Abstract:
A frost management system for use in a refrigeration cabinet having a base and sidewalls defining an opening to provide access into the refrigeration cabinet. A heating member is positioned proximate to the opening exterior of the sidewalls for heating of frost accumulated on the sidewalls. The first heating member may be activated for a time to cause accumulated frost to be melted, thereby permitting the resulting liquid to flow down the sidewalls toward the base and be refrozen. For full defrost operation of the device, there may be a second heating member positioned proximate to the base of the refrigeration cabinet. The second heating member may be activated to heat a portion of the ice to enable its removal. There is also disclosed a method for managing frost in a refrigeration cabinet.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to refrigerated cabinets such as chest freezers and, in particular, to frost management systems for such devices. 
       BACKGROUND OF THE INVENTION 
       [0002]    In refrigeration cabinets such as cold-wall freezers, a principal concern is the accumulation of frost on the inside liner walls. The formation of frost within the freezer may cause refrigeration system degradation, loss of cooling efficiency, cleanability and aesthetic issues. Freezer accessories such as baskets may be “locked” into position by frost accumulation. Freezers with frost accumulation may provide the impression that the last cleaning was prior to the frost accumulation. Conventional defrost systems may create a dry humidity environment which may adversely effect food products, such as ice cream. 
         [0003]    A principal concern with frost is that it may form an insulating cushion between the cooling evaporator tubing coils and an interior portion of the cabinet. This insulating cushion reduces heat transfer efficiency in the evaporator tubing coils through the inner walls of the cabinet and impedes proper air circulation of refrigerated air above the freezer contents, which frequently is food. 
         [0004]    The cabinets of cold-wall type freezers may for example be of the vertical closed type construction with insulated hinged solid or glass doors. The cabinets may also for example be of the horizontal open or closed type with solid insulated hinged, glass hinged or sliding glass lids. In vertical type freezers with hinged doors the warm ambient air is drawn into the freezer cabinet with every door opening. Higher density cooler air escapes with each door opening by dropping down to ground level. As the cool air flows down and out of the freezer, warmer moist air is drawn into the cabinet to make up the difference in air pressure within the freezer. In horizontal chest freezers the warmer low pressure ambient air is drawn into the freezer cabinet with each lid opening due to pressure differences between the cold low pressure air inside the freezer and the warmer higher pressure ambient air surrounding the freezer cabinet. The moisture from the ambient air drawn into the cabinet will condense along the inside liner walls in the form of frost. The frost accumulates preferentially along the liner walls in the open volume area between the upper level of the freezer contents and top of the freezer chest liner. 
         [0005]    Conventional freezer defrosting requires a user to remove frozen food or other products contained within the freezer cabinet, followed by turning off the compressor. Frost is removed by melting with placement of a fan directed into the cabinet, spraying warm water on the cabinet walls, or simply letting the cabinet sit for a number of hours with the lid open to the ambient air. 
         [0006]    Another defrosting method is to scrape frost off the cabinet walls without increasing the ambient temperature. A difficulty with this method is that it must be frequently done, and even so scraping may be physically demanding or cumbersome for the user. There is also a risk of damaging the freezer liner. 
         [0007]    Yet another defrosting method is to use hot gas installed within the cabinet walls. In a defrost cycle of this method, there is a sudden release of hot high-pressure refrigerant gas into the extremely cold evaporator tubing for melting of the frost. Hot gas defrosting may require integration with refrigeration circuits, thus failure of one circuit may lead to mass failure of the apparatus. Hot gas defrosting may be costly to manufacture and install. There may be compressor failure if the defrost cycle is too long or if the hot gas solenoid valve is left on due to malfunction thereby resulting in compressor winding overheating and eventual burn out. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides to a frost management system for use in a refrigerated cabinet such as a cold-wall freezer which addresses the shortcomings of prior devices. 
