Description

The present invention relates to a thermal accumulator for a cold/heat storage device.

The present invention further relates to a method of manufacture of said thermal accumulator for a cold/heat storage device as well as the production of the heat-accumulating medium, a kit of parts for the manufacture of a heat- accumulating medium, an insulated container with said thermal accumulator, a means of transport with said thermal accumulator and finally the use of a heat- accumulating medium in said thermal accumulator.

Thermal accumulators are latent forms of thermal storage in which a certain capacity of thermal energy is stored and can be released over a certain period, for example for cooling products. Thermal accumulators may be used for various applications, including storage in insulated containers, in which certain products such as food are to remain cooled or frozen. These containers may sometimes be used as temporary or permanent storage, or may be used as insulated trailers for transport of products that must be kept at a certain temperature, such as food, plants, ice cream, etc. These trailers consist of a compartment or container, generally with the floor, the walls and the roof provided with insulating material, such as polyurethane foam. The products must be kept at the correct temperature. This correct temperature is generally between -30°C and +30°C, but may more particularly be well above the freezing point, just above it for a refrigerating temperature, or well below it for a freezing temperature. For maintaining the correct temperature, these containers are generally provided with a refrigeration unit. The refrigeration unit or heat pump provides, by means of a circuit consisting of a compressor, evaporator, expansion valve and condenser, the compression and expansion of a liquid, wherein temperature increase and decrease occur. By means of a heat exchanger, depending on which side of the system, this raised or lowered temperature is used for introducing heat or cold into the container. Generally, for most applications, use is made of the addition of cold for lowering and maintaining the temperature of the products in the container. The active part of the system (the compressor/evaporator) is driven by a combustion engine, especially in transport applications of insulated trailers. This may in principle be the same combustion engine as the engine that drives the vehicle, but is usually mounted on the trailer as a separate engine.

Refrigerating systems of this kind are also largely employed in the same way for stationary cooling, wherein the container is not on a trailer, but may be placed for a short or long time in a certain spot. Mostly such containers are indeed arranged for simple transportation, for example by being made and configured in standard container dimensions in order to be placed on a trailer by the prongs of a fork-lift truck. However, the characteristics of the container and the refrigerating system broadly coincide.

However, from the environmental standpoint these diesel or petrol engines have various disadvantages. They consume fossil fuels, produce high levels of C02, particulates and other undesirable emissions, are often noisy, and above all are not environmentally friendly. Another disadvantage of refrigerating systems driven by combustion engines is that energy conversion of this kind is not flexible. For example, sustainably produced (electrical) energy cannot be used. Peak shaving is also not possible, because the energy must be taken when it is needed, and not when it is available or can be purchased advantageously. Consequently there is a need for alternatives that do not have at least some of these disadvantages or wherein these disadvantages are present to a smaller extent.

An object of the present invention is to provide an improved thermal accumulator that may be used as an alternative for known refrigerating systems. A further object of the present invention is to provide an improved passive thermal accumulator that comprises a PCM but wherein at least some of the aforementioned disadvantages are eliminated or minimized.

These objects are achieved according to a first aspect of the present invention with a thermal accumulator for a cold/heat storage device that is configured for use in a refrigerated container for refrigerating and/or maintaining the temperature of products that are present in the refrigerated container, said thermal accumulator comprising:

- a compartment for containing a heat-accumulating medium, wherein the compartment is made of heat-insulated wall components and by means of a thermal interface, thermal energy is given up from the heat-accumulating medium to the refrigerated container; wherein the heat-accumulating medium is a composition comprising: - a phase change material, as well as

- an antibacterial additive, comprising bronopol.

