HIGH PERFORMANCE REFRIGERATOR HAVING INSULATED EVAPORATOR COVER

Abstract

A high performance refrigerator includes a cabinet with a refrigerated interior, an insulating cover separating a portion of the cabinet from the refrigerated interior, and a refrigeration fluid circuit having an evaporator located within the portion of the cabinet separated by the insulating cover from the refrigerated interior. The refrigerator also includes a controller that commands the refrigerator to perform a defrosting cycle when the evaporator coil requires defrosting. This defrosting cycle includes closing dampers in the insulating cover during the defrosting of the evaporator coil, thereby keeping the refrigerated interior thermally isolated from the evaporator during the defrost cycle. The controller is also operable to stop operation of a defrost heater when the evaporator reaches a first target temperature above the freezing point of water, and to re-open the dampers when the evaporator reaches a second target temperature above the freezing point of water.

Description

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the priority benefit of U.S. Provisional Patent Application No. 61/548,795 (pending), filed Oct. 19, 2011, the disclosure of which is hereby incorporated by reference in its entirety herein.

FIELD OF THE INVENTION

The present invention relates generally to refrigerators or freezers and, more particularly, to refrigeration systems for use with high performance blood bank refrigerators or plasma freezers.

BACKGROUND OF THE INVENTION

Refrigeration systems are known for use with laboratory refrigerators and freezers of the type known as “high performance refrigerators,” which are used to cool their interior storage spaces to relative low temperatures such as about −30° C. or lower, for example. These high performance refrigerators are used to store blood and/or plasma, in one example.

Known refrigeration systems of this type include a single loop circulating a refrigerant. The system transfers energy (i.e., heat) from the refrigerant to the surrounding environment through a condenser, and the system transfers heat energy to the refrigerant from the cooled space (e.g., a cabinet interior) through an evaporator. The refrigerant is selected to vaporize and condense at a selected temperature close to the desired temperature for the cooled space, such that the refrigeration system can maintain the cooled space near that selected temperature during operation.

One common problem with known refrigeration systems is that the evaporator includes coils that tend to produce and accumulate frost along the outer surface if any moisture is ambient within the cooled space. If enough frost accumulation occurs, the ability of the evaporator to remove heat from the cooled space is detrimentally impacted. Consequently, known refrigeration systems require a defrost cycle where the evaporator coils are heated to remove the frost. This defrost cycle may be a manual defrost or an automatic defrost, but both types of defrost cycles are undesirable for various reasons.

In a manual defrost cycle, all of the products stored in the cabinet are removed and the cooled space is left exposed to the ambient environment to heat up the evaporator coils and melt the frost. This cycle is undesirable because the products stored in the cabinet need to be stored in an alternative refrigerator for the duration of the defrost cycle, and also because the melting process can produce a significant amount of moisture that needs to be removed from the cabinet. In an automatic defrost cycle, the evaporator coils are rapidly heated by a local heating unit or hot gas flow to remove the frost, which is collected by a trough and delivered out of the cooled space. The cooled space necessarily undergoes a temperature spike during this automatic defrost cycle, which can jeopardize the products stored in the cabinet.

There is a need, therefore, for a refrigerator that substantially minimizes or eliminates a temperature spike within the cooled space during a defrost cycle.

SUMMARY OF THE INVENTION

In one embodiment, a refrigerator includes a cabinet with a refrigerated interior and a refrigeration fluid circuit for circulating a refrigerant. The refrigeration fluid circuit includes a compressor, a condenser, an expansion device, and an evaporator located within the cabinet. The evaporator includes an evaporator coil, an evaporator fan producing air flow through the evaporator coil, and a defrost heater. The refrigerator also includes an insulating cover separating a portion of the cabinet containing the evaporator from the refrigerated interior. The insulating cover includes at least one damper which opens to permit air circulation from the refrigerated interior through the evaporator.

