TECHNICAL FIELD

[0001] The present invention relates to transport units, such as reefer containers and refrigerated trucks and trailers, for transporting cargo in an atmosphere-controlled environment, and methods of controlling an atmosphere therein.

BACKGROUND

[0002] Transport units, such as containers for transporting cargo on container vessels, are ubiquitous in global cargo transportation. As cargo ships, container vessels carry their load in intermodal containers which are designed to be moved from one mode of transport to another, e.g. without unloading and reloading, in a technique called “containerization”. The standard (ISO) intermodal container is designated as twenty feet (6.10 m) long and 8 feet (2.44 m) wide, leading to the twenty-foot equivalent unit (TEU) as a unit of cargo capacity often used to describe the capacity of container vessels and terminals. Typical loads on a container vessel are a mix of 20-foot and 40-foot (2-TEU) ISO containers. Most non-bulk cargo worldwide is transported by container vessels, with a majority of the world’s container volume made up of 2-TEU containers. The largest modern container ships have capacities over 23,000 TEU.

[0003] A transport unit may comprise an atmosphere control system for controlling an atmosphere in the transport unit. This may be to facilitate the transportation of, for example, perishable goods, such as fruit and vegetables, in the transport unit. Such transport units include reefer containers, which may be TEU or 2-TEU containers designed to be shipped on container vessels, and/or refrigerated trucks or trailers. The transport units may be configured for transporting ripenable produce. Keeping the ripenable produce in, for example, a temperature-controlled environment may prevent ripening of the produce. One example of ripenable produce is bananas. When a shipment of bananas reaches its destination, the bananas may need to be ripened in a warehouse for a period of time. After the bananas have spent time in the ripening warehouse, the bananas can be distributed to marketplaces and/or distribution centres with acceptable ripeness. Other examples of ripenable produce include avocados, plums, mangos, and other fruits or vegetables. Most respirating produce may be transported in this way.

[0004] It is therefore advantageous if the ripening process can be controlled during shipment in such a way that the produce can be distributed to distribution centres or even to supermarkets in a sufficiently ripened state. In this way, it is possible to reduce a cost of ripening, as the cost of ripening in current ripening rooms and warehouses can be avoided. Furthermore, since the goods do not need to be ripened in a ripening warehouse, the transport route may be shorter and total delivery time may be shorter.

[0005] The ripening of certain produce, such as bananas, is an autocatalytic and exothermic process. That is, the ripening of bananas and other produce may be triggered by exposing the bananas to a gas, such as ethylene. Thereafter, the bananas may continue to ripen, respirate and generate heat, the levels of which should be controlled to control the ripening process. The bananas may change colour during the ripening process, thereby providing an indicator of a level of ripeness of the bananas. The period of ripening of the bananas during transport may be between 8 to 14 days, such as between 10 to 12 days, depending on journey length.

[0006] Some known transport units have controlled atmospheres, but are largely inefficient and often do not carefully control the ripening process. Current solutions to this problem include transporting containers at reduced capacity, thereby providing additional space between goods within the transport unit. However, shipping goods at a reduced capacity is inconsistent with the goal of reducing per-unit cost and/or per-unit carbon emissions. Embodiments of the present invention aim to provide solutions to these problems.

SUMMARY

[0007] A first aspect of the present invention provides a transport unit comprising a compartment for holding cargo; an atmosphere control system for controlling an atmosphere in the compartment; and first and second ports for supplying conditioned gas from the atmosphere control system to the compartment, the first and second ports opening into the compartment at different, spaced-apart locations in the compartment. The atmosphere control system is operable: in a first mode of operation, in which the atmosphere control system is configured to supply conditioned gas to the compartment through the first port at a higher supply flow rate than through the second port; and in a second mode of operation, in which the atmosphere control system is configured to supply conditioned gas to the compartment through the second port at a higher supply flow rate than through the first port.

[0008] The cargo may be perishable produce. The cargo may be packaged and/or stacked in the compartment, in use.

[0009] Optionally, the atmosphere control system is configured to switch between the first mode of operation and the second mode of operation based on at least one predetermined criterion being met. Switching between the first and second modes of operation may provide a more even distribution of conditioned gas in the compartment over time.

[0010] Optionally, the atmosphere control system is configured to determine that the at least one predetermined criterion has been met on the basis of one or more of: an elapsed time since the atmosphere control system last switched between the first mode of operation and the second mode of operation; one or more signals representative of temperatures of respective portions of the compartment; and one or more signals representative of temperatures of respective portions of the atmosphere control system. The one or more signals may be representative of a temperature of respective portions of cargo held in the compartment in use.

[0011] In this way, the atmosphere control system may be configured to switch between the first and second modes of operation if a temperature in the compartment and/or in the atmosphere control system is determined to exceed a predetermined temperature. This may provide a higher flow rate of conditioned gas supplied to the compartment through one of the first and second ports, if a temperature of gas in proximity to the respective first and second ports exceeds the predetermined temperature.

[0012] Optionally, the compartment comprises a base, and the second port is spaced further from the base than the first port. The cargo may be supportable on or above the base in use.

[0013] Optionally, there is more than one first port and/or more than one second port. In this way, in the first mode of operation, the atmosphere control system may be configured to supply conditioned gas through the more than one first port at a higher supply flow rate than through the more than one second port, and vice versa in the second mode of operation. [0014] Optionally, the transport unit comprises a raised floor in the compartment on which cargo is supportable in use. The raised floor may be spaced from the base to form a first space between the raised floor and the base, and a second space between the raised floor and a top of the compartment that is opposite the base. The first port may open into the first space and the second port may open into the second space. In this way, the atmosphere control system may be configured to supply conditioned gas to the first and second spaces at different supply flow rates in dependence on the mode of operation. The second space may comprise a void between the cargo and the top of the compartment in use.

[0015] Optionally, the atmosphere control system is configured in each of the first and second modes of operation, to regulate a temperature of conditioned gas supplied to the compartment towards a first temperature setpoint. Optionally, the atmosphere control system is configured, upon switching between the first and second modes of operation, to regulate the temperature of conditioned gas supplied to the compartment towards a second temperature setpoint that is different to the first temperature setpoint, until at least one predetermined condition is met. The atmosphere control system may be configured to determine that the predetermined condition has been met on the basis of one or more of: an elapsed time since the atmosphere control system last switched between the first mode of operation and the second mode of operation; one or more signals representative of a temperature of respective portions of the compartment; and one or more signals representative of a temperature of respective portions of the atmosphere control system. In each of the first and second modes of operation, the atmosphere control system may be configured to regulate the temperature of conditioned gas supplied to the compartment towards the first temperature setpoint when the at least one predetermined condition has been met.

[0016] Optionally, the atmosphere control system is configured in the respective first and second modes of operation to regulate the temperature of conditioned gas supplied to the compartment towards, respectively, the first temperature setpoint and a third temperature setpoint. The atmosphere control system may be configured, upon switching to the respective first and second modes of operation, to regulate the temperature of conditioned gas supplied to the compartment towards, respectively, the second temperature setpoint and a fourth temperature setpoint, until the at least one predetermined condition is met. The second and fourth temperature setpoints may be lower than the first and third temperature setpoints, respectively. The first and third temperature setpoints may be the same as each other or different to each other. The second and fourth temperature setpoints may the same as each other or different to each other. In the first and second modes of operation, the atmosphere control system may be configured to regulate the temperature of conditioned gas supplied to the compartment towards the first and third temperature setpoints, respectively, when the at least one predetermined condition has been met.

