Cooling unit with multi-parameter defrost control

Abstract

A cooling unit apparatus and method for controlling a defrost cycle using a multi-parameter defrost control system. The unit includes a refrigeration assembly with a compressor and an evaporator, a defrost temperature sensor that senses a temperature related to the defrost cycle, a controller configured to control a defrost cycle based on an elapsed defrost time and the defrost temperature. The controller is programmed with a defrost set point and a maximum defrost time. The controller ends the defrost cycle when the elapsed defrost time is greater than the maximum defrost time or when the defrost temperature is greater than the defrost set point, whichever occurs first.

1 . A cooling unit with a multi-parameter defrost control system, comprising:
 a refrigeration assembly including a compressor and an evaporator;   a defrost temperature sensor that senses a defrost temperature; and   a controller configured to control a defrost cycle of the refrigeration system, track an elapsed defrost time of the defrost cycle and monitor the defrost temperature, the controller programmed with a defrost set point and a maximum defrost time;   wherein the controller is configured to end the defrost cycle when the elapsed defrost time has reached the maximum defrost time;   wherein the controller is configured to end the defrost cycle when the defrost temperature has reached the defrost set point.   
   
   
       2 . The cooling unit of  claim 1 , further comprising a user input connected to the controller, wherein the defrost set point and the maximum defrost time can be set by the user input. 
   
   
       3 . The cooling unit of  claim 1 , wherein the refrigeration assembly includes a hot gas bypass valve configured to allow heated refrigerant to heat the evaporator when the controller opens the hot gas bypass valve during the defrost cycle. 
   
   
       4 . The cooling unit of  claim 3 , wherein the refrigeration assembly includes an evaporator pan and an evaporator pan heater that is energized by the controller during the defrost cycle to heat the evaporator pan. 
   
   
       5 . The cooling unit of  claim 4 , wherein the defrost temperature sensor is in thermal communication with the evaporator pan so that the defrost temperature indicates a temperature of the evaporator pan. 
   
   
       6 . The cooling unit of  claim 5 , wherein the defrost set point is 42 degrees Fahrenheit. 
   
   
       7 . The cooling unit of  claim 5 , wherein the controller is configured to continue the defrost cycle when the elapsed defrost time is less than a minimum defrost time. 
   
   
       8 . The cooling unit of  claim 4 , wherein the defrost temperature sensor is in thermal communication with the evaporator so that the defrost temperature indicates a temperature of the evaporator. 
   
   
       9 . The cooling unit of  claim 8 , wherein the controller is configured to not end the defrost cycle when the elapsed defrost time is less than a minimum defrost time. 
   
   
       10 . The cooling unit of  claim 1 , wherein the evaporator is a plate evaporator. 
   
   
       11 . The cooling unit of  claim 10 , wherein the defrost temperature sensor is in thermal communication with the plate evaporator so that the defrost temperature indicates a temperature of the plate evaporator. 
   
   
       12 . The cooling unit of  claim 11 , wherein the defrost set point is 42 degrees Fahrenheit. 
   
   
       13 . A method for controlling a defrost cycle of a cooling unit with a refrigeration assembly including a compressor and an evaporator, a defrost temperature sensor that senses a defrost temperature, and a controller programmed with a defrost set point and a maximum defrost time, the method comprising:
 monitoring the defrost temperature;   tracking an elapsed defrost time of the defrost cycle beginning at a start time of the defrost cycle;   ending the defrost cycle when the elapsed defrost time has reached the maximum defrost time; and   ending the defrost cycle when the defrost temperature has reached the defrost set point.   
   
   
       14 . The method of  claim 13 , wherein the refrigeration assembly includes a hot gas bypass valve configured to allow heated refrigerant to heat the evaporator when the controller opens the hot gas bypass valve during the defrost cycle;
 wherein the refrigeration assembly further includes an evaporator pan and an evaporator pan heater that is energized during the defrost cycle to heat the evaporator pan; and   wherein the defrost temperature sensor is in thermal communication with the evaporator pan so that the defrost temperature indicates a temperature of the evaporator pan.   
   
   
       16 . The method of  claim 14 ; wherein the defrost temperature is monitored by a defrost temperature sensor that is in thermal communication with one of the evaporator and the evaporator pan. 
   
   
       17 . The method of  claim 16 , wherein the defrost set point is 42 degrees Fahrenheit. 
   
   
       18 . The method of  claim 13 , wherein the evaporator is a plate evaporator that is defrosted when the refrigeration system is not energized. 
   
   
       19 . The method of  claim 18 , wherein the defrost temperature is monitored by a defrost temperature sensor that is in thermal communication with the plate evaporator. 
   
   
       20 . The method of  claim 19 , wherein the defrost set point is 42 degrees Fahrenheit.