Patent Publication Number: US-2016245575-A1

Title: Co2 refrigeration system for ice-playing surfaces

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application is a divisional of U.S. patent application Ser. No. 13/247,562 filed on Sep. 28, 2011 which claims the benefit of U.S. Provisional Patent Applications No. 61/387,087, filed on Sep. 28, 2010, and No. 61/415,982, filed on Nov. 22, 2010 and which claims priority to Canadian Patent Application No. 2,724,255, filed on Dec. 17, 2010, now Canadian Patent No. 2,724,255, issued on Sep. 13, 2011. All of the above-mentioned applications are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE APPLICATION 
     The present application relates to refrigeration systems used in industrial refrigeration applications, such as rinks, curling centers and arenas, to refrigerate an ice-skating or ice-playing surface, and more particularly to such refrigeration systems using CO 2  refrigerant. 
     BACKGROUND OF THE ART 
     With the growing concern for global warming, the use of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) as refrigerant has been identified as having a negative impact on the environment. These chemicals have non-negligible ozone-depletion potential and/or global-warming potential. 
     As alternatives to CFCs and HCFCs, ammonia, hydrocarbons and CO 2  are used as refrigerants. Although ammonia and hydrocarbons have negligible ozone-depletion potential and global-warming potential as does CO 2 , these refrigerants are highly flammable and therefore represent a risk to local safety. On the other hand, CO 2  is environmentally benign and locally safe. 
     Ice-playing surfaces typically have large-scale heat exchangers disposed under the ice surface to refrigerate the ice surface. Considering the specific use of such refrigeration systems, and thus the requirement for a refrigerant at a precise range of temperature, brine is currently used in such refrigeration systems. The brine circulates in a closed circuit and is in a heat-exchange relation with a refrigeration circuit. However, these refrigeration circuits often use refrigerants that are harmful to the environment. 
     SUMMARY OF THE APPLICATION 
     It is therefore an aim of the present disclosure to provide a CO 2  refrigeration system for ice surfaces, that addresses issues associated with the prior art. 
     Therefore, in accordance with the present application, there is provided a CO 2  refrigeration system comprising a CO 2  condensation reservoir in which CO 2  refrigerant is accumulated and circulates between a supracompression loop and an evaporation loop; the supracompression loop comprising a compression stage in which CO 2  refrigerant from at least the CO 2  condensation reservoir is compressed to at least a supracompression state, a cooling stage in which the CO 2  refrigerant from the compression stage releases heat, and a pressure-regulating unit in a line extending from the cooling stage to the CO 2  condensation reservoir to maintain a pressure differential therebetween; and the evaporation loop comprising an evaporation stage in which the CO 2  refrigerant from at least the CO 2  condensation reservoir absorbs heat in a heat exchanger, the heat exchanger being connected to an ice-playing surface refrigeration circuit in which cycles a second refrigerant, such that the CO 2  refrigerant absorbs heat from the second refrigerant in the heat exchanger. 
     Further in accordance with the present application, there is provided a CO 2  refrigeration system comprising a CO 2  condensation exchanger for heat exchange between a supracompression loop of CO 2  refrigerant and an evaporation loop of CO 2  refrigerant; the supracompression loop comprising a compression stage in which CO 2  refrigerant having absorbed heat in the condensation exchanger is compressed to at least a supracompression state, a cooling stage in which the CO 2  refrigerant from the compression stage releases heat, and a pressure-regulating unit in a line extending from the cooling stage to the condensation exchanger to maintain a pressure differential therebetween; and the evaporation loop comprising a condensation reservoir in which CO 2  refrigerant having released heat in the condensation exchanger is accumulated in a liquid state, and an evaporation stage in which the CO 2  refrigerant from the condensation reservoir absorbs heat to cool an ice-playing surface, to then return to one of the condensation reservoir and the condensation exchanger. 
