated A/C circuit of FIG. 2.

[0050] FIG. 6 illustrates an enlarged view of section 100d of the refrigeration system and integrated A/C circuit of FIG. 2.

[0051] FIG. 7 illustrates an enlarged view of section 100e of the refrigeration system and integrated A/C circuit of FIG. 2.

[0052] FIG. 8 illustrates a CO.sub.2 refrigeration system according to an alternative embodiment as compared with the refrigeration system shown in FIG. 2, including an integrated A/C circuit configured in accordance with an embodiment of the present invention.

[0053] FIG. 9 illustrates an enlarged view of section 200a of the refrigeration system and integrated A/C circuit of FIG. 8.

[0054] FIG. 10 illustrates an enlarged view of section 200b of the refrigeration system and integrated A/C circuit of FIG. 8.

[0055] FIG. 11 illustrates an enlarged view of section 200c of the refrigeration system and integrated A/C circuit of FIG. 8.

[0056] FIG. 12 illustrates an enlarged view of sections 200d and 200e of the refrigeration system and integrated A/C circuit of FIG. 8.

DETAILED DESCRIPTION OF EMBODIMENT(S) OF THE INVENTION

[0057] In an embodiment, the present invention includes an integrated air-conditioning (A/C) circuit (100e/200e) for a carbon dioxide (CO.sub.2) refrigeration system (100/200), and a refrigeration system (100/200) incorporating same, with one system embodiment (100) configured and detailed in FIGS. 2 to 7 and another system embodiment (200) configured and detailed in FIGS. 8 to 12. The reader will appreciate that the system shown in FIG. 2 includes sections 100a, 100b, 100c, 100d and 100e, which are shown in enlarged views in FIGS. 3 to 7 respectively, and the system shown in FIG. 8 includes sections 200a, 200b, 200c and 200d/e which are shown in enlarged views in FIGS. 9 to 12 respectively.

[0058] The refrigeration systems (100/200) illustrated and described herein represent examples of CO.sub.2 refrigeration systems into which the respective A/C circuits (100e/200e) may be integrated. However, it will be understood that the present invention may apply equally to alternate CO.sub.2 refrigeration circuits, provided they incorporate a gas cooling component (e.g., high pressure gas cooler (154/122)) within which the A/C circuit may be nested, as described in greater detail below. An alternative gas cooling component may be a water gas cooler/heat exchanger (not shown) (e.g., in a shell-and-tube refrigeration design with cooled water used to cool or condense the CO.sub.2 gas).

[0059] In the embodiment depicted in FIGS. 2 to 7, the refrigeration system (100) represents an example installation according to the system described in the Applicant's co-pending international Patent Cooperation Treaty (PCT) Application No. PCT/AU2022/050704. In particular, the refrigeration system (100) includes a CO.sub.2 based refrigerant circuit including one or more refrigerant compression devices (152) (also referred to as Medium Temperature or MT compressors), a refrigerant cooling heat exchanger (154) (i.e., the gas cooler, also referred to as a condenser), and a refrigerant heating heat exchanger (not shown) (also referred to as an evaporator with medium temperature or MT output) with an associated upstream expansion device (not shown) (also referred to herein as an expansion valve). The skilled reader will appreciate that the refrigerant cooling heat exchanger (154) is responsible for passing refrigerant received from the compression devices (152) at a high pressure in heat exchange relationship with a cooling medium, and that the refrigerant heating heat exchanger is responsible for passing refrigerant at a low pressure in heat exchange relationship with a heating medium.

[0060] The example CO.sub.2 based refrigeration system (100) depicted in FIGS. 2 to 7 also includes a flash tank receiver (160) downstream of the refrigerant cooling heat exchanger (154) and upstream of the refrigerant heating heat exchanger, at least one ejector (162) downstream of the refrigerant cooling heat exchanger (154) and upstream of the flash tank receiver (160), and a three-way valve (164) disposed at an entry side of the refrigerant compression devices (152) and operable to switch between different modes of operation of the refrigeration system (100) as described in greater detail below.

