GB2498777A

GB2498777A - Refrigeration apparatus with fluid control between a reservoir and a headspace

Info

Publication number: GB2498777A
Application number: GB1201435.3A
Authority: GB
Inventors: Ian Tansley
Original assignee: True Energy Ltd
Current assignee: True Energy Ltd
Priority date: 2012-01-27
Filing date: 2012-01-27
Publication date: 2013-07-31
Anticipated expiration: 2032-01-27
Also published as: GB201201435D0; GB2498777B

Abstract

An apparatus for cooling objects such as food items, beverages or vaccines has a payload space 20 within which items can be placed for temperature-controlled storage. The apparatus has a thermally-insulated reservoir 18 within which the payload space is disposed and a headspace 16 disposed in fluid communication with the reservoir. The reservoir contains a fluid such as water, which at least partially immerses the payload space and extends into the headspace; the headspace including cooling means 32 for cooling the fluid therein. The invention also provides a method of controlling the rate of fluid transfer by allowing fluid at a critical temperature to sink into the reservoir below the headspace. In embodiments, the means to control the rate of fluid transfer comprises valve means 52, the valve controlling the transfer of heat and/or fluid between the reservoir and the headspace so as to control the temperature of the payload space. The critical temperature may be at the juncture of the positive/negative change of temperature coefficient of thermal expansion, which for water occurs at approximately 4 degrees Celsius.

Description

REFRIGERATION APPARATUS

FIELD OF THE INVENTION

The present invention relates to a refrigeration apparatus. In particular, but not exclusively, the invention relates to a refrigeration apparatus for use in storing and transporting vaccines, perishable food items, packaged beverages or the like, and for the cooling or temperature control of equipment such as batteries, in the absence of a reliable supply of electricity. Aspects of the invention relate to an apparatus and to a method.

BACKGROUND

A large proportion of the world's population do not have access to a consistent and reliable supply of mains electricity. Underdeveloped countries, or regions remote from populated areas, frequently suffer from rationing of electrical power, often implemented by means of "load shedding", being the creation of intentional power outages, or failures of the distribution network.

The storage of vaccines, food items and beverages at appropriate temperatures is difficult in such areas where this absence of a constant and/or reliable supply of electrical power restricts the widespread use of conventional refrigeration equipment. Vaccines, for example, are required to be stored within a narrow temperature range between approximately 2 -8CC, outside of which their viability can be compromised or destroyed. Similar problems arise in connection with the storage of food, particularly perishable food items, and packaged beverages such as canned or bottled drinks.

In response to this problem, the present applicants have previously proposed a form of refrigeration apparatus, disclosed in co-pending patent application no. PCT/GB2O1O/051129, which permits a refrigerated storage space to be maintained within a temperature range of 4 -8CC for up to 30 days following a loss of electrical power. This prior art apparatus comprises a payload space for vaccines, food items, drinks container or any other item to be cooled, the payload space being disposed at a lower region of a thermally insulated reservoir of water. Above the reservoir, and in fluid communication therewith, a water-filled head space containing a cooling element or low-temperature thermal mass, provides a supply of cold water to the reservoir.

This prior art apparatus relies upon the known property that water is at its maximum density at approximately 4°C. Thus, water cooled to this temperature by the cooling element or thermal niass in the head space tends to sink down into the reservoir, settling at the lower region surrounding the payload space which, through thermal transfer, is cooled to a temperature at or close to 4°C.

The applicants have, however, recognised that it may, in some circumstances, be required to cool items to a temperature higher than 4°C and have therefore identified a need to provide a means by which the teniperature of the payload space in an apparatus of the type described in PCT/GB2O1O/051129 may be varied. It is against this background that the present invention has been conceived. Embodiments of the invention may provide a method or apparatus for regulating or controlling the temperature of the payload space within a range of temperatures from approximately ambient temperature down to approximately 4°C or lower. Other aims and advantages of the invention will become apparent from the

following description, claims and drawings.

STATEMENT OF INVENTION

Aspects of the invention therefore provide an apparatus and a method as claimed in the appended claims.

According to another aspect of the invention for which protection is sought, there is provided an apparatus comprising: a thermally-insulated reservoir in thermal communication with a heat exchange surface to be cooled; a headspace disposed in fluid communication with the reservoir, the reservoir containing liquid that at least partially immerses the heat exchange surface and extends into the headspace; cooling means for cooling fluid within the headspace; and means for controlling the transfer of heat and/or fluid between the reservoir and the headspace.

Advantageously, the means for controlling the transfer of heat and/or fluid between the reservoir and the headspace allows the temperature of the heat exchange surface to be controlled to a desired temperature, or within a desired range.

In an embodiment, the means for controlling the transfer of fluid comprises valve means.

The valve means may comprise any suitable form of valve capable of setting, controlling or varying a flow of fluid therethrough. For example, the valve means may comprise one or more of, without limitation, a butterfly valve, a choke valve, a diaphragm valve, a poppet valve, a ball valve or a globe valve, a gate valve. Alternatively, or in addition, the valve means may comprise a restriction in a conduit fluidly connecting the reservoir and the headspace.

In an embodiment, the valve means is adjustable so as to limit the rate at which the displacement of fluid at different temperatures occurs within the apparatus.

In an embodiment, the apparatus comprises control means for controlling the position of the valve so as to vary the flow of fluid between the reservoir and the headspace. In this respect, the valve means may function as a throttle arrangement.

The apparatus may comprise a payload space in thermal communication with the heat exchange surface. The payload space may be arranged to store items such as vaccines, perishable food items, packaged beverages or the like, or to house equipment or other objects requiring cooling or temperature control.

Sensor means may be provided to measure or detect the temperature of the payload space.

The sensor means may be configured to generate a signal indicative of the temperature of the payload space. The temperature signal may be applied to the control means so as to control the valve means in dependence thereon.

In an embodiment, the headspace and the reservoir are arranged, in use, to contain a fluid having a negative temperature coefficient of thermal expansion below a critical temperature and a positive temperature coefficient of thermal expansion above the critical temperature.

The fluid may comprise water or a fluid having similar thermal properties to water.

Thus the fluid may comprise a liquid having a critical temperature above which a density of the liquid decreases with increasing temperature and below which the density of the liquid decreases with decreasing temperature.

The cooling means may be arranged to cool fluid in the headspace to a temperature below the critical temperature. The apparatus may be configured such that fluid at the critical temperature sinks into the fluid reservoir, displacing fluid at temperatures on either side of the critical temperature towards the headspace.