     Still further in accordance with the present application, there is provided a CO 2  refrigeration system comprising a CO 2  condensation reservoir in which CO 2  refrigerant is accumulated and circulates between a supracompression loop and an evaporation loop; the supracompression loop comprising a compression stage in which CO 2  refrigerant from at least the CO 2  condensation reservoir is compressed to at least a supracompression state, a cooling stage in which the CO 2  refrigerant from the compression stage releases heat, and a pressure-regulating unit in a line extending from the cooling stage to the CO 2  condensation reservoir to maintain a pressure differential therebetween; the evaporation loop comprising an evaporation stage of pipes under an ice-playing surface in which circulates the CO 2  refrigerant to absorb heat to cool an ice-playing surface, to then return to the CO 2  condensation reservoir; and a geothermal well loop in heat-exchange relation with the CO 2  refrigerant, the geothermal well loop having a geothermal heat exchanger for heat exchange between the CO 2  refrigerant of one of the evaporation loop and the compression loop and another refrigerant absorbing heat from the CO 2  refrigerant, the geothermal well loop extending to a geothermal well in which the other refrigerant releases heat geothermally. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a CO 2  refrigeration system for skating surfaces in accordance with a first embodiment; 
         FIG. 2  is a block diagram of a CO 2  refrigeration system for skating surfaces in accordance with a second embodiment; 
         FIG. 3  is a block diagram of a CO 2  refrigeration system with a geothermal well in accordance with a third embodiment; 
         FIG. 4  is a block diagram of a CO 2  refrigeration system with a geothermal well in accordance with a fourth embodiment; and 
         FIG. 5  is a schematic view of a modulated pressure-relief system for use with the CO 2  refrigeration systems of the previous figures. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a CO 2  refrigeration system in accordance with an embodiment is illustrated at  1 . The CO 2  refrigeration system  1  has a CO 2  refrigeration circuit comprising a CO 2  condensation reservoir  12 . The condensation reservoir  12  accumulates CO 2  refrigerant in a liquid and gaseous state, and may be in a heat-exchange relation with a closed condensation circuit that absorbs heat from the CO 2  refrigerant, with examples given hereinafter. 
     Line  14  directs CO 2  refrigerant from the condensation reservoir  12  to an evaporation stage via pump(s)  15  or expansion valve(s). As is shown in  FIG. 1 , the CO 2  refrigerant is supplied in a liquid state by the condensation reservoir  12  into line  14 . The pump  15  ensures a suitable flow of liquid CO 2  refrigerant to the evaporation exchanger  16 . In some instances, expansion valve(s)  15  may be used to control the pressure of the CO 2  refrigerant, which is then fed to the evaporation exchanger  16 . Any appropriate means may be used to put the CO 2  refrigerant in suitable condition, such as heat exchangers to vaporize the refrigerant. 
     The evaporation exchanger  16  features the heat exchange between the CO 2  refrigerant and the refrigerant of the ice-playing surface. The ice-playing surface refrigerant circulating in the ice-playing surface is typically brine, but may be other types of fluid, such as alcohol-based fluid (e.g., glycol) or the like. In one embodiment, the CO 2  circulates in pipes upon which fins are provided. The pipes of the evaporator exchanger  16  are typically positioned in a bath of the ice-playing surface refrigerant. In another embodiment, the refrigeration system  1  is retrofitted to an existing ice-playing surface refrigeration circuit  17 . It is pointed out that the expansion valve(s)  15  may be part of a refrigeration pack in the mechanical room, as opposed to being at the evaporation exchanger  16 . 
     The CO 2  refrigerant exiting the evaporation stage  16  is returned to the condensation reservoir  12  via line  18 . Alternatively, the CO 2  refrigerant may be directed to the inlet of compressors of the transcritical circuit or loop, via line  19 . In such a case, it may be required to provide some form of protection in line  19  to vaporize the CO 2  refrigerant fed to the inlet of the compressors, such as an evaporator, a heat exchanger or source of heat, valves, among numerous possibilities. 
