The invention relates to a reefer unit for the transport of perishable goods, such as fruit and flowers, and to a method for reducing ethylene in such a reefer unit.

Reefer units are known from practice and are widely used in international shipping for refrigerated transport of perishable goods of various nature, including for example fruit, flowers and plants. In order to preserve the goods that are stored in the storage space of the reefer unit during transport, the conditions in the storage space, such as temperature and gas composition, need to be controlled.

This is especially true for ethylene, which is a gas that is produced by many perishable goods including fruits and flowers. It is known that many fruit species, during ripening, produce ethylene, which ethylene in turn accelerates the ripening process of the fruit. Similarly, it is known that fresh flowers produce ethylene, which accelerates decay of the flowers. Thus, if no measures are taken to reduce the production of ethylene or increase the removal thereof, most perishable goods will have decayed beyond use upon arrival.

In traditional reefer units the accumulation of ethylene is prevented by refrigerating the transported products to reduce the production of ethylene by the products. Alternatively and/or additionally, the reefer units are vented during transportation to expel excess ethylene and therewith prevent accumulation of ethylene in the storage space. Although this approach did reduce ethylene production and accumulation to a certain extent, between 10 - 20% of the total amount of transported product was lost nevertheless. This amount would increase if one or more decayed or decaying products were already present upon loading. In addition, the energy costs associated with refrigerating and venting the storage space were also considerable.

In order to reduce the losses of product due to ethylene production during transport, reefer units comprising ozone generators were developed. In such ozonated reefer units, ozone was produced and added to the gas that was circulated in the storage space. The ozone in the refrigerated gas stream would react with ethylene to form several different compounds, such as formaldehyde, dioxymethylene, ethane -ozonide, 1 ,2,4-trioxolane and/or ethane-epoxide, which are less volatile to the stored products than ethylene as such.

A disadvantage associated with such reefer units is that, even despite attempts to regulate the ozone content (and the ensuing associated chemical reactions) in the gas stream, it is concluded that is not possible to control the chemical reaction between the ozone and the ethylene to control the type and amount of the compounds that are produced in the chemical reaction. Such produced compounds include for example formaldehyde, dioxymethylene, ethane -ozonide, 1 ,2,4-trioxolane and/or ethane -epoxide, some of which are carcinogenic to humans. The invention is therefore aimed at obviating the aforementioned disadvantage and providing a reefer unit in which the ethylene is reduced in a safer and more environmentally friendly manner.

To that end, the invention provides a reefer unit for transporting perishable goods, such as fruit, the reefer unit comprising:

- a number of reefer unit walls enclosing a reefer inner space;

- a gas displacement unit that is operatively connected to the reefer inner space and is configured for displacing gas;

- at least one plasma generating unit that is operatively connected to the gas displacement unit and/or to the reefer inner space and that is configured to provide plasma to gas displaced by the gas displacement unit;

wherein the reefer unit inner space, the gas displacement unit and the at least one plasma unit form a gas circulation system that is configured for circulating a gas flow in at least the reefer unit inner space.

An advantage of the reefer unit according to the invention is that the plasma generated by the plasma generating unit eliminates ethylene present in the circulating gas in a safe and environmentally friendly manner. In the basis, the plasma produced by the plasma generating unit incites the following chemical reaction in the gas that is brought into contact with the plasma:

C ₂ H ₄ + 30 ₂ ® 2 C0 ₂ + 2 H ₂ 0

In other words, the chemical reaction that eliminates, or at least reduces the amount of, ethylene only produces carbon dioxide and water, which are harmless to the stored product. In this respect the invention differs significantly from an ozone -based ethylene reduction system, because a (cold) reaction of ozone injected in the refrigerated gas stream and ethylene would result in one or more of the following reactions and (resulting) compounds:

Another advantage is that the produced compounds are also harmless to people that open the reefer unit at the destination. Therewith, the use of a plasma generating unit provides a safe and environmentally friendly way of reducing or eliminating ethylene in the reefer unit.

