Internal air circulation control in a refrigerated transport container

Abstract

Disclosed is a system for and a method of controlling internal air circulation within a refrigerated transport container ( 1 ), the refrigerated transport container ( 1 ) comprising a cooling unit ( 40 ), and a control unit, where the cooling unit ( 40 ) comprises at least a compressor ( 6 ) and an evaporator ( 16 ) comprising one or more evaporator fans ( 10 ) wherein the method comprises the step of: controlling the operation of the one or more evaporator fans ( 10 ) based on one or more predetermined heat load related indicators during periods where the compressor ( 6 ) is inactive wherein the one or more evaporator fans ( 10 ) are controlled to increase internal air circulation when the one or more predetermined heat load related indicators indicate a heat load increase and wherein the one or more evaporator fans ( 10 ) are controlled to decrease internal air circulation when the one or more predetermined heat load related indicators indicate a heat load reduction.

1 . A method of controlling internal air circulation within a refrigerated transport container ( 1 ), the refrigerated transport container ( 1 ) comprising a transport volume ( 45 ), a cooling unit ( 40 ), and a control unit, where the cooling unit ( 40 ) comprises at least a compressor ( 6 ) and an evaporator ( 16 ) comprising one or more evaporator fans ( 10 ) wherein the method comprises the step of:
 controlling the operation of the one or more evaporator fans ( 10 ) based on one or more predetermined heat load related indicators during periods where the compressor ( 6 ) is inactive wherein the one or more evaporator fans ( 10 ) are controlled to increase internal air circulation when the one or more predetermined heat load related indicators indicate a heat load increase and wherein the one or more evaporator fans ( 10 ) are controlled to decrease internal air circulation when the one or more predetermined heat load related indicators indicate a heat load reduction.   
     
     
         2 . The method according to  claim 1 , wherein the one or more evaporator fans ( 10 ) have a given speed setting selected from the group of: a first speed setting (HIGH) with a predetermined first speed and a second speed setting (LOW) with a predetermined second speed, where the first speed is greater than the second speed, wherein the step of controlling the operation of the one or more evaporator fans ( 10 ) during periods where the compressor ( 6 ) is inactive comprises:
 controlling the given speed setting of the one or more evaporator fans ( 10 ) according to one or more predetermined heat load related criteria, wherein
 the first speed setting (HIGH) is either maintained or changed to the second speed setting (LOW), depending on a first set of one or more predetermined heat load related criteria and the one or more predetermined heat load related indicators, and 
 the second speed setting (LOW) is either maintained or changed to the first speed setting (HIGH) depending on a second set of one or more predetermined heat load related criteria and the one or more predetermined heat load related indicators. 
   
     
     
         3 . The method according to  claim 2 , wherein the one or more evaporator fans ( 10 ) have a given speed setting selected from the group of: the first speed setting (HIGH), the second speed setting (LOW), and a third speed setting (OFF) with a predetermined third speed, where the second speed is greater than the third speed, wherein the step of controlling the operation of the one or more evaporator fans ( 10 ) during periods where the compressor ( 6 ) is inactive further comprises:
 if hardware limitations or considerations of the one or more evaporator fans ( 10 ) require that the third speed setting (OFF) is used between the second (LOW) and first speed setting (HIGH) then the third speed setting (OFF) is used only in a pre-determined maximum period of time.   
     
     
         4 . The method according to  claim 1 , wherein the one or more evaporator fans ( 10 ) have a given speed setting selected from the group of: a first speed setting (HIGH) with a predetermined first speed, a second speed setting (LOW) with a predetermined second speed, and a third speed setting (OFF) with a predetermined third speed, where the first speed is greater than the second speed and the second speed is greater than the third speed, wherein the step of controlling the operation of the one or more evaporator fans ( 10 ) during periods where the compressor ( 6 ) is inactive comprises:
 controlling the given speed setting of the one or more evaporator fans ( 10 ) according to one or more predetermined heat load related criteria, wherein
 the first speed setting (HIGH) is either maintained or changed to the second speed setting (LOW) depending on a first set of one or more predetermined heat load related criteria and the one or more predetermined heat load related indicators, and 
 the second speed setting (LOW) is either maintained or changed to the third speed setting (OFF) or changed to the first speed setting (HIGH) depending on a second set of one or more predetermined heat load related criteria and the one or more predetermined heat load related indicators, 
 and the method further comprises the steps of 
 the third speed setting (OFF) is either maintained or changed to the second speed setting (LOW) depending on a third set of one or more predetermined heat load related criteria and the one or more predetermined heat load related indicators. 
   
