US20160084565A1 - Refrigerator appliance and method of operating a refrigerator appliance - Google Patents

Abstract

The present invention provides a refrigerator appliance and for operation of a refrigerator appliance. The refrigerator appliance and method of operating a refrigerator appliance include features for regulating the time between evaporator defrost cycles to efficiently defrost the evaporator. Features are also included for increasing the temperature of refrigerant circulating through a refrigeration system of the refrigerator appliance to prevent condensation on outer surfaces of the refrigerator.

Description

FIELD OF THE INVENTION
• The subject matter of the present disclosure relates generally to methods and systems for regulating the time between evaporator defrost cycles and increasing the temperature of the refrigerant to prevent condensation on external surfaces of the refrigerator appliance.
BACKGROUND OF THE INVENTION
• Generally, refrigerator appliances include a cabinet that defines a fresh food chamber for receipt of food items for storage. Many refrigerator appliances further include one or more freezer chambers for receipt of food items for freezing and storage. Various mullions typically divide the various chambers. For example, a mullion can be disposed between the fresh food chamber and freezer chamber. In “french door” style refrigerator appliances, an articulating mullion can be mounted to one of the fresh food chamber doors and positioned between the fresh food chamber doors when closed.
• One problem frequently encountered with modern refrigerators is condensation on the outside of the cabinet or other surfaces of the refrigerator, such as the mullions. Condensation occurs when a surface is at a temperature below the dew point temperature of the surrounding air. Once air contacts such surface, moisture in the air will condense on the surface. As such condensation accumulates, it may be unsightly and may eventually drip or run onto the floor.
• Various attempts to reduce such condensation have been made. For example, electric heaters have been embedded in the various components, such as the mullions, to heat the mullions and reduce condensation. However, the use of such heaters increases the energy use of the associated refrigerator appliance. Additionally, such electric heaters and associated components, such as humidity sensors, can increase the cost and the complexity of wiring of the associated refrigerator appliance. Therefore, other methods of increasing the temperature of the refrigerator surfaces, such as increasing the temperature of refrigerant circulating in proximity to such surfaces, could be more cost and energy efficient.
• Another problem encountered with modern refrigerators is inefficient defrosting of the evaporator of the refrigeration system. For example, when the evaporator is off, frost can accumulate on the evaporator and thereby reduce the efficiency of the evaporator. One effort to reduce or eliminate frost has been to utilize a heater, such as an electric heater, to heat the evaporator when the evaporator is not operating, with a set period of time elapsing between applications of heat. However, different environmental and use conditions of the refrigerator can cause different amounts of frost to accumulate on the evaporator during the set period of time. Therefore, applying heat only at set intervals such that heat must be applied for different intervals of time is an inefficient use of the heater and may increase the energy consumption of the system and/or increase the wear on the refrigeration components.
• Accordingly, improved refrigerator appliances are desired. In particular, a refrigerator appliance with features for regulating the time between evaporator defrost cycles and increasing the temperature of the refrigerant to prevent condensation would be advantageous. Additionally, a method of operating a refrigerator appliance to regulate the time between evaporator defrost cycles and to increase the temperature of the refrigerant to prevent condensation would be beneficial.
BRIEF DESCRIPTION OF THE INVENTION
• The present invention provides a refrigerator appliance and for operation of a refrigerator appliance. The refrigerator appliance and method of operating a refrigerator appliance include features for regulating the time between evaporator defrost cycles to efficiently defrost the evaporator. Features are also included for increasing the temperature of refrigerant circulating through a refrigeration system of the refrigerator appliance to prevent condensation on outer surfaces of the refrigerator. Additional aspects and advantages of the invention will be set forth in part in the following description, may be apparent from the description, or may be learned through practice of the invention.