The refrigerator further includes a controller operable to command the refrigerator to perform a series of steps defining a defrost cycle when the evaporator coil requires defrosting. The series of steps includes stopping operation of the compressor and the evaporator fan, closing the at least one damper to thermally isolate the evaporator from the refrigerated interior, and starting operation of the defrost heater. The refrigerated interior remains thermally isolated from the evaporator during operation of the defrost heater.

In one aspect, the refrigerator also includes a temperature sensor for detecting the temperature of the evaporator. The controller operates during defrosting as follows: when the temperature sensor detects that the evaporator has reached a first target temperature above the freezing point of water, the defrost heater stops. After any remaining moisture drips off the evaporator coils, the compressor starts. When the temperature sensor detects that the evaporator has reached a second target temperature below the freezing point of water, the at least one damper opens and the evaporator fan starts. In one example, the first target temperature is about 10° C. and the second target temperature is about −25° C. The controller may also be operable to perform the defrost cycle steps as an adaptive defrost cycle, which includes varying time periods between defrost cycles and varying lengths of defrost cycles dependent upon multiple operating parameters.

In another embodiment of the invention, a method of operating a refrigerator is provided, the refrigerator including a cabinet with a refrigerated interior, a refrigeration fluid circuit including a compressor, a condenser, and an evaporator, and an insulating cover with at least one damper separating the evaporator from the refrigerated interior. The method includes stopping operation of the compressor and an evaporator fan. The at least one damper closes to thermally isolate the evaporator from the refrigerated interior. A defrost heater starts operation to remove moisture from evaporator coils. The refrigerated interior remains thermally isolated from the evaporator during operation of the defrost heater.

In yet another embodiment, a method of operating a refrigerator is provided, the refrigerator including a cabinet with a refrigerated interior, a refrigeration fluid circuit including a compressor, a condenser, and an evaporator, and an insulating cover with at least one damper separating the evaporator from the refrigerated interior. The method includes starting operation of a defrost heater when the at least one damper is closed. When the evaporator reaches a first target temperature above the freezing point of water, the defrost heater is stopped and the compressor is started. When the evaporator reaches a second target temperature below the freezing point of water, the at least one damper opens and an evaporator fan starts operating.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with a general description of the invention given above, and the detailed description of the embodiment given below, serve to explain the principles of the invention.

FIG. 1 is a perspective view of a refrigerator including an insulating cover according to an exemplary embodiment.

FIG. 2 is a schematic representation of the refrigeration fluid circuit used with the refrigerator of FIG. 1.

FIG. 3 is a perspective view of the insulating cover (shown in phantom) and dampers used with the refrigerator of FIG. 1.

FIG. 4 is a perspective view of an evaporator used with the refrigerator of FIG. 1, with some of the side panels shown in phantom to reveal interior elements.

FIG. 5 is a cross-sectional side view of the refrigerator of FIG. 1, with the dampers in a closed position.

FIG. 6 is a cross-sectional side view of the refrigerator of FIG. 5, with the dampers in an open position.

FIG. 7 is a schematic diagram of the controller and damper drive elements used with the refrigerator of FIG. 1.

FIG. 8 is a schematic flowchart illustrating an operational sequence of a controller associated with the refrigerator of FIG. 1.

DETAILED DESCRIPTION

With reference to the figures, and more specifically to FIG. 1, an exemplary high performance refrigerator 10 according to one embodiment of the present invention is illustrated. Although the terms “high performance refrigerator” and “refrigerator” are used throughout the specification, it will be understood that the invention encompasses any type of cooling device, including a refrigerator that comprises a freezer. The refrigerator of FIG. 1 includes a cabinet 12 for storing items that require cooling to temperatures of about −30° C. or lower, for example. The cabinet 12 includes a cabinet housing 14 defining a generally rectangular cross-section and a door 16 providing access into an interior 18 of the cabinet 12. The cabinet 12 supports one or more components that jointly define a single-stage refrigeration fluid circuit 20 (FIG. 2) that thermally interacts with the air within the cabinet 12 to cool the interior 18 thereof. In this regard, the refrigeration fluid circuit 20 described in further detail below interacts with warmed air in the interior 18 and cools this air to maintain a desired cold temperature in the cabinet 12.

