Patent Publication Number: US-7900467-B2

Title: Combined receiver and heat exchanger for a secondary refrigerant

Description:
BACKGROUND 
     The present invention relates to a refrigeration system. More particularly, the present invention relates to a refrigeration system having multiple refrigeration circuits. 
     In some configurations, a liquid recirculation refrigeration system includes a primary refrigeration circuit that circulates a first refrigerant to remove heat from (i.e., cool) a second refrigerant circulating through a secondary refrigeration circuit. Typically, the secondary refrigeration circuit requires a net positive suction head in order for a pump to effectively circulate the second refrigerant. In such a system, a heat exchanger of the primary circuit is provided to cool the second refrigerant. The heat exchanger is typically located above a liquid holding tank or receiver of the secondary circuit to allow a gravity feed and facilitate 100% liquid (i.e., refrigerant) return. However, locating the heat exchanger above the receiver, and the receiver above the pump, creates an overall height which can be objectionable in some circumstances. In addition, the material costs for these types of refrigeration systems can also be expensive in comparison to a traditional vapor compression refrigeration system. 
     SUMMARY 
     In one embodiment, the invention provides a refrigeration system including a first circuit configured to circulate a first refrigerant. The first circuit includes an evaporator. The refrigeration system also includes a second circuit configured to circulate a second refrigerant. The second circuit includes a receiver associated with the evaporator such that the second refrigerant within the receiver is in a heat exchange relationship with the first refrigerant within the evaporator. 
     In another embodiment, the invention provides a method of exchanging heat between a first refrigerant and a second refrigerant. The method includes circulating the first refrigerant through a first circuit having an evaporator, circulating the second refrigerant through a second circuit having a receiver associated with the evaporator, and exchanging heat between the first refrigerant within the evaporator and the second refrigerant within the receiver. 
     In yet another embodiment, the invention provides a refrigeration system including a first circuit having a first evaporator and a second circuit having a receiver. The refrigeration system also includes a first refrigerant within the first evaporator being in a heat exchange relationship with a second refrigerant within the receiver. The refrigeration system further includes a third circuit having a second evaporator associated with the receiver such that a third refrigerant with the second evaporator is in a heat exchange relationship with the second refrigerant within the receiver. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of a refrigeration system according to one embodiment of the invention. 
         FIG. 2  is a schematic of an integral heat exchanger and receiver for use with the refrigeration system shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     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 are 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. 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. 
       FIG. 1  illustrates a refrigeration system  10  including a primary refrigeration circuit  14  and a secondary refrigeration circuit  18 . In the illustrated embodiment, the refrigerant system  10  is used in a commercial setting (e.g., a grocery store) to keep food product at a suitable refrigerated or freezing temperature. However, it should be readily apparent to one skilled in the art that the refrigerant system  10  may be adapted or configured for use in other smaller applications (e.g., personal refrigerators, air-conditioning systems, etc.), as well as larger industrial applications (e.g., oil refineries, chemical plants, metal refineries, etc.), where refrigeration is desired or required. 
     The primary circuit  14  operates as a reverse-Rankine vapor compression refrigeration cycle and includes a compressor system  22 , a primary condenser  26 , a primary refrigerant receiver  30 , an expansion device  34 , and a primary evaporator  38 . The primary circuit  14  circulates a refrigerant (i.e., a first refrigerant) to remove heat from a secondary fluid. In the illustrated embodiment, the primary circuit  14  is associated with the secondary circuit  18  such that the refrigerant in the primary circuit  14  removes heat from a refrigerant (i.e., a second refrigerant) in the secondary circuit  18 . The first refrigerant may be, for example, refrigerant 404a. 
     The compressor system  22  may include a single compressor or multiple compressors arranged in parallel or in series to compress a vaporous refrigerant. The compressor(s) may be, for example, a centrifugal compressor, a rotary screw compressor, a reciprocating compressor, or the like. In the illustrated embodiment, the compressor system  22  compresses the refrigerant and delivers the compressed refrigerant to the primary condenser  26 . 