• In a first exemplary embodiment, a method for operating a refrigerator appliance is provided. The refrigerator appliance comprises a refrigeration system for cycling a refrigerant therethrough that includes a compressor, a condenser, and an evaporator. The method includes the steps of activating a defrost heater configured to melt ice built up on the evaporator; counting a time t_defrost; determining if evaporator is defrosted and, if so, then deactivating the defrost heater; determining whether to increase the refrigerant temperature to prevent condensation on the external surfaces of the refrigerator appliance and, if so, then decreasing a condenser fan speed.
• In a second exemplary embodiment, a method for operating a refrigerator appliance is provided. The refrigerator appliance comprising a refrigeration system for cycling a refrigerant therethrough that includes a compressor, a condenser, and an evaporator. The method includes the steps of activating a defrost heater configured to melt ice built up on the evaporator; counting a time t_defrost; determining if evaporator is defrosted and, if so, then deactivating the defrost heater; determining whether to increase the refrigerant temperature to prevent condensation on the external surfaces of the refrigerator appliance and, if so, then increasing the compressor speed.
• In a third exemplary embodiment, a refrigerator appliance is provided. The refrigerator appliance includes at least one compartment for storing food items and a refrigeration system for cycling a refrigerant therethrough that includes a compressor, a condenser, a condenser fan, an evaporator, and a defrost heater configured to melt ice accumulated on the evaporator. The refrigerator appliance also includes a controller in operative communication with the compressor and the condenser fan. The controller is configured for activating a defrost heater configured to melt ice built up on the evaporator; counting a time t_defrost; determining if evaporator is defrosted and, if so, then deactivating the defrost heater; determining whether to increase the refrigerant temperature to prevent condensation on the external surfaces of the refrigerator appliance and, if so, then decreasing a condenser fan speed.
• These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
• A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:
• FIG. 1 provides a front view of a refrigerator appliance according to an exemplary embodiment of the present subject matter.
• FIG. 2 provides a schematic view of a refrigeration system of the exemplary refrigerator appliance ofFIG. 1.
• FIG. 3 provides a chart illustrating an exemplary method for operating a refrigerator appliance according to the present subject matter.
• FIG. 4 provides a graph of the mass of accumulated ice on the evaporator and the time interval between defrost cycles as a function of defrost time according to an exemplary embodiment of the present subject matter.
• FIG. 5 provides an exemplary time-moisture curve according to one embodiment of the present subject matter.
DETAILED DESCRIPTION OF THE INVENTION
• Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
• FIG. 1 provides a front view of arepresentative refrigerator appliance10 in an exemplary embodiment of the present invention. More specifically, for illustrative purposes, the present invention is described with arefrigerator appliance10 having a construction as shown and described further below. As used herein, a refrigerator appliance includes appliances such as a refrigerator/freezer combination, side-by-side, bottom mount, compact, and any other style or model of a refrigerator appliance. Accordingly, other configurations including multiple and different styled compartments could be used withrefrigerator appliance10, it being understood that the configuration shown inFIG. 1 is by way of example only.
• Refrigerator appliance10 includes a freshfood storage compartment12 and afreezer storage compartment14.Freezer compartment14 andfresh food compartment12 are arranged side-by-side within anouter case16 and defined byinner liners18 and20 therein. A space betweencase16 andliners18 and20, and betweenliners18 and20, is filled with foamed-in-place insulation.Outer case16 normally is formed by folding a sheet of a suitable material, such as pre-painted steel, into an inverted U-shape to form the top and side walls ofcase16. A bottom wall ofcase16 normally is formed separately and attached to the case side walls and to a bottom frame that provides support forrefrigerator appliance10.Inner liners18 and20 are molded from a suitable plastic material to formfreezer compartment14 andfresh food compartment12, respectively. Alternatively,liners18,20 may be formed by bending and welding a sheet of a suitable metal, such as steel.
• Abreaker strip22 extends between a case front flange and outer front edges ofliners18,20.Breaker strip22 is formed from a suitable resilient material, such as an extruded acrylo-butadiene-styrene based material (commonly referred to as ABS). The insulation in the space betweenliners18,20 is covered by another strip of suitable resilient material, which also commonly is referred to as amullion24. In one embodiment,mullion24 is formed of an extruded ABS material.Breaker strip22 andmullion24 form a front face, and extend completely around inner peripheral edges ofcase16 and vertically betweenliners18,20.Mullion24, insulation between compartments, and a spaced wall of liners separating compartments, sometimes are collectively referred to herein as acenter mullion wall26. In addition,refrigerator appliance10 includesshelves28 and slide-outstorage drawers30, sometimes referred to as storage pans, which normally are provided infresh food compartment12 to support items being stored therein.