[0017] Optionally, the atmosphere control system is configured in either or both of the first and second modes of operation to regulate a temperature of conditioned gas supplied to the compartment towards a temperature setpoint that is lower than a predetermined threshold temperature associated with cargo in the compartment, in use. The cargo may be produce. The predetermined threshold temperature may be a temperature at which the cargo may be damaged. The atmosphere control system may be configured to switch between the first and second modes of operation in such a way that a temperature of the cargo, or an average temperature of the cargo, remains above the predetermined threshold temperature, in use. For example, the atmosphere control system may be configured to operate in either of the first and second modes of operation no more than 50% of the time. The atmosphere control system may be configured to operate in either of the first and second modes of operation, following switching to the respective mode of operation, for no longer than: 30 minutes, 15 minutes, 10 minutes, or 5 minutes, for example. The atmosphere control system may be configured to supply conditioned gas at more than: 1, 2, or 5 degrees Celsius below the predetermined threshold temperature, for example. In this way, the cargo may be cooled more rapidly following a switch in the mode of operation, without the cargo being damaged.

[0018] Optionally, in the first mode of operation, the second supply flow rate of conditioned gas through the second port is zero, and, in the second mode of operation, the supply flow rate of conditioned gas through the first port is zero.

[0019] Optionally, in the first mode of operation, the atmosphere control system is configured to receive return gas from the compartment through the second port, and, in the second mode of operation, the atmosphere control system may be configured to receive return gas from the compartment through the first port. In this way, in the first mode of operation, conditioned gas may be supplied to the compartment by the atmosphere control system through the first port and return gas may be returned to the atmosphere control system from the compartment through the second port. Similarly, in the second mode of operation, conditioned gas may be supplied to the compartment by the atmosphere control system through the second port and return gas may be returned to the atmosphere control system from the compartment through the first port. Return gas received from the compartment may have a higher temperature than conditioned gas supplied to the compartment.

[0020] Optionally, the atmosphere control system comprises a heat exchanger for conditioning gas and, optionally, a reversible-flow gas moving device for reversibly moving gas through the atmosphere control system. The atmosphere control system may be configured, in the first mode of operation, to operate the gas moving device to move return gas received through the second port to the first port via the heat exchanger, and, in the second mode of operation, to operate the gas moving device to move return gas received through the first port to the second port via the heat exchanger.

[0021] In this way, the atmosphere control system may be configured to control the heat exchanger to condition return gas, for instance to adjust a temperature of return gas, for instance to cool return gas. The temperature-adjusted return gas may comprise at least a part of conditioned gas to be supplied to the compartment. The reversible-flow gas moving device may be a reversible-flow fan. A direction of rotational motion of blades of the fan may be modulated to modulate the direction of the flow of gas therethrough. Alternatively, a position of the blades of the fan may be modulated, relative to a hub of the fan to which the blades are mounted, to modulate the direction of flow of gas therethrough. For example, an angle of attack of the blades may be reversed to reverse a flow of gas through the fan. The reversible- flow gas moving device be operated at a variable speed, such as using a frequency convertor.

[0022] Optionally, the transport unit comprises a first gas temperature sensor for sensing a temperature of gas flowing through the first port, and a second gas temperature sensor for sensing a temperature of gas flowing through the second port. Optionally, the atmosphere control system is configured to control the heat exchanger to regulate a temperature of conditioned gas supplied to the compartment on the basis of signals received at the atmosphere control system from the first and second gas temperature sensors. In this way, in the first mode of operation, the first gas temperature sensor may be configured to sense a temperature of conditioned gas and the second gas temperature sensor may be configured to sense a temperature of return gas. In the second mode of operation, the first gas temperature sensor may be configured to sense a temperature of return gas and the second gas temperature sensor may be configured to sense a temperature of conditioned gas.

[0023] The atmosphere control system may be configured to control an amount of heat removed from return gas by the heat exchanger to regulate the temperature of conditioned gas towards a target temperature setpoint, such as towards the first to fourth temperature setpoints, in dependence on the mode of operation. The atmosphere control system may be configured to compare the conditioned gas temperature, sensed by one of the first and second gas temperature sensors, with the return gas temperature, sensed by the other of the first and second gas temperature sensors, in order to control the amount of heat removed from the gas by the heat exchanger to regulate the temperature of conditioned gas towards the target temperature setpoint.

[0024] Optionally, the first and second gas temperature sensors are located: in the atmosphere control system; in the respective first and second ports; and/or in the compartment, such as in the respective first and second locations into which the respective first and second ports open. There may be more than one first gas temperature sensor, and/or more than one second gas temperature sensor.

[0025] Optionally, the heat exchanger comprises an evaporator of a refrigeration system. Optionally, the atmosphere control system is configured to set a superheat of the evaporator at a first target superheat, and to raise the target superheat of the evaporator to a second target superheat, higher than the first target superheat, as the mode of operation of the atmosphere control system is switched between the first mode of operation and the second mode of operation. The superheat may be a temperature of refrigerant in the refrigeration system above a boiling point of the refrigerant at a given pressure. A superheat of refrigerant may be a superheat of a vapour. In this way, the superheat of the evaporator may be a temperature of refrigerant above its boiling point at an outlet of the evaporator.

[0026] Raising the evaporator superheat as the mode of operation of the atmosphere control system is switched may ensure that all refrigerant flowing through the evaporator is sufficiently vaporised before it leaves the evaporator, and/or enters a downstream compressor of the refrigeration system. This may improve an operational life of the compressor. The atmosphere control system may be configured to control the superheat of the evaporator towards the first target superheat following the raising of the target superheat. The first target superheat may be around 5 Kelvin, for example. The second target superheat may be around 10 Kelvin, for example.

[0027] Optionally, the evaporator is oriented so that an aggregate flow direction of refrigerant through the evaporator is nonorthogonal to the direction of flow of gas through the evaporator in use. The evaporator may be oriented so that the aggregate flow direction of refrigerant through the evaporator is substantially parallel to the flow of gas through the evaporator. Alternatively, the evaporator may be oriented so that the aggregate flow direction of refrigerant through the evaporator is inclined to the direction of flow of gas through the evaporator. That is, the aggregate flow direction of refrigerant through the evaporator may be greater than 10, 20, or 30 degrees and/or less than 70, 60, or 50 degrees, such as 45 degrees, to the direction of flow of gas through the evaporator.

[0028] The gas may flow substantially vertically through the evaporator with respect to the base of the compartment in use. The evaporator may comprise coils, or tubes, through which refrigerant flows, and fins for transferring heat between the gas and the refrigerant in the coils or tubes. The evaporator, and/or fins thereof, may be inclined at an angle to the vertical direction, for instance to permit the collection of condensates forming on the evaporator. The coils or tubes may be configured to form a winding or circuitous path through the evaporator along which refrigerant flows in use. Refrigerant may be injected into the evaporator at a lower end of the evaporator (i.e. an end closer to the base of the compartment) and may exit the evaporator at an upper end of the evaporator (i.e. an end further from the base of the compartment), or vice versa.

[0029] Optionally, the transport unit is a reefer container or a refrigerated truck or trailer. The transport unit may be for ripening produce during transport of the produce. The produce may be bananas, or other fruits or vegetables. The transport unit may be for temperature drawdown of hot goods during transport. The atmosphere control system may be configured to provide a more uniform temperature distribution in the compartment, such as to reduce a vertical variation in temperature in the compartment. Modulating the atmosphere control system between the first and second modes may reduce an effective stack height of the cargo, in use. In this way, the transport unit may provide a more uniform ripening of produce in the compartment, or a more uniform drawdown of the temperature of goods in the compartment. [0030] The atmosphere control system may be configured to inject a second gas into conditioned gas supplied to the compartment. The second gas may be a gas for triggering a ripening process of the produce, such as ethylene. The second gas may be a gas for regulating a ripening rate of the produce, such as oxygen.

