CA2552454A1 - Frost management system for a refrigerated cabinet - Google Patents

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

FROST MANAGEMENT SYSTEM FOR A REFRIGERATED CABINET
FIELD OF THE INVENTION
This invention relates to refrigerated cabinets such as chest freezers and, in particular, to frost management systems for such devices.

BACKGROUND OF THE INVENTION
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.
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 INVENTION
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.
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.

BRIEF DESCRIPTION OF THE DRAWINGS
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.
Figure 1 shows a perspective sectional view of a horizontal cold-wall type freezer in accordance with an embodiment of the present invention;
Figure 2 shows a perspective partial sectional view of a cabinet wall of Figure 1;
Figure 3 shows a perspective view of a foil heater of the freezer of Figure 1 and a block diagram of an example of controller circuitry;
Figure 4 shows a sectional side view of the freezer of Figure 1;
Figure 5 shows the same view as Figure 4 in a first mode of operation;
Figure 6 shows the same view as Figure 4 in a second or full defrost mode of operation; and Figure 7 shows a perspective sectional view of a vertical cold-wall type freezer in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION
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 Figures 1 and 2. Figure 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. Figure 2 shows a perspective partially sectional view of a cabinet wall 22 of the freezer of Figure 1.
Figure 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 Figures 4 to 6) on top of the cabinet walls 22.
The evaporator tubing 16 is connected to a compressor (96 in Figure 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.
In Figure 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.
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 (Figure 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.
Reference is now made to Figure 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 wal122.
The components of the heater foil 18 are shown in Figure 3. In the example shown, heater foil 18 has two heat conductive sheets 44, 46 having heater wires 33, 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 Figure 2. Heater wire 33 defines an upper region in the heater foil corresponding to upper portion 24 of the cabinet wall 22 as shown in Figure 2.
Similarly, heater wire 34 defines a lower region in the heater foil 18 corresponding to lower portion 26 of the cabinet wal122 as shown in Figure 2. The heater wires 33, 34 (Figure 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.
Figures 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 wa1122, and lower heater wire 34 is located to heat the lower portion 26 of the cabinet wall 22. Frost 50 is shown in Figure 4 as formed on the upper portion 24 of the cabinet wall 22. Figure 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 wa1122. Figure 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 (Figure 3) for automatically effecting a predetermined cycle of operation of the compressor 96 and the heater wires 33, 34 at predetermined, preferably regular, intervals.
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. (TM) 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 3/4 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 Figure 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.
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 Figure 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 Figure 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.
In another embodiment, as best illustrated in Figure 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.

Figure 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.
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 Figure 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.
Heater foi178 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 wal192. At an end of the condenser tubing 80 is an expansion valve (e.g.
97 in Figure 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.
The heater foil 78 is similar to the heater foil 18 as shown in Figure 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.
The operation of the vertical freezer 70 is similar to the operation of the horizontal freezer 10, as illustrated in Figures 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 Figure 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.
In the second mode of operation, the compressor 96 may be temporarily turned off by the controller 98. As shown in Figure 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 Figure 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.
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 (14)

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 claims 1 or 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.

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 claims 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 claims 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 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.