Method of producing a thermal storage device, and such a thermal storage device

Abstract

The invention relates to a method of producing a thermal storage device that comprises a tank that is insulated with an insulation layer, comprising the steps of: - providing the tank, said tank having an outer surface; - placing the tank inside a mold, wherein the outer surface of the tank is arranged at an offset relative to an inner surface of the mold; - providing the insulation layer, comprising the step of in situ foaming of an expanded polymeric foam by applying heat to a granular base material of said foam inside an open space that is defined by said offset in between the outer surface of the tank and the inner surface of the mold; and - removing the tank with insulation layer from the mold. The invention further relates to a thermal storage device, comprising a tank that is insulated with an insulation layer, wherein: - the insulation layer comprises an expanded polymeric foam that is foamed in situ around the tank inside a mold; and - an outer surface of the insulation layer defines an outer surface of the thermal storage device.

Description

[0001] Title: METHOD OF PRODUCING A THERMAL STORAGE DEVICE, AND SUCH A THERMAL STORAGE DEVICE

[0002] Description:

[0003] The present invention is related to a method of producing a thermal storage device, in particular a thermal storage device that comprises a tank that is insulated with an insulation layer. The invention is moreover related to such a thermal storage device.

[0004] It is common practice that thermal storage devices, such as hot water appliances, comprise a tank that is thermally insulated with an insulation layer of foam plastic. Conventionally, this is achieved by forming the insulation layer of foam plastic between an outer casing of the thermal storage device and the tank. In practice, polyurethane-based foams, in particular polyurethane rigid foam (PUR), are used for this purpose. The insulation layer is foamed between an inner wall of the outer casing and an outer wall of the hot water tank. PUR foaming is a chemical process that produces polyurethane foam by combining two primary components, polyols and isocyanates. When mixed, these components undergo an exothermic chemical reaction that generates gas, causing the material to expand into a foam. If sufficient foam is formed, the expansion thereof will fill the complete interior space in between the tank and the outer casing, and will thereby provide a contiguous insulation around the tank. PUR foam is considered to be highly advantageous for insulating tanks, such as hot water tanks, due to its excellent thermal insulation properties and structural rigidity. With its closed-cell structure, PUR foam effectively traps gas within its cells, minimizing heat transfer and thereby reducing thermal conductivity to levels lower than many other insulation materials. This helps maintain the desired temperature of the stored hot medium, i.e. hot water in a hot water tank, for extended periods, reducing energy loss and lowering heating costs. The rigidity of PUR foam provides a durable and stable layer of insulation that adheres to tank surfaces, ensuring long-term durability even in high-temperature environments. Its moisture-resistant qualities further protect the tank from condensation, making PUR foam an ideal choice for hot water tank insulation. Despite the many advantages of PUR, it also has a disadvantage of PUR being often non-recyclable. Moreover, it contains petrochemical derivatives, raising environmental concerns for disposal. Furthermore, in the event of tank repairs or replacements, the foam can be difficult to remove because PUR foam adheres to the tank, adding complexity and cost to maintenance. This conventional method, where rigid polyurethane foam is injected into the space between a hot water storage tank body and an outer case, is for example known from WO 2024 / 176946 A1 , which is representative of the current industrial standard for high-performance thermal storage appliances.

[0005] For over a decade, the Applicant has been insulating hot water tanks with an insulation material that is based on an expanded polymeric foam, in particular an EPS, that features enhanced insulation capabilities by the addition of graphite. This insulation material is made in dedicated pre-formed blocks, that are assembled around the hot water tanks.

[0006] Despite such an enhanced EPS providing a more sustainable material, especially considering end-of-life, and the material not containing any fluorocarbons (CFCs, HCFCs or HFCs) or other halogenated cell gases, it unfortunately also resulted in new challenges and disadvantages. The biggest disadvantage is that the insulation properties are less than PUR, which is also a major reason that PUR is such a common choice of material. In other words, to obtain a certain level of insulation, a thickness of the insulation layer made out of enhanced EPS has to be thicker than if the same insulation layer would have been made out of PUR. This is a significant drawback, because it results in an increase of the overall dimensions of the thermal storage device. The overall dimension of such devices is a key concern, because they are often applied in domestic situations, where space is limited. For example, a hot water boiler may be placed in a kitchen, or at an attic of a residential building.