Operation of the valve means may limit or substantially prevent the displacement of fluid between the reservoir and the head space. In an embodiment, the temperature of the fluid in the reservoir is dependent on, or proportional to, the position of the valve means, for example the degree of closure of the valve means. For example, the temperature of the fluid in the reservoir, and hence the temperature of the payload space, may be increased by moving the valve means towards a closed position, whereby the displacement of fluid between the reservoir and the headspace is limited or substantially prevented. Conversely, the temperature of the fluid in the reservoir, and hence the temperature of the payload space, may be decreased by moving the valve means towards an open position, whereby the displacement of fluid between the reservoir and the headspace is substantially freely permitted.

The arrangement may be such that fluid in the reservoir may be maintained at a substantially constant temperature, from approximately the critical temperature or below up to approximately ambient temperature, for extended periods of time. Conveniently, the arrangement is such that the temperature of the payload space can be maintained above 0°C and thus prevent items stored therein from freezing. This is particularly advantageous for the storage of vaccines which can be destroyed by temperatures at or around 0°C.

The cooling means may include a refrigeration unit that can cool water within the headspace and a power supply unit that can act as a source of power for the refrigeration unit. The power supply may comprise a solar power supply, such as a plurality of photovoltaic cells, for converting sunlight into electrical power. Alternatively, or in addition, a mains power supply may be used.

In typical embodiments, the refrigeration unit includes an electrically-powered compressor.

However, refrigeration units using other refrigeration technology might be used to increase the electrical efficiency of the refrigerator. One example of such alternative technology is a Stirling engine cooler, which may be operated in solar direct drive mode.

The apparatus may comprise a sensor disposed to detect the formation of ice in the fluid reservoir. The sensor may be operative to cause operation of the refrigeration unit to be interrupted upon detection of the formation of ice.

In alternative embodiments of the invention, the cooling means includes a thermal mass that, for use and at least initially, is at a temperature below a target temperature of the payload space. For example, the thermal mass may be a body of water ice. Such an arrangement may be used on its own (i.e. without a refrigeration unit) or in combination with a refrigeration unit.

Such embodiments may include a compartment for receiving the thermal mass in thermal communication with water in the headspace. For example, the compartment may be suitable for receiving ice. Alternatively, the thermal mass may be immersed in fluid within the headspace. In this latter case, the thermal mass may be an ice pack.

In an embodiment, the payload space may comprise one or more shelves for supporting items or objects to be cooled. The payload space may be open fronted. Alternatively, the payload space may comprise a closure for thermal insulation thereof.

The payload space may comprise one or more bottle coolers. The payload space may comprise one or more fluid pipelines through which a fluid to be cooled flows, in use. For example, the payload space may comprise a pipeline for a beverage dispensing apparatus.

In an embodiment, the payload space may be arranged to contain one or more batteries.

In an embodiment, the apparatus is configured to be disposed within a conventional refrigerator or the like. In this embodiment, the cooling means may comprise the existing cooling element of the refrigerator. The apparatus may be arranged to be positioned within the refrigerator such that the headspace is in thermal communication with the existing cooling element so as to cool the fluid therein.

The apparatus may for example be in the form of a structure formed to fit within a conventional refrigerator. The apparatus may be moulded or otherwise formed to fit within a conventional refrigerator.

Optionally the heat exchange surface is in thermal communication with a chamber.

Advantageously the heat exchange surface defines a wall of the chamber.

Further advantageously the chamber comprises a payload space within which items can be placed for temperature-controlled storage.

Optionally the chamber comprises a flexible membrane whereby a wall of the chamber may contact and conform to a surface of an object to be cooled.

Thus thermal contact between fluid in the reservoir and an object to be cooled may be enhanced.

The object may for example be a beverage container such as a bottle, can or other container, the apparatus being arranged to allow the container to be placed in the membrane for relatively rapid cooling to a desired temperature. The membrane may for example be in the form of a sock such as a polymer sock such as a rubber sock that is immersed in the reservoir. The sock may be suspended between opposed walls of the reservoir with an opening in one or both of the walls to allow an object to be inserted in the sock.

Optionally the chamber comprises a fluid conduit through which fluid may be passed to cool the fluid by means of the heat exchange surface.

The fluid may be a beverage to be cooled, a coolant to be cooled, a gas, or any other suitable substance, material, solid, liquid or object.

Optionally the heat exchange surface is in fluid communication with the headspace by means of a conduit through which the fluid may flow from the headspace to the heat exchange surface.

The headspace and reservoirs may be provided in separate housings in fluid communication by means of the conduit. Apparatus according to the present invention may therefore by provided in modular form, for example a headspace module, a reservoir module and a conduit for coupling the modules.

Thus the heat exchange surface may be located remote from the headspace. thus in some arrangements the headspace may be located in a compartment above the heat exchange surface. An article to be cooled may therefore be located away from the headspace, for example on a floor below that at which the headspace is located.

The heat exchange surface may for example be arranged to be placed in thermal communication with an article to be cooled such as a battery.

The battery may be part of a telecommunications installation such as a telecommunications transmitter and/or receiver facility. The facility may be part of a cellular communications infrastructure.

In a further aspect of the invention for which protection is sought there is provided a method comprising: cooling a fluid contained in a headspace; allowing fluid at a critical temperature to sink into a reservoir below the headspace so as to displace fluid therein towards the headspace; absorbing heat from a heat exchange surface that is at least partially immersed in fluid in the reservoir; and controlling the rate of fluid transfer between the headspace and the reservoir.

Advantageously the method comprises increasing a rate of fluid transfer between the headspace and the reservoir when a temperature of the reservoir is above a desired or target temperature.

Further advantageously the method comprises decreasing a rate of fluid transfer between the headspace and the reservoir when a temperature of the reservoir is below a desired or target temperature.

Advantageously, the step of controlling the rate of fluid transfer comprises operating valve means disposed in or adjacent to a fluid flowpath between the headspace and the reservoir.

Advantageously, increasing the rate of fluid transfer comprises increasing a degree of opening of the valve means.

Advantageously, decreasing the rate of fluid transfer may comprise decreasing a degree of opening of the valve means.

According to another aspect of the invention for which protection is sought, there is provided a method of cooling an item or object, comprising cooling a fluid contained in an upper region of a reservoir, allowing fluid at a critical temperature to sink into a lower region of the reservoir so as to displace fluid therein towards the upper region, absorbing heat from an item or object disposed within the lower region of the reservoir and controlling the rate of fluid transfer between the upper and lower regions of the reservoir.

In an embodiment, controlling the rate of fluid transfer comprises operating valve means disposed in or adjacent to a fluid flowpath between the upper and lower regions of the reservoir.

In an embodiment, the method comprises increasing a rate of fluid transfer between the upper and lower regions of the reservoir when a temperature of the lower region of the reservoir is above a desired or target temperature. Increasing the rate of fluid transfer may comprise increasing a degree of opening of the valve means.

