Patent Description:
A typical refrigerated cargo container, such as those 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, condenser, expansion valve and evaporator. A volume of refrigerant circulates throughout the refrigeration unit, and one or more evaporator fans of the refrigeration unit blow a flow of supply air across the evaporator thereby cooling the supply air and forcing it out into the container.

An atmosphere control system controls the amount of oxygen and carbon dioxide inside the refrigerated container to, for example, change the rate of ripening of produce stored in the container. The atmosphere control system may control the amount of oxygen (O2) and carbon dioxide (CO2) in the container. Existing atmosphere control systems may add nitrogen (N2) to the container.

<CIT>, discloses a method for obtaining a desired atmosphere within an interior space during an initial startup phase of a controlled atmosphere system (CAS). During the initial startup phase of the CAS, nitrogen is provided to the system to reach a desired nitrogen purity range. If the atmosphere change rate is not sufficient to reach a desired atmosphere set point, nitrogen is added to reach a second desired nitrogen range. If the atmosphere change rate is still not sufficient to reach a desired atmosphere set point, ambient air is added. Once the atmosphere concentration has reached the desired atmosphere set point, the CAS operates in a standard operation mode.

<CIT> discloses a method and procedure for automatically checking predetermined functions and the operating performance of a controlled atmosphere system for a refrigerated container.

<CIT> discloses a refrigerated container which has a refrigeration system and a controlled atmosphere system. A refrigeration controller is programmed with certain acceptable conditions under which the controller atmosphere system will be allowed to operate. When these conditions are satisfied, the refrigeration controller will send an enabling signal to the controlled atmosphere system's controller allowing it to operate.

<CIT> discloses a method for controlling operation of a system for controlling the atmosphere within a confined space. The system includes an air compressor and a separator for dividing air into streams of oxygen and nitrogen, as well as an oxygen sensor and a carbon dioxide sensor. The compressor is operated to an on or off position response to inputs from the oxygen sensor and the carbon dioxide sensor.

<CIT> discloses a controlled atmosphere system to output a controlled atmosphere, the controlled atmosphere system includes: an air compressor to output compressed air, a heater to heat the compressed air output by the compressor, a nonelectric separator to divide the heated air into separate streams including oxygen and nitrogen. A controller is coupled to the compressor, the heater and the nonelectric separator to regulate temperature of the nonelectric separator to control a discharge pressure of the compressor.

<CIT> discloses systems and methods for creating and maintaining modified and controlled atmospheres in a rigid sealable container having at least one refrigeration unit with an integrated oxygen reduction means.

<CIT> discloses a method for maintaining produce in a near "just harvested" state during transport in a truck trailer by limiting the formation of Ethylene, scrubbing the atmosphere to remove any that does form, and by exhausting the atmosphere of any residual Ethylene.

<CIT> discloses a system and method for maintaining a desired carbon dioxide concentration within an interior space of a transport unit during transport. The method includes determining the carbon dioxide concentration in the interior space; and enabling a carbon dioxide injection system when the carbon dioxide concentration is not at a set point value.

<CIT> discloses a method of controlling the atmosphere in a closeable space filled with agricultural or horticultural products. The method comprises directly detecting the respiration of the agricultural or horticultural products and adjusting an oxygen content, a carbon dioxide content and/or a nitrogen content in the space subject to the detected respiration.

Viewed from a first aspect of the invention, a method of operating an atmosphere control system to control an atmosphere in a refrigerated container, the method comprising: operating the atmosphere control system in a start up phase to control an oxygen level in the container; the start up phase comprises adding nitrogen to the container; ending the start up phase if: (i) a carbon dioxide level in the container is not greater than an upper threshold, the oxygen level in the container is greater than or equal to an oxygen pulldown limit, and the carbon dioxide level in the container is greater than a carbon dioxide upper control limit; or (ii) the carbon dioxide level in the container is greater than the upper threshold; or (iii) the carbon dioxide level in the container is not greater than an upper threshold, and the oxygen level in the container is not greater than or equal to the oxygen pulldown limit; the method further comprising: operating the atmosphere control system in a control phase to control the oxygen level and the carbon dioxide level in the container; wherein the control phase comprises: determining that the oxygen level in the container is less than an oxygen lower control limit; adding outside air to the container until the oxygen level in the container equals an oxygen upper control limit; determining that the carbon dioxide level in the container is greater than a carbon dioxide upper threshold and when the carbon dioxide level in the container is greater than the carbon dioxide upper threshold, adding outside air to the container until the carbon dioxide level in the container equals a carbon dioxide lower control limit; determining that the oxygen level in the container is greater than an oxygen upper threshold; adding nitrogen to the container until the oxygen level in the container equals the oxygen pulldown limit; determining that the carbon dioxide level in the container is greater than a carbon dioxide upper control limit; and when the carbon dioxide level in the container is greater than a carbon dioxide upper control limit, adding nitrogen to the container until the carbon dioxide level in the container equals a carbon dioxide lower control limit.

