[1] This invention relates generally to an air-conditioning integrated parallel compression transcritical refrigeration rack system. More particularly, this invention relates to a particular air- conditioning integration configuration and, in embodiments, control methodology thereof, which eliminates the need for a separate suction group, associated componentry and controllers therefor which reduces capital expenditure and installation cost.

Background of the Invention

[2] Figure 1 illustrates a prior art CO2 parallel compression refrigeration rack system 100 with optional heat recovery.

[3] The standard refrigeration cycle requires that refrigerant be condensed into a liquid at section 102 to pool in a liquid receiver 103 for distribution to the various electronically controlled expansion devices (EXV) 104, 105, 106 at the actual point of cooling, such as cooling coils of the refrigeration cases 107, 108, air conditioning coils and the like. An EXV requires liquid coolant input for expansion.

[4] Any flash gas within the reservoir 103 is recycled using a flash gas bypass system which may comprise a flash gash bypass valve (FGBV) 109 and/or parallel compression (PC) group 110.

[5] In the embodiment shown, the system 100 comprises two suction groups comprising a medium temperature (MT) and low-temperature (LT) suction groups.

[6] Evaporated refrigerant from the EXVs 105, 106 is re-compressed utilising dedicated compressor groups 111, 112 for each suction group.

[7] For the MT suction group, the system 100 comprises MT compressor group 111 for MT suction line 114. The MT suction line may operate at -6°C, for example. For the LT suction group, the system 100 comprises LT compressor group 112 for LT suction line 113. The LT suction line 113 may operate at -27°C, for example.

[8] In embodiments shown, the LT compressors 112 "boosts" into the MT suction line 114, hence the name "booster system".

[9] Boosting allows the LT suction group to achieve very low SSTs at very high efficiencies since the LT compressors 112 rejects heat into an already relatively cool MT suction line 114.

[10] The parallel and MT compressor groups 110, 111 feed into high-temperature (HT) line 119 from which heat may be scavenged utilising a water heat exchanger 120.

[11] The HT line feeds back into a condenser/gas cooler 116 which outputs cooled refrigerant. [12] For conventional refrigeration systems, the condenser 116 condenses the refrigerant into a liquid which is fed directly into the liquid receiver 103.

[13] However, for transcritical refrigeration systems, such as CO2 refrigeration systems, the CO2 output from the gas cooler 116 may be in supercritical state (being above critical temperature 31.10 °C and critical pressure 7.39 MPa). Such supercritical CO2 refrigerant acts like a gas in that it expands to fill containers but exhibits a density typical of a liquid.

[14] As such, transcritical CO2 refrigeration systems utilise an expansion/metering device between the gas cooler 116 and the liquid receiver 103 referred to as the electronically controlled high-pressure control valve (HPCV) 115.

[15] The HPCV 115 receives the high-pressure supercritical CC from the gas cooler 116 and rapidly expands the CC as it passes, creating a substantial pressure/temperature drop such that a portion of the CO2 condenses into useful liquid for the liquid receiver 103.

[16] Flash gas associated therewith however, which is useless for refrigeration, is recycled from the liquid receiver 103 either through the FGBV 109 into the MT line 114 for recompression and reuse, or for larger flash gas loads, through the PC group 110 into the HT line 119.

[17] The HPCV 115 is controlled utilising an HPCV controller (not shown) to maintain the requisite gas cooler pressure at section 102 and liquid levels of the liquid receiver 103. In operation, as demand decreases, the HPCV controller may derive efficiencies by "floating" (i.e. increasing) the pressure within the liquid receiver 103.

[18] Mechanical integration of an AC integration 101 typically entails the creation of a further AC suction group by the addition of a braised plate heat exchanger (AC BHPE) 117 for chilling water of the air-conditioning integration 101 and an electronically controlled AC EXV 104 feeding the AC BHPE 117.

[19] AC integration 101 may therefore involve three suction groups, comprising the LT suction group, MT suction group and the flash gas management and air-conditioning suction group (AC suction group). In a typical installation, the LT suction group evaporates at -27°C, the MT suction group at -6°C and the AC suction group at 3.3°C.

[20] The AC EXV 104 for the AC BPHE 117 similarly requires liquid coolant from the liquid receiver 103 which is why the AC EXV 104 must be located downstream from the liquid receiver 103.

[21] Furthermore, since the flash gas management and AC suction group share the same PC group 110, an electronic pressure regulator (EPR) 118 is required to regulate any pressure/temperature differential of greater than approx. 1-2°C therebetween.

[22] Typically, the capacity of the PC compressor group 110 is increased to account for the additional load of the air-conditioning system 101. [23] The present invention seeks to provide a refrigeration system, which will overcome or substantially ameliorate at least some of the deficiencies of the prior art, or to at least provide an alternative.

[24] It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms part of the common general knowledge in the art, in Australia or any other country.