In an embodiment, the method comprises decreasing a rate of fluid transfer between the upper and lower regions of the reservoir when a temperature of the lower region of the reservoir is below a desired or target temperature. Decreasing the rate of fluid transfer may comprise decreasing a degree of opening of the valve means.

According to another aspect of the invention for which protection is sought, there is provided an apparatus comprising a payload container within which items can be placed for temperature-controlled storage, a thermally-insulated reservoir within which the payload container is disposed, the reservoir containing water that at least partially immerses the payload container and extends into a headspace that is higher than the payload container, cooling means that can cool water within the headspace and means for controlling the transfer of heat and/or fluid between the reservoir and the headspace and/or between upper and lower regions of the reservoir.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples, features and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings may be taken independently or in any combination thereof. For example, features described in connection with one embodiment are applicable to all embodiments, unless there is incompatibility of features.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a graph of the density of water against temperature; Figure 2 is a cross-section through an apparatus embodying one form of the invention; Figures 3a and 3b illustrate schematically a portion of the apparatus of Figure 2 illustrating the principle of operation of the invention; Figure 4 is a schematic view of a first form of valve means for use with the invention; Figure 5 is a schematic view of another form of valve means for use with the invention; Figure 6 is a schematic view of a further form of valve means for use with the invention; Figure 7 is a schematic view of a still further form of valve means for use with the invention; Figure 8 is a graph illustrating how the useable life of a battery varies with temperature; Figure 9 is a schematic illustration of an apparatus embodying one form of the invention; Figure 10 is an expanded view of a section of a heat exchanger being a part of the apparatus of Figure 9; and Figure 11 is a schematic illustration of an apparatus embodying a second form of the invention.

Within the following description, as far as possible, like reference numerals indicate like parts.

It will be understood from the foregoing that operation of the present invention relies upon one of the well-known anomalous properties of water: namely, that its density is maximum at approximately 4°C, as shown in Figure 1. That is to say, water has a negative temperature coefficient of thermal expansion below approximately 4°C and a positive temperature coefficient of thermal expansion above approximately 4°C. Hereinafter, the term "critical temperature" will be used to refer to the temperature, being approximately 4°C, at which the density of water is at its maximum. -lo-

in the apparatus disclosed in co-pending POT application no. POT/GB2O1O/051129, the contents and teaching of which are expressly incorporated by reference herein, the temperature of the payload space is maintained at or around 4°C by the sinking of water at this critical temperature from the headspace into the reservoir, displacing warmer (or colder) water towards the headspace. This arrangement is advantageous for the storage of certain items such as vaccines, beverages or food packages but prohibits the use of the apparatus for items requiring storage at higher temperatures.

In response to this problem, the applicants have identified that it is possible to control or regulate the temperature of the payload space to a higher temperature, which temperature can be set simply and easily and, optionally, dynamically adjusted as desired.

Referring firstly to Figure 2, a refrigeration apparatus similar to that disclosed in PCT/0B2010/051129 is shown. The apparatus comprises a casing 10 shaped generally as an upright cuboid having an internal space 12 which, in use, contains a volume of water. For example, the casing 10 may be formed as a one-piece rotational moulding of plastic material. Insulating material 14 is carried on outer surfaces of the casing 10 to minimise flow of heat through the casing to or from the water contained within it. The water largely fills the internal space 12, but a small volume may be left unfilled to allow for expansion.

The internal space 12 is partially divided, by means of a dividing wall 15 extending into the internal space from a side wall of the casing 10, into respective upper and lower fluid volumes 16, 18, the upper volume defining a headspace 16 and the lower volume defining a fluid reservoir 18.

A payload space 20 is formed within the fluid reservoir region 18 of the casing 10. The payload space 20 is defined, at least in part, by a generally cuboidal box 22 that has one open face which opens horizontally to the exterior of the casing 10. The typical volume of the payload space in embodiments may be in the range of 50 to 100 litres, but other embodiments, for specialist purposes, may have greater or lesser capacities. The other faces are located within the casing 10 and are submerged under the water that is contained within the reservoir. The submerged faces of the cuboidal box 22 have no insulation so that they are in thermal communication with the surrounding water in a cooling region of the reservoir 18. The box 22 may optionally be integrally formed with the casing 10. When the refrigerator is disposed for use, the payload space 20 extends from close to the lowermost surface of the internal space 12 of the casing 10 to appropriately half way towards the uppermost surface of the internal space 12.

A door (not shown) is mounted to the casing 10 and can be opened to gain access to the payload space 20 through the open face. Insulating material is carried on the door so that, when it is closed, it minimises the amount of heat that can be transferred through it into or out of the payload space 20.

Cooling means, in the form of a refrigeration unit 30, is carried on a top surface of the casing 10. In this embodiment, the refrigeration unit is a conventional electrical compressor-based cooling unit. The refrigeration unit 30 is connected to a cooling element 32 that is disposed in the headspace 16 of the internal space 18 and is submerged in the water. The cooling element 32 is disposed such that it is spaced from the box 22 by the wall 15 and a layer of water and is likewise spaced from the uppermost surface of the internal space 12.

The refrigeration apparatus has an external power supply (not shown) to feed the refrigeration unit 30. The power supply can operate from a supply of mains power in the absence of bright sunlight. The power supply can also operate from photovoltaic panels, whereby the refrigeration unit 30 can be run without the need of a mains supply during sunny daytime conditions.

In alternative embodiments, the cooling means comprises a thermal mass, that, for use and at least initially, is at a temperature below a target temperature of the payload space. This can provide a refrigerator that is simple in construction and that has no moving parts in operation. For example, the thermal mass may be a body of water ice. Such an arrangement may be used on its own (i.e. without a refrigeration unit) or in combination with a refrigeration unit. Cooling means having a combination of a thermal mass supplied from a source external to the refrigerator and in addition a refrigeration unit can cool the refrigerator to its working temperature more quickly than can the refrigeration unit alone.

Operation of the refrigeration apparatus will now be described.

When the apparatus is first started, it can be assumed that all of the water is at or around the ambient temperature. The refrigeration unit 30 is run to cause its refrigeration element 32 to cool to a temperature that is typically well below the freezing point of water -for example, as low as -30°C. This, in turn, causes water in the headspace 16 immediately surrounding the cooling element 32 to cool. As the water in the headspace 16 cools, its density increases, with water at approximately 4°C being at its most dense and being caused to sink from the headspace 16 into the reservoir 18 surrounding the payload space 20, so displacing warmer, less dense water therein.

After a period of operation, ice may form in the water surrounding the cooling element 32.

Since the density of water decreases from its maximum below the critical temperature, however, any ice formed remains in the headspace 16 and does not sink into the reservoir 18.