Application of refrigerating engineering is currently known, wherein a petrol or diesel combustion engine is not required. A known example of this is the use of a simple electrically-driven Peltier element. However, in comparison with combustion engines, this has yet other disadvantages. Thus, a Peltier element is less efficient in conversion to cold, and said element requires a source of electric power, which in the absence of a combustion engine will have to be provided by one or more batteries. There are yet further disadvantages in using such batteries,

Another known alternative is the use of a thermal accumulator in the form of a cold buffer wherein in particular passive cooling is employed. By means of a passive refrigerating system, thermal energy is stored in a coolant that serves as a cold buffer. This cold buffer is charged before use by cooling the coolant to a low temperature. Once cooled, the coolant is ready for use and may be used in the container according to the required capacity and refrigerating temperature. The efficiency of this form of cold storage can be improved considerably using a so-called Phase Change Material, PCM. The principle behind a PCM is that on transition from the solid phase to liquid or vice versa, the material can absorb (in the phase change from solid to liquid), or give up (in the phase change from liquid to solid) large amounts of heat from or to the environment.

The use of a latent, passive thermal accumulator of this kind has important advantages compared to the active refrigerating systems driven by combustion engines. Passive cold buffers are far more environmentally friendly because there are no emissions of CO2 or other greenhouse gases, they are reusable, do no produce any sound, etc. Especially the absence of CO2 emissions and the prevention of noise pollution are essential for many fields of application. Transport of products is mostly time-consuming because vehicles with high CO2 emissions and/or high noise levels are simply not allowed in city centres. Such products can be delivered right to the destination with a vehicle with an insulated trailer that is provided with a passive cold buffer.

The use of a thermal accumulator with a heat-accumulating medium based on a PCM has further benefits that are not limited to the application of transport with insulated containers. These thermal accumulators may be used preeminently in static storage solutions wherein products or food are stored in an insulated space (a container or other space). Use in such an application has the advantage that energy that is obtained from sustainable sources such as solar or wind energy may be used as the primary energy source, it is also possible to uncouple the storage and use of the thermal energ on account of the latent properties of the medium. This means that peak shaving is possible, wherein the primary energy is taken at a favourable time.

The thermal accumulator with a heat-accumulating medium based on a PCM is also especially suitable for use in buildings wherein for example the accumulator can receive cold at night and give it up again in the daytime for cooling the space. The thermal accumulator according to the invention is also suitable for numerous other applications wherein transfer of heat, cold or thermal energy is to take place. An example of this is use in a data centre in which the space of the data centre must be cooled or wherein the computer systems and the heat producing components therein such as the CPUs can be cooled.

The thermal accumulator according to the invention is also especially suitable as a backup system wherein a primary refrigerating system provides the supply of a certain required refrigerating capacity and wherein the thermal accumulator according to the invention may be employed as a secondary backup system if the primary system fails, thereby allowing the refrigerating capacity to be maintained for a certain time corresponding to the refrigerating capacity of the backup refrigerating system. In particular, the two systems may be arranged so that the primary refrigerating system provides charging of the thermal accumulator of the secondary refrigerating system.

However, there are also disadvantages to using a PC -containing heat-accumulating medium. The materials from which the PCM heat accumulating medium is manufactured may become separated from one another over the course of time. This has an adverse effect on the operation of the device. Owing to separation, the PCM may lose its ability to absorb/give up heat at constant temperature. A temperature fluctuation then arises during thawing of the PCM.

As a result, it is difficult to find the right composition wherein constant heat exchange takes place. Bacteria and viruses may also develop in a PCM heat- accumulating medium, which are harmful for the products to be stored or transported, in particular in the case of consumer goods or medicines. These bacteria and/or viruses may also alter the composition of the PCM so that the aforementioned complications may arise. Disinfecting additives may be used to prevent this.

As mentioned above, the use of passive thermal accumulators with PCMs has many advantages over active refrigerating systems, wherein the thermal accumulator is presented hereunder as an example for application in the transport of products in cities. However, the use of PCMs also has the disadvantages described above.

For many products or goods it is not only important to bring these to the correct temperature, but above all to keep them at this temperature. Examples of such products where this is especially applicable are for example perishable foodstuffs, pharmaceuticals, chemicals, etc.