[0061] Whilst not shown in FIGS. 2 to 7, refrigeration system (100) will typically include a controller for operating each of the components at the required time, including switching the system between different modes of operation according to detected ambient conditions.

[0062] In a first mode of operation, the flash tank receiver (160) receives refrigerant exclusively from the refrigerant cooling heat exchanger (154), and vapour refrigerant from the flash tank receiver (160) is caused to pass through a first refrigerant line (166) from the flash tank receiver (160) to the refrigerant compression devices (152) such that refrigerant passing from the refrigerant heating heat exchanger (see directional arrow shown in FIGS. 2 and 5) to the refrigerant compression devices (152) is mixed with the vapour refrigerant from the flash tank receiver (160).

[0063] In a second mode of operation, the vapour refrigerant from the flash tank receiver (160) is caused to pass through a second refrigerant line (168) from the flash tank receiver (160) to the refrigerant compression devices (152) such that the refrigerant compression devices (152) are supplied refrigerant exclusively from the flash gas receiver (160). Refrigerant from the refrigerant heating heat exchanger (see directional arrow shown in FIGS. 2 and 5) is diverted through a third refrigerant line (170) to the at least one ejector (162) where the refrigerant is mixed with refrigerant from the refrigerant cooling heat exchanger (154). In this way, the flash tank receiver (160) receives a mix of refrigerants from the refrigerant heating heat exchanger (56) and the refrigerant cooling heat exchanger (154). Also depicted in the system (100) of FIG. 2 is a flash gas by-pass valve (172) that is open in the first mode of operation thereby managing flash gas as it accumulates in the flash gas receiver (160), whilst the flash gas by-pass valve (172) is closed in the second mode of operation.

[0064] In the first mode of operation, since the ejector suction valve is always closed, the at least one ejector (162) acts as a high pressure valve for receiving high pressure refrigerant exclusively from the refrigerant cooling heat exchanger (154). Such ejectors typically include a nozzle through which high pressure refrigerant from the refrigerant cooling heat exchanger (154) enters. Each ejector further includes a suction valve that is open during the second mode of operation, and enables refrigerant of a significantly lower pressure from the refrigerant heating heat exchanger to enter the ejector (162) and, by utilising the energy provided by the higher pressure refrigerant, the lower pressure is entrained by the higher pressure refrigerant as a result of the venturi effect.

[0065] The abovementioned entrainment is caused by a lift in refrigerant pressure resulting from the ejector operating under a high pressure differential (i.e., the high pressure differential between the discharge pressure upstream of the ejector (162), and the pressure in the receiver (160) downstream from the ejector (162)).

[0066] In the first mode of operation, the ejector suction valve is always closed and hence, as mentioned earlier, the at least one ejector (162) acts as a high pressure valve for receiving high pressure refrigerant exclusively from the refrigerant cooling heat exchanger (154). In the second mode of operation, the ejector suction valve is opened to allow refrigerant from the refrigerant heating heat exchanger to be mixed with the refrigerant from the refrigerant cooling heat exchanger (154) to form a pre-compressed vapour and liquid that is subsequently injected into the flash tank receiver (160).

[0067] Accordingly, whilst in the first mode of operation, the at least one ejector (162) is required to handle refrigerant exclusively from the refrigerant cooling heat exchanger (154). In the second mode of operation, the at least one ejector (162) is required to also accommodate refrigerant from the refrigerant heating heat exchanger (i.e., the entire mass flow of the MT refrigerant). In other words, in the second mode of operation, the system (100) no longer takes a portion of the flash gas mass flow for re-compressing same. Instead, the entire volume from the refrigerant heating heat exchanger is drawn through the ejector (162). This has a number of effects which are described in the Applicant's above referenced co-pending international Patent Application.

[0068] The system (100) may be caused by the controller to switch from the first to the second mode when a particular ambient condition is detected.

