CO2 REFRIGERATION SYSTEM

Abstract

A CO.sub.2 refrigeration system for an ice-playing surface comprises an evaporation stage in which heat is absorbed from an ice-playing surface. CO.sub.2 compressors in a compression stage compress CO.sub.2 refrigerant subcritically and transcritically. A gas cooling stage has a plurality of heat-reclaim units reclaiming heat from the CO.sub.2 refrigerant. A pressure-regulating device is downstream of the gas cooling stage, to control a pressure of the CO.sub.2 refrigerant in the gas cooling stage. A reservoir is downstream of the pressure-regulating device for receiving CO.sub.2 refrigerant in a liquid state. A controller operates the pressure-regulating device to control the pressure of the CO.sub.2 refrigerant in the gas cooling stage as a function of the heat demand of the plurality of heat-reclaim units, the controller causing the pressure of the CO.sub.2 refrigerant to reach a transcritical level as a function of a heat demand of the plurality of heat-reclaim units.

Claims

1. A method for operating a CO.sub.2 refrigeration system for an ice-playing surface, comprising: operating a refrigeration cycle by sequentially compressing CO.sub.2 refrigerant, releasing heat from the CO.sub.2 refrigerant in a gas cooling stage after the compressing, absorbing heat from at least one ice-playing surface after the releasing, and directing the CO.sub.2 refrigerant having absorbed heat to the compressing; and for a heat demand of a plurality of heat-reclaim units, causing the pressure of the CO.sub.2 refrigerant to reach a transcritical level as a function of said heat demand for the plurality of heat-reclaim units to absorb heat from the CO.sub.2 refrigerant in the gas cooling stage.

2. The method according to claim 1, further including causing the pressure of the CO.sub.2 refrigerant to return to a subcritical level from said transcritical level as a function of said heat demand.

3. The method according to claim 1, wherein causing the pressure of the CO.sub.2 refrigerant to reach a transcritical level includes controlling a pressure-regulating device downstream of the gas cooling stage.

4. The method according to claim 1, further including accumulating CO.sub.2 refrigerant in a liquid state in a reservoir prior to said absorbing heat.

5. The method according to claim 1, wherein absorbing heat from at least one ice-playing surface includes circulating CO.sub.2 refrigerant in a circuit of pipes to absorb heat from the at least one ice-playing surface.

6. The method according to claim 5, wherein circulating CO.sub.2 refrigerant in a circuit of pipes includes vaporizing the CO.sub.2 refrigerant with at least one expansion valve.

7. The method according to claim 5, wherein circulating CO.sub.2 refrigerant in a circuit of pipes includes pumping the CO.sub.2 refrigerant in the liquid state into the circuit of pipes.

8. The method according to claim 1, wherein at least one of the plurality of heat-reclaim units absorbs heat from the CO.sub.2 refrigerant in the gas cooling stage by heat exchange with a secondary refrigerant.

9. The method according to claim 8, wherein the secondary refrigerant heats water in at least one water tank.

10. The method according to claim 1, wherein the plurality of heat-reclaim units absorbs heat from the CO.sub.2 refrigerant in the gas cooling stage in series.

11. The method according to claim 1, wherein the plurality of heat-reclaim units absorbs heat from the CO.sub.2 refrigerant in the gas cooling stage in parallel.

12. The method according to claim 1, wherein at least one of the plurality of heat-reclaim units absorbs heat from the CO.sub.2 refrigerant in the gas cooling stage by blowing air on a coil in which circulates the CO.sub.2 refrigerant.

13. The method according to claim 1, further including collecting oil downstream of said compressing, and directing the oil upstream of said compressing for the CO.sub.2 refrigerant in said compressing to have an oil content.

14. The method according to claim 13, wherein collecting oil includes collecting oil from a bottom of a reservoir.

15. The method according to claim 3, wherein controlling the pressure-regulating device downstream of the gas cooling stage includes modulating a valve to maximize the heat reclaim as a function of the heat demand of the plurality of heat-reclaim units.

16. The method according to claim 1, wherein causing the pressure of the CO.sub.2 refrigerant to reach a transcritical level as a function of said heat demand includes causing the pressure of the CO.sub.2 refrigerant to reach a pressure of at least 1400 Psi as a function of the heat demand during a winter month period.

17. The method according to claim 16, wherein causing the pressure of the CO.sub.2 refrigerant to reach a transcritical level as a function of said heat demand includes causing the pressure of the CO.sub.2 refrigerant to reach a pressure including 550 Psi as a function of the heat demand during a summer month period, wherein an outdoor temperature is warmer in the summer month period than in the winter month period.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is a block diagram of a CO.sub.2 refrigeration system in accordance with an embodiment of the present application;

[0022] FIG. 2 is a block diagram of the CO.sub.2 refrigeration system of FIG. 1, with an example of operating pressures for a cold climate application;

[0023] FIG. 3 is a block diagram of the CO.sub.2 refrigeration system of FIG. 1, with an example of operating pressures for a warm climate application; and

[0024] FIG. 4 is a schematic view of a line used with the CO.sub.2 refrigeration system, in accordance with another embodiment of the present application.