Such products must often be kept in the cooled or in particular frozen state in a certain place for some time. This is for example the case when holding stocks of such products at a supermarket, pharmacy or factory. However, such products must also be transported to these locations. This can be done by means of vehicles with refrigerated trailers, or with a variant thereof such as a bus with a refrigerated cargo space, etc. In both the static and the mobile variant, the products are kept at the correct temperature by means of a cold solution in the refrigerated container. Adequate insulation of the refrigerated container ensures that the cold that is supplied by the cold solution is not transferred to the environment outside the container.

The technology that is used for producing the cold solution relates to a passive thermal accumulator. That means that there is no use of electrical energy or conversion of fossil fuel during use (storage, or transport). By means of a Phase Change Material, PCM, thermal energy is stored prior to use and is released again during use, as latent energy or in particular latent cold. Such a solution is quiet, lightweight, emissions-free, low-maintenance, modular and relatively inexpensive compared to the refrigerating systems that are electrically-driven or run on fossil fuel.

The latent energy or in particular the latent cold is stored in a thermal accumulator. The thermal accumulator is configured to be accommodated in the refrigerated container (or more generally an insulated container) with the products that are to be cooled. This may actually be in the container itself, wherein the thermal accumulator is surrounded by the container, but it may also be incorporated in the wall of the container, or may be fastened to a wall or near a wall of the container, whether or not detachable from the outside.

The thermal accumulator consists of a compartment that is made from a number of wall components so that a space is formed between the closed wall components. The wall components have a high thermal insulation value and may for example be of double-wall construction, wherein in particular a heat-insulating material is applied between the walls. This may be a foamed material such as cork, cellulose flakes, glass wool, rock wool, perlite, extruded polystyrene, expanded polystyrene, polyurethane, polyisocyanurate, resol rigid foam, blister padding, etc. The closed space formed by the walls is filled with a heat-accumulating medium. The compartment is preferably formed in such a way that the heat-accumulating medium can be taken out of and added to the compartment. More particularly, the compartment comprises a closable opening for this purpose.

The compartment is further provided with a thermal interface for bringing into thermal communication on the one hand the environment within the refrigerated container, for example the air present therein, and on the other hand the heat-accumulating medium in the thermal accumulator. More particularly, the thermal interface is a heat exchanger that is provided with tubes that are in thermal contact with the heat-accumulating medium and/or cooling plates or fins for creating the thermal interface. The medium in the tubes/cooling circuit may be a coolant or a more general thermal medium such as glycol or Freon (or other synthetic and/or natural coolants).

The heat-accumulating medium comprises PCM, so that a greater latent cold capacity may be given up more efficiently and more constantly over time. However, the use of PCM as latent coolant also leads to difficulties. One of these is that measures must be taken to counteract bacterial growth and the development of viruses. Disinfecting additives may be used to prevent bacterial growth or development of viruses.

However, there are disadvantages in using these disinfecting additives. Many disinfecting additives are not strong enough. Therefore a high dosage must be used. This high dosage is so high that the composition of the heat-accumulating medium is altered significantly. This has an adverse effect on the action of the PCM and therefore the thermal accumulator and the refrigerating system in general. More powerful disinfecting additives or antibacterial additives are often harmful to human health. Such additives consequently require special measures for working with these harmful substances. This applies both during production and to some extent during use, and in particular when the products to be cooled in the insulated container are medicines or food.

However, the inventors came to the surprising realization that an antibacterial additive in the form of bronopol is effective as an antibacterial and virus- inhibiting agent, but above all, does not have any adverse effect on the phase change parameters of the PCM. Therefore this additive seems very suitable for use in this kind of application with PCM in a refrigerated container and moreover is sufficiently active at low concentrations, so that the effectiveness of the PCM is unaffected or only minimally affected.