Optionally, in an embodiment of the invention the method further comprises after ending the start up phase, adding nitrogen to the container until the carbon dioxide level in the container equals a carbon dioxide lower control limit.

Technical effects of embodiments of the present disclosure include controlling atmosphere in the interior of a container.

Shown in <FIG> is a refrigerated container <NUM>. The container <NUM> has a generally rectangular construction, with a top wall <NUM>, a directly opposed bottom wall <NUM>, opposed side walls <NUM> and a front wall <NUM>. The container <NUM> further includes a door or doors (not shown) at a rear wall <NUM>, opposite the front wall <NUM>. The container <NUM> is configured to maintain a cargo <NUM> located inside the container <NUM> at a selected temperature through the use of a refrigeration unit <NUM> located at the container <NUM>. The container <NUM> is mobile and is utilized to transport the cargo <NUM> via, for example, a truck, a train or a ship. The container <NUM> may be integrated with a trailer or chassis. The refrigeration unit <NUM> is located at the front wall <NUM>, and includes a compressor <NUM>, a condenser <NUM>, an expansion device <NUM> (e.g., a TXV or EXV), an evaporator <NUM> and an evaporator fan <NUM> (shown in <FIG>), as well as other ancillary components.

Referring to <FIG>, the refrigeration unit <NUM> flows return air <NUM> across the evaporator <NUM> via the evaporator fan <NUM>, thus cooling the return air <NUM> to a selected temperature and urges the cooled return airflow <NUM>, now referred to as supply air <NUM>, through a refrigeration unit outlet <NUM> into the container <NUM> via, for example, openings <NUM> in one or more T-bars <NUM> extending along the bottom wall <NUM> of the container <NUM> to cool the cargo <NUM>.

The refrigeration unit <NUM> is separated into an evaporator section <NUM> containing the evaporator <NUM>, the evaporator fan <NUM> and an evaporator fan motor <NUM> and a condenser section <NUM> containing the compressor <NUM>, the condenser <NUM> and the expansion device <NUM>. The expansion device <NUM> may be located in the evaporator section <NUM>. The evaporator section <NUM>, which may be located above the condenser section <NUM>, is separated from the condenser section <NUM> by a panel <NUM> that extends across the refrigeration unit <NUM>. The condenser section <NUM> is exposed to ambient air and may be covered by panels having openings formed therein. In operation, refrigerant is circulated in serial fashion through the compressor <NUM>, the condenser <NUM>, the expansion device <NUM>, the evaporator <NUM> and back to the compressor <NUM>. It is understood that the refrigeration unit <NUM> may include additional components (e.g., economizer, receiver, SMV, etc.) that are not shown.

Referring now to <FIG>, the refrigeration unit <NUM> includes a housing <NUM> to contain components of the refrigeration unit <NUM>. Optionally, the housing <NUM> is separate and distinct from the container <NUM>, while alternatively, the housing <NUM> is an integral part of the container <NUM>. A condenser fan <NUM> is driven by a condenser motor (not shown) to drive air over the condenser <NUM> and discharge the air outside the refrigeration unit <NUM>. The condenser <NUM> may be radially disposed about the condenser fan <NUM>. A controller <NUM> controls operation of the refrigeration unit <NUM>, for example, by controlling the compressor <NUM> (e.g., on/off/variable speed), evaporator fan motor <NUM> (e.g., on/off/variable speed), condenser fan motor (e.g., on/off/variable speed), etc. The controller <NUM> may be implemented user a processor-based device including a microprocessor, memory, user interface, I/O inputs, etc. The controller <NUM> controls components of the refrigeration unit <NUM> to maintain a desired temperature within the interior of the container <NUM>, as known in the art. An air compressor <NUM> is located in the condenser section <NUM>. The air compressor <NUM> is a component of an atmosphere control system <NUM> (<FIG>) that operates to regulate atmosphere (e.g., oxygen and carbon dioxide) in the interior of the container <NUM>.

