FIELD OF THE INVENTION

[0001] The present invention relates to an integrated air-conditioning (A/C) circuit for a carbon dioxide (CO2) refrigeration system, and a CO2 refrigeration system incorporating same. The nesting of the integrated air-conditioning (A/C) circuit in the refrigeration system and in particular, the linking of the A/C circuit to a refrigeration system immediately before and after the gas cooler, enables the cooling load of each of the air-conditioning and refrigeration circuits to be individually served.

BACKGROUND OF THE INVENTION

[0002] Carbon Dioxide (CO2) refrigeration systems, using CO2 as a refrigerant (commonly known as R744 refrigerant), have increasingly become commercially feasible, energy efficient and an environmentally acceptable technology in recent years. R744 refrigerant is a natural, non-toxic and non-flammable refrigerant. Numerous component improvements have been introduced in recent times to improve the efficiency of these systems, particularly at high ambient conditions, including high-pressure liquid and vapour ejector technology.

[0003] The most simplistic configuration for a CO2 system is known as a ‘booster’ system (described in greater detail below). This system does not make use of any additional energy improvements and has been successfully implemented in temperate and cold climates resulting in an inherent energy efficiency advantage as compared with traditional Hydrofluorocarbon (HFC) systems.

[0004] However, CO2 system efficiency has lagged HFC systems in environments with high ambient conditions. In these conditions, a CO2 booster system will lose its efficiency advantage as gas cooler outlet temperatures increase above a point where the system can maintain a traditional vapour-compression cycle (i.e., temperature at the condenser discharge of approximately 27 degrees Celsius and above), which typically occurs when dry-bulb ambient temperatures exceed approximately 25 degrees Celsius. It is at this point, when the ambient temperature can no longer maintain a CO2 system in a sub-critical mode, that the system will start operating in transcritical mode, which typically entails a substantial decrease in system efficiency.

[0005] An ejector provides its primary benefits when a CO2 refrigeration cycle is operating in transcritical mode, and hence is commonly used when a CO2 system is used in high ambient temperatures. At the condenser (also referred to herein as a refrigerant cooling heat exchanger, or gas cooler) outlet, in ambient conditions of around 25 degrees Celsius or higher (or when a CO2 system will typically start operating in transcritical mode), the ejector system utilises high pressure CO2 to entrain and ‘lift’ lower-pressure CO2 gas from other parts of the refrigeration circuit and inject the mixed gas into the receiver, thus substantially increasing the efficiency of the system in high ambient conditions. Analysis from various sources available to the refrigeration industry has confirmed that a CO2 system using an ejector is more efficient than an HFC system at any ambient condition, and is more efficient than competing CO2 technologies (both Parallel-Compression and High-Pressure-Cooling systems) at every ambient temperature over approximately 28 degrees Celsius.

[0006] A known CO2 system (10) using an ejector (12) is shown in Figure 1 , in which it will be appreciated that such systems have a design similar to a standard refrigeration system. Such systems will typically operate in three modes, a baseline or “booster” mode, an “intermediate” mode in which parallel compression (or any other parallel step that utilises additional energy improvements) is activated, and “ejector” mode. In this regard, skilled readers will recognise that Figure 1 depicts the flow that occurs in ejector mode only.

[0007] The system of Figure 1 utilises medium temperature (MT) compressors (also referred to herein as refrigerant compression devices) (14) to compress and send refrigerant to a condenser (16) to reject unwanted heat. The refrigerant subsequently passes through the ejector (12) (which in baseline mode operates as a high pressure valve) to a receiver (also referred to herein as a gas tank receiver, or vessel) (18) which separates the refrigerant into gas and liquid phases.

[0008] Refrigerant in the liquid phase is sent from the receiver (18) to the evaporators (also referred to herein as refrigerant heating heat exchangers) (20). Liquid refrigerant that flows to each evaporator (20) first flows through an associated expansion valve (also referred to herein as an expansion device) (22). Since such refrigeration systems typically supply both refrigerators and freezers, there are two different pressure lines (i.e., a medium temperature (MT) line (24) which supplies the refrigerators, and a low temperature (LT) line (26) which supplies the freezers). The system further includes LT compressors (27) used to raise the pressure of the LT line (26) prior to mixing with refrigerant from the MT line (24) at the MT suction.

[0009] Gas refrigerant (also known as flash gas) from the receiver (18) is managed differently depending upon the mode of operation of the system (10). For example, in baseline or booster mode, a flash gas bypass valve (28) is exclusively used to manage the vessel pressure by effectively ejecting the flash gas from the circuit. In the intermediate mode, the flash gas is taken directly out of the receiver (18) by a parallel compressor (or group of compressors) (30) that manages the gas by recompressing and discharging the flash gas into the common MT discharge line (31 ).