[0025] FIG. 5 is a block diagram of a CO.sub.2 refrigeration system in accordance with another embodiment,

[0026] FIG. 6 is a schematic view of a line configuration for a refrigeration unit, in accordance with yet another embodiment of the present application;

[0027] FIG. 7 is a block diagram of a CO.sub.2 refrigeration system in accordance with another embodiment, with dedicated compression for defrost;

[0028] FIG. 8 is a block diagram of a CO.sub.2 refrigeration system in accordance with another embodiment, e.g., for a skating rink application;

[0029] FIG. 9 is a block diagram of a CO.sub.2 refrigeration system in accordance with another embodiment, with a supra-compression providing defrost;

[0030] FIG. 10 is a block diagram of a CO.sub.2 refrigeration system in accordance with another embodiment, with cascaded compression;

[0031] FIG. 11 is a block diagram of a CO.sub.2 refrigeration system in accordance with another embodiment, with suction accumulation upstream of a supra-compression stage;

[0032] FIG. 12 is a block diagram of a CO.sub.2 refrigeration system in accordance with another embodiment, with a heat-exchanger for defrost refrigerant; and

[0033] FIG. 13 is a schematic view of a desiccant system in accordance with another embodiment of the present application.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0034] Referring to FIG. 1, a CO.sub.2 refrigeration system in accordance with an embodiment is illustrated at 1. The CO.sub.2 refrigeration system 1 has a CO.sub.2 refrigeration circuit comprising a CO.sub.2 compression stage 10. CO.sub.2 refrigerant is compressed in the compression stage 10, and is subsequently directed via line 11 to a condensation reservoir 12, or to a heat-reclaim stage 13.

[0035] The condensation reservoir 12 accumulates CO.sub.2 refrigerant in a liquid and gaseous state, and is in a heat-exchange relation with a condensation circuit that absorbs heat from the CO.sub.2 refrigerant. The condensation circuit is described in further detail hereinafter. Moreover, a transcritical circuit and a defrost circuit may supply CO.sub.2 refrigerant to the condensation reservoir 12, as is described in further detail hereinafter.

[0036] The heat-reclaim stage 13 is provided to absorb heat from the CO.sub.2 refrigerant exiting from the compression stage 10. The heat-reclaim stage 13 may take various forms, such as that of a heat exchanger by which the CO.sub.2 refrigerant is in heat exchange with an alcohol-based refrigerant circulating in a closed loop. As another example, the heat-reclaim stage 13 features coils by which the CO.sub.2 refrigerant releases heat to a water tank.

[0037] Line 14 directs CO.sub.2 refrigerant from the condensation reservoir 12 to an evaporation stage via expansion valves 15. As is shown in FIG. 1, the CO.sub.2 refrigerant is supplied in a liquid state by the condensation reservoir 12 into line 14. The expansion valves 15 control the pressure of the CO.sub.2 refrigerant, which is then fed to either low-temperature evaporation stage 16 or medium-temperature evaporation stage 17. Both the evaporation stages 16 and 17 feature evaporators associated with refrigerated enclosures, such as closed or opened refrigerators, freezers or the like. It is pointed out that the expansion valves 15 may be part of a refrigeration pack in the mechanical room, as opposed to being at the refrigeration cabinets. As a result, flexible lines (e.g., plastic non-rigid lines) could extend from the expansion valves 15 to diffuser upstream of the coils of the evaporation stages 16 and 17. The valves 15 may be at the refrigeration cabinets, at the refrigeration pack in a mechanical room, or any other suitable location.

[0038] CO.sub.2 refrigerant exiting the low-temperature evaporation stage 16 is directed to the CO.sub.2 compression stage 10 via line 18 to complete a refrigeration cycle. A heat exchanger 19 is provided in the line 18, and ensures that the CO.sub.2 refrigerant is fed to the compression stage 10 in a gaseous state. Other components, such as a liquid accumulator, may be used as an alternative to the heat exchanger 19. As described hereinafter, the heat exchanger 19 may be associated with a condensation circuit.

[0039] CO.sub.2 refrigerant exiting the medium-temperature evaporation stage 17 is directed to the transcritical circuit as is described hereinafter.

[0040] A condensation circuit has a heat exchanger 20. The heat exchanger 20 is in fluid communication with the condensation reservoir 12, so as to receive CO.sub.2 refrigerant in a gaseous state. The condensation circuit is closed and comprises a condensation refrigerant that also circulates in the heat exchanger 20 so as to absorb heat from the CO.sub.2 refrigerant.