         [0009]    In a first aspect, the invention provides a frost management system for use in a refrigeration cabinet having a base and sidewalls defining an opening to provide access into the refrigeration cabinet, the sidewalls being conductive for heat transfer through the sidewalls. There is a first heating member positioned proximate to the opening exterior of the sidewalls which may be activated to melt frost accumulated on an interior of the sidewalls. A first activator is provided for the first heating member, the first heating member being activated for a time to cause the frost to be melted, thereby permitting the resulting liquid to flow down the sidewalls toward the base and be refrozen. In another aspect, the invention provides a second heating member positioned proximate to the base of the refrigeration cabinet and exterior of the sidewalls for heating of ice accumulated on the sidewalls. There is provided a second activator for the second heating member. The second heating member is activated for a time to melt a portion of the ice adjacent the sidewalls to enable its removal. 
         [0010]    In yet another aspect, the invention provides a method for managing frost in a refrigeration cabinet having a base and sidewalls defining an opening to provide access into the refrigeration cabinet, including the step of heating a region on the sidewalls proximate to the opening for melting frost accumulated on an interior of the sidewalls into a liquid, thereby permitting the resulting liquid to flow down the sidewalls toward the base and be refrozen. In another aspect, a full defrost may be initiated by heating a lower portion and/or an upper portion of the sidewalls for melting a surface of the ice, and mechanically removing the ice from the refrigeration cabinet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Embodiments will now be described by way of example with reference to the accompanying drawings, through which like reference numerals are used to indicate similar features. 
           [0012]      FIG. 1  shows a perspective sectional view of a horizontal cold-wall type freezer in accordance with an embodiment of the present invention; 
           [0013]      FIG. 2  shows a perspective partial sectional view of a cabinet wall of  FIG. 1 ; 
           [0014]      FIG. 3  shows a perspective view of a foil heater of the freezer of  FIG. 1  and a block diagram of an example of controller circuitry; 
           [0015]      FIG. 4  shows a sectional side view of the freezer of  FIG. 1 ; 
           [0016]      FIG. 5  shows the same view as  FIG. 4  in a first mode of operation, 
           [0017]      FIG. 6  shows the same view as  FIG. 4  in a second or full defrost mode of operation; and 
           [0018]      FIG. 7  shows a perspective sectional view of a vertical cold-wall type freezer in accordance with another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    For clarity, “frost” may mean any deposition of vapors in saturated air, including water vapors, and may include ice-like or other crystalline formations. Usually, frost includes air or gas-filled interstices. A “refrigeration device” may mean any appliance that uses heat exchanging for cooling of an interior of such a device. Examples are cold-wall type freezers, which may for example be vertical or horizontal freezers. 
         [0020]    Reference is now made to  FIGS. 1 and 2 .  FIG. 1  shows a perspective view of a horizontal freezer  10  in accordance with an aspect of the present invention with portions cut away to reveal interior detail.  FIG. 2  shows a perspective partially sectional view of a cabinet wall  22  of the freezer of  FIG. 1 . 
         [0021]      FIG. 1  shows the freezer  10  having four cabinet walls  22  and a base  14 . In the example shown, there are four inner walls  12 , a spiral coil of evaporator tubing  16  outwardly from the out sides of inner walls  12 , a heater foil  18  adhered on the evaporator tubing  16  and inner wall  12 , a thermal insulation  28  disposed on an outer side of the heater foil  18 , a condenser tubing  30  on an outer side of the thermal insulation  28 , and an outer wall  32  externally of the condenser tubing  30 . The four inner walls  12  may be upstanding to form a rectangular box, and thereby define an interior  20  of the freezer  10  and an opening  21  for access to the interior  20 . The inner walls  12  may be formed of any suitable heat conductive material, for example metallic or plastic material. Accordingly, the inner walls  12  may be used to conductively exchange heat for cooling of the interior  20 . The opening  21  may be open to the ambient or a door may be constructed thereon as a lid ( 60  as shown on  FIGS. 4 to 6 ) on top of the cabinet walls  22 . 
         [0022]    The evaporator tubing  16  is connected to a compressor ( 96  in  FIG. 3 ), as is known in the art. The evaporator tubing  16  acts as a cooling member, so that the interior  20  of the freezer  10  becomes cooled by heat transfer through the inner walls  12 . As will be apparent to the skilled person, the evaporator tubing  16  may be a serpentine coil or a spiral coil connected to an exterior of at least one of the inner walls  12 . 