     The transcritical circuit or loop (i.e., supracompression circuit) is provided to compress the CO 2  refrigerant exiting from the condensation reservoir  12  to a transcritical state, for heating purposes, or supracompressed state. In both compression states, the CO 2  refrigerant is pressurized with a view to maintaining the condensation reservoir  12  at a high enough pressure to allow vaporized CO 2  refrigerant to be circulated in the evaporation stage  16 , as opposed to liquid CO 2  refrigerant. In one embodiment, the pressure is high enough for the CO 2  refrigerant to circulate to the evaporation exchanger  16  via the action of the pump  15 . 
     A line  30  (using valve  30 A) relates the condensation reservoir  12  to a heat exchanger  31  and subsequently to a supracompression stage  32 . The heat exchanger  31  or any other appropriate means may be provided to vaporize the CO 2  refrigerant fed to the supracompression stage  32  (e.g., feed from a top of the condensation reservoir  12 , multiple reservoirs in specific arrangement, etc). The supracompression stage  32  features one or more compressors (e.g., Bock™, Dorin™), that compress the CO 2  refrigerant to a supra-compressed or transcritical state. 
     In the supracompressed or transcritical state, the CO 2  refrigerant is used to heat a secondary refrigerant via heat-reclaim exchanger  34 , or may be used directly in a heating unit, with a fluid such as air blown thereon to heat parts of the building related to the ice-playing surface. In the heat-reclaim exchanger  34 , the CO 2  refrigerant is in a heat-exchange relation with the secondary refrigerant circulating in the secondary refrigerant circuit  35 , or with a fluid blown on the heat exchanger  34 . In the event that a secondary refrigerant is used, 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 supracompressed or transcritical state of the CO 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  may be the largest of the circuits of the refrigeration system  1  in terms of quantity of refrigerant. Therefore, the compression of the CO 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. It is pointed out that heat-reclaim exchanger  34  may include individual heating units used to produce heat locally. Such heating units  35  are typically a coil and fan assembly. The control of the amount of refrigerant sent to each heating unit  35  is described hereinafter. 
     A gas-cooling stage  36  is provided in the transcritical circuit. The gas-cooling stage  36  absorbs excess heat from the CO 2  refrigerant in the transcritical state, with a view to re-injecting the CO 2  refrigerant into 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 2  refrigerant directed to the gas-cooling stage  36 , in view of the heat demand from the heat-reclaim exchanger  34 . 
     In warmer climates in which the demand for heat is smaller, the CO 2  refrigerant is compressed to a supracompressed state, namely at a high enough pressure to allow the expansion of the CO 2  refrigerant at the exit of the condensation reservoir  12 , so as to reduce the amount of CO 2  refrigerant circulating in the refrigeration circuit. A by-pass line is provided to illustrate that the heat-reclaim exchanger  34  and the gas-cooling stage  36  may be optional for warmer climates. 
     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 . 
     Lines  37  and  38  return the CO 2  refrigerant to the condensation reservoir  12 , and thus to the refrigeration circuit. The line  37  may feed the heat exchanger  31  such that the CO 2  refrigerant exiting the stages  34  and  36  releases heat to the CO 2  refrigerant fed to the supracompression stage  32 , for the CO 2  refrigerant fed to the supracompression stage  32  to be in a gaseous state. 
     In the case of transcritical compression, a CO 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 2  transcritical pressure-regulating valve  39  is for instance a Danfoss™ valve. Any other suitable pressure-control, pressure-regulating, pressure-reducing device may be used as an alternative to the valve  39 , such as any type of valve or loop. 
     The condensation circuit and the supracompression circuit allow the condensation reservoir  12  to store refrigerant at a relatively medium pressure. The pump  15  then ensures the circulation of the CO 2  refrigerant in the evaporation exchanger  16 . In the embodiment featuring expansion valve  15 , as CO 2  refrigerant is vaporized downstream of the expansion valve  15 , the amount of CO 2  refrigerant in the refrigeration circuit is reduced, especially if the expansion valve  15  is in the refrigeration pack. 
     It is considered to operate the supracompression circuit (i.e., supra-compression  32 ) with higher operating pressure. CO 2  refrigerant has a suitable efficiency at a higher pressure. More specifically, more heat can be extracted when the pressure is higher. 