[0007] Moreover, the assembly of pre-formed blocks leads to small gaps in between the blocks. These gaps require post processing to prevent heat loss via said gaps, as well as prevent the assembly of pre-formed blocks falling apart. One option is to arrange a jacket around the assembly of pre-formed blocks in order to hold them together.

[0008] It is further known to use expanded polymeric foams, such as expanded polystyrene, as an insulation material that is foamed in-situ. However, in such methods, the foam is conventionally applied as a filler material inside a permanent housing that encloses the tank. For example, GB 1 466 239 discloses locating an inner casing within a mold and foaming a plastics foam material such as expanded polystyrene in situ, but this is done to create an assembly which is then disposed within a separate outer casing with an air gap in between. It was also known from an earlier technological era, for example from US 2,981 ,984, to form an expanded outer shell wall from expandable polystyrene beads for the purpose of ornamenting and protecting a container. In these known approaches, the expanded foam is either not the final outer surface of the device, or it is not used in a manner suitable for the structural and thermal demands of a modern thermal storage appliance.

[0009] Moreover, a skilled person would recognize a fundamental difference between the manufacturing processes for these foams. The foaming of polyurethane (PUR), as used in the industrial standard, is an exothermic chemical reaction between liquid components. In contrast, the foaming of expanded polymeric foams like expandable polystyrene involves an endothermic process, requiring the application of heat, typically by injecting steam, to a granular base material within a closed mold. This endothermic process is generally slower and requires more complex, pressureresistant moulding equipment compared to the self-expanding exothermic reaction of PUR. This technical distinction has created a prejudice in the field that the in-situ foaming of expanded polymeric foams is less suitable for the mass production of thermal storage devices.

[0010] The German patent application DE 35 18 935 A1 , US patent applications US 4,768,678 A and US 4,344,303 A are acknowledged as further prior art.

[0011] An objective of the present invention is to provide a method of producing a thermal storage device, that is improved relative to the prior art and wherein at least one of the above stated problems is obviated or alleviated.

[0012] Said objective is achieved with the method of producing a thermal storage device that comprises a tank that is insulated with an insulation layer according to claim 1 , said method comprising the steps of:

[0013] - providing the tank, said tank having an outer surface;

[0014] - placing the tank inside a mold, wherein the outer surface of the tank is arranged at an offset relative to an inner surface of the mold; - providing the insulation layer, comprising the step of in situ foaming of an expanded polymeric foam by applying heat to a granular base material of said foam inside an open space that is defined by said offset in between the outer surface of the tank and the inner surface of the mold; and

[0015] - removing the tank with insulation layer from the mold.

[0016] According to the invention, the Applicant continues to apply an insulation layer that comprises an expanded polymeric foam, rather than the obvious choice to apply PUR foam. The reason for sticking to expanded polymeric foam remains unchanged relative to the previously applied pre-formed blocks made out of such expanded polymeric foam: sustainability and avoiding off-gassing typically associated with application of PUR foam.

[0017] In addition to the surprising choice to apply expanded polymeric foam - that has lower insulation properties than PUR and therefore requires a thicker layer of insulation that results in thermal storage devices having larger dimensions - the same sustainability motives now result in the further surprising choice of in-situ foaming of said expanded polymeric foam inside a mold. This is a counterintuitive choice for several reasons.

[0018] First of all, the foaming process of expanded polymeric foam is slower than the foaming process of PUR, which is disadvantage for the mass production of thermal storage devices, and hence counterintuitive. The reason that this foaming process is slower is because the foaming process of expanded polymeric foams is significantly different from the foaming process of PUR. As mentioned above, PUR is foamed in an exothermic chemical reaction of two components, polyols and isocyanates. To the contrary, expanded polymeric foam is foamed by applying heat, often in the form of steam, to a granular base material. In an endothermic process, beads of the granular base material start to foam.