         [0023]    In  FIG. 1 , for illustrative purposes, heater foil  18  is shown cutaway so that the evaporator tubing  16  may be seen. A heating of the heater foil  18  will melt frost accumulation on the inner walls  12  as will be described in greater detail below. 
         [0024]    Thermal insulation  28  is exterior of the heater foil  18  and provides insulation between the evaporator tubing  16  and condenser tubing  30 . The thermal insulation  28  may be foam injected between the inner walls  12  and the outer walls  32 . In the example shown, the condenser tubing  30  is spirally attached to an inside surface of the outer wall  32 . At an end of the condenser tubing  30  is an expansion valve  97  ( FIG. 3 ), as is known in the art. Four of the outer walls  32  define an exterior of the freezer  10 . The outer walls  32  may be formed of metal or other conductive material and may be utilized as a heat transfer surface for the condenser tubing  30 . Accordingly, heat from the condenser tubing  30  is released to an exterior of the freezer via the outer walls  32 , as is known in the art. Alternatively, condenser tubing  30  may be a serpentine coil rather than a spiral coil for heat exchanging to an exterior of the freezer  10 . 
         [0025]    Reference is now made to  FIG. 2 , which shows a cabinet wall  22  of the freezer  10 . It shows an upper portion  24  and a lower portion  26  of the cabinet wall  22 . 
         [0026]    The components of the heater foil  18  are shown in  FIG. 3 . In the example shown, heater foil  18  has two heat conductive sheets  44 ,  46  having heater wires  33 ,  34  disposed therebetween. Each conductive sheet  44 ,  46  may be formed of conductive, for example metal, foil and may have a peel off adhesive on one side and a non-adhesive side. In one embodiment, heater wires  33 ,  34  are adhered to the adhesive side of conductive sheet  44 . The other conductive sheet  46  then has its non-adhesive side adhered to the adhesive side of conductive sheet  44 . The adhesive side of conductive sheet  46  may then be adhered to an exterior of the inner walls  12 , as shown in  FIG. 2 . Heater wire  33  defines an upper region in the heater foil  18  corresponding to upper portion  24  of the cabinet wall  22  as shown in  FIG. 2 . Similarly, heater wire  34  defines a lower region in the heater foil  18  corresponding to lower portion  26  of the cabinet wall  22  as shown in  FIG. 2 . The heater wires  33 ,  34  ( FIG. 3 ) are shown in a serpentine configuration for heating of the upper and/or lower portions of heater foil  18 . Lead wires  36 ,  38  extend from heater wire  33  and may be connected to a controller  98 . When a current is applied to lead wires  36 ,  38 , heat is generated in heater wire  33 . Accordingly, activation or energizing of either heating wire  33 ,  34  will heat a corresponding region in the conductive sheets  44 ,  46  by way of heat conduction, and will thereby heat the upper portion  24  and lower portion  26  of the cabinet wall  22 . Lead wires  40 ,  42  extend from heater wire  33  and may be connected to the controller  98 . Lead wires  40 ,  42  operate in a similar manner to lead wires  36 ,  38 . The controller  98  may also be used for setting appropriate heating times as will be described further. 
         [0027]      FIGS. 4 to 6  show the operation of the freezer  10 . As shown, the upper heater wire  33  is located to heat the upper portion  24  of the cabinet wall  22 , and lower heater wire  34  is located to heat the lower portion  26  of the cabinet wall  22 . Frost  50  is shown in  FIG. 4  as formed on the upper portion  24  of the cabinet wall  22 .  FIG. 5  shows a first mode of operation, wherein the frost  50  is melted and reformed as ice  52  on the lower portion  26  of the cabinet wall  22 .  FIG. 6  shows a second mode or full defrost mode of operation, wherein a portion of the ice  52  and any additional frost is melted for removal by a user. The operation is controlled by the controller  98  ( FIG. 3 ) for automatically effecting a predetermined cycle of operation of the compressor  96  and the heater wires  33 ,  34  at predetermined, preferably regular, intervals. 
