Heat pump system variable defrost

Abstract

A heat pump system includes an outdoor unit, an indoor unit, and a sealed system coupled between the outdoor unit and the indoor unit to circulate refrigerant through an indoor heat exchanger of the indoor unit and an outdoor heat exchanger of the outdoor unit. The sealed system includes a reversing valve to selectively reverse flow direction of the refrigerant. A method of operating the heat pump system may include, and/or a controller of the heat pump system may be configured for, measuring an ambient condition of an outdoor environment around the outdoor unit and determining a termination criterion for a defrost operation based on the measured ambient condition. The defrost operation is exited when the determined termination criterion is satisfied.

What is claimed is: 
     
         1 . A method of operating a heat pump system, the heat pump system comprising an outdoor unit, an indoor unit, and a sealed system coupled between the outdoor unit and the indoor unit to circulate refrigerant through an indoor heat exchanger of the indoor unit and an outdoor heat exchanger of the outdoor unit, the sealed system comprising a reversing valve to selectively reverse flow direction of the refrigerant, the method comprising:  
       measuring an ambient condition of an outdoor environment around the outdoor unit;  
       determining a termination criterion for a defrost operation based on the measured ambient condition;  
       initiating the defrost operation; and 
       exiting the defrost operation when the determined termination criterion is satisfied. 
     
     
         2 . The method of  claim 1 , wherein the ambient condition is an outdoor temperature. 
     
     
         3 . The method of  claim 2 , further comprising measuring a humidity of the outdoor environment around the outdoor unit, wherein the termination criterion is also determined based on the measured humidity. 
     
     
         4 . The method of  claim 1 , wherein the termination criterion comprises a temperature of the outdoor heat exchanger. 
     
     
         5 . The method of  claim 4 , further comprising determining a thermal accumulation limit for the defrost operation based on the measured ambient condition, wherein the defrost operation is exited when the determined termination temperature of the outdoor heat exchanger and the thermal accumulation limit and are both satisfied. 
     
     
         6 . The method of  claim 1 , wherein determining the termination criterion comprises comparing the measured ambient condition to a threshold, selecting a first termination criterion when the measured ambient condition is greater than the threshold, and selecting a second termination criterion when the measured ambient condition is less than or equal to the threshold, wherein the second termination criterion is greater than the first termination criterion. 
     
     
         7 . The method of  claim 1 , wherein determining the termination criterion comprises comparing the measured ambient condition to a first threshold and a second threshold, the first threshold greater than the second threshold, selecting a first termination criterion when the measured ambient condition is greater than the first threshold, selecting a second termination criterion when the measured ambient condition is less than or equal to the first threshold and greater than the second threshold, and selecting a third termination criterion when the measured ambient condition is less than or equal to the second threshold, wherein the third termination criterion is greater than the second termination criterion and the second termination criterion is greater than the first termination criterion. 
     
     
         8 . The method of  claim 1 , wherein determining the termination criterion comprises calculating the termination criterion by inputting the measured ambient condition into a linear function. 
     
     
         9 . The method of  claim 1 , wherein determining the termination criterion comprises calculating the termination criterion by inputting the measured ambient condition into a linear function. 
     
     
         10 . A heat pump system, comprising:  
       an outdoor unit;  
       an indoor unit;  
       a sealed system coupled between the outdoor unit and the indoor unit to circulate refrigerant through an indoor heat exchanger of the indoor unit and an outdoor heat exchanger of the outdoor unit, the sealed system comprising a reversing valve to selectively reverse flow direction of the refrigerant; and 
       a controller, the controller configured for: 
 measuring an ambient condition of an outdoor environment around the outdoor unit;  
 determining a termination criterion for a defrost operation based on the measured ambient condition;  
 initiating the defrost operation; and 
 exiting the defrost operation when the determined termination criterion is satisfied. 
 
     
     
         11 . The heat pump system of  claim 10 , wherein the ambient condition is an outdoor temperature. 
     
     
         12 . The heat pump system of  claim 11 , wherein the controller is further configured for measuring a humidity of the outdoor environment around the outdoor unit, wherein the termination criterion is also determined based on the measured humidity. 
     
     
         13 . The heat pump system of  claim 10 , wherein the termination criterion comprises a temperature of the outdoor heat exchanger. 
     
     
         14 . The heat pump system of  claim 13 , wherein the controller is further configured for determining a thermal accumulation limit for the defrost operation based on the measured ambient condition, wherein the defrost operation is exited when the determined termination temperature of the outdoor heat exchanger and the thermal accumulation limit and are both satisfied. 
     
     
         15 . The heat pump system of  claim 10 , wherein determining the termination criterion comprises comparing the measured ambient condition to a threshold, selecting a first termination criterion when the measured ambient condition is greater than the threshold, and selecting a second termination criterion when the measured ambient condition is less than or equal to the threshold, wherein the second termination criterion is greater than the first termination criterion. 
     
     
         16 . The heat pump system of  claim 10 , wherein determining the termination criterion comprises comparing the measured ambient condition to a first threshold and a second threshold, the first threshold greater than the second threshold, selecting a first termination criterion when the measured ambient condition is greater than the first threshold, selecting a second termination criterion when the measured ambient condition is less than or equal to the first threshold and greater than the second threshold, and selecting a third termination criterion when the measured ambient condition is less than or equal to the second threshold, wherein the third termination criterion is greater than the second termination criterion and the second termination criterion is greater than the first termination criterion.  
     
     
         17 . The heat pump system of  claim 10 , wherein determining the termination criterion comprises calculating the termination criterion by inputting the measured ambient condition into a linear function. 
     
     
         18 . The heat pump system of  claim 10 , wherein determining the termination criterion comprises calculating the termination criterion by inputting the measured ambient condition into a non-linear function.