     Referring now to  FIG. 2 , there is illustrated a CO 2  refrigeration system  2  for ice-playing surfaces. The CO 2  refrigeration system  2  is similar to the CO 2  refrigeration system  1  of  FIG. 1 , whereby like elements will bear like reference numerals. One difference between refrigeration systems  1  and  2  is that the refrigeration system  2  features two closed circuits of refrigerant in addition to the ice-playing surface refrigeration circuit  17 . More specifically, the CO 2  refrigeration circuit  2  of  FIG. 2  has a condensation exchanger  50  by which the refrigerant circulating in the main refrigeration circuit  40  (i.e., CO 2  or other refrigerants, if suitable) is in a heat-exchange relation with CO 2  refrigerant circulating in the transcritical/supracompression circuit. Accordingly, in the condensation exchanger  50 , the CO 2  refrigerant circulating in the supracompression/transcritical circuit is used to absorb heat from the refrigerant circulating in the main refrigeration circuit  40 . In an embodiment, both refrigerants are CO 2 . 
     Referring to  FIG. 3 , there is illustrated a CO 2  refrigeration system  3  similar to the CO 2  refrigeration systems  1  and  2 , whereby like elements and components will bear like reference numerals. The valve  30 A in line  30  may be an expansion valve, evaporative pressure-regulating valve, control valve or the like so as to ensure that the compressors  32  are fed with vaporized CO 2  refrigerant. The refrigeration system  3  has one or more heating units  35  at the outlet of the supracompression stage  32 , in any given arrangement with the exchanger  34  and gas-cooling stage  36 . The heating units  35  are typical direct-heating units, having coils in which CO 2  refrigerant circulates and upon which air is blown for heating purposes. 
     According to an embodiment, there are a plurality of the heating units  35 . In another embodiment, the heating units  35  are in a parallel relation, and they may or may not be fed with CO 2  refrigerant as a function of the heating requirements. Moreover, the speed of the fans of the heating units  35  may also be controlled for this purpose. A valve or valves  35 A are used to control the amount of CO 2  refrigerant sent to each of the heating units  35  and/or to heat-reclaim exchanger  34 . For instance, if two of the heating units  35  cover two different zones having different heating requirements, the valves  35 A and fans of each unit may be adjusted to meet the local heating requirements. One configuration is to have thermostats for the various zones to adjust the amount of refrigerant sent to the heating units  35  via the adjustment of the valves  35 A. 
     A reservoir  55  may be provided between lines  37  and  38  to receive CO 2  refrigerant, and ensure it is fed in suitable condition to the condensation exchanger  50 . For instance, the line  38  may tap into a bottom of the reservoir  55  to direct liquid CO 2  refrigerant to the condensation exchanger  50 . A valve  56  (e.g., expansion valve) may be provided to ensure that the CO 2  refrigerant is in a suitable state to absorb heat from the CO 2  refrigerant. In an embodiment, valve  56  is used as pressure differential valve instead of valve  39  (not required in such a case to reduce the pressure), with the supracompression pressure maintained upstream of valve  56 . With this configuration, the pressure of the CO 2  refrigerant in the main refrigeration circuit  40  may be kept lower, or other refrigerants may be used in the main refrigeration circuit  40 . 
     Still referring to  FIG. 3 , a heat exchanger  60  is illustrated as extending from the condensation reservoir  12  and in fluid communication therewith so as to receive a feed of CO 2  refrigerant. The heat exchanger  60  is in fluid communication with a geothermal well  61  by a geothermal circuit. A refrigerant (e.g., glycol, or any appropriate refrigerant such as alcohol-based refrigerants or the like) circulates in the geothermal circuit, so as to absorb heat from the CO 2  refrigerant in the heat exchanger  60  and release the heat in the well  61 . Appropriate pumps  62  and/or  63  or flow controlling means may be used to ensure that there is a suitable flow of refrigerant to the heat exchanger  60 . The pumps  62  and  63  are variably controlled. 