[0041] In the condensation circuit, the condensation refrigerant circulates between the heat exchanger 20 in which the condensation refrigerant absorbs heat, a compression stage 21 in which the condensation refrigerant is compressed, and a condensation stage 22 in which the condensation refrigerant releases heat. The compression stage 21 may use Turbocor compressors. In an example, the condensation stage 22 features heat reclaiming (e.g., using a heat exchanger with a heat-transfer fluid) in parallel or in series with other components of the condensation stage 22, so as to reclaim heat from the CO.sub.2 refrigerant. Although not shown, the condensation circuit may be used in conjunction with the heat exchanger 19, so as to absorb heat from the CO.sub.2 refrigerant being directed to the compression stage 10. In this case, the condensation refrigerant is in a heat-exchange relation with the CO.sub.2 refrigerant.

[0042] It is pointed out that the condensation circuit may be used with more than one CO.sub.2 refrigeration circuit. In such a case, the condensation circuit features a plurality of heat exchangers 20, for instance with one for each of the CO.sub.2 refrigeration circuits.

[0043] Examples of the condensation refrigerant are refrigerants such as R-404 and R-507, amongst numerous examples. It is observed that the condensation circuit may be confined to its own casing as illustrated in FIG. 1. Moreover, considering that the condensation circuit is preferably limited to absorbing heat from stages on a refrigeration pack (e.g., condensation reservoir 12, suction header in line 18), the condensation circuit does not contain a large volume of refrigerant when compared to the CO.sub.2 refrigeration circuit, of a secondary refrigerant circuit defined hereinafter.

[0044] The transcritical circuit (i.e., supra-compression circuit) is provided to compress the CO.sub.2 refrigerant exiting from the medium-temperature evaporation stage 17 to a transcritical state, for heating purposes, or supra-compressed state. In both compression states, the CO.sub.2 refrigerant is pressurized in view of maintaining the condensation reservoir 12 at a high enough pressure to allow vaporized CO.sub.2 refrigerant to be circulated in the evaporation stages 16 and 17, as opposed to liquid CO.sub.2 refrigerant.

[0045] A line 30 relates the medium-temperature evaporation stage 17 to a heat exchanger 31 and subsequently to a supra-compression stage 32. The heat exchanger 31 is provided to vaporize the CO.sub.2 refrigerant fed to the transcritical compression stage 32. The supra-compression stage 32 features one or more compressors (e.g., Bock, Dorin), that compress the CO.sub.2 refrigerant to a supra-compressed or transcritical state.

[0046] In the transcritical state, the CO.sub.2 refrigerant is used to heat a secondary refrigerant via heat-reclaim exchanger 34. In the heat-reclaim exchanger 34, the CO.sub.2 refrigerant is in a heat-exchange relation with the secondary refrigerant circulating in the secondary refrigerant circuit 35. The secondary refrigerant is preferably an environmentally-sound refrigerant, such as water or glycol, that is used as a heat-transfer fluid. Because of the transcritical state of the CO.sub.2 refrigerant, the secondary refrigerant circulating in the circuit 35 reaches a high temperature. Accordingly, due to the high temperature of the secondary refrigerant, lines of smaller diameter may be used for the secondary refrigerant circuit 35. It is pointed out that the secondary refrigerant circuit 35 is the largest of the circuits of the refrigeration system 1 in terms of quantity of refrigerant. Therefore, the compression of the CO.sub.2 refrigerant into a transcritical state by the transcritical circuit allows the lines of the secondary refrigerant circuit 35 to be reduced in terms of diameter.

[0047] A gas cooling stage 36 is provided in the transcritical circuit. The gas cooling stage 36 absorbs excess heat from the CO.sub.2 refrigerant in the transcritical state, in view of re-injecting the CO.sub.2 refrigerant in the condensation reservoir 12. Although it is illustrated in a parallel relation with the heat-reclaim exchanger 34, the gas cooling stage 36 may be in series therewith, or in any other suitable arrangement. Although not shown, appropriate valves are provided so as to control the amount of CO.sub.2 refrigerant directed to the gas cooling stage 36, in view of the heat demand from the heat-reclaim exchanger 34.

[0048] In warmer climates in which the demand for heat is smaller, the CO.sub.2 refrigerant is compressed to a supra-compressed state, namely at a high enough pressure to allow the expansion of the CO.sub.2 refrigerant at the exit of the condensation reservoir 12, so as to reduce the amount of CO.sub.2 refrigerant circulating in the refrigeration circuit. A by-pass line is provided to illustrate that the heat-reclaim exchanger 24 and the gas cooling stage 36 are optional for warmer climates.