[0069] It will be appreciated that the system (200) of FIG. 2 may also incorporate a second refrigerant heating heat exchanger (not shown) with an associated upstream second expansion device. The second refrigerant heating heat exchanger may also be configured to pass refrigerant at a low pressure in heat exchange relationship with a heating medium, but configured to output low temperature (LT) refrigerant rather than MT refrigerant. Refrigeration systems are typically required to provide refrigeration as well as freezing, and the reason for including the second evaporator is to ensure that the system (100) is suitable for providing cooling in freezers in addition to cooling in refrigerators. In other words, the MT refrigerant from the first refrigerant heating heat exchanger is suitable for providing cooling in refrigerators, and the LT refrigerant from the second refrigerant heating heat exchanger is suitable for providing cooling in freezers, hence the system (100) is capable of servicing a building requiring both refrigerator and freezer cooling.

[0070] As a result of integration of A/C circuit (100e) into refrigeration system (100), the system is also capable of servicing the air-conditioning requirements of a building. As depicted in FIG. 2, and more particularly in the enlarged view of the A/C circuit (100e) depicted in FIG. 7, the A/C circuit (100e) is nested within, although operates independently from, the CO.sub.2 refrigeration system (100) and diverts discharge from an outlet line (174) of the refrigerant cooling heat exchanger (154) into the independent air-conditioning circuit (100e). The system (100e) includes a means (176) of reducing the pressure of the refrigerant diverted from the outlet line (174) of the refrigerant cooling heat exchanger (154), and further downstream, a refrigerant heating heat exchanger (178) for receiving the refrigerant of reduced pressure and passing the refrigerant in heat exchange relationship with a heating medium to generate chilled water or chilled air.

[0071] The means of reducing the pressure of the refrigerant may be in the form of an expansion valve (176) located upstream of the refrigerant heating heat exchanger (178), as depicted in FIG. 7, which expands the refrigerant directly into the refrigerant heating heat exchanger (178).

[0072] The refrigerant heating heat exchanger (178) may be selected based upon the desired output. For example, a CO.sub.2:H.sub.2O heat exchanger may be used where chilled water is required to be generated. Alternatively, the refrigerant heating heat exchanger (178) may be a CO.sub.2:air heat exchanger in circumstances where chilled air is required to be generated.

[0073] The air-conditioning circuit (100e) further includes a means (180) of re-compressing the refrigerant from the refrigerant heating heat exchanger (178) before passing the refrigerant back to an inlet line (182) of the refrigerant cooling heat exchanger (154) in the refrigeration circuit.

[0074] The means (180) of re-compressing the refrigerant from the refrigerant heating heat exchanger before passing the refrigerant back to the inlet line of the refrigerant cooling heat exchanger may include one or more refrigerant compression devices. For example, the one or more refrigerant compression devices (180) may be one or more dedicated A/C compressors located downstream of the refrigerant heating heat exchanger. As depicted in FIG. 3, when more than one compressor is utilised, there may be more than one line (i.e., an outlet line associated with each compressor) that feeds refrigerant back into the inlet line (182) of the high pressure refrigerant cooling heat exchanger (154). Such compressors will typically operate at approximately +5 to +7 degrees Celsius. The skilled addressee will appreciate that a dedicated compressor that is utilised in this way for A/C load is far more efficient than the use of a parallel compressor (PC) group running at +3 to +5 degrees Celsius or an MT group running at 5 to 8 degrees Celsius in typical installations.

[0075] Skilled readers will appreciate that the A/C circuit (100e) is created within the refrigeration circuit (100) and linked at two points thereto, immediately before the inlet line (182) and immediately after the outlet line (174) of the high pressure refrigerant cooling heat exchanger (154). In this way, the A/C circuit (100e) is not reliant upon the liquid receiver (160) in the refrigeration circuit (100) to feed, for example, an A/C evaporator for the purpose of air-conditioning a space, since each of the refrigeration circuit (100) and the A/C circuit (100e) are independently managed. This arrangement is what allows higher suction pressures to be used at the one or more refrigerant compression devices (180) (which renders the arrangement more directly suited to A/C applications), and greater cooling stability for both the refrigeration and the A/C circuit. Additional advantages arising from nesting the A/C circuit (100e) into the refrigeration system (100) include enabling a higher coefficient of performance (COP), more accurate capacity control, more refined/accurate plant sizing, and the use of a smaller plant to achieve the same result as compared with present systems.

