FAN SPEED CONTROL FOR PREVENTING FROST CONDITION OF AN EVAPORATOR

Abstract

A water heating appliance includes: a reservoir for storing water to be heated; a refrigerant path having a compressor that directs a thermal exchange media through the refrigerant path having an evaporator that absorbs heat from process air, an evaporator fan that directs the process air across a surface of the evaporator, and a condensing coil that delivers the heat to the reservoir; a temperature sensing system that monitors a temperature of the water to be heated and a surface temperature of the evaporator; and a controller in communication with the temperature sensing system and the evaporator fan.

Claims

1. A water heating appliance comprising: a reservoir for storing water to be heated; a refrigerant path having a compressor that directs a thermal exchange media through the refrigerant path having an evaporator that absorbs heat from process air, an evaporator fan that directs the process air across a surface of the evaporator, and a condensing coil that delivers the heat to the reservoir; a temperature sensing system that monitors a temperature of the water to be heated and a surface temperature of the evaporator; and a controller in communication with the temperature sensing system and the evaporator fan, wherein the controller monitors a rate of change of the surface temperature, wherein in response to the rate of change of the surface temperature being a decreased rate, the controller compares the decreased rate to at least a rate of change of the temperature of the water to be heated, wherein in response to the decreased rate diverging from the rate of change of the temperature of the water, indicative of a frost condition, the controller operates the evaporator fan at an increased speed to direct an increased flow of the process air over the surface of the evaporator to increase the surface temperature and define the rate of change of the surface temperature to be an increased rate.

2. The water heating appliance of claim 1, further comprising: a motor operable to drive the evaporator fan at a plurality of speeds.

3. The water heating appliance of claim 2, wherein the controller operates the evaporator fan at the increased speed until a temperature difference between the surface temperature and the temperature of the water to be heated is within a threshold difference indicative of a standard operating condition.

4. The water heating appliance of claim 3, wherein the controller, in response to the temperature difference reaching the standard operating condition, operates the evaporator fan at a base speed setting of the plurality of speeds.

5. The water heating appliance of claim 4, wherein the plurality of speeds of the evaporator fan includes the base speed setting, a medium speed setting that is faster than the base speed setting, and a high speed setting that is faster than the medium speed setting.

6. The water heating appliance of claim 2, wherein the evaporator fan includes an air funnel that directs the process air over the surface of the evaporator at an even rate, the air funnel having an inner surface that maintains an air pressure of the process air to be generally consistent within the evaporator.

7. The water heating appliance of claim 6, wherein the air funnel includes a pressure regulation portion that is downstream of the evaporator, wherein the pressure regulation portion operates to gradually and evenly decrease the air pressure of the process air between a pressure maintenance portion and a converging section that defines a rounded port.

8. The water heating appliance of claim 7, wherein the pressure regulation portion and the converging section operate to evenly increase an air velocity of the process air as it moves between the evaporator and the evaporator fan in each speed setting of the plurality of speeds.

9. The water heating appliance of claim 1, wherein the temperature sensing system measures the temperature of the water at a lower portion of the reservoir.

10. A heat pump system for a water heating appliance, the heat pump system comprising: a refrigerant path that includes an evaporator that absorbs heat from process air, an evaporator fan that directs the process air across coils of the evaporator, a compressor for directing a thermal exchange media through the refrigerant path, and a condenser that includes a condensing coil and water to be heated; and a controller that monitors a surface temperature of a surface of the coils, a rate of change of the surface temperature, a temperature difference between a media temperature of the water to be heated and the surface temperature, and a rate of change of the temperature difference, wherein in response to a rate of change of the surface temperature defining a decreased rate, the controller compares the decreased rate to at least a rate of change of the temperature difference, wherein in response to the rate of change of the temperature difference being beyond a threshold rate, indicative of a frost condition, the controller increases a speed of the evaporator fan to deliver additional process air across the surface of the coils, wherein the additional process air operates to increase the surface temperature of the coils of the evaporator and decrease the temperature difference to be within a standard operating condition.

11. The heat pump system of claim 10, wherein a motor of the evaporator fan defines a plurality of speeds of the evaporator fan, and wherein the controller operates the motor of the evaporator fan based upon a rate of change that the temperature difference increases beyond the threshold rate.

12. The heat pump system of claim 11, wherein the controller operates the motor of the evaporator fan at an increased speed of the plurality of speeds until the temperature difference is below the threshold rate.

13. The heat pump system of claim 11, wherein the controller, in response to the temperature difference reaching the standard operating condition, operates the evaporator fan at a base speed setting of the plurality of speeds.

14. The heat pump system of claim 13, wherein the plurality of speeds includes the base speed setting, a medium speed setting that is faster than the base speed setting, and a high speed setting that is faster than the medium speed setting.

15. The heat pump system of claim 10, wherein the evaporator fan includes an air funnel that directs the process air over a surface of the evaporator at an even rate, the air funnel having an inner surface that maintains an air pressure of the process air to be generally consistent within the evaporator.

16. The heat pump system of claim 15, the air funnel having a pressure regulation portion that is downstream of the evaporator, wherein the pressure regulation portion operates to gradually and evenly decrease the air pressure of the process air between a pressure maintenance portion and a converging section that defines a rounded port.

17. A water heating appliance comprising: a refrigerant path having a compressor that directs a thermal exchange media through the refrigerant path, the refrigerant path having an evaporator that absorbs heat from process air, an evaporator fan that directs the process air across a surface of the evaporator, and a condensing portion that delivers the heat to water within a reservoir; a temperature sensing system that monitors a media temperature of the water and a surface temperature of the evaporator; and a controller in communication with the temperature sensing system to determine a rate of change of the surface temperature, wherein in response to the rate of change of the surface temperature defining a decreased rate, the controller compares the decreased rate to a temperature difference between the media temperature and the surface temperature and a rate of change of the temperature difference, wherein in response to the rate of change of the temperature difference increasing to a frost condition, the controller operates a motor of the evaporator fan to increase the flow of the process air across the surface of the evaporator to increase the surface temperature of the evaporator and decrease the temperature difference to be below a threshold difference and within a standard operating condition, wherein in response to the temperature difference reaching the standard operating condition, the controller operates the motor of the evaporator fan to decrease the flow of the process air across the surface of the evaporator.

18. The water heating appliance of claim 17, wherein the motor of the evaporator fan defines a plurality of speeds of the evaporator fan.

19. The water heating appliance of claim 18, wherein the controller operates the motor of the evaporator fan based upon the rate of change of the surface temperature and the temperature difference.

20. The water heating appliance of claim 17, wherein the evaporator fan includes an air funnel that directs the process air over the surface of the evaporator at an even rate, the air funnel having an inner surface that maintains an air pressure of the process air to be generally consistent within the evaporator, wherein the air funnel includes a pressure regulation portion that is downstream of the evaporator, and wherein the pressure regulation portion operates to gradually and evenly decrease the air pressure of the process air between a pressure maintenance portion and a converging section that defines a rounded port that is coupled to a housing for the evaporator fan.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In the drawings:

[0009] FIG. 1 is a perspective view of a water heating appliance that incorporates a heat pump system having an aspect of a fan speed control;

[0010] FIG. 2 is a side elevation view of the water heating appliance of FIG. 1;

[0011] FIG. 3 is a top plan view of the water heating appliance of FIG. 1;

[0012] FIG. 4 is an exploded perspective view of an upper portion of the water heating appliance of FIG. 1 that contains the heat pump system having an aspect of an air funnel and an aspect of the fan speed control;

[0013] FIG. 5 is a cross-sectional view of the water heating appliance of FIG. 2 taken along line V-V;

[0014] FIG. 6 is a cross-sectional view of the water heating appliance of FIG. 1 taken along line VI-VI;

[0015] FIG. 7 is a cross-sectional view of the water heating appliance of FIG. 1 taken along line VII-VII;

[0016] FIG. 8 is a schematic diagram illustrating an aspect of the heat pump system that incorporates the fan speed control for limiting the occurrence of the frost condition;

[0017] FIG. 9 is a schematic diagram illustrating operation of the fan speed control utilizing a temperature sensing system;

[0018] FIG. 10 is a schematic flow diagram illustrating a method for operating a fan speed control that addresses a frost condition of an evaporator; and

[0019] FIG. 11 is a schematic flow diagram illustrating a method for operating a fan speed control that addresses a frost condition of an evaporator.