• Refrigerator appliance10 can be operated by one ormore controllers11 or other processing devices according to programming and/or user preference via manipulation of acontrol interface32 mounted, e.g., in an upper region of freshfood storage compartment12 and connected withcontroller11.Controller11 may include one or more memory devices and one or more microprocessors, such as a general or special purpose microprocessor operable to execute programming instructions or micro-control code associated with the operation of the refrigerator appliance. The memory may represent random access memory such as DRAM, or read only memory such as ROM or FLASH. In one embodiment, the processor executes programming instructions stored in memory. The memory may be a separate component from the processor or may be included onboard within the processor.Controller11 may include one or more proportional-integral (“PI”) controllers programmed, equipped, or configured to operate the refrigerator appliance according to exemplary aspects of the control methods set forth herein. Accordingly, as used herein, “controller” includes the singular and plural forms.
• Controller11 may be positioned in a variety of locations throughoutrefrigerator appliance10. In the illustrated embodiment,controller11 may be located e.g., behind aninterface panel32 ordoors42 or44. Input/output (“I/O”) signals may be routed between the control system and various operational components ofrefrigerator appliance10 along wiring harnesses that may be routed through e.g., the back, sides, ormullion26. Typically, throughuser interface panel32, a user may select various operational features and modes and monitor the operation ofrefrigerator appliance10. In one embodiment, the user interface panel may represent a general purpose I/O (“GPIO”) device or functional block. In one embodiment, theuser interface panel32 may include input components, such as one or more of a variety of electrical, mechanical or electro-mechanical input devices including rotary dials, push buttons, and touch pads. Theuser interface panel32 may include a display component, such as a digital or analog display device designed to provide operational feedback to a user.User interface panel32 may be in communication withcontroller11 via one or more signal lines or shared communication busses.
• In one exemplary embodiment of the present invention, one or more temperature sensors are provided to measure the temperature in thefresh food compartment12 and the temperature in thefreezer compartment14. For example, first temperature sensor52 may be disposed in thefresh food compartment12 and may measure the temperature in thefresh food compartment12.Second temperature sensor54 may be disposed in thefreezer compartment14 and may measure the temperature in thefreezer compartment14. This temperature information can be provided, e.g., tocontroller11 for use in operatingrefrigerator10 as will be more fully discussed below. These temperature measurements may be taken intermittently or continuously during operation of the appliance and/or execution of a control system as further described below.
• Ashelf34 andwire baskets36 are also provided infreezer compartment14. In addition, anice maker38 may be provided infreezer compartment14. Afreezer door42 and afresh food door44 close access openings to freezer andfresh food compartments14,12, respectively. Eachdoor42,44 is mounted to rotate about its outer vertical edge between an open position, as shown inFIG. 1, and a closed position (not shown) closing the associated storage compartment. In alternative embodiments, one or bothdoors42,44 may be slidable or otherwise movable between open and closed positions.Freezer door42 includes a plurality ofstorage shelves46, andfresh food door44 includes a plurality ofstorage shelves48.
• Referring now toFIG. 2,refrigerator appliance10 may include arefrigeration system200. In general,refrigeration system200 is charged with a refrigerant that is flowed through various components and facilitates cooling of thefresh food compartment12 and thefreezer compartment14. For example,refrigeration system200 may include acompressor202 for compressing the refrigerant, as is generally understood, thus raising the temperature and pressure of the refrigerant.Compressor202 may for example be a variable speed compressor, such that the speed of thecompressor202 can be varied between zero and100 percent bycontroller11.Refrigeration system200 may further include acondenser204, which may be disposed downstream (in the direction of flow of the refrigerant) of thecompressor202. Thus,condenser204 may receive refrigerant from thecompressor202, and may condense the refrigerant, as is generally understood, by lowering the temperature of the refrigerant flowing therethrough due to, e.g., heat exchange with ambient air. Acondenser fan206 may be used to force air overcondenser204 as illustrated to facilitate heat exchange between the refrigerant and the surrounding air.Condenser fan206 can be a variable speed fan—meaning the speed ofcondenser fan206 may be controlled or set anywhere between and including, e.g., 0 and 100 percent. The speed ofcondenser fan206 can be determined by, and communicated to,fan206 bycontroller11.