[0049] The gas cooling stage 36 may feature a fan blowing a gas refrigerant on coils. The speed of the fan may be controlled as a function of the heat demand of the heat reclaim exchanger 34. For an increased speed of the fan, there results an increase in the temperature differential at opposite ends of the gas cooling stage 36.

[0050] Lines 37 and 38 return the CO.sub.2 refrigerant to the condensation reservoir 12, and thus to the refrigeration circuit. The line 37 feeds the heat exchanger 31 such that the CO.sub.2 refrigerant exiting the stages 34 and 36 release heat to the CO.sub.2 refrigerant fed to the supra-compression stage 32. Accordingly, the CO.sub.2 refrigerant fed to the supra-compression stage 32 is in a gaseous state.

[0051] In the case of transcritical compression, a CO.sub.2 transcritical pressure-regulating valve 39 is provided to maintain appropriate pressures at the stages 34 and 36, and in the condensation reservoir 12. The CO.sub.2 transcritical pressure-regulating valve 39 is for instance a Danfoss valve. Any other suitable pressure-control device may be used as an alternative to the valve 39, such as any type of valve or loop.

[0052] The condensation circuit and the supra-compression circuit allow the condensation reservoir 12 to store refrigerant at a relatively medium pressure. Accordingly, no pump may be required to induce the flow of refrigerant from the condensation reservoir 12 to the evaporation stages 16 and 17. As CO.sub.2 refrigerant is vaporized downstream of the expansion valves 15, the amount of CO.sub.2 refrigerant in the refrigeration circuit is reduced, especially if the expansion valves 15 are in the refrigeration pack.

[0053] It is considered to operate the supra-compression circuit (i.e., supra compression 32) with higher operating pressure. CO.sub.2 refrigerant has a suitable efficiency at a higher pressure. More specifically, more heat can be extracted when the pressure is higher.

[0054] The refrigeration system 1 may be provided with a refrigerant defrost system. In FIG. 1, a portion of the CO.sub.2 refrigerant exiting from the compression stage 10 is directed to the evaporation stages 16 and 17. Although not shown, appropriate valves and pressure-reducing devices are provided to stop the flow of cooling CO.sub.2 refrigerant in the evaporators in view of the defrost. The defrost CO.sub.2 refrigerant releases heat to defrost any frost build-up on the evaporators of the evaporation stages 16 and/or 17.

[0055] Although not shown, other compression configurations may be used to supply defrost refrigerant to the evaporators, such as dedicated compressors, cascaded compressors of the like.

[0056] Line 41 directs the defrost CO.sub.2 refrigerant having released heat to the defrost reservoir 42. The defrost reservoir 42 accumulates the defrost CO.sub.2 refrigerant, and features a line 43 with a control valve (e.g., exhaust valve, check valve), so as to allow gaseous CO.sub.2 refrigerant to be sucked back into the CO.sub.2 refrigeration circuit by the CO.sub.2 compression stage 10. The defrost reservoir 42 is an option, as the evaporation stages 16 and 17 may direct the refrigerant to other reservoirs or accumulators of any other refrigeration system presenter herein.

[0057] A flush of the defrost reservoir 42 may be performed periodically, so as to empty the defrost reservoir 42. Accordingly, lines 44 and 45, with appropriate valves, allow the flush of the liquid CO.sub.2 refrigerant from the defrost reservoir 42 to the condensation reservoir 12.

[0058] A pressure-reducing valve 46 may be provided in the line 40 or line 11 to regulate a pressure of the defrost CO.sub.2 refrigerant fed to the evaporation stage 16 and/or 17 for defrost. Valves, such as check valve 47, are as relief valves for the evaporation stages 16 and 17. For instance, in case of a power shortage, the CO.sub.2 refrigerant in the evaporators may increase in pressure. Accordingly, the check valves 47 open at a threshold pressure to allow the CO.sub.2 refrigerant to reach the defrost reservoir 42.

[0059] Considering that the compressors of the CO.sub.2 compression stage 10 or of the compression stage 21 are low-consumption compressors, these compressors may be operated during a power outage to maintain suitable refrigerating conditions in the evaporation stages 16 and 17. The compressors of the compression stage 21 may also be Turbocor compressors.

[0060] As an alternative to the defrost circuit, the evaporators of the evaporation stages 16 and 17 may be equipped with electric coils for the electric defrost of the evaporators.

[0061] In an embodiment, the casing enclosing the condensation circuit may also comprise an air-conditioning unit 50. Accordingly, the roof-top equipment associated with the refrigeration system 1 is provided in a single casing, thereby facilitating the installation thereof. Moreover, it is considered to unite as many components of the refrigeration system 1 in a single refrigeration pack. For instance, the compressors of the CO.sub.2 compression stage 10, the condensation reservoir 12, the expansion valves 15, and optionally the compressors from the supra-compression stage 32, as well as the defrost reservoir 42 may all be provided in a same pack, with most of the lines joining these components. The installation is therefore simplified by such a configuration.