With reference to FIG. 2, details of the exemplary refrigeration fluid circuit 20 are illustrated. The refrigeration fluid circuit 20 includes, in sequence, a compressor 22, a condenser 24, a filter/dryer 26, an expansion device 28, an evaporator 30, and a suction/accumulator 32. Each of these elements of the refrigeration fluid circuit 20 is coupled by piping or tubing 34 configured to circulate the refrigerant 36 passing through the refrigeration fluid circuit 20. A plurality of sensors S₁ through S₅ are arranged to sense different conditions of the fluid circuit 20 and/or properties of the refrigerant (shown by arrows 36) at various locations within the fluid circuit 20. Each of these sensors S₁ through S₅ is operatively coupled to a controller 50 accessible through a controller interface 52, which permits controlling of the operation of the fluid circuit 20. It will be appreciated that more or fewer sensors may be provided than the number shown in the exemplary embodiment of the fluid circuit 20.

The refrigeration fluid circuit 20 is configured to circulate the refrigerant 36 between the condenser 24 and the evaporator 30. Generally speaking, heat energy in the refrigerant 36 is transferred to ambient air outside the cabinet 12 at the condenser 24. Heat energy is removed from the interior 18 of the cabinet 12 and transferred to the refrigerant 36 at the evaporator 30. Thus, circulating the refrigerant 36 through the fluid circuit 20 continuously removes heat energy from the interior 18 to maintain a desired internal temperature, such as, for example −30° C.

The refrigerant 36 enters the compressor 22 in a vaporized state and is compressed to a higher pressure and higher temperature gas in the compressor 22. The fluid circuit 20 of this exemplary embodiment also includes an oil loop 54 for lubricating the compressor 22. Specifically, the oil loop 54 includes an oil separator 56 in fluid communication with piping 34 downstream of the compressor 22 and an oil return line 58 directing oil back into the compressor 22. It will be understood that the oil loop 54 may be omitted in some embodiments of the fluid circuit 20.

Upon leaving the compressor 22, the vaporized refrigerant 36 travels to the condenser 24. A fan 60 controlled by the control interface 52 directs ambient air across the condenser 24 and through a filter 62 so as to facilitate the transfer of heat from the refrigerant 36 to the surrounding environment. The air flow through the condenser 24 is shown by arrows in FIG. 2. The refrigerant 36 condenses within the condenser 24 as a result of this heat transfer. The liquid-phase refrigerant then passes through the filter/dryer 26 and into the expansion device 28. In this embodiment, the expansion device 28 is in the form of a capillary tube, although it is contemplated that it could instead take another form such as, and without limitation, an expansion valve (not shown). The expansion device 28 causes a pressure drop in the refrigerant 36 immediately before the refrigerant 36 enters the evaporator 30.

In the evaporator 30, the refrigerant 36 receives heat from the interior 18 through a plurality of evaporator coils (not shown in FIG. 2). An evaporator fan 64 controlled by the control interface 52 forces air flow from the interior 18 of the cabinet 12 through the evaporator coils when first and second dampers 66, 68 are opened. The first and second dampers 66, 68 are also controlled by the control interface 52. The control of the first and second dampers 66, 68 is further described with reference to FIG. 8, below. By virtue of the lowered pressure and the heat transfer from the cabinet 12, the refrigerant 36 vaporizes within the evaporator 30. The vaporized refrigerant 36 is then directed to the suction/accumulator device 32. The suction/accumulator 32 passes the refrigerant 36 in gaseous form to the compressor 22, while also accumulating excessive amounts of the refrigerant 36 in liquid form and feeding it to the compressor 22 at a controlled rate.

