IMPROVEMENTS IN AND RELATING TO ATMOSPHERE MODIFYING UNITS

Abstract: An apparatus for atmosphere modification comprising: a reservoir (2) capable of containing fluid; heat exchange means (3) disposed to act on any fluid within the reservoir; and fluid distribution means (7) for introducing said fluid into an atmospheric flow.

Description: IMPROVEMENTS IN AND RELATING TO ATMOSPHERE MODIFYING UNITS TECHNICAL FIELD This invention relates to improvements in and relating to atmosphere modifying units. BACKGROUND ART This invention will be discussed in relation to refrigerated containers. However, it must be appreciated that the present invention is not limited to cooling applications and that the same principles could be employed to modify the atmosphere to a higher temperature. Refrigerated containers are used to store and transport produce such as fresh fruit and vegetables. The quality of the produce is maintained for much longer periods when kept under refrigeration. One drawback to refrigeration is that moisture from the air is removed as it is cooled by the refrigeration unit. Produce such as fresh fruit and vegetables lose their quality as water is removed. It should be appreciated that different produce have different requirements. For example, produce with a high water content such as lettuce, asparagus and broccoli require a high relative humidity, say in the order of 95 - 98%. Soft skinned fruits such as peaches require a relative humidity in the range of 90 - 95%. Hard skinned fruit such as oranges require a much lower relative humidity, say in the order of 85%. In addition to correct humidity conditions, it is also important that the temperature within the container is kept within a certain range and that there is sufficient air flow to prevent moulds and the like growing on the produce. Refrigerated containers function by passing the air to be cooled over finned tubes of a refrigeration unit known as the evaporator. The evaporator contains cooling fluid produced by the refrigeration unit and an exchange of heat from the air to the cooling fluid results. This cooling action, while effective in lowering the temperature of the air, also has a substantial dehumidifying effect. Water vapour in the air tends to condense from the air stream onto the evaporator. This condensed water is usually vented to the outside of the container. A disadvantage is that the condensed water vapour often turns to ice on the finned tubes due to the low temperature of the cooling fluid passing through the evaporator. Over a period of time, typically three to six hours, the formation of ice reduces the cooling capacity of the evaporator and restricts the flow of air. To remove the build-up of ice a defrost cycle is initiated. The refrigeration unit is stopped and heating elements warm the evaporator so that the ice melts. This water is usually collected and drained to the exterior of the container. During the defrost cycle the produce in the container is not kept refrigerated and the temperature rises. This causes air in the container to expand and be released to the outside of the container. Upon cooling a vacuum is created and outside air enters the container. This air requires cooling and results in a change in the composition and character of the air inside the container. These temperature fluctuations and changes to the air composition can lead to deterioration in the quality of the produce. While these systems can provide an environment that roughly approximates what is required, there is no ability to fine tune the system to provide the ideal environment without the fluctuations which lead to deterioration of produce. Apparatus is known that collects water condensed on the evaporator and resprays this into the air circulated after the evaporator. Although this attempts to address the problem in providing high humidity cooled air the system has drawbacks. The accumulation of ice on the evaporator occurs at a faster rate due to the higher content of water vapour in the air. Defrost cycles may consequently become more frequent. It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice. Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only. DISCLOSURE OF INVENTION According to one aspect of the present invention there is provided an apparatus for atmosphere modification comprising: a reservoir capable of containing fluid; heat exchange means disposed to act on any fluid held within the reservoir; and fluid distribution means for introducing said fluid into an atmospheric flow. While the present invention can apply to either the cooling or heating of the fluid, reference throughout the specification will be made to cooling fluid for ease of reference. The heat exchange mechanism means will now be referred to as an evaporator, but this is an example only and this term should not be seen as limiting. In an alternate aspect of the present invention there is provided a method for modifying the atmosphere within a container characterised by the steps of: a) modifying the temperature of fluid within a reservoir, and b) introducing the fluid into an atmospheric flow within the container In contrast to other systems for modifying the atmosphere, the present invention does not cool the atmosphere directly. Instead, the present invention cools (or heats) fluid which is then introduced into the atmosphere. This has a number of advantages over the prior art. One advantage is that the introduction of cooled fluid into the air does not have the dehumidifying effect of cooled air systems. In conventional systems the evaporator is required to be exposed to the air it is cooling and thus, condensed water vapour from the air tends to settle on the evaporator and reduce the