• Refrigeration system200 may further include anevaporator210 disposed downstream of thecondenser204. Alternatively, it should be noted that condensation of the refrigerant may occur in somerefrigeration systems200 without acondenser204, such as in suitably configured conduits extending betweencompressor202 andevaporator210. Additionally, anexpansion device208 may be utilized to expand the refrigerant, thus further reduce the pressure of the refrigerant, leavingcondenser204 before being flowed toevaporator210.Evaporator210 generally is a heat exchanger that transfers heat from air passing over theevaporator210 to refrigerant flowing throughevaporator210, thereby cooling the air and causing the refrigerant to vaporize. Anevaporator fan212 may be used to force air overevaporator210 as illustrated. As such, cooled air is produced and supplied torefrigerated compartments12,14 ofrefrigerator appliance10. In one exemplary embodiment of the present invention,evaporator fan212 can be a variable speed evaporator fan—meaning the speed offan212 may be controlled or set anywhere between and including, e.g., 0 and 100 percent. The speed ofevaporator fan212 can be determined by, and communicated to,evaporator fan212 bycontroller11.
• Evaporator210 may be in communication withfresh food compartment12 andfreezer compartment14 to provide cooled air tocompartments12,14. Alternatively,refrigerator loop200 may include more two or more evaporators, such that at least one evaporator provides cooled air tofresh food compartment12 and at least one evaporator provides cooled air tofreezer compartment14. In other embodiments,evaporator210 may be in communication with any suitable component of therefrigerator appliance10. For example, in some embodiments,evaporator210 may be in communication withice maker38, such as with an ice compartment of theice maker38. Fromevaporator210, refrigerant may flow back to and throughcompressor202, which may be downstream ofevaporator210, thus completing a closed refrigeration loop or cycle.
• As shown inFIG. 2, adefrost heater214 may be utilized to defrostevaporator210, i.e., to melt ice that accumulates onevaporator210.Heater214 may be activated periodically; that is, a period of time t_iceelapses between whenheater214 is deactivated and whenheater214 is reactivated to melt a new accumulation of ice onevaporator210. The period of time t_icemay be a preprogrammed period such that time t_iceis the same between each period of activation ofheater214, or the period of time may vary, as will be further described below. Alternatively,heater214 may be activated based on some other condition, such as the temperature ofevaporator210 or any other appropriate condition.
• Additionally, adefrost termination thermostat216 may be used to monitor the temperature ofevaporator210 such that defrostheater214 is deactivated whenthermostat216 measures that the temperature ofevaporator210 is above freezing, i.e., greater than 32° F. In some embodiments,thermostat216 may send a signal tocontroller11 or other suitable device to deactivateheater214 whenevaporator210 is above freezing. In other embodiments, defrosttermination thermostat216 may comprise a switch such thatheater214 is switched off whenthermostat216 measures that the temperature ofevaporator210 is above freezing.
• As further shown inFIG. 2,refrigeration system200 may also include aloop100 that may be routed through portions ofrefrigerator appliance10. For example, referring back toFIG. 1, a portion ofloop100 may be positionedadjacent mullion24.Loop100 contains refrigerant that has been heated from being pressurized bycompressor202 and, thus, is at a higher temperature than the ambient air and/or casing ofrefrigerator10. Accordingly, as the refrigerant circulates aboutloop100, heat is released and is available for exchange with air and/or components in contact withloop100. By selecting a particular routing forloop100 withinrefrigerator10, i.e., betweenouter case16 andinner liners18,20, this heat may be made available at various locations in the refrigerator as needed for the heating of outer surfaces such asmullion24 to prevent the formation of condensation on such surfaces.
