Temperature control in a refrigerated transport container

Abstract

Disclosed is a system for and a method of controlling temperature within a refrigerated transport container ( 1 ), the refrigerated transport container ( 1 ) comprising at least a transport volume ( 45 ), a control unit ( 7 ), and a cooling space ( 41 ), one or more evaporator fans ( 10 ) providing an air flow through the cooling space ( 41 ), where air passing through the cooling space passes at least a return air temperature sensor ( 5 ), a cooling unit ( 16 ), and a supply air temperature sensor ( 25 ), wherein the method comprises controlling unmeasured temperatures in the transport volume ( 45 ) within a temperature range adjacent to a setpoint or target temperature (Tset), using two or more transport volume temperature indicators, where the indicators are based on at least measured supply air temperature and/or measured return air temperature. In this way, control of unmeasured temperatures in the transport volume is provided that enables improved control over temperatures of the loaded perishable produce thereby reducing the rate of quality loss of the transported produce.

1 . A method of controlling temperature within a refrigerated transport container ( 1 ), the refrigerated transport container ( 1 ) comprising at least a transport volume ( 45 ), a control unit ( 7 ), and a cooling space ( 41 ), one or more evaporator fans ( 10 ) providing an air flow through the cooling space ( 41 ), where air passing through the cooling space passes at least a return air temperature sensor ( 5 ), a cooling unit ( 16 ), and a supply air temperature sensor ( 25 ), wherein the method comprises:
 controlling unmeasured temperatures in the transport volume ( 45 ) within a temperature range adjacent to a setpoint or target temperature (Tset), using two or more transport volume temperature indicators, where the indicators are based on at least measured supply air temperature and/or measured return air temperature.   
     
     
         2 . The method according to  claim 1 , wherein the at least two transport volume temperature indicators are one or more selected from the group consisting of:
 current and/or recent supply air temperature (Tsup), or a function thereof,   current and/or recent return air temperature (Tret), or a function thereof,   an estimator for temperature (Tcold) in a coldest spot of the transport volume ( 45 ),   one or more estimators for temperatures (Twarm) in one or more warmer spots in the transport volume ( 45 ),   
       where upon activation of the controller ( 7 ), the estimators are initialized using:
 current and/or recent return air temperatures Tret and/or, 
 current and/or recent supply air temperatures Tsup and/or, 
 earlier estimates if available and/or 
 a history of power supply to the cooling unit within a predetermined period of time. 
 
     
     
         3 . The method according to  claim 2 , wherein
 the estimator for temperature (Tcold) in a coldest spot of the transport volume ( 45 ) estimates temperature (Tcold) in a coldest spot of the transport volume ( 45 ) based on current and/or recent supply air temperatures (Tsup) and one or more previous estimates of the temperature (Tcold) in a coldest spot of the transport volume ( 45 ), and/or   the one or more estimators for temperatures (Twarm) in one or more warmer spots in the transport volume ( 45 ) estimates temperatures (Twarm) in one or more warmer spots of the transport volume ( 45 ) based on current and/or recent supply air temperatures (Tsup), current and/or recent return air temperatures (Tret), and one or more previous estimates for temperatures (Twarm) in one or more warmer spots in the transport volume ( 45 ).   
     
     
         4 . The method according to  claim 1 , wherein the method comprises:
 using an estimator for temperature (Tcold) in a coldest spot of the transport volume and one or more estimators for temperatures (Twarm) in one or more warmer spots of the transport volume ( 45 ), and controlling a weighted average of these estimators to the temperature setpoint (Tset).   
     
     
         5 . The method according to  claim 3 , wherein the method comprises:
 constraining the estimator for temperature (Tcold) in the coldest spot to a minimum constraint and/or a maximum constraint.   
     
     
         6 . The method according to  claim 1 , wherein the method comprises:
 using supply air temperature (Tsup) or a time-averaged function thereof, and return air temperature (Tret) or a time-averaged function thereof as indicators for the coldest and the warmest temperature in the transport volume, respectively, and   controlling a weighted average of the supply air temperature and the return air temperature to the temperature setpoint entered into the control unit.   
     
     
         7 . The method according to  claim 6 , wherein the method comprises:
 constraining the supply air temperature, or a time-averaged function thereof, to a minimum constraint and/or a maximum constraint.   
     
     
         8 . The method according to  claim 1 , wherein the method comprises:
 controlling by a slave-controller the supply air temperature or a time-averaged function thereof to a supply air temperature setpoint (Tset_slave), and adjusting the supply air temperature setpoint (Tset_slave) as a function of a temperature setpoint (Tset) and a measured return air temperature by a master-controller ( 203 ).   
     
     
         9 . The method according to  claim 8 , wherein the adjustment of the supply air temperature setpoint is made such that the weighted average of the supply air temperature and the return air temperature substantially equals the temperature setpoint (Tset). 
     
     
         10 . The method according to  claim 8 , wherein the method comprises
 constraining the supply air temperature setpoint (Tset_slave) to a minimum constraint and/or a maximum constraint.   
     