     The primary condenser  26  is positioned downstream of the compressor system  22  to receive the vaporous, compressed refrigerant from the compressor system  22 . The condenser  26  may be, for example, an air-cooled condenser or a water-cooled condenser. In the illustrated embodiment, the condenser  26  is remotely located (e.g., on a roof of a building) from the other components of the refrigeration system  10 . The condenser  26  removes heat from the vaporous refrigerant to change the vaporous refrigerant into a liquid refrigerant and delivers the liquid refrigerant to the primary receiver  30 . 
     The primary receiver  30  is positioned downstream of the condenser  26  to receive the liquid refrigerant from the condenser  26 . The receiver  30  is configured to store or retain a supply of liquid refrigerant. As shown in  FIG. 1 , a portion of the refrigerant within the receiver  30  may also be vaporous. The refrigerant enters the receiver  30  through a top of the receiver  30  and exits the receiver  30  through a bottom of the receiver  30  to ensure only the liquid refrigerant leaves the receiver  30 . In some embodiments, such as the illustrated embodiment, the receiver  30  can include a float sensor  42  to detect and monitor the liquid refrigerant level within the receiver  30 . 
     The expansion device  34  is positioned downstream of the receiver  30  to receive the liquid refrigerant from the receiver  30 . The expansion device  34  may be any suitable type of throttle valve that is operable to abruptly decrease the pressure of the liquid refrigerant. As the liquid refrigerant decreases in pressure, all or a portion of the refrigerant vaporizes and, thereby, decreases in temperature. The cool refrigerant exiting the expansion device  34  is directed toward the primary evaporator  38 . 
     The primary evaporator  38  is positioned downstream of the expansion device  34  to receive the cool refrigerant. The evaporator  38  includes an evaporator coil  46  configured to facilitate heat exchange between the first refrigerant and the second refrigerant. In the illustrated embodiment, the evaporator coil  46  is positioned within a secondary receiver  48  of the secondary circuit  18  such that the first refrigerant removes heat from the second refrigerant. The first refrigerant warms in the evaporator  38  and is circulated back toward the compressor system  22 . 
     The secondary circuit  18  includes the secondary receiver  48 , a pump  50 , and display cases  54 . The secondary circuit  18  circulates the second refrigerant to remove heat from the surrounding environment. In the illustrated embodiment, the second refrigerant removes heat from air within the display cases  54 ; however, in other applications, the second refrigerant may remove heat from other fluids and/or structures. The second refrigerant may be, for example, carbon dioxide. 
     The secondary receiver  48  stores or retains a supply of liquid refrigerant  58  circulating through the secondary circuit  18 . As shown in  FIG. 1 , a portion of the refrigerant may also be vaporous. In the illustrated embodiment, the receiver  48  is combined with the primary evaporator  38  into a single, integral unit or structure by passing the primary evaporator coil  46  through a tank of the secondary receiver  48 . In such a configuration, the secondary receiver  48  is also considered a heat exchanger for the secondary circuit  18 , thereby eliminating the need, in some embodiments, for a separate heat exchanger in addition to a secondary receiver. 
     In the embodiment shown in  FIG. 1 , the evaporator coils  46  are positioned above the liquid second refrigerant  58 . In such an arrangement, vaporous second refrigerant  62  within the receiver  48  is cooled to reach a liquid state. In the embodiment shown in  FIG. 2 , the evaporator coils  46  are positioned in contact with the liquid second refrigerant  58 . In such an arrangement, the liquid second refrigerant  58  is cooled to likewise cool and liquefy the adjacent vaporous refrigerant  62 . In other embodiments, the evaporator coil  46  may be positioned partially above and partially in contact with the liquid second refrigerant  58 , or the evaporator coil  46  may alternate between being above and being in contact with the liquid refrigerant  58 . 
     The pump  50  is positioned downstream of the receiver  48  to draw the liquid refrigerant  58  from the receiver  48 . The pump  50  may be any positive displacement pump, centrifugal pump, or the like suitable to move and circulate a liquid. In the illustrated embodiment, the pump  50  draws the cool, liquid refrigerant  58  from the receiver  48  and directs the refrigerant toward the display cases  54 . 
     The display cases  54 , or refrigerated merchandisers, are positioned downstream from the pump  50  to receive the cool refrigerant. The display cases  54  include heat exchangers to facilitate heat exchange between the refrigerant and the surrounding environment (e.g., the air within the display cases  54 ). Removing heat from the surrounding environment allows the display cases  54  to store food product at a reduced temperature suitable for refrigerating or freezing the food product. In the illustrated embodiment, the secondary circuit  18  includes three display cases  54 . However, it should be readily apparent to one skilled in the art that the secondary circuit  18  may include fewer or more display cases  54  depending on the operating capacity of the refrigeration system  10 . 
