Abstract:
A refrigeration system including a compressor operable to discharge compressed refrigerant. A first heat exchanger is operable to cool the compressed refrigerant. The first heat exchanger includes a first inlet, an outlet, and a second inlet disposed between the first inlet and the outlet. A second heat exchanger is disposed adjacent a cool space. A valve is movable between a first position to direct the compressed refrigerant to the first inlet and then to the second heat exchanger to cool the second heat exchanger and a second position to direct the compressed refrigerant to the second heat exchanger and then to the second inlet to heat the second heat exchanger.

Description:
RELATED APPLICATION DATA  
       [0001]     This application claims benefit under 35 U.S.C. Section 119(e) of U.S. Provisional Application No. 60/529,301 filed Dec. 12, 2003.  
       BACKGROUND  
       [0002]     The present invention relates generally to a refrigeration system. More particularly, the present invention relates to a refrigeration system that includes a defrost cycle.  
         [0003]     Refrigeration systems cool a space by supplying cold refrigerant to an evaporator. Water vapor in the space being cooled sometimes condenses onto the outer surface of the evaporator and forms layers of ice. These layers of ice reduce the efficiency of the evaporator and make it difficult to maintain the desired temperature within the space.  
       SUMMARY  
       [0004]     In one embodiment, the invention provides a refrigeration system including a compressor operable to discharge compressed refrigerant. A first heat exchanger is operable to cool the compressed refrigerant. The first heat exchanger includes a first inlet, an outlet, and a second inlet disposed between the first inlet and the outlet. A second heat exchanger is disposed adjacent a cool space. A valve is movable between a first position to direct the compressed refrigerant to the first inlet and then to the second heat exchanger to cool the second heat exchanger and a second position to direct the compressed refrigerant to the second heat exchanger and then to the second inlet to heat the second heat exchanger.  
         [0005]     In another embodiment, the invention provides a refrigeration system including a plurality of compressors. Each compressor is operable to discharge compressed refrigerant. A first heat exchanger is operable to cool the compressed refrigerant. The first heat exchanger includes a first inlet, an outlet, and a second inlet between the first inlet and the outlet. The system also includes a plurality of evaporators and a receiver in fluid communication with the first heat exchanger and in selective fluid communication with each of the plurality of evaporators. The system further includes a hot gas header and a valve that is movable between a first position to direct the compressed refrigerant to the first inlet and a second position to direct the compressed refrigerant to the hot gas header. A plurality of defrost valves are movable between a first position to place the receiver in fluid communication with one of the plurality of evaporators to cool the evaporator and a second position to place the hot gas header in fluid communication with the one of the plurality of evaporators to heat the evaporator. The evaporator discharges refrigerant to the second inlet when the defrost valve is in the second position.  
         [0006]     In yet another embodiment, the invention provides a method of operating a refrigeration system including operating a compressor to deliver compressed refrigerant. The method also includes directing the compressed refrigerant to a first inlet of a first heat exchanger and condensing the compressed refrigerant within the first heat exchanger. The method further includes expanding a portion of the compressed refrigerant and passing the portion of the expanded compressed refrigerant through a second heat exchanger to cool the heat exchanger. The method also includes manipulating a valve to redirect the compressed refrigerant to the second heat exchanger to heat the second heat exchanger and directing the compressed refrigerant to a second inlet of the first heat exchanger. The second inlet is disposed downstream of the first inlet.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The detailed description particularly refers to the accompanying figures in which:  
         [0008]      FIG. 1  is a circuit diagram for a refrigeration system illustrating the flow paths in a refrigeration mode; and  
         [0009]      FIG. 2  is a circuit diagram for a refrigeration system illustrating the flow paths in a defrost mode. 
     
    
     DETAILED DESCRIPTION  
       [0010]     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 figures. 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. 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.  