[0031] A second aspect of the present invention provides a method of controlling an atmosphere in a transport unit, the transport unit comprising a compartment for holding cargo, and first and second ports for supplying conditioned gas from an atmosphere control system to the compartment, the first and second ports opening into the compartment at different, spaced- apart locations in the compartment. The method comprises, in a first mode, supplying conditioned gas from the atmosphere control system to the compartment through the first port at a higher supply flow rate than through the second por, and, in a second mode, supplying conditioned gas from the atmosphere control system to the compartment through the second port at a higher supply flow rate than through the first port.

[0032] The cargo may be perishable produce. The cargo may be packaged and/or stacked in the compartment, in use.

[0033] Optionally, the method comprises switching between the first mode and the second mode. Optionally, the switching is based on at least one predetermined criterion being met. Switching between the first and second modes may provide a more even distribution of conditioned gas in the compartment over time. The at least one predetermined criterion being met may be determined on the basis of one or more of: an elapsed time since the atmosphere control system last switched between the first mode and the second mode; one or more signals representative of temperatures of respective portions of the compartment; and one or more signals representative of temperatures of respective portions of the atmosphere control system. The one or more signals may be representative of a temperature of respective portions of cargo held in the compartment in use.

[0034] In this way, the method may comprise switching between the first and second modes if a temperature in the compartment and/or in the atmosphere control system is determined to exceed a predetermined temperature. This may provide a higher flow rate of conditioned gas supplied to the compartment through one of the first and second ports, if a temperature of gas in proximity to the respective first and second ports exceeds the predetermined temperature.

[0035] Optionally, the transport unit comprises the atmosphere control system. Alternatively, the atmosphere control system is remote from the transport unit. For example, the atmosphere control system may be part of a marine vessel.

[0036] Optionally, the compartment comprises a base, and the second port is spaced further from the base than the first port. The cargo may be supportable on or above the base in use.

[0037] Optionally, there is more than one first port and/or more than one second port. In this way, in the first mode, the method may comprise supplying conditioned gas through the more than one first port at a higher supply flow rate than through the more than one second port, and vice versa in the second mode.

[0038] Optionally, the transport unit comprises a raised floor in the compartment on which cargo is supportable in use. The raised floor may be spaced from the base to form a first space between the raised floor and the base, and a second space between the raised floor and a top of the compartment that is opposite the base. The first port may open into the first space and the second port may open into the second space. In this way, the method may comprise supplying conditioned gas to the first and second spaces at different supply flow rates in dependence on the mode of operation. The second space may comprise a void between the cargo and the top of the compartment in use.

[0039] Optionally, the method comprises, in each of the first and second modes, regulating a temperature of conditioned gas supplied to the compartment towards a first temperature setpoint. Optionally, the method comprises, upon switching between the first and second modes, regulating the temperature of conditioned gas supplied to the compartment towards a second temperature setpoint that is different to the first temperature setpoint, until at least one predetermined condition is met. The method may comprise determining that the predetermined condition has been met on the basis of one or more of: an elapsed time since the atmosphere control system last switched between the first mode and the second mode; one or more signals representative of a temperature of respective portions of the compartment; and one or more signals representative of a temperature of respective portions of the atmosphere control system. In each of the first and second modes, the method may comprise regulating the temperature of conditioned gas supplied to the compartment towards the first temperature setpoint when the at least one predetermined condition has been met.

[0040] Optionally, the method comprises, in the respective first and second modes, regulating the temperature of conditioned gas supplied to the compartment towards, respectively, the first temperature setpoint and a third temperature setpoint. The method may comprise, upon switching to the respective first and second modes, regulating the temperature of conditioned gas supplied to the compartment towards, respectively, the second temperature setpoint and a fourth temperature setpoint, until the at least one predetermined condition is met. The second and fourth temperature setpoints may be lower than the first and third temperature setpoints, respectively. The first and third temperature setpoints may be the same as each other or different to each other. The second and fourth temperature setpoints may the same as each other or different to each other. In the first and second modes, the method may comprise regulating the temperature of conditioned gas supplied to the compartment towards the first and third temperature setpoints, respectively, when the at least one predetermined condition has been met.

[0041] Optionally, the method comprises, in either or both of the first and second modes of operation, regulating a temperature of conditioned gas supplied to the compartment towards a temperature setpoint that is lower than a predetermined threshold temperature associated with cargo in the compartment, in use. The cargo may be produce. The predetermined threshold temperature may be a temperature at which the cargo may be damaged. The method may comprise switching between the first and second modes of operation in such a way that a temperature of the cargo, or an average temperature of the cargo, remains above the predetermined threshold temperature, in use. For example, the atmosphere control system may be configured to operate in either of the first and second modes of operation no more than 50% of the time. The method may comprise operating in either of the first and second modes of operation, following switching to the respective mode of operation, for no longer than: 30 minutes, 15 minutes, 10 minutes, or 5 minutes, for example. The method may comprise supplying conditioned gas at greater than: 1, 2, or 5 degrees Celsius below the predetermined threshold temperature, for example. In this way, the cargo may be cooled more rapidly following a switch in the mode of operation, without the cargo being damaged. [0042] Optionally, the method comprises, in the first mode, supplying no conditioned gas from the atmosphere control system to the compartment through the second port, and, in the second mode, supplying no conditioned gas from the atmosphere control system to the compartment through the first port.

[0043] Optionally, the method comprises, in the first mode, receiving return gas at the atmosphere control system from the compartment through the second port, and, in the second mode, receiving return gas at the atmosphere control system from the compartment through the first port. In this way, in the first mode, the method may comprise supplying conditioned gas from the atmosphere control system to the compartment through the first port and receiving return gas at the atmosphere control system from the compartment through the second port. Similarly, in the second mode, the method may comprise supplying conditioned gas from the atmosphere control system to the compartment through the second port and receiving return gas at the atmosphere control system from the compartment through the first port. Return gas received from the compartment may have a higher temperature than conditioned gas supplied to the compartment. The method may comprise conditioning return gas to constitute conditioned gas for supplying to the compartment.

[0044] Optionally, the atmosphere control system comprises a heat exchanger for conditioning gas, and the method may comprise, in the first mode, moving return gas received at the atmosphere control system through the second port to the first port via the heat exchanger, and, in the second mode, moving return gas received at the atmosphere control system through the first port to the second port via the heat exchanger. Optionally, the method comprises conditioning return gas, for instance to adjust a temperature of return gas, for instance to cool return gas. The temperature-adjusted return gas may comprise at least a part of conditioned gas to be supplied to the compartment.

[0045] The atmosphere control system may comprise a reversible-flow gas moving device for reversibly circulating gas through the atmosphere control system, and the method may comprise operating the reversible gas moving device in different directions to modulate a direction of flow of gas through the atmosphere control system in dependence on the mode of operation. The reversible-flow gas moving device may be a reversible-flow fan. That is, switching the mode of operation may comprise switching a direction of action of the fan, such as by switching a direction of rotational motion of blades of the fan. Alternatively, or in addition, a position of the blades of the fan may be modulated, relative to a hub of the fan to which the blades are mounted, to modulate the direction of the flow of gas therethrough. For example, an angle of attack of the blades may be reversed to reverse a flow of gas through the fan. The method may comprise operating the reversible-flow gas moving device at a variable speed, such as using a frequency convertor.

[0046] Optionally, the method comprises, in each of the first and second modes, sensing a temperature of return gas received at the atmosphere control system from the compartment and a temperature of conditioned gas supplied to the compartment from the atmosphere control system. Optionally, the method comprises, in each of the first and second modes, controlling the heat exchanger to regulate a temperature of conditioned gas supplied to the compartment on the basis of the temperatures sensed.

[0047] Optionally, the atmosphere control system comprises a first gas temperature sensor for sensing a temperature of gas flowing through the first port, and a second gas temperature sensor for sensing a temperature of gas flowing through the second port. Optionally, the method comprises, in the first mode, sensing a temperature of conditioned gas supplied to the compartment using the first gas temperature sensor, and sensing a temperature of return gas received from the compartment using the second gas temperature sensor. Optionally, the method comprises, in the second mode, sensing a temperature of conditioned gas supplied to the compartment using the second gas temperature sensor, and sensing a temperature of return gas received from the compartment using the first gas temperature sensor.