[0020] The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles described herein.

DETAILED DESCRIPTION

[0021] As required, detailed embodiments of the present disclosure are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to a detailed design; some schematics may be exaggerated or minimized to show function overview. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

[0022] For purposes of description herein, the terms upper, lower, right, left, rear, front, vertical, horizontal, and derivatives thereof shall relate to the concepts as oriented in FIG. 1. However, it is to be understood that the concepts may assume various alternative orientations, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.

[0023] The present illustrated embodiments reside primarily in combinations of method steps and apparatus components related to a heat pump system for a water heating appliance, and more specifically, to a fan speed control for preventing a frost condition within an evaporator for the heat pump system. Accordingly, the apparatus components and method steps have been represented, where appropriate, by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Further, like numerals in the description and drawings represent like elements.

[0024] As used herein, the term and/or, when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items, can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

[0025] In this document, relational terms, such as first and second, top and bottom, and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms comprises, comprising, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element preceded by comprises . . . a does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0026] As used herein, the term about means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. When the term about is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point referred to. Whether or not a numerical value or end-point of a range in the specification recites about, the numerical value or end-point of a range is intended to include two embodiments: one modified by about, and one not modified by about. It will be further understood that the end-points of each of the ranges are significant both in relation to the other end-point, and independently of the other end-point.

[0027] The terms substantial, substantially, and variations thereof as used herein are intended to note that a described feature is equal or approximately equal to a value or description. For example, a substantially planar surface is intended to denote a surface that is planar or approximately planar. Moreover, substantially is intended to denote that two values are equal or approximately equal. In some embodiments, substantially may denote values within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.

[0028] As used herein the terms the, a, or an, mean at least one, and should not be limited to only one unless explicitly indicated to the contrary. Thus, for example, reference to a component includes embodiments having two or more such components unless the context clearly indicates otherwise.

[0029] Referring to FIGS. 1-8, reference numeral 10 generally designates a heat pump system incorporated within a water heating appliance 12. The heat pump system 10 utilizes a thermal exchange media 14 for transferring heat 16 collected within an evaporator 18 and into a media, such as water 20, that is to be heated within a reservoir 22. The heat pump system 10 can be utilized within a tank-type water heating appliance, or within a tankless-type water heating appliance. Additionally, certain hybrid configurations of water heaters can utilize the heat pump system 10 that may include a reservoir 22 of water 20 to be heated, as well as a tankless-component of a water heating appliance 12.

[0030] Referring again to FIGS. 1-8, the water heating appliance 12 includes the reservoir 22 for storing a fluid, typically water 20, to be heated. The heat pump system 10 includes a refrigerant path 40 that includes a compressor 42 that directs a thermal exchange media 14 through the refrigerant path 40. The refrigerant path 40 includes the evaporator 18 that absorbs heat 16 from ambient air 44. An evaporator fan 46, which can include a blower 48 having a blower housing 50, directs the ambient air 44 across a surface 52 of coils 54 for the evaporator 18. A condensing portion 56, which can include one or more coils 54, is included within the heat pump system 10 that delivers the heat 16, absorbed by the evaporator 18, to the reservoir 22. This heat 16, in turn, is delivered from the thermal exchange media 14 within the coils 54 off the condensing portion 56 and into the water 20 being heated therein. A temperature sensing system 58 monitors a media temperature 60 of the water 20 being heated as well as a temperature of the evaporator 18, typically in the form of a surface temperature 62 of the coils 54 for the evaporator 18. A controller 64 is in communication with the temperature sensing system 58 and the evaporator fan 46. The controller 64 monitors a temperature difference 66 between the media temperature 60 of water 20 within the reservoir 22 and the surface temperature 62 of the coils 54 for the evaporator 18. The controller 64 also monitors a rate of change 92 of the surface temperature 62. In response to the rate of change 92 of the surface temperature 62 defining a decreased rate 80, the controller 64 monitors a rate of change 92 of the temperature difference 66. The rate of change 92 of the temperature difference 66 exceeding a threshold rate 82, in combination with the decreased rate 80, is typically indicative of a frost condition 70. When the frost condition 70 is determined, the controller 64 operates a motor 72 for the evaporator fan 46 to direct additional amounts of ambient air 44 over the surface 52 of the evaporator 18, typically through an increased speed 76 of the evaporator fan 46. The increased airflow 74 of ambient air 44 over the evaporator 18 serves to increase the surface temperature 62 of the coils 54 for the evaporator 18. Additionally, the increase in the surface temperature 62 of the coils 54 for the evaporator 18 modifies the rate of change 92 of the surface temperature 62 from the decreased rate 80, indicative of the frost condition 70, to an increased rate 96. The increased airflow 74 of ambient air 44 over the evaporator 18 also decreases the temperature difference 66 between the media temperature 60 of the water 20 within the reservoir 22 and the surface temperature 62 of the coils 54 for the evaporator 18. The evaporator fan 46 is operated at the increased speed 76 until such time as the temperature difference 66 is below the threshold difference 68 indicative of a standard operating condition 78 of the evaporator 18 and the heat pump system 10.

[0031] In the context of the device, as disclosed herein, the term decreased rate 80 refers to a variation in the rate of change that produces a lesser rate of increase of the surface temperature 62 of the evaporator 18. Additionally, the decreased rate 80 can also refer to a negative rate of change where the surface temperature 62 of the evaporator 18 decreases. This can also be referred to as a negative rate of change, a negative slope, a cooling rate of change, or other similar terminology. The decreased rate 80 with respect to the rate of change of the surface temperature 62 is described herein to mark the conditions where the controller 64 looks to other operating parameters of the heat pump system 10 for verifying the existence of a frost condition 70. The decreased rate 80, described herein, is typically the initial indicator of the frost condition 70. Once this initial indicator is determined, the controller 64 looks to other temperature and operational readings for verification that the frost condition 70 is in its beginning stages or the frost condition 70 is presently occurring.

[0032] The motor 72 for the evaporator fan 46 can be a multi-speed fan that is configured to operate at a plurality of speeds 90 of the evaporator fan 46. The controller 64 operates the motor 72 of the evaporator fan 46 based upon a rate of change 92 that the temperature difference 66 changes, typically increasing, which is indicative of the frost condition 70. Minor fluctuations in the temperature difference 66 between the media temperature 60 of the water 20 and the surface temperature 62 of the coils 54 of the evaporator 18 can occur in the standard operating condition 78 of the heat pump system 10. Where the rate of change 92 of the temperature difference 66 includes a more rapid rate of change 92, this can be indicative of an onset of a frost condition 70 or the occurrence of a frost condition 70. In these more drastic rates of change 92, the frost condition 70 can be marked by a lesser increase in the media temperature 60, in combination with a decrease in the surface temperature 62 of the coils 54 for the evaporator 18. This type of change in the temperature difference 66, indicative of the frost condition 70, is reflected by a rapid rate of change 92 in the temperature difference 66.

[0033] In certain aspects of the device, the temperature difference 66 can be used to set the speed of the motor 72 for the evaporator fan 46. By way of example, and not limitation, where the decreased rate 80 of the surface temperature 62 decreases rapidly and the temperature difference 66, in turn, increases rapidly, the controller 64 can operate the motor 72 at a high speed setting 94 to generate a high degree of airflow 74 of ambient air 44 across the surface 52 of the evaporator 18. By increasing the airflow 74 of this warmer ambient air 44 across the evaporator 18, the surface temperature 62 of the evaporator 18 tends to increase, thereby preventing frost condition 70, or, if needed, decreasing the amount of frost on the evaporator 18. Stated another way, increasing the airflow 74 of the ambient air 44 across the evaporator 18 causes the evaporator 18 to absorb greater amounts of heat 16. While absorbing greater amounts of heat 16, the surface temperature 62 of the evaporator 18 tends to increase, thereby preventing, or mitigating, a frost condition 70 of the evaporator 18.

