Abstract:
The present invention provides a refrigeration system including a first refrigerant circuit including a first heat exchanger for transferring heat from refrigerant, a second refrigerant circuit including a second heat exchanger for transferring heat to refrigerant, and a third refrigerant circuit. The third refrigerant circuit includes a compressor, a condenser connected to the first refrigerant circuit such that heat exchange can occur between the refrigerants of the first and refrigerant circuits, an expansion device, and an evaporator connected to the second refrigerant circuit such that heat exchange can occur between the refrigerant of the second and third refrigerant circuits. The refrigerant can travel along the third refrigerant circuit in a common direction during operation in both heating and cooling modes. Refrigerant can be prevented from moving between first, second, and third refrigerant circuits during operation in heating and cooling modes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/933,713, filed Jun. 8, 2007, the entire contents of which is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a refrigeration system and a method of manufacturing a refrigeration system, and more particularly to a refrigeration system having both an air heating or heat pump mode and an air conditioning or cooling mode. 
       SUMMARY 
       [0003]    In principal, a CO 2  heat pump system can be switched from a heat pump or heating mode (HP) to air conditioning or cooling (A/C) mode by changing the flow direction in the system cycle so that the A/C mode evaporator operates as a HP mode gas cooler, and the A/C mode gas cooler operates as an HP mode evaporator. However, there are some practical limitations to this method, which include, but are not limited to, the need for valves able to accommodate high pressure CO 2 , appropriately sized accumulators, and heat exchangers in such a system able to withstand higher system pressures for a fully-reversible system. 
         [0004]    In accordance with one feature of the present invention, a refrigeration system is provided that can be operated in both HP and A/C modes without changing the general direction of refrigerant flow through the system. This is done by employing two secondary coolant loops, and adding additional heat exchangers. One desirable application for this system is the cabin heating and cooling required for truck idle-off. In some embodiments, CO 2  can be used as a refrigerant in at least one refrigerant circuit. 
         [0005]    In some embodiments, the invention provides a refrigeration system having both a heating mode for providing heat to a load space and a cooling mode for removing heat from the load space. The system can include a first refrigerant circuit including a first heat exchanger for transferring heat from refrigerant of the first refrigerant circuit to air, a second refrigerant circuit including a second heat exchanger for transferring heat from air to refrigerant of the second refrigerant circuit, and a third refrigerant circuit. The third refrigerant circuit can include a compressor for increasing pressure of refrigerant of the third refrigerant circuit, a condenser connected to the compressor for receiving refrigerant from the compressor and connected to the first refrigerant circuit such that heat exchange can occur between the refrigerant traveling through the first refrigerant circuit and the refrigerant traveling through the third refrigerant circuit, an expansion device for reducing the pressure of the refrigerant of the third refrigerant circuit, and an evaporator connected to the expansion device and connected to the second refrigerant circuit such that heat exchange can occur between the refrigerant traveling through the second refrigerant circuit and the refrigerant traveling through the third refrigerant circuit. The refrigerant can travel along the third refrigerant circuit in a common direction during operation in both the heating mode and the cooling mode. The refrigerant can be prevented from moving between the first refrigerant circuit, the second refrigerant circuit, and the third refrigerant circuit during operation in the heating and cooling modes. 
         [0006]    In some embodiments, the present invention provides a refrigeration system having both a heating mode for providing heat to a load space and a cooling mode for removing heat from the load space. The refrigeration system can include a first refrigerant circuit extending between a compressor, an evaporator, an expansion device, and a condenser. The first refrigerant circuit can define a flow path for a refrigerant traveling in a direction along the refrigerant circuit during operation of the refrigeration system in the heating mode and the cooling mode. The refrigeration system can also include a second refrigerant circuit extending between the condenser and a heat exchanger, the second refrigerant circuit including a first refrigerant pump, and a third refrigerant circuit extending between the evaporator and the heat exchanger. The third refrigerant circuit can include a second refrigerant pump. The second refrigerant pump can be operational during operation in the heating mode and can be idle during operation in the cooling mode. 