efficiency of the evaporator. This leads to defrost cycles and fluctuations of the temperature within the container. With the present invention, there is no requirement of the evaporator to be exposed to the air and thus, formation of ice is unlikely to occur, elimination the need for a defrost cycle. Various embodiments of the invention may be used in conjunction with, or provided with, a container. Such combinations will be referred to herein. A container, where the term is used, is defined as being an enclosure. In the preferred embodiment the container comprises a shipping container. However, the invention may typically be used in cool stores, road transport units, refrigerators, ship holds, refrigerated display units, or any other suitable domestic or industrial enclosure. Although the present invention can in some embodiments operate as a stand alone unit, in preferred embodiments the present invention can work in conjunction with existing refrigeration utilising capacity control systems (hereinafter referred to as capacity control refrigeration systems) i.e. gas bypass, evaporative pressure regulation, unloading cylinders, inverter control of compressor, or any other means of regulating the capacity of the refrigeration system which already act on shipping containers and other enclosures. Thus, the present invention can be used to fine tune the environment within the shipping container. The reservoir of the present invention may comprise tubing or individual containers made of suitable materials such as metals or plastics to contain a fluid. In one embodiment of the present invention, the reservoir is fabricated of metal, preferably aluminium or a stainless steel, in which the bulk of fluid is housed. The reservoir may have baffles to minimise fluid motion during transport. The reservoir may have a fluid level indicator and means to introduce or withdraw fluid so that a certain quantity of fluid is maintained. In another preferred embodiment, the reservoir is constructed in a plastics material. For example, the reservoir may comprise of a series of plates or layers which provide rigidity and baffles. Preferably, the reservoir includes open cell plastic foam in its construction. This foam can be used within the reservoir and has a number of advantages over conventional reservoirs made out of either plastic or metal. One advantage of the open cell foam is that the foam provides more rigidity to the reservoir structure. Conventional reservoirs with a hollow interior often have the sides the reservoirs bulging under the pressure of the fluid that the reservoir contains. Open cell foam is also lightweight in construction and provides its own baffle system within the reservoir. A further advantage of open cell plastic foam is ease of manufacture. For example, the outer skin of the reservoir may be rotationally moulded from plastics material. The plastic foam can be readily introduced into the interior of the reservoir during the rotational moulding process or at a later time. Heat exchange means or evaporators used in the present invention may comprise a variety of means including conventional arrangements, or the use of printed circuit heat exchangers. Printed circuit heat exchangers consist of a stacked array of metal sheets which are chemically etched into coolant channels on one side and fluid channels on the other side. Coolant flows across the stack in one set of channels while the fluid flows in the other set of channels. Printed circuit heat exchangers have the advantage that they can freeze up without their internal construction breaking. Devices such as Peltier-effect devices, to cool the fluid may also be employed. In one embodiment of the present invention the heat exchanger or evaporator circuits of a refrigeration unit are immersed (partially or wholly) in the reservoir. Refrigerant flows through the evaporator circuits and heat is absorbed from the fluid circulated through the evaporator to reduce its temperature. This offers the advantage of being fully flooded providing even fluid distribution throughout the evaporator which produces a more even temperature, thereby reducing the possibility of the evaporator icing up. The pump may be positioned anywhere with respect to the evaporator. However in preferred embodiments the pump is positioned before the evaporator. It is believed that the pump works more efficiently if the static head of the pump is not on the suction end. Further, such positioning of the pump reduces the possibility of foaming of the fluid. The fluid in the reservoir is in some embodiments pure water. The fluid may however contain one or more substances to reduce the freezing point of the water. The substance may comprise chloride salts such as sodium chloride, calcium chloride or magnesium chloride. Preferably the substance comprises alcohols or glycols. Food grade propylene glycol is particularly suitable for the present invention. The proportion of glycol within the water regulates to some degree the humidity in the atmosphere. Thus, the selection of the glycol concentration for a particular situation can be quite critical. In some embodiments of the present invention, there may be provided an additional storage container which includes additives to the water such as glycol. A hydrometer (or some other sensor) may determine the concentration of glycol (or any other substance) in the fluid. The appropriate amount of substance may then either be introduced manually or automatically into the fluid within the reservoir bringing the concentrations up to the ideal concentration. Other substances may be included in the storage container or perhaps in different storage containers which can be introduced into a fluid. For