         [0011]     The basic configuration of a refrigeration system  10  generally includes the conventional components of a vapor-compression or refrigeration cycle (i.e., compressor(s)  15 , condenser(s)  20 , evaporator(s)  25 , a receiver(s)  30 , and expansion valve(s)  35 ). As one of ordinary skill will realize, refrigeration systems may incorporate multiple compressors  15 , evaporators  25 , and/or condensers  20  in parallel or in series to accomplish the goals of the particular system. As such, the invention should not be limited to systems that include components arranged or numbered as illustrated herein. It should be understood that the invention hereinafter described is not dependent upon the number or size of such components.  
         [0012]     Before describing the figures in detail, it should also be noted that the figures have been simplified for the purpose of illustration. Components such as check valves, drain and fill valves, pressure taps, flow meters, sensors, parallel piping, as well as other types of components have been omitted for clarity.  
         [0013]      FIGS. 1 and 2  show the basic layout of one arrangement of a refrigeration system  10  incorporating a reverse flow defrost.  FIG. 1  shows the flow through a portion of the system when operating in a refrigeration mode and  FIG. 2  illustrates the same portion of the system operating in a defrost mode.  
         [0014]     With reference to  FIG. 1 , the flow in refrigeration mode begins when one or more compressors  15  draw superheated refrigerant vapor (e.g., R12, ammonia, CFCs, HCFCs, HFCs, etc.) from a suction header  40 . The term “superheated” as used herein includes any refrigerant that contains vapor at or above the saturation temperature for the refrigerant at the particular pressure. The compressor  15  compresses the vapor to produce a flow of superheated, high-pressure refrigerant. The vapor passes through a defrost differential valve  45  that is maintained in an open position when operating in refrigeration mode. From the defrost differential valve  45 , the flow passes through the condenser  20 , entering through a condenser inlet  50  and exiting through a condenser outlet  55 . In the condenser  20 , the flow cools and condenses to produce a high-pressure flow of cool liquid refrigerant that is directed into the receiver  30 . From the receiver  30 , liquid refrigerant is directed to a liquid header  60  that is positioned to supply refrigerant to one, or more than one, of a plurality of cooling paths  65 . It should be noted that the term “header” should be read broadly to include structures as simple as a pipe or manifold that are able to deliver or receive a fluid to/from a plurality of flow paths.  
         [0015]     For the sake of simplicity, only one complete cooling path  65  is illustrated in  FIGS. 1 and 2 . The remaining cooling paths  65  are similar to the illustrated path  65 . Each cooling path  65  includes an expansion valve  35  and the evaporator  25 . The expansion valve  35  expands the flow of vapor to reduce the temperature and pressure of the flow prior to its entry into the evaporator  25 . After the flow passes through the evaporator  25 , it is returned to the suction header  40  and the cycle repeats.  
         [0016]     Each evaporator  25  is positioned to cool a space. Alternatively, multiple evaporators may be used to cool a single space if necessary. The cold refrigerant passes through the evaporator  25  and is heated by the environment in which the evaporator  25  is positioned. Typically, air or another fluid moves across the evaporator  25  and is cooled by the refrigerant as the refrigerant is heated. In some constructions, fans (not shown) are used to move the air across the evaporator  25 . The refrigerant is usually heated such that it leaves the evaporator  25  as superheated refrigerant, while the air is cooled and returned to the cool space. Depending on the environment in which the evaporator  25  is positioned, the cold temperature of the evaporator  25  may cause some of the water vapor in the air to condense and freeze onto the evaporator  25 . The freezing water forms layers of ice that reduce the efficiency of the heat exchange between the environment being cooled and the refrigerant within the evaporator  25 . To improve the evaporator efficiency, the layers of ice generally need to be removed.  
         [0017]     To remove the ice, the refrigeration system  10  periodically transitions into a defrost mode. The flows within the refrigeration system  10  when in the defrost mode are illustrated in  FIG. 2 . A portion of the hot compressed gas exiting the compressors is directed to a hot gas header  70 . The defrost differential valve  45  at least partially controls the quantity of hot compressed gas that is directed to the hot gas header  70 . For example, when additional hot gas is required in the hot gas header  70 , the defrost differential valve is closed slightly or closed completely to reduce the size of the flow path to the condenser  20 . The reduced flow path effectively redirects an increased quantity of hot gas to the hot gas header  70 . As one of ordinary skill will realize, other constructions could position the defrost differential valve  45  differently. For example, one construction places the defrost differential valve  45  in the flow path to the hot gas header  70 . In this position, opening the valve increases the flow to the hot gas header  70 .  