     
         11 . The method according to  claim 4 , wherein the value for the minimum constraint and/or the maximum constraint is dependent on the temperature setpoint and/or the time elapsed since activation of the controller ( 7 ). 
     
     
         12 . The method according to  claim 1 , where the refrigerated transport container is not a transport container but another type of refrigerated space in connection with a cooling unit. 
     
     
         13 . A system for controlling temperature within a refrigerated transport container ( 1 ), the refrigerated transport container ( 1 ) comprising at least a transport volume ( 45 ), and a cooling space ( 41 ), one or more evaporator fans ( 10 ) providing an air flow through the cooling space ( 41 ), where air passing through the cooling space passes at least a return air temperature sensor ( 5 ), a cooling unit ( 16 ), and a supply air temperature sensor ( 25 ), wherein the system comprises a control unit ( 7 ) adapted to:
 control unmeasured temperatures in the transport volume ( 45 ) within a temperature range adjacent to a setpoint or target temperature (Tset), using two or more transport volume temperature indicators, where the indicators are based on at least measured supply air temperature and/or measured return air temperature.   
     
     
         14 . The system according to  claim 13 , wherein the at least two transport volume temperature indicators are one or more selected from the group consisting of:
 current and/or recent supply air temperature (Tsup), or a function thereof,   current and/or recent return air temperature (Tret), or a function thereof,   an estimator for temperature (Tcold) in a coldest spot of the transport volume ( 45 ),   one or more estimators for temperatures (Twarm) in one or more warmer spots in the transport volume ( 45 ),   
       where upon activation of the controller ( 7 ), the estimators are initialized using:
 current and/or recent return air temperatures Tret and/or, 
 current and/or recent supply air temperatures Tsup and/or, 
 earlier estimates if available and/or 
 a history of power supply to the cooling unit within a predetermined period of time. 
 
     
     
         15 . The system according to  claim 14 , wherein
 the estimator for temperature (Tcold) in a coldest spot of the transport volume ( 45 ) estimates temperature (Tcold) in a coldest spot of the transport volume ( 45 ) based on current and/or recent supply air temperatures (Tsup) and one or more previous estimates of the temperature (Tcold) in a coldest spot of the transport volume ( 45 ), and/or   the one or more estimators for temperatures (Twarm) in one or more warmer spots in the transport volume ( 45 ) estimates temperatures (Twarm) in one or more warmer spots of the transport volume ( 45 ) based on current and/or recent supply air temperatures (Tsup), current and/or recent return air temperatures (Tret), and one or more previous estimates for temperatures (Twarm) in one or more warmer spots in the transport volume ( 45 ).   
     
     
         16 . The system according to  claim 13 , wherein the controller ( 7 ) is adapted to:
 use an estimator for temperature (Tcold) in a coldest spot of the transport volume and one or more estimators for temperatures (Twarm) in one or more warmer spots of the transport volume ( 45 ), and controlling a weighted average of these estimators to the temperature setpoint (Tset).   
     
     
         17 . The system according to  claim 15 , wherein the controller ( 7 ) is adapted to:
 constrain the estimator for temperature (Tcold) in the coldest spot to a minimum constraint and/or a maximum constraint.   
     
     
         18 . The system according to  claim 13 , wherein the controller ( 7 ) is adapted to:
 use supply air temperature (Tsup) or a time-averaged function thereof, and return air temperature (Tret) or a time-averaged function thereof as indicators for the coldest and the warmest temperature in the transport volume, respectively, and   control a weighted average of the supply air temperature and the return air temperature to the temperature setpoint entered into the control unit.   
     
     
         19 . The system according to  claim 18 , wherein the controller ( 7 ) is adapted to:
 constrain the supply air temperature, or a time-averaged function thereof, to a minimum constraint and/or a maximum constraint.   
     
     
         20 . The system according to  claim 13 , wherein the controller ( 7 ) is adapted to:
 control by a slave-controller the supply air temperature or a time-averaged function thereof to a supply air temperature setpoint (Tset_slave), and adjust the supply air temperature setpoint (Tset_slave) as a function of a temperature setpoint (Tset) and a measured return air temperature by a master-controller ( 203 ).   
     
     
         21 . The system according to  claim 20 , wherein the adjustment of the supply air temperature setpoint is made such that the weighted average of the supply air temperature and the return air temperature substantially equals the temperature setpoint (Tset). 
     
     
         22 . The system according to  claim 20 , wherein the controller ( 7 ) is adapted to
 constrain the supply air temperature setpoint (Tset_slave) to a minimum constraint and/or a maximum constraint.   
     
     
         23 . The system according to  claim 16 , wherein the value for the minimum constraint and/or the maximum constraint is dependent on the temperature setpoint and/or the time elapsed since activation of the controller ( 7 ). 
     
     
         24 . The system according to  claim 13 , wherein the refrigerated transport container is not a transport container but another type of refrigerated space in connection with a cooling unit.