[0019] Secondly, the different nature of the foaming process of expanded polymeric foam relative to traditional PUR requires the use of molds. After all, it is not possible to simply allow the exothermic process to occur in an open space in between a tank and an outer casing. Instead, the foaming process of expanded polymeric foam is endothermic, and therefore requires that heat is provided in a controlled manner to the granular base material to control the foaming process. This requires the use of molds, that are not required for foaming of PUR, nor when pre-formed blocks made out of expanded polymeric foam are used. This greatly reduces the flexibility of producing differently sized insulated water tanks, as each size of tank typically requires a unique mold.

[0020] Relative to applying pre-formed blocks, in-situ foaming of an insulation layer made out of expanded polymeric foam provides a number of advantages, most of them being linked to an improved sustainability.

[0021] First, the in-situ foaming results in a substantially continuous insulation layer around the tank, without the gaps that would have been present if a number of pre-formed blocks would be assembled around a tank. Also, because the insulation is foamed in situ around the tank, this also allows the insulation layer to form a close fitting around accessories extending from the tank, such as conduits, e.g. of a condenser, an integrated vacuum panel, components of a heat pump, etc. Both the substantially continuous insulation layer and the close fitting around accessories contributes to an improved insulation of the thermal storage device as a whole. Improved insulation result in a better efficiency of the thermal storage device.

[0022] Moreover, end-of-life care of the thermal storage device is improved by in-situ foaming of expanded polymeric foam. First and foremost, it is possible to recycle expanded polymeric foam, whereas PUR is often non-recyclable. Next, expanded polymeric foam does not adhere to the tank, like PUR, and can therefore be easily removed from the tank for recycling. The tank itself is recyclable, but of course requires the insulation layer to be removed therefrom first. Because of the substantially continuous foamed insulation layer, it will stay around the tank without the need for additional components, such as brackets, tapes, or a jacket, as would be required to hold an assembly of pre-formed expanded polymeric foam blocks together. The number of different component, likely also encompassing different materials, is reduced. The in-situ foaming of the expanded polymeric foam moreover may define the outer side or the thermal storage device. In such a case, there is no need for an outer casing anymore, such as the metal outer casings that are normally used in conventional thermal storage devices, wherein PUR is foamed in between the tank and the outer casing. It is remarked that the PUR not only adheres to the tank, but also to this outer casing. The present invention thus not only provides a sustainable alternative wherein the insulation layer doesn’t adhere to the outer casing, but the outer casing as such is redundant as a whole. This reduces the number of parts, that are often also made out of different materials.

[0023] Moreover, while the outer casing enclosing traditional PUR-insulated thermal storage devices is generally made from sheet metal resulting in a fairly consistently curved shape, an in-situ foaming process allows the production of an inconsistent outer shape without the need for machining operations afterwards. Such an inconsistent outer shape may simply be formed by a corresponding anti-shape in the mold. This results in improved freedom of form, thereby allowing the foamed insulation layer to be shaped by the in-situ foaming process for improved fit or improved interfacing with environments or other objects. In addition, while the consistently curved sheet metal shape of traditional PUR-insulated thermal storage devices is consistent itself, the shape itself does normally feature interruptions such as weld lines and openings for components that might interfere with fit or interfacing with the environment - something in-situ foaming does not suffer from as it is not premade and assembled later on.

[0024] Furthermore, the number of unique parts that need to be in stock is reduced in order to be able to insulate tanks in a variety of dimensions and types. Also, transporting and storing the granular base material takes considerably less space during logistics and storage, compared to transporting and storing the previously necessary large number of unique parts.

[0025] Finally, an insulation layer made out of an expanded polymeric foam shows less degradation in thermal insulation capacity over time than a PUR-insulation layer without a (metal) outer housing. As a result, a thermal storage device comprising a insulation layer made out of expanded polymeric foam will show a more constant insulation efficiency over its lifetime, thereby further improving the sustainability of such a thermal storage device.

[0026] Summarizing, the surprising choices of using expanded polymeric foam as an insulation layer on the first hand, and the in-situ foaming thereof on the second hand, provide a more sustainable thermal storage device.