     In  FIG. 3 , although the refrigeration system  3  is shown with an evaporation exchanger  16  and ice-rink cooling, the refrigeration system  3  may be used for any appropriate type of refrigeration, with or without an evaporation exchanger  16 . Moreover, the refrigeration system  3  may be operated without a geothermal well in appropriate conditions. 
     Referring to  FIG. 4 , a CO 2  refrigeration system  4  similar to the CO 2  refrigeration systems  1 ,  2  and  3  is illustrated, whereby like elements and components will bear like reference numerals. The refrigeration system  4  features a geothermal well loop, but does not have a condensation exchanger  50  as does the refrigeration system  3 . The CO 2  refrigeration system  4  may be used to refrigerate a skating rink or the like. For simplicity purposes, the evaporation stage is generally shown as  17 . In the embodiment in which the CO 2  refrigerant is sent directly in the pipes of the ice-playing surface as part of the evaporation stage  17 , the pump(s)  15  is well suited to induce a suitable flow of liquid CO 2  refrigerant into the pipes of the ice-playing surface. 
     The refrigeration systems  1 - 3  may be used with existing ice-playing surface piping, or as part of new ice-rink refrigeration systems. The evaporation exchanger  16  is modified to receive CO 2  refrigerant. It may be required that the coils be modified in view of the specifications of the CO 2  refrigerant versus the brine or other refrigerant used in the ice-playing surface piping. The CO 2  refrigeration systems  1 - 3  advantageously use the existing hardware related to the ice-playing surface refrigeration. It is pointed out that the CO 2  refrigeration systems  1 - 3  need not be used only in a retrofit configuration. 
     Referring to  FIG. 5 , there is illustrated a modulated pressure-relief system which may be used with any one of the CO 2  refrigeration systems  1 - 4  of the previous figures, if appropriate. The modulated pressure-relief system has a line  70  that is in fluid communication with the evaporators of the refrigeration system. A pair of valves  71  and  72  are in a parallel arrangement with the line  70 , and are part of exhaust lines opened to the atmosphere, for exhausting CO 2  refrigerant. Valve  71  is a modulating valve, automatically operable from a set point pressure. The modulating valve  71  therefore gradually opens upon the pressure in the line reaching the set point pressure. Any other gradually-opening type of valve may be used as valve  71 . For instance, valve  71  may be operated by a controller (e.g., central processing unit of the CO 2  refrigeration systems), or may be a mechanical valve with an appropriate controlled-opening mechanism. 
     Valve  72  is a pressure-relief valve. The pressure-relief valve  72  has its own set point pressure, which is higher than the set point pressure of the modulating valve  71 . The pressure-relief valve  72  opens when the set point pressure is reached. Accordingly, if the pressure is high in the evaporators, but not at the set point of relief, the pressure increase in the evaporators  70  will be modulated to reduce the pressure increase. The opening of valve  72  in a relief condition may be controlled so as to be a slow release to limit the release of refrigerant to the atmosphere. Valve  72  may be any appropriate type of relief valve, such as a mechanical valve, or a valve controlled by the controller of the CO 2  refrigeration system. 
     The CO 2  refrigeration systems described above for  FIGS. 1-4  are generally separated into a supracompression loop and an evaporation loop. The supracompression loop comprises the supracompression stage, while the evaporation loop comprises the evaporation stage. The loops may be separated from one another by the condensation exchanger  50  ( FIGS. 2 and 3 ), in which case the CO 2  refrigerant does not circulate between loops. In  FIGS. 1 and 4 , the loops are interrelated by the condensation reservoir  12 , in which case the CO 2  refrigerant circulates between loops. 
     The CO 2  refrigeration systems described above for  FIGS. 1-4  are used for ice-playing surfaces, which may include ice-skating surfaces of arenas or of outdoor applications, skating rinks (e.g., speed skating), the playing surface of curling centers, or any other application in which a relatively large-scale refrigerated surface is used. Moreover, although the word “ice” is used (and thus water), it is understood that the medium used for the surface may be any appropriate fluid reaching a solid state.