The refrigerant 36 used in the refrigeration fluid circuit 20 may be chosen based on several factors, including the expected operating temperature within the cabinet 12 and the boiling point and other characteristics of the refrigerant 36. For example, in refrigerators with an expected cabinet temperature of about −30° C., an exemplary refrigerant 36 suitable for the presently described embodiment includes refrigerants commercially available under the respective designations R404A. Moreover, in specific embodiments, the refrigerant 36 may be combined with an oil to facilitate lubrication of the compressor 22. For example, and without limitation, the refrigerant 36 may be combined with Mobil EAL Arctic 32 oil. It will be understood that the precise arrangement of the components illustrated in the figures is intended to be merely exemplary rather than limiting.

With reference to FIGS. 3-6 and in particular FIG. 3, the refrigerator 10 includes an insulated cover 70 that divides the interior 18 of the cabinet 12 into an evaporator portion 72 and a refrigerated portion 74. The insulated cover 70 is coupled to one or more of the top wall 76, the side walls 78 (including a rear wall 78), and/or the bottom wall 80 collectively defining the cabinet housing 14. More particularly, the insulated cover 70 is coupled to the top wall 76 and the side walls 78 of the cabinet housing 14 to thermally isolate the evaporator portion 72 from the heat energy within the interior 18 as that heat energy rises within the interior 18 of the cabinet 12. The insulated cover 70 of the illustrated embodiment includes a vertical panel portion 82 extending downwardly from the top wall 76 of the cabinet housing 14 and a horizontal panel portion 84 extending between the vertical panel portion 82 and the side walls 78 of the cabinet housing 14. The vertical panel portion 82 and the horizontal panel portion 84 are formed from one or more thermally insulating panels, such as the hollow vacuum insulated panel 86 shown in FIG. 3. It will be understood that other types of insulating panels may be used in other embodiments of the invention, including but not limited to foam-based panels.

As shown in FIG. 3, the evaporator portion 72 is defined as a generally rectilinear space by the vertical panel portion 82, the horizontal panel portion 84, the side walls 78, and the top wall 76. The evaporator 30 mounts into a divider panel 88 located generally centrally within the evaporator portion 72 so as to divide the evaporator portion 72 into an inlet side 90 and an outlet side 92. The divider panel 88 is another vacuum insulated panel or foam-based insulated panel in this embodiment, although it will be understood that other types of dividing panels may also be used in other embodiments. The horizontal panel portion 82 of the insulated cover 70 includes an inlet aperture 94 on the inlet side 90 of the divider panel 88 and an outlet aperture 96 on the outlet side 92 of the divider panel 88. The first damper 66 includes an insulated panel that is operable to rotate to open or close flow through the inlet aperture 94 between the inlet side 90 and the refrigerated interior 18 of the cabinet 12. Similarly, the second damper 68 includes an insulated panel that is operable to rotate to open or close flow through the outlet aperture 96 between the outlet side 92 and the refrigerated interior 18 of the cabinet 12. Thus, the first and second dampers 66, 68 may be operated to enable flow through the evaporator 30.

Also shown in FIG. 3, the first and second dampers 66, 68 are operatively connected to a damper drive mechanism 100 such as respective first and second servo motors 102, 104 and first and second drive shafts 106, 108. The control and operation of the damper drive mechanism 100 is further described in detail with reference to FIG. 7 below. It will be understood that the first and second drive shafts 106, 108 may be connected by a conventional drive linkage (not shown) in some embodiments so that only a single servo motor would be required to open and close the first and second dampers 66, 68. In this regard, the first and second dampers 66, 68 are typically opened (or closed) simultaneously so that flow is enabled through the evaporator portion 72 and the evaporator 30.