[0076] Whilst not shown, the air-conditioning circuit (100e) may further include a means of pumping the generated chilled water or chilled air to an evaporator (not shown) for the purpose of utilising the chilled water or air for air-conditioning.

[0077] It will also be understood by skilled readers that whilst a CO.sub.2 refrigeration system according to a particular embodiment developed by the present Applicant is depicted in FIGS. 2 to 7, the air-conditioning circuit (100) could be integrated into one of several alternately configured and known refrigeration systems. For example, a similar air-conditioning circuit could be integrated into the CO.sub.2 refrigeration system depicted in FIG. 1, or the CO.sub.2 refrigeration system (200) depicted in FIGS. 8 to 12. Each of these systems are described in turn below.

[0078] The alternative refrigeration system depicted in FIG. 1 includes similar system components as compared with the system depicted in FIG. 2, including a gas cooler (16), but operating in three modes. In particular, and as described above, this alternative system is configured to transition from a baseline (or booster) mode, to an intermediate (or parallel compression) mode, to an ejector mode during operation.

[0079] In the baseline mode, the flash tank receiver (18) receives refrigerant exclusively from the gas cooler (16), and vapour refrigerant from the flash tank receiver (18) is caused to pass from the flash tank receiver (18) to a first set of refrigerant compression devices (14) such that refrigerant passing from a refrigerant heating heat exchanger (20) to the first set of refrigerant compression devices (14) is mixed with said vapour refrigerant from the flash tank (18). In this baseline mode, the flash gas receiver (18) has associated therewith a flash gas bypass valve (28) to manage flash gas as it accumulates in the flash gas receiver (18). It will be recognised that FIG. 1 depicts the system operating in ejector mode, and not an initial baseline mode of operation.

[0080] In the second (parallel compression) mode, the flash gas bypass valve (18) is closed and vapour refrigerant from the flash tank receiver (18) is caused to pass through refrigerant line (34) to a second set of refrigerant compression devices (30) that operate in parallel with the first set (14). These parallel compressor(s) (30) manage the flash gas as it accumulates in the flash gas receiver (18) by recompressing and discharging same to the inlet line (31) of the gas cooler (16).

[0081] When this alternative refrigeration system subsequently transitions to the third (ejector) mode of operation, a three-way valve (32) disposed at an entry side of the first set of refrigerant compression devices (14) is operated to cause vapour refrigerant from the flash tank receiver (18) to pass through to the first set of refrigerant compression devices (14) in addition to passing through the second refrigerant line to the second set of refrigerant compression devices. The operation of the valve (32) further causes low-pressure gaseous refrigerant from the suction side of the refrigerant heating heat exchanger (20) to be diverted through to the at least one ejector (12) where the refrigerant is mixed with high-pressure refrigerant from the gas cooler (16), thereby receiving a mixture of refrigerants from the refrigerant heating heat exchanger and the gas cooler (16) which are mixed and ejected into the liquid tank receiver (18).

[0082] Skilled readers will appreciate that the inlet and outlet lines of the gas cooler (16) of FIG. 1 is also an appropriate location within which to nest an A/C circuit configured in accordance with circuit (100e) described above.

[0083] The refrigeration system (200) shown in FIGS. 8 to 12 represents a variation on the system (100) shown in FIGS. 2 to 7 in that the system skips the second (parallel compression) mode described above. The refrigeration system (200) similarly includes a CO.sub.2 based refrigerant circuit including one or more refrigerant compression devices (220), a refrigerant cooling heat exchanger (222), and a flash tank receiver (224) downstream of the refrigerant cooling heat exchanger (222) and upstream of refrigerant heating heat exchanger(s) (i.e., evaporators (not shown)). However, rather than utilizing a three-way valve and seeking to re-direct the entire mass-flow of the system through an alternative piping arrangement, as described above with reference to system (100), the system includes a liquid ejector (226), suction accumulator (228), and flash gas bypass valve (230). In particular, the system (200) uses high-pressure gas from the receiver (224) to entrain a portion of the liquid recovered from the suction accumulator (228) (after the evaporators) and re-injects this liquid back into the receiver (224). The suction accumulator (228) captures any liquid in the vapour return lines, and the liquid ejector (226) feeds this un-used liquid back into the receiver (224) where it is useful and can be fed to the evaporator valves. In other words, the ejector (226) entrains and re-uses as much recovered liquid from the vapour return line as possible and then uses high-pressure gas to re-inject this mix to the vessel (224) as useful fluid.