In a preferred embodiment, the plasma generating unit and the gas displacement unit are connected in series, such that the gas from the reefer inner space is treated by the plasma generating unit as part of the circulation of the gas.

It is noted that the plasma generating unit can be formed as an integral part of a gas circulation system for a new reefer unit or that, alternatively, the plasma generating unit can be retrofitted to existing reefer units in order to create a reefer unit according to the invention.

In an embodiment according to the invention, the plasma generating capacity of the plasma generating unit may be adapted to the volume of the reefer inner space, and preferably the plasma generating capacity is adapted to be an overcapacity related to the reefer inner space. In other words, a higher volume of the reefer inner space leads to a higher plasma generating capacity of the plasma generating unit. Preferably, the plasma generating capacity is chosen such that it forms a slight overcapacity with regard to the maximum volume in order to safeguard that sufficient plasma can be generated at all times.

In an embodiment according to the invention, the reefer unit may comprise two plasma generating units.

An advantage of providing two plasma generating units, each of which separately is sufficient to produce the required amount of plasma, is that an increased redundancy is achieved. This means that the capacity for generating plasma is maintained even if one of both plasma generating units is rendered unusable, for example by malfunctioning or breaking down.

In an embodiment according to the invention, the reefer unit may comprise three plasma generating units.

An advantage of providing three separate plasma generating units, preferably each of which separately is sufficient to produce the required amount of plasma, is that an even further increased redundancy is achieved. In addition, the use of three plasma generating units allows switching between two or all three units during normal operations. This decreases the wear on the plasma generating units and increases the life-time of the units as such. In addition, ascertains that the plasma generating capacity of the reefer unit is sufficient under all circumstances. This may for example be especially useful when the stored product already from the start contain a number of spoiled products that produce high quantities of ethylene.

In an embodiment according to the invention, the reefer may comprise a number of sensors, wherein the number of sensors preferably comprise one or more of: an ethylene sensor, a temperature sensor, a humidity sensor, a flow sensor and/or a weight sensor. An advantage of providing a number of sensors on the reefer unit is that the sensor input can be logged in a memory to determine the status of the stored products during transport, which allows determination of liability in case of spoiled cargo at arrival.

Another advantage is that the sensor input of the number of sensors may also be used to adapt the conditions in the reefer inner space to correct any deviations from the desired conditions. This may for example be performed using a feedback control system or, in some cases, even a feedforward control system. For example, in a feedback control system the actual ethylene concentration is measured. This enables effective control of the at least one plasma generating unit, thereby preventing unnecessary use and energy consumption, and unnecessary plasma generation. In another example, in a feedforward control system measurements can be used to predict future ethylene concentrations such that the plasma generating unit can be controlled pro-actively. This also contributes to unnecessary use and energy consumption, and unnecessary plasma generation. In addition, a feedforward control system may take into account the expected remaining residence time of the products in the reefer. This may further enhance possibilities for maintaining product quality of the transported products. In a further example, a feedback control system is used in combination with, or fully integrated with, a feedforward control system. This may achieve the aforementioned results in an even wider range of conditions and situations. It enables a self- controlled and stand-alone reefer unit that is capable of reducing product loss even in case of unexpected transport delays, for example.

Another advantage of providing a number of sensors on the reefer unit is that it allows the condition within and/or on the outside of the reefer unit to be established during transport. This would otherwise be (virtually) impossible, especially on large container ships that can carry up to and over 21,000 TEU. For this particular advantage, it is preferred that each of the sensors or the reefer unit as such is provided with a communication unit and/or transmitter for transmitting the sensor data to a controller and/or memory.

In an embodiment according to the invention, the reefer may comprise a control unit that is configured to switch the at least one plasma generating unit between an inactive state and an active state in which plasma is generated and vice versa.

