Demand defrost for heat pumps

Abstract

A heat exchanger includes a motor that rotates a motor shaft to rotate a fan. An operating speed of the motor shaft determines an airflow through a heat exchanger coil. The heat exchanger also includes a sensor that detects a parameter of the motor shaft and a control. The parameter detected by the sensor is communicated to the control. The parameter is one of the operating speed of the motor shaft and a motor shaft torque. If the parameter is the operating speed, the control initiates a defrost cycle when the operating speed of the motor shaft is less than or equal to a threshold value. If the parameter is the motor shaft torque, the control initiates the defrost cycle when the torque application to the motor shaft is greater than or equal to a threshold value.

1 . A heat exchanger comprising:
 a motor that rotates a motor shaft to rotate a fan, wherein an operating speed of the motor shaft determines an airflow through a heat exchanger coil;   a sensor that detects a parameter of the motor shaft; and   a control, wherein the parameter is communicated to the control, wherein the parameter is one of the operating speed of the motor shaft and a motor shaft torque,   wherein, when the parameter is the operating speed, the control initiates a defrost cycle when the operating speed is less than or equal to a threshold value, and   wherein, when the parameter is the motor shaft torque, the control initiates the defrost cycle when the torque application to the motor shaft is greater than or equal to a threshold value.   
     
     
         2 . The heat exchanger as recited in  claim 1  wherein the heat exchanger is an outdoor heat exchanger. 
     
     
         3 . The heat exchanger as recited in  claim 1  wherein the threshold value is programmed in the control. 
     
     
         4 . The heat exchanger as recited in  claim 1   wherein, when the parameter is the operating speed, the operating speed decreases as frost forms on the heat exchanger coil, and an amount of frost buildup is at a maximum allowed amount when the operating speed is less than or equal to the threshold value, and   wherein, when the parameter is the torque applied to the motor shaft, the torque of the motor shaft increases as frost forms on the heat exchanger coil, and an amount of frost buildup is at a maximum allowed amount when the torque applied to the motor shaft is greater than or equal to the threshold value.   
     
     
         5 . The heat exchanger as recited in  claim 1  wherein the defrost cycle ends after a predetermined amount of time. 
     
     
         6 . The heat exchanger as recited in  claim 1  including a temperature sensor that detects a temperature in the heat exchanger coil, wherein the defrost cycle ends after the temperature sensor detects a predetermined temperature in the heat exchanger coil. 
     
     
         7 . The heat exchanger as recited in  claim 1  including a defrost heater, wherein the defrost heater is activated when the defrost cycle is initiated. 
     
     
         8 . The heat exchanger as recited in  claim 1  including a valve on a line from an output of a compressor, wherein the valve is opened to direct hot refrigerant from the compressor to the heat exchanger coil when the defrost cycle is initiated. 
     
     
         9 . A heat pump comprising:
 a compressor for compressing a refrigerant;   an indoor heat exchanger;   an expansion device for expanding the refrigerant; and   an outdoor heat exchanger including a motor that rotates a motor shaft to rotate a fan, wherein an operating speed of the motor shaft determines an airflow through a heat exchanger coil of the outdoor heat exchanger, the outdoor heat exchanger including a sensor that detects a parameter of the motor shaft and a control, wherein the parameter is one of the operating speed of the motor shaft and a motor shaft torque;   wherein the parameter is detected by the sensor and communicated to the control,   wherein, when the parameter is the operating speed, the control initiates a defrost cycle when the operating speed is less than or equal to a threshold value, and   wherein, when the parameter is the motor shaft torque, the control initiates the defrost cycle when the torque application to the motor shaft is greater than or equal to a threshold value.   
     
     
         10 . The heat pump as recited in  claim 9  wherein the indoor heat exchanger is an evaporator and the outdoor heat exchanger is a condenser during a cooling mode, and the indoor heat exchanger is the condenser and the outdoor heat exchanger is the evaporator during a heating mode. 
     
     
         11 . The heat pump as recited in  claim 9  wherein the threshold value is programmed in the control. 
     
     
         12 . The heat pump as recited in  claim 9   wherein, when the parameter is the operating speed, the operating speed decreases as frost forms on the heat exchanger coil, and an amount of frost buildup is at a maximum allowed amount when the operating speed is less than or equal to the threshold value, and   wherein, when the parameter is the torque applied to the motor shaft, the torque applied to the motor shaft increases as frost forms on the heat exchanger coil, and an amount of frost buildup is at a maximum allowed amount when the torque applied to the motor shaft is greater than or equal to the threshold value.   
     
     
         13 . The heat pump as recited in  claim 9  including a temperature sensor that detects a temperature in the heat exchanger coil, wherein the defrost cycle ends after the temperature sensor detects a predetermined temperature in the heat exchanger coil. 
     
     
         14 . The heat pump as recited in  claim 9  wherein the defrost cycle ends after a predetermined amount of time. 
     
     
         15 . The heat pump as recited in  claim 9  including a defrost heater, wherein the defrost heater is activated when the defrost cycle is initiated. 
     
     
         16 . The heat pump as recited in  claim 9  including a valve on a line from an output of the compressor, wherein the valve is opened to direct hot refrigerant from the compressor to the heat exchanger coil when the defrost cycle is initiated. 
     
     
         17 . A method of determining when to initiate a defrost cycle, the method comprising the steps of:
 rotating a motor shaft to rotate a fan, wherein an operating speed of the motor shaft determines an airflow through a heat exchanger coil;   detecting a parameter of the motor shaft, wherein the parameter is one of the operating speed of the motor shaft and the torque applied to the motor shaft; and   initiating a defrost cycle if an event occurs, and the event is one of the operating speed being less than or equal to a threshold value if the parameter is the operating speed, or the torque applied to the motor shaft being greater than or equal to a threshold value if the parameter is the torque applied to the motor shaft.