Bronopol is an antibacterial additive that is used in the cosmetic sector. However, studies showed that bronopol is one of the few antibacterial additives that are suitable as formaldehyde substitute for application in thermal accumulators. The heat-accumulating medium is liquid, but preferably in gel form. The use of bronopol as an antibacterial additive is not obvious for such an application because it is available as a solid substance and does not mix readily with the liquid heat- accumulating medium. Surprisingly, however, bronopol seems especially effective as an antibacterial additive, even in minimal concentrations with a percentage by weight that is between 0.01 and 1 %, and preferably between 0.02 and 0.5%, more preferably between 0.03 and 0.1 %, most preferably or mainly 0.04% or more particularly about 0.0375%. As an alternative, a bronopol-containing antibacterial additive composition may also be added with a percentage by weight that is between 0.1 and 5%, preferably between 0.2 and 3%, more preferably between 0.4 and 0.55% and most preferably about 0.5%. The bronopol part of the aforementioned percentages is about 7.5%.

Another surprising advantage in using a solid substance as additive is that it simplifies transport and storage. In addition, the use is especially favourable when using a kit of parts. The individual components of the kit, the PCM, the antibacterial additive and preferably the thickener may then be supplied separately and combined on the spot to obtain the heat-accumulating medium.

As an alternative to bronopol, the invention also relates to the use of an antibacterial additive or an antibacterial additive composition in the form of isothiazolinone compounds or in particular under the name BMC50, which is commercially available as such, but also to an additive based on methylisothiazolinone, which preferably comprises a composition of 5-chloro-2- methyl-2H-isothiazol-3-one and 2-methyl-2H-isothiazol-3-one. More preferably, the composition of 5-chloro-2-methyl-2H-isothiazol-3-one and 2-methyl-2H-isothiazol-3- one makes up between 1 and 5 wt% in the antibacterial additive. The advantage of an antibacterial additive of this kind is that it is a very effective biocide that has a broad range of action for combating various bacteria, algae and slime in water or fluid circuits. The antibacterial and antivirus action is very effective even at low concentrations and comprises quick-acting and long-acting components. It is also biodegradable and does not contain any heavy metal compounds or chlorophenol and is safe for the commonest metals.

In one example the antibacterial additive comprises a percentage by weight that is between 0.01 and 1 %, and preferably between 0.02 and 0.5%, more preferably between 0.03 and 0.1 %, most preferably or mainly 0.04%.

It was found that the action of the antibacterial additive based on bronopol is especially effective at a proportion by weight in the heat-accumulating medium of between 0.01 and 0.1 %. For an optimum action, wherein the influence on the phase change of the PCM and the overall action of the heat accumulating medium is minimum, and the antibacterial and virus-inhibiting action is sufficient, the heat-accumulating medium comprises preferably or mainly 0.0375 wt% of antibacterial additive.

In one example the phase change material is an inorganic phase change material, and consists of a composition of at least one water-soluble salt with a percentage by weight that is between 10 and 55%, as well as water with a percentage by weight that is between 45 and 90%.

Inorganic materials such as water cover a wide temperature range and generally have a higher enthalpy of fusion per volume compared to organic materials. Among other things, this is related to the higher density. Inorganic materials have the advantage that they have good thermal conductivity, they have a low cost price and they are non-flammable. An example of an inorganic phase change material is a salt solution or salt hydrates. Preferably the composition of the PCM consists of about 20 wt% salt. With this salt fraction, the PCM will melt and solidify consistently. In a preferred embodiment the composition of the PCM consists of about 19.5 wt% salt, wherein in particular the salt comprises potassium chloride, about 80 wt% water and 0.0375 wt% of antibacterial additive.

In one example the composition consists of at least inorganic salts with a percentage by weight that is between 10 and 55%, as well as water with a percentage by weight that is between 45 and 90%. Preferably the composition of the PCM consists of about 30 wt% NaNOs, 13 wt% NH ₄ CI, 0.5 wt% K ₂ S0 ₄ , 0.5 wt% Na ₂ HP0 , 54 wt% water and 0.0375 wt% bronopol.