Turning to FIG. 4, the evaporator 30 is shown in further detail. To this end, the evaporator 30 includes an evaporator housing 110 enclosing an evaporator coil 112 extending in a serpentine manner across a width of the evaporator 30. The evaporator coil 112 is operatively connected to the piping 34 of the refrigeration fluid circuit 20, which carries liquid-phase refrigerant to the evaporator coil 112 and removes vaporized and any remaining liquid-phase refrigerant from the evaporator coil 112. The evaporator fan 64 is mounted along the evaporator housing 110 at the inlet side 90 of the evaporator portion 72 so as to actuate air flow through the evaporator housing 110 and through the evaporator coil 112. After flowing through the evaporator coil 112, cooled air exits the evaporator housing 110 and enters the outlet side 92 of the evaporator portion 72.

The evaporator 30 also includes a defrost heater 114 for removing frost build up on the evaporator coil 112 as needed or on a regular basis. The defrost heater 114 is shown mounted adjacent to the evaporator coil 112 in FIGS. 4 and 5, but it will be appreciated that the defrost heater 114 may be mounted anywhere within the evaporator housing 110. The defrost heater 114 is operated by the controller 50 and the control interface 52 previously described with reference to FIG. 2 to heat up the evaporator coil 112 and melt any frost. The evaporator housing 110 further includes a drip pan 116 located below the evaporator coil 112 and configured to collect and dispose of melted frost to a location outside the refrigerator 10. In this regard, the drip pan 116 is generally angled from a horizontal orientation so that moisture dripping from the evaporator coil 112 automatically flows to a moisture outlet (not shown).

With reference to FIGS. 5 and 6, the refrigerator 10 further includes an upper compartment 120 located above the top wall 76 of the cabinet housing 14. The upper compartment 120 contains elements of the refrigeration fluid circuit 20 other than the evaporator 30 (e.g., the compressor 22, the condenser 24, etc.), thereby removing most of the space-using or heat generating components from the interior 18 of the cabinet 12. These other elements located within the upper compartment 120 are not shown in FIGS. 5 and 6, although they are schematically shown in FIG. 2. The piping 34 for the refrigerant 36 extends through the top wall 76 to deliver refrigerant between the components in the upper compartment 120 and the evaporator 30 in the cabinet 12.

FIGS. 5 and 6 also illustrate two operating states for the refrigerator 10. More particularly, in FIG. 5 the first and second dampers 66, 68 are closed, which thermally isolates the evaporator portion 72 from the refrigerated portion 74. The evaporator fan 64 is generally inactive when the first and second dampers 66, 68 are closed because air cannot be circulated into and out of the evaporator portion 72. The defrost heater 114 is only operated in this operational state of the refrigerator 10 so that substantially all of the heat energy generated by the defrost heater 114 remains within the evaporator portion 72 during a defrost cycle or process. To this end, the temperature spike within the refrigerated portion 74 of the interior 18 is reduced or eliminated during the defrost cycle. In contrast, the first and second dampers 66, 68 are open in FIG. 6 so that air from the refrigerated portion 74 may flow through the evaporator 30 and the evaporator coil 112 for cooling. The air flow actuated by the evaporator fan 64 is schematically shown in FIG. 6 by arrows 122. Thus, relatively warm air enters the evaporator portion 72 through the inlet aperture 94 and relatively cold air exits the evaporator portion 72 through the outlet aperture 96 in this operating state of the refrigerator 10.