[0034] In addition, the speed of the motor 72 can be determined by the effect of a previous increase in the speed of the motor 72 for the evaporator fan 46. Where the frost condition 70 is recognized by the controller 64, the temperature sensing system 58 continues to monitor the rate of change 92 of the surface temperature, the temperature difference 66, and the rate of change 92 in the temperature difference 66. Where the increase in speed of the motor 72 for the evaporator fan 46 does not result in a change in the rate of change 92 of the surface temperature 62 to be the increased rate 96, or a decrease in the temperature difference 66, or a decrease in the rate of change 92 in the temperature difference 66, the controller 64 can operate the motor 72 and the evaporator fan 46 to further increase the speed of the motor 72 to direct greater amounts of ambient air 44 over the coils 54 for the evaporator 18. It is contemplated that further increases in the speed of the motor 72 can be utilized where needed, depending on the design of the heat pump system 10 and the motor 72 of the evaporator fan 46. When the surface temperature 62 increases at the increased rate 96, the rate of change 92 of the surface temperature 62 for the evaporator 18 will be greater than the rate of change 92 of the media temperature 60 for the water 20 to be heated within the reservoir 22. When the surface temperature 62 increases relative to the media temperature 60 to define the threshold difference 68, the temperature difference 66 again defines the standard operating condition 78 and the evaporator fan 46 is again operated at the base speed setting 110.

[0035] In the various aspects of the device, the motor 72 is a variable speed motor that can be controlled, typically by the controller, to operate according to the plurality of speeds 90 through discrete steps, or through a gradual increase and decrease of speeds. In certain aspects of the device, the motor 72 for the evaporator fan 46 is a variable speed motor with infinitely variable speed control. In such an aspect of the device, the motor 72 can be operated through the plurality of speeds 90, which can include a range of precise and continuously variable speed settings.

[0036] Referring now to FIGS. 5-9, the controller 64 operates the motor 72 for the evaporator fan 46 to define the plurality of speeds 90 of the evaporator fan 46. Under the standard operating condition 78, the controller 64 operates the motor 72 for the evaporator fan 46 at a base speed setting 110. As discussed herein, for the fan speed control system 188, the controller 64 can operate the motor 72 of the evaporator fan 46 based on the rate of change 92 of the surface temperature and at least partially based upon the temperature difference and the rate of change 92 of the temperature difference 66 between the media temperature 60 of the water 20 within the reservoir 22 and the surface temperature 62 of the coils 54 for the evaporator 18. Where the surface temperature 62 changes at the decreased rate 80 and the temperature difference 66 increases minimally, the controller 64 can operate the evaporator fan 46 at a medium speed setting 112 that is faster than the base speed setting 110. Additionally, where the surface temperature 62 changes at the decreased rate 80 and the temperature difference 66 increases at a higher rate, the controller 64 can operate the motor 72 for the evaporator fan 46 at the high speed setting 94, which is faster than the medium speed setting 112, to greatly increase the amount of ambient air 44, and heat 16, moving over the surface 52 of the evaporator 18. When the temperature difference 66 returns to the standard operating condition 78, the controller 64 can instruct the motor 72 for the evaporator fan 46 to return to the base speed setting 110 indicative of a normal operation of the heat pump system 10.

[0037] Referring again to FIGS. 1-7, the water heating appliance 12 includes an outer housing 120 that encloses the various components of the heat pump system 10, the reservoir 22 and other components of the water heating appliance 12. The water heating appliance 12 includes an upper housing 124 that encloses components of the heat pump system 10. The water heating appliance 12 also includes a lower housing 126 that encloses the reservoir 22 for storing water 20 and maintaining the temperature of the heated water 20. The upper housing 124 of the water heating appliance 12 includes an air inlet 128 and an air outlet 130 that are each positioned, typically, within a top wall 132 of the upper housing 124. These apertures provide for the expedient movement of process air 162, typically in the form of ambient air 44, through the upper housing 124 to be acted upon by the evaporator fan 46 and the evaporator 18 of the heat pump system 10.

[0038] Referring again to FIGS. 1-7, the heat pump system 10 includes the evaporator 18 that receives the thermal exchange media 14, typically from an expansion device 150. The thermal exchange media 14 leaving the evaporator 18 is heated within the coils 54 of the evaporator 18 by absorbing the heat 16 from the ambient air 44. The thermal exchange media 14, containing the absorbed heat 16 from the ambient air 44, is then directed to the compressor 42. The thermal exchange media 14 leaving the compressor 42 is pressurized, heated, and typically in the form of gas. This form of the thermal exchange media 1 is then directed to the condensing portion 56 of the heat pump system 10, such as the coils 54 of the condensing portion 56, where heat 16 from the thermal exchange media 14 is rejected into a separate media. In the case of the water heating appliance 12, the condensing portion 56 is typically in the form of the coils 54 of the condensing portion 56 that act on the reservoir 22. The media being heated is water 20 to be heated in the reservoir 22, or a conduit of water 20 that is heated as it moves through the condensing portion 56 of the heat pump system 10. After leaving the condensing portion 56 of the heat pump system 10, the thermal exchange media 14 is delivered to the expansion device 150 where the thermal exchange media 14 is converted to a cooled liquid form. This cooled liquid form of the thermal exchange media 14 is then delivered into the evaporator 18 of the heat pump system 10 to receive additional amounts of heat 16 from the ambient air 44. This heat 16 can then be transferred to the condensing portion 56 of the heat pump system 10. This process continues to move heat 16 from the ambient air 44 and to the water 20 within the reservoir 22.

[0039] Typically, the compressor 42, the evaporator 18, and the expansion device 150 are located within the upper housing 124 of the water heating appliance 12. The condensing portion 56 of the heat pump system 10 is typically located in the lower housing 126 proximate the reservoir 22 of water 20 to be heated. Other locations of these components are also contemplated.

[0040] Referring again to FIGS. 3-7, the evaporator 18 of the heat pump system 10 is positioned adjacent to the blower 48 such that the process air 162, typically in the form of the flow of ambient air 44, can move through the evaporator 18. In this configuration, heat 16 is extracted from the process air 162 and delivered into the thermal exchange media 14 via the evaporator 18. The even movement of process air 162 through the evaporator 18, which is typically generated by an air funnel 164, ensures that the process air 162 moves through the evaporator 18 at an even and consistent rate. In this manner, a maximum amount of heat 16 can be extracted from the process air 162 delivered into the thermal exchange media 14.

[0041] According to the various aspects of the device, it is contemplated that the thermal exchange media 14 can be in the form of refrigerant, water, air, glycol, and other similar substances that are effective at absorbing and releasing heat 16 within a heat pump system 10.

[0042] The temperature sensing system 58 for the heat pump system 10 includes a plurality of temperature sensors 180 that are positioned in communication with portions of the heat pump system 10. For monitoring the surface temperature 62 of the coils 54 for the evaporator 18, an evaporator sensor 182 is positioned on an upstream portion of the coils 54 for the evaporator 18, near the expansion device 150. For monitoring a media temperature 60 of the water 20 within the reservoir 22, a media sensor 184 is positioned on or within the reservoir 22 for measuring the media temperature 60 within the reservoir 22. The water 20 within a lower portion 186 of the reservoir 22 can be used for consistently and accurately monitoring the media temperature 60 of the water 20. As the heat pump system 10 operates, the water 20 within the reservoir 22 is heated. Through the process of convection, the warmer water 20 tends to rise within the reservoir 22 and cooler water 20 tends to descend within the reservoir 22 causing a mixing of the heated and cooled water 20 within the reservoir 22. By monitoring the media temperature 60 of the water 20 within the lower portion 186 of the reservoir 22, a more accurate temperature reading is provided for use in the fan speed control system 188. Additional temperature sensors 180 can be located within an airflow path 190 for monitoring a temperature of the ambient air 44, on a position of the refrigerant path 40 upstream of the compressor 42, a position of the refrigerant path 40 downstream of the compressor 42, an upper portion 192 of the reservoir 22, and other sections of the heat pump system 10. For purposes of implementing an aspect of the fan speed control system 188, as described herein, the evaporator sensor 182 and the media sensor 184 are typically utilized for measuring the temperature difference 66 between the media temperature 60 of the water 20 within the reservoir 22 and the surface temperature 62 of the coils 54 for the evaporator 18.