In another example, the PCM may also comprise an organic material. This may be especially advantageous on account of possible problems of supercooling and phase separation in inorganic phase change materials based on salt hydrates. Paraffin is an example of a organic phase change material that is suitable and favourable on account of the low cost price, high heat storage capacity and wide availability.

In one example the heat-accumulating medium is a refrigerating composition comprising:

- a salt solution that consists of a composition of at least one water- soluble salt with a percentage by weight that is between 15 and 50%, preferably between 15 and 35%, more preferably between 18 and 25%, most preferably between at least mainly 20%, as well as water with a percentage by weight that is between 50 and 85%, more preferably or mainly the remaining percentage by weight;

- an antibacterial additive based on bronopol.

In one example the heat-accumulating medium is a refrigerating composition comprising:

- a salt solution that consists of a composition of at least one water- soluble salt with a percentage by weight that is between 15 and 50%, preferably between 30 and 50%, more preferably between 40 and 50%, most preferably between at least mainly 45%, as well as water with a percentage by weight that is between 50 and 85%, more preferably or mainly the remaining percentage by weight;

- an antibacterial additive based on bronopol.

The heat-accumulating medium may be produced according to a composition wherein the ratio of the water to the salt dissolved in the water is in various ranges. The salt is then also preferably completely dissolved in the water, and in the context of the invention it must be understood that the solubility in water is at least 50g/l, at a temperature of 20 degrees Celsius. Investigations showed that the composition possesses especially favourable properties at at least mainly 20 wt% salt and 80 wt% water, wherein the antibacterial additive amounts to at least mainly 0.0375 wt%. A latent heat accumulating medium of this kind with a PCM based on a salt solution is preferably suitable for a eutectic with a melting temperature of -1 1 degrees Celsius. This configuration is especially suitable for keeping products cooled (but not frozen). It was also found that the composition has especially favourable properties at at least mainly 45 wt% salt and 55 wt% water, wherein the antibacterial additive amounts to at least mainly 0.0375 wt%. A latent heat accumulating medium of this kind with a PCM based on a salt solution is preferably suitable for a eutectic with a melting temperature of -33 degrees Celsius. Such a configuration is especially suitable for storing products in the container in the frozen state.

In one example the salt solution consists of a composition of water and one or more from the group comprising sodium nitrate, ammonium chloride, potassium sulphate and sodium hydrogen phosphate. The -33 eutectic is preferably made from a salt solution with a composition of at least one, preferably several, most preferably all of the group comprising sodium nitrate, ammonium chloride, potassium sulphate and sodium hydrogen phosphate. In a further example the salt solution consists of between 54 and 56 wt% water, between 30 and 32 wt% sodium nitrate, between 12 and 14 wt% ammonium chloride, between 0.4 and 0.6 wt% potassium sulphate and between 0.3 and 0.5 wt% sodium hydrogen phosphate. Moreover, the heat-accumulating medium comprises, besides the salt solution, between 0.4 and 0.6 wt% of antibacterial additive.

In one example the composition of the heat-accumulating medium further comprises at least one viscosity-modifying additive for adjusting the viscosity of the heat-accumulating medium, wherein the viscosity-modifying additive is preferably a viscosity-increasing thickener and more preferably guar gum.

In the solid state there cannot be any leakage of the PCM onto the products that are in the container outside the thermal accumulator. However, if the phase of the PCM changes, with transition of the PCM to a liquid state, it is important that the compartment is properly closed to prevent leakage onto the products in the container. To reduce the chance of this further, besides the manufacture of a properly closed compartment, the inventors realized that the use of a viscosity- increasing thickener as an additive to the PCM ensures that the PCM is less fluid, and can leak less quickly between the seams of the wall components and onto the products. The additive also ensures that there is a reduced chance of mutual separation of the elements from the composition. Preferably an additive is added that not only thickens the PCM, but thickens it in such a way that in the non-solid state the PCM is in the form of gel. This may be achieved by adding guar gum or guar gum derivatives or a combination thereof. These thickeners have little influence on the effectiveness of the PCM but prevent phase separation occurring, even at the microscopic scale.

