Predictive Failure Algorithm For Refrigeration Systems

Abstract

An apparatus and method for predicting failure of a ultralow temperature freezer is disclosed. The freezer includes a variety of temperature sensors, which monitor the temperature of the freezer at various components, such as at the heat exchanger, the condenser, and the evaporator. A controller is in communication with these sensors. The controller monitors these sensors and may determine that the freezer has experienced a performance degradation, or a severe performance degradation. In some embodiments, the controller also monitors other events, such as the actuation of the compressors, and closing of the freezer door. The controller uses temperature information, either absolute sensor readings, or the difference between two different sensor to estimate refrigerant volume and flow rate in the system. In some embodiment, the controller also uses elapsed time from a specific event and a temperature reading to estimate refrigerant volume and flow rate in the system.

What is claimed is: 
     
         1 . A method of predicting failure of an ultralow temperature freezer, comprising:
 monitoring a duty cycle of a compressor used in said freezer;   comparing said monitored duty cycle to a first predetermined value to determine if said freezer is operating properly; and   comparing said monitored duty cycle to a second predetermined value to determine if said freezer has experienced a severe performance degradation; and   alerting an operator if said freezer has experienced a severe performance degradation.   
     
     
         2 . The method of  claim 1 , further comprising determining said freezer has experienced a performance degradation if said monitored duty cycle between said first predetermined value and said second predetermined value. 
     
     
         3 . The method of  claim 2 , wherein said alerting step comprising actuating a different alert if a severe performance degradation is determined to exist. 
     
     
         4 . A method of predicting failure of an ultralow temperature freezer, wherein said freezer comprises two cascaded refrigeration stages, an evaporator disposed in a storage chamber of said freezer to remove heat from said storage chamber, and a heat exchanger disposed between said two cascaded stages to remove heat from a second refrigeration stage, comprising:
 monitoring a temperature of said evaporator;   comparing said monitored temperature of said evaporator to a first predetermined value;   monitoring a temperature of said heat exchanger;   comparing said monitored temperature of said heat exchanger to a second predetermined value;   determining said freezer has experienced a severe performance degradation if said monitored temperature of said evaporator is less than said first predetermined value and said monitored temperature of said heat exchanger is less than said second predetermined value; and   alerting an operator of said severe degradation.   
     
     
         5 . A method of predicting failure of an ultralow temperature freezer, comprising:
 determining a door of said freezer has been closed;   measuring elapsed time from said determination until a storage chamber of said freezer reaches a predetermined temperature;   alerting an operator of a performance degradation if said elapsed time is greater than a first predetermined value.   
     
     
         6 . The method of  claim 5 , further comprising alerting an operator of a severe performance degradation if said elapsed time is greater than a second predetermined value, greater than the first predetermined value. 
     
     
         7 . The method of  claim 5 , wherein said measuring and alerting steps are only performed if an ambient temperature is within a predetermined range. 
     
     
         8 . A method of predicting failure of an ultralow temperature freezer, wherein said freezer comprises two cascaded refrigeration stages, a first compressor disposed in a first refrigeration stage and a heat exchanger disposed between said two cascaded stages to remove heat from a second refrigeration stage, comprising:
 determining said first compressor is actuated;   monitoring an elapsed time from said actuation until said heat exchanger reaches a predetermined temperature; and   alerting an operator of a performance degradation if said elapsed time is greater than a first predetermined value.   
     
     
         9 . The method of  claim 8 , further comprising:
 alerting an operator of a severe performance degradation if said elapsed time is greater than a second predetermined value, greater than said first predetermined value.   
     
     
         10 . A method of predicting failure of an ultralow temperature freezer, comprising:
 monitoring a temperature of a compressor used in said freezer;   monitoring an ambient temperature outside said freezer;   comparing said monitored temperature of said compressor to said ambient temperature;   alerting an operator of a performance degradation if a difference between said monitored temperature of said compressor and said ambient temperature is greater than a first predetermined value.   
     
     
         11 . The method of  claim 10 , further comprising:
 alerting an operator of a severe performance degradation if a difference between said monitored temperature of said compressor and said ambient temperature is greater than a second predetermined value, greater than said first predetermined value.