[0048] Optionally, the method comprises controlling an amount of heat removed from the gas by the heat exchanger to regulate the temperature of conditioned gas towards a temperature setpoint, such as the first to fourth temperature setpoints, in dependence on the mode of operation. Optionally, the method comprises comparing the conditioned gas temperature, sensed by one of the first and second gas temperature sensors, with the return gas temperature, sensed by the other of the first and second gas temperature sensors, in order to control the amount of heat removed from the gas by the heat exchanger to regulate the temperature of conditioned gas towards the target temperature setpoint.

[0049] Optionally, the first and second gas temperature sensors are located: in the atmosphere control system; in the respective first and second ports; and/or in the compartment, such as in the respective first and second locations into which the respective first and second ports open. There may be more than one first gas temperature sensor, and/or more than one second gas temperature sensor.

[0050] Optionally, the heat exchanger comprises an evaporator of a refrigeration system. The method may comprise setting a superheat of the evaporator at a first target superheat. The method may comprise raising the target superheat of the evaporator to a second target superheat, higher than the first target superheat, as the mode of operation of the atmosphere control system is switched between the first mode and the second mode. The method may comprise setting the superheat of the evaporator at the first target superheat following the raising of the target superheat, such as after a period of time following the raising of the target superheat, and then regulating the superheat towards the first target superheat. The superheat may be a temperature of refrigerant in the refrigeration system above a boiling point of the refrigerant at a given pressure. A superheat of refrigerant may be a superheat of a vapour. In this way, the superheat of the evaporator may be a temperature of refrigerant above its boiling point at, or downstream from, an outlet of the evaporator.

[0051] Raising the evaporator superheat as the mode of operation of the atmosphere control system is changed may ensure that all refrigerant flowing through the evaporator is sufficiently vaporised before it leaves the evaporator, and/or enters a downstream compressor of the refrigeration system. This may improve an operational life of the compressor. The atmosphere control system may be configured to control the superheat of the evaporator towards the first target superheat following the raising of the target superheat. The first target superheat may be around 5 Kelvin, for example. The second target superheat may be around 10 Kelvin, for example.

[0052] The evaporator may be oriented so that an aggregate flow direction of refrigerant through the evaporator is nonorthogonal to the direction of flow of gas through the evaporator in use. The evaporator may be oriented so that the aggregate flow direction of refrigerant through the evaporator is substantially parallel to the flow of gas through the evaporator. Alternatively, the evaporator may be oriented so that the aggregate flow direction of refrigerant through the evaporator is inclined to the direction of flow of gas through the evaporator. That is, the aggregate flow direction of refrigerant through the evaporator may be greater than 10, 20, or 30 degrees and/or less than 70, 60, or 50 degrees, such as 45 degrees, to the direction of flow of gas through the evaporator.

[0053] The gas may flow substantially vertically through the evaporator with respect to the base of the compartment in use. The evaporator may comprise coils, or tubes, through which refrigerant flows, and fins for transferring heat between the gas and the refrigerant in the coils or tubes. The evaporator, and/or fins thereof, may be inclined at an angle to the vertical direction, for instance to permit the collection of condensates forming on the evaporator. The coils or tubes may be configured to form a winding or circuitous path through the evaporator along which refrigerant flows in use. Refrigerant may be injected into the evaporator at a lower end of the evaporator (i.e. an end closer to the base of the compartment) and may exit the evaporator at an upper end of the evaporator (i.e. an end further from the base of the compartment), or vice versa.

[0054] Optionally, the transport unit is a reefer container or a refrigerated truck or trailer.

[0055] Optionally, the method is a method of controlling the atmosphere in the transport unit in order to ripen produce during transport of the produce in the transport unit. The produce may be bananas, or other fruits or vegetables. The method may be a method of controlling the atmosphere in the transport unit in order to provide temperature drawdown of hot goods during transport of the hot goods in the transport unit. The method may provide a more uniform temperature distribution in the compartment, such as to reduce a vertical variation in temperature in the compartment. Switching between the first and second modes may reduce an effective stack height of the cargo, in use. In this way, the method may provide a more uniform ripening of produce in the compartment, or a more uniform drawdown of the temperature of goods in the compartment.

[0056] Optionally, the method comprises injecting a second gas into conditioned gas supplied to the compartment. The second gas may be a gas for triggering a ripening process of the produce, such as ethylene. The second gas may be a gas for regulating a ripening rate of the produce, such as oxygen. [0057] According to a third aspect of the present invention, there is provided a controller configured to cause an atmosphere control system to perform the method of the second aspect of the present invention.

[0058] Optionally, the controller is comprised in a transport unit according to the first aspect of the present invention or in the atmosphere control system thereof, thereby to locally operate the atmosphere control system. Alternatively, the atmosphere control system may be located remotely from the transport unit. For example, the atmosphere control system may be part of a marine vessel. The controller may be located remotely from any transport unit, and/or from the atmosphere control system, thereby to remotely operate the atmosphere control system. The controller may communicate with the transport unit and/or the atmosphere control system via a wireless network, such as a cloud, and/or may be communicatively coupled to the transport unit and/or the atmosphere control system using a wired connection. The controller may be configured to, e.g. simultaneously, control an atmosphere control system of each one of a plurality of transport units.

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0060] Figure 1 is a schematic diagram of a transport unit comprising an atmosphere control system, according to an example;

[0061] Figure 2 is a schematic diagram of the transport unit of Figure 1, showing additional components and alternative configurations according to examples;

[0062] Figure 3 is a schematic diagram showing temperatures of conditioned gas supplied to the transport unit of Figures 1 or 2, along with corresponding temperatures of cargo in the transport unit.

[0063] Figures 4A and 4B are side-profile schematic views of the evaporator according to the example shown in Figure 2. [0064] Figure 5 is a flow diagram showing a method of controlling an atmosphere in a transport unit, according to an example.

[0065] Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings.

DETAILED DESCRIPTION

[0066] Details of methods and systems according to examples will become apparent from the following description, with reference to the Figures. In this description, for the purpose of explanation, numerous specific details of examples are set forth. Reference in the specification to ‘the example’ or similar language means that a particular feature, structure, or characteristic described in connection with the example is included in at least that one example, but not necessarily in other examples. It should further be noted that the examples illustrated in the figures are described in various different ways and are described schematically with certain features omitted and/or necessarily simplified for ease of explanation and understanding of the concepts underlying the example.

[0067] In the following description, embodiments of the invention are described in relation to a reefer container. It will be understood that the invention is not limited to this purpose and may be applied to any kind of transport unit, for example to a refrigerated truck or trailer.

[0068] Figure 1 shows an example transport unit 100 comprising a compartment 200 for holding cargo (not shown), in use. The transport unit 100 comprises an atmosphere control system 300 for controlling an atmosphere in the compartment 200 The compartment 200 is substantially airtight. In some examples, the compartment 200 is not airtight, and/or comprises an opening or valve for releasing gas from the compartment 200 to an external atmosphere. In some examples, the compartment 200 is substantially hermetically sealed and comprises a check valve for regulating a pressure inside the compartment 200, for example to prevent an excessive build-up of pressure in the compartment 200 The transport unit 200 may comprise a door (not shown) that can be opened for loading and unloading the transport unit 100, and closed and, optionally, sealed for storage and shipping. [0069] The compartment 200 comprises a base 220 and a top 240 opposite the base 220. Cargo is supportable on or above the base 220, in use. Features of the transport unit 100 are described with respect to a coordinate system as shown in Figure 1, wherein a z-direction is a substantially vertical direction with respect to the base 220 in normal use, and wherein x- and y-directions are horizontal directions in substantially the same plane as the base 220 in normal use.