An additional advantage of the use of guar gum is that the heat accumulating ability of the PCM was found to be optimum at concentrations of guar gum that are between 4 wt% and 6.5 wt%. In the known applications guar gum is only used in low concentrations, for example up to a maximum of 0.5 wt%; it was found that a higher concentration has a positive effect on the accumulating ability. However, use at these higher percentages than those used hitherto is not obvious. Higher percentages mean that during production of the heat-accumulating medium, solidification occurs too quickly and further mixing of the components is almost impossible. This effect is, however, still controllable up to about 6.5 wt%, whereas a better heat accumulating ability is achieved than with the known percentages up to 0.4 or preferably 0.5 wt%.

Yet another additional advantage is that on using more thickener, the chance of separation of the components decreases. The chance of leakage also decreases considerably. The corrosion of the corrosion-sensitive components in the thermal accumulator also decreases at lower viscosity.

In one example the viscosity-modifying additive comprises a percentage by weight that is between 1 and 10%, but preferably between 4 and 6.5%.

This additive is preferably present in the heat-accumulating medium at a proportion by weight that is between 1 and 10%, more preferably between 2 and 9%, more preferably between 3 and 7%, but most preferably between 4 and 6.5%.

In one example the walls of the compartment for containing the heat- accumulating medium are at least partially deformable to compensate expansion of the heat-accumulating medium during phase change.

Because during the phase change of the PCM the heat-accumulating medium may increase or decrease in volume, the walls of the compartment are preferably deformable, or at least partially deformable. The result is that the pressure in the compartment remains the same.

In a second aspect of the invention, a method is provided for making a refrigerating composition of a heat-accumulating medium for a thermal accumulator according to one of the above descriptions, wherein the method comprises the steps of:

- supplying water;

- adding at least one water-soluble salt to the water;

- obtaining a salt solution by mixing the water with the soluble salt until the salt is mainly dissolved in the water;

- adding an antibacterial additive based on bronopol to the salt solution.

In one example the method further comprises the step of:

- adding a viscosity-modifying additive to the salt solution, wherein the viscosity-modifying additive is preferably a viscosity-increasing thickener and more preferably comprises guar gum.

In a third aspect of the invention a kit of parts is provided, comprising a first component that consists of a salt solution or another PCM, and a second component that consists of an antibacterial additive based on bronopol, for making a heat-accumulating medium with the kit of parts, for a thermal accumulator according to one of the above descriptions.

The kit of parts comprises at least two parts, namely a PCM material and an antibacterial additive as described. The PCM is preferably a salt or mixture of salts, but may also be a PCM based on paraffins or other known PCMs. Preferably the kit further comprises a thickener in the form of for example guar gum or an alternative viscosity increasing additive. The kit of parts may be used on a large scale to mix the components ex-works so that a ready-for-use PCM material is obtained, but the kit of parts may also be made as a kit with individual components and sold as such, so that a user combines the components if necessary, for example shortly before commissioning.

In a further example the kit of parts comprises a third component that consists of a viscosity-modifying additive, preferably guar gum, more preferably in a percentage by weight between 1 and 10%, more preferably roughly between 2 and 8%, 3 and 7%, or most preferably between 4 and 6.5%. In a fourth aspect of the invention an insulated container is provided for keeping at low temperature one or more products contained in the container, said container comprising a thermal accumulator according to one of the above descriptions.

In one example the insulated container comprises a refrigerating system for cooling the heat-accumulating medium in the thermal accumulator to a predefined temperature.

In one example the insulated container comprises a heat exchanger system for transferring the thermal energy of the thermal accumulator to the insulated container, wherein the heat exchanger system is included at least partly in the thermal accumulator and at least partly in the insulated container for thermal communication between the accumulator and the container.