Summary of the Disclosure

[25] There is provided herein an air-conditioning integrated parallel compression transcritical refrigeration rack system having the characterising configuration of an air-conditioning heat exchanger (AC BPHE) upstream of the liquid receiver as is shown in Figure 2. Specifically, in accordance of the present configuration, the upstream AC BPHE is inserted between the HPCV 115 and the liquid receiver 103.

[26] Such a configuration advantageously dual-purposes the HPCV 115 in acting both as the supercritical CO2 high pressure control valve and the AC expansion device, thereby reducing system componentry.

[27] Such configuration negates the need for the dedicated AC suction group and the elimination therefore of the associated componentry and controllers.

[28] Such configuration may save space, eliminate the requirement for capital intensive EXVs and associated electronic valve controllers therefor, reduced pipework and the like.

[29] Furthermore, the upstream AC BHPE may be inserted/retrofitted into an existing refrigeration plant more easily as compared to the installation of a further dedicated AC suction group

[30] Such a configuration is not obvious given that, as alluded to above, EXVs require liquid coolant which is why AC suction groups must be located downstream of the liquid receiver 103 to receive liquid therefrom. The present configuration however employs 2-phase CO2 for AC cooling.

[31] Installation of the upstream AC BPHE is not without technical difficulty however in that, in a preferred embodiment, the HPCV controller may need updating to control the pressure and liquid reservoir of the liquid receiver 103 within tighter control bounds so as to also indirectly control the AC BPHE effectively.

[32] Specifically, the HPCV controller for the present configuration may be controlled according to a lower control bound such that the AC BHPE input pressure/temperature does not drop below approximately 1°C so as to avoid physical damage of the AC BPHE via freezing of the water-side of the cooling circuit 101. [33] Furthermore, the HPCV controller may be controlled at an upper control bound such that floating of the liquid receiver 103 does not retard efficient operation of the air-conditioning integration 101. Specifically, the chilled water circuit of the air-conditioning integration 101 may enter the AC BPHE at approximately 13°C and exit at approximately 7°C. The chilled water circuit may comprise an input valve/pump and an output temperature sensor to control the flow rate of water through the AC BPHE which may therefore be adjusted according to AC load using an AC integration controller.

[34] However, at operational control extremities of the AC integration controller, the AC integration controller may signal the HPCV controller to reduce floating by reducing the liquid reservoir input temperature/pressure. For example, should the flowrate/low control have increased the flowrate of water through the upstream AC BPHE to substantially a maximum flowrate amount yet be unable to efficiently achieve cooling required for the present AC demand, the AC integration controller may signal the HPCV controller to drop the AC BPHE pressure/temperature until such time that AC demand can be met. As reduction of AC BPHE pressure/temperature hinders reservoir floating, the HPCV controller may be configured for maximising floating while meeting a dynamic maximum AC BPHE pressure/temperature.

[35] Furthermore, given that the AC BPHE pressure/temperature is controlled indirectly by the liquid reservoir pressure/temperature, substantial pressure/temperature differentials there between cannot exist, thereby advantageously eliminating the need for the electronic suction pressure regulator valve (EPR) as is required for existing arrangements.

[36] As such, with the foregoing in mind, in accordance with one aspect, there is provided air- conditioning integrated parallel compression transcritical refrigeration rack system comprising: a high- pressure control valve feeding a liquid receiver; the liquid receiver feeding at least one suction group; the at least one suction group feeding a gas cooler; the gas cooler feeding the high-pressure control valve, wherein the system comprises an AC heat exchanger between the high-pressure control valve and the liquid receiver.

[37] The system may further comprise a high-pressure control valve controller for controlling the high-pressure control valve according to the pressure/temperature requirements of the liquid receiver and wherein the high-pressure control valve controller may be further configured for controlling the pressure/temperature of the AC heat exchanger.

[38] The controller may be configured for controlling the high-pressure control valve according to a lower operational control bound such that the pressure/temperature of the AC heat exchanger does not decrease below a lower threshold.

[39] The lower threshold may be approximately 1°C. [40] The controller may be configured for controlling the high-pressure control valve according to an upper operational control bound such that the pressure/temperature of the AC heat exchanger may be sufficient to meet the dynamic AC load thereon.

[41] The system may further comprise an AC integration controller configured for controlling flowrate through the AC heat exchanger according to dynamic AC load.

[42] The upper operational control bound corresponds with a flowrate threshold.

[43] The at least one suction group feeds into at least one compressor group which feeds into a high-temperature line which feeds into the gas cooler and wherein the system further may comprise a heat exchanger operably coupled to the high-temperature line.

[44] The at least one suction group may comprise a medium temperature suction group comprising: a medium temperature compressor group feeding into a high-temperature line which feeds into the gas cooler; a medium temperature suction line feeding into the medium temperature compressor group; and a medium temperature electronically controlled expansion valve feeding into the medium temperature suction line; and a low temperature suction group comprising: a low temperature compressor group feeding into the medium temperature suction line; a low temperature suction line feeding into the low temperature compressor group; and a low temperature electronically controlled expansion valve feeding into the low temperature suction line.