[0070] The atmosphere control system 300 is configured to supply conditioned gas to the compartment 200. In the present example, the atmosphere control system 300 is configured to supply temperature-controlled gas to the compartment 200. In some examples, the atmosphere control system 300 is alternatively, or in addition, configured to supply compositionally controlled gas to the compartment 200, for example to supply gas having varying levels of oxygen, ethylene, or other component of gas to the compartment 200. In some examples, the atmosphere control system 300 is configured to inject ethylene into conditioned gas supplied to the compartment 200 to initiate a ripening of ripenable produce, such as bananas, in the compartment 200 in use. In some examples, the atmosphere control system 300 is configured to control a level of oxygen in conditioned gas supplied to the compartment 200, for example to control a rate of ripening of the ripenable produce in the compartment 200, in use.

[0071] In the present example, the transport unit 100 comprises first and second ports 210, 211 for supplying conditioned gas from the atmosphere control system 300 to the compartment 200. The first and second ports 210, 211 are spaced apart from one another. That is, the first and second ports 210, 211 open into the compartment 200 at different, spaced-apart locations in the compartment 200. Specifically, in the present example, the second port 211 is located further from the base 220 than the first port 210. That is, the second port 211 is higher than the first port 210 with respect to the base 220 of the compartment 200, so that conditioned gas is supplied to the compartment 200 through the second port 211 at a higher location in the compartment 200 than conditioned gas supplied through the first port 210. In other examples, the first and second ports 210, 211 are located at the same height in the compartment 200 and are spaced apart in the x- and/or y-directions. In some examples, there is more than one first port and/or more than one second port.

[0072] In the present example, the atmosphere control system 300 is operable in a first mode of operation, in which the atmosphere control system 300 is configured to supply conditioned gas to the compartment 200 through the first port 210 at a higher supply flow rate than through the second port 211. According to the present example, the atmosphere control system 300 is operable in a second mode of operation, in which the atmosphere control system 300 is configured to supply conditioned gas to the compartment 200 through the second port 211 at a higher supply flow rate than through the first port 210.

[0073] A direction and magnitude of the supply flow rate of conditioned gas supplied to the compartment 200 through each of the first port 210 and the second port 211 is illustrated, respectively, by arrows A and B in Figure 1. The magnitude of the flow rate of conditioned gas supplied through the second port 211 (arrow A) is shown as being greater than the magnitude of the flow rate of conditioned gas supplied through the first port 210 (arrow B). That is, Figure 1 shows the transport unit 100 when the atmosphere control system 300 is operating in the first mode of operation. Herein, a flow rate is defined as a volume flow rate, represented in the Standard International system of units (SI) in units of m ^A 3/s (cubic metres per second). A positive direction of flow of conditioned supplied to the compartment 200 is shown as being generally in the x-direction. In some examples, the direction of flow of conditioned gas may have a component of flow substantially in the y- and/or z-directions.

[0074] Figure 2 is a schematic diagram of the transport unit 100 of Figure 1, showing additional components and configurations of the transport unit 100 according to an example. The transport unit 100 comprises a raised floor 230 in the compartment 200 on which cargo 110 is supportable in use. The raised floor 230 is spaced from the base 220 to form a first space 250 between the raised floor 230 and the base 220, and a second space 251 between the raised floor 230 and the top 240 of the compartment 200. In some examples, the raised floor 230 comprises a drain hole (not shown), for example to permit the drainage of condensate and/or other deposits from the second space 251 into the first space 250, and/or into a drain conduit (not shown).

[0075] In the present example, the second space 251 comprises a void 252 between the cargo 110 and the top 240 of the compartment 200 in use. The first port 210 opens into the first space 250 and the second port 211 opens into the second space 251, specifically into the void 252 between the cargo 110 and the top 240 of the compartment 200 in use. In some examples, the transport unit 100 does not comprise a raised floor 230, and the first and second ports 210, 211 open into the compartment 200 at any suitably space-apart locations. [0076] In the present example, the atmosphere control system 300 is configured to supply conditioned gas to the first and second spaces 250, 251 at different supply flow rates in dependent on the mode of operation. That is, in the first mode of operation, the atmosphere control system 300 is configured to supply conditioned gas to the first space 250 at a higher supply flow rate than to the second space 251, and vice versa in the second mode of operation. Conditioned gas is distributed through the compartment 200 naturally, for example by diffusion and convection, and/or mechanically, for example using one or more gas moving devices.

[0077] In the present example, in the first mode of operation, the second supply flow rate of conditioned gas through the second port 211 is zero, and the supply flow rate of gas through the first port 210 is positive. Specifically, in the first mode of operation, the direction of flow of gas through the second port 211 is towards the atmosphere control system 300 from the compartment 200 so that the atmosphere control system 300 is configured to receive return gas from the compartment 200 through the second port 211. In the second mode of operation, the directions of flow are reversed. That is, in the second mode of operation, the supply flow rate of gas through the first port 210 is towards the atmosphere control system 300 from the compartment 200 so that the atmosphere control system 300 is configured to receive return gas from the compartment 200 through the first port 210. This is shown by the arrows C and D in Figure 1, whereby solid arrows indicate the direction of flow of conditioned gas through the first and second ports 210, 211 in the first mode of operation, while dashed arrows indicate the same in the second mode of operation. In other words, gas is drawn from the compartment 200 into the atmosphere control system 300 through one of the first and second ports 210, 211, conditioned by the atmosphere control system 300, and returned to the compartment 200 through the other of the first and second ports 210, 211. That is, gas is circulated through the atmosphere control system 300 and the compartment 200. Switching between the first and second modes of operation reverses the direction of circulation of gas through the atmosphere control system 300. In some examples, no conditioned gas is supplied through second port 211 and no return gas is received through the second port 211 in the first mode of operation. In some examples, no conditioned gas is supplied through the first port 210 and no return gas is received through the first port 210 in the second mode of operation.

[0078] In the present example, conditioned gas is supplied to the compartment 200 through either of the first and second ports 210, 211 and return gas is returned to the atmosphere control system 300 through the other of the first and second ports 210, 211. In other examples, conditioned gas is supplied to the compartment 200 through either or both of the first and second ports 210, 211 and either expelled into an external atmosphere external to the compartment 200 (i.e. the gas is not circulated through the compartment 200) or transport unit 100, and/or returned to the atmosphere control system 300 by any suitable mechanism, such as any suitable port, conduit or channel between the compartment 200 and the atmosphere control system 300. In other examples, gas may be drawn from a location external to the transport unit 100, conditioned by the atmosphere control system 300, and supplied to the compartment 200 through either or both of the first and second ports 210, 211.

[0079] In the present example, the atmosphere control system 300 comprises a heat exchanger 320 for conditioning gas, specifically to adjust a temperature of gas flowing therethrough. The direction of flow 350 of gas through the heat exchanger 320 is dependent on the mode of operation. Consistent with arrows C and D described above, the solid arrow 350 shown in Figure 2 illustrates the direction of flow 350 of gas through the heat exchanger 320 in the first mode of operation. The dashed arrow 350 illustrates the same in the second mode of operation. The direction of flow 350 is shown as being in the z-direction, though in other examples the direction of flow 350 has components in any other direction.

[0080] In the present example, the transport unit 100 comprises first and second gas temperature sensors 340, 341. The first gas temperature sensor 340 is for sensing a temperature of gas flowing through the first port 210. The second gas temperature sensor 341 is for sensing a temperature of gas flowing through the second port 211. The first and second gas temperature sensors 340, 341 are located in the atmosphere control system 300. In other examples, the first and second gas temperature sensors 340, 341 are located in the respective first and second ports 210, 211, and/or in the compartment 200, such as in the respective first and second spaces 250, 251. In other examples, there is more than one first gas temperature sensor 340 and/or more than one second gas temperature sensor 341.