Water at the critical temperature thus tends to pool in the reservoir 18 which, as described above, is disposed in thermal communication with the payload space 20. Heat from the payload space 20 is thus absorbed by the cooled volume of water in the reservoir 18 and the temperature of the payload space, and hence the objects or items stored therein, decreases.

Water within the reservoir 18 raised in temperature above the critical temperature due to the absorption of heat from the payload space 20 is displaced into the headspace 16 by the more dense water sinking therefrom, and is thus cooled, both by the cooling element 32 and any ice formed thereby. This cycle of heat transfer by the substantially continuous displacement of water between the headspace 16 and the reservoir 18 maintains the average temperature of the reservoir 18, and thus the temperature of the payload space 20, at or around the critical temperature.

The formation of ice in the reservoir 18 may unbalance the thermal transfer processes within the apparatus and so, in embodiments, an ice probe (not shown) is provided extending into the reservoir 18. Upon detection of ice by the ice probe, the refrigeration unit 30 is stopped so as to prevent further formation of ice within the reservoir 18.

If the refrigeration unit 30 stops, for example due to a loss of electrical power, assuming that ambient temperature is higher than the temperature of the water, energy will pass through the walls of the casing 10 into the water, which will start to warm. In the reverse of the cooling process, water in the reservoir 18 will tend to stay around 4CC while any ice in the headspace melts. Following complete melting, the water will continue to warm, but water above 4°C will tend to rise into the headspace 16. Thus, the payload space 20, being disposed within the reservoir 16, will be maintained at or around 4°C for as long as possible.

As is well-known, a large amount of energy is required to melt ice -the latent heat of fusion.

This acts as a sink of a large amount of energy that is absorbed by the water, the payload space 20 being maintained at a substantially constant temperature during the time that the ice in the headspace 16 melts. The payload of the refrigerator is therefore maintained at around 4°C, which is an ideal temperature for storage of vaccine and of food.

Further details of the operation of the apparatus of Figure 2 are disclosed in PCT/GB2O1O/051129, the contents of which are, as stated above, expressly incorporate herein by reference.

It will be understood that maintaining the temperature of the payload space 20 at or around the critical temperature relies upon the substantially continuous transfer of heat between the fluid in the reservoir 18 and fluid in the headspace 16 and that this transfer is achieved by the sinking of water at the critical temperature from the headspace 16 into the reservoir 18 and the consequent displacement of warmer water into the headspace 16.

It will be further understood that such displacement occurs through a flowpath or conduit 40 defined between the free end of the wall 15 and the adjacent wall of the casing 10. The applicants have recognised that the rate of displacement may determine the temperature at which the payload space 20 is maintained. The applicants have further recognised that this rate of displacement is dependent on, or proportional to, the effective cross sectional area of the flowpath 40 and that varying this effective area may enable the temperature of the payload space 20 to be controlled to a temperature other than the critical temperature.

Figures 3a and 3b illustrate the reduction in effective cross sectional area of the flowpath 40 from an initial value X to a reduced value Y. This reduction in cross sectional area restricts the rate of transfer of fluid between the reservoir 18 and the headspace 16. Thus, the rate at which fluid in the reservoir 18 warmed by the absorption of heat from the payload space 20 is displaced by water at the critical temperature sinking from the headspace 16 is likewise reduced. As a consequence, the average temperature of the fluid in the reservoir 18, and thus the temperature of the payload space 20 in thermal communication therewith, increases.

The applicants have discovered that the temperature of the payload space 20 can be set to a desired temperature between approximately the critical temperature and ambient temperature by controlling the effective cross sectional area of the flowpath 40.

Embodiments of the invention therefore include valve means disposed in or adjacent to the flowpath 40 so as to vary the cross section thereof. Figures 4 to 7 each illustrates schematically a portion of the apparatus indicated by the dashed line II in Figure 2 showing such valve means arranged to vary the flow of fluid through the flowpath 40.

Figure 4, for example, illustrates an embodiment wherein the valve means comprises a gate valve 50 disposed at the junction between the headspace 18 and the flowpath 40. Figure 5, on the other hand, illustrates an embodiment wherein the valve means comprises a butterfly valve 52 disposed within the flowpath 40.

In both embodiments, rotational movement of the valve means 50, 52 between open and closed positions varies the effective cross sectional area of the flowpath 40 and thus allows the rate of fluid transfer between the reservoir and the headspace to be adjusted. In this respect, the valve means functions as a throttle arrangement, controlling the flow of fluid therethrough.

The movement of the valve means 50, 52 may be achieved by any suitable means, numerous examples of which will be immediately apparent to the skilled person. By way of example, the valve means 50, 52 may be manually operable, whereby the user rotates the valve into the desired position via an input device such as a handle or wheel.

Alternatively, an electrically operable actuator, such as a stepper motor (not shown), may be provided to rotate the valve means 50, 52 to the desired position. The actuator may be controlled by control means in the form of a system (not shown) comprising, for example, a microprocessor or the like, an input device, such as a keypad interface for permitting the user to select a desired temperature for the payload space, and a temperature sensor for measuring the actual temperature of the payload space and arranged to send a signal indicative thereof to the microprocessor. The microprocessor may be configured to compare the actual temperature of the payload space as measured by the sensor with the desired temperature set by the user via the input device and to control the actuator to rotate the valve means to the required position in dependence on the comparison.

For example, if the user inputs a desired temperature of 10°C into the processor via the input device and if the actual temperature of the payload space is measured to be 4°C by the sensor, then the microprocessor controls the actuator to move the valve means 50, 52 towards the closed position, thereby reducing the effective cross sectional area of the flowpath 40. As described above, reducing the effective cross sectional area of the flowpath reduces the rate of fluid transfer (and thus heat transfer) between the reservoir 18 and the headspace 16, causing the temperature of the fluid within the reservoir 18, and thus the temperature of the payload space 20, to rise.

On the other hand, if the user inputs a desired temperature of 5°C into the processor via the input device and if the actual temperature of the payload space is measured to be 8°C by the sensor, then the microprocessor controls the actuator to move the valve means 50, 52 towards the open position, thereby increasing the effective cross sectional area of the flowpath 40. Increasing the effective cross sectional area of the flowpath 40 increases the rate of fluid transfer (and thus heat transfer) between the reservoir 18 and the headspace 16, causing the temperature of the fluid within the reservoir 18, and thus the temperature of the payload space 20, to decrease towards the critical temperature.

In Figures 6 and 7 a structurally different (but functionally identical) configuration is shown.

In these embodiments, the headspace 16 and the reservoir 18 are in fluid communication via a conduit 40. In the embodiment of Figure 6, the valve means comprises a poppet valve 54 reciprocally mounted in the conduit 40 and arranged to seat against the opening thereof.

The poppet valve 54 is mounted to a shaft or valve stem 56 extending through the conduit which is itself connected to a suitable actuator. As in the embodiments of Figures 4 and 5, the actuator may be manually operable, by means of a handle or wheel for example, or may be electrically operable under the control of a control system.

