FROST MANAGEMENT SYSTEM FOR A REFRIGERATED CABINET
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.
This invention relates to refrigerated cabinets such as chest freezers and, in particular, to frost management systems for such devices.
BACKGROUND OF THE INVENTIONIn 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.
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.
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.
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.
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.
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 INVENTIONThe 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.
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.
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.
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.
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.
Reference is now made to
The evaporator tubing 16 is connected to a compressor (96 in
In
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 (
Reference is now made to
The components of the heater foil 18 are shown in
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.
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.
In another embodiment, the ice 52 acts as a “holdover cooling” feature, as best illustrated in
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
In another embodiment, as best illustrated in
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
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.
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
The heater foil 78 is similar to the heater foil 18 as shown in
The operation of the vertical freezer 70 is similar to the operation of the horizontal freezer 10, as illustrated in
In the second mode of operation, the compressor 96 may be temporarily turned off by the controller 98. As shown in
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.
Claims
1. 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, comprising:
- a first heating member positioned proximate to the opening and exterior of the sidewalls for heating of frost accumulated on an interior of the sidewalls; and
- a first activator for the first heating member,
- wherein the first heating member is 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.
2. The frost management system of claim 1, further comprising:
- 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 interior of the sidewalls; and
- a second activator for the second heating member, the second heating member being activated for a time to melt a portion of the ice adjacent the sidewalls to enable its removal.
3. The frost management system of claim 1, wherein the first heating member comprises a foil heater having a first conductive sheet, a second conductive sheet having a surface adhered to a surface of the first conductive sheet, and a wire heater located between the first conductive sheet and second conductive sheet for heating the first conductive sheet and second conductive sheet.
4. The frost management system of claim 3, wherein the foil heater has an adhesive surface for adhering to the sidewalls.
5. The frost management system of claim 3, wherein the wire heater is positioned in a serpentine configuration between the first conductive sheet and second conductive sheet.
6. The frost management system of claim 1, further comprising a cooling member located exterior the sidewalls for cooling the interior of the sidewalls through heat transfer through the sidewalls.
7. The frost management system of claim 6, further comprising a controller for automatically effecting a predetermined cycle of operation for the cooling member and the first activator at predetermined intervals.
8. The frost management system of claim 6, wherein the predetermined intervals are regular intervals.
9. The frost management system of claim 7, wherein the regular intervals are 12-hour intervals.
10. A method for managing frost on 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.
11. The method of claim 8, including the step of:
- heating a region on the sidewalls for melting a portion of ice accumulated on the interior of the sidewalls to enable its removal; and
- removing the ice from the refrigeration cabinet.
12. The method of claim 11, wherein the step of heating a region on the sidewalls proximate to the opening is on a predetermined cycle of operation at predetermined intervals.
13. The frost management system of claim 12, wherein the predetermined intervals are regular intervals.
14. The frost management system of claim 13, wherein the regular intervals are 12-hour intervals.
15. The frost management system of claim 2, wherein the first heating member comprises a foil heater having a first conductive sheet, a second conductive sheet having a surface adhered to a surface of the first conductive sheet, and a wire heater located between the first conductive sheet and second conductive sheet for heating the first conductive sheet and second conductive sheet.
Type: Application
Filed: Mar 13, 2007
Publication Date: May 8, 2008
Inventors: Greg HALL (Guelph), Marian VIDOVIC (Mississauga), James SCOTT (Cambridge)
Application Number: 11/685,642
International Classification: F25D 21/00 (20060101);