Method for defrosting a heat pump

Abstract

A method for defrosting a heat pump includes operating a fan at a particular speed. The fan is positioned to circulate air across the exterior coil of the heat pump. The method also includes measuring a power of the fan while the fan is operating at the particular speed and initiating a defrost of the exterior coil of the heat pump when the power of the fan is less than a threshold power.

What is claimed is: 
     
         1 . A method for defrosting a heat pump, comprising:
 operating the heat pump in a heating mode to transfer heat from an exterior coil of the heat pump to an interior coil of the heat pump;   operating a fan at a particular speed, the fan positioned to circulate air across the exterior coil of the heat pump;   measuring a power of the fan while the fan is operating at the particular speed; and   initiating a defrost of the exterior coil of the heat pump when the power of the fan is less than a threshold power.   
     
     
         2 . The method of  claim 1 , wherein the threshold power corresponds to the power of the fan when airflow across the exterior coil of the heat pump with the fan is blocked by frost or ice on the exterior coil. 
     
     
         3 . The method of  claim 1 , wherein the threshold power is about ten percent less than the power of the fan when airflow across the exterior coil of the heat pump with the fan is not blocked by frost or ice on the exterior coil. 
     
     
         4 . The method of  claim 1 , further comprising measuring a temperature of the exterior coil of the heat pump, the threshold power being a function of the temperature of the exterior coil. 
     
     
         5 . The method of  claim 4 , further comprising looking up the threshold power within a table in a controller of the heat pump based upon the temperature of the exterior coil. 
     
     
         6 . The method of  claim 1 , wherein initiating the defrost of the exterior coil of the heat pump comprises one or more of activating a heating element on the exterior coil or deactivating the heat pump for a period of time. 
     
     
         7 . The method of  claim 1 , wherein operating the fan at a particular speed comprises delivering a particular voltage input to the fan, an inverter of the fan driving a motor of the fan to provide a particular torque at the particular voltage input. 
     
     
         8 . The method of  claim 7 , wherein measuring the power of the fan comprises receiving a signal from a sensor of the fan, a frequency of the signal directly proportional to a speed of the fan at the particular voltage input. 
     
     
         9 . The method of  claim 1 , wherein the heat pump does not include a humidity sensor at the exterior coil of the heat pump. 
     
     
         10 . The method of  claim 1 , wherein the heat pump is positioned within a heat pump water heater appliance or a packaged terminal air conditioner. 
     
     
         11 . A method for defrosting a heat pump, comprising:
 operating the heat pump in a heating mode such that the heat pump transfers heat from an exterior coil of the heat pump to an interior coil of the heat pump;   delivering a particular voltage input to a fan while operating the heat pump in the heating mode, the fan positioned to circulate air across the exterior coil of the heat pump;   measuring a power of the fan while the fan is operates with the particular voltage input; and   initiating a defrost of the exterior coil of the heat pump when the power of the fan is less than a threshold power.   
     
     
         12 . The method of  claim 11 , wherein the threshold power corresponds to the power of the fan when airflow across the exterior coil of the heat pump with the fan is blocked by frost or ice on the exterior coil. 
     
     
         13 . The method of  claim 11 , wherein the threshold power is about ten percent less than the power of the fan when airflow across the exterior coil of the heat pump with the fan is not blocked by frost or ice on the exterior coil. 
     
     
         14 . The method of  claim 11 , further comprising measuring a temperature of the exterior coil of the heat pump, the threshold power being a function of the temperature of the exterior coil. 
     
     
         15 . The method of  claim 14 , further comprising looking up the threshold power within a table in a controller of the heat pump based upon the temperature of the exterior coil. 
     
     
         16 . The method of  claim 11 , wherein initiating the defrost of the exterior coil of the heat pump comprises one or more of activating a heating element on the exterior coil or deactivating the heat pump for a period of time. 
     
     
         17 . The method of  claim 11 , wherein an inverter of the fan drives a motor of the fan to provide a particular torque at the particular voltage input. 
     
     
         18 . The method of  claim 17 , wherein measuring the power of the fan comprises receiving a signal from a sensor of the fan, a frequency of the signal directly proportional to a speed of the fan at the particular voltage input. 
     
     
         19 . The method of  claim 11 , wherein the heat pump does not include a humidity sensor at the exterior coil of the heat pump. 
     
     
         20 . The method of  claim 11 , wherein the heat pump is positioned within a heat pump water heater appliance or a packaged terminal air conditioner.