Method for controlling the atmosphere inside a refrigerated container

Abstract

To provide a method of controlling an atmosphere in a refrigerated container.SOLUTION: A method of operating an atmosphere control system to control an atmosphere in a refrigerated container includes operating the atmosphere control system in a start-up phase to control an oxygen level in the container; ending the start-up phase; and operating the atmosphere control system in a control phase to control the oxygen level and a carbon dioxide level in the container.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Patent Application No. 62 / 833,071, the entire contents of which are incorporated herein by reference.

[0002] The subject matter disclosed herein relates to atmosphere control systems for refrigerated containers, and in particular to systems for adjusting the atmosphere (e.g., the amount of nitrogen, oxygen and / or carbon dioxide) within a refrigerated container to obtain an atmosphere composition that extends the post-harvest shelf life or quality of perishable goods, such as fruits, vegetables, pharmaceuticals, and the like. [Background technology]

[0003] A typical refrigerated cargo container, such as a container utilized to transport cargo via sea, rail, or road, is a container modified to include a refrigeration unit located at one end of the container. The refrigeration unit includes a compressor, a condenser, an expansion valve, and an evaporator. A quantity of refrigerant circulates throughout the refrigeration unit, and one or more evaporator fans in the refrigeration unit drive a supply airflow through the evaporator, thereby cooling the supply air, and pushing the supply air into the container.

[0004] The atmosphere control system controls the amount of oxygen and carbon dioxide within the refrigerated container, for example, to vary the ripening rate of the produce stored within the container. The atmosphere control system may control the amount of oxygen (O2) and carbon dioxide (CO2) within the container. Existing atmosphere control systems may also add nitrogen (N2) to the container. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a method for controlling the atmosphere within a refrigerated container. [Means for solving the problem]

[0006] In one embodiment, a method of operating an atmosphere control system to control an atmosphere within a refrigerated container includes operating the atmosphere control system in a startup phase to control an oxygen level within the container, terminating the startup phase, and operating the atmosphere control system in a control phase to control the oxygen and carbon dioxide levels within the container.

[0007] In addition to or as an alternative to one or more of the features described herein, further embodiments may include, wherein the start-up phase includes adding nitrogen to the container until the oxygen level in the container is equal to the oxygen pull-down limit.

[0008] In addition to or as an alternative to one or more of the features described herein, further embodiments may include, wherein the start-up phase includes adding nitrogen to the container until the oxygen level in the container is less than the oxygen pull-down limit.

[0009] In addition to or as an alternative to one or more of the features described herein, further embodiments may include, wherein the control phase includes determining that the carbon dioxide level in the container is greater than an upper carbon dioxide threshold.

[0010] In addition to or as an alternative to one or more of the features described herein, further embodiments may include, when the carbon dioxide level within the container is greater than the upper carbon dioxide threshold, adding outside air to the container until the carbon dioxide level within the container is equal to the lower carbon dioxide control limit.

[0011] In addition to or as an alternative to one or more of the features described herein, further embodiments may include, wherein the control phase includes determining that the oxygen level in the container is greater than an upper oxygen threshold, and adding nitrogen to the container until the oxygen level in the container is equal to an oxygen pull-down limit.

[0012] In addition to or as an alternative to one or more of the features described herein, further embodiments may include, wherein the control phase includes determining that the oxygen level within the container is below a lower oxygen control limit and adding outside air to the container until the oxygen level within the container is equal to the upper oxygen control limit.

[0013] In addition to or as an alternative to one or more of the features described herein, further embodiments may include, wherein the control phase includes determining that the carbon dioxide level in the container is greater than an upper carbon dioxide control limit, and when the carbon dioxide level in the container is greater than the upper carbon dioxide control limit, adding nitrogen to the container until the carbon dioxide level in the container is equal to the lower carbon dioxide control limit.

[0014] In addition to or as an alternative to one or more of the features described herein, further embodiments may include adding outside air to the container until the oxygen level within the container is equal to the oxygen upper control limit.