[0043] Referring again to FIGS. 3-9, during operation of the heat pump system 10, the controller 64 operates the motor 72 of the evaporator fan 46 through the plurality of speeds 90. As discussed herein, under the standard operating condition 78, the motor 72 operates at the base speed setting 110 of the plurality of speeds 90. When the rate of change 92 of the surface temperature 62 is defined by the decreased rate 80, and when the temperature difference 66 exceeds the threshold difference 68 between the media temperature 60 and the surface temperature 62 to indicate a frost condition 70, the controller 64 operates the motor 72 at an increased speed 76 to increase the flow of ambient air 44 across the coils 54 for the evaporator 18. The controller 64 operates the motor 72 at this increased speed 76 until the temperature difference 66 returns to the threshold difference 68, or below the threshold difference 68, that is indicative of the standard operating condition 78. Stated another way, when the temperature difference 66 returns to the standard operating condition 78, the controller 64 will again operate the motor 72 for the evaporator fan 46 at the base speed setting 110.

[0044] According to the various aspects of the device, as illustrated in FIGS. 8 and 9, fluctuations occur in the media temperature 60 and the surface temperature 62. Typically, these changes happen contemporaneously such that the temperature difference 66 between the media temperature 60 and the surface temperature 62 remains at a generally consistent amount. As exemplified in FIG. 9, the center of the graph is indicative of a draw of water 20 from the reservoir 22. After this draw of water 20 occurs, additional water 20 from a municipal water supply, well, or other outside source is added to the reservoir 22. This addition of water decreases the media temperature 60 such that the heat pump system 10 activates to increase the temperature of the water 20. During this activation of the heat pump system 10, the surface temperature 62 of the coils 54 for the evaporator 18 and the media temperature 60 of the water 20 within the reservoir 22 both increase, with the media temperature 60 generally increasing at a faster rate. Under the standard operating condition 78, this similar rate of increase is typical and produces the temperature difference 66 being at or below the threshold difference 68, as shown on the left half of the graph.

[0045] During operation of the water heating appliance 12, fluctuations in the surface temperature 62 can be severe or drastic when measured over short periods of time, such as seconds or approximately one minute. To account for these drastic localized changes, the controller 64 can calculate averages of the surface temperature 62 to arrive at the surface temperature 62 and the rate of change 92 of the surface temperature 62. It is contemplated that the surface temperature 62 can be measured frequently, such as from approximately every few seconds to approximately every minute. Several of these measurements can be averaged together to arrive at the surface temperature 62 and the rate of change 92 of the surface temperature 62. The averaging calculation can be performed for approximately every five minutes to approximately every 30 minutes to arrive at the surface temperature 62 and the rate of change 92 of the surface temperature 62.

[0046] Referring again to FIG. 9, during a frost condition 70, which is exemplified, in a non-limiting manner on the right side of the graph, the surface temperature 62 of the coils 54 for the evaporator 18, sometimes referred to as the saturated suction temperature or the evaporating temperature, increases only marginally. This marginal increase in the surface temperature can be indicative of an onset of or precursor to a frost condition 70. As the condition persists, the surface temperature 62 begins to decrease, which can be indicative of the frost condition 70. At the same time, the media temperature 60 of the water 20 within the reservoir 22 increases. This creates a greater temperature difference 66 beyond the threshold difference 68. Stated another way, the rate of change 92 of the surface temperature 62 (the decreased rate 80) and the rate of change 92 of the media temperature 60 (increasing) diverge from one another resulting in a consistently increasing temperature difference 66. The diverging rates of change 92 and the increased temperature difference 66 are each indicative of the frost condition 70. This condition, in combination with the decreasing rate of the surface temperature 62 below the threshold rate 82, can activate the controller 64 to operate the evaporator fan 46 at one of the medium speed setting 112 or the high speed setting 94. Operation of the medium speed setting 112 or the high speed setting 94 can depend upon the decreasing rate of the surface temperature 62 and the rate of change 92 of the temperature difference 66, as well as the degree of variance between the surface temperature 62 of the coils 54 and the media temperature 60 of the water 20 within the reservoir 22. A greater rate of change 92 in the temperature difference 66, resulting in a greater variation between the surface temperature 62 of the coils 54 and the media temperature 60 of the water 20, can cause the controller 64 to activate the high speed setting 94 of the motor 72. Where the temperature difference 66 is only minimally beyond the threshold difference 68, the controller 64 can operate the motor 72 for the evaporator fan 46 at the medium speed setting 112.

[0047] Typically, the plurality of speeds 90 of the motor 72 for the evaporator fan 46 includes the base speed setting 110, the medium speed setting 112 that is faster than the base speed setting 110, and a high speed setting 94 that is faster the medium speed setting 112. It is contemplated that additional speed settings can be included within the fan speed control system 188 based upon the design of the heat pump system 10 and the water heating appliance 12.

[0048] Referring again to FIGS. 8 and 9, during operation of the heat pump system 10, the media sensor 184 and the evaporator sensor 182 monitor the temperatures of the water 20 within the reservoir 22 and the surface temperature 62 of the coils 54, respectively. During the standard operating condition 78, the temperature difference 66 between the media temperature 60 and the surface temperature 62 maintains a generally consistent temperature difference 66 within the threshold difference 68. In certain conditions, the surface temperature 62 may have a rate of change 92 that is the decreasing rate, and the media temperature 60 experiences a similar decrease, which is typically at a more accelerated rate of change 92. An example of such a condition may be where there is a draw of water 20 from the reservoir 22 and cool or cold water 20 is added to the reservoir 22 to replace the used water 20. In such a situation, the frost condition 70 is not present and the controller 64 will maintain the motor 72 at the base speed setting 110.

[0049] Referring again to FIGS. 8 and 9, under certain conditions, this temperature difference 66 between the surface temperature 62 and the media temperature 60 can increase. Typically, this increase in the temperature difference 66 occurs when airflow 74 through the evaporator 18 is impeded by some obstruction. In the case of a frost condition 70, the formation of ice crystals on the coils 54 for the evaporator 18 can impede the flow of ambient air 44 through the evaporator 18. When ambient air 44 is unable to move across sections of the evaporator 18, heat 16 may not be absorbed from ambient air 44 into thermal exchange media 14 via the coils 54 of the evaporator 18. This results in the surface temperature 62 of the coils 54 decreasing, or not increasing at an appropriate rate, due to the decreased amount of heat 16 surrounding at least some portions of the evaporator 18. This condition can become exacerbated as lesser amounts of ambient air 44 are able to move past portions of the evaporator 18 and ice crystals may form more rapidly around more of the evaporator 18. This can result in the rate of change 92 in the surface temperature 62 defining a decreased rate 80. Contemporaneously, the media sensor 184 of the temperature sensing system 58 may indicate a consistent temperature or slightly increasing temperature of the water 20 within the reservoir 22. Conversely, the surface temperature 62 of the coils 54 will tend to decrease at the decreased rate 80, thereby increasing the temperature difference 66 between the media temperature 60 and the surface temperature 62, and possibly the rate of change 92 of the temperature difference 66.

[0050] Referring again to FIG. 9, at the initial stages of this increase in the temperature difference 66 between the media temperature 60 and the surface temperature 62, and the rate of change 92 of the surface temperature 62 being the decreasing rate, the fan speed control system 188 can be operated where the controller 64 operates the motor 72 for the evaporator fan 46 at one of the increased speeds 76. Initially, the controller 64 may operate the motor 72 at the medium speed setting 112 to moderately increase the amount of ambient air 44 moving across the coils 54 for the evaporator 18. The increased flow of ambient air 44 also results in an increased amount of heat 16 that can be absorbed by the evaporator 18. As described herein, this increased amount of heat 16 moving over the coils 54 and being absorbed by the evaporator 18 also increases the surface temperature 62 of the coils 54 for the evaporator 18. Using this system, the increased surface temperature 62 results in preventing the formation and/or the melting of ice crystals that may have accumulated on the surface 52 of the coils 54 for the evaporator 18.