         [0007]    The present invention also provides a method of operating a refrigeration system. The method can include the acts of directing a refrigerant along a refrigerant circuit in a direction between a compressor, an evaporator, an expansion device, and a condenser during operation of the refrigeration system in a cooling mode, operating a first pump when the refrigeration system is operating in the cooling mode to circulate refrigerant through a heat exchanger, and transferring heat from a load space to the refrigerant in the refrigerant circuit when the refrigeration system is operating in the cooling mode. The method can also include the acts of stopping the first pump when the refrigeration system is operating in a heating mode, directing the refrigerant along the refrigerant circuit in the direction during operation of the refrigeration system in the heating mode, operating a second pump when the refrigeration system is operating in the heating mode to circulate refrigerant through the heat exchanger in heat exchange relation with the refrigerant of the refrigerant circuit, and transferring heat to the load space from the refrigerant in the refrigerant circuit when the refrigeration system is operating in the heating mode. 
         [0008]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1A  is a schematic illustrating a refrigeration system according to some embodiments of the present invention and showing the refrigeration system operating in a cooling mode. 
           [0010]      FIG. 1B  is a schematic illustrating the refrigeration system of  FIG. 1A  and showing the refrigeration system operating in a heating mode. 
           [0011]      FIG. 2A  is a schematic illustrating a refrigeration system according to an alternate embodiment of the present invention and showing the refrigeration system operating in a cooling mode. 
           [0012]      FIG. 2B  is a schematic illustrating the refrigeration system of  FIG. 2A  and showing the refrigeration system operating in a heating mode. 
           [0013]      FIG. 3A  is a schematic illustrating a refrigeration system according to another alternate embodiment of the present invention and showing the refrigeration system operating in a cooling mode. 
           [0014]      FIG. 3B  is a schematic illustrating the refrigeration system of  FIG. 3A  and showing the refrigeration system operating in a heating mode. 
           [0015]      FIG. 4A  is a schematic illustrating a refrigeration system according to a yet another alternate embodiment of the present invention and showing the refrigeration system operating in a cooling mode. 
           [0016]      FIG. 4B  is a schematic illustrating the refrigeration system of  FIG. 4A  and showing the refrigeration system operating in a heating mode. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
         [0018]    Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
         [0019]    Also, it is to be understood that phraseology and terminology used herein with reference to device or element orientation (such as, for example, terms like “central,” “upper,” “lower,” “front,” “rear,” and the like) are only used to simplify description of the present invention, and do not alone indicate or imply that the device or element referred to must have a particular orientation. In addition, terms such as “first”, “second”, and third” are used herein for purposes of description and are not intended to indicate or imply relative importance or significance. 
         [0020]      FIGS. 1A and 1B  show a schematic illustrating a refrigeration system  10  according to some embodiments of the present invention. During operation in an air conditioning or cooling (A/C) mode, refrigerant, such as, for example, CO 2  leaves a compressor  12  and enters a first evaporator, which, in the illustrated embodiment of  FIGS. 1A and 1B , is an air-cooled gas cooler  14 . In the embodiment shown in  FIG. 1A , the flow of refrigerant is shown by three solid arrows. Depending on one or more of the operating conditions, the anticipated heating or cooling load, and the type of refrigerant employed, the refrigerant may exit the compressor in a supercritical state. While reference is made herein to the use of CO 2  as a refrigerant, in some embodiments, other refrigerants, including, but not limited to, water, R12, engine coolant, any other organic refrigerant, R245fa, glycol, air, and the like can also or alternatively be used. As shown in  FIG. 1A , a fan  16  can be positioned adjacent to or along an airflow path opening onto the air-cooled gas cooler  14  to reject heat from the gas cooler  14  to the ambient environment via transfer of heat from the refrigerant to an ambient air flow provided by the fan  16 . 