[0081] In some examples, the atmosphere control system 300 receives gas other than gas from the compartment 200, such as external air, and in the first and second modes of operation the second and first gas temperature sensors 341, 340, respectively, are configured to sense a temperature of gas received by the atmosphere control system 300. [0082] In some examples, the atmosphere control system 300 is configured to switch between the first and the second modes of operation based on at least one predetermined criterion being met. In some examples, the at least one predetermined criterion being met is based on one or more signals representative of a temperature of respective portions of the transport unit 100, such as temperatures sensed by the first and second gas temperature sensors 340, 341. In some examples, cargo temperature sensors (not shown) are provided in the cargo 110 in use, and the temperatures are sensed using the cargo temperature sensors. In some examples, the cargo temperature sensors are required, and/or approved for use, by the United States Department of Agriculture (USDA), and/or any other national regulatory department concerned with the transport of perishable goods.

[0083] In some examples, the at least one predetermined criterion being met is determined on the basis of one or more signals representative of a temperature of return gas received by the atmosphere control system 300, such as when the temperature of return gas exceeds a threshold. In some examples, the at least one predetermined criterion being met is determined on the basis of a temperature of gas or cargo in a portion of the compartment 200, such as when the temperature of gas or cargo in the portion of the compartment 200 exceeds a threshold. In other examples, the at least one predetermined criterion being met is based on an elapsed time since the atmosphere control system 300 last switched between the first mode of operation and the second mode of operation, such as when the elapsed time exceeds a threshold. In this way, in some examples, the switching between the first and second modes of operation is intelligently controlled by the atmosphere control system 300. In each example, the predetermined criterion being met is generally indicative of a temperature in one of the first space 250 and the second space 251 becoming too high, which in some examples is indicative of hotspots in the compartment 200 or the cargo 110, in use. Switching the mode of operation may provide a higher flow rate of conditioned gas to the space 250, 251 having the highest temperature, thereby to provide a more uniform temperature distribution in the compartment 200.

[0084] In the present example, the atmosphere control system 300 is configured to control the heat exchanger 320 to regulate a temperature of conditioned gas supplied to the compartment 200 on the basis of signals received from the first and second gas temperature sensors 340, 341. That is, the atmosphere control system 300 controls an amount of heat removed from return gas by the heat exchanger 320 to regulate the temperature of conditioned gas towards a target temperature setpoint. In the present example, this is by the atmosphere control system 300 comparing the temperature of conditioned gas to the temperature of return gas to determine an amount of heat to be removed by the heat exchanger 320 from return gas passing through the heat exchanger 320 to regulate the temperature of conditioned gas towards the target temperature setpoint. The atmosphere control system 300 is further configured to adjust the temperature setpoint in dependence on the mode of operation, for instance to set the target temperature setpoint to any one of a first, second, third or fourth target temperature setpoint. In some examples, the atmosphere control system 300 is configured to adjust the temperature setpoint in dependence on a temperature of the compartment 200 and/or a temperature of the cargo 110, in use.

[0085] By way of example, in the first mode of operation, the atmosphere control system 300 is configured to compare a temperature of return gas sensed by the second gas temperature sensor 341 with a temperature of return gas sensed by the first gas temperature sensor 340 and to control the heat exchanger 320 to regulate the temperature of conditioned gas towards the first temperature setpoint. The first temperature setpoint is set so that it provides sufficient cooling to the compartment 200, without damaging the cargo 110 held in the compartment 200, in use. The first temperature setpoint may be, for example in units of degrees Celsius (C), between 12 C and 16 C, such as between 13 C and 15 C, such as 14 C. In other examples, the first temperature setpoint may be any other suitable temperature setpoint depending on the cargo 111 held in the compartment 200 in use. For example, the temperature setpoint may be less than 10 Celsius, such as less than 5 Celsius, such as below 0 C in the case of chilled or frozen goods. In some examples, the temperature setpoint may be greater than 16 C, such as greater than 18 C or greater than 20 C, for example when bringing the cargo 111 to a temperature of an external atmosphere, or for adjusting a rate of ripening of ripenable produce, for example towards an end of a journey.

[0086] In some examples, the first temperature set point is lower, such as up to 1 C, more than 1 C, up to or more than 2 C, or up to or more than 5 C lower, than a predetermined threshold temperature associated with the cargo 110. The predetermined threshold temperature may be a temperature at or below which the cargo 110 held in the compartment 200 may be damaged, in use. In such examples, the atmosphere control system 300 is configured to switch between the first and second modes of operation in such a way that a temperature of the cargo 110 remains at or above the predetermined threshold temperature, in use, for instance to prevent damage to the cargo 110. In some examples, this is by a frequency of switching between the first and second modes of operation being, for example, less than 30 minutes, less than 15 minutes, less than 10 minutes, or less than 5 minutes.

[0087] Figure 3 shows such an example, wherein the cargo 110 is ripenable produce, such as bananas, and wherein the cargo 110 generates heat during ripening of the produce in the transport unit 100, in use. The predetermined threshold temperature associated with the cargo 110 is 14 C. The thick, solid black lines show the temperature of conditioned gas supplied to the compartment 200 through the first port 210 in the first mode of operation. The thick, dashed black lines show the temperature of conditioned gas supplied to the compartment 200 through the second port 211 in the second mode of operation. In each mode, the conditioned gas is supplied at a temperature of 12 C, which is below the predetermined threshold temperature. The thin, solid black line shows a temperature of a lower portion of the cargo 110, such as a temperature in a lower half of the cargo 110, associated with the first port 210. The thin, dashed black line shows a temperature of a raised point of the cargo 110, such as a temperature in an upper half of the cargo 110, associated with the second port 211.

[0088] The atmosphere control system 300 is operated in the first mode of operation for a first 15 minute period, during which the temperature of the lower portion of the cargo 110 (thin, solid line) is reduced from 14.1 C to 14 C due to the conditioned gas supplied through the first port 210 at 12 C. During the first 15-minute period, the temperature of the upper portion of the cargo 110 (thin, dashed line) increases from 14 C to 14.1 C due to the heat generated by the cargo 110 when no, or a reduced amount of conditioned gas is supplied through the second port 211. Following the first 15-minute period, the atmosphere control system 300 is switched to operate in the second mode of operation for a second 15-minute period. During the second 15- minute period the temperature of the upper portion of the cargo 110 (thin, dashed line) reduces from 14.1 C to 14 C due to the conditioned gas supplied through the second port 211 at 12 C. Further, the temperature of the lower portion of the cargo 110 (thin, solid line) increases from 14 C to l4.1 C due to the heat generated by the cargo 110 when no, or a reduced amount of conditioned gas is supplied through the first port 210. This process is repeated, with the atmosphere control system 300 configured to switch between the first and second modes of operation every 15 minutes or less. It will be understood that the switching frequency may be any other suitable switching frequency, and the temperatures may be any other suitable temperatures, depending on the type of cargo 110 located in the transport unit 100, in use. In some examples, the temperature of a respective upper and lower portion of the cargo 110 may change by more or less than 0.1 C, such as up to 1 C, more than 1 C, up to or more than 2 C, or up to or more than 5 C, during each period of operation in either of the first and second modes of operation.

[0089] Returning to the example shown in Figure 2, when the atmosphere control system 300 switches to the second mode of operation, the atmosphere control system 300 is configured to compare a temperature of return gas sensed instead by the first gas temperature sensor 340 with a temperature of conditioned gas sensed instead by the second gas temperature sensor 341 to control the heat exchanger 320 to regulate the temperature of conditioned gas supplied to the compartment 200 towards the third temperature setpoint. In the present example, the third temperature setpoint is the same as the first temperature setpoint. In some examples, the first and third temperature setpoints are different to each other.