[0010] The ejector mode, shown in Figure 1 , is triggered by operating a three-way valve (32) operable to switch the system (10) from intermediate to ejector mode. This causes flash gas to flow through a bypass line (34) into the suction line of the MT compressors (14), whilst the parallel compressor (30) continues to operate. At the same time, 100% of the MT mass flow is caused to flow into the ejector (12). The ejector (12) includes a main nozzle through which high pressure refrigerant from the condenser (16) enters, as well as a suction valve (opened only in ejector mode) which enables the MT mass flow of a much lower pressure to enter the ejector (12). By utilising the energy provided by the higher pressure refrigerant, the MT mass flow is entrained (transported and compressed) using the venturi effect, i.e., by the higher pressure refrigerant passing through the ejector (12), such that the mixture of refrigerants can be injected into the receiver (18). Accordingly, in ejector mode, having never re-compressed the MT refrigerant from the evaporators (20), the refrigerant is effectively re-injected into the receiver (18) and re-used.

[0011] In ejector mode, since the MT compressors (14) are not used to manage MT suction, they instead begin to manage the receiver flash gas and therefore shift from standard suction operation of typically - 6 to -8 saturation suction temperature (SST) to typically +2 SST, thereby significantly reducing the pressure differential between suction and discharge at the MT compressors (14). This substantial increase in suction temperature and reduction in pressure differential greatly increases compressor efficiency and capacity.

[0012] The SST values mentioned above and throughout this document are exemplary only, and these values may vary depending upon factors including the ambient temperature (since there is likely to be a reduced entrainment of the MT suction in lower ambient conditions), and how the evaporator cases accommodate the higher liquid temperatures in the receiver (since if evaporator case performance is affected, a controller will typically lower the receiver pressure/temperature).

[0013] As mentioned above, the parallel compressor (30) continues to operate in ejector mode, and typically the suction into the MT compressors (14) is lifted to match the parallel compressor (30) such that both sets of compressors (14) and (30) are effectively operating as if they were a single suction group responsible for managing the required suction pressure of the evaporators, thereby indirectly managing the receiver vessel pressure. In other words, the evaporators (20) are driving the requirements of the combined MT and parallel compressor suction group. The parallel compressors (30) adjust to match the MT compressor (14) objective of managing the evaporator case pressures, and an indirect result is that the receiver pressure is also managed.

[0014] The above description relating to the refrigeration system of Figure 1 is provided for context only and there exist a variety of alternatively configured CO2 refrigeration systems which have not been described.

[0015] It is common for air-conditioning (A/C) plants to be integrated into HFC refrigeration systems, and these types of integrated applications are known as “splitheader” arrangements. Such plants combine refrigeration and air-conditioning loads to generate chilled water or air that may, for example, be pumped around a building to provide air conditioning by collecting unwanted heat (by evaporative cooling). The integration of A/C plants into HFC refrigeration systems is possible since with HFC refrigerants (e.g., refrigerant 404a), a single liquid reservoir is typically held at about 20 to 30 degrees Celsius and can thus easily service various suction loads running at much lower temperatures (e.g., 5 degrees Celsius for an A/C air-handling evaporator, or - 6 degrees Celsius for a medium temperature refrigerated cabinet or cool room). In other words, the temperature and pressure differential between the liquid reservoir and the various suction loads operating at much lower temperatures drives the circuit naturally. [0016] However, this arrangement is not possible in CO2 refrigeration systems such as the system described above with reference to Figure 1 since the main liquid receiver (18) is typically maintained at about 3 to 5 degrees Celsius, and it is therefore not possible for liquid CC from the receiver (18) to easily feed an A/C air-handling evaporator having a suction temperature of about +5 degrees Celsius, since there is no (or very little) pressure differential and therefore no (or very little) natural flow. Whilst a liquid pump could be added, this adds additional complexity and cost, comprises a single point of failure, and introduces the risk of liquid flood back to the compressor.

[0017] Integrated A/C plants for CO2 refrigeration systems presently exist, although in such plants, chilled water (for evaporatively cooling a building) is typically generated using an integrated liquid CO2 to liquid H2O heat-exchanger. In particular, liquid CO2 from the main receiver vessel (18) is provided to the heat exchanger for the purpose of generating chilled water. However, as a result, heat is rejected into the receiver, creating flash gas, which increases the receiver pressure. The air-conditioning cooling load is therefore indirectly managed by either the parallel compressor group (where such equipment has been installed) or via the flash gas bypass valve and the MT compressor group, since these elements in the system directly manage the receiver pressure.