In an alternative arrangement (not shown), the valve stem 56 is connected to a bimetallic strip or other such device arranged to convert a temperature change into a mechanical displacement. The bimetallic strip may be disposed within the reservoir 18 and configured to raise or lower the valve stem 56, thereby opening or closing the poppet valve 54, in dependence on the temperature of the fluid within the reservoir 18.

In the embodiment of Figure 7, the valve means comprises a restriction 58, being a narrowed portion of the conduit 40, disposed at a midpoint of the conduit 40 and arranged to reduce the cross sectional area of the conduit 40 at that point. Where the ambient conditions are known and fixed, or the target temperature is not critical, a fixed-width restriction may be employed. Alternatively, where a more dynamic arrangement is required, a variable restriction may be employed whereby the cross sectional area of the conduit 40 can be varied between fully open and fully closed positions. As with the previously-described embodiments, the degree of restriction may be dependent on one or more of the desired target temperature, the temperature of the payload space or item to be cooled and the ambient temperature, or on the difference therebetween.

Control of the degree of restriction may be achieved in various ways, as will be immediately apparent to the skilled person. Such methods may include manual adjustment, the expansion of gas or liquid in a sealed system, movement of a bimetallic strip or the like or operation of an electro-mechanical device such as a solenoid. In one embodiment, the conduit 40 is formed from an elastomeric material and the restriction 58 is formed by axially stretching the conduit 40 so as to reduce its diameter or width.

The above description assumes that the maximum density of water occurs at 4°C, which is the case for pure water. The temperature at which the maximum density occurs can be altered by introduction of impurities into the water. For example, if salt is added to the water to a concentration of 3.5% (approximately that of sea water) then the maximum density occurs at nearer 2°C. This can be used to adjust the range of temperatures across which the payload space 20 may be set, as required for specific applications. Other additives may be employed to raise or lower the critical temperature, as required.

It will be appreciated that the present invention provides a novel and inventive device for storing and cooling items such as vaccines, perishable food items as well as a plurality of beverage containers such as bottles or drinks cans, within a desired temperature range following loss of power to the device for many hours. Embodiments of the invention also provide a means for simply and easily adjusting the temperature at which the items are stored.

Embodiments of the invention permit storage of energy in a low cost and abundant material (water) and can employ substantially any desired means of cooling. The apparatus is not dependent upon a power supply during operation and can maintain its cooling effect during periods of power loss -this is of particular importance for renewable energy sources, poor grid (intermittent power supply) or smart grids. In addition, the apparatus enables the temperature of the payload space to be controlled to relatively precise levels and the use of a highly insulated storage space improves energy storage efficiency.

It will be appreciated that the method of operation of the present invention allows the payload space to be prevented from freezing. By maintaining the temperature of the payload space at or around 4°C, the contents thereof are prevented from becoming damaged due to excessively low temperatures. Vaccines, in particular, are susceptible to damage or destruction at temperatures around Ut.

It will also be appreciated that the apparatus can be scaled and is applicable to small portable units or cooling systems for rooms or buildings.

Other embodiments of the invention provide a battery cooler for cooling batteries used as back-up power supplies. In this case, the battery may be housed in the payload space 20 or in another area in thermal communication with the reservoir 18.

The above described embodiments represent advantageous forms of the invention but are provided by way of example only and are not intended to be limiting. In this respect, it is envisaged that various modifications and/or improvements may be made to the invention within the scope of the appended claims.

Some embodiments of the invention find application in cooling of batteries. Referring to the graph of Figure 8, this illustrates the variance of battery life (abscissa) with temperature.

According to the Arrhenius equation, battery life generally decays exponentially with temperature increase and a general rule of thumb is that the lifetime of the battery reduces by 50% for each 10°C increase in battery temperature.

It can thus be seen from Figure 8 that the lifetime of a battery operating at a temperature of 35°C (line 35) is approximately half that of a battery operating at a temperature of 25°C (line 25) and approximately 25% that of a battery operating at a temperature of 15°C (line 15).

It will be understood that battery operating temperature is dependent on both ambient temperature and current draw from the battery which also has a heating effect on the battery, and thus the temperature of an operating battery in an ambient temperature of 15°C may be similar to, or even higher than, that of a quiescent battery in an ambient temperature of 35°C. Thus, the operation of batteries for extended periods in high ambient temperatures can reduce the lifetime of the batteries by over 75%, requiring regular replacement.

However, the cost and logistics of replacing batteries may be prohibitive in underdeveloped countries or geographically remote areas.

Referring next to Figure 9, an apparatus embodying one form of the invention is shown, in schematic form, generally at 10. The apparatus 10 is intended for cooling one or more batteries. In the illustrated embodiment, the apparatus is arranged to cool a single battery 40. Herein, the term battery" is used to encompass either a single battery or cell, or a plurality of cells collectively forming a battery. The invention may be used to cool each of a plurality of cells, or a single battery comprising such a plurality.

The apparatus 10 comprises a thermal store in the form of a lagged (i.e. thermally insulated) fluid headspace 12 containing a volume of fluid. In the illustrated embodiment, the fluid is water. The headspace 12 is preferably not completely filled with water so as to permit expansion of the water volume due to temperature changes during use.

An electrically-powered cooling element 14, similar to that found in a conventional refrigerator or freezer apparatus, is provided inside the headspace 12, or at least in thermal communication with the fluid therein. Electrical power to the cooling element 14 may be supplied from a power supply 16 such as a mains power outlet or, alternatively, a solar panel or other photovoltaic supply. Advantageously, it is not essential that the cooling element 14 be continuously powered -indeed, one of the primary purposes of the invention is to enable continued cooling of the battery in the absence of an electrical power supply to the cooling element 14.

A fluid conduit or pipe 18 connects the bottom of the headspace 12 to an inlet of a heat exchanger or reservoir 20 such that the heat exchanger 20 and the headspace 12 are in fluid communication. That is to say, the headspace 12 and the heat exchanger 20 form a single, contiguous fluid chamber. A valve means 50 is provided in the bottom of the headspace 12 and the conduit 18. In the embodiment of Figure 9 the valve means 50 is a gate valve similar to that of the embodiment of Figure 4 although any other suitable valve means may also be used. In a similar manner to the embodiment of Figure 4, rotational movement of the valve means 50 between open and closed positions varies the effective cross sectional area of the flowpath from the headspace 12 to the conduit 18 and thus allows the rate of fluid transfer between the headspace 12 and the heat exchanger 20 to be adjusted. In this respect, the valve means functions as a throttle arrangement, controlling the flow of fluid therethrough.