• Referring now toFIG. 3, an exemplary method for operatingrefrigerator appliance10 is illustrated, which may be performed in whole or in part bycontroller11 or any other suitable device or devices. Atstep302, defrostheater214 is activated to melt ice built up onevaporator210. Atstep304,controller11 begins counting time t_defrost, which is the time required to melt the ice built up onevaporator210. Next,controller11 determines atstep306 whetherevaporator210 has been defrosted. As described,controller11 may determine whetherevaporator210 has been defrosted by monitoringdefrost termination thermostat216, which may indicate thatevaporator210 is defrosted when the measured temperature ofevaporator210 is greater than freezing. Ifevaporator210 is not defrosted,controller11 continues to count time t_defrostand to determine whetherevaporator210 has been defrosted. However, if atstep306evaporator210 has been defrosted, defrostheater214 is deactivated atstep308 andcontroller11 stops counting time t_defrost.
• Using time t_defrost,controller11 can regulate the defrost cycle and adjust the refrigerant temperature to prevent excessive ice buildup onevaporator210 and to prevent condensation from forming on external surfaces ofrefrigerator appliance10. Atstep310 ofmethod300, time interval t_iceis established. As discussed, defrostheater214 may be activated periodically such that a period of time t_iceelapses between whenheater214 is deactivated and whenheater214 is reactivated. Time t_icemay be established based on the time t_defrostthat was required to defrost the evaporator.
• In some embodiments, a correlation between time t_defrostand time t_icemay be determined experimentally, e.g., prior to or during the manufacture ofrefrigerator appliance10, and plotted as a defrost curve that is programmed intocontroller11. As shown in the exemplary correlation ofFIG. 4, the time t_defrostrequired to defrostevaporator210 is proportional to the mass of the ice that has built up onevaporator210; that is, a longer time t_defrostis required to melt more ice. As time t_defrostincreases, time t_icebetween defrost cycles may be decreased because a larger time t_defrostindicates the environmental and use conditions are such that more ice is likely to accumulate onevaporator210, as further described below. Thus,evaporator210 should be defrosted more often (time t_iceshould be shorter) such that the operation ofevaporator210 is not hindered by the accumulation of ice. How much shorter t_iceshould be can be determined by trial and error until optimal values, i.e., the values of t_icethat best preserve the efficiency ofevaporator210, are found. That is, different values of t_icemay be used for a given time t_defrostuntil an optimal value of t_iceis determined. The optimal values for a range of times t_defrostmay then be plotted as shown inFIG. 4 and programmed intocontroller11. Alternatively, one or more equations may be derived from the correlation and programmed intocontroller11. Then, using either the curve or one or more equations derived from the correlation,controller11 may establish time t_icefor the measured time t_defrost.
• As discussed and as shown inFIG. 4, the time t_defrostrequired to defrostevaporator210 is proportional to the mass of the ice that has built up onevaporator210. Thus, the mass of ice accumulated onevaporator210 may be determined based on time t_defrostfor different environmental and use conditions. Further, experimental data for the time t_defrostrequired to defrostevaporator210 following a certain number of door openings at a certain humidity may be used to generate one or more time-moisture curves, as shown inFIG. 5. For example, in an exemplary experiment performed, e.g., prior to or during the manufacture ofrefrigerator appliance10, the environmental absolute humidity may be regulated to 0.04 lb_H2O/lb_airand following45 openings ofrefrigerator doors42,44, a defrost cycle may be initiated and t_defrostmay be measured. These measurements may be repeated for a range of absolute humidity and door opening values, and then the data may be plotted to generate one or more curves, such as the curve shown inFIG. 5. Alternatively, one or more transfer functions may be derived from the data. These curves and/or transfer functions may be programmed intocontroller11 during the manufacture ofrefrigerator10 such thatcontroller11 can regulate the operation ofrefrigerator10, as describe, without requiring, e.g., components to measure the humidity or the number of openings ofdoors42,44.
• Using time-moisture curves or functions, the relative magnitude of time t_defrostmay be ascertained, which can indicate the environmental and use conditions experienced byrefrigerator10. That is, for a given time t_defrost,controller11 may determine whether the time t_defrostis greater or less than the previous time t_defrostand how the time t_defrostcompares to the minimum and maximum times t_defrost(e.g., whether the time t_defrostis almost equal to the minimum or maximum value or whether the time t_defrostis closer to either the minimum and maximum values). The relative magnitude of time t_defrostmay indicate whetherdoors42,44 were opened more or less frequently or the humidity increased or decreased following the previous defrost cycle. Other methods of determining the relative magnitude of time t_defrostand/or the mass of ice accumulated onevaporator210 may also be used.