     
     
         5 . The method according to  claim 4 , wherein the step of controlling the operation of the one or more evaporator fans ( 10 ) during periods where the compressor ( 6 ) is inactive further comprises:
 if hardware limitations require that the first speed setting (HIGH) is used between the third (OFF) and the second (LOW) speed setting then the first speed setting is used only in a pre-determined maximum period of time.   
     
     
         6 . The method according to  claim 2 , wherein the one or more predetermined heat load related indicators comprise a parameter representing a change in return ( 50 ) or supply air ( 55 ) temperature and wherein the method further comprises the step of:
 measuring a current return or supply air flow temperature (Tret_t) by a return air temperature sensor ( 5 ) or supply air temperature sensor ( 25 ), where return or supply air flow ( 50 ,  55 ) is received from or supplied to the refrigerated transport volume ( 45 ) to derive the parameter representing a change in return or supply air temperature,   
       and wherein
 the first set of one or more predetermined heat load related criteria comprises changing the given speed setting from the first speed setting (HIGH) to the second speed setting (LOW)
 when a change between current return or supply air flow temperature after a predetermined period of time (Tret_ 5 ) and a return or supply air flow temperature from the start of the given speed setting (Tret_ 0 ) is within a predetermined first change range (ΔTret 5 _rate_HIGH), and 
 
 the second set of one or more predetermined heat load related criteria comprises changing the given speed setting from the second speed setting (LOW) to the first speed setting (HIGH)
 when a change between current return or supply air flow temperature (Tret_t) and a return or supply air flow temperature from the start of the given speed setting (Tret_ 0 ) exceeds a predetermined second change range. 
 
 
     
     
         7 . The method according to  claim 4 , wherein the one or more predetermined heat load related indicators comprise a parameter representing a change in return or supply air temperature and wherein the method further comprises the step of:
 measuring a current return ( 50 ) or supply air ( 55 ) flow temperature (Tret_t) by a return air temperature sensor ( 5 ) or a supply air temperature sensor ( 25 ), where return or supply air flow ( 50 ,  55 ) is received from or supplied to the refrigerated transport volume ( 45 ),   
       and wherein
 the first set of one or more predetermined heat load related criteria comprises changing the given speed setting from the first speed setting (HIGH) to the second speed setting (LOW)
 when a change between current return or supply air flow temperature after a predetermined period of time (Tret_ 5 ) and return or supply air flow temperature from the start of the given speed setting (Tret_ 0 ) is within a predetermined first change range threshold (ΔTret 5 _rate_HIGH), 
 
 the second set of one or more predetermined heat load related criteria comprises changing the given speed setting from the second speed setting (LOW) to the first speed setting (HIGH)
 when a change between current return or supply air flow temperature (Tret_t) and return or supply air flow temperature from the start of the given speed setting (Tret_ 0 ) exceeds a predetermined second change range for the given speed setting and a previous fan speed was the first speed (HIGH), where the previous fan speed is the fan speed of the most recent period, during which the compressor ( 6 ) was inactive, that was not the second speed (LOW), 
 
 the second set of one or more predetermined heat load related criteria comprises changing the given speed setting from the second speed setting (LOW) to the third speed setting (OFF)
 when a previous speed setting was the third speed setting (OFF) and after a predetermined period of time (Tret_ 5 ) since changing to the second speed setting (LOW) the magnitude of the change or rate of change is within a predetermined third change range (ΔTret 5 _rate_LOW), where the change or rate of change is a change or rate of change between return or supply air temperature (Tret_t) and return or supply air temperature (Tret_ 0 ) at the start of a preceding period with the third speed setting (OFF), and 
 
 the third set of one or more predetermined criteria comprises changing the given speed setting from the third speed setting (OFF) to the second speed setting (LOW)
 when a change between current return or supply air flow temperature (Tret_t) and return or supply air flow temperature from the start of the given speed setting (Tret_ 0 ) exceeds a predetermined fourth change range for the given speed setting. 
 