[0062] In order to illustrate the operating pressures of the CO.sub.2 refrigeration system 1 in cold and warm climates, FIGS. 2 and 3 are respectively provided with pressure values. It is pointed out that all values are just an illustration, whereby pressure values could be higher or lower. FIG. 2 shows operating pressures for the CO.sub.2 refrigeration system 1 as used in cold climates (e.g., winter conditions in colder regions), with a demand for heat by the secondary refrigerant circuit 35. FIG. 3 shows operating pressures for the CO.sub.2 refrigeration system as used in warm climates (e.g., summer conditions, warmer regions).

[0063] Although not fully illustrated, numerous valves are provided to control the operation of the CO.sub.2 refrigeration system 1 as described above. Moreover, a controller A ensures that the various stages of the refrigeration system 1 operate as described, for instance by having a plurality of sensors places throughout the refrigeration system 1.

[0064] Referring to FIG. 3, there is illustrated a safety valve circuit 55 so as to ensure that the refrigerant pressure in the coils of the evaporation stages 16 and 17 does not exceed a given maximum value (e.g., 410 Psi), which may result in damages to the coils. The safety valve circuits 55 extends from the evaporation stages 16 and 17 (e.g., lines at the exit of the coils) to the defrost reservoir 42. A safety valve 56 is provided in the circuit, and operates by monitoring the pressure in the coils and opening as a result of the pressure reaching the maximum value. The defrost reservoir 42 then absorbs the excess pressure by receiving the refrigerant. The defrost reservoir 42 subsequently discharges the refrigerant using the lines described previously.

[0065] Referring to FIG. 4, a line that may be used in the CO.sub.2 refrigeration system 1 is illustrated at 60. The line 60 is a flexible hose adapted to support the relatively high pressures associated with CO.sub.2 refrigerant. One suitable example of flexible hose is the Transfer Oil hydraulic hose by Gomax. The hose 60 is rodded into a conduit of sleeves 61 of an insulating material, such as urethane, positioned end to end to cover the length of hose 60. A plurality of hoses 60 may be used with a single sleeve 61, provided the inner diameter of the sleeve 61 is large enough to receive the hoses 60. Therefore, by the use of flexible hoses, the installation of the lines is simplified. Previous lines required welding operation to join tubes of metallic material.

[0066] Referring to FIG. 5, an alternative embodiment of the CO.sub.2 refrigeration system 1 of FIGS. 1-3 is illustrated at 70. The CO.sub.2 refrigeration systems 1 and 70 have numerous common stages and lines, whereby like elements will bear like reference numerals. One difference between the CO.sub.2 refrigeration systems 1 and 70 is the absence of a condensation circuit such as the one having the heat exchanger 20 in FIGS. 1-3. Rather, the CO.sub.2 refrigerant in the condensation reservoir 12 is cooled by the transcritical circuit (i.e., supra-compression circuit) featuring the heat exchanger 31.

[0067] Therefore, a line 71 extends from the condensation reservoir 12 and directs CO.sub.2 refrigerant to the hot side of the heat exchanger 31, which heat exchanger 31 is optional and is used to vaporize the CO.sub.2 refrigerant if necessary. The line 71 may be collecting gas CO.sub.2 refrigerant at a top of the condensation reservoir 12 to direct the CO.sub.2 refrigerant to the heat exchanger 31. A pressure-reducing valve 72 is provided in line 71 to ensure that the CO.sub.2 refrigerant reaches the heat exchanger 31 at a suitable pressure. The CO.sub.2 refrigerant goes through the supra-compression circuit in the manner described previously, so as to lose heat, and return to the condensation reservoir 12 primarily in a liquid state.

[0068] It is pointed out that the configuration of the CO.sub.2 refrigeration system 70 of FIG. 5 is such that a single refrigerant, namely CO.sub.2 refrigerant, is used therein.

[0069] Referring to FIG. 6, an alternative line configuration is shown at 80, which line configuration is typically used to supply refrigerant to large refrigeration units (e.g., in freezer rooms). Line 81, typically a large diameter line, diverges into a plurality of smaller lines, from an expansion valve 82. Each smaller line may have a valve 83, and each feeds an own smaller refrigeration unit 84. As a result, some of the units 84 may be turned off, so as to meet more precisely the cool demand of an enclosure.

[0070] Referring to FIG. 7, yet another embodiment of a CO.sub.2 refrigeration system is illustrated at 90. The CO.sub.2 refrigeration systems 1 and 90 have numerous common stages and lines, whereby like elements will bear like reference numerals. One difference between the CO.sub.2 refrigeration systems 1 and 90 is the presence of at least one dedicated compressor 10 to compress defrost refrigerant. The discharge of the dedicated compressor 10 goes at least partially to the defrost circuit, whereas the discharge of the other compressors 10 is directed to the refrigeration circuit. A line and valve (not shown) may be used to direct some excess refrigerant from the dedicated compressor 10 to the refrigeration circuit. The CO.sub.2 dedicated compressor 10 may also be used to flush the defrost reservoir 42.