The reefer unit may advantageously be provided with a control unit that is at least configured to control the active/inactive state of the plasma generating unit. In other words, the control unit is configured to determine and control whether each of the plasma generating units is on or off. This allows the plasma generation (i.e. production) to be determined on the basis of necessity and/or based on a specific predetermined schedule of plasma production, such as for example a software-based schedule.

The control unit may also be used for other control actions, including temperature regulation, data logging etc. In an embodiment according to the invention, input signals of the number of sensors may be used by the control unit to switch the at least one plasma generating unit between the inactive state and the active state and vice versa.

An advantage of this embodiment is that the control unit is used to actively control the conditions in the reefer inner space by controlling the plasma generating units and/or the gas displacement unit to correct any deviations from the desired conditions. This may for example be performed using a feedback control system or, in some cases, even a feedforward control system that is embodied in the control unit.

In an embodiment according to the invention, the control unit may additionally be configured to control one or more of: time interval, cycle time and/or intensity of each of the at least one plasma generating unit and/or the number of plasma generating units that is

simultaneously in the active state.

In a more advanced configuration of the control unit, the control unit is configured to control multiple aspects of the plasma generating unit to allow a more detailed control of the conditions, and especially ethylene level, in the reefer inner space.

In a first option, this includes for example the duty cycle (D) of the plasma generating unit, which is defined as a ratio of the time in active status in relation to a predetermined time interval. In other words:

D = (T _aaive / Ί i _nterval ) * 100% wherein:

D is the duty cycle (in percentage);

T _active is time in the active state for each time interval in seconds; and

T i _nterval is the time of a time interval in seconds;

In a second option, this may, additionally or alternatively to the first option, concern the intensity (I) of the plasma generating unit is, for the purpose of the invention, defined as the ratio between the used capacity (C _use ) and the total capacity (C _T ) of a plasma generating unit. In other words:

I ¹ - c '-'use / O ^v ~' _r 1 ·

This means that the plasma generating unit may, subject to the requirements of the gas composition in the reefer unit, be used at full capacity or at lower capacity. Also, it is noted that an additional control configuration as mentioned above may especially be relevant when having a combination of multiple plasma generating units. This may for example entail three plasma generating units, which are switched to the active and inactive state subsequently according to a duty cycle. If one of the plasma generating units malfunctions or is defect, the control unit can easily adapt the duty cycle of the remaining units in order to compensate for the defective plasma generating unit. Such a control configuration requires at least two plasma generating units, and is not limited to an upper limit. Additionally or alternatively to adapting the cycle time of the remaining plasma generating units, the control unit may also adapt the intensity of the plasma generating unit, for example by increasing the intensity of the remaining plasma generating units up to 100%.

In an embodiment according to the invention, the reefer unit may comprise a sensor configured to detect malfunctioning of an associated plasma generating unit, wherein the control unit is configured to switch a malfunctioning plasma generating unit to the inactive state, while simultaneously switching another one of the plasma generating units to the active state.

An advantage of having a status sensor that is configured to measure the operational status of a plasma generating unit has the advantage that a more redundant reefer unit is achieved. The control unit may, preferably directly upon detection of a malfunction in a plasma generating unit, switch that plasma generating unit from the active to the inactive state. This reduces the risk of adverse effects due to the malfunction, including fire and/or electric hazards.

Another advantage is that the control unit, upon detection of a malfunction, can switch another plasma generating unit from the inactive to the active state to continue the required ethylene elimination or reduction process. Therewith, maintenance of the desired conditions in the reefer inner space are ascertained.

In an embodiment according to the invention, the reefer unit may additionally comprise an engine bay that is separated from the reefer inner space and operatively connected thereto, the engine bay comprising a gas recirculation conduit that has an inlet and an outlet that both are connected to the reefer inner space, and wherein the plasma generating unit and the gas displacement unit are positioned in the gas recirculation conduit.