[45] The medium temperature suction line may operate at approximately -6°C.

[46] The low temperature suction line may operate at approximately -27°C.

[47] The system may further comprise a flash gas bypass system feeding from the liquid receiver.

[48] The flash gas bypass system may comprise a flash gas bypass valve interfacing the liquid receiver and the medium temperature suction line.

[49] The flash gas bypass system may comprise a parallel compressor group interfacing the liquid receiver and the high-temperature suction line.

[50] Other aspects of the invention are also disclosed.

Brief Description of the Drawings

[51] Notwithstanding any other forms which may fall within the scope of the present invention, preferred embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:

[52] Figure 1 illustrates a typical prior art CO2 parallel compression refrigeration rack system with optional heat recovery; and

[53] Figure 2 illustrates an air-conditioning integrated parallel compression transcritical refrigeration rack system in accordance with an embodiment. Description of Embodiments

[54] Figure 2 illustrates an air-conditioning integrated parallel compression transcritical refrigeration rack system 200 in accordance with an embodiment.

[55] The system 200 typically employs CO2 but may employ other transcritical refrigerants.

[56] The system 200 comprises an HPCV 115 feeding into a liquid reservoir 103.

[57] The liquid reservoir 103 feeds at least one suction group which, in turn, feed into a gas cooler 116.

[58] The gas cooler 116 feeds back into the HPCV 115.

[59] The system 200 is characterised in comprising an AC BPHE 121 upstream of the liquid receiver 103 for an AC integration 101.

[60] Specifically, the system 200 comprises the AC BPHE 121 located between the HPCV 115 and the liquid reservoir 103.

[61] As such, the HPCV 115 serves dual purpose in 1) condensing the supercritical CO2 from the gas cooler 116 into liquid for the requirements of the liquid receiver 103 and as the expansion device for cooling the AC BPHE 112.

[62] The AC integration 101 may utilise a chilled water circuit which may feed the AC BPHE 121 at approximately 13°C for cooling to approximately 7°C.

[63] The AC integration 101 may comprise a valve/pump 122 for regulating the flow rate of water through the AC BPHE 121.

[64] The AC integration 101 may employ an AC integration controller configured for controlling the flow rate of water through the AC BPHE 121 according to dynamic AC load requirements. The AC integration controller may take readings from a temperature sensor 122 for control purposes.

[65] As such, as the AC demand increases, the AC integration controller may increase flowrate through the AC BPHE 121 and vice versa.

[66] Furthermore, the system 200 may comprise an HPCV controller for controlling the HPCV 115.

[67] The HPCV controller primarily controls the HPCV 115 according to the requisite liquid level requirements of the liquid reservoir 103 which dynamically vary according to the demands of the downstream EXVs 105, 106.

[68] However, the HPCV controller additionally controls the HPCV 115 according to the pressure/temperature requirements of the AC BPHE 121.

[69] Specifically, the HPCV controller may control the HPCV 115 according to a lower control bound such that the pressure/temperature of the AC BPHE 121 does not fall beneath a lower threshold set point, such as approximately 1°C so as to not physically damage the AC BPHE 121. [70] Furthermore, the HPCV controller may control the HPCV 115 according to a dynamically changing upper operational pressure/temperature setpoint of the AC BPHE 121.

[71] Specifically, the dynamic upper operational pressure/temperature setpoint of the AC BPHE 121 may vary dynamically according to the current AC load of the AC integration 101.

[72] As such, in embodiments, the HPCV controller may control the HPCV 115 to maximise floating so as to derive operational efficiencies for the refrigeration circuits yet while meeting the dynamic upper operational pressure/temperature setpoint of the AC BPHE 121 such that the AC BPHE 121 is able to meet the load requirements of the AC integration 101.

[73] In embodiments, the dynamic upper operational pressure/temperature setpoint of the AC BPHE may be dictated by the maximum flowrate through the AC BPHE 121. For example, as the AC controller increases the flowrate through the pump/valve 120, as the flowrate approaches a maximum flowrate, the AC controller may signal the HPC via the controller to decrease the pressure/temperature of the AC BPHE 121.

[74] In the embodiment shown, the system 200 comprises two suction groups comprising the MT suction group and the LT suction group.

[75] The MT suction group may comprise an MT compressor group 111 feeding into the HT line 119 and MT suction line 114 which feeds into the MT compressor group 11. Furthermore, an MT EXV 105 may feed into the MT suction line 114.

[76] The LT suction group may comprise an LT compressor group 112 feeding into the MT suction line 114. An LT suction line 113 may feed into the LT compressor group 112 and a low temperature EXV of the 106 may feed into the LT suction line 113.

[77] In the embodiments shown, the LT suction line 113 may feed via a passive LT liquid subcooler to reduce or eliminate flash gas input to the LT EXV 106.

[78] The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that specific details are not required in order to practice the invention. Thus, the foregoing descriptions of specific embodiments of the invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed; obviously, many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, they thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the following claims and their equivalents define the scope of the invention.