The heat exchanger 20 comprises a thin-walled, cuboidal container having a relatively high surface-to-volume ratio. In the illustrated embodiment, the heat exchanger 20 is rectangular in shape having a height and width that is significantly greater than its depth. Conveniently, though not essentially, the heat exchanger 20 generally corresponds in size and surface area to the shape of the battery 40 to be cooled.

Nevertheless, the heat exchanger 20 may take substantially any shape according to the desired application, although high surface-to-volume ratio arrangements may optimise heat transfer between the fluid therein and the battery. The heat exchanger 20 is conveniently formed from a material having a high thermal conductivity or transmissivity such as a metal material, again to improve heat transfer. Although not shown in the drawings, the heat exchanger 20 is perforated, having apertures extending therethrough from one radiating surface to the other, the purpose of which is described below.

The heat exchanger 20 is disposed in a housing 22 such that it is positioned, in a generally upright orientation, close to or adjacent the battery to be cooled. The housing 22 has an air inlet 24 in fluid communication with a fan or compressor 26 via a ducting 28. The fan or compressor 26 is arranged to draw in ambient air and pump it into the housing 22 via the ducting 28 and the inlet 24.

As shown in Figure 10, the housing 22 features a plurality of apertures 30 in the wall thereof facing the battery 40. Air drawn into the ducting 28 by the fan or compressor 26 thus flows into the housing 22 via the inlet 24 and is expelled through the apertures 30 towards the battery 40. In passing through the housing 22, some of the air flows around the heat exchanger 20 whilst a majority of the air flows through the apertures formed therein. The housing apertures 30 are relatively small in size such that the air expelled therethrough takes the form of a plurality of fine air jets which are directed at the external surface of the battery 40.

It is to be understood that the valve means 50 may be controlled to maintain to open and close under the control of a control means in order to maintain the temperature of liquid in the heat exchanger 20 at a required target temperature. Arrangements for achieving this may be similar to those described with respect to other embodiments of the invention.

Operation of the apparatus of Figure 9 will now be described.

In order to cool the battery 40, the water in the headspace 12 is cooled by means of the cooling element 14 using electrical power from the external power supply 16. During this time, the electrical apparatus to which the battery 40 is connected may also be powered by the external power supply 16 such that the battery 40 is quiescent and thus its temperature is at or around ambient temperature.

Before the cooling element 14 is activated, it is assumed that all of the water contained within the headspace 12 and the heat exchanger 20 is at or around ambient temperature. As the cooling element 14 is located within or close to the headspace 12, the water contained therein cools relatively quickly. As the temperature of the water in the headspace 12 decreases, its density increases relative to the ambient temperature water contained in the heat exchanger 20 and thus tends to sink under gravity into the heat exchanger 20 below, displacing the water therein.

A cycle is thus established within the fluid volume defined by the headspace 12 and heat exchanger 20 whereby the cooled water sinks from the headspace 12 through the fluid conduit 18 into the heat exchanger 20 so displacing the warmer (and thus less dense) water below. This warmer water rises into the headspace 12 through the conduit 18 and is, in turn, cooled by the cooling element 14 such that the average temperature of all of the water within the apparatus 10 falls. Once the temperature of the water in the apparatus 10 approaches a target temperature controlled by the valve means 50 the rate of displacement decreases, causing the water within the heat exchanger 20 to become comparatively stagnant at the target temperature. In the case where water is contained in the apparatus the lowest target temperature value will be around 4°C.

Because the density of water is at its maximum at 4CC, subsequent fluctuations in the temperature of the water in the headspace 12 do not cause the cycle to be re-established since water at temperatures either side of 4°C will tend to rise to the top of the headspace 12.

For example, even if the water in the headspace 12, in close proximity to the cooling elements 14 falls below 4°C, or even begins to freeze, its density will remain less than that of the water contained in the heat exchanger 20, causing it to remain in the headspace 12.

Similarly, a rise in temperature of the water in the headspace 12 above 4°C will decrease its density causing it, too, to remain in the headspace 12.

Consequently, any heat transfer from the water in the headspace 12 to the water in the heat exchanger 20 is generally effected by means of conduction rather than convection. Since water is not a particularly efficient conductor of heat, relatively minor temperature fluctuations in the water contained in the headspace 12 are generally not transmitted to the water in the heat exchanger 20.

It can therefore be seen that the temperature of the water in the heat exchanger 20 remains at approximately the target temperature substantially irrespective of temperature fluctuations in the water contained in the headspace 12.

The fan or compressor 26, powered by the external power supply 16, draws in ambient air and forces it, via the ducting 28, through the inlet 24 and into the housing 22. The air in the housing 22 flows around, or through the apertures formed in the heat exchanger 20 whereby it is cooled due to heat absorption by the water contained therein. The cooled air is then expelled through the apertures 30 in the front wall of the housing 22 in an array of fine air jets directed towards the surface of the battery 40.

Heat from the battery 40 is absorbed by the cooled air thereby lowering the temperature of the battery 40. Hence, a battery 40 subject to high ambient temperatures can be simply and efficiently cooled, allowing it to be maintained at a lower temperature and mitigating the adverse effects of high ambient temperatures on battery life It will be understood that heat absorbed from the flow of ambient air across the heat exchanger 20 raises the temperature of the water therein. The heat absorbed by the water in the heat exchanger 20 is transferred to the water above in one of two ways, depending on the temperature gradient within the water volume.

For example, if the temperature of the water in the system is substantially uniform at a target temperature of approximately 4°C, the increase in temperature of the water in the heat exchanger 20 decreases its density relative to the water above. A cycle is thus re-established whereby the warmer and therefore less dense water in the heat exchanger 20 is displaced by the cooler water above. The warmer water rises towards the headspace 12 where it is cooled again by the cooling elements 14 and then sinks back down into the heat exchanger 20. Thus, heat is transferred from the heat exchanger 20 to the headspace 12 primarily by fluid transfer therebetween.

Whilst power from the external power supply 16 is supplied to the cooling elements 14 and the fan or compressor 26, therefore, this recirculation within the water volume defined by the headspace 12 and heat exchanger 20 may continue indefinitely, advantageously maintaining the battery 40 at a lower than ambient temperature and thereby prolonging its usable life.

On the other hand, if the temperature of the water in the headspace 12 is significantly lower than that of the water in the heat exchanger 20, for example at or below freezing, the density of the water in the heat exchanger 20 remains greater than that of the water in the headspace 12, despite the increase in temperature. Thus the water in the heat exchanger tends to remain in the heat exchanger 20 and no circulation of water is established. In this case, heat absorbed by the water in the heat exchanger 20 is transferred to the colder water in the headspace 12 primarily by conduction, the rate of which depends on the temperature differential between the heat exchanger 20 and the headspace 12.