         [0021]    The refrigerant can then enter a second evaporator, which, in the illustrated embodiment of  FIG. 1A , is a liquid-cooled gas cooler  18  that is cooled by a secondary, high temperature coolant loop  19 . In the illustrated embodiment of  FIG. 1A , liquid coolant flows through the loop  19  during A/C operation (possibly at a lower mass flow rate than refrigerant from the air-cooled gas cooler  14 ) to further reduce the temperature of the refrigerant, however, compared to the air-cooled gas cooler  14 , the heat load of the liquid-cooled gas cooler  18  can be small. In other embodiments, the heat load of the liquid-cooled gas cooler  18  can be substantially equal to or larger than the heat load experienced by the air-cooled gas cooler  14 , depending upon one or more of the relative sizes and cooling capacities of the air-cooled gas cooler  14  and the liquid-cooled gas cooler  18 , the mass flow rates of refrigerant and coolant flows through and across the air-cooled gas cooler  14  and the liquid-cooled gas cooler  18 , the presence or absence of a fan  16  for the air-cooled gas cooler  14 , and the types and cooling capacities of the coolants used in the air-cooled gas cooler  14  and the liquid-cooled gas cooler  18 . 
         [0022]    As shown in  FIG. 1A , from the liquid-cooled gas cooler, the refrigerant can enter the high pressure side of a suction line heat exchanger (SLHX)  20  for more cooling before going through an expansion device or valve  22 . After the refrigerant exits the expansion valve  22 , the refrigerant can enter an air-to-refrigerant evaporator  24 . A fan (not shown) can be positioned adjacent to or along an airflow path opening onto the evaporator  24 . In some embodiments, the fan can be turned off during periods of reduced cooling demand and/or to limit power consumption and improve efficiency of the refrigeration system  10 . In embodiments in which the fan can be turned off or operated at a reduced speed, the heat duty of the evaporator  24  can be limited to far less than the heat duty of a liquid-to-refrigerant evaporator  26  that receives the refrigerant from the heat exchanger  24 . 
         [0023]    In the liquid-to-refrigerant evaporator  26 , the refrigerant can evaporate, receiving heat energy from and thereby cooling down a coolant (e.g., glycol, water, R12, engine coolant, any organic refrigerant, R245fa, air, and the like) flowing through the liquid-to-refrigerant evaporator  26  from another secondary, low temperature coolant loop  28 . It should be noted that the air-heated evaporator  24  can be placed either upstream or downstream of the liquid-heated evaporator  24  with respect to the flow of the refrigerant. The same can be said of the liquid-cooled gas cooler  18  with respect to the air-cooled gas cooler  14 . However, it can be desirable to avoid excess heating and/or boiling of the slow moving or stagnant liquid in the liquid-cooled gas cooler  18  during operation of the refrigeration system  10  in the A/C mode. 
         [0024]    After traveling through the evaporator  26 , the refrigerant can reject heat to the high pressure refrigerant in the SLHX  20 . An accumulator (not shown in  FIGS. 1A-2B ) can be positioned upstream of the SLHX  20  on the low-pressure-side. This accumulator can be a separate unit, or alternatively, can be directly integrated with the SLHX  20 . 
         [0025]    In addition to the liquid-refrigerant evaporator  26 , the low temperature coolant loop  28  can include a pump  29  for moving liquid coolant through the liquid side of the evaporator  26 . While heat from the coolant is transferred to the refrigerant in the evaporator  26 , a heat exchanger cooler core  30 , which can be mounted in an inside space  32 , such as, for example, the cabin of a truck or another vehicle, can operate to transfer heat away from the low temperature coolant in the coolant loop  28 . The cooler core  30  can be accompanied by an air mover  34 , such as a fan or blower, and can cool down the air inside the space  32  and/or remove humidity from the air in the space  32 . In some embodiments, if the air stream through or across the heat exchanger  30  is cooled below the dew point, a small amount of liquid coolant can be circulated through the hot coolant loop  19  to reheat the air entering the cabin (as shown by three dashed arrows). 