 
     
     
         8 . The method according to  claim 2 , wherein a minimum duration period is associated with each of the first, the second, and the third speed setting and no change of a given speed setting is allowed until the minimum duration period for the given speed setting has elapsed. 
     
     
         9 . The method according to  claim 2 , wherein the first and the second speed setting is associated with a maximum duration period, and
 the first set of one or more predetermined heat load related criteria comprises changing the given speed setting from the first speed setting (HIGH) to the second speed setting (LOW) if the given speed setting has lasted more than the maximum duration (tmax_HIGH) for the first speed setting,   the second set of one or more predetermined heat load related criteria comprises changing the given speed setting from the second speed setting (LOW) to the first speed setting (HIGH) if the given speed setting has lasted more than the maximum duration (tmax_LOW) for the second speed.   
     
     
         10 . The method according to  claim 4 , wherein the first, the second, and the third speed setting is associated with a maximum duration period, and
 the first set of one or more predetermined heat load related criteria comprises changing the given speed setting from the first speed setting (HIGH) to the second speed setting (LOW) if the given speed setting has lasted more than the maximum duration for the first speed setting,   the second set of one or more predetermined heat load related criteria comprises changing the given speed setting from the second speed setting (LOW) to the third speed setting (OFF) if the given speed setting has lasted more than the maximum duration (tmax_LOW) for the second speed setting and a previous fan speed was the first speed (HIGH), where the previous fan speed is the fan speed of the most recent period, during which the compressor was inactive, that was not the second speed (LOW), and   the third set of one or more predetermined heat load related criteria comprises changing the given speed setting from the third speed setting (OFF) to the second speed setting (LOW) if the given speed setting has lasted more than the maximum duration (tmax_OFF) for the third speed setting.   
     
     
         11 . The method according to  claim 1 , wherein the method comprises the further step of:
 maintaining the speed of the one or more evaporator fans ( 10 ) to be at a maximum or the first speed (HIGH) during a period of time where the compressor ( 6 ) is inactive if a predetermined heat load related indicator indicates a heat load larger than a predetermined heat load value.   
     
     
         12 . The method according to  claim 1 , wherein the one or more predetermined heat load related indicators comprise a duration of a previous period of time where the compressor ( 6 ) was inactive, and wherein the method further comprises the steps of:
 comparing the duration with a predetermined circulation time threshold t ct , and   maintaining the speed of the one or more evaporator fans ( 10 ) at a maximum or the first (HIGH) speed during a current period where the compressor ( 6 ) is inactive if the previous period where the compressor ( 6 ) was inactive was shorter than the predetermined circulation time threshold t ct .   
     
     
         13 . The method according to  claim 12 , wherein the predetermined heat load related indicator is a function of both duration of a previous period where the compressor ( 6 ) was inactive and measured supply and/or return air temperatures during that period. 
     
     
         14 . The method according to  claim 1 , wherein the one or more predetermined heat load related indicators comprise the difference between supply and return air temperature, and wherein the method further comprises the steps of:
 maintaining the speed of the one or more evaporator fans ( 10 ) at the first speed setting (HIGH) during a period where the compressor ( 6 ) is inactive, if an observed difference, or a function of differences observed previously, between supply and return air temperature exceeds a predetermined limit value (ΔTmax).   
     
     
         15 . The method according to  claim 14 , wherein the method further comprises the steps of:
 relating the predetermined limit value (ΔTmax) to ambient temperature.   
     
     
         16 . The method according to  claim 1 , wherein the method further comprises the step of:
 maintaining the speed of the one or more evaporator fans ( 10 ) at a maximum or the first (HIGH) speed if a temperature setpoint is in a predetermined temperature setpoint range where very temperature-critical cargoes are known to be carried.   
     
     
         17 . The method according to  claim 2 , wherein the method further comprises:
 maintaining the one or more evaporator fans ( 10 ) at at least the second predetermined speed setting (LOW) when a requirement for heating is determined.   
     