         [0018]     The hot gas header  70  is selectively connected with each of the cooling paths  65 . A defrost valve  72  is positioned within each cooling path  65  to inhibit the flow of refrigerant to the hot gas header  70  when in the cooling mode. In the illustrated construction, a solenoid-operated valve is used as the defrost valve  72  in each cooling path  65 . However, other constructions may use other types of valves or other actuation means (e.g., manual) for the defrost valves  72 . To transition one of the cooling paths  65  from the refrigeration mode to the defrost mode, the system may close the defrost differential valve  45  to direct additional hot compressed refrigerant to the hot gas header  70  if necessary. The defrost valve  72  corresponding to the cooling path  65  to be heated is opened to direct a flow of hot compressed refrigerant to the evaporator. In addition, an isolation valve  74  is closed to inhibit flow of hot gas from the hot gas header  70  directly to the suction header  40 .  
         [0019]     As with the refrigeration mode, the defrost cycle begins when the compressor  15  draws superheated refrigerant vapor from the suction header  40 . However, with the defrost differential valve  45  reducing or completely preventing flow to the condenser  20 , part or all of the flow is redirected to the hot gas header  70 . The hot gas header  70  directs the flow of superheated, high-pressure refrigerant vapor through the evaporator  25  in the opposite direction it would flow if in the refrigeration mode. The superheated high-pressure vapor heats the evaporator  25  and melts the accumulated ice. After passing through the evaporator  25 , the refrigerant collects in a hot gas return header  75 .  
         [0020]     The hot gas return header  75  directs the refrigerant to the condenser  20 . The flow enters the condenser  20  at a defrost inlet  80  located downstream of the condenser inlet  50 . After passing through the condenser  20 , the now cooled liquid flows into the receiver tank  30 . In an alternative construction, a separate heat exchanger (not shown), having the ability to remove heat (heat removed via air/water or other means) and condense the refrigerant from a vapor to a liquid, receives the flow of refrigerant vapor from the hot gas return header  75  and directs the condensed refrigerant to a reentry point at or after the condenser outlet  55 .  
         [0021]     As one of ordinary skill will realize, operation in defrost mode directs vapor from the suction header  40  to the hot gas header  70 , through the evaporator  25  being defrosted, through the condenser  20 , and finally to the receiver tank  30 . However, if none of the evaporators  25  in the system are operating in refrigeration mode, none of the refrigerant will be drawn from the receiver tank  30 . As such, no refrigerant will flow to the suction header  40 , and eventually no refrigerant will be available to the compressors  15 . As such, at least one cooling path  65  is generally maintained in the refrigeration mode during a defrost cycle to assure that refrigerant is always available to the compressors  15 . With at least one evaporator  25  operating in refrigeration mode, refrigerant is drawn from the receiver tank  30  and returned to the suction header  40 , thus completing the defrost cycle.  
         [0022]     For the sake of clarity, only one evaporator  25  is illustrated herein. However, it should be understood that multiple evaporators  25  are typically employed in systems of this type. In fact, to operate in the defrost mode for a long duration, one evaporator  25  should be operated in the refrigeration mode as just described to prevent the depletion of the refrigerant. Typically, several evaporators  25  within the system operate in refrigeration mode with the remaining evaporators  25  operating in defrost mode. Of course, all of the evaporators  25  can be operated in refrigeration mode at the same time if desired.  
         [0023]     Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of the invention. Thus, the invention provides, among other things, a new and useful system and method of cooling multiple spaces and defrosting the individual evaporators. The constructions of the system and the methods of operation of the system 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 invention. Various features and advantages of the invention are set forth in the following claims.