FIG. 7 schematically illustrates the control and actuation mechanisms for the first and second dampers 66, 68. More specifically, the first and second dampers 66, 68 are connected to the damper drive mechanism 100, which is coupled to the controller 50. As understood in the art, the controller 50 may include at least one central processing unit (“CPU”) coupled to a memory. Each CPU is typically implemented in hardware using circuit logic disposed on one or more physical integrated circuit devices or chips. Each CPU may be one or more microprocessors, micro-controllers, field programmable gate arrays, or ASICs, while memory may include random access memory (RAM), dynamic random access memory (DRAM), static random access memory (SRAM), flash memory, and/or another digital storage medium, and also typically implemented using circuit logic disposed on one or more physical integrated circuit devices, or chips. As such, memory may be considered to include memory storage physically located elsewhere in the refrigerator 10, e.g., any cache memory in the at least one CPU, as well as any storage capacity used as a virtual memory, e.g., as stored on a mass storage device such as a hard disk drive, another computing system, a network storage device (e.g., a tape drive), or another network device coupled to the controller 50 through at least one network interface by way of at least one network. The computing system, in specific embodiments, is a computer, computer system, computing device, server, disk array, or programmable device such as a multi-user computer, a single-user computer, a handheld computing device, a networked device (including a computer in a cluster configuration), a mobile telecommunications device, a video game console (or other gaming system), etc. The controller 50 includes at least one serial interface to communicate serially with an external device, such as the damper drive mechanism 100, for example. Thus, the controller 50 functions to actuate operation of the damper drive mechanism 100.

As previously described, the damper drive mechanism 100 may be one or more servo motors 102, 104 connected to the first and second dampers 66, 68 via corresponding drive shafts 106, 108. However, the damper drive mechanism 100 may include other types of actuation mechanisms and devices in other embodiments. For example, the damper drive mechanism 100 may be hydraulically driven, pneumatically driven, or mechanically driven such as by various types of motors. The damper drive mechanism 100 may be configured to rotate the dampers 66, 68 between open and closed positions as shown in the illustrated embodiment, but it will be understood that the damper drive mechanism 100 may alternatively slide or otherwise move the dampers 66, 68 in non-rotational manners as well.

An exemplary operation of the refrigerator 10 is shown schematically in the flowchart of FIG. 8. In this regard, the controller 50 is operable to command the refrigerator 10 to execute the steps of the method 200 shown in that Figure. To this end, the controller 50 determines whether a defrost cycle is necessary at step 202. For example, in a time-based defrost cycle, the controller 50 at step 202 determines whether a predetermined amount of time has elapsed since the most recent defrost cycle. If so, then the controller 50 begins the defrost cycle at step 204. If not, then the controller 50 continues to wait and periodically checks to see if the predetermined amount of time has elapsed. In one example, the refrigerator 10 may defrost every six hours, in which case the predetermined amount of time would be six hours. Alternatively, the controller 50 may be operable to perform adaptive defrosts that are spaced by varying amounts of time depending on operational characteristics measured between defrost cycles, as described in further detail below.

Returning to FIG. 8, when a defrost cycle is required to remove frost build up from the evaporator coil 112, the controller 50 stops the compressor 22 and the evaporator fan 64 at step 204. This stops refrigerant flow through the refrigeration fluid circuit 20 and the evaporator 30 and also stops air flow through the evaporator 30. The controller 50 then closes the first and second dampers 66, 68 at step 206 to thermally isolate the evaporator portion 72 from the refrigerated portion 74 of the cabinet 12. With the evaporator portion 72 thermally isolated from the remainder of the cabinet 12, the controller 50 starts operation of the defrost heater 114 at step 208. The defrost heater 114 warms the evaporator 30 and the evaporator coil 112 to melt frost and cause the moisture to drip onto the drip pan 116 for removal from the evaporator 30. The operational state of the refrigerator 10 at this point is shown in FIG. 5.

One of the sensors S₃ connected to the evaporator 30 may be configured to measure the temperature of the evaporator 30. At step 210, the controller 50 determines whether that sensor S₃ is reading a temperature of the evaporator 30 which is at or exceeding a first target temperature above the freezing point of water (0° C.). In one example, this first target temperature may be about 10° C. If the evaporator 30 is not at or above that first target temperature, then the controller 50 continues to operate the defrost heater 114 to remove frost from the evaporator coil 112. If the evaporator 30 is at or above the first target temperature, then the controller 50 turns off the defrost heater 114 and allows a set period of time for additional moisture to drip off the evaporator coil 112 onto the drip pan 116 at step 212. After this “drip time” has occurred, the controller 50 starts the compressor 22 to cause refrigerant flow through the evaporator 30 again at step 214, thereby cooling the evaporator portion 72.