Again, whilst power from the external power supply 16 is supplied to the cooling elements 14 and the fan or compressor 26, a relatively large negative temperature differential is maintained between the water in the heat exchanger 20 and the water in the headspace 12.

Thus, heat transfer from the heat exchanger 20 may continue indefinitely, advantageously maintaining the battery 40 at a lower than ambient temperature and thereby prolonging its usable life.

Even in the event that the power from the external power supply 16 fails, for example during a rolling blackout or following an unexpected event, such that power is no longer supplied to the cooling elements 14, the apparatus 10 is able to provide a temporary cooling effect on the battery 40, as described below.

Due to the high specific heat capacity of water, the volume of water in the apparatus 10 is able to absorb a large amount of heat from the ambient air flowing across it without a significant increase in temperature. By way of example, a system containing 1000 litres of water at an average of 4°C would require absorption of approximately 130MJ of heat from the air flowing across it before its temperature reached 35°C. Where the temperature of the water in the headspace 12 was lower than 4°C at the point that power to the cooling elements 14 was cut, the amount of energy able to be absorbed would increase.

The rate at which the heat absorbed by the water in the heat exchanger is transferred through the water volume after electrical power is cut depends on the thermal gradient between the headspace 12 and the heat exchanger 20. Assuming that much of the water in the headspace 12 is in the form of ice, there will be a large negative temperature differential between the heat exchanger 20 and the headspace 12 such that heat is conducted away from the water in the heat exchanger 20 and absorbed by the ice in the headspace 12.

Since a relatively large amount of energy is required to melt ice within the headspace 12, known as the latent heat of melting, it acts as a sink for the energy that is absorbed by the water in the heat exchanger 20. While the temperature of the water in the headspace 12 is less than 4°C, its density remains lower than that of the water contained in the heat exchanger 20 and therefore does not sink. Thus, the water contained in the heat exchanger tends to remain at the target temperature, thereby maintaining the cooling effect on the battery 40.

Eventually, the temperature of the water in the headspace 12 reaches approximately 4°C. At this point, any increase in temperature of the water in the heat exchanger 20 reduces its density below that of the water above and the above-described cycle is re-established whereby heat is transferred away from the water in the heat exchanger 20 primarily by fluid displacement.

As long as the average temperature of the water in the system remains below ambient temperature, heat continues to be absorbed from the air flowing across the heat exchanger 20, thereby cooling the air directed towards the battery 40. During this time, therefore, the cooling effect on the battery 40 is maintained although, it will be appreciated, to a lesser degree than when power is supplied to the cooling elements 14.

Even once the temperature of the water in the apparatus 10 reaches ambient, the jets of ambient temperature air directed towards the battery 40 assist transfer of heat away from the battery 40 which, during use, operates at a significantly higher than ambient temperature.

The applicants have determined that the apparatus of the present invention may provide a cooling effect on the battery 40 for several hours following loss of electrical power to the cooling elements 14, although it will be understood that the precise length of time for which this cooling effect is maintained will depend on a number of parameters such as the ambient temperature, the volume of water in the heat exchanger 20, and the volume and temperature of water/ice in the headspace 12 when electrical power was cut.

It will be appreciated that the requirement for cooling of the batteries is at its greatest when the batteries are supplying current, i.e. when external power is not available. The present invention thus obviates the need for the batteries to store sufficient energy to cool themselves during discharge, which would otherwise itself add to the heating load. Instead, the present invention provides a store of energy, contained in ice and/or cold water, that can be deployed to cool the batteries with substantially no additional load on the batteries and which can be regenerated or replenished during periods when external power is available, for example from a mains source, from a fossil fuel generator or from solar panels.

The present invention provides a simple yet effective method and apparatus for cooling one or more batteries. During periods in which mains or other external electrical power is available, embodiments of the invention may cool the batteries significantly below ambient temperature, thereby maintaining their usable life. Following loss of external electrical power, embodiments of the invention are able to maintain a cooling effect on the batteries so as to reduce their rate of temperature increase and thus at least partially mitigate the adverse effect of temperature on the batteries' useable life.

The above described embodiment represents one advantageous form of the invention but is provided by way of example only and is not intended to be limiting. In this respect, it is envisaged that various modifications and/or improvements may be made to the invention within the scope of the appended claims.

For example, while the apparatus 10 of Figure 9 is shown cooling a single battery, the apparatus may equally be used to cool a plurality of batteries, as shown in Figure 11. In this embodiment, a second housing 22b and heat exchanger 20b are provided adjacent the second battery 40b and the ducting 28 is extended so as to communicate therewith.

Likewise, a second fluid conduit 18b is provided between the headspace 12 and the second heat exchanger 20b with valve means 50, 50b between the headspace 12 and respective conduits 18, 18b. Where further batteries are to be cooled by the apparatus 10, these features are duplicated as necessary. It will be appreciated that as the number of batteries to be cooled increases, it may be necessary to increase the size of the headspace 12 so as to increase the thermal capacity of the system.

In an embodiment (not shown), the or each heat exchanger 20 may communicate with the headspace 12 by dual fluid conduits 18 so as to facilitate recirculation of water within the system. Each fluid conduit 18 in the pair may open into the respective heat exchanger 20 at spaced apart locations, for example at opposite ends thereof in the manner of a conventional convection radiator. Valve means may be provided between one or both of the conduits of a pair of conduits 18 and the headspace 12.

The number and size of the apertures 30 in the housing 22 can be selected as desired. It is, however, considered that the provision of a plurality of small diameter holes producing an array of fine air jets may assist penetration of the boundary layer on the surface of the battery 40 and thus facilitate heat transfer away from the battery. However, the location of the or each heat exchanger in a housing 22 is itself not essential and the heat exchanger 20 may simply be positioned close to or adjacent the battery 40, or may be mounted directly thereto.

It is also envisaged that where the heat exchanger 20 is mounted in physical contact with the battery 40, this may provide a sufficient cooling effect without the need for a flow of air therethrough. In this case, the fan 26, ducting 28 and housing 22 can be eliminated from the system.

Where a fan or compressor 26 is provided, this may be a low power device arranged to be supplied with power from the external power supply 16 or, if the external power supply 16 fails, froni the battery 40 itself. The use of photovoltaic cells to supply power to the fan or compressor 26 is considered particularly advantageous.

Likewise, the cooling elements 14 may be supplied with power from photovoltaic cells. In such an arrangement, loss of electrical power due to a reduction in available solar energy generally coincides with periods of darkness or poor weather conditions when the ambient temperature is lower and thus the requirement to cool the batteries is reduced.

It is to be understood that the temperature at which the water in the system has the highest density may be varied by means of an additive, such as a salt. For example the addition of a salt such as sodium chloride or potassium chloride may lower the temperature at which water is of its highest density. Other fluids that exhibit a negative thermal expansion coefficient (i.e. a decrease in density with decreasing temperature) below a certain temperature and a positive thermal expansion coefficient above that temperature may also be useful.