example, there may be provided substances which can treat the produce for bacteria, diseases, fungi, insects and so forth. There may even be included substances which can act to ripen the produce. In some embodiments of the present invention substances for the treatment of the produce may be in gaseous form and just sprayed into the container rather than being introduced through the fluid. The fluid from the reservoir is introduced into an atmospheric flow by fluid distribution means. In the preferred embodiment the fluid distribution means comprises one or more pumps and associated plumbing to fluid spray means. The fluid spray means may comprise one or more headers provided with nozzles which can form fluid droplets of various sizes. In some embodiments, nozzles may not be used. Instead, the pump may introduce the fluid into the atmosphere in a y. z ' . In some embodiments it may be suitable to have large droplets of water and in other embodiments fine atomised spray may be preferable. A large volume of fluid flow through the spray nozzles has been found to be suitable in the present invention. This allows the use of larger spray nozzles to avoid any blockage which may occur. In preferred embodiments of the present invention, the volume of fluid flow through the spray nozzles may be varied with controlled action of the pumps. The volume of flow from the pumps may be controlled by varying the speed of the pump (utilising such devices as an inverter to change the frequency of the power supply to the pump or other similar such devices). The volume of flow may also be adjusted by restricting and therefore reducing the flow of the fluid either from the pump to the nozzles or at the nozzles themselves. Varying the flow of the fluid allows the volumes of fluid in contact with the atmosphere to vary and thus varies the capacity of the fluid to absorb heat from the atmosphere. As the fluid flow is reduced the temperature of the fluid is required to be decreased in order to achieve the same cooling capacities. Decreasing the temperature of the fluid causes moisture in the atmosphere to condense into the fluid. Thus, decreasing the temperature of the fluid decreases the relative humidity of the atmosphere. Therefore, at a given atmospheric temperature the humidity may be increased or decreased by varying the volume and temperature of the fluid. In some embodiments of the present invention, the humidity of the atmosphere within the container may be controlled by having a humidistat controlled pump, that is, a pump which has a sensor that determines the relative humidity within the container and varies the output of the pump accordingly. In some embodiments of the present invention, the whole of the atmosphere within the container may be microprocessor controlled, including the introduction of produce treatment substances, temperature and humidity. For example, an operator may input the type of produce going into the container, for example cabbages. The microprocessor may then modify the percentage of glycol in the fluid in the reservoir, the output of the pumps and the introduction of any other substances into the container atmosphere to provide the ideal atmosphere for cabbage. Sensors within the container can provide feedback to the microprocessor which can make adjustments as required. According to another aspect of the present invention there is provided an atmospheric control unit substantially as described above wherein one or more mass transfer units are disposed near the fluid distribution means, so that fluid from the fluid distribution means can be transferred onto the mass transfer units and atmosphere from the container can pass through the mass transfer units to modify, or maintain within a desired range or characteristics, the atmosphere. A mass transfer unit is defined as being a material providing a large surface area that a fluid may be distributed over. The mass transfer unit may comprise a mesh, grid, fibrous or foamed material and is so named as it allows for a mass or quantity of fluid and/or thermal energy to be transferred into the atmosphere. The mass transfer units will now be referred to as pads throughout this specification, although it should be appreciated that this term should not be seen as limiting. The pads may be made of any suitable material, for example cardboard or plastic. However in preferred embodiments the pads are made of an open cell foamed plastic similar to that used in preferred reservoir constructions. Fluid spray may be directed onto the pads to provide a large surface area for fluid. The atmosphere of the container may be directed through the pad or pads to cool and humidify the atmosphere of the container. Varying the surface area of the pads has a similar effect to changing the volume of fluid passing through the container or module. The larger the surface area the greater the amount of fluid that will come into contact with the atmosphere. Thus, in some embodiments of the present invention it may be possible to either exchange pads of actually varying surface areas or varying the surface area of pads (perhaps by unfolding) within the storage container. It is envisaged that this operation will most likely only be carried out where fine tuning of the atmosphere for a particular produce cannot be readily achieved by using the methods described previously. The fluid sprayed onto the pads may also comprise fluid passed through the evaporator to be cooled and then sprayed on one portion of the pad. The fluid that has not passed through the evaporator may be sprayed on the remaining proportion of the pad. The atmosphere firstly passes through the pad with the cooled water and this is cooled and humidified by same. Then