[0071] As an alternative, defrost could be made by directing refrigerant from the supra-compression circuit, into the defrost circuit, using an appropriate pressure-reducing valve.

[0072] Referring to FIG. 8, yet another embodiment of a CO.sub.2 refrigeration system is illustrated at 100. The CO.sub.2 refrigeration systems 70 (FIG. 5) and 90 have numerous common stages and lines, whereby like elements will bear like reference numerals. The CO.sub.2 refrigeration system 100 is well suited for applications requiring low-temperature cooling, such as ice-skating rinks and industrial freezer applications.

[0073] The CO.sub.2 refrigeration system 100 may be configured to operate without the CO.sub.2 compression stages, due to the heat removal capacity of the supra-compression circuit. In such a configuration, a pump may circulate the refrigerant in the refrigeration circuit, from the condensation reservoir 12 to the low-temperature evaporation 16. In the ice-skating rink applications, the various heat absorbing components (e.g., the heat reclaim stage 13, the heat reclaim exchanger 34) may be used to melt zamboni residue in an ice dump. It is preferred not to use the supra-compression circuit when the CO.sub.2 refrigeration system 100 is operated in warmer countries. The CO.sub.2 refrigeration system 100 is more efficient with CO.sub.2 compression in such climates.

[0074] Considering the nature of the refrigerant, plastic tubing or non-rigid lines may be used as an alternative to the rigid metallic lines previously used, between the mechanical room and the stages of the systems, such as the condensation stage 12 and the evaporation stages 16 and 17. One known type of pipes that can be used is Halcor Cusmart pipes, and features a non-rigid copper core with a plastic insulation sleeve about the core. Such configurations are cost-efficient in that no weld joints are required to interconnect pipes, as is the case for rigid metallic lines. Gutters, for instance having a trapezoid cross-section, may be used as a guide for lines.

[0075] Referring to FIG. 9, yet another embodiment of a CO.sub.2 refrigeration system is illustrated at 110. The CO.sub.2 refrigeration systems 1 and 110 have numerous common stages and lines, whereby like elements will bear like reference numerals. One difference between the CO.sub.2 refrigeration systems 1 and 110 is line 111 directing CO.sub.2 refrigerant from the supra-compression stage 32 to the evaporator stages 16 and 17 for defrost. Accordingly, the CO.sub.2 refrigerant fed to the evaporation stage 16/17 is at a relatively high pressurevalve 114 may be provided to lower the pressure of the CO.sub.2 refrigerant to an appropriate level (e.g., 500 Psi). The defrost refrigerant is then directed to the defrost reservoir 42. A valve 112 is provided to control the amount of defrost refrigerant from the reservoir 42 reintegrating the refrigeration cycle. Moreover, in order to maintain a suitable compression ratio in view of the operating pressure of the condensation reservoir 12, a pressure-reducing valve 113 is provided in the line 11, so as to reduce the pressure of the CO.sub.2 refrigerant feeding the condensation reservoir 12.

[0076] Moreover, the refrigeration system 110 has a line 115 (with appropriate valves) selectively directing refrigerant from the supra-compression stage 32 to the defrost reservoir 42, to flush the reservoir 42 when required. It is pointed out that the heat exchangers 19 and 31 are optional, as is the condensation circuit featuring the compression stage 21.

[0077] Referring to FIG. 10, yet another embodiment of a CO.sub.2 refrigeration system is illustrated at 120. The CO.sub.2 refrigeration systems 70 and 120 have numerous common stages and lines, whereby like elements will bear like reference numerals. The CO.sub.2 refrigeration system 120 has a cascaded arrangement for the two stages of CO.sub.2 compression, namely compression stage 10 and supra-compression stage 32. More specifically, the refrigerant discharge from the compression stage 10 is fed to a suction accumulator 121, and CO.sub.2 refrigerant in a gas state is sucked from a top of the accumulator 121 by the supra-compression stage 32.

[0078] The suction accumulator 121 also receives CO.sub.2 refrigerant from the evaporation stage 17, optionally via heat exchanger 31. Gas CO.sub.2 refrigerant from the condensation reservoir 12 may also be directed to the suction accumulator 121. The liquid CO.sub.2 refrigerant from the suction accumulator 121 may be directed to the compression stage 10.