While the function of the apparatus relies on the headspace 12 being disposed above the heat exchanger 20, it is not essential that the headspace 12 be vertically aligned and it can be positioned generally as desired according to the application and any packaging restrictions.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

<claim-text>CLAIMS1. An apparatus comprising: a thermally-insulated reservoir in thermal communication with a heat exchange surface to be cooled; a headspace disposed in fluid communication with the reservoir, the reservoir containing liquid that at least partially immerses the heat exchange surface and extends into the headspace; cooling means for cooling fluid within the headspace; and means for controlling the transfer of heat and/or fluid between the reservoir and the headspace.</claim-text> <claim-text>2. An apparatus as claimed in claim 1, wherein the means for controlling the transfer of heat and/or fluid comprises valve means.</claim-text> <claim-text>3. An apparatus as claimed in claim 2, wherein the valve means comprises one or more of: a butterfly valve; a choke valve; a diaphragm valve; a poppet valve; a ball valve; a globe valve; a gate valve; and a restriction.</claim-text> <claim-text>4. An apparatus as claimed in claim 2 or claim 3, wherein the valve means is disposed in or adjacent to a flowpath or conduit fluidly connecting the reservoir and the headspace.</claim-text> <claim-text>5. An apparatus as claimed in claim 4, wherein the valve means is adjustable so as to vary the effective cross sectional area of the flowpath or conduit.</claim-text> <claim-text>6. An apparatus as claimed in claim 3 or claim 4, wherein the valve means is arranged to reduce the rate at which heat and/or fluid is transferred between the reservoir and the headspace.</claim-text> <claim-text>7. An apparatus as claimed in any preceding claim comprising actuator means for moving the valve means between open and closed positions thereof.</claim-text> <claim-text>8. An apparatus as claimed in claim 7, wherein the actuator means comprises a manually operable input member, for example a handle or a wheel.</claim-text> <claim-text>9. An apparatus as claimed in claim 7 or claim 8 comprising control means for controlling the operation of the actuator means so as to control the flow of fluid between the reservoir and the headspace.</claim-text> <claim-text>10. An apparatus as claimed in claim 9, wherein the control means comprises a microprocessor or the like.</claim-text> <claim-text>11. An apparatus as claimed in claim 9 or claim 10, wherein the control means comprises part of a control system further comprising sensor means for measuring or detecting the temperature of the payload space and for generating a temperature signal indicative thereof, the control means being arranged to receive the temperature signal and to control the actuator means in dependence thereon.</claim-text> <claim-text>12. An apparatus as claimed in any one of claims 9 to 11, wherein the control means further comprises a user-operable input device for inputting a desired or target temperature, the control means being arranged to compare the desired or target temperature with the temperature of the payload space and to control the actuator means in dependence on the comparison.</claim-text> <claim-text>13. An apparatus as claimed in any one of claims 9 to 12, wherein the control means is arranged to control the actuator means to increase the degree of opening of the valve means if the temperature of the payload space is above a desired or target temperature and to reduce the degree of opening of the valve means if the temperature of the payload space is below a desired or target temperature.</claim-text> <claim-text>14. An apparatus as claimed in any preceding claim, wherein the headspace and the reservoir are arranged, in use, to contain a fluid having a negative temperature coefficient of thermal expansion below a critical temperature and a positive temperature coefficient of thermal expansion above the critical temperature.</claim-text> <claim-text>15. An apparatus as claimed in any preceding claim, wherein the fluid comprises water or a fluid having similar thermal properties to water.</claim-text> <claim-text>16. An apparatus as claimed in any preceding claim, wherein the cooling means is arranged to cool fluid in the headspace to a temperature below a critical temperature thereof.</claim-text> <claim-text>17. An apparatus as claimed in claim 14 or any claim dependent from claim 14, being arranged such that fluid at the critical temperature sinks into the fluid reservoir, displacing fluid at temperatures on either side of the critical temperature towards the headspace.</claim-text> <claim-text>18. An apparatus as claimed in any preceding claim, wherein the temperature of the fluid in the reservoir is dependent on, or proportional to, the position of the valve means, for example the degree of closure of the valve means.</claim-text> <claim-text>19. An apparatus as claimed in any preceding claim wherein the heat exchange surface is in thermal communication with a chamber.</claim-text> <claim-text>20. An apparatus as claimed in claim 19 wherein the heat exchange surface defines a wall of the chamber.</claim-text> <claim-text>21. An apparatus as claimed in claim 19 or 20 wherein the chamber comprises a payload space within which items can be placed for temperature-controlled storage.</claim-text> <claim-text>22. An apparatus as claimed in any one of claims 19 to 21 wherein the chamber comprises a flexible membrane whereby a wall of the chamber may contact and conform to a surface of an object to be cooled.</claim-text> <claim-text>23. An apparatus as claimed in claim 19 or 20 wherein the chamber comprises a fluid conduit through which fluid may be passed to cool the fluid by means of the heat exchange surface.</claim-text> <claim-text>24. An apparatus as claimed in any preceding claim wherein the heat exchange surface is in fluid communication with the headspace by means of a conduit through which the fluid may flow from the headspace to the heat exchange surface.</claim-text> <claim-text>25. A method comprising: cooling a fluid contained in a headspace; allowing fluid at a critical temperature to sink into a reservoir below the headspace so as to displace fluid therein towards the headspace; absorbing heat from a heat exchange surface that is at least partially immersed in fluid in the reservoir; and controlling the rate of fluid transfer between the headspace and the reservoir.</claim-text> <claim-text>26. A method as claimed in claim 25, comprising increasing a rate of fluid transfer between the headspace and the reservoir when a temperature of the reservoir is above a desired or target temperature.</claim-text> <claim-text>27. A method as claimed in claim 25 or claim 26, comprising decreasing a rate of fluid transfer between the headspace and the reservoir when a temperature of the reservoir is below a desired or target temperature.</claim-text> <claim-text>28. A method as claimed in any of claims 25 to 27, wherein controlling the rate of fluid transfer comprises operating valve means disposed in or adjacent to a fluid flowpath between the headspace and the reservoir.</claim-text> <claim-text>29. A method as claimed in claim 28, wherein increasing the rate of fluid transfer comprises increasing a degree of opening of the valve means.</claim-text> <claim-text>30. A method as claimed in claim 28 or claim 29, wherein decreasing the rate of fluid transfer may comprise decreasing a degree of opening of the valve means.</claim-text> <claim-text>31. An apparatus or a method constructed and/or arranged substantially as described herein with reference to Figures 3 to 7 and 9 to 11 of the accompanying drawings.</claim-text>