<FIG> depicts the atmosphere control system <NUM>. The atmosphere control system <NUM> operates to control levels of at least one gas inside the container <NUM>. Advantageously, the atmosphere control system <NUM> operates to control levels of oxygen and/or carbon dioxide. The atmosphere control system <NUM> includes the air compressor <NUM> located in the condenser section <NUM> and thus outside the interior of the container <NUM>. The controller <NUM> may turn on the air compressor <NUM> by sending a signal to a relay or contactor that applies power to the air compressor <NUM>. When turned on, the air compressor <NUM> draws air from outside the container <NUM> through a first filter <NUM> (e.g., a <NUM> micron particulate filter). The compressed air produced by the air compressor <NUM> flows from the condenser section <NUM> into the evaporator section <NUM> to a heat exchanger <NUM>. The heat exchanger may be an air-cooled heat exchanger of various types (e.g., round tube plate fin, microchannel, etc.). At heat exchanger <NUM>, the compressed air is cooled to facilitate water removal. From the heat exchanger <NUM>, the compressed air flows to a water separator <NUM> where water is removed. From the water separator <NUM>, the compressed air flows to a second filter <NUM> (e.g., a <NUM> micron particulate filter) and a third filter <NUM> (e.g., a <NUM> micron particulate filter). The second filter <NUM> and the third filter <NUM> may be located in the condenser section or the evaporator section <NUM>.

From the second filter <NUM> and the third filter <NUM>, the compressed air flows to a first valve, V1. The first valve V1 has two outlets, which can be controlled by controller <NUM>. 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 <NUM>. The first valve V1 may be located to provide the air upstream of the evaporator <NUM>. When the first valve V1 is in a second position (e.g., a closed position when not energized), the compressed air is directed to a separator <NUM>. The separator <NUM> may be a membrane separator that generates an output of highly pure, separated nitrogen upstream of evaporator <NUM>. Other atmospheric gases, including oxygen, argon and carbon dioxide, are vented to the condenser section <NUM> and outside of the refrigeration unit <NUM>. The nitrogen from separator <NUM> is directed to a second valve V2. The second valve V2 is a bleeder port that allows a small portion of the nitrogen from the separator <NUM> to be sent to a nitrogen sensor <NUM> to measure the purity of the nitrogen. The second valve V2 may be controlled by the controller <NUM>.

When nitrogen is provided upstream of the evaporator <NUM>, the nitrogen enters the interior of the container <NUM> and forces oxygen and/or carbon dioxide out of the interior of the container <NUM>. Reducing the oxygen level in the container <NUM> reduces ripening of produce. Reducing the carbon dioxide level in the container <NUM> prevents damage to cargo in the container due to high carbon dioxide levels.

In operation, the controller <NUM> monitors levels of at least one gas inside the container <NUM>, using oxygen sensor <NUM> and/or carbon dioxide sensor <NUM> in communication with the controller <NUM>. The oxygen sensor <NUM> and/or carbon dioxide sensor <NUM> may be located in the evaporator section <NUM>, upstream of the evaporator <NUM>. To add outside air to the container, the controller <NUM> sends a signal to turn on the air compressor <NUM> and sends a signal to the first valve V1 to set the first valve V1 to the open position. This directs the compressed air from the air compressor <NUM> to the interior of the container <NUM>. To add nitrogen to the container to control the levels of other gasses, the controller <NUM> sends a signal to turn on the air compressor <NUM> and closes valve V1. This directs the compressed air from the air compressor <NUM> to the separator <NUM>, which produces nitrogen that is directed to the interior of the container <NUM> (e.g., upstream or downstream of the evaporator <NUM>). To measure purity of the nitrogen generated by the separator <NUM>, the controller <NUM> opens the bleeder port of the second valve V2 to direct a portion of the nitrogen to the nitrogen sensor <NUM> in communication with the controller <NUM>. In some embodiments, a separate nitrogen sensor <NUM> is not used, as the measurements from the oxygen sensor <NUM> provides an indication of the nitrogen level in the container <NUM>.

<FIG> depicts a process for controlling the atmosphere control system <NUM>. The process is executed by the controller <NUM>. The process includes a start up phase <NUM> and a control phase <NUM>. The process may regulate oxygen and carbon dioxide levels (measured, for example, in percentages) in the container <NUM> using control bands. <FIG> depicts an example control band for the carbon dioxide level in the container <NUM>. The control band includes a lower control limit and an upper control limit which define a control band. A setpoint is typically set in the middle of the control band, but may be at any location. <FIG> depicts example values for controlling the carbon dioxide level in the container <NUM>. The oxygen level in the container <NUM> may be controlled using a similar control band, although with different numerical values.