     
         18 . The method according to  claim 17 , wherein the method further comprises the step of:
 maintaining the one or more evaporator fans ( 10 ) at the first predetermined speed setting (HIGH) when an increased requirement for heating is determined.   
     
     
         19 . A method according to  claim 1 , wherein the refrigerated transport container ( 1 ) is not a transport container but another type of refrigerated space in connection with a refrigeration unit. 
     
     
         20 . A system for controlling internal air circulation within a refrigerated transport container ( 1 ), the refrigerated transport container ( 1 ) comprising a transport volume ( 45 ), a cooling unit ( 40 ), and a control unit, where the cooling unit ( 40 ) comprises at least a compressor ( 6 ) and an evaporator ( 16 ) comprising one or more evaporator fans ( 10 ) wherein the system comprises a control system comprising a processing unit adapted to:
 control the operation of the one or more evaporator fans ( 10 ) based on one or more predetermined heat load related indicators during periods where the compressor ( 6 ) is inactive wherein the one or more evaporator fans ( 10 ) are controlled to increase internal air circulation when the one or more predetermined heat load related indicators indicate a heat load increase and wherein the one or more evaporator fans ( 10 ) are controlled to decrease internal air circulation when the one or more predetermined heat load related indicators indicate a heat load reduction.   
     
     
         21 . The system according to  claim 20 , wherein the one or more evaporator fans ( 10 ) have a given speed setting selected from the group of: a first speed setting (HIGH) with a predetermined first speed and a second speed setting (LOW) with a predetermined second speed, where the first speed is greater than the second speed, wherein the processing unit is adapted to control the operation of the one or more evaporator fans ( 10 ) during periods where the compressor ( 6 ) is inactive by:
 controlling the given speed setting of the one or more evaporator fans ( 10 ) according to one or more predetermined heat load related criteria, wherein
 the first speed setting (HIGH) is either maintained or changed to the second speed setting (LOW), depending on a first set of one or more predetermined heat load related criteria and the one or more predetermined heat load related indicators, and 
 the second speed setting (LOW) is either maintained or changed to the first speed setting (HIGH) depending on a second set of one or more predetermined heat load related criteria and the one or more predetermined heat load related indicators. 
   
     
     
         22 . The system according to  claim 21 , wherein the one or more evaporator fans ( 10 ) have a given speed setting selected from the group of: the first speed setting (HIGH), the second speed setting (LOW), and a third speed setting (OFF) with a predetermined third speed, where the second speed is greater than the third speed, and wherein the processing unit is adapted to control the operation of the one or more evaporator fans ( 10 ) during periods where the compressor ( 6 ) is inactive by:
 if hardware limitations or considerations of the one or more evaporator fans ( 10 ) require that the third speed setting (OFF) is used between the second (LOW) and first speed setting (HIGH) then the third speed setting (OFF) is used only in a pre-determined maximum period of time.   
     
     
         23 . The system according to  claim 20 , wherein the one or more evaporator fans ( 10 ) have a given speed setting selected from the group of: a first speed setting (HIGH) with a predetermined first speed, a second speed setting (LOW) with a predetermined second speed, and a third speed setting (OFF) with a predetermined third speed, where the first speed is greater than the second speed and the second speed is greater than the third speed, wherein the processing unit is adapted to control the operation of the one or more evaporator fans ( 10 ) during periods where the compressor ( 6 ) is inactive by:
 controlling the given speed setting of the one or more evaporator fans ( 10 ) according to one or more predetermined heat load related criteria, wherein
 the first speed setting (HIGH) is either maintained or changed to the second speed setting (LOW) depending on a first set of one or more predetermined heat load related criteria and the one or more predetermined heat load related indicators, and 
 the second speed setting (LOW) is either maintained or changed to the third speed setting (OFF) or changed to the first speed setting (HIGH) depending on a second set of one or more predetermined heat load related criteria and the one or more predetermined heat load related indicators, 
   and the processing unit is adapted to
 maintain the third speed setting (OFF) or change it to the second speed setting (LOW) depending on a third set of one or more predetermined heat load related criteria and the one or more predetermined heat load related indicators. 
   