[0084] The flash gas bypass valve (230) is used to manage flash gas build-up in the vessel (224), which can also occur whilst the ejector (226) is running. The objective of the valve (230) is exclusively to ensure that any build-up of flash gas in the vessel (224) is mitigated.

[0085] As depicted in FIG. 8, and more particularly in the enlarged view of the A/C circuit (200e) depicted in FIG. 12, the A/C circuit (200e) is nested within, although operates independently from, the CO.sub.2 refrigeration system (200) and diverts discharge from an outlet line (232) of the refrigerant cooling heat exchanger (222) into the nested air-conditioning circuit (200e). In a similar configuration to system (100), the system (200) may include an expansion valve (234) operable to reduce the pressure of the refrigerant diverted from the outlet line (232) of the refrigerant cooling heat exchanger (222), and further downstream, a refrigerant heating heat exchanger (236) for receiving the refrigerant of reduced pressure and passing the refrigerant in heat exchange relationship with a heating medium to generate chilled water or chilled air. Once again, the refrigerant heating heat exchanger (236) may be selected based upon the desired output. For example, a CO.sub.2:H.sub.2O heat exchanger may be used where chilled water is required to be generated, or a CO.sub.2:air heat exchanger may be used in circumstances where chilled air is required to be generated. Refrigerant is re-compressed before being passed back to the inlet line (240) of the refrigerant cooling heat exchanger (222) by one or more particular refrigerant compression devices (A/C compressors) (238) which may operate at approximately +5 to +7 degrees Celsius.

[0086] Also shown in air-conditioning circuit (200e) is a sub-cooler (242) which is a passive pre-cooler for condensed gas coming from the gas cooler (222) through outlet line (232). The sub-cooler (242) is used to swap heat between the A/C suction and the A/C liquid lines, enabling the cooling of incoming liquid using the outgoing suction (incoming and outgoing relative to feeding the valve at A/C compressor (238)). In the example shown, expanded CO.sub.2 vapour from the refrigerant heating heat exchanger (236) is approximately +10 to +15 degrees Celsius and is used to slightly pre-cool the liquid coming from the outlet of the gas cooler (222) before the liquid enters the expansion valve (234) at the chilled water plate associated with heat exchanger (236). This has the effect of sub-cooling because it cools the liquid beyond what it needs to condense, which increases the cooling effect via expansion. It further superheats the CO.sub.2 vapour, thereby boiling off any remaining liquid before the gas reaches the suction inlet of A/C compressor(s) (238). In this way, the sub-cooler (242) helps achieve optimised temperatures at the correct point in the system (e.g., sub-cooled liquid before expansion to increase the cooling effect during expansion).

[0087] It should now be appreciated that in contrast to previous attempts at integrating an A/C circuit into CO.sub.2 refrigeration systems, the present invention provides an integrated A/C circuit (100e/200e) configured to ensure that other than the use of a common discharge line (174/232), the A/C circuit functions entirely independently of the rest of the refrigeration circuit (100/200). In this way, the A/C load may be managed directly rather than indirectly since there is no longer reliant upon the receiver (160/224) to feed an A/C evaporator. As a result, there is no requirement for components of the refrigeration circuit (100/200) to manage the A/C load.

[0088] Throughout this specification and the claims which follow, unless the context requires otherwise, the word comprise, and variations such as comprises and comprising, will be understood to mean the inclusion of a stated feature or step, or group of features or steps, but not the exclusion of any other feature or step, or group of features or steps.

[0089] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any suggestion that the prior art forms part of the common general knowledge.