[0090] In the present example, the atmosphere control system 300 is configured, upon switching to the first or second mode of operation, such as before, during, or after switching to the first or second modes of operation, to control the heat exchanger 320 regulate the temperature of conditioned gas supplied to the compartment 200 towards the second or fourth temperature setpoints, respectively, until at least one predetermined condition is met. Note that the predetermined condition being met is different to the predetermined criterion for switching the mode of operation being met. In the present example, in the first and second modes of operation, the atmosphere control system 300 is configured to regulate the temperature of conditioned gas supplied to the compartment 200 towards the first and third temperature setpoints, respectively, when the at least one predetermined condition has been met.

[0091] The second and fourth temperature setpoints are lower than the first and third temperature setpoints, respectively. In this way, the atmosphere control system 300 is configured to provide additional cooling to the first space 250 or the second space 251 when the atmosphere control system 300 is switched, respectively, to the first mode of operation and to the second mode of operation, until the at least one predetermined condition is met. This is advantageous if a temperature in one of the first and second spaces 250, 251 is higher than a temperature in the other of the first and second spaces 250, 251, which, in some examples, occurs following continuous operation of the atmosphere control system 300 in one of the first and second modes of operation. In such a case, upon switching the mode of operation, the space 250, 251 having the highest temperature is supplied with conditioned gas at a temporarily reduced temperature until the at least one predetermined condition is met. Thereafter, the space previously having the highest temperature is supplied with conditioned gas at a baseline temperature for that mode of operation.

[0092] In some examples, the predetermined condition being met is determined on the basis of an elapsed time since the atmosphere control system 300 last switched between the first mode of operation and the second mode of operation. In some examples, the predetermined condition being met is determined on the basis of one or more signals representative of a temperature of respective portions of the compartment 200 and/or the atmosphere control system 300. In this way, in some examples, the atmosphere control system 300 is configured to intelligently control the temperature of conditioned gas supplied to the compartment 200.

[0093] It will be understood that, in some examples, when the predetermined condition is met, the second and fourth temperature setpoints are gradually adjusted towards the first and third temperature setpoints, respectively. In the present example, the second and fourth temperature setpoints are the same as each other, though in other examples this is not the case. In some examples, the second and fourth temperature setpoints are the same as the first and third temperature setpoints, respectively, so that the atmosphere control system 300 does not provide additional cooling to the first and second spaces 250, 251 upon switching to the first and second modes of operation, respectively.

[0094] In the present example, the atmosphere control system 300 comprises a reversible-flow gas moving device 330 for reversibly moving gas through the atmosphere control system 300, such as through the heat exchanger 320. In the present example, the reversible-flow gas moving device 330 is a reversible-flow fan 330. A direction of rotational motion of the blades of the fan 330 is modulated to modulate a direction of flow of gas through the fan 330, such as to modulate the direction of flow 350 of gas through the heat exchanger 320. In some examples, a position of the blades of the fan 330 is modulated, relative to a hub of the fan 330 to which the blades are mounted, to modulate the direction of flow of gas therethrough. It will be understood that, in other examples, any suitable reversible-flow gas moving device 330 can be used to move gas through the atmosphere control system 300. In some examples, the transport unit 100 alternatively, or in addition, comprises one or more gas moving devices, each associated with a respective first or second port 210, 211. In other examples, the transport unit 100 comprises a unidirectional gas moving device, such as a one-way fan, for directing gas through the atmosphere control system 300 and into the compartment 200. In such examples, the transport unit 100 comprises valves (not shown) for directing gas at different flow rates through the first and second ports 210, 211 in dependence on the mode of operation.

[0095] In the present example, switching the mode of operation comprises operating the reversible-flow gas moving device 330 to reverse the flow of gas therethrough. In some examples, the reversible-flow gas moving device 330 is operable to provide a variable flow rate of gas therethrough, such as by being driven by a frequency convertor. In some examples, the flow rate of gas through the reversible-flow gas moving device 330 is varied to modulate the temperature of conditioned gas supplied to the compartment 200, such as to supplement the operation of the heat exchanger 320. For example, an increased flow rate may reduce the temperature of conditioned gas supplied to the compartment 200.

[0096] In the present example, the heat exchanger 320 is an evaporator 320 of a refrigeration system (not shown). In other examples, the heat exchanger 320 is any other suitable liquid-to gas or gas-to-gas heat exchanger, such as a water-cooled heat exchanger. In the present example, the refrigeration system is any suitable refrigeration system. In the present example, the refrigeration system comprises a condenser configured to reject heat from the refrigeration system to an atmosphere away from the transport unit 100, such as to an external atmosphere external to the transport unit 100.

[0097] Figures 4A and 4B show side profile schematic views of the evaporator 320 shown in Figure 2. The evaporator 320 is oriented so that a direction of an aggregate flow 325 of refrigerant through the evaporator 320 is inclined to the direction of flow 350 of gas through the evaporator 320 at a flow angle 324. In some examples, the flow angle 324 is greater than 10, 20 or 30 degrees to the direction of flow 350 of gas through the evaporator 320. In some examples, the flow angle 324 is less than 70, 60, or 40 degrees, such as 45 degrees, to the direction of flow 350 of gas through the evaporator 320. In some examples, the flow angle 324 is zero so that the direction of aggregate flow 325 of refrigerant is substantially aligned with the direction of flow 350 of gas through the evaporator 320. In such examples of inclined and aligned flow, the direction of aggregate flow 325 of refrigerant through the evaporator 320 is non-orthogonal to the direction of flow 350 of gas through the evaporator 320. In the present example, this is by the refrigerant being injected into the evaporator 320 at an inlet 322 located at a lower end of the evaporator 320 (i.e. at an end closer to the base 220 of the compartment 200 in the z-direction) and leaving the evaporator 320 at an outlet 323 located at an upper end of the evaporator 320 (i.e. at an end further from the base 220 of the compartment 200). There may be one or more inlets 322 and one or more outlets 323. The evaporator 320 comprises coils 321, or tubes 321, between the or each inlet 322 and the or each outlet 323. The coils 321 or tubes 321 form a circuitous path through the evaporator 320 in the horizontal (x, y) and vertical (z) directions, relative to the base 220 of the container 200. In some examples, the evaporator 320 further comprises fins (not shown) for transferring heat between the coils 321 or tubes 321 and gas flowing through the evaporator 320. In the present example, the fins are inclined at an angle to the vertical direction, for example to permit the collection of condensates forming on the evaporator 320 in use. In other examples, the evaporator 320 is any other suitable evaporator 320.

[0098] In the present example, the atmosphere control system 300 is configured to control a superheat of the evaporator 320. The superheat of the evaporator 320 is a temperature of the refrigerant above its boiling point at, or downstream from, the outlet 323 of the evaporator 320. The superheat of the evaporator 320 is set to ensure that all refrigerant leaving the evaporator 320 is fully vaporised so that no liquid is present when the refrigerant reaches a compressor of the refrigeration system. In the present example, the atmosphere control system 300 is configured to set the superheat of the evaporator 320 at a target superheat. In this way, the atmosphere control system 300 is configured to control the refrigeration system to regulate the superheat of refrigerant leaving the evaporator 320 towards the target superheat.