[0027] The above-mentioned objective is furthermore achieved with the thermal storage device, comprising a tank that is insulated with an insulation layer, according to the invention, wherein: - the insulation layer comprises an expanded polymeric foam that is foamed in situ around the tank inside a mold; and

[0028] - an outer surface of the insulation layer defines an outer surface of the thermal storage device.

[0029] Contrary to prior art thermal storage devices that use PUR as an insulation material in between a tank and an outer casing, such an outer casing is now redundant. The insulation layer made out of an expanded polymeric foam as such is already capable of forming the outer surface of the thermal storage device. As mentioned above, the foamed insulation layer itself defining the outer surface of the thermal storage device also provides improved freedom of form allowing the foamed insulation layer to be shaped for improved fit or improved interfacing with environments or other objects.

[0030] Preferred embodiments of the method and the device are the subject of the dependent claims. The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, and in particular the aspects and features described in the attached dependent claims, may be an invention in its own right that is related to a different problem relative to the prior art.

[0031] In the following description preferred embodiments of the present invention are further elucidated with reference to the drawing, in which:

[0032] Figures 1A-1 F show perspective views of successive steps of a method of producing a thermal storage device that comprises a tank that is insulated with an insulation layer according to a preferred embodiment of the invention;

[0033] Figures 2A-2C show successive steps of a method of producing a thermal storage device with a mold according to first preferred embodiment;

[0034] Figure 3 shows a perspective view corresponding to Figure 2C, but showing a tank with a smaller height;

[0035] Figures 4A and 4B show successive steps of a method of producing a thermal storage device with a mold according to second preferred embodiment;

[0036] Figure 5 shows a perspective view corresponding to Figure 4B, but showing a tank with a smaller height; and Figure 6 shows a final step wherein the mold according to the second preferred embodiment is opened to allow the insulated thermal storage device to be released out of said mold.

[0037] A method of producing a thermal storage device 1 that comprises a tank 2 that is insulated with an insulation layer 3 according to the invention is shown in the successive steps shown in Figures 1A-1 F. It is noted that these Figures 1A-1 F show a basic mold 4, with two mold halves 4-1 , 4-2, that is shaped to provide to foam an insulation layer 3 around a tank 2 of specific dimensions. For mass production such a basic mold 4, that is relatively simple, would be used. However, for smaller batches two alternatives comprising adjustable molds 4, 4A, 4B are proposed. Figures 2A-3 show an adjustable mold 4, 4A according to a first preferred embodiment, whereas Figures 4A-6 show an adjustable mold 4, 4B according to a second preferred embodiment. It is however remarked that the process works similar to the process of the basic mold 4 for mass production, and is now further explained mainly with reference to Figures 1A-1 F.

[0038] In Figure 1A, a basic mold 4 comprising two mold-parts 4-1 and 4-2 is shown. The mold 4 comprises a mold cavity 10 that is configured to receive the tank 2. In Figure 1 B this tank 2 is provided with accessories 11 , such as a an inlet conduit 12, an outlet conduit 13, a condenser coil 14 and a vacuum panel 15. The tank 2 is placed inside the mold cavity 10 (Figure 1 C), wherein an outer surface 5 of the tank 2 is arranged at an offset 6 relative to an inner surface 7 of the mold 4. The offset 6 defines an open space 9 in between the outer surface 5 of the tank 2 and the inner surface 7 of the mold 4. Any conduits or spaces that are intended to be left open are covered with caps 24, or access to those areas that are intended to be left open is deliberately limited by the design of the mold 4. In Figure 1 C, two caps 24 are arranged on the outer ends of the condenser coil 14. A granular base material is inserted into this open space 9, and the mold is closed (Figure 1 D). In a next step, the mold applies heat, e.g. in the form of steam, to the granular base material. This causes an endothermic process to take place, wherein the granular base material foams and expands, thereby filling the open space 9 that is defined by said offset 6 in between the outer surface 5 of the tank 2 and the inner surface 7 of the mold 4. This in-situ foaming process takes place inside the closed mold 4 of Figure 1 D. The expanding foam fills the open space 9 substantially completely and thereby encloses the accessories 11 , such as the inlet conduit 12, the outlet conduit 13, the condenser coil

