Method of triggering defrost

Abstract

A method for determining when to initiate a defrost mode of a heat pump includes monitoring a heating capacity of a heat exchanger of the heat pump during operation of the heat pump in a heating mode, initiating the defrost mode when the heating capacity of the heat exchanger is less than or equal to a reduced defrost threshold when a capacity demand of the heat exchanger is less than a maximum capacity demand, and initiating the defrost mode when the heating capacity of the heat exchanger is less than or equal to a maximum defrost threshold when the capacity demand of the heat exchanger is equal to the maximum capacity demand.

What is claimed is: 
     
         1 . A method for determining when to initiate a defrost mode of a heat pump, the method comprising:
 monitoring a heating capacity of a heat exchanger of the heat pump during operation of the heat pump in a heating mode;   initiating the defrost mode when the heating capacity of the heat exchanger is less than or equal to a reduced defrost threshold when a capacity demand of the heat exchanger is less than a maximum capacity demand; and   initiating the defrost mode when the heating capacity of the heat exchanger is less than or equal to a maximum defrost threshold when the capacity demand of the heat exchanger is equal to the maximum capacity demand.   
     
     
         2 . The method of  claim 1 , wherein monitoring the heating capacity of the heat exchanger further comprises monitoring at least one parameter or operating condition of the heat pump associated with the heating capacity. 
     
     
         3 . The method of  claim 2 , wherein the at least one parameter or operating condition is a refrigerant mass flow. 
     
     
         4 . The method of  claim 2 , wherein the at least one parameter or operating condition comprises a temperature of an air discharged from the heat exchanger. 
     
     
         5 . The method of  claim 2 , wherein the at least one parameter or operating condition comprises at least one of a pressure at an outlet of the heat exchanger, a pressure at an inlet of a compressor arranged directly downstream from the heat exchanger relative to a fluid flow through the heat pump in the heating mode, and a pressure between the outlet of the heat exchanger and the inlet of the compressor. 
     
     
         6 . The method of  claim 2 , wherein the at least one parameter or operating condition comprises at least one of a pressure at an inlet of the heat exchanger, a pressure at an outlet of an expansion device, the expansion device being arranged directly upstream from the heat exchanger relative to a fluid flow through the heat pump in the heating mode, and a pressure between the outlet of the expansion device and the inlet of the heat exchanger. 
     
     
         7 . The method of  claim 2 , wherein the at least one parameter or operating condition comprises a temperature at an inlet of the heat exchanger, at an outlet of an expansion device, the expansion device being arranged directly upstream from the heat exchanger relative to a fluid flow through the heat pump in the heating mode, or between the outlet of the expansion device and the inlet of the heat exchanger. 
     
     
         8 . A system for conditioning air comprising:
 a refrigeration circuit including a compressor, and expansion valve, and a heat exchanger;   a controller configured to transition the refrigeration circuit between operation in a heating mode and a defrost mode;   wherein the controller is configured to:
 transition the refrigeration circuit from the heating mode to the defrost mode in response to a heating capacity of the heat exchanger reaching a first defrost threshold when the capacity demand of the heat exchanger is less than the maximum capacity demand; and 
 transition the refrigeration circuit from the heating mode to the defrost mode in response to the heating capacity of the heat exchanger reaching a second defrost threshold when the capacity demand of the heat exchanger is equal to the maximum capacity demand. 
   
     
     
         9 . The system of  claim 8 , further comprising at least one sensor operably coupled to the controller, the at least one sensor being configured to monitor at least one parameter or operating condition of the system associated with the heating capacity. 
     
     
         10 . The system of  claim 9 , wherein the at least one parameter or operating condition is a refrigerant mass flow. 
     
     
         11 . The system of  claim 9 , wherein the at least one parameter or operating condition comprises a temperature of an air discharged from the heat exchanger. 
     
     
         12 . The system of  claim 9 , wherein the at least one parameter or operating condition comprises at least one of a pressure at an outlet of the heat exchanger, a pressure at an inlet of the compressor arranged directly downstream from the heat exchanger relative to a fluid flow through the system in the heating mode, and a pressure between the outlet of the heat exchanger and the inlet of the compressor. 
     
     
         13 . The system of  claim 9 , wherein the at least one parameter or operating condition comprises at least one of a pressure at an inlet of the heat exchanger, a pressure at an outlet of an expansion device, the expansion device being arranged directly upstream from the heat exchanger relative to a fluid flow through the system in the heating mode, and a pressure between the outlet of the expansion device and the inlet of the heat exchanger. 
     
     
         14 . The system of  claim 9 , wherein the at least one parameter or operating condition comprises a temperature at an inlet of the heat exchanger, at an outlet of an expansion device, the expansion device being arranged directly upstream from the heat exchanger relative to a fluid flow through the heat pump in the heating mode, or between the outlet of the expansion device and the inlet of the heat exchanger