[0015] In addition to or as an alternative to one or more of the features described herein, further embodiments may include adding nitrogen to the container after the start-up phase has ended until the carbon dioxide level in the container is equal to the carbon dioxide lower control limit.

[0016] In addition to or as an alternative to one or more of the features described herein, further embodiments may include adding outside air to the container until the oxygen level within the container is equal to the oxygen upper control limit.

[0017] In addition to or as an alternative to one or more of the features described herein, further embodiments may include adding nitrogen to the container after the start-up phase has ended until the carbon dioxide level in the container is equal to the carbon dioxide lower control limit.

[0018] In addition to or as an alternative to one or more of the features described herein, further embodiments may include adding outside air to the container until the oxygen level within the container is equal to the oxygen upper control limit.

[0019] Technical effects of embodiments of the present disclosure include controlling the atmosphere inside a container.

[0020] Unless expressly indicated otherwise, the foregoing features and elements may be combined in various non-exclusive combinations. These features and elements, and their operation, will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, that the following description and drawings are intended to be exemplary and explanatory in nature, and not limiting.

[0021] The present disclosure is illustrated by way of example and not limitation in the accompanying drawings in which like reference numerals indicate similar elements.

[0022] The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. [Brief description of the drawings]

[0023] [Figure 1] 1 illustrates a refrigerated container in an exemplary embodiment. [Diagram 2] 1 illustrates a refrigeration unit in an exemplary embodiment. [Diagram 3] 1 illustrates a refrigeration unit with an atmosphere control system in an exemplary embodiment. [Figure 4] 1 illustrates an atmosphere control system in an exemplary embodiment. [Diagram 5] 1 illustrates a process for controlling an atmosphere within a container in an exemplary embodiment. [Figure 6] 4 illustrates carbon dioxide control parameters in an exemplary embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] An embodiment of a refrigerated container 10 is shown in FIG. 1. The container 10 has a substantially rectangular structure with a top wall 12, an opposing bottom wall 14, opposing side walls 16, and a front wall 18. The container 10 further includes a door or doors (not shown) on a rear wall 20 opposite the front wall 18. The container 10 is configured to maintain a cargo 22 located within the container 10 at a selected temperature by utilizing a refrigeration unit 24 located on the container 10. The container 10 is mobile and is utilized to transport the cargo 22 via, for example, a truck, train, or ship. The container 10 may be integrated with a trailer or chassis. The refrigeration unit 24 is located on the front wall 18 and includes a compressor 26, a condenser 28, an expansion device 30 (e.g., TXV or EXV), an evaporator 32, and an evaporator fan 34 (shown in FIG. 2), as well as other auxiliary components.

[0025] Referring to FIG. 2 , the refrigeration unit 24 flows return air 36 through the evaporator 32 via an evaporator fan 34, thereby cooling the return air 36 to a selected temperature, and forces the cooled return air stream 36, referred to herein as supply air 38, through a refrigeration unit exhaust 40 and into the container 10, for example through openings 42 in one or more T-sections 44 extending along the bottom wall 14 of the container 10, to cool the cargo 22.

[0026] The refrigeration unit 24 is divided into an evaporator section 54, including the evaporator 32, the evaporator fan 34, and the evaporator fan motor 56, and a condenser section 58, including the compressor 26, the condenser 28, and the expansion device 30. In some embodiments, the expansion device 30 may be located in the evaporator section 54. The evaporator section 54 is separated from the condenser section 58 by a panel 50, which in some embodiments is located above the condenser section 58 and extends across the refrigeration unit 24. The condenser section 58 is exposed to the atmosphere and may be covered by a panel having an opening formed therein. During operation, the refrigerant is circulated in series through the compressor 26, the condenser 28, the expansion device 30, the evaporator 32, and back to the compressor 26. It is understood that the refrigeration unit 24 may include additional components (e.g., economizers, receivers, SMVs, etc.) that are not shown.