[0051] Referring again to FIG. 9, where the medium speed setting 112 may be inadequate for mitigating the increase in temperature difference 66 between the media temperature 60 and the surface temperature 62, the controller 64 can operate the motor 72 at the high speed setting 94 to greatly increase the flow of ambient air 44 moving across the evaporator 18. This greater increase of ambient air 44 results in a greater amount of heat 16 that can be absorbed by the evaporator 18, thereby further increasing the surface temperature 62 of the coils 54 for the evaporator 18. As discussed herein, this has the effect of decreasing the temperature difference 66. When the temperature difference 66 has returned to within the threshold difference 68, indicative of the standard operating condition 78, the controller 64 can again operate the motor 72 for the evaporator fan 46 at the base speed setting 110.

[0052] Referring to FIGS. 1-9, according to the various aspects of the device, the heat pump system 10 for the water heating appliance 12 includes the heat exchange loop that includes the evaporator 18 that absorbs heat 16 from ambient air 44. The evaporator fan 46 directs the ambient air 44 across the coils 54 for the evaporator 18. The compressor 42 is used for directing the thermal exchange media 14 through the refrigerant path 40. The compressor 42 receives the heat 16, via the thermal exchange media 14, from the evaporator 18 and delivers this heat 16 to the water 20 to be heated within the reservoir 22. The controller 64 monitors the temperature difference 66 between the media temperature 60 of the water 20 to be heated within the reservoir 22 and the surface temperature 62 of the surface 52 of the coils 54 for the evaporator 18. The measurement of the media temperature 60 and the surface temperature 62 defines the temperature difference 66. An increase in the temperature difference 66 can be indicative of the frost condition 70. In response to the temperature difference 66 exceeding the threshold difference 68 and reaching the frost condition 70, the controller 64 increases the speed of the motor 72 for the evaporator fan 46 to deliver additional ambient air 44 across the surface 52 of the coils 54 for the evaporator 18. The additional ambient air 44 operates to increase the surface temperature 62 of the coils 54, thereby decreasing the temperature difference 66 to be within the standard operating condition 78, the temperature difference 66 of the standard operating condition 78 being less than the temperature difference 66 of the frost condition 70.

[0053] According to various aspects of the device, the heat pump system 10 can include the air funnel 164 that is configured to maintain a consistent and even air pressure 200 and a consistent and even air velocity 202 within the evaporator 18. To maximize the capture of heat 16 from within the evaporator 18 during the standard operating condition 78 and during operation of the fan speed control system 188 for mitigating the frost condition 70, the even and consistent movement of process air 162 through the entirety of the evaporator 18 is useful for preventing and mitigating a frost condition 70. This even and consistent movement of process air 162 serves to increase the efficiency of the heat pump system 10 to deliver heat 16 into the water 20 to be heated within the reservoir 22. The air funnel 164, as described more fully herein, includes a series of sections that operate sequentially to maintain the substantially even and consistent air pressure 200 within the evaporator 18, and to also maintain a substantially consistent decline of air pressure 200 of the process air 162 as it moves between a downstream surface 210 of the evaporator 18 and through a port 212 of the air funnel 164, and into the evaporator fan 46. Typically the evaporator fan 46 includes the motor 72 that rotates the blower 48 within a blower housing 50. During operation of the evaporator fan 46, the air funnel 164 assists in directing the process air 162 moving between an upstream surface 214 of the evaporator 18 and the downstream surface 210 of the evaporator 18. As described herein, the air funnel 164 maintains a consistent and even air pressure 200 and air velocity 202 within the evaporator 18. This configuration minimizes the occurrence of a pressure drop of the process air 162 within the evaporator 18. The existence of a pressure drop can be indicative of a lack of airflow 74 within a portion of the evaporator 18. In this manner, by maintaining the airflow 74 to be consistent and even, the entirety of the evaporator 18 or substantially all of the evaporator 18 can be utilized for transferring heat 16 from the process air 162 and into the thermal exchange media 14 for moving through the evaporator 18 of the heat pump system 10.

[0054] Referring again to FIGS. 4-7, the air funnel 164 that is attached to the evaporator 18 includes a transition section 230 that engages the evaporator 18. This transition section 230 includes a pressure maintenance portion 232 and a pressure regulation portion 234. The pressure maintenance portion 232 of the air funnel 164 is positioned around the evaporator 18 such that the pressure maintenance portion 232 operates to maintain the air pressure 200 and air velocity 202 of the process air 162 moving through the evaporator 18 to be at a consistent and even rate. Subsequently, the pressure regulation portion 234 of the transition section 230 operates on the process air 162 leaving the evaporator 18 to manage the transfer of the process air 162 between the downstream surface 210 of the evaporator 18 and the port 212 that is coupled with and leads into the blower 48 for the evaporator fan 46. The geometry of this pressure regulation portion 234 of the air funnel 164 collects the flow 160 of process air 162 from the rectangular evaporator and generates a consistent and even decrease in air pressure 200, as well as a consistent and even increase in air velocity 202, of the process air 162 as the process air 162 transitions to the rounded port 212, typically in the form of a rounded port 212, that leads to the evaporator fan 46. This phenomena, as commonly referred to as a Venturi effect, is caused by a narrowing of a flow 160 of the process air 162 moving through space. The pressure regulation portion 234 of the air funnel 164 manages the Venturi effect to ensure that, as the process air 162 moves through the pressure regulation portion 234, each section of the flow 160 of process air 162 experiences a similar decrease in air pressure 200 and increase in air velocity 202 as it approaches the port 212. This even and consistent movement of the process air 162 minimizes pressure drop and, in turn, minimizes locations where the evaporator 18 is not absorbing a sufficient amount of heat 16 to prevent a frost condition 70.

[0055] Referring again to FIGS. 1-7, the air funnel 164 also includes a converging section 250 that is downstream of the transition section 230 and forms the rounded port 212 that directs the process air 162 into the blower 48. This converging section 250 of the air funnel 164 directs the process air 162 from the transition section 230 and into an inner perimeter 252 of the port 212. Once through the port 212, the process air 162 is moved by the blower 48 through the air outlet 130 and out of the upper housing 124.

[0056] Referring again to FIGS. 3-7, the pressure maintenance portion 232 of the air funnel 164 extends across a depth 270 of the evaporator 18 between the upstream surface 214 of the evaporator 18 and the downstream surface 210 of the evaporator 18. It is contemplated that this pressure maintenance portion 232 is substantially rectangular to match the profile of the evaporator 18. In certain aspects of the device, the pressure maintenance portion 232 can also extend at least partially into the space of the air funnel 164 that is immediately adjacent to the downstream surface 210 of the evaporator 18. This pressure maintenance portion 232 of the air funnel 164 can be defined by a flange 274 of the air funnel 164 that engages the rectangular outer edge 272 of the evaporator 18. This flange 274 can engage a single surface of the evaporator 18. Additionally, the flange 274 can extend around multiple surfaces of the outer edge 272 of the evaporator 18 to encircle a portion of the evaporator 18 or the entirety of the outer edge 272 of the evaporator 18.

[0057] According to various aspects of the device, the pressure regulation portion 234 of the air funnel 164 includes a concave shape that is positioned to extend from the downstream surface 210 of the evaporator 18. This pressure regulation portion 234 includes a cross-sectional profile that is generally in the shape of a parabolic arc that proceeds from the rectangular downstream surface 210 of the evaporator 18 and toward the circular converging section 250 the air funnel 164. This parabolic curvature of the pressure regulation portion 234 operates to gradually and evenly decrease the air pressure 200 of the process air 162, thereby managing the Venturi effect within the air funnel 164. Additionally, the pressure regulation portion 234 maintains the flow 160 of process air 162 between the rectangular configuration of the evaporator 18 and around the configuration of the converging section 250.