         [0026]      FIG. 1B  shows a schematic illustrating the refrigeration system  10  during operation in the heating (HP) mode. As shown by three solid arrows, the refrigerant flows through the system  10  in the same direction as described above with respect to operation in the A/C mode. However, the fan  16  adjacent to the air-cooled gas cooler  14  is deactivated and high temperature liquid coolant is pumped through the high temperature coolant loop  19  by a pump  35  to provide cooling to the refrigerant in the liquid-cooled gas cooler  18 . In the cold temperature loop  28 , the cold pump  29  is turned off and the air-to-refrigerant fan  34  can be activated. This allows for additional heating inside of the space  32  by the transfer of heat from the high temperature coolant to the air flow in an air-to-coolant heat exchanger heater core  36 . To increase the coefficient of performance (COP) of the system  10  while operating in HP mode during cold weather, a waste heat air stream  40  from a waste heat source  42 , such as a cooling system  43  for an auxiliary power unit  44  can be routed through the air-to-refrigerant evaporator  24 . 
         [0027]    In other embodiments, the waste heat source  42  and/or a different waste heat source  42  can also or alternatively provide heat to a liquid-to-liquid heat exchanger evaporator or an integrated auxiliary power unit (APU) stack cooler and evaporator coolant loop. In the latter-case, the waste heat source  42  can remove the need for an extra air-heated evaporator, and the “cooler” core can add heat to the space air. 
         [0028]      FIGS. 2A and 2B  illustrate an alternate embodiment of a refrigeration system  10  according to the present invention. The refrigeration system shown in  FIGS. 2A and 2B  is similar in many ways to the illustrated embodiments of  FIGS. 1A and 1B  described above. Accordingly, with the exception of mutually inconsistent features and elements between the embodiment of  FIGS. 2A and 2B  and the embodiments of  FIGS. 1A and 1B , reference is hereby made to the description above accompanying the embodiments of  FIGS. 1A and 1B  for a more complete description of the features and elements (and the alternatives to the features and elements) of the embodiment of  FIGS. 2A and 2B . 
         [0029]      FIG. 2A  illustrates a simpler version of the refrigeration system  10 . In this embodiment of the refrigeration system  10 , the low temperature fluid loop  28 , the high temperature loop  19 , and the coolant lines  46  of an APU coolant system  43  are directly plumbed into each other, and only one liquid pump  47  (not including the APU coolant loop pump) is required for the loops  19  and  28 . 
         [0030]    As shown in  FIG. 2A , a matrix  48  of liquid valves  50 ,  52 ,  54 ,  56 ,  58  and  59  can be used to direct the coolant flows to the desired location during HP and A/C modes. This allows for the elimination of the air-to-refrigerant evaporator  24 , and for the functions of the cooler and heater cores  30  and  36  to be combined in one heat exchanger in the form of a heater/cooler core  60 . 
         [0031]    For example, during operation in A/C mode, by opening valve  59  (shown unshaded), closing valves  56  and  58  (shown in solid), opening valves  52  and  54 , and closing valve  50 , the APU coolant will not enter the low temperature loop  28  (which is heating the evaporator  26 ), and no coolant will pass to the liquid-cooled gas cooler  18  via the high temperature loop  19 , while the coolant in the low temperature loop  28  rejects heat to the refrigerant in the evaporator  26  and receives heat from the air stream passing through the heater/cooler core  60 . In some applications, it may be desirable for a small amount of cold liquid to pass through the valve  50  and the liquid-cooled gas cooler  18 . This can allow the refrigerant temperature to fall below the ambient temperature, thus potentially improving system COP. 
         [0032]    As shown in  FIG. 2B , in HP mode, by closing or modulating the valve  59  (now shown in solid), opening the valves  56  and  58  (now shown unshaded), closing the valves  52  and  54  and opening the valve  50 , the APU coolant can be directed to the liquid-to-refrigerant evaporator  26 , and then circulated directly back to the APU  44  without passing through the combined heater/cooler core  60 , while the coolant in the high temperature loop  19  is circulated through the liquid-cooled gas cooler  18  to receive heat from the refrigerant and then through the heater/cooler core  60  to reject heat to the air stream passing therethrough. 