[0099] In the present example, switching the mode of operation of the atmosphere control system 300, and thereby changing the direction of flow 350 of gas through the evaporator 320, affects a superheat of the evaporator 320. In the present example, in the first mode of operation, the direction of flow of gas 350 through the evaporator 320 is towards the base 220. In this way, warmer return gas received from the compartment 200 first encounters heated refrigerant leaving the evaporator 320 at the outlet 323. The gas then leaves the evaporator 320 as conditioned gas at the lower end of the evaporator 320, which comprises cool refrigerant received through the inlet 222. Reversing the direction of flow 350 of gas through the evaporator 320 reverses this, so that warmer return gas received from the compartment 200 first encounters cool refrigerant entering the evaporator 320 at the inlet 322. The gas then leaves the evaporator 320 as conditioned gas at the upper end of the evaporator 320, which comprises heated refrigerant flowing towards the outlet 323. Furthermore, immediately following a switch in the mode of operation, return gas received at the evaporator 320 may be cooler than return gas received at the evaporator 320 in the previous mode of operation. Thus, in the present example, changing the mode of operation changes a temperature pattern over the evaporator 320. This may result in insufficient vaporisation of refrigerant leaving the evaporator 320.

[0100] In the present example, the atmosphere control system 300 is configured, in each of the first and second modes of operation, to set the evaporator 320 superheat at a first target superheat. The atmosphere control system 300 is configured to raise the target superheat to a second target superheat, higher than the first target superheat, upon switching between the first and second modes of operation, for example before, during or after switching between the first and second modes of operation. This is to accommodate the change in the temperature pattern over the evaporator 320, for example to ensure the refrigerant is sufficiently vaporised before it leaves the evaporator 320. The atmosphere control system 300 may be configured to control the refrigeration system to regulate the superheat of the evaporator 320 towards the first target superheat following the raising of the target superheat to the second target superheat. In the present example, the first target superheat is around 5 Kelvin and the second target superheat is around 10 Kelvin. In other examples, the first target superheat may be any suitable value and the second target superheat may be any suitable value higher than the first target superheat. It will be understood that, in some examples, different first and second target superheats are used in the first mode of operation than in the second mode of operation.

[0101] In the present example, raising the target superheat is temporary following a switch in the mode of operation. The target superheat is raised, for instance, for a predetermined period of time, or until a temperature of conditioned gas received by the atmosphere control system 300 reaches a threshold. If the direction of aggregate flow 325 of refrigerant through the evaporator 320 were to be substantially orthogonal to the direction of flow 350 of gas through the evaporator 320, such as at a flow angle 324 of between 80 and 90 degrees to the direction of flow 350 of gas, the temperature pattern may not be significantly affected by reversing the direction of flow 350 of gas. In such examples, temporarily raising the superheat in this way may not be required. [0102] Figure 5 shows a flow diagram illustrating a method 400 of controlling an atmosphere in a transport unit 100, the transport unit 100 comprising a compartment 200 for holding cargo 110, and first and second ports 210, 211 for supplying conditioned gas from an atmosphere control system 300 to the compartment 200, the first and second ports 210, 211 opening into the compartment 200 at different, spaced-apart locations in the compartment 200. The transport unit 100 may comprise the atmosphere control system 300, or the atmosphere control system 300 may be separate from the transport unit 100, such as part of a container vessel on which the transport unit 100 is to be transported. The transport unit may, for example, be any of those described above with reference to any one of Figures 1 to 4.

[0103] In some examples, a controller (not shown) is provided to cause the atmosphere control system 300 to perform the method 400. In some examples, the controller is comprised in the transport unit 100, such as in the atmosphere control system 300, thereby to locally operate the atmosphere control system 300. Alternatively, in some examples, the atmosphere control system 300 is located remotely from the transport unit 100. For example, the atmosphere control system 300 may be part of a marine vessel (not shown). The controller may be located remotely from any transport unit 100, and/or from the atmosphere control system 300, thereby to remotely operate the atmosphere control system 300. The controller may communicate with the transport unit 100 and/or the atmosphere control system 300 via a wireless network, such as a cloud, and/or may be communicatively coupled to the transport unit 100 and/or the atmosphere control system 300 using a wired connection. The controller may be configured to, e.g. simultaneously, control an atmosphere control system 300 of each one of a plurality of transport units 100, for example to cause each atmosphere control system 300 to perform the method 400.

[0104] The method 400 comprises, in a first mode, supplying 410 conditioned gas from the atmosphere control system 300 to the compartment 200 through the first port 210 at a higher supply flow rate than through the second port 211, and, in a second mode, supplying 430 conditioned gas from the atmosphere control system 300 to the compartment 200 through the second port 211 at a higher supply flow rate than through the first port 210. In the present example, the method 400 comprises, in the first mode, receiving 411 return gas at the atmosphere control system 300 from the compartment 200 through the second port 211 and, in the second mode, receiving 431 return gas at the atmosphere control system 300 from the compartment 200 through the first port 210. In some examples, no conditioned gas is supplied 410 and no return gas is received 411 through the second port 211 in the first mode, and no conditioned gas is supplied 430 and no conditioned gas is received 431 through the first port 210 in the second mode.

[0105] The dashed lines in Figure 5 indicate optional actions which are performed by the method 400 of the present example, but which may not be performed in other examples. It will be understood that the dashed actions 411 to 421 illustrated as following on from the supplying 410 corresponding to the first mode of operation may be performed simultaneously with, and/or sequentially with, and/or in any suitable permutation with, any of the other actions 410 to 421 corresponding to the first mode of operation. Similarly, the dashed actions 431 to 435 illustrated as following on from the supplying 430 corresponding to the second mode of operation may be performed simultaneously with, and/or sequentially with, and/or in any suitable permutation with, any of the other actions 430 to 435 corresponding to the second mode of operation. In some examples, the method 400 comprises additional actions that are not shown in Figure 5.

[0106] In the present example, the method 400 comprises switching 420 between the first mode and the second mode based on at least one predetermined criterion being met. The at least one predetermined criterion being met is determined as described above in relation to the transport unit 100 of Figures 1 to 4. The switching 420 the mode of operation comprises switching a direction of operation of the reversible-flow gas moving device 330, for example. In the present example, the method 400 comprises, in the first mode, moving 412 return gas from the second port 211 to the first port 210 via the heat exchanger 320, and, in the second mode, moving 432 return gas from the first port 210 to the second port 211 via the heat exchanger 320.

[0107] In the present example, the method 400 comprises, in each of the first and second modes, sensing 413, 433 a temperature of return gas received at the atmosphere control system 300 from the compartment 200 and a temperature of conditioned gas supplied to the compartment 200 from the atmosphere control system 300. The method 400 further comprises, in each of the first and second modes, controlling 414, 434 the heat exchanger 320 to regulate a temperature of conditioned gas supplied to the compartment 200 on the basis of the temperatures sensed. [0108] In the present example, the method 400 comprises, in the first mode, setting 415 a superheat of the evaporator 320 at a first target superheat. In some examples, the setting 415 the superheat comprises regulating the superheat of the evaporator 320 towards the first target superheat. The method 400 further comprises raising 421 the target superheat of the evaporator 320 to a second target superheat, higher than the first target superheat, as the mode of operation of the atmosphere control system 300 is changed. The raising 421 the target superheat is illustrated as being before the supplying 430 corresponding to the second mode, but it will be understood that the raising 421 may be performed before, during or after the switching 420 the mode of operation, such as after the supplying 430 corresponding to the second mode. The method comprises setting 435 the superheat of the evaporator 320 at the first target superheat following the raising 421 of the target superheat, such as after a predetermined period of time has elapsed following the raising of the target superheat. In the present example, the switching 420 is illustrated as switching 420 from the first mode to the second mode. It will be understood that, in some examples, the switching 420 is switching 420 from the second mode to the first mode, and is performed, for example, following the setting 435 the superheat in the second mode. In such examples, the associated raising 421 of the target superheat occurs before, during or after the switching 420.

[0109] The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. For example, the transport unit 100 described with reference to Figures 1 to 4, and/or the method 400 described with reference to Figure 5, is not limited to transporting ripenable produce such as bananas, but may alternatively, or in addition, be used for temperature drawdown of hot goods during transport. Furthermore, embodiments of the invention have been described in relation to a reefer container but other embodiments may be applied to a refrigerated truck or trailer.

[0110] It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.