[0039] 14 and the vacuum panel 15. It is noted here that some accessories 11 may be fully covered by the insulation layer 3, such as the condenser coil 14 and the vacuum panel

[0040] 15 that are now fully integrated inside the insulation layer 3. However, other accessories 11 , such as the inlet conduit 12 and the outlet conduit 13, may extend through the insulation layer 3, that still provides a tight fit around these conduits 12, 13 over the thickness of the insulation layer 3. When the foaming process has ended, the mold 4 is opened (Figure 1 E), and the tank 2 is now covered with the insulation layer 3. The thermal storage device 1 that comprises the tank 2 that is now insulated with the insulation layer 3 may be removed from the mold 4 (Figure 1 F). In Figure 1 F, the two caps 24 are already removed, thereby allowing access to the ends of the condenser coil 14, while the condenser coil itself is now insulated by insulation layer 3.

[0041] For sake of completeness, it is remarked that precautionary measures may be taken to prevent the foam to contact, or even enter, undesired parts. In this way, the foam may be taken away from plumbing fittings (e.g., the inlet and outlet fittings, an annode fitting, a pressure relief valve, etc. For example, holes may be plugged and a pressure relief valve may have some sort of cover on it to prevent foaming the needed openings.

[0042] Summarizing, the method of producing the thermal storage device 1 that comprises the tank 2 that is insulated with the insulation layer 3 thus comprises the steps of:

[0043] - providing the tank 2, said tank having an outer surface 5 (Figure 1 B);

[0044] - placing the tank 2 inside the mold 4, 4A, 4B, wherein the outer surface 5 of the tank 2 is arranged at an offset 6 relative to an inner surface 7 of the mold 4, 4A, 4B (Figures 1 C, 2C, 3, 4B, 5);

[0045] - providing the insulation layer 3, comprising the step of in situ foaming of an expanded polymeric foam 8 by applying heat to a granular base material of said foam inside an open space 9 that is defined by said offset 6 in between the outer surface 5 of the tank 2 and the inner surface 7 of the mold 4, 4A, 4B (Figure 1 D); and

[0046] - removing the tank 2 with insulation layer 3 from the mold 4, 4A, 4B

[0047] (Figure 1 F). The inner surface 7 of the mold 4 may comprise specific shaping features 16 that define an anti-shape of the final outer surface 17 of the insulation layer 3. In the exemplary embodiment of Figures 1 A-1 F, the mold 4 comprises a recess 18 that defines such a shaping feature 16. As the expanding foam fills the open space 9, the final outer surface 17 of the insulation layer 3 comprises a ridge 19 that is complementary to the recess 18 inside the mold 4.

[0048] The insulation layer 3 defines a substantially continuous insulation layer around the tank 2. There are no gaps between pre-fab blocks as in the prior art, so it is not necessary anymore to apply a covering, such as a jacket, to cover any gaps in between pre-fab blocks. Also, because the insulation 3 is foamed in situ around the tank 3, this also allows the insulation layer 3 to form a close fitting with the accessories 11.

[0049] As shown in Figure 1 F, the outer surface 17 of the insulation layer 3 defines an outer surface of the thermal storage device 1. Thus, contrary to the prior art thermal storage devices that use PUR as an insulation material in between a tank and an outer casing, such an outer casing is now redundant. The insulation layer made out of an expanded polymeric foam as such is already capable of forming the outer surface of the thermal storage device. Of course, an outer casing may still be applied, if desired.

[0050] According to a preferred embodiment, the expanded polymeric foam is an EPS or EPP foam that is enhanced with particles of an Infrared (IR) reflective material. According to a further preferred embodiment, the Infrared (IR) reflective material is a material out of the group of graphite, aluminum, titanium dioxide, silica or biopolymers.