Referring to <FIG>, the start up phase <NUM> begins at <NUM> and flows to <NUM> where an oxygen pulldown operation is started. The oxygen pulldown operation at <NUM> includes powering on the air compressor <NUM> and setting valve V1 to the closed position to add nitrogen to the container <NUM>. The oxygen pulldown operation at <NUM> may last for a period of time (e.g., <NUM> hours). When the oxygen pulldown operation at <NUM> ends, flow proceeds to <NUM> where the controller <NUM> compares the carbon dioxide level in the container <NUM> (measured by CO2 sensor <NUM>) to a carbon dioxide upper threshold. The carbon dioxide upper threshold may be equal to the carbon dioxide setpoint, plus the carbon dioxide control band plus a first offset (e.g., <NUM>%). If at <NUM> the carbon dioxide level in the container <NUM> is greater than the carbon dioxide upper threshold at <NUM>, then flow proceeds to <NUM> where the oxygen pulldown operation is considered complete.

If at <NUM> the carbon dioxide level in the container <NUM> is not greater than the upper threshold, then flow proceeds to <NUM> where the controller <NUM> determines if the oxygen level in the container <NUM> (measured by O2 sensor <NUM>) is greater than or equal to an oxygen pulldown limit (e.g., a minimum oxygen level achievable by adding nitrogen to the container <NUM>). If at <NUM>, the oxygen level in the container <NUM> is not greater than or equal to the oxygen pulldown limit, then flow proceeds to <NUM> where the oxygen pulldown operation is considered complete. At <NUM>, the controller <NUM> turns off the air compressor <NUM>.

If at <NUM>, the oxygen level in the container <NUM> is greater than or equal to the oxygen pulldown limit, then flow proceeds to <NUM>, where the controller <NUM> determines if the carbon dioxide level in the container <NUM> is greater than a carbon dioxide upper control limit. If the carbon dioxide level in the container <NUM> is greater than a carbon dioxide upper control limit then flow proceeds to <NUM> where the oxygen pulldown operation is considered complete. If at <NUM>, the carbon dioxide level in the container <NUM> is not greater than the carbon dioxide upper control limit then flow proceeds to <NUM> where the oxygen pulldown operation is continued for additional time (e.g., <NUM> hours) and the process continues.

From block <NUM>, the process flows to block <NUM> of the control phase <NUM>, referred to as normal operation. Flow proceeds to block <NUM> where the controller <NUM> compares the carbon dioxide level in the container <NUM> to the carbon dioxide upper threshold. If at <NUM> the carbon dioxide level in the container <NUM> is greater than the carbon dioxide upper threshold, flow proceeds to <NUM>. An alarm may be generated at <NUM>. At <NUM>, the air compressor <NUM> is turned on and valve V1 is set to the open position to add air to the container <NUM>. The system stays in this state until the carbon dioxide level in the container <NUM> equals the carbon dioxide lower control limit. At this point, the air compressor <NUM> is turned off and flow proceeds to <NUM>.

If at <NUM> the carbon dioxide level in the container <NUM> is not greater than the carbon dioxide upper threshold, flow proceeds to <NUM>. At <NUM>, the controller <NUM> compares the oxygen level in the container <NUM> to an oxygen upper threshold. The oxygen upper threshold may be equal to the oxygen setpoint, plus the oxygen control band plus a second offset (e.g., <NUM>%). If at <NUM> the oxygen level in the container <NUM> is greater than the oxygen upper threshold, flow proceeds to <NUM>. At <NUM>, the air compressor <NUM> is turned on and valve V1 is set to the closed position to add nitrogen to the container <NUM>. The system stays in this state until the oxygen level in the container <NUM> equals the oxygen pulldown limit. At this point, the air compressor <NUM> is turned off and flow proceeds to <NUM>.

If at <NUM> the oxygen level in the container <NUM> is not greater than the oxygen upper threshold, flow proceeds to <NUM>. At <NUM>, the controller <NUM> compares the oxygen level in the container <NUM> to an oxygen lower control limit. If at <NUM> the oxygen level in the container <NUM> is less than the oxygen lower control limit, flow proceeds to <NUM>. At <NUM>, the air compressor <NUM> is turned on and valve V1 is set to the open position to add air to the container <NUM>. The system stays in this state until the oxygen level in the container <NUM> equals the oxygen upper control limit. At this point, the air compressor <NUM> is turned off and flow proceeds to <NUM>.