• Becausedefrost heater214 must be activated longer to melt a larger mass of ice, a larger value for time t_defrostindicates more ice accumulated onevaporator210 from, e.g., higher humidity and/or more frequent opening ofrefrigerator doors42,44. Likewise, if time t_defrostis a smaller value, then less ice accumulated onevaporator210. To avoid a larger time t_defrostwhendefrost heater214 is next activated (i.e., to shorten the next defrost cycle),controller11 may determine that time interval t_iceshould be shortened from the previous time interval t_ice. Accordingly, following a relatively longer defrost cycle (when time t_defrostis relatively large), the time t_iceto the next defrost cycle may be shorter. Then, if the time t_defrostof the next defrost cycle is shorter, the next time interval t_icemay be lengthened. In this way, the defrost cycles ofrefrigerator appliance10 can be adapted to the environmental and use conditions of the appliance optimize the defrosting ofevaporator210, which can provide benefits such as energy savings and reducing wear on the refrigeration components.
• After establishing time t_ice, atstep312controller11 determines whether to increase the temperature of the refrigerant flowing throughrefrigeration system200 to prevent condensation from forming on such surfaces.Controller11 may use time t_defrostto determine whether to increase the temperature of the refrigerant. Given the time that was required to defrost the evaporator and the frequency of door openings,controller11 will select the outside absolute humidity from the one or more programmed time-moisture curves to determine, at various temperatures, the rate of condensation on the exterior of thecase16 and/or other components ofrefrigerator10. As discussed, if a larger time t_defrostis required to melt the ice accumulated onevaporator210,refrigerator appliance10 may be operating in a higher humidity environment and/orrefrigerator doors42,44 may have been opened more often, which causes more ice to accumulate onevaporator210. In addition to increasing the mass of ice that builds up onevaporator210, higher humidity may cause condensation to form on the outer surfaces ofrefrigerator appliance10, such as, e.g.,breaker strip22 andmullion24, if the outer surfaces are too cool. Accordingly, if time t_defrostis sufficiently large, e.g., when compared to a time-moisture curve or used in a transfer function as described,controller11 may determine that the refrigerant temperature should be increased, andmethod300 proceeds to step314. However, if atstep312controller11 determines the temperature of the refrigerant should not be increased,method300 proceeds to step316, described below.
• To reduce condensation on the outer surfaces, the temperature of the outer surfaces may be raised by increasing the temperature of the refrigerant flowing throughrefrigeration system200 may be increased. As discussed,refrigeration system200 may includeloop100 positioned adjacent the outer surfaces ofrefrigerator appliance10 to heat such surfaces. Thus, increasing the temperature of the refrigerant circulating throughloop100 will increase the temperature of the outer surfaces.
• The refrigerant temperature may be increased in several ways. For example, the speed ofcondenser fan206 may be decreased to slow the rate of heat exchange between the refrigerant and ambient air as the refrigerant circulates throughcondenser204. In this way, the temperature of the refrigerant will not be as greatly reduced as the refrigerant passes throughcondenser204. As a further example, the speed ofcompressor202 may be increased, thereby increasing the pressure and the temperature of the refrigerant as it passes throughcompressor202 more than ifcompressor202 was operated at a lower speed. In some embodiments, both the condenser fan speed and the compressor speed may be modulated to increase the temperature of the refrigerant flowing throughrefrigeration system200. Therefore, at step314,controller11 may decrease the speed ofcondenser fan206, increase the speed ofcompressor202, or both. As appropriate,controller11 may also regulate other components ofrefrigeration system200 to increase the temperature of the refrigerant. For example, the evaporator fan speed may be increased to increase the mass flow through the compressor and the condenser, thus raising the pressure and temperature of the refrigerant flowing through the condenser. As a further example, electric heaters may also be provided for heating the external surfaces ofrefrigerator appliance10, and such heaters may be modulated to regulate moisture condensation and accumulation on external surfaces such as, e.g.,breaker strip22 andmullion24.
• After the condenser fan and/or compressor speeds are modulated to increase the refrigerant temperature, or if the refrigerant temperature does not need to be increased,controller11 waits time interval t_ice, as established atstep310, before returning to step302 and reactivatingdefrost heater214.
• This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims (19)