[0058] By managing the Venturi effect, sections of the flow 160 of process air 162 are prevented from moving at a greatly accelerated rate or decelerated rate, relative to adjacent portions of the flow 160 of process air 162. Undesirable and isolated changes in air pressure 200 and air velocity 202 may result in a section of the process air 162 that experiences a pressure drop. These sections of pressure drop with the process air 162 can have an impact upstream that may result in an uneven flow 160 of process air 162 through the evaporator 18. Additionally, as described herein, pressure drop within a portion of the coils 54 of the evaporator 18 may result in the initiation of the frost condition 70. This pressure drop may also result in a decreased ability to mitigate a frost condition 70 within the evaporator 18. By managing the Venturi effect to create a consistent decrease in air pressure 200 and a consistent increase in air velocity 202, the process air 162 is able to move evenly and consistently through the entirety of the coils 54 for the evaporator 18 to efficiently transfer heat 16 from ambient air 44 and into the thermal exchange media 14 within the coils 54 of the evaporator 18. The ability of the air funnel 164 and the portions thereof operates to manage the Venturi effect, as described herein, through operation of the evaporator fan 46 though the plurality of speeds 90 of the evaporator fan 46.

[0059] Referring again to FIGS. 3-7, the pressure regulation portion 234 of the transition section 230 moves into the converging section 250 of the air funnel 164 and transitions from the concave portion of the air funnel 164 to a convex portion of the air funnel 164, which is located in the converging section 250. This convex portion of the converging section 250 of the air funnel 164 further directs the flow 160 of process air 162 through the port 212 and into the blower 48. Again, this transition of the air funnel 164 between the pressure regulation portion 234 and the converging section 250 of the air funnel 164 maintains a consistent and even decrease of air pressure 200, as well as consistent and even increase in air velocity 202 as the flow 160 of process air 162 moves through the port 212 and into the blower housing 50.

[0060] In certain aspects of the device, the converging section 250 of the air funnel 164 can be positioned in an eccentric position with respect to the transition section 230. Stated another way, the converging section 250 and the port 212 can be positioned in an off-axis or off-center position within the air funnel 164 with respect to the transition section 230 as well as the evaporator 18. The curvature of the concave portion of the pressure regulation portion 234 directs the process air 162 to maintain a consistent and even increase in air velocity 202, and corresponding consistent decrease in air pressure 200.

[0061] To accommodate the off-axis position of the port 212, the pressure regulation portion 234 includes a non-symmetrical curvature of the concave portion. This non-symmetrical configuration of the concave portion directs the process air 162 in a consistent increase in air velocity 202 and corresponding decrease in air pressure 200. In this manner, the curvature of the concave portion can define a steeper curve on the short side of the air funnel 164, the short side being that side of the air funnel 164 where the port 212 is closer to the outer edge 272 of the evaporator 18. Similarly, for the long side of the air funnel 164, that portion of the concave portion where the port 212 is farther from the outer edge 272 of the evaporator 18 can have a shallower curve.

[0062] In certain aspects of the device, the port 212 and the converging section 250 can be centrally located within the air funnel 164. In such configuration, the evaporator fan 46 of the blower 48 is also centrally located within the air funnel 164.

[0063] According to the various aspects of the device, whether the port 212 is eccentrically positioned or centrally positioned, it is typically contemplated that the converging section 250 of the air funnel 164 is symmetrical about the port 212.

[0064] Referring to FIGS. 3-7, a plate 280 of the air funnel 164 is configured to engage the blower housing 50 of the blower 48. The plate 280 can be configured to extend across the entirety of the upper housing 124. Through this configuration, the plate 280 separates the volume of the upper housing 124 between a heat exchange section 282 and a blower section 284. Within the heat exchange section 282 of the upper housing 124, various portions of the heat pump system 10 can be located, including the evaporator 18, the compressor 42, and other components of the heat pump system 10. The blower section 284 of the upper housing 124 includes the blower 48, including the evaporator fan 46 of the blower 48 and the blower housing 50. In dividing the upper housing 124 into the heat exchange section 282 and the blower section 284, operation of the blower 48 serves to efficiently direct process air 162 from the air inlet 128, into the heat exchange section 282, and through the evaporator 18. Because the plate 280 divides the upper housing 124 between the heat exchange section 282 and the blower section 284, all, or substantially all, of the ambient air 44 that is drawn through the air inlet 128 is moved through the evaporator 18 as process air 162.

[0065] Referring again to FIGS. 3-7, the pressure regulation portion 234 of the air funnel 164 can include tapered fillets 290 that assist in converging the rectangular outer perimeter of the pressure maintenance portion 232 of the air funnel 164 into the circular profile of the converging section 250 of the air funnel 164. The tapered fillets 290 extend between parabolic panels 292 that form the remainder of the pressure regulation portion 234. Together, the tapered fillets 290 and the parabolic panels 292 cooperate to define an inner surface 294 of the air funnel 164 that operates to regulate the manipulation of process air 162 as it moves between the evaporator 18 and the converging section 250 of the air funnel 164. The tapered fillets 290 and the parabolic panels 292 cooperate to consistently regulate the increase in air velocity 202 of the process air 162 as well as the consistent decrease in air pressure 200 of the process air 162.

[0066] Referring to FIGS. 1-9, the water heating appliance 12 includes the refrigerant path 40 having the compressor 42 that directs the thermal exchange media 14 through the refrigerant path 40. The refrigerant path 40 includes the evaporator 18 that absorbs heat 16 from ambient air 44. The refrigerant path 40 also includes the evaporator fan 46 that directs the ambient air 44 across the surface 52 of the coils 54 for the evaporator 18. The refrigerant path 40 also includes the coils 54 of the condensing portion 56 that deliver the absorbed heat 16 to the media, typically water 20 within the reservoir 22. The temperature sensing system 58 monitors a media temperature 60 of the water 20 within the reservoir 22 and a surface temperature 62 of the coils 54 for the evaporator 18. A controller 64 is in communication with the temperature sensing system 58 and the evaporator fan 46 to determine the rate of change 92 of the surface temperature 62. In response to the rate of change 92 of the surface temperature 62 defining a decreased rate 80, the controller 64 compares the decreased rate 80 to a temperature difference 66 between the media temperature 60 and the surface temperature 62 and the rate of change 92 of the temperature difference 66.

[0067] In exemplary operation, the controller 64 monitors the surface temperature 62 and the media temperature 60, determines a first change in the surface temperature 62 over time, determines a second change in the media temperature 60 over time, and communicates an output to control the evaporator fan 46 based on the first change and the second change. The changes over time may be for the same duration or a different duration (e.g., 5 minutes, 10 minutes, etc.). Further, the changes over time may be calculated, or determined, at different intervals (e.g., the starting and ending points for measuring the changes can be different). For example, there may be an immediate correlation or a delayed correlation between the first change and the second change at the onset of, or at the earliest stages of, a frost condition 70. In some examples, the correlation is approximately immediate. In general, the changes can be with respect to rates of change, such as the rate of change 92 of the surface temperature 62 and a rate of change of the media temperature 60.

[0068] By way of example, the controller 64 can determine a frost condition 70 of the evaporator 18 in response to determining a positive rate of change of the media temperature 60 commensurate, simultaneous, or overlapping with the rate of change 92 of the surface temperature 62 being negative. Accordingly, a method of operating a heat pump system 10 can include the steps of monitoring a surface temperature 62 and a media temperature 60, determining a first change in the surface temperature 62 over time, determining a second change in the media temperature 60 over time, and communicating an output to control the evaporator fan 46 based on the first change and the second change. The method can further include adjusting a speed of the evaporator fan 46 in response to the output. For example, the adjustment of the speed can be performed via a variable-frequency drive (VFD) or a stepper motor. The method can further include determining a change in the rates of change, such as determining a greater or lesser slope of either or both of the first and second changes, and adjusting the output based on the changes in the rates of changes. For example, if increasing the speed of the motor 72 results in a shallower slope of the rate of change 92 (e.g., a lower or zero rate of decrease) while the media temperature 60 continues to increase, the control circuitry (e.g., controller 64) can adjust the output to increase the speed of the motor 72 due to the controller 64 determining that the increase in speed was effectual but perhaps too little. Stated differently, the controller 64 can determine various conditions following corrective action to prevent full frosting of the coils 54 based on continued monitoring of the first and second changes.