In a further example the insulated container comprises a plurality of cooling elements, which are in particular cooling tubes and/or cooling fins, said cooling elements being arranged for transporting a coolant flowing through the cooling elements, wherein the cooling elements are included at least partially in the insulated container and at least partially in the thermal accumulator and are in thermal communication with the heat-accumulating medium present therein;

- a pump, which is arranged for pumping the coolant through the cooling elements;

- a control unit, which controls the pump and is arranged for regulating the flow rate of the pump for regulating the rate of supply of thermal energy from the thermal accumulator to the products in the insulated container.

The insulated container comprises roughly the insulated container, a refrigerating system or more especially a heat exchanger and a thermal accumulator or more especially a cold accumulator. The cold accumulator is the primary thermal energy source for maintaining a low temperature of the products in the container. The way in which the thermal energy is transferred is by means of a heat exchanger. The heat exchanger is, however, provided with a pump and a control unit with which the pump can be controlled so as to control the flow rate of the coolant in the tubes of the heat exchanger. The harder the pump pumps, the quicker the coolant travels through the cooling circuit of tubes and the more thermal energy is transferred from the accumulator to the container. The coolant in the circuit may comprise water and preferably with an antifreeze additive, but may also comprise alcohol or the like. In a fifth aspect of the invention a lorry, bus or other vehicle is provided comprising a refrigerated container according to a foregoing description.

In a sixth aspect of the invention, the use of a heat-accumulating medium in a thermal accumulator according to one of the above descriptions is provided, wherein the heat-accumulating medium is a composition comprising:

- a phase change material;

- an antibacterial additive based on bronopol, as well as

- a viscosity-modifying additive, wherein the viscosity-modifying additive is a viscosity-increasing thickener and preferably comprises guar gum.

In all the aforementioned aspects of the invention, bronopol is mentioned as antibacterial additive. However, the invention also envisages in all aspects the use of an antibacterial additive in the form of isothiazolinone compounds or in particular under the name BMC50, which is commercially available as such, but also an additive based on methylisothiazolinone, in the concentrations mentioned in the various aspects of the invention.

The invention will now be explained in greater detail on the basis of a drawing, said drawing showing successively:

Fig. 1 , a thermal accumulator according to one aspect of the invention, which is included in a refrigerating system for cooling an insulated container.

Fig. 1 shows, merely for purposes of illustration, one of the many applications of a thermal accumulator 15 according to one aspect of the invention. A thermal accumulator 15 of this kind is a latent form of thermal storage in which a certain capacity of thermal energy is stored and can be given up over a certain period of time, for example, as shown in Fig. 1 , in the form of an insulated container 1 1 for the cooling of products.

The example shown here in Fig. 1 of the application of a thermal accumulator for an insulated container 10 is just one of the many applications in which use is made of a thermal accumulator according to the invention. The invention should not be construed as being limited to this context. Other applications for the thermal accumulator relate in principle to any application where it is a question of (latent) thermal heat. This may thus be as primary or secondary back-up or redundant refrigerating system for housebuilding, but also non-residential building such as in factories, offices, schools, storage spaces, hospitals, shops, garages, cinemas, power stations, water-treatment plants, etc. Furthermore, the thermal accumulator may also be used for example for the cooling of installations. The cooling of (chemical) processes, or the cooling of heat-producing electronics such as processors in data centres, may also be considered. For the sake of clarity, these applications will not be described and elaborated further, instead this example in Fig. 1 is based on an embodiment of the invention wherein the thermal accumulator provides a cold capacity of a refrigerating system of an insulated container.

The insulated container 1 1 is arranged for the storage of products that can be put in the container via the doors 12. These products may be stored for a short time or a long time or may be put in the container and then transported. For this, the container 1 1 may be provided with fasteners 13, which are fitted on the underside of the container 1 1 and make it possible for the container 1 1 to be placed on a trailer and safely transported. The container 1 1 may, however, also be fastened inseparably to a trailer of a vehicle. This makes no difference for the action of the thermal accumulator 15.