[0027] 3, the refrigeration unit 24 includes a housing 46 for housing the components of the refrigeration unit 24. In some embodiments, the housing 46 is separate and distinct from the container 10, while in other embodiments, the housing 46 is an integral part of the container 10. The condenser fan 29 is driven by a condenser motor (not shown) to move air over the condenser 28 and exhaust the air outside the refrigeration unit 24. The condenser 28 may be arranged radially around the condenser fan 29. The controller 70 controls the operation of the refrigeration unit 24, for example, by controlling the compressor 26 (e.g., on / off / variable speed), the evaporator fan motor 56 (e.g., on / off / variable speed), the condenser fan motor (e.g., on / off / variable speed), etc. The controller 70 may be implemented by a user. A processor-based device including a microprocessor, memory, a user interface, I / O inputs, etc. The controller 70 controls the components of the refrigeration unit 24 to maintain a desired temperature inside the container 10, as known in the art. An air compressor 80 is located in the condenser section 58. The air compressor 80 is a component of an atmosphere control system 74 (FIG. 4) that operates to regulate the atmosphere (e.g., oxygen and carbon dioxide) inside the container 10.

[0028] FIG. 4 illustrates an atmosphere control system 74 in an exemplary embodiment. The atmosphere control system 74 operates to control the level of at least one gas within the container 10. In an embodiment, the atmosphere control system 74 operates to control the level of oxygen and / or carbon dioxide. The atmosphere control system 74 includes an air compressor 80 located outside the condenser portion 58 and thus the interior of the container 10. The controller 70 may turn on the air compressor 80 by sending a signal to a relay or contactor that applies power to the air compressor 80. When turned on, the air compressor 80 pumps air outside the container 10 through a first filter 82 (e.g., a 50 micron particulate filter). The compressed air generated by the air compressor 80 flows from the condenser portion 58 into the evaporator portion 54 and reaches a heat exchanger 84. The heat exchanger may be various types of air-cooled heat exchangers (e.g., tube-plate-fin, microchannel, etc.). At the heat exchanger 84, the compressed air is cooled to facilitate moisture removal. From the heat exchanger 84, the compressed air flows to a water separator 86 where moisture is removed. From the water separator 86, the compressed air flows to a second filter 88 (e.g., a 5 micron particulate filter) and a third filter 89 (e.g., a 0.01 micron particulate filter). The second filter 88 and the third filter 89 may be located in the condenser section or the evaporator section 54.

[0029] From the second filter 88 and the third filter 89, the compressed air flows to the first valve V1. The first valve V1 has two exhaust ports that are controllable by the controller 70. When the first valve V1 is in a first position (e.g., an open position when energized), the compressed air is output from the first valve V1 to the interior of the container 10. The first valve V1 may be positioned to provide air upstream of the evaporator 32. When the first valve V1 is in a second position (e.g., a closed position when de-energized), the compressed air is directed to the separator 90. The separator 90 may be a membrane separator that produces a very pure, separated nitrogen output upstream of the evaporator 32. Other atmospheric gases, including oxygen, argon, and carbon dioxide, are exhausted to the condenser section 58 and further outside the refrigeration unit 24. The nitrogen from the separator 90 is directed to the second valve V2. The second valve V2 is a bleed that allows a small portion of the nitrogen from the separator 90 to be sent to a nitrogen sensor 96 for measuring the purity of the nitrogen. The second valve V2 may be controlled by the controller 70.

[0030] When nitrogen is provided upstream of the evaporator 32, it enters the interior of the container 10 and pushes oxygen and / or carbon dioxide out of the interior of the container 10. Reducing the oxygen level within the container 10 inhibits ripening of the produce. Reducing the carbon dioxide level within the container 10 inhibits damage to the cargo within the container due to high carbon dioxide levels.