[0069] It is contemplated that after the decreased rate 80 is determined to exist in relation to the surface temperature 62, the controller 64 can also monitor certain other temperatures to determine whether the frost condition 70 exists. By way of example, and not limitation, the controller 64 can monitor the temperature of the ambient air 44 moving over the coils 54 for the evaporator 18. The controller 64 can also monitor the operation of the expansion device 150, as described herein. The controller 64 can further monitor various temperatures of the refrigerant path 40 and the reservoir 22 for determining whether the rate of change 92 of the surface temperature 62 being the decreased rate 80 is indicative of the frost condition 70.

[0070] In response to the rate of change 92 of the temperature difference 66 increasing to a frost condition 70, the controller 64 operates a motor 72 of the evaporator fan 46 to increase the flow of process air 162 across the surface 52 of the evaporator 18. As described herein, this increase in the flow of process air 162 leads to an increase in the surface temperature 62 of the evaporator 18. The rate of change 92 of the surface temperature 62 to an increased rate 96 corresponds to a decrease in the temperature difference between the surface temperature 62 and the media temperature 60 to be closer to the threshold difference 68. As discussed herein, the temperature difference 66 being below the threshold difference is typically indicative of the standard operating condition 78. The decreases in the temperature difference 66 to be within the threshold difference 68 and below a temperature difference 66 are indicative of the standard operating condition 78. In response to the temperature difference 66 being within the standard operating condition 78, the controller 64 operates the motor 72 for the evaporator fan 46 to decrease the flow of ambient air 44 across the surface 52 of the evaporator 18. As described herein, this lowest speed is typically in the form of a base speed setting 110.

[0071] Using the fan speed control system 188 described herein, the presence of a frost condition 70 within the evaporator 18 can be determined at its earliest stages, when the surface temperature 62 of the coils 54 starts to diverge from the media temperature 60 of the water 20 within the reservoir 22 resulting in an increased temperature difference 66. Using this information, the fan speed control system 188 and the controller 64 for the water heating appliance 12 can operate the motor 72 for the evaporator fan 46 to increase the flow of ambient air 44 moving across the coils 54 for the evaporator 18. This increase in ambient air 44 serves to increase the amount of heat 16 that can be absorbed by the evaporator 18. The increased amount of ambient air 44 also serves to increase the surface temperature 62 of the coils 54 for the evaporator 18. The increased surface temperature 62 can be used to prevent the formation of ice crystals or to melt the ice crystals that are formed on the coils 54.

[0072] Referring now to FIGS. 1-10, having described various aspects of the fan speed control system 188, a method 400 is disclosed for operating an evaporator fan 46 for preventing a frost condition 70. According to the method 400, a heat pump system 10 for a water heating appliance 12 is operated (step 402). A controller 64 monitors a surface temperature 62 of coils 54 for an evaporator 18 and a rate of change 92 of the surface temperature 62 (step 404). In response to the rate of change 92 of the surface temperature 62 of the coils 54 defining a decreased rate 80, the controller 64 monitors a media temperature 60 of water 20 being heated within a reservoir 22 (step 406). In response to the rate of change 92 of the surface temperature 62 defining the decreased rate 80, the controller 64 monitors a difference between the surface temperature 62 and the media temperature 60 to determine a temperature difference 66 (step 408). In response to the temperature difference 66 exceeding a threshold difference 68, the controller 64 operates a motor 72 for the evaporator fan 46 at an increased speed 76 (step 410). As described herein, the increased speed 76 of the evaporator fan 46 results in an increased flow of ambient air 44 over the evaporator 18. This increased flow of ambient air 44 delivers additional amounts of heat 16 to be absorbed by the evaporator 18, thereby increasing the surface temperature 62 of the coils 54 for the evaporator 18. According to the method 400, a step 412 includes operating the evaporator fan 46 to increase the surface temperature 62 of the coils 54 for the evaporator 18 to also decrease the temperature difference 66 between the surface temperature 62 and the media temperature 60. In response to the temperature difference 66 returning to a standard operating condition 78, the speed of the evaporator fan 46 is decreased to a base speed setting 110 (step 414).

[0073] According to the various aspects of the device, as exemplified in FIGS. 1-9, in addition to utilizing the rate of change 92 of the surface temperature 62 and the temperature difference 66 between the media temperature 60 and the surface temperature 62 for assessing the existence of a frost condition 70, an alternative aspect of the device can include using the electronic expansion device 150 for assessing the existence of a frost condition 70. The electronic expansion device 150 includes an expansion device motor 300, which is typically in the form of a stepper motor that can operate through a wide range of positions or steps. Typically, the expansion device 150 operates according to the standard operating condition 78 that is indicative of a standard position of the expansion device motor 300. The electronic expansion device 150 can operate according to a temperature difference 66 between the surface temperature 62 of the coils 54 for the evaporator 18, as measured by the evaporator sensor 182, and a surface temperature 62 of the refrigerant path 40 upstream of the compressor 42, as measured by a suction line sensor 302. These temperature differences 66 are typically within a range of from approximately 12 to approximately 17. Other temperature ranges can be utilized depending upon the design of the water heating appliance 12. Under a frost condition 70, this temperature difference 66 tends to decrease indicating that heat 16 is not being absorbed by the coils 54 of the evaporator 18. As described herein, this phenomena can be indicative of a frost condition 70 where ice crystals accumulate on the coils 54 for the evaporator 18. Stated another way, where ice crystals accumulate on the coils 54 for the evaporator 18, less heat 16 can be absorbed by the coils 54. This results in a lesser temperature difference in the thermal exchange media 14 entering the evaporator 18 near the evaporator sensor 182 compared to the thermal exchange media 14 leaving the evaporator 18 near the suction line sensor 302.

[0074] In response to this frost condition 70, the expansion device motor 300 of the expansion device 150 operates to partially close. This closure limits and decreases the amount of thermal exchange media 14 that can move through the evaporator 18. This closure tends to drop the pressure and saturation temperature in the evaporator 18, thereby increasing the temperature difference 66 between the surface temperature 62 of the coils 54 and the surface temperature 62 of the refrigerant path 40 upstream of the compressor 42. By monitoring the position of this expansion device motor 300 of the expansion device 150, the fan speed control system 188 can obtain this information and can instruct the motor 72 for the evaporator fan 46, via the controller 64, to increase the speed of the motor 72 to one of the medium speed setting 112 or the high speed setting 94, depending upon the position of the expansion device motor 300 for the expansion device 150. When the expansion device motor 300 returns to a standard operating condition 78, the controller 64 can operate the motor 72 for the evaporator fan 46 at the base speed setting 110.

[0075] In certain aspects of the device, it is contemplated that when the controller 64 operates the evaporator fan 46 at the high speed setting 94, a user interface of the appliance can indicate that a frost condition 70 may be occurring. It is also contemplated that the user interface can indicate the presence of a frost condition 70 or an imminent frost condition 70 when the evaporator fan 46 operates at the medium speed setting 112.

[0076] Referring now to FIGS. 1-9 and 11, having described various aspects of the fan speed control system 188, a method 500 is disclosed for operating an evaporator fan 46 for preventing a frost condition 70 using an electronic expansion device 150. According to the method 500, a heat pump system 10 for a water heating appliance 12 is operated (step 502). A controller 64 monitors a surface temperature 62 of coils 54 for an evaporator 18 at an upstream position of the refrigerant path 40 (step 504). The controller 64 also monitors the surface temperature 62 of coils 54 for an evaporator 18 at a downstream position of the refrigerant path 40 between the evaporator 18 and a compressor 42 (step 506). The controller 64 monitors a difference between the surface temperatures 62 to determine a temperature difference 66 (step 508). In response to the temperature difference 66 falling below the threshold difference 68, the controller 64 operates the expansion device motor 300 for the expansion device 150 to partially close, thereby deceasing a movement of thermal exchange media 14 through the evaporator 18 (step 510). In response to the partial closing of the expansion device motor 300, the controller 64 operates a motor 72 for the evaporator fan 46 at an increased speed 76 (step 512). Again, as described herein, the increased speed 76 of the evaporator fan 46 results in an increased flow of ambient air 44 over the evaporator 18. This increased flow of ambient air 44 delivers additional amounts of heat 16 to be absorbed by the evaporator 18, thereby increasing the surface temperature 62 of the coils 54 for the evaporator 18 and increasing the temperature difference 66 of the evaporator 18 between the upstream surface 214 and the downstream surface 210 of the evaporator 18. According to the method 500, a step 514 includes operating the evaporator fan 46 to increase the surface temperature 62 of the coils 54 for the evaporator 18 to also increase the temperature difference 66 between the surface temperature 62 of the coils 54 on the upstream surface 214 of the evaporator 18 and the surface temperature 62 of the coils 54 on the downstream surface 210 of the evaporator 18. In response to the temperature difference 66 returning to a standard operating condition 78, the speed of the evaporator fan 46 is decreased to a base speed setting 110 (step 516).