     
     
         24 . The system according to  claim 23 , wherein the processing unit is adapted to control the operation of the one or more evaporator fans ( 10 ) during periods where the compressor ( 6 ) is inactive by:
 if hardware limitations require that the first speed setting (HIGH) is used between the third (OFF) and the second (LOW) speed setting then using the first speed setting only in a pre-determined maximum period of time.   
     
     
         25 . The system according to  claim 21 , wherein the one or more predetermined heat load related indicators comprise a parameter representing a change in return ( 50 ) or supply air ( 55 ) temperature and wherein the processing unit is adapted to:
 measure a current return or supply air flow temperature (Tret_t) by a return air temperature sensor ( 5 ) or supply air temperature sensor ( 25 ), where return or supply air flow ( 50 ,  55 ) is received from or supplied to the refrigerated transport volume ( 45 ) to derive the parameter representing a change in return or supply air temperature,   
       and wherein
 the first set of one or more predetermined heat load related criteria comprises changing the given speed setting from the first speed setting (HIGH) to the second speed setting (LOW)
 when a change between current return or supply air flow temperature after a predetermined period of time (Tret_ 5 ) and a return or supply air flow temperature from the start of the given speed setting (Tret_ 0 ) is within a predetermined first change range (ΔTret 5 _rate_HIGH), and 
 
 the second set of one or more predetermined heat load related criteria comprises changing the given speed setting from the second speed setting (LOW) to the first speed setting (HIGH)
 when a change between current return or supply air flow temperature (Tret_t) and a return or supply air flow temperature from the start of the given speed setting (Tret_ 0 ) exceeds a predetermined second change range. 
 
 
     
     
         26 . The system according to  claim 23 , wherein the one or more predetermined heat load related indicators comprise a parameter representing a change in return or supply air temperature and wherein the processing unit is adapted to:
 measure a current return ( 50 ) or supply air ( 55 ) flow temperature (Tret_t) by a return air temperature sensor ( 5 ) or a supply air temperature sensor ( 25 ), where return or supply air flow ( 50 ,  55 ) is received from or supplied to the refrigerated transport volume ( 45 ),   
       and wherein
 the first set of one or more predetermined heat load related criteria comprises changing the given speed setting from the first speed setting (HIGH) to the second speed setting (LOW)
 when a change between current return or supply air flow temperature after a predetermined period of time (Tret_ 5 ) and return or supply air flow temperature from the start of the given speed setting (Tret_ 0 ) is within a predetermined first change range threshold (ΔTret 5 _rate_HIGH), 
 
 the second set of one or more predetermined heat load related criteria comprises changing the given speed setting from the second speed setting (LOW) to the first speed setting (HIGH)
 when a change between current return or supply air flow temperature (Tret_t) and return or supply air flow temperature from the start of the given speed setting (Tret_ 0 ) exceeds a predetermined second change range for the given speed setting and a previous fan speed was the first speed (HIGH), where the previous fan speed is the fan speed of the most recent period, during which the compressor ( 6 ) was inactive, that was not the second speed (LOW), 
 
 the second set of one or more predetermined heat load related criteria comprises changing the given speed setting from the second speed setting (LOW) to the third speed setting (OFF)
 when a previous speed setting was the third speed setting (OFF) and after a predetermined period of time (Tret_ 5 ) since changing to the second speed setting (LOW) the magnitude of the change or rate of change is within a predetermined third change range (ΔTret 5 _rate_LOW), where the change or rate of change is a change or rate of change between return or supply air temperature (Tret_t) and return or supply air temperature (Tret_ 0 ) at the start of a preceding period with the third speed setting (OFF), and 
 
 the third set of one or more predetermined criteria comprises changing the given speed setting from the third speed setting (OFF) to the second speed setting (LOW)
 when a change between current return or supply air flow temperature (Tret_t) and return or supply air flow temperature from the start of the given speed setting (Tret_ 0 ) exceeds a predetermined fourth change range for the given speed setting. 
 
 
     
     
         27 . The system according to  claim 21 , wherein a minimum duration period is associated with each of the first, the second, and the third speed setting and no change of a given speed setting is allowed until the minimum duration period for the given speed setting has elapsed. 
     