     In some embodiments, such as the illustrated embodiment, the refrigeration system  10  includes an auxiliary refrigeration circuit  66 . The auxiliary circuit  66  includes an auxiliary compressor  70 , an auxiliary condenser  74 , an auxiliary receiver  78 , an auxiliary expansion device  82 , and an auxiliary evaporator  84 . The components of the auxiliary circuit  66  function and are configured in a similar manner to the corresponding components in the primary circuit  14 . The auxiliary circuit  66  circulates a refrigerant (i.e., a third refrigerant) to provide supplemental or backup cooling to the second refrigerant. For example, in some embodiments, the auxiliary circuit  66  may be connected to a generator or power source to run during a failure of or a loss of power to the primary circuit  14 . The third refrigerant may be, for example, refrigerant 404a. 
     Similar to the primary evaporator  38 , the auxiliary evaporator  84  includes an evaporator coil  86  positioned within the secondary receiver  48 . In the embodiment shown in  FIG. 1 , the auxiliary evaporator coil  86  is positioned above the liquid second refrigerant  58  to exchange heat with the vaporous second refrigerant  62 . In the embodiment shown in  FIG. 2 , the auxiliary evaporator coil  86  is positioned in contact with the liquid second refrigerant  58  to exchange heat with the liquid second refrigerant  58 . In the illustrated embodiments, the primary evaporator coil  46  and the auxiliary evaporator coil  86  are either both positioned above the liquid second refrigerant  58  or both positioned in contact with the liquid second refrigerant  58 . In other embodiments, the primary evaporator coil  46  and the auxiliary evaporator coil  86  may be arranged such that one coil is positioned above the liquid second refrigerant  58  and the other coil is positioned below the liquid second refrigerant  58 . 
     In operation, the vaporous first refrigerant is compressed in the compressor system  22 , condensed to a liquid at the primary condenser  26 , and temporarily stored within the primary receiver  30 . The liquid refrigerant is drawn from the primary receiver  30  through the expansion device  34  to rapidly reduce in pressure and cool, and passed through the evaporator coil  46  of the primary evaporator  38 . As the first refrigerant passes through the evaporator  38 , the first refrigerant removes heat from the second refrigerant stored in the receiver  48 . The first refrigerant is then circulated back toward the compressor system  22 . 
     The cool, liquid second refrigerant  58  is drawn from the receiver  48  by the pump  50  and directed toward the display cases  54 . In the display cases  54 , the second refrigerant removes heat from the surrounding environment, reducing the temperature to a suitable level for food storage. As such, the second refrigerant warms and partially or fully vaporizes in the display cases  54 . The warm refrigerant is then directed back toward the receiver  48  for cooling and temporary storage. 
     In arrangements where the refrigeration system  10  includes the auxiliary circuit  66 , the auxiliary circuit  66  is powered or turned on in response to the primary circuit  14  failing or losing power. In such a scenario, vaporous third refrigerant is compressed in the auxiliary compressor  70 , condensed to a liquid in the auxiliary condenser  74 , and temporarily stored within the auxiliary receiver  78 . The liquid third refrigerant is drawn from the auxiliary receiver  78  through the auxiliary expansion device  82  to rapidly reduce in pressure and cool, and passed through the auxiliary evaporator coil  86  of the evaporator  84 . As the third refrigerant passes through the evaporator  84 , the third refrigerant removes heat from the second refrigerant stored in the receiver  48 . Additionally or alternatively, the third refrigerant may remove heat from the first refrigerant passing through the primary evaporator coil  46 . The third refrigerant is then circulated back toward the auxiliary compressor  70 . 
     The refrigeration system  10  described above simplifies construction by reducing the overall number of parts or components required and reducing the number of braze joints required. As such, the labor time required to assemble the refrigeration system  10  is likewise reduced. In addition, the refrigeration system  10  decreases the refrigerant charge or volume required to be circulated through each refrigeration circuit. 
     Various features and advantages of the invention are set forth in the following claims.