At step 216, the temperature sensor S₃ measures the temperature of the evaporator 30 and the controller 50 determines whether this temperature is at or below a second target temperature below the freezing point of water (0° C.). In one example, this second target temperature may be about −25° C. If the evaporator 30 is not at or below the second target temperature, the controller 50 continues to operate the compressor 214 to cool the evaporator 30. Once the controller 50 determines that the evaporator 30 is at or below the second target temperature, then the controller 50 opens the first and second dampers 66, 68 at step 218. The controller 50 also starts the evaporator fan 64 at step 220, to thereby force air flow from the refrigerated portion 74 through the evaporator portion 72 and the evaporator 30 for further cooling. This final step of the defrost cycle or method 200 returns the refrigerator 10 to the operational state shown in FIG. 6, which is the normal cooling operational state. As a result of the insulated cover 70, the defrost cycle does not cause a significant temperature spike within the refrigerated interior 18 of the cabinet 12, and the refrigerator 10 therefore is advantageous over conventional refrigerator designs.

As briefly noted above, in one alternative embodiment the defrost cycle will be an adaptive defrost cycle selectively actuated at step 202 of the method 200. In this adaptive defrost cycle, the period between defrost cycles and the time duration of the defrost cycles are modified based on a plurality of operational parameters monitored by the controller 50. For example, the conventional time-based defrost cycle may operate the defrost heater 114 for 10 minutes every six hours. By contrast, the adaptive defrost cycle may monitor the actual temperature being maintained in the cabinet 12, as well as the number of door openings and amount of total time the door is open. These and other factors are considered to determine how long the period should be before the next defrost cycle is started, and also how long the defrost heater 114 should be operated in the next defrost cycle. In this regard, if the door of the cabinet 12 is not opened often during a six hour period and the evaporator 30 is having little trouble maintaining the desired temperature within the refrigerated portion 74, then the next defrost cycle may be delayed by an additional number of hours and/or shortened in duration. Thus, the adaptive defrost cycle is highly energy efficient because the evaporator coil 112 is only defrosted when that cycle becomes necessary. Moreover, the adaptive defrost cycle automatically adjusts the refrigerator 10 for proper and efficient operation in a variety of environmental conditions.

While the present invention has been illustrated by a description of an exemplary embodiment and while this embodiment has been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.

Claims

1. A refrigerator, comprising:

a cabinet having a refrigerated interior;

a refrigeration fluid circuit for circulating a refrigerant, the refrigeration fluid circuit including a compressor, a condenser, an expansion device, and an evaporator located within the cabinet and including an evaporator coil, an evaporator fan producing air flow through the evaporator coil, and a defrost heater;

an insulating cover separating a portion of the cabinet containing the evaporator from the refrigerated interior, the insulating cover including at least one damper that may open to permit air circulation from the refrigerated interior through the evaporator; and

a controller operable to command the refrigerator to perform the following steps when the evaporator coil requires defrosting: stop operation of the compressor and the evaporator fan; close the at least one damper to thermally isolate the evaporator from the refrigerated interior; and start operation of the defrost heater, wherein the refrigerated interior remains thermally isolated from the evaporator during operation of the defrost heater.

2. The refrigerator of claim 1, further comprising a temperature sensor for detecting the temperature of the evaporator, and wherein the controller is further operable to command the refrigerator to perform the following steps during defrosting of the evaporator:

when the temperature sensor detects that the evaporator has reached a first target temperature above the freezing point of water, stopping operation of the defrost heater and allowing for any remaining moisture to drip off the evaporator coils;

starting the compressor after the remaining moisture drips off the evaporator coils; and

when the temperature sensor detects that the evaporator has reached a second target temperature below the freezing point of water, opening the at least one damper and starting operation of the evaporator fan.