the air may pass through the second pad sprayed with fluid from a reservoir which has not been cooled which can further humidify the atmosphere. It should be noted that the warmer the fluid, the more readily it evaporates into the air. In some embodiments the atmosphere modifying unit may comprise a cooled fluid reservoir in which the fluid is piped to one or more cooling and humidification units. The excess fluid may be transferred back to the reservoir for cooling. The use of the present invention in a cool store may allow air to enter from the front of the atmosphere modifying unit and be directed through the cooling and humidification sections. The cooled and humidified air can then be directed to any part of the cool store to maintain the quality of the produce. According to another aspect of the present invention there is provided an atmosphere modifying unit substantially as described above wherein apparatus for creating an atmospheric flow is provided. In some embodiments of the present invention the atmospheric flow may be provided from external, existing units (preferably with capacity control systems) while in other embodiments means for providing an airflow may be included. The atmospheric flow is generally directed through an inlet port of the present invention to encounter the mass transfer units and fluid distribution means. The atmospheric flow may then be passed through a filter to remove any water droplets. In a further embodiment one or more fans or blowers may direct air through the atmospheric control unit to provide a cooled and humidified atmosphere which is circulated through the container. The atmosphere is preferably withdrawn from the top of the container and passed through the atmosphere modifying unit. The cooled humidified air is then vented to the base of the container. In the preferred embodiment of the present invention the speed of the fans may be varied to increase or decrease the volume of atmospheric flow required for a given product. The atmosphere modifying unit may come as a module which can be retrofitted to an existing refrigeration unit with capacity control system. The module may be connected to the existing refrigeration unit to provide coolant flow through the evaporator of the present invention. The coolant flow through the existing evaporator may be stopped or used to further cool the atmosphere. When the module is connected to an existing refrigeration unit a number of modes of operation may be utilised. For example: a) The existing evaporator of the refrigeration unit is not used and the cooling and humidification of the air is effected by the present invention. b) Both evaporators have coolant flowing, providing cooling of the air by the existing evaporator and cooling and humidification of the air by use of the present invention. c) The existing evaporator is used to provide cooling of the air. The evaporator of the present invention and its associated cooling and humidification apparatus are not used. The fluid used in the present invention may be removed to prevent this form freezing if low temperatures are to be provided by the existing evaporator. d) The existing evaporator is used to cool the air while the fluid of the present invention is sprayed to humidify the air. e) The existing evaporator may also be used to control the amount of fluid in the reservoir. Condensation and/or ice on the existing evaporator reduces the amount of fluid in the reservoir and when running the condensation and melted ice is run to waste, the amount of fluid is reduced. f) Heater elements may be employed in conjunction with modes a to e to heat the air before entering the atmosphere modifying unit of the present invention. The module may also utilise the atmospheric flow of an existing atmospheric control unit. The modular unit has the advantage that it can be removed and reinstalled as required depending on the produce. BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present invention will become apparent from the ensuing description which is given by way of example only and with reference to the accompanying drawings in which: Figure 1 is a schematic view of the apparatus of a preferred embodiment of the present invention, and Figure 2 is a schematic view of the present invention retrofitted to an existing refrigeration unit, and Figure 3 is a schematic view of an alternate apparatus for shipping containers in accordance with the present invention, and Figure 4 is schematic view of an alternate apparatus for shipping containers in accordance with the present invention, and Figure 5 is schematic view of an alternate apparatus for a coolstore in accordance with the present invention, and BEST MODES FOR CARRYING OUT THE INVENTION Figure 1 shows one embodiment of an atmosphere unit as indicated by arrow 1. The atmospheric modifying unit 1 comprises a reservoir 2 which contains a fluid 4. The fluid 4 is mainly comprised of water with an amount of anti-freeze added to reduce its freezing point. Food grade propylene glycol has been found to be a suitable anti-freeze to meet food and drug regulations. The fluid 4 is cooled by an evaporator 3. The evaporator 3 is linked to a refrigeration unit (not shown) and the coolant of the refrigeration unit flows through evaporator 3. The fluid 4 is transferred to the spraying means 6 by pump 5. Spraying means 6 has a number of spray nozzles 7 which distribute the fluid 4 in a fine mist spray. The fluid 4 from the spray nozzles 7 is transferred to pads 8 and 9 which provide a large surface area for the fluid 4 to pass over. Air from the container is withdrawn from the roof portion by a fan 12. Air passes through inlet port 10 of the atmospheric modifying unit 1. The air passes