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.

What is claimed is: 
     
         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.