[0077] According to the various aspects of the device, the use of temperature sensors 180 within the temperature sensing system 58 operates to instruct the controller 64 about the presence of an oncoming frost condition 70 or the presence of an actual frost condition 70 on the coils 54 for the evaporator 18. Utilizing this information, the controller 64 is able to instruct the motor 72 for the evaporator fan 46 to increase in speed to provide additional amounts of ambient air 44, and additional amounts of heat 16 to the coils 54 for the evaporator 18. By increasing the amount of heat 16 to the coils 54 for the evaporator 18, the frost condition 70 can be stopped before it starts, or can be mitigated if the ice crystals have already begun to form on the coils 54 for the evaporator 18. Utilizing the fan speed control system 188 described herein, the frost condition 70 can be eliminated before it starts or when it is in its most early stages.

[0078] According to an aspect of the present disclosure, a water heating appliance includes: a reservoir for storing water to be heated; a refrigerant path having a compressor that directs a thermal exchange media through the refrigerant path having an evaporator that absorbs heat from process air, an evaporator fan that directs the process air across a surface of the evaporator, and a condensing coil that delivers the heat to the reservoir; a temperature sensing system that monitors a temperature of the water to be heated and a surface temperature of the evaporator; and a controller in communication with the temperature sensing system and the evaporator fan. The controller monitors a rate of change of the surface temperature. In response to the rate of change of the surface temperature being a decreased rate, the controller compares the decreased rate to at least a rate of change of the temperature of the water to be heated. In response to the decreased rate diverging from the rate of change of the temperature of the water, indicative of a frost condition, the controller operates the evaporator fan at an increased speed to direct an increased flow of the process air over the surface of the evaporator to increase the surface temperature and define the rate of change of the surface temperature to be an increased rate.

[0079] According to another aspect, the water heating appliance further includes a motor operable to drive the evaporator fan at a plurality of speeds.

[0080] According to another aspect, the controller operates the evaporator fan at the increased speed until a temperature difference between the surface temperature and the temperature of the water to be heated is within a threshold difference indicative of a standard operating condition.

[0081] According to another aspect, the controller, in response to the temperature difference reaching the standard operating condition, operates the evaporator fan at a base speed setting of the plurality of speeds.

[0082] According to another aspect, the plurality of speeds of the evaporator fan includes the base speed setting, a medium speed setting that is faster than the base speed setting, and a high speed setting that is faster than the medium speed setting.

[0083] According to another aspect, the evaporator fan includes an air funnel that directs the process air over the surface of the evaporator at an even rate, the air funnel having an inner surface that maintains an air pressure of the process air to be generally consistent within the evaporator.

[0084] According to another aspect, the air funnel includes a pressure regulation portion that is downstream of the evaporator, wherein the pressure regulation portion operates to gradually and evenly decrease the air pressure of the process air between a pressure maintenance portion and a converging section that defines a rounded port.

[0085] According to another aspect, the pressure regulation portion and the converging section operate to evenly increase an air velocity of the process air as it moves between the evaporator and the evaporator fan in each speed setting of the plurality of speeds.

[0086] According to another aspect, the temperature sensing system measures the temperature of the water at a lower portion of the reservoir.

[0087] According to another aspect of the present disclosure, a heat pump system for a water heating appliance includes a refrigerant path that includes an evaporator that absorbs heat from process air, an evaporator fan that directs the process air across coils of the evaporator, a compressor for directing a thermal exchange media through the refrigerant path, and a condenser that includes a condensing coil and water to be heated. The heat pump system further includes a controller that monitors a surface temperature of a surface of the coils, a rate of change of the surface temperature, a temperature difference between a media temperature of the water to be heated and the surface temperature, and a rate of change of the temperature difference. In response to a rate of change of the surface temperature defining a decreased rate, the controller compares the decreased rate to at least a rate of change of the temperature difference. In response to the rate of change of the temperature difference being beyond a threshold rate, indicative of a frost condition, the controller increases a speed of the evaporator fan to deliver additional process air across the surface of the coils. The additional process air operates to increase the surface temperature of the coils of the evaporator and decrease the temperature difference to be within a standard operating condition.

[0088] According to another aspect, a motor of the evaporator fan defines a plurality of speeds of the evaporator fan, and wherein the controller operates the motor of the evaporator fan based upon a rate of change that the temperature difference increases beyond the threshold rate.

[0089] According to another aspect, the controller operates the motor of the evaporator fan at an increased speed of the plurality of speeds until the temperature difference is below the threshold rate.

[0090] According to another aspect, the controller, in response to the temperature difference reaching the standard operating condition, operates the evaporator fan at a base speed setting of the plurality of speeds.

[0091] According to another aspect, the plurality of speeds includes the base speed setting, a medium speed setting that is faster than the base speed setting, and a high speed setting that is faster than the medium speed setting.

[0092] According to another aspect, the evaporator fan includes an air funnel that directs the process air over a surface of the evaporator at an even rate, the air funnel having an inner surface that maintains an air pressure of the process air to be generally consistent within the evaporator.

[0093] According to another aspect, the air funnel has a pressure regulation portion that is downstream of the evaporator, wherein the pressure regulation portion operates to gradually and evenly decrease the air pressure of the process air between a pressure maintenance portion and a converging section that defines a rounded port.

[0094] According to yet another aspect of the present disclosure, a water heating appliance includes a refrigerant path having a compressor that directs a thermal exchange media through the refrigerant path. The refrigerant path has an evaporator that absorbs heat from process air, an evaporator fan that directs the process air across a surface of the evaporator, and a condensing portion that delivers the heat to water within a reservoir. The water heating appliance also includes a temperature sensing system that monitors a media temperature of the water and a surface temperature of the evaporator. The water heating appliance further includes a controller in communication with the temperature sensing system to determine a rate of change of the surface temperature. In response to the rate of change of the surface temperature defining a decreased rate, the controller compares the decreased rate to a temperature difference between the media temperature and the surface temperature and a rate of change of the temperature difference. In response to the rate of change of the temperature difference increasing to a frost condition, the controller operates a motor of the evaporator fan to increase the flow of the process air across the surface of the evaporator to increase the surface temperature of the evaporator and decrease the temperature difference to be below a threshold difference and within a standard operating condition. In response to the temperature difference reaching the standard operating condition, the controller operates the motor of the evaporator fan to decrease the flow of the process air across the surface of the evaporator.

[0095] According to another aspect, the motor of the evaporator fan defines a plurality of speeds of the evaporator fan.

[0096] According to another aspect, the controller operates the motor of the evaporator fan based upon the rate of change of the surface temperature and the temperature difference.

[0097] According to another aspect, the evaporator fan includes an air funnel that directs the process air over the surface of the evaporator at an even rate, the air funnel having an inner surface that maintains an air pressure of the process air to be generally consistent within the evaporator, wherein the air funnel includes a pressure regulation portion that is downstream of the evaporator, and wherein the pressure regulation portion operates to gradually and evenly decrease the air pressure of the process air between a pressure maintenance portion and a converging section that defines a rounded port that is coupled to a housing for the evaporator fan.

[0098] It will be understood by one having ordinary skill in the art that construction of the described disclosure and other components is not limited to any specific material. Other exemplary embodiments of the disclosure disclosed herein may be formed from a wide variety of materials, unless described otherwise herein.