[0079] In order to maintain suitable conditions for the refrigerant at the inlet of the compression stage, a first suction accumulator 122 is provided downstream of the compression stage 10, which suction accumulator 122 receives CO.sub.2 refrigerant from the suction accumulator 121 through a line (e.g., capillary) having a heat exchanger 123 for heat exchange with a discharge of the supracompression stage 32, or with a discharge of the compression stage 10. Moreover, liquid refrigerant from the suction accumulator 122 may be heated by line 124, in heat exchange with the discharge of the compression stage 10 or with supracompression stage 32, or simply by using an electric heater. The line 124 may then direct the vaporized refrigerant to the suction of the compression stage 10. In an embodiment, the line 124 collects liquid CO.sub.2 refrigerant and oil at a bottom of the suction accumulator 122. Accordingly, the vaporized refrigerant has an oil content when fed to the compressors of the compression stage 10. The oil is then recuperated for instance in the suction accumulator 121. A similar loop may be performed to feed a mixture of CO.sub.2 refrigerant and oil to the supra-compression stage 32.

[0080] In the embodiment in which the line 124 directs vaporized refrigerant to the suction of the compression stage 10, a valve 125 is provided in that case to maintain a pressure differential between the suction accumulator 122 and the suction of the compression stage 10, to allow the flow of refrigerant from line 124 into CO.sub.2 compression stage 10. It is considered to use other components than suction accumulator 121, suction accumulator 122, line 124 and heat exchanger 123 to vaporize the refrigerant, such as a heating element, an air conditioning system, a heat exchanger and the like. It is also considered that CO.sub.2 refrigerant leaving suction accumulator 121 and suction accumulator 122 be directed elsewhere in the CO.sub.2 refrigeration system.

[0081] The cascaded compressor configuration of FIG. 10 is well suited to preserve the oil in the compression stage 10. More specifically, oil accumulating in the suction accumulator 121 is returned to the suction accumulator 122 via the line of heat-exchanger 123. The oil may then be sucked with refrigerant by the compression stage 10. Accordingly, the oil cycles between stages 10, 121 and 122. A similar cycle may be used for feeding an oil and refrigerant mixture to the supra-compression stage 32.

[0082] The defrost of the evaporation stages 16 and 17 may be performed at low pressure so as to avoid damaging the evaporator coils. Accordingly, the refrigeration cycle 120 may be retrofitted to existing evaporator coils, considering the relatively low defrost pressures. The defrost CO.sub.2 refrigerant may be fed by the compression stage 10, or by the supra compression stage 32, with valve 46 controlling the pressure.

[0083] In order to protect the evaporator coils from high defrost pressures, a set of lines 126 extends from the evaporator coils to any reservoir or accumulator of the refrigeration system 120. For instance, the lines 126 are connected to one of the accumulators 121 and 122 while being separated by a valve 127. The valve 127 opens if the pressure in the evaporator coils is above a given threshold. Accordingly, if the defrost pressure in the evaporator coils is too high, the defrost CO.sub.2 refrigerant is discharged to one of the accumulators 121 and 122, whereby the CO.sub.2 refrigerant stays in the refrigeration system 120. As another safety measure, a pressure-relief valve system 128 is provided on the appropriate accumulators, such as 122 as shown but alternatively on the accumulator 121 or on the condensation reservoir 12.

[0084] For instance, the method for relieving CO.sub.2 refrigerant pressure from evaporators during a defrost cycle comprises providing a pressure-relief valve for each evaporator line, the pressure relief-valve opening at a pressure threshold. CO.sub.2 refrigerant is then fed to evaporators in the evaporator line to defrost the evaporator. The evaporators are exhausted from the CO.sub.2 refrigerant with the pressure-relief valve when the CO.sub.2 refrigerant pressure is above the pressure threshold; and directing the exhausted CO.sub.2 refrigerant to an accumulator in a refrigeration cycle.

[0085] In specific conditions, it may be required to cool the CO.sub.2 refrigerant fed to the evaporation stages 16 and/or 17 during the refrigeration cycle. Accordingly, a heat-exchanger system 129, for instance with an expansion valve, may direct refrigerant from the line 71 and feed same to the heat-exchanger system 129, to cool the CO.sub.2 refrigerant fed to the evaporation stages 16 and/or 17.

[0086] The valve 39 is controlled (e.g., modulated) to maximize the heat reclaim via the heat reclaim exchanger 34. When the heat demand is high (e.g., during Winter in colder climates), the valve 39 may maintain a high refrigerant pressure downstream of the compression stage 32, to ensure the heat reclaim exchanger 34 extracts as much heat as possible from the CO.sub.2 refrigerant. The amount of refrigerant sent to the gas cooling stage 36 is controlled simultaneously.