[0031] During operation, the controller 70 monitors the level of at least one gas within the container 10 using an oxygen sensor 92 and / or a carbon dioxide sensor 94 in communication with the controller 70. The oxygen sensor 92 and / or the carbon dioxide sensor 94 may be located in the evaporator portion 54, upstream of the evaporator 32. To add fresh air to the container, the controller 70 signals the air compressor 80 to turn on and signals the first valve V1 to set the first valve V1 to an open position, which directs compressed air from the air compressor 80 to the interior of the container 10. To add nitrogen to the container and control the level of other gases, the controller 70 signals the air compressor 80 to turn on and signals the valve V1 to close, which directs compressed air from the air compressor 80 to a separator 90, which produces nitrogen that is directed to the interior of the container 10 (e.g., upstream or downstream of the evaporator 32). To measure the purity of the nitrogen produced by the separator 90, the controller 70 opens an outlet of the second valve V2 to direct a portion of the nitrogen to a nitrogen sensor 96 in communication with the controller 70. In some embodiments, a separate nitrogen sensor 96 is not used because measurements from the oxygen sensor 92 provide an indication of the nitrogen level in the container 10.

[0032] FIG. 5 illustrates a process for controlling the atmosphere control system 74 in an exemplary embodiment. The process is executed by the controller 70. The process includes a start-up phase 100 and a control phase 200. The process may regulate the oxygen and carbon dioxide levels (e.g., measured in percentages) in the container 10 using control bands. FIG. 6 illustrates an exemplary control band for the carbon dioxide level in the container 10. The control band includes a lower control limit and an upper control limit that define the control band. The set point is typically set in the middle of the control band, but may be at any location. FIG. 6 illustrates exemplary values ​​for controlling the carbon dioxide level in the container 10. The oxygen level in the container 10 may be controlled using similar control bands, although with different values.

[0033] Referring to FIG. 5, the start-up phase 100 begins at 102 and flows to 104, where an oxygen pull-down operation is initiated. The oxygen pull-down operation at 104 includes energizing the air compressor 80 to add nitrogen to the container 10 and setting the valve V1 to a closed position. The oxygen pull-down operation at 104 may last for a period of time (e.g., 40 hours). Once the oxygen pull-down operation at 104 is complete, flow proceeds to 106, where the controller 70 compares the carbon dioxide level (measured by the CO2 sensor 94) in the container 10 to an upper carbon dioxide threshold. The upper carbon dioxide threshold may be equal to the carbon dioxide control band plus a first offset (e.g., 2%) plus the carbon dioxide set point. If the carbon dioxide level in the container 10 at 106 is greater than the upper carbon dioxide threshold at 106, flow proceeds to 108, where the oxygen pull-down operation is considered complete.

[0034] If the carbon dioxide level in container 10 is equal to or less than the upper threshold at 106, flow proceeds to 110, where controller 70 determines whether the oxygen level in container 10 (as measured by O2 sensor 92) is equal to or greater than the oxygen pulldown limit (e.g., the minimum oxygen level achievable by adding nitrogen to container 10). If the oxygen level in container 10 is less than the oxygen pulldown limit at 110, flow proceeds to 112, where the oxygen pulldown operation is considered complete. At 112, controller 70 turns off air compressor 80.

[0035] If, at 110, the oxygen level within the container 10 is greater than or equal to the oxygen pulldown limit, flow proceeds to 114, where the controller 70 determines whether the carbon dioxide level within the container 10 is greater than the carbon dioxide upper control limit. If the carbon dioxide level within the container 10 is greater than the carbon dioxide upper control limit, flow proceeds to 116, where the oxygen pulldown operation is considered complete. If, at 114, the carbon dioxide level within the container 10 is less than or equal to the carbon dioxide upper control limit, flow proceeds to 104, where the oxygen pulldown operation is continued for an additional period of time (e.g., 10 hours) and the process continues.

[0036] From block 112, the process flows to block 202 of a control phase 200 called normal operation. Flow proceeds to block 204 where the controller 70 compares the carbon dioxide level in the container 10 to the carbon dioxide upper threshold. If the carbon dioxide level in the container 10 is greater than the carbon dioxide upper threshold at 204, flow proceeds to 206. An alert may be generated at 204. At 206, the air compressor 80 is turned on and valve V1 is set to an open position to add air to the container 10. The system remains in this state until the carbon dioxide level in the container 10 is equal to the carbon dioxide lower control limit. At this point, the air compressor 80 is turned off and flow proceeds to 202.

