Heat pump outdoor fan control

Abstract

An illustrative example method of controlling a heat pump system includes operating in a defrost mode to provide heat to an outdoor heat exchanger for defrosting at least a portion of the outdoor heat exchanger, controlling a fan to be inoperative during the defrost mode, operating in a heating mode to provide heat within a temperature-conditioned space subsequent to operating in the defrost mode, controlling the fan to remain inoperative for an initial period at a beginning of operating in the heating mode, and controlling the fan to operate during the heating mode after the initial period to cause airflow across at least the portion of the outdoor heat exchanger.

I claim: 
     
         1 . A heat pump system, comprising:
 an indoor heat exchanger configured to be situated inside a temperature-conditioned space;   a compressor;   an outdoor heat exchanger configured to be situated outside the temperature-conditioned space;   a fan associated with the outdoor heat exchanger; and   a controller that is configured to
 selectively control the system to operate in a defrost mode to provide heat to the outdoor heat exchanger for defrosting at least a portion of the outdoor heat exchanger, 
 control the fan to be inoperative during the defrost mode, 
 selectively control the system to operate in a heating mode to provide heat within the temperature-conditioned space subsequent to operating in the defrost mode, 
 control the fan to remain inoperative for an initial period at a beginning of the heating mode, and 
 control the fan to operate during the heating mode after the initial period to cause airflow across at least the portion of the outdoor heat exchanger. 
   
     
     
         2 . The heat pump system of  claim 1 , wherein the controller is configured to determine when the initial period expires based on one of a temperature of the portion of the outdoor heat exchanger or a temperature of a refrigerant fluid in the outdoor heat exchanger. 
     
     
         3 . The heat pump system of  claim 2 , wherein the initial period expires when a difference between the temperature of the portion of the outdoor heat exchanger and an outside air temperature satisfies at least one preselected criterion. 
     
     
         4 . The heat pump system of  claim 3 , wherein the initial period expires when the difference between the temperature of the portion of the outdoor heat exchanger and the outside air temperature is below a threshold. 
     
     
         5 . The heat pump system of  claim 4 , wherein the threshold is 3° F. (1.7° C.). 
     
     
         6 . The heat pump system of  claim 2 , wherein the initial period expires when the one of the temperature of the portion of the outdoor heat exchanger or the temperature of the refrigerant fluid in the outdoor heat exchanger falls below an outside air temperature in a vicinity of the outdoor heat exchanger. 
     
     
         7 . The heat pump system of  claim 2 , wherein the initial period expires when a temperature of the portion of the outdoor heat exchanger is within a preselected range above freezing. 
     
     
         8 . The heat pump system of  claim 1 , comprising a reversing valve and wherein the controller is configured to control the reversing valve to direct refrigerant fluid from the compressor to the outdoor heat exchanger in the defrost mode and to direct refrigerant fluid from the outdoor heat exchanger to the compressor in the heating mode. 
     
     
         9 . A method of controlling a heat pump system that includes an indoor heat exchanger configured to be situated inside a temperature-conditioned space, a compressor, an outdoor heat exchanger configured to be situated outside the temperature-conditioned space, and a fan associated with the outdoor heat exchanger, the method comprising:
 operating in a defrost mode to provide heat to the outdoor heat exchanger for defrosting at least a portion of the outdoor heat exchanger,   controlling the fan to be inoperative during the defrost mode,   operating in a heating mode to provide heat within the temperature-conditioned space subsequent to operating in the defrost mode,   controlling the fan to remain inoperative for an initial period at a beginning of operating in the heating mode, and   controlling the fan to operate during the heating mode after the initial period to cause airflow across at least the portion of the outdoor heat exchanger.   
     
     
         10 . The method of  claim 9 , comprising determining when the initial period expires based on one of a temperature of the portion of the outdoor heat exchanger or a temperature of a refrigerant fluid in the outdoor heat exchanger. 
     
     
         11 . The method of  claim 10 , wherein the initial period expires when a difference between the temperature of the portion of the outdoor heat exchanger and an outside air temperature satisfies at least one preselected criterion. 
     
     
         12 . The method of  claim 11 , wherein the initial period expires when the difference between the temperature of the portion of the outdoor heat exchanger and the outside air temperature is below a threshold. 
     
     
         13 . The method of  claim 12 , wherein the threshold is 3° F. (1.7° C.). 
     
     
         14 . The method of  claim 10 , wherein the initial period expires when the one of the temperature of the portion of the outdoor heat exchanger or the temperature of the refrigerant fluid in the outdoor heat exchanger falls below an outside air temperature in a vicinity of the outdoor heat exchanger. 
     
     
         15 . The method of  claim 10 , wherein the initial period expires when a temperature of the portion of the outdoor heat exchanger is within a preselected range above freezing. 
     
     
         16 . The method of  claim 9 , comprising controlling a reversing valve to direct refrigerant fluid from the compressor to the outdoor heat exchanger in the defrost mode and to direct refrigerant fluid from the outdoor heat exchanger to the compressor in the heating mode. 
     
     
         17 . The method of  claim 9 , comprising controlling the initial period to avoid condensation of refrigerant vapor inside the outdoor heat exchanger during the heating mode. 
     
     
         18 . The method of  claim 9 , comprising controlling the initial period to direct heat of a refrigerant vapor in the outdoor heat exchanger toward the compressor. 
     
     
         19 . A controller comprising a processor and memory including instructions that are executable by the processor to perform a method comprising:
 operating in a defrost mode to provide heat to an outdoor heat exchanger for defrosting at least a portion of the outdoor heat exchanger,   controlling a fan associated with the outdoor heat exchanger to be inoperative during the defrost mode,   operating in a heating mode to provide heat within a temperature-conditioned space subsequent to operating in the defrost mode,   controlling the fan to remain inoperative for an initial period at a beginning of operating in the heating mode, and   controlling the fan to operate during the heating mode after the initial period to cause airflow across at least the portion of the outdoor heat exchanger.   
     
     
         20 . The controller of  claim 19 , wherein
 the memory includes instructions for determining when the initial period expires based on one of a temperature of the portion of the outdoor heat exchanger or a temperature of a refrigerant fluid in the outdoor heat exchanger;   and   the initial period expires when the one of the temperature of the portion of the outdoor heat exchanger or the temperature of the refrigerant fluid in the outdoor heat exchanger falls below an outside air temperature in a vicinity of the outdoor heat exchanger, or   the initial period expires when a temperature of the portion of the outdoor heat exchanger is within a preselected range above freezing.