The products in the container are to be maintained at a certain temperature. These may be food, but also plants, ice cream, medicines, etc. These trailers consist of a compartment or container 1 1 , of which generally both the floor, the walls and the roof are provided with insulating material, such as polyurethane foam. The insulating material is contained between the double wall 14 of the container. The products must be kept at the correct temperature. This correct temperature is generally between -30°C and +30°C, but more particularly may be well above the freezing point, just above it at refrigerating temperature, or well below it for a freezing temperature. However, a temperature that is often selected is -1 1 or - 33°C. The thermal accumulator 15 is then also preferably suitable for these temperatures.

The thermal accumulator 15 consists of a compartment 15 or housing in which the heat-accumulating medium 16 is contained. The walls of the compartment 15 are preferably of double construction and heat-insulated in order to prevent any heat or cold being lost from the heat-accumulating medium 16 to the environment via the walls of the compartment 15. The walls are in addition preferably at least partly deformable or compressible so as to compensate volume expansion on phase change of the medium 16.

By means of a thermal interface 18, 20, 21 , 22, the thermal energy from the heat-accumulating medium 16 can be transferred to the container 1 1 . This thermal interface may be constructed in various ways and the example shown in Fig. 1 is only for purposes of illustration. Other thermal interfaces based on semiconductor technology such as Peltier elements, or based on convection by means of fans are also possible for transferring the thermal energy to the container. In a preferred embodiment, however, the refrigerating system consists of a thermal accumulator 15 with a heat exchanger 18 that comprises a system of tubes 20, 21 that are located partly 20 in the thermal accumulator, and partly 21 outside the thermal accumulator in the container 1 1 . A medium such as a liquid or a gas that serves as the thermal energy carrier between the accumulator 15 and the container 1 1 flows through the tubes 20, 21 . As stated, preferably a gas or a liquid flows through the tubes. This need not be the case, however; the tubes may also be so- called heat pipes, wherein the tubes may or may not be of massive construction from a material with very good thermal conductivity such as copper. In the case of a liquid or gas in the tubes, the flow rate of this medium is regulated by controlling a pump 18. The pump is controlled by control unit 19. The flow rate may thus be controlled according to whether there is a certain thermal energy demand. For example, when the products are put in the container 1 1 , a temporary increase in cold capacity may be required. This may then be supplied by causing the pump to pump harder and fetch more cold from the thermal accumulator 15 and transfer it to the products in the container 1 1 . The capacity supplied or the output of the thermal interface or heat exchanger 18, 20, 21 may be increased still further by using radiator elements 22, which may be mounted as metal fins perpendicular to the tubes 21 , and increase the supplied capacity considerably. The container 1 1 may be provided with a temperature sensor or preferably several temperature sensors for monitoring the temperature of the products in the container. If this temperature falls below a preset threshold value, the pump will be activated or will pump more quickly in order to increase the cooling capacity. Preferably a sensor is placed near the door 12; this ensures that when the door is opened, the temperature will drop quickly and temporary extra cooling capacity may be drawn upon to prevent the products in the container cooling down too quickly.

The thermal accumulator 15 comprises a so-called heat-accumulating medium 16. The largest part of the accumulator housing is preferably filled with this medium 16. The medium 16 may be fetched/stopped in and from the container via a filling hole 17. The medium 1 1 is a composition and comprises a phase change material and an antibacterial additive, wherein the antibacterial additive comprises bronopol. In a practical embodiment, the medium 1 1 further comprises a viscosity modifier such as guar gum or a similar gelling agent so that the medium 1 1 in liquid form undergoes gel formation and is maintained as a gel and among other things counteracts separation of the components of the composition.

It should be clear to a person skilled in the art that the embodiments, aspects and examples described and the examples shown in the figures describe just one of the many forms and show where the invention finds application. Thus, the invention is not limited to these examples and the extent of protection of the invention is expressly defined by the following claims.