[0087] Referring to FIG. 11, yet another embodiment of a CO.sub.2 refrigeration system is illustrated at 130. The CO.sub.2 refrigeration systems 1 and 130 have numerous common stages and lines, whereby like elements will bear like reference numerals. The CO.sub.2 refrigeration system 130 is particularly well suited for hot climate applications. In the CO.sub.2 refrigeration system 130, the discharge of the compression stage 10 is directed to the heat exchanger 20 prior to reaching the condensation reservoir 12, for relatively low pressure condensation. Alternatively, the refrigerant exiting the heat exchanger 20 may be directed to the suction accumulator 133, thereby bypassing the condensation reservoir 12. A gaseous portion of the CO.sub.2 refrigerant in the condensation reservoir 12 is directed via line 131 and pressure-reducing valve 132 into the heat exchanger 31 to reach the suction accumulator 133. The CO.sub.2 refrigerant passing through the heat exchanger 31 absorbs heat from the CO.sub.2 refrigerant exiting the supra-compression circuit via line 134. A line 135 relates a top of the suction accumulator 133 to the supra-compression stage 32, to feed gaseous CO.sub.2 refrigerant to the compressors. Liquid CO.sub.2 refrigerant may be directed to another suction accumulator 136, at the suction of the compression stage 10, in similar fashion to the CO.sub.2 refrigeration system 120 of FIG. 10 (with appropriate heat exchange with the discharge of stage 10 if necessary). The supra-compression circuit is typically used to reclaim heat, while the evaporation stages 16 and 17 are part of a HVAC unit, amongst other possibilities.

[0088] Referring to FIG. 12, yet another embodiment of a CO.sub.2 refrigeration system is illustrated at 140. The CO.sub.2 refrigeration systems 1 and 140 have numerous common stages and lines, whereby like elements will bear like reference numerals. The CO.sub.2 refrigeration system 140 has a heat exchanger 141 collecting defrost CO.sub.2 refrigerant at the outlet of the evaporators 16/17, to vaporize the defrost CO.sub.2 refrigerant and return same into the refrigeration cycle, namely to feed the suction of the compression stage 10 via line 142 or the supra-compression stage 32 via line 143. The heat exchanger 141 allows heat exchange between the defrost CO.sub.2 refrigerant and the CO.sub.2 refrigerant exiting the supra-compression stage 32 via lines 144, and may also be any other heat source (e.g. electric heater, heat reclaim, air-conditioning unit, or the like).

[0089] An air-conditioning unit 145 may be in fluid communication with the defrost reservoir 42 so as to use the defrost CO.sub.2 refrigerant accumulated therein for air-conditioning purposes. The discharge of the air-conditioning unit 145 may be returned to the suction of the supra-compression stage 32, amongst other possibilities. In the various refrigerant systems described above, it is pointed out that the defrost refrigerant may be fed to the evaporators of stages 16 and 17 from either direction (as opposed to being fed in a direction opposed to that of refrigerant in the refrigeration cycle). Moreover, it is considered to provide the valves controlling the flow of defrost refrigerant to the evaporators 16 and 17 in the refrigeration pack, and have a plurality of lines for each single valve.

[0090] Referring to FIG. 13, a desiccant system is generally shown at 150. The desiccant system 150 may be used with any of the refrigeration systems described above, or with other refrigeration systems, to dry air being entered into a building for ventilating or refrigerating purposes. The desiccant system 150 is a closed circuit in which circulates a desiccant fluid.

[0091] The system 150 has a dryer 151, upon which exterior air flows when entering the building. The dryer 151 is a structural device upon which the desiccant fluid is sprayed. For instance, the dryer 151 may provide a honeycomb body. The desiccant fluid sprayed on the dryer 151 is in a suitable cooled state to absorb humidity from the warm exterior air entering the building. The desiccant fluid reaches a substantially liquid state after the absorption of humidity, and drips into pan 152 (or any oter collector).

[0092] By way of a line and pump, the desiccant fluid passes through a heating exchanger 153 to be heated. Although not shown, the heating exchanger 153 may be connected to one of the above-referred refrigeration circuits, so as to provide the necessary energy to heat the desiccant fluid. Alternatively, the heating exchanger 153 may have an electric coil or the like.

[0093] The desiccant fluid, in a heated state, is then sprayed onto a humidifier 154. The humidifier 154 is similar to the dryer 151 in construction, but releases water to the exterior air. The desiccant fluid is heated as a function of the exterior temperature, for the desiccant fluid to release the previously-absorbed water to the air. The liquid desiccant is then collected in another pan 155 (or the like).

[0094] By way of a line and pump, the desiccant fluid passes through a cooling exchanger 156 to be cooled. Although not shown, the cooling exchanger 156 may be connected to one of the above-referred refrigeration circuits, so as to provide the necessary energy to cool the desiccant fluid. The desiccant fluid is cooled as a function of the exterior temperature, for the desiccant to absorb water from the outdoor air entering the building. Once it is cooled, the desiccant fluid is directed to the dryer 151.