What is claimed is:

1. A method for operating a refrigerator appliance, the refrigerator appliance comprising a refrigeration system for cycling a refrigerant therethrough that includes a compressor, a condenser, and an evaporator, the method comprising the steps of:

activating a defrost heater configured to melt ice built up on the evaporator;

counting a time t_defrost;

determining if evaporator is defrosted and, if so, then

deactivating the defrost heater;

determining whether to increase the refrigerant temperature to prevent condensation on the external surfaces of the refrigerator appliance.

2. The method ofclaim 1, further comprising the step of decreasing the condenser fan speed if the refrigerant temperature is determined to be increased.

3. The method ofclaim 1, further comprising the step of increasing the compressor speed if the refrigerant temperature is determined to be increased.

4. The method ofclaim 1, wherein the step of determining whether to increase the refrigerant temperature comprises determining the relative magnitude of the time t_defrost.

5. The method ofclaim 1, wherein the step of determining if the evaporator is defrosted comprises monitoring a defrost termination thermostat.

6. The method ofclaim 1, further comprising the steps of:

waiting a time interval t_iceif the defrost heater is deactivated; and then reactivating the defrost heater.

7. The method ofclaim 1, further comprising the step of establishing a time interval t_iceduring the step of deactivating the defrost heater.

8. The method ofclaim 7, wherein time interval t_iceis based at least in part on time t_defrost.

9. A method for operating a refrigerator appliance, the refrigerator appliance comprising a refrigeration system for cycling a refrigerant therethrough that includes a compressor, a condenser, and an evaporator, the method comprising the steps of:

activating a defrost heater configured to melt ice built up on the evaporator;

counting a time t_defrost;

determining if evaporator is defrosted and, if so, then

deactivating the defrost heater,

waiting a time interval t_ice, and

reactivating the defrost heater;

determining whether to increase the refrigerant temperature to prevent condensation on the external surfaces of the refrigerator appliance.

10. The method ofclaim 9, further comprising the step of decreasing the condenser fan speed if the refrigerant temperature is determined to be increased.

11. The method ofclaim 9, further comprising the step of decreasing a condenser fan speed if the refrigerant temperature is determined to be increased.

12. The method ofclaim 9, wherein the step of determining whether to increase the refrigerant temperature comprises determining the relative magnitude of the time t_defrost.

13. The method ofclaim 9, wherein the step of determining if the evaporator is defrosted comprises monitoring a defrost termination thermostat.

14. The method ofclaim 9, further comprising the step of establishing the time interval t_iceduring the step of deactivating the defrost heater.

15. The method ofclaim 9, wherein time t_iceis based at least in part on time t_defrost.

16. A refrigerator appliance, comprising:

at least one compartment for storing food items;

a refrigeration system for cycling a refrigerant therethrough, the refrigeration system comprising

a compressor;

a condenser;

a condenser fan;

an evaporator; and

a defrost heater configured to melt ice accumulated on the evaporator;

a controller in operative communication with the compressor and the condenser fan, the controller configured for

activating a defrost heater configured to melt ice built up on the evaporator;

counting a time t_defrost;

determining if evaporator is defrosted and, if so, then

deactivating the defrost heater;

determining whether to increase the refrigerant temperature to prevent condensation on the external surfaces of the refrigerator appliance.

17. The refrigerator appliance ofclaim 16, wherein the controller is further configured for decreasing the condenser fan speed if the controller determines to increase the refrigerant temperature.

18. The refrigerator appliance ofclaim 16, wherein the controller is further configured for increasing the compressor speed if the controller determines to increase the refrigerant temperature.

19. The refrigerator appliance ofclaim 16, wherein the controller is further configured for

establishing a time interval t_iceduring the step of deactivating the defrost heater;

waiting time interval t_ice; and

reactivating the defrost heater,

wherein time interval t_iceis based at least in part on time t defrost.

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