         [0028]    The first mode of operation is preferably performed on the freezer  10  at regular intervals, for example, a 12-hour compressor  96  run time interval. In the first mode of operation, a first step in the cycle is that the compressor  96  may be temporarily turned off by the controller  98 . The next step is the upper heater wire  33  is then energized by the controller  98  to melt the frost  50 , the melted water being reformed as ice  52  on the lower portion  26  of the cabinet wall  22 . Since the compressor  96  is only recently turned off, the lower portion  26  remains sufficiently cold for refreezing of the melted frost. Frost  50  is undesirable as it may act as an insulator that reduces heat transfer efficiency in the evaporator tubing  16  through the inner walls  12  of the cabinet and impedes proper air circulation. On the other hand, ice  52  has a higher density than frost  50 , and is substantially free from gas or air filled interstices. Accordingly, ice  52  has less insulating properties than frost  50 , and heat transfer between the evaporator tubing  16  and the interior  20  of the freezer  10  may be improved when frost  50  is melted into ice  52 . The upper heater wire  33  is thus activated by the controller  98  for a time to melt the frost  50 . As can be appreciated, the upper heater wire  33  is preferably heated for a selected time, dependent on the wattage, sufficient to melt the frost  50 , but not so as to substantially increase the temperature of the interior  20  of the freezer  10 . The last step in the cycle is that the controller  98  de-energizes the upper heater wire  33  and turns the compressor  96  back on for normal operation of the freezer  10 . After the next predetermined interval, for example after 12 hours of compressor  96  run time, the above described cycle is repeated, by melting the frost  50  and refreezing the melted water into ice  52 . The desired time of operation and the wattage of the heater wires  33 ,  34  may vary depending on the freezer  10  and may be determined by experimentation. 
         [0029]    The following configuration may be used in one preferred form of the first mode of operation. The upper heater wire  33  and lower heater wire  34  may for example be rated at 2.5 watts per-linear foot. This value is in compliance with the Underwriters Laboratories Inc.™ Commercial Freezers standard 471, which requires that resistance-type heater Wires employed to prevent condensation are considered in compliance if the insulation is rated 176° F. (80° C.) or higher, the input is less than 2.5 watts per foot (8.3 W/m), and adjacent heater wires are maintained not less the ¾ inch (19.1 mm) apart. Each heater wire  33 ,  34  will generate approximately 150 watts of heat. It is suitable for the inner walls  12  to reach a maximum of about 50° F. (10° C.). This configuration has been found to be suitable for melting of the frost  50 , without significantly increasing the temperature of the interior  20  of the freezer  10 . The thermal mass of the food product may also assist in compensating against the slight increase in temperature within the interior  20  of the freezer  10 . 
         [0030]    In another embodiment, the ice  52  acts as a “holdover cooling” feature, as best illustrated in  FIG. 5 . In the interior  20  of the freezer  10 , the ice  52  may be frozen to temperatures of around −25° F. (−32° C.) and lower. When the compressor  96  is turned off (either for the first mode of operation or other reasons, such as blackout or circuit malfunction), the ice  52  assists in maintaining the low temperature of the interior  20  of the freezer  10 . 
         [0031]    The second mode or full defrost mode of operation is preferably performed on the freezer  10  when necessary, such as once every few months. A manual or automatic timer may be used to perform the cycle of operation constituting the second mode. In a first step of the cycle, the compressor  96  may be temporarily turned off by the controller  98 . As shown in  FIG. 6 , the lower heater wire  34  is then energized by the controller  98  to melt a portion of the ice  52 . The ice  52  may then be removed by a user by gently prying the ice  52  from the inner walls  12  using a plastic object such as a spatula (not shown). The ice  52  may also fall to the base  14  of the freezer  10  for removal by a user, as shown in  FIG. 6 . The controller  98  then de-energizes the upper heater wire  33  and turns the compressor  96  back on for normal operation of the freezer  10 . 
         [0032]    In another embodiment, as best illustrated in  FIG. 6 , instead of solely the bottom heater wire  34  being energized by the controller  98 , both the top heater wire  33  and bottom heater wire  34  are activated to melt a portion of any ice  52  or frost. This facilitates removal of any ice  52  or frost accumulated anywhere on the inner walls  12 , by gently prying or removing by a user. 