     
         28 . The system according to  claim 21 , wherein the first and the second speed setting is associated with a maximum duration period, and
 the first set of one or more predetermined heat load related criteria comprises changing the given speed setting from the first speed setting (HIGH) to the second speed setting (LOW) if the given speed setting has lasted more than the maximum duration (tmax_HIGH) for the first speed setting,   the second set of one or more predetermined heat load related criteria comprises changing the given speed setting from the second speed setting (LOW) to the first speed setting (HIGH) if the given speed setting has lasted more than the maximum duration (tmax_LOW) for the second speed.   
     
     
         29 . The system according to  claim 23 , wherein the first, the second, and the third speed setting is associated with a maximum duration period, and
 the first set of one or more predetermined heat load related criteria comprises changing the given speed setting from the first speed setting (HIGH) to the second speed setting (LOW) if the given speed setting has lasted more than the maximum duration for the first speed setting,   the second set of one or more predetermined heat load related criteria comprises changing the given speed setting from the second speed setting (LOW) to the third speed setting (OFF) if the given speed setting has lasted more than the maximum duration (tmax_LOW) for the second speed setting and a previous fan speed was the first speed (HIGH), where the previous fan speed is the fan speed of the most recent period, during which the compressor was inactive, that was not the second speed (LOW), and   the third set of one or more predetermined heat load related criteria comprises changing the given speed setting from the third speed setting (OFF) to the second speed setting (LOW) if the given speed setting has lasted more than the maximum duration (tmax_OFF) for the third speed setting.   
     
     
         30 . The system according to  claim 20 , wherein the processing unit is adapted to:
 maintain the speed of the one or more evaporator fans ( 10 ) to be at a maximum or the first speed (HIGH) during a period of time where the compressor ( 6 ) is inactive if a predetermined heat load related indicator indicates a heat load larger than a predetermined heat load value.   
     
     
         31 . The system according to  claim 20 , wherein the one or more predetermined heat load related indicators comprise a duration of a previous period of time where the compressor ( 6 ) was inactive, and wherein the processing unit is adapted to:
 compare the duration with a predetermined circulation time threshold t ct , and   maintain the speed of the one or more evaporator fans ( 10 ) at a maximum or the first (HIGH) speed during a current period where the compressor ( 6 ) is inactive if the previous period where the compressor ( 6 ) was inactive was shorter than the predetermined circulation time threshold t ct .   
     
     
         32 . The system of according to  claim 31 , wherein the predetermined heat load related indicator is a function of both duration of a previous period where the compressor ( 6 ) was inactive and measured supply and/or return air temperatures during that period. 
     
     
         33 . The system according to  claim 20 , wherein the one or more predetermined heat load related indicators comprise the difference between supply and return air temperature, and wherein the processing unit is adapted to:
 maintain the speed of the one or more evaporator fans ( 10 ) at the first speed setting (HIGH) during a period where the compressor ( 6 ) is inactive, if an observed difference, or a function of differences observed previously, between supply and return air temperature exceeds a predetermined limit value (ΔTmax).   
     
     
         34 . The system according to  claim 33 , wherein the processing unit is adapted to:
 relate the predetermined limit value (ΔTmax) to ambient temperature.   
     
     
         35 . The system according to  claim 20 , wherein the processing unit is adapted to:
 maintain the speed of the one or more evaporator fans ( 10 ) at a maximum or the first (HIGH) speed if a temperature setpoint is in a predetermined temperature setpoint range where very temperature-critical cargoes are known to be carried.   
     
     
         36 . The system according to  claim 21 , wherein the processing unit is adapted to:
 maintain the one or more evaporator fans ( 10 ) at at least the second predetermined speed setting (LOW) when a requirement for heating is determined.   
     
     
         37 . The system according to  claim 36 , wherein the processing unit is adapted to:
 maintain the one or more evaporator fans ( 10 ) at the first predetermined speed setting (HIGH) when an increased requirement for heating is determined.   
     
     
         38 . A system according to  claim 20 , wherein the refrigerated transport container ( 1 ) is not a transport container but another type of refrigerated space in connection with a refrigeration unit.