[0051] During the in-situ foaming process, i.,e. during the step of providing the insulation layer 3 by in situ foaming of the expanded polymeric foam inside the open space 9, the tank 2 inside the mold 4 may be heated from the inside. For example, a hot fluid may be introduced into the tank 2 via the inlet conduit 12 in the step shown in Figure 1 D. By heating the tank 2 from the inside, it is prevented that the tank 2 acts as a heat sink during the foaming process. If less heat is absorbed by the tank 2, the heat will be effective for the process of foaming the insulation layer 3. Heating the tank 2 from the inside therefor speeds up the foaming process of the insulation layer 3, and provides a better control of the foaming process. In an alternative embodiment, the step of applying heat to the granular base material may be performed by means of radiative heat transfer. Preferably, this is achieved using radiofrequency electromagnetic radiation, for example in the form of radio waves or microwaves. This method of heating provides significant advantages over the use of steam, as it allows for volumetric heating of the granular material without introducing moisture into the mold cavity 10. The absence of steam condensation results in a drier final product and prevents potential issues with water being trapped in the foam's cellular structure, thereby improving the final insulation properties and consistency of the thermal storage device 1. Furthermore, as the insulated thermal storage device is substantially free from moisture upon removing the tank 2 with insulation layer 3 from the mold 4, a separate drying step is rendered unnecessary, allowing the device to proceed without delay to subsequent manufacturing processes, such as final packaging.

[0052] As already briefly mentioned, for smaller batch sizes two alternatives comprising adjustable molds 4, 4A, 4B are proposed. Figures 2A-3 show an adjustable mold 4, 4A according to a first preferred embodiment, whereas Figures 4A-6 show an adjustable mold 4, 4B according to a second preferred embodiment. These molds 4A, 4B each comprise a mold cavity 10 with a variable height to allow said mold 4A, 4B to accommodate tanks 2 of various heights. In this way, it is possible to provide insulation layers 3 around tanks 2 with a variety of internal volumes, obtained by varying the height of the tank 2, without the need to have dedicated molds for tanks 2 of different internal volumes. The overall principle is exactly the same as the embodiment shown in Figures 1 A-1 F, with the sole difference that the method will comprises a further step of adjusting the height of the mold cavity 10 of the adjustable mold 4A, 4B in dependency of a height of the tank 2 placed inside said mold 4A, 4B. The height of the mold cavity 10 is thus adjusted in correspondence with the height of the to be insulated tank 2 and the desired final dimensions of the insulation layer 3.

[0053] In order to prevent unnecessary repetition, the discussion on the two adjustable molds 4A, 4B is limited to how their adjustment works.

[0054] For the adjustable mold 4A shown in Figures 2A-3, the step of adjusting the height of the mold cavity 10 comprises sliding mold parts 4A-1 , 4B-1 relative to each other. The sliding direction S corresponds to a height direction of the tank 2. In this embodiment, the mold parts 4A-1 , 4A-2 have an L-shaped cross section with a long leg 20 of the L-shape extending in a height direction of the tank 2, and a short leg 21 of the L-shape extending in a radial direction of the tank 2. In Figure 2A, the mold cavity 10 is shown. In Figure 2B, the mold 4A is closed. Figure 2C corresponds to Figure 2B, but the mold part 4A-1 is partly removed to show how the tank 2 is accommodated inside the mold cavity 10. Comparing Figure 3 with Figure 2C shows how the height offset H1 of Figure 2C may be increased to the height offset H2 of Figure 3 if a tank 2 with a smaller height is to be accommodated inside the mold cavity 10.

[0055] For the adjustable mold 4A shown in Figures 4A-6, the step of adjusting the height of the mold cavity 10 comprises adjusting a position of a cover 23 in the longitudinal direction of the longitudinal mold cavity 10 inside a mold housing 22. The cover 23 thus defines a mold part that is slidable relative to the mold housing 22. In analogy with the design of a combustion engine, in this embodiment, the mold cavity 10 inside the mold housing 22 may be interpreted as defining a bore, wherein the cover 23 is movable like a piston.

[0056] Although it is conceivable that the mold housing 22 is a single piece, it is preferred that this mold housing 22 is an assembly of at least two mold parts 4B-1 and 4B-2 that each define a mold housing part. In this way, also thermal storage devices 1 that have an outer shape, such as the ridge 19 shown in Figure 1 F, are still releasable from the mold 4B. The cover 23 is then defined by a further mold part 4B- 3.