         [0033]      FIGS. 3A and 3B  illustrate an alternate embodiment of a refrigeration system  10  according to the present invention. The refrigeration system shown in  FIGS. 3A and 3B  is similar in many ways to the illustrated embodiments of  FIGS. 1A-2B  described above. Accordingly, with the exception of mutually inconsistent features and elements between the embodiment of  FIGS. 3A and 3B  and the embodiments of  FIGS. 1A-2B , reference is hereby made to the description above accompanying the embodiments of  FIGS. 1A-2B  for a more complete description of the features and elements (and the alternatives to the features and elements) of the embodiment of  FIGS. 3A and 3B . 
         [0034]    The refrigeration system  10  of  FIGS. 3A and 3B  differs from that of  FIGS. 1A and 1B  in that the air-to-refrigerant evaporator  24  has been eliminated and replaced with an air-heated coolant heat exchanger  66  that has been added to a bypass line  68  in the low temperature fluid loop  28 , with a three-way valve  70  (or series of two-way valves) controlling the flow of coolant through the cooler core  30  and the ambient air-heated coolant heat exchanger  66 . 
         [0035]    As shown in  FIG. 3A , during operation in the A/C mode, the valve  70  can direct coolant through the cooler core  30 , rather than the heat exchanger  66 , so that the coolant flowing in the low temperature loop  28  can absorb heat from the air flow passing through the cooler core  30 . The operation of the high temperature loop can be substantially similar to the version of the system  10  in  FIGS. 1A and 1B . It should be appreciated that the heat exchanger  66  could be replaced by any other type of heat exchanger that would utilize any other heat source, such as, for example, a liquid waste heat stream from a generator. 
         [0036]    As shown in  FIG. 3B , during operation in the HP mode, the valve  70  is used to direct the coolant through the heat exchanger  66 , rather than through the cooler core  30 , so that heat from the ambient air passing through the heat exchanger  66  is transferred to the coolant flowing in the low temperature loop  28 . 
         [0037]      FIGS. 4A and 4B  illustrate an alternate embodiment of a refrigeration system  10  according to the present invention. The refrigeration system shown in  FIGS. 4A and 4B  is similar in many ways to the illustrated embodiments of  FIGS. 1A-3B  described above. Accordingly, with the exception of mutually inconsistent features and elements between the embodiment of  FIGS. 4A and 4B  and the embodiments of  FIGS. 1A-3B , reference is hereby made to the description above accompanying the embodiments of  FIGS. 1A-3B  for a more complete description of the features and elements (and the alternatives to the features and elements) of the embodiment of  FIGS. 4A and 4B . 
         [0038]    As shown in  FIGS. 4A and 4B , this system  10  differs from that of  FIGS. 1A and 1B  in that the liquid-cooled gas cooler  14  and the air-to-refrigerant evaporator  24  have both been eliminated, the functions of the cooler and heater cores  30  and  36  are combined in a heater/cooler core  60  such as discussed in connection with  FIGS. 2A and 2B , and an air-heated coolant heat exchanger  66 , such as discussed in connection with  FIGS. 3A and 3B , has been plumbed into both the high temperature loop  19  and the low temperature loop  28  with a three-way valve  74  (or series of two-way valves) provided in the high temperature loop  19  and a three-way valve  78  provided in the low temperature loop  28  to control the coolant flow in both of the loops  19  and  20  through the heat exchangers  60  and  66 . 
         [0039]    As shown in  FIG. 4A , during operation in the A/C mode, the valve  78  directs the coolant in the low temperature loop  19  through the core  60 , rather than through the heat exchanger  66 , to remove heat from the cabin  32 , and the valve  74  directs the coolant from the high temperature loop  19  through the heat exchanger  66 , rather than the core  60 , to reject heat absorbed by the coolant from the gas cooler  18  to the ambient air flow through the heat exchanger  66 . 
         [0040]    As shown in  FIG. 4B , during operation in the HP mode, the coolant in the high temperature loop  19  is directed by the valve  74  through the heater/cooler core  60 , rather than through the heat exchanger  66 , while the valve  78  in the low temperature loop  28  directs coolant through the heat exchanger  66 , rather than the heater/cooler core  60 , so as to absorb heat from the ambient air flowing through the heat exchanger  68 . 
         [0041]    The embodiments described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated by one having ordinary skill in the art that various changes are possible.