through pad 8 in which the air is cooled and humidified. The air then travels through the spraying means 6 and through pad 9 where it is further cooled and humidified. The air finally exits through exit port 11. A pad 13 may also be positioned at the exit port 11 to prevent fluid droplets from exiting with the air flow. The air flow is then directed to the base of the container to cool and humidify the produce. Airflow through the container and through the atmospheric modifying unit 1 is indicated by the arrows. The air is cooled through several stages as it passes through the atmosphere modifying unit 1. The air is slightly cooled at the fluid surface level and then by droplets falling from pad 8. A significant amount of cooling and humidifying occurs through pad 8 as a large surface area of cooled fluid is available to the air flow. The air is further humidified and cooled by the spraying means 6 and pad 9. With reference to Figure 2 an atmospheric modifying unit 1 is retrofitted to an existing refrigeration unit 20 and its atmospheric modifying system 21. The evaporator 3 of the present invention is linked to the same plumbing as evaporator 23 of the existing refrigeration unit. Evaporator 23 may be closed so that no refrigerant flow occurs through the evaporator. In this mode the air of the container is cooled and humidified by the atmospheric modifying unit 1. In a second mode of operation both evaporators 3 and 23 operate to cool and humidify the atmosphere of the container. In a third mode of operation evaporator 3 may be closed and preferably fluid 4 is drained from the reservoir 2. In this mode evaporator 23 can be used to cool or freeze the produce inside the container as in standard operation. Figure 3 illustrates an alternate embodiment of an atmosphere modifying unit generally indicated by arrow 30, to that illustrated in Figure 1. This embodimentis suitable for shipping containers. The unit 30 has a storage container 33 which contains glycol (and possibly other fluids) for introduction into the reservoir 34. There is also included a gas bottle 35 for introducing various substances into the atmosphere. A solenoid 36 controls the action of the nozzles 37. Figure 4 illustrates a unit very similar to that shown in Figure 3. The main difference in this unit is the pattern of air flow. This pattern of air flow works particularly well with containers of this particular configuration which makes up approximately 30% of all current shipping containers. Figure 5 illustrates a further embodiment 50 suitable for use in a coolstore. The unit 50 has the same basaic features as described in the earlier embodiments but a different position of the fan 52 and a different air flow. Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope of the appended claims.

Claims: CLAIMS 1. Apparatus for atmosphere modification comprising:, a reservoir capable of containing fluid: heat exchange means disposed to act on any fluid within the reservoir: and fluid distribution means for introducing said fluid into an atmospheric flow. 2. Apparatus as claimed in claim 1 wherein the fluid is cooled by heat exchange means. 3. Apparatus as claimed in either claim 1 or claim 2 which is adapted to work with capacity control refrigeration systems. 4. Apparatus as claimed in any one of claims 1 to 3 wherein the reservoir includes open cell plastic foam in its construction. 5. Apparatus as claimed in any one of claims 1 to 4 wherein the heat exchange means is in the form of a printed circuit heat exchanger. 6. Apparatus as claimed in any one of claims 1 to 5 wherein the heat exchange means is immersed partially or wholly in the reservoir. 7. Apparatus as claimed in any one of claims 1 to 6 wherein the fluid includes glycol. 8. Apparatus as claimed in any one of claims 1 to 7 which includes a storage container capable of holding additives to the fluid. 9. Apparatus as claimed in claim 8 wherein the additives include substances which can treat bacteria, diseases, fungi and insects. 10. Apparatus as claimed in either claim 8 or claim 9 which includes a device to control the amount of additives in the fluid. 11. Apparatus as claimed in any one of claims 1 to 10 wherein the fluid distribution means is a pump 12. Apparatus as claimed in any one of claims 1 to 11 wherein the action of the fluid distribution means is controlled. 13. Apparatus as claimed in any one of claims 1 to 12 which is microprocessor controlled. 14. Apparatus as claimed in any one of claims 1 to 13 which includes one or more mass transfer units disposed near the fluid distribution means so that fluid from the fluid distribution means can be transferred on to the mass transfer units and atmosphere from the container can pass through the mass transfer units to modify, or maintain with in a desired range of characteristics of the atmosphere. 15. A method for modifying the atmosphere within a container characterised by the steps of: a) modifying the temperature of fluid within reservoir, and b) introducing the fluid into a atmospheric flow within he container 16. A method for modifying the atmosphere within a container characterised by the step of operating apparatus as claimed in any one of claims 1 to 14. 17. Apparatus as substantially as herein described with reference to and as illustrated by the accompanying drawings. 18. A method as substantially as herein described with reference to and as illustrated by the accompanying drawings.

Inventors: WEBSTER GRAEME BRUCE, WEBSTER, GRAEME, BRUCE
Applicants: CONTAINER SUPPORT SYSTEMS LIMI, WEBSTER GRAEME BRUCE, CONTAINER SUPPORT SYSTEMS LIMITED, WEBSTER, GRAEME, BRUCE
Application year: 1995
Main classification: F24F6
IPC codes: A23B7, A23L3, F24F1, F24F6, F25D17, F25D23