The reefer unit may be provided with a separate engine bay in which a number of components of the gas circulation system are provided. Preferably, the engine bay is situated next to the inner reefer space and is operatively connected thereto by means of an opening in a wall between the reefer inner space and the engine bay. The engine bay further includes the gas displacement unit, the plasma generating unit (or units) and optionally a refrigeration unit, all of which are connected to each other by means of a gas recirculation conduit. The control unit is in this embodiment preferably also situated in the engine bay and is operatively connected to the abovementioned components. The gas recirculation conduit has an inlet that is connected to the opening to the reefer inner space and an opposite end forming an outlet for providing gas to the reefer inner space.

An advantage of an engine bay is that the reefer unit components that are used to control the conditions in the reefer inner space are easily accessible without having to open the reefer unit. As a result, the components can be accessed even if stored products are present in the reefer inner space. In addition, the engine bay may be partially open to the environment, which would improve heat transfer from the components to the environment, therewith obviating or at least reducing the need for a separate cooling system for the components.

In an embodiment according to the invention, the reefer unit may comprise an electric protection device that is configured to provide the control unit and/or the plasma generating unit with protection against one or more of: voltage drop, voltage peak and polarity switch.

An advantage of providing an electric protection device is that it increases the reliability of the reefer unit, and specifically the electronic components such as the control unit and the plasma generating unit, with regard to electric malfunctioning. The electric protection device increases the ability of the reefer unit to remain functional even when subjected to adverse (environmental) conditions, such as thunderstorms, lightning strikes and/or electric overload situations due to electric short-cuts.

In an embodiment according to the invention, the reefer unit may comprise a refrigeration unit that is part of the circulation system and that is configured for refrigerating the reefer inner space and/or products stored therein.

For the purpose of the invention, the phrase refrigeration unit should also be construed as encompassing the synonyms of cooling unit, conditioning unit and/or other similar phrases. An advantage of providing a refrigeration unit in combination with a plasma generating unit is that the reefer unit according to the invention can be under a variety of different circumstances, which include warm climates.

In a preferred embodiment, the refrigeration unit is controlled by the control unit, which allows an integral control of the reefer inner space.

In an embodiment according to the invention, the gas displacement unit and the plasma generating unit may be configured to simultaneously be switched between an operative state and an inoperative state, wherein the switching is preferably controlled by the control unit.

An advantage of the simultaneous switching of the plasma generating unit and the gas displacement unit is that plasma is only produced when the gas is circulated through the reefer inner space. Therewith, it is prevented that plasma is produced when no circulation is present and an accumulation of plasma can occur. By coupling the plasma generating unit and the gas displacement unit such an accumulation is substantially prevented. In an embodiment according to the invention, the reefer unit additionally may comprises one or more of a memory module that is connected to the control unit, a communication module that is configured to sent data to and/or receive data from the control unit and a user interface and/or an interface for connecting external devices, such as computing devices, wherein the user interface and/or the interface for connecting external devices are operatively connected to the control unit.

It is preferred that the reefer unit according to the invention is provided with means that allow storing and/or communicating of data, including log data of the reefer unit, that can be used to improve the storage conditions.

Providing a memory that is connected to the control unit provides a number of advantages. An advantage is that the memory may be provided with software -based predefined programs for the storage of a particular product, such as bananas or a specific type of flower. This allows an easy-to-use quick selection of a product that is to be transported, after which the control unit will autonomously run the software during transport to preserve the product and keep conditions, especially the ethylene level, at a predetermined level.

Furthermore, the memory is, alternatively or additionally, useable to store a log containing the control history of one or more specific voyages, which allows an ex-post analysis of the control actions that were performed during the voyage. This may for example be used in conjunction with a liability determination in case the product is not delivered according to the specifications on which was agreed.

By providing the reefer unit with a communication module, any data that is collected by the control unit and/or stored on the memory, may be transferred to a remote location, such as a server, a computing device or similar. This allows the shipping company and/or the crew of a transport to evaluate the conditions in the reefer inner space without having to visually inspect the reefer unit, which is often difficult. The communication module may, if a number of sensors is provided to the reefer unit, be configured to relay sensor data to a remote location as disclosed above.

