Anti-sweat heater control system and method

Abstract

An improved anti-sweat heater control system is disclosed for reducing and/or eliminating sweat on cooled surfaces of a refrigerated container. A method for reducing or eliminating sweat from forming on cooled surfaces of a refrigerated container is also disclosed. A refrigerated container incorporating the anti-sweat heater control is also disclosed.

1 . A refrigeration system comprising: 
 a container subsystem including: 
 an interior;  
 at least one exposed surface,  
 a container temperature sensor;  
 a surrounding air temperature sensor; and  
 a humidity sensor;  
   a container cooling subsystem adapted to cool the interior of the container to a desired interior temperature;    an anti-sweat heater subsystem; and    a control subsystem adapted to control the cooling subsystem and the anti-sweat heaters, where the anti-sweat heater subsystem is designed to maintain all exposed outer surfaces at a temperature above a dewpoint temperature of the container's surroundings or to maintain all locations on the exposed surfaces in a substantially sweat-free condition and where the controller controls the anti-sweat heater subsystem at a frame sensor temperature plus a diversity factor, where the diversity factor is a difference between the container sensor temperature and a coldest outer surface temperature.    
   
   
       2 . The system of  claim 1 , further comprising a door frame and at least one door.  
   
   
       3 . The system of  claim 1 , wherein the at least one door includes a transparent member exposed to the container's surrounding.  
   
   
       4 . A refrigerated display apparatus comprising a case including a frame having a door, a sensor system adapted to measure a surrounding air temperature, a working temperature and a surrounding air humidity, a cooling system designed to cool an interior of the case to a desired reduced temperature, a heater system adapted heat the frame and door and a controller adapted to supply power to the cooling system sufficient to cool the interior of the case, the heater system sufficient to maintain all locations of the frame and the door at a temperature above a dewpoint temperature of the container's surroundings or to maintain all locations on the frame and the door in a substantially sweat-free condition, to the sensor system and to receive data from the sensor corresponding to the surrounding air temperature, the working temperature and the surrounding air humidity, where the controller determines the dewpoint temperature from the surrounding air temperature and humidity and supplies power to the heater system corresponding to the dewpoint temperature plus a diversity factor corresponding to a temperature difference between the working temperature and a coldest door or frame temperature.  
   
   
       5 . The system of  claim 1 , where the door includes a transparent member.  
   
   
       6 . A method for controlling sweat on a refrigerated container comprising the steps of: 
 providing the container comprising one surface or a plurality of outer surfaces exposed to their surrounding, a heater system, a sensor system including a surrounding air humidity sensor, a surrounding air temperature sensor and a frame temperature sensor, a cooling system and a control system;    measuring a surrounding air humidity, a surrounding air temperature, and a frame temperature;    determining a diversity factor corresponding to a temperature different between the frame temperature and a coldest temperature corresponding to a coldest temperature location on the outer surfaces when the container is in a stable cooled condition;    calculating a surrounding's dewpoint temperature from the surrounding air temperature and humidity;    calculating a relative set point temperature derived from the dewpoint temperature corrected by the diversity factor; and    supplying power to the heater system sufficient to maintain the temperature of the outer surfaces at a temperature above or equal to the relative set point temperature.    
   
   
       7 . A method for determining a diversity factor comprising the steps of: 
 providing a refrigerated container comprising one surface or a plurality of outer surfaces exposed to their surrounding, a heater system, a sensor system including a surrounding air humidity sensor, a surrounding air temperature sensor and a frame temperature sensor, a cooling system and a control system;    turning off power to the heater system;    cooling the container for a time sufficient for the container to achieve a sable cooled temperature,    determining a coldest outer surface temperature;    subtracting the coldest outer surface temperature from a frame sensor temperature to produce a diversity factor.