[0037] If the carbon dioxide level in the container 10 is equal to or less than the carbon dioxide upper threshold at 204, flow proceeds to 208. At 208, the controller 70 compares the oxygen level in the container 10 to the oxygen upper threshold. The oxygen upper threshold may be equal to the oxygen control band plus a second offset (e.g., 0.2%) plus the oxygen set point. If the oxygen level in the container 10 is greater than the oxygen upper threshold at 208, flow proceeds to 210. At 210, the air compressor 80 is turned on and valve V1 is set to a closed position to add nitrogen to the container 10. The system remains in this state until the oxygen level in the container 10 is equal to the oxygen pulldown limit. At this point, the air compressor 80 is turned off and flow proceeds to 202.

[0038] If the oxygen level in container 10 is below the upper oxygen threshold at 208, flow proceeds to 212. At 212, controller 70 compares the oxygen level in container 10 to the lower oxygen control limit. If the oxygen level in container 10 is below the lower oxygen control limit at 212, flow proceeds to 214. At 214, air compressor 80 is turned on and valve V1 is set to an open position to add air to container 10. The system remains in this state until the oxygen level in container 10 is equal to the upper oxygen control limit. At this point, air compressor 80 is turned off and flow proceeds to 202.

[0039] If the oxygen level in container 10 is equal to or greater than the lower oxygen control limit at 212, then flow proceeds to 216. At 216, controller 70 compares the carbon dioxide level in container 10 to the upper carbon dioxide control limit. If the carbon dioxide level in container 10 is equal to or less than the upper carbon dioxide control limit at 216, then flow proceeds to 202. If the carbon dioxide level in container 10 is greater than the upper carbon dioxide control limit at 216, then flow proceeds to 218. Note also that blocks 108 and 116 also feed into block 218.

[0040] At 218, the air compressor 80 is turned on and valve V1 is set to a second position to add nitrogen to the container 10. The system remains in this state until the carbon dioxide level in the container 10 is equal to the carbon dioxide lower control limit.

[0041] From 218, the process flows to 220, where the controller 70 determines whether to enter fresh air mode. At 220, the controller 70 determines whether the oxygen level within the container 10 is below the lower oxygen control limit. If the oxygen level within the container 10 is below the lower oxygen control limit, fresh air mode is enabled and the process flows to 214. Otherwise, the process returns to 202.

[0042] 5 only requires control of the air compressor 80 and the first valve V1, which simplifies the control process and eliminates the need for a dedicated controller for the atmosphere control system 74. The control process properly maintains the atmosphere within the container 10 and compensates for wide variations in container leakage and / or cargo respiration.

[0043] As discussed above, the embodiments may take the form of processor-implemented processes and apparatus for performing those processes, such as a processor in the controller 70. The embodiments may also take the form of computer program code including instructions embodied in a tangible medium, such as a network cloud storage, an SD card, a flash drive, a floppy diskette, a CD-ROM, a hard drive, or any other computer-readable storage medium. The embodiments may also take the form of computer program code transmitted over a transmission medium, such as over electrical wires or cables, through optical fibers, or via electromagnetic radiation. When implemented on a general-purpose microprocessor, the computer program code configures the microprocessor to create specific logic circuits.

[0044] Although the present invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present invention is not limited to such disclosed embodiments. Rather, the present invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present invention. In addition, while various embodiments of the present invention have been described, it should be understood that aspects of the present invention may include only some of the described embodiments. Thus, the present invention should not be deemed limited by the above description, but only by the scope of the appended claims.