The communication module may advantageously also be used to locate the reefer unit during transport, which allows a shipping company and/or an end user to locate the position of the reefer unit, preferably in conjunction with as estimated time of arrival (ETA). The communication module may also be configured to allow remote access to the control unit in order to evaluate and/or adapt the programming thereon during a transport. It is preferred that such a communication module and/or the data sent therewith is provided with adequate encryption and/or safety protocols.

An advantage of providing a user interface and/or an interface for connecting external devices is that the control unit and/or the other components as disclosed above may be tested and/or (re)programmed by a technician. This obviates the need to (partially) disassemble the reefer unit in order to provide such maintenance to the reefer unit and/or components thereof such as the plasma generating unit or the control unit.

In an embodiment according to the invention, the control unit may comprise a memory and a CPU, and wherein the control unit is configured for storing and/or executing software programs that are specifically adapted to control storage conditions for a single product, such as bananas or carnations.

The control unit may advantageously be provided with a memory and a CPU that are configured for respectively storing and executing a specific number of predefined transport programs for specific products. This may for example concern a program that is specifically designed to provide control input for storing and transporting bananas or, alternatively carnations. Such a software program may for example provide specific instructions to the control unit on the time interval and duty cycle of a plasma generating unit during a transport period. Such transport programs reduce the setup time that is required for specifying the transport conditions and is especially useful if a reefer unit is only used for a limited number of products.

It is preferred that such predefined transport programs can easily be selected, either locally at the reefer unit or at a remote location using communication means, in order to reduce the time required for setting up the transport conditions.

The invention also relates to a method for reducing ethylene in a reefer unit, the method comprising the steps of:

- providing a reefer unit according to any one of the previous claims;

- loading the reefer unit with a product to be shipped;

- circulating the gas from the reefer inner space by the gas displacement unit and generating plasma by the plasma generating unit; and

- exposing the circulating gas to the plasma to reduce ethylene content in the circulating gas.

The method according to the invention provides the same effects and advantages as the reefer unit according to the invention as mentioned above.

An advantage of the method according to the invention is that the plasma generated by the plasma generating unit is highly effective with regard to reducing ethylene content in the reefer inner space, while obviating the production of harmful side compounds such as formaldehyde. Instead, only harmless compounds as water and carbon dioxide are produced as reaction products. Thus, the method according to the invention provides a well-defined, well-controllable method for reducing ethylene without producing harmful compounds as byproducts of the (reduction) reaction.

In an embodiment according to the method of the invention, the method additionally may comprise the step of controlling, by the control unit, one or more of the cycle time, interval time and/or intensity of the plasma generating unit and/or a circulation speed of the circulated gas. The method according to the invention may comprise executing more complex control actions by the control unit, which result in a more advanced and specific control of the plasma generating units. This may for example include controlling, for example by adapting, the duty cycle (D) of the plasma generating unit, which is defined as a ratio of the time in active status in relation to a predetermined time interval. In other words:

D = (T _aaive / T i _nterval ) * 100% wherein:

D is the duty cycle (in percentage);

T _active is time in the active state for each time interval in seconds; and

i _nterval ' ^s the time of a time interval in seconds;

In addition, it may concern the intensity (I) of the plasma generating unit is, for the purpose of the invention, defined as the ratio between the used capacity (C _use ) and the total capacity (C _T ) of a plasma generating unit. In other words:

I - c /cv

This means that according to the method controlling by the control unit, subject to the requirements of the gas composition in the reefer unit, controlling the plasma generating unit to operate at full capacity or at lower capacity.