If at <NUM> the oxygen level in the container <NUM> is not less than the oxygen lower control limit, flow proceeds to <NUM>. At <NUM>, the controller <NUM> compares the carbon dioxide level in the container <NUM> to the carbon dioxide upper control limit. If at <NUM> the carbon dioxide level in the container <NUM> is not greater than the carbon dioxide upper control limit, flow proceeds to <NUM>. If at <NUM> the carbon dioxide level in the container <NUM> is greater than the carbon dioxide upper control limit, flow proceeds to <NUM>. It is also noted that block <NUM> and block <NUM> also lead to block <NUM>.

At <NUM>, the air compressor <NUM> is turned on and valve V1 is set to the second position to add nitrogen to the container <NUM>. The system stays in this state until the carbon dioxide level in the container <NUM> equals the carbon dioxide lower control limit.

From <NUM>, the process flows to <NUM> where the controller <NUM> determines if a fresh air mode should be entered. At <NUM>, the controller <NUM> determines if the oxygen level in the container <NUM> is less than the oxygen lower control limit. If the oxygen level in the container <NUM> is less than the oxygen lower control limit, fresh air mode is enabled, and the process flows to <NUM>. Otherwise, the process returns to <NUM>.

The control process of <FIG> only requires control of the air compressor <NUM> and the first valve V1. This simplifies the control process and eliminates for a dedicated controller for the atmosphere control system <NUM>. The controls process maintains proper atmosphere in the container <NUM> and accounts for wide variations in container leakage and/or cargo respiration.

As described above, embodiments can be in the form of processor-implemented processes and devices for practicing those processes, such as a processor in controller <NUM>. Embodiments can also be in the form of computer program code containing instructions embodied in tangible media, such as network cloud storage, SD cards, flash drives, floppy diskettes, CD ROMs, hard drives, or any other computer-readable storage medium. Embodiments can also be in the form of computer program code transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation. When implemented on a general-purpose microprocessor, the computer program code configure the microprocessor to create specific logic circuits.

Claim 1:
A method of operating an atmosphere control system (<NUM>) to control an atmosphere in a refrigerated container (<NUM>), the method comprising:
operating the atmosphere control system (<NUM>) in a start up phase (<NUM>) to control an oxygen level in the container;
the start up phase (<NUM>) comprises adding nitrogen to the container (<NUM>);
ending the start up phase (<NUM>) if:
(i) a carbon dioxide level in the container (<NUM>) is not greater than an upper threshold, the oxygen level in the container (<NUM>) is greater than or equal to an oxygen pulldown limit, and the carbon dioxide level in the container (<NUM>) is greater than a carbon dioxide upper control limit; or
(ii) the carbon dioxide level in the container (<NUM>) is greater than the upper threshold; or
(iii) the carbon dioxide level in the container (<NUM>) is not greater than an upper threshold, and the oxygen level in the container (<NUM>) is not greater than or equal to the oxygen pulldown limit;
the method further comprising: operating the atmosphere control system in a control phase (<NUM>) to control the oxygen level and the carbon dioxide level in the container (<NUM>);
wherein the control phase (<NUM>) comprises:
determining that the oxygen level in the container (<NUM>) is less than an oxygen lower control limit;
adding outside air to the container (<NUM>) until the oxygen level in the container (<NUM>) equals an oxygen upper control limit;
determining that the carbon dioxide level in the container (<NUM>) is greater than a carbon dioxide upper threshold and when the carbon dioxide level in the container (<NUM>) is greater than the carbon dioxide upper threshold, adding outside air to the container (<NUM>) until the carbon dioxide level in the container equals a carbon dioxide lower control limit;
determining that the oxygen level in the container (<NUM>) is greater than an oxygen upper threshold;
adding nitrogen to the container (<NUM>) until the oxygen level in the container (<NUM>) equals the oxygen pulldown limit;
determining that the carbon dioxide level in the container (<NUM>) is greater than a carbon dioxide upper control limit; and
when the carbon dioxide level (<NUM>) in the container is greater than a carbon dioxide upper control limit, adding nitrogen to the container (<NUM>) until the carbon dioxide level in the container (<NUM>) equals a carbon dioxide lower control limit.