3. The refrigerator of claim 2, wherein the first target temperature is about 10° C. and the second target temperature is about −25° C.

4. The refrigerator of claim 1, wherein the at least one damper includes a first damper and a second damper, the first damper in an open position permitting air flow into the evaporator from the refrigerated interior, the second damper in an open position permitting air flow from the evaporator into the refrigerated interior.

5. The refrigerator of claim 1, wherein the insulated cover further includes a plurality of insulated panels that collectively divide the cabinet into an evaporator chamber and the refrigerated interior when the at least one damper is closed.

6. The refrigerator of claim 5, wherein each of the insulated panels is a vacuum insulated panel.

7. The refrigerator of claim 1, wherein the expansion device includes at least one of a capillary tube or a valve.

8. The refrigerator of claim 1, wherein the refrigeration fluid circuit further includes an accumulator operatively connected to the evaporator and the compressor.

9. The refrigerator of claim 1, wherein the refrigeration fluid circuit further includes a filter/dryer operatively connected to the condenser and the expansion device.

10. The refrigerator of claim 1, wherein the controller is operable to modify an amount of time between defrost cycles and to modify an amount of time the defrost heater is operating during a defrost cycle based on at least one measurable operating parameter.

11. A method of operating a refrigerator including a cabinet having a refrigerated interior, a refrigeration fluid circuit including a compressor, a condenser, and an evaporator located within the cabinet and having an evaporator fan and defrost heater, the refrigerator further including an insulating cover with at least one damper configured to separate the evaporator from the refrigerated interior of the cabinet, and the method comprises:

stopping operation of the compressor and the evaporator fan;

closing the at least one damper to thermally isolate the evaporator from the refrigerated interior; and

starting operation of the defrost heater,

wherein the refrigerated interior remains thermally isolated from the evaporator during operation of the defrost heater.

12. The method of claim 11, further comprising:

when the evaporator has reached a first target temperature above the freezing point of water, stopping operation of the defrost heater and allowing for any remaining moisture to drip off the evaporator coils;

starting the compressor after the remaining moisture drips off the evaporator coils; and

when the evaporator has reached a second target temperature below the freezing point of water, opening the at least one damper and starting operation of the evaporator fan.

13. The method of claim 12, wherein the first target temperature is about 10° C. and the second target temperature is about −25° C.

14. The method of claim 11, wherein the at least one damper includes a first damper and a second damper, the first damper in an open position permitting air flow into the evaporator from the refrigerated interior, the second damper in an open position permitting air flow from the evaporator into the refrigerated interior, and the first and second dampers are simultaneously closed by the refrigerator when the operation of the evaporator fan is stopped.

15. A method of operating a refrigerator including a cabinet having a refrigerated interior, a refrigeration fluid circuit including a compressor, a condenser, and an evaporator located within the cabinet and having an evaporator fan and defrost heater, the refrigerator further including an insulating cover with at least one damper configured to separate the evaporator from the refrigerated interior of the cabinet, and the method comprises:

starting the operation of the defrost heater when the at least one damper is closed; and

when the evaporator has reached a first target temperature above the freezing point of water, stopping operation of the defrost heater and starting operation of the compressor; and

when the evaporator has reached a second target temperature below the freezing point of water, opening the at least one damper and starting operation of the evaporator fan.

16. The method of claim 15, wherein the first target temperature is about 10° C. and the second target temperature is about −25° C.

17. The method of claim 15, wherein the at least one damper includes a first damper and a second damper, the first damper in an open position permitting air flow into the evaporator from the refrigerated interior, the second damper in an open position permitting air flow from the evaporator into the refrigerated interior, and the first and second dampers are simultaneously opened by the refrigerator when the operation of the evaporator fan is started.