Also, it is noted that controlling the abovementioned parameters may especially be relevant when having a combination of multiple plasma generating units. This may for example entail controlling three plasma generating units by alternatively switching them to the active and inactive state, preferably according to a duty cycle for each plasma generating unit. If one of the plasma generating units malfunctions or is defect, the control unit controls the plasma generating by adapting the duty cycle of the remaining units in order to compensate for the defective plasma generating unit. Such a control configuration requires at least two plasma generating units, and is not limited to an upper limit. Additionally or alternatively to adapting the cycle time of the remaining plasma generating units, the control unit may also adapt the intensity of the plasma generating unit, for example by increasing the intensity of the remaining plasma generating units up to 100%.

In an embodiment according to the method of the invention, the method may additionally comprise the steps of measuring characteristics of the circulating gas, and adapting the controlling based on the measured characteristics. It is preferred that the control exercised by the control unit with regard to the plasma generating unit is based on measurements that indicate the characteristics of the circulated gas. In other words, when a high ethylene level or a high temperature is measured, the control unit may advantageously control the plasma generating unit to increase the plasma production in order to attain the desired reduction in ethylene in the circulated gas.

In an embodiment according to the method of the invention, the method may comprise the steps of providing a software program configured to control the at least one plasma generating unit at least based on predetermined settings, such as type of product, providing the software program to the control unit, selecting, by a user or an automated system, the type of product selected, and adapting the control settings to the predetermined control settings provided in the software program.

An advantage of providing a software program to the control unit that comprises predetermined settings for a specific product allows an operator to quickly adapt the control unit to the specific product. As a result, the time that is required to prepare the reefer unit for transport is significantly reduced. This is especially advantageous in view of larger shipments of 10 reefer units and above.

Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which:

Figure 1 shows a perspective view of an example of a reefer unit according to the invention;

Figure 2 shows a top view of the example of figure 1 ;

Figure 3 shows a side view of the example of figure 1 ;

Figure 4 shows a top view of a second example of a reefer unit according to the invention;

Figure 5 shows a side view of the example of figure 4;

Figure 6 shows a schematic example of different components in a reefer unit according to the invention; and

Figure 7 shows an example of active control of multiple plasma generating units according to the invention.

An example of reefer unit 2 according to the invention is shown in figures 1-3. Reefer unit 2 in this example comprises reefer units walls 6, 8, 10, 12, 14, 16 which enclose reefer inner space 18. Reefer unit wall 16 in this example comprises two doors 16a, 16b, that are hingedly connected to reefer unit 2 and that provide entrance for providing products 4, such boxes of bananas 4 or boxes of carnations 4, to reefer inner space 18. Side wall 6, that is positioned opposite side wall 16, is provided with a number of components. More specifically, gas displacement unit 20, which in this example is a fan 20, plasma generating unit 22 and refrigeration unit 36 are all provided in side wall 16 and together with inner reefer space 18 form gas circulation system 24. In this example, plasma generating unit 22 is a redundant plasma generating unit 22 comprising three plasma generating units 22a, 22b, 22c.

Reefer unit 2 further comprises a number of sensors 24a - 24e for measuring different characteristics of reefer unit 2 and/or the gas present in reefer inner space 18. Reefer unit 2 also comprises control unit 26, which is connected to gas displacement unit 20, plasma generating unit 22 and refrigeration unit 36 for actively controlling these units 20, 22, 36 to circulate and refrigerate gas from reefer inner space 18, while simultaneously reducing the ethylene content of the circulated gas.

Reefer unit 2 in this example further includes sensor 28 that is configured to detect whether one or more of plasma generating units 22a, 22b, 22c is malfunctioning. In such a case, control unit 26 receives a signal from sensor 28 and switches the malfunctioning plasma generating unit to inactive, while simultaneously switching one of the other plasma generating units to active state.

Reefer unit 2 is further provided with electric protection unit 36, which in this example provides protection against voltage drops, voltage peaks and/or polarity switches.