         [0033]      FIG. 7  shows a perspective sectional view of a vertical cold-wall type freezer  70  in accordance with another embodiment of the present invention. The freezer  70  has three side cabinet walls  82 , an upper cabinet wall  83 , and a base  74 . The side cabinet walls  82 , upper cabinet wall  83 , and base  74  form a rectangular box, and thereby define an interior  84  of the freezer  10  and an opening  81  for access to the interior  84 . In the example shown, there are three inner side walls  72 , a serpentine coil of evaporator tubing  76 , a heater foil  78  adhered thereon, a thermal insulation  88 , a condenser tubing  80 , and an outer wall  92 . There is also a shelf  90  for support of products in the freezer  70 . The opening  81  usually has a door (not shown) constructed thereon. 
         [0034]    The inner side walls  72  may be used to conductively exchange heat for cooling of the interior  84 . The evaporator tubing  76  surrounds an exterior of the inner side walls  72  for cooling of the interior  84  of the freezer  70 . The evaporator tubing  76  is connected to a compressor (e.g.,  96  in  FIG. 3 ), as is known in the art. The evaporator tubing  76  acts as a cooling member, so that the interior  84  of the freezer  70  becomes cooled by heat transfer through the inner side walls  72 . 
         [0035]    Heater foil  78  is adhered exterior to the three inner side walls  72  and also covers a region of the inner side walls  72  proximate to the opening  81 . For illustrative purposes, heater foil  78  is shown cutaway so that the evaporator tubing  76  may be shown. A heating of the heater foil  78  will melt frost accumulation on the inner side walls  72 . 
         [0036]    Thermal insulation  88  is exterior of the heater foil  78  and provides insulation between the evaporator tubing  76  and condenser tubing  80 . In the example shown, the condenser tubing  80  is in a serpentine configuration and attached to an inside surface of the outer wall  92 . At an end of the condenser tubing  80  is an expansion valve (e.g.  97  in  FIG. 3 ), as in known in the art. The outer walls  82  may be formed of metal or other conductive material and may be utilized as a heat transfer surface for the condenser tubing  80 . Accordingly, heat from the condenser tubing  80  is released to an exterior of the freezer via the outer walls  82 , as is known in the art. 
         [0037]    The heater foil  78  is similar to the heater foil  18  as shown in  FIG. 3 , as explained above. Thus, similar to heater foil  18 , there is a heater wire (not shown) defining an upper region and a heater wire (not shown) defining a lower region. 
         [0038]    The operation of the vertical freezer  70  is similar to the operation of the horizontal freezer  10 , as illustrated in  FIGS. 4 to 6 , explained above. Thus, the freezer  70  is operable in a first mode of operation and in a second or full defrost mode of operation. For illustrative purposes, the heater foil  18  will be used, as shown in  FIG. 3 . In the first mode of operation, the first step is the compressor  96  may be temporarily turned off by the controller  98 . The next step is the upper heater wire  33  is then energized by the controller  98  to melt the frost  50 , the melted water being reformed as ice  52  on the side cabinet wall  82 . The upper heater wire  33  is thus activated by the controller  98  for a time to melt the frost  50 . The controller  98  then de-energizes the upper heater wire  33  and turns the compressor  96  back on for normal operation of the freezer  70 . 
         [0039]    In the second mode of operation, the compressor  96  may be temporarily turned off by the controller  98 . As shown in  FIG. 6 , the lower heater wire  34  is then energized by the controller  98  to melt a portion of the ice  52 . The ice  52  may then be removed by a user by gently prying the ice  52  from the inner side walls  72  using a plastic object such as a spatula (not shown). The ice  52  may also fall to the base  74  of the freezer  70  for removal by a user. The controller  98  then de-energizes the upper heater wire  33  and turns the compressor  96  back on for normal operation of the freezer  70 . In another embodiment, as best illustrated in  FIG. 6 , instead of solely the bottom heater wire  34  being energized by the controller  98 , both the top heater wire  33  and bottom heater wire  34  are activated to melt a portion of any ice  52  or frost. This facilitates removal of any ice  52  or frost accumulated anywhere on the inner side walls  72 , by gently prying or removing by a user. 
         [0040]    While the invention has been described in detail in the foregoing specification, it will be understood by those skilled in the art that variations may be made without departing from the scope of the invention, being limited only by the appended claims.