[0057] The methods described above are used for producing the thermal storage device 1 that comprises a tank 2 that is insulated with an insulation layer 3, as shown in e.g. Figure. 1 F. The insulation layer 3 comprises an expanded polymeric foam that is foamed in situ around the tank 2 inside a mold 4, 4A, 4B. An outer surface 17 of the insulation layer 3 defines an outer surface of the thermal storage device 1.

[0058] Due to the in-situ foaming, the open space 9 is filled with foam. Consequently, the insulation layer 3 defines a substantially continuous insulation layer 3 around the tank 2. This insulation layer 3 also encloses further components of the thermal storage device 1. As describe above, such components may comprise a variety of accessories 11 , such as an inlet conduit 12, an outlet conduit 13, a condenser coil 14 and a vacuum panel 15, etc. In the shown preferred embodiment, the expanded polymeric foam is an EPS or EPP foam that is enhanced with particles of an Infrared (IR) reflective material. The Infrared (IR) reflective material is preferably a material out of the group of graphite, aluminum, titanium dioxide, silica or biopolymers. Although they show preferred embodiments of the invention, the above described embodiments are intended only to illustrate the invention and not to limit in any way the scope of the invention. Accordingly, it should be understood that where features mentioned in the appended claims are followed by reference signs, such signs are included solely for the purpose of enhancing the intelligibility of the claims and are in no way limiting on the scope of the claims. Furthermore, it is particularly noted that the skilled person can combine technical measures of the different embodiments. The scope of protection is defined solely by the following claims.

Claims

CLAIMS1. Method of producing a thermal storage device that comprises a tank that is insulated with an insulation layer, said method comprising the steps of:- providing the tank, said tank having an outer surface;- placing the tank inside a mold, wherein the outer surface of the tank is arranged at an offset relative to an inner surface of the mold;- providing the insulation layer, comprising the step of in situ foaming of an expanded polymeric foam by applying heat to a granular base material of said foam inside an open space that is defined by said offset in between the outer surface of the tank and the inner surface of the mold; and- removing the tank with insulation layer from the mold.

2. Method according to claim 1 , wherein the insulation layer defines a substantially continuous insulation layer around the tank.

3. Method according to claim 1 or 2, wherein an outer surface of the insulation layer defines an outer surface of the thermal storage device.

4. Method according to any of the foregoing claims, wherein the expanded polymeric foam is an EPS or EPP foam that is enhanced with particles of an Infrared (IR) reflective material.

5. Method according to claim 4, wherein the Infrared (IR) reflective material is a material out of the group of graphite, aluminum, titanium dioxide, silica or biopolymers.

6. Method according to any of the foregoing claims, comprising the step of heating an inside of the tank during the step of providing the insulation layer by in situ foaming of the expanded polymeric foam.

7. Method according to any of the foregoing claims, comprising the step of adjusting a height of a mold cavity of the mold in dependency of a height of the tank placed inside said mold.

8. Method according to claim 7, wherein the step of adjusting the height of the mold cavity comprises sliding mold parts relative to each other.

9. Method according to claim 8, wherein the mold parts have an L- shaped cross section with a long leg of the L-shape extending in a height direction of the tank, and a short leg of the L-shape extending in a radial direction of the tank.

10. Method according to claim 8, wherein:- a mold housing comprises a longitudinal mold cavity; and- a further mold part defines a cover that is adjustable in the longitudinal direction of the mold cavity.

11. Method according to claim 10, wherein the mold housing is an assembly of two or more mold housing parts.

12. Method according to any of the foregoing claims, wherein the step of in situ foaming of the expanded polymeric foam by applying heat to the granular base material of said foam comprises applying heat by means of radiative heat transfer using radiofrequency electromagnetic radiation.

13. Method according to claim 12, wherein the radiofrequency electromagnetic radiation comprises radio waves.

14. A thermal storage device, comprising a tank that is insulated with an insulation layer, wherein:- the insulation layer comprises an expanded polymeric foam that is foamed in situ around the tank