In a second example of reefer unit 2 according to the invention (see figure 4 and 5), reefer unit 2 also comprises engine bay 30, in which gas displacement unit 20, plasma generating unit 22 and refrigeration unit 36 are disposed. Gas recirculation conduit 32 has inlet 32a that emanates in reefer inner space 18 and outlet 32b that also emanates in reefer inner space 18. Furthermore, gas recirculation conduit 32 connects gas displacement unit 20, plasma generating unit 22 and refrigeration unit 36 with each other. Gas recirculation conduit 32, gas displacement unit 20, plasma generating unit 22 and refrigeration unit 36 together with reefer inner space 18 in this example form gas recirculation system 24 in which the gas in reefer unit 2 is circulated.

Reefer unit 2 may be provided with various additional components that are connected to control unit 26. Figure 6 shows a schematic example of various components of reefer unit 2 that may be applied to reefer unit 2. The example shows gas displacement unit 20, plasma generating unit 22, refrigerator 36 as well sensors 24a, 24b, 24c, 24d, 24e being connected to control unit 26.

In addition, control unit 26 is connected to memory module 38 in which various actions of control unit 26 are logged for (later) retrieval. Memory 38 may also be used to store different storage programs embodied in software and configured to perform a predetermined sequence of control actions for a specific type of product. Furthermore, in this example control unit 26 is connected to communication module 40 as well as to user interface 42 and interface 44 for connecting external devices. It is noted that not all of these components 38, 40, 42, 44 need be present together, yet may also individually or in any combination be provided in reefer unit 2.

Communication module 40 in this example is provided as a wireless transmitting module that is configured to, preferably on request, transmit control data stored in memory 38 by control unit 26 with regard to the control actions performed over a predefined time period, such as a sea voyage. In addition, communication module 40 may be configured for receiving a signal that causes control unit 26 to start or end control actions, and/or start and/or stop recording control actions performed respectively. In addition or alternatively, commands and/or logs can be retrieved using user interface 42 or interface 44 for connecting an external device such as a computing device.

Control actions issued by control unit 26 to other components, such as plasma generating unit 22, are in this example initiated based on the specific measurements provided by one or more of sensors 24a - 24e and/or sensor 28.

Control unit 26 may also be provided with CPU 48 and memory 46, which obviates the need for memory 38 and communication module 40 (even though these may be present nevertheless). In this case, CPU 48 and memory 46 are configured for respectively causing the control unit 26 to perform actions and storing required or performed actions by control unit 26.

This type of construction is most useful in case a predefined program embodied in software is used.

In use, reefer unit 2 is filled with perishable products 4 to be transported, that are in this example stored in boxes. After filling reefer unit 2 with the desired quantity of boxes 4, doors 16a, 16b are closed and sealed to create a closed environment in reefer inner space 18. An operator activates control unit 26, for example using communication module 40 or user interface 42, which starts a control program that is configured to keep the product under predefined conditions as stored in memory 38 or memory 46. Examples of control actions to be performed are switching plasma generating unit 22 to an active state, switching refrigeration unit 36 to an active state in which it cools the circulating gas.

In use, plasma generating unit 22 generates plasma, which reacts with ethylene contained in the recirculating gas according to the following reaction:

C ₂ H ₄ + 30 ₂ 2C0 ₂ + 2H ₂ 0

Reefer unit 2 is in an example of the invention provided with multiple plasma generating units 22 to obtain a redundant reefer unit 2. Each of the plasma generating units 22 is controlled by control unit 26 and separately switchable from an active to an inactive state and vice versa. In this case, control unit 26 is configured to alternatively switch each of plasma generating units 22 between an active and an inactive state (see figure 7). In case one of plasma generating units 22 malfunctions or is defective, control unit 26 is configured to increase the amount of time remaining plasma generating units 22 are in the active state. This is visually depicted for this example in figure 7, left graph, in which it is shown that each of three plasma generating units 22-1, 22-2, 22-3 is alternatively switched between active and inactive state during a specific time interval. In the right hand graph, first plasma generating unit 22-1 is defective, which means that control unit 26 has increased active time of plasma generating units 22-2 and 22-3.

The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims within the scope of which many modifications can be envisaged.