Claims

1. 1. A method of operating an atmosphere control system to control an atmosphere within a refrigerated container, comprising: operating the atmosphere control system during a start-up phase, the operating including adding nitrogen to the container to control oxygen and carbon dioxide levels within the container; (i) terminating the start-up phase when the oxygen level is greater than an oxygen pull-down limit corresponding to a reduced oxygen level achievable by adding nitrogen to the container, and (ii) the carbon dioxide level is equal to or greater than a carbon dioxide upper control limit; operating the atmosphere control system in a control phase to control the oxygen and carbon dioxide levels within the container; Including, the control phase including determining that the carbon dioxide level in the container is greater than an upper carbon dioxide threshold; When the carbon dioxide level within the container is greater than the upper carbon dioxide threshold, adding outside air to the container until the carbon dioxide level within the container is below the lower carbon dioxide control limit.

2. 2. The method of claim 1, wherein the start-up phase comprises adding nitrogen to the container until the oxygen level in the container is equal to an oxygen pull-down limit.

3. 2. The method of claim 1, wherein the start-up phase comprises adding nitrogen to the container until the oxygen level in the container is less than an oxygen pull-down limit.

4. the control phase determining that the oxygen level within the container is greater than an upper oxygen threshold; 10. The method of claim 1, comprising adding nitrogen to the container until the oxygen level in the container is equal to an oxygen pulldown limit.

5. the control phase determining that the oxygen level within the container is below an oxygen lower control limit; 10. The method of claim 1, comprising adding ambient air to the container until the oxygen level within the container is equal to an oxygen upper control limit.

6. the control phase determining that the carbon dioxide level in the container is greater than a carbon dioxide upper control limit; 2. The method of claim 1, further comprising: when the carbon dioxide level in the container is greater than an upper carbon dioxide control limit, adding nitrogen to the container until the carbon dioxide level in the container is equal to a lower carbon dioxide control limit.

7. 7. The method of claim 6, further comprising adding ambient air to the container until the oxygen level within the container is equal to an oxygen upper control limit.

8. 3. The method of claim 2, further comprising adding nitrogen to said container after completion of said start-up phase until said carbon dioxide level in said container is equal to a carbon dioxide lower control limit.

9. 10. The method of claim 8, further comprising adding ambient air to the container until the oxygen level within the container is equal to an oxygen upper control limit.

10. 2. The method of claim 1, further comprising adding nitrogen to said container after completion of said start-up phase until said carbon dioxide level in said container is equal to a carbon dioxide lower control limit.

11. 11. The method of claim 10, further comprising adding outside air to the container until the oxygen level within the container is equal to an oxygen upper control limit.

12. A method of operating an atmosphere control system to control an atmosphere within a refrigerated container, comprising the steps of: operating the atmosphere control system during a start-up phase, the operating including adding nitrogen to the container to control oxygen and carbon dioxide levels within the container; (i) terminating the start-up phase when the oxygen level is greater than an oxygen pull-down limit corresponding to a reduced oxygen level achievable by adding nitrogen to the container, and (ii) the carbon dioxide level is equal to or greater than a carbon dioxide upper control limit; operating the atmosphere control system in a control phase to control the oxygen and carbon dioxide levels within the container; Including, the control phase including determining that the carbon dioxide level in the container is greater than an upper carbon dioxide threshold; when the carbon dioxide level within the container is greater than the upper carbon dioxide threshold, adding outside air to the container until the carbon dioxide level within the container is equal to or below the lower carbon dioxide control limit; the start-up phase includes adding nitrogen to the container until the oxygen level in the container is below the oxygen pull-down limit; the control phase includes determining that the oxygen level in the container is greater than an upper oxygen threshold; and adding nitrogen to the container until the oxygen level in the container is below the oxygen pull-down limit; the control phase comprising: determining that the carbon dioxide level in the container is greater than an upper carbon dioxide control limit; and when the carbon dioxide level in the container is greater than the upper carbon dioxide control limit, adding nitrogen to the container until the carbon dioxide level in the container is equal to or less than the lower carbon dioxide control limit; The method further comprising adding ambient air to the container until the oxygen level within the container is at or above an oxygen upper control limit.

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