[0018] A problem that arises from the above-described integrated A/C plant configuration includes increased capital expenditure. This is due to the requirement for a vessel that is large enough to hold chilled CO2 sufficient to fully absorb rejected heat from the A/C load into the vessel without “starving” the refrigerated cases of refrigerant (by accidentally boiling it all into flash gas). In other words, a needless energy cost arises to keep the liquid receiver at not more than about +4 degrees Celsius, which is lower than what is required for an A/C circuit.

[0019] Another problem is the creation of a turbulent environment within the vessel due to the presence of the integrated liquid CO2 to liquid H2O heat-exchanger, which causes substantial amounts of saturated flash gas (barely in the gas phase) to be generated within the vessel which much be sucked into either the parallel compressor or MT compressor groups, which could inadvertently condense and flood back liquid into the compressors.

[0020] A still further problem that arises is system inefficiency, noting that this problem can arise even if allowance is given to the abovementioned risks from an engineering perspective. This is because the parallel compressor (PC) group runs at +3 to +5 degrees Celsius and the MT group runs at -5 to -8 degrees Celsius in a typical installation. The person skilled in the art will appreciate that if the suction (all else, e.g., load and ambient conditions, being equal) can be raised, the Coefficient Of Performance (COP) of the circuit will rapidly improve on the basis that reducing the pressure differential between the compressor suction and discharge reduces the amount of power (kWe) needed to the same amount of work.

[0021] In view of the above, there is a need for an integrated A/C circuit for a CO2 refrigeration system that enables the cooling load of each of the air-conditioning and refrigeration circuits to be individually served.

[0022] It is an object of the present invention to overcome or at least ameliorate some of the aforementioned problems, or to provide the public with one or more useful alternatives.

[0023] 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.

SUMMARY OF THE INVENTION

[0024] In one aspect, the present invention provides 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 (gas cooler) 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 CO2 refrigeration system, and includes, a means of directing discharge from an outlet line of the refrigerant cooling heat exchanger (gas cooler) 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.

[0025] In an embodiment, the air-conditioning circuit further includes a means of recompressing the refrigerant from the refrigerant heating heat exchanger before passing the refrigerant to an inlet line of the refrigerant cooling heat exchanger.

[0026] Skilled readers will appreciate that the A/C circuit is created within the refrigeration circuit, linked at two points to the refrigeration circuit immediately before (the inlet) and immediately after (the outlet) of the high pressure refrigerant cooling heat exchanger. In this way, the A/C circuit has no reliance on the liquid receiver in the refrigeration circuit to feed, for example, an A/C evaporator for the purpose of evaporative air-conditioning, since each of the refrigeration circuit and the A/C circuit are independently managed. This arrangement allows higher suction pressures to be used for the A/C circuit, and greater cooling stability for both the refrigeration and the A/C circuit. Additional advantages that arise from nesting the A/C circuit according to the present invention include enabling a higher COP, more accurate capacity control, more refined/accurate plant sizing, and the use of a smaller capacity plant achieve the same outcome as compared with present arrangements.

[0027] In an embodiment, chilled water is generated when the refrigerant heating heat exchanger is a CO2:H2O heat exchanger.

[0028] In an embodiment, chilled air is generated when the refrigerant heating heat exchanger is a CO2:ambient air heat exchanger. [0029] In an embodiment, 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.

[0030] In an embodiment, 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.

[0031] In an embodiment, 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. The operation of one or more dedicated compressors operating at approximately 7 degrees Celsius (for example) for the A/C load is more efficient than the earlier described PC and MT groups.

[0032] In an embodiment, the air-conditioning circuit further includes 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.

[0033] In an embodiment, in addition to including a high pressure refrigerant cooling heat exchanger, the CO2 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 CO2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said refrigerant heating heat exchanger.

[0034] In an embodiment, the refrigeration system further includes a flash tank receiver disposed in the CO2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said expansion device, at least one ejector disposed in the CO2 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.

[0035] In an alternative embodiment, the refrigeration system further includes a flash tank receiver disposed in the CO2 based refrigerant circuit downstream from said refrigerant cooling heat exchanger and upstream of said expansion device, at least one ejector disposed in the CO2 based refrigerant circuit downstream from 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 ambient condition has been detected.

[0036] It is to be understood that the integrated A/C circuit can be operated at any time during the above-described modes of operation of the refrigeration system. However, in practice, the A/C circuit can be configured to operate only when a store requires cooling (e.g., for space temperature or dehumidification reasons).

[0037] In a still further alternative embodiment in which the system operates two modes of operation rather than in three modes, i.e., where the parallel compression mode is skipped, the refrigeration system further includes a flash tank receiver disposed in the CO2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said expansion device, the flash tank receiver having associated therewith a flash gas bypass valve, at least one liquid ejector disposed in the CO2 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 liquid ejector is operated in a second mode of operation to entrain a portion of liquid refrigerant recovered from the suction accumulator and to re-inject said liquid back into the flash tank receiver, the flash gas bypass valve operable to manage flash gas buildup in the receiver.

[0038] In an embodiment, 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. Accordingly, the MT refrigerant is suitable for providing cooling in refrigerators, and the LT refrigerant is suitable for providing cooling in freezers.

[0039] In this way, the refrigeration system is capable of servicing a building requiring both refrigerator and freezer cooling, and the integrated A/C circuit is capable of servicing the air-conditioning requirements of the building, whilst the cooling load of each of the respective circuits is individually managed.

[0040] In another aspect, the present invention provides a Carbon Dioxide (CO2) refrigeration system including an integrated A/C circuit configured in accordance with one or more of the preceding statements.

[0041] In yet another aspect, the present invention provides a Carbon Dioxide (CO2) refrigeration system including, 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, 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 CO2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said expansion device, at least one ejector disposed in the CO2 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.

[0042] In a still further aspect, the present invention provides a Carbon Dioxide (CO2) refrigeration system including, 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, 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 CO2 based refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said expansion device, at least one ejector disposed in the CO2 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, with 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. [0043] In a further aspect, the present invention provides a Carbon Dioxide (CO2) refrigeration system including, 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, 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 CO2 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 CO2 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, 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.

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] Figure 1 illustrates a prior art Carbon Dioxide (CO2) refrigeration system operating in ejector mode.

[0046] Figure 2 illustrates a CO2 refrigeration system including an integrated air- conditioning (A/C) circuit configured in accordance with an embodiment of the present invention.

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

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

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

[0050] Figure 6 illustrates an enlarged view of section 10Od of the refrigeration system and integrated A/C circuit of Figure 2.

[0051] Figure 7 illustrates an enlarged view of section 10Oe of the refrigeration system and integrated A/C circuit of Figure 2.

[0052] Figure 8 illustrates a CO2 refrigeration system according to an alternative embodiment as compared with the refrigeration system shown in Figure 2, including an integrated A/C circuit configured in accordance with an embodiment of the present invention.

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

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

[0055] Figure 11 illustrates an enlarged view of section 200c of the refrigeration system and integrated A/C circuit of Figure 8. [0056] Figure 12 illustrates an enlarged view of sections 200d and 200e of the refrigeration system and integrated A/C circuit of Figure 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 (CO2) refrigeration system (100/200), and a refrigeration system (100/200) incorporating same, with one system embodiment (100) configured and detailed in Figures 2 to 7 and another system embodiment (200) configured and detailed in Figures 8 to 12. The reader will appreciate that the system shown in Figure 2 includes sections 100a, 100b, 100c, 100d and 100e, which are shown in enlarged views in Figures 3 to 7 respectively, and the system shown in Figure 8 includes sections 200a, 200b, 200c and 200d/e which are shown in enlarged views in Figures 9 to 12 respectively.

[0058] The refrigeration systems (100/200) illustrated and described herein represent examples of CO2 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 CO2 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 CO2 gas).

[0059] In the embodiment depicted in Figures 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 CO2 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 CO2 based refrigeration system (100) depicted in Figures 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 Figures 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 Figures 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 Figures 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 Figure 2 is a flash gas bypass 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 Figure 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 Figure 2, and more particularly in the enlarged view of the A/C circuit (100e) depicted in Figure 7, the A/C circuit (100e) is nested within, although operates independently from, the CO2 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 Figure 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 CO2:H2O heat exchanger may be used where chilled water is required to be generated. Alternatively, the refrigerant heating heat exchanger (178) may be a CO2: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 recompressing 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 Figure 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 CO2 refrigeration system according to a particular embodiment developed by the present Applicant is depicted in Figures 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 CO2 refrigeration system depicted in Figure 1 , or the CO2 refrigeration system (200) depicted in Figures 8 to 12. Each of these systems are described in turn below.

[0078] The alternative refrigeration system depicted in Figure 1 includes similar system components as compared with the system depicted in Figure 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 Figure 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 Figure 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 Figures 8 to 12 represents a variation on the system (100) shown in Figures 2 to 7 in that the system skips the second (parallel compression) mode described above. The refrigeration system (200) similarly includes a CO2 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 Figure 8, and more particularly in the enlarged view of the A/C circuit (200e) depicted in Figure 12, the A/C circuit (200e) is nested within, although operates independently from, the CO2 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 CO2:H2O heat exchanger may be used where chilled water is required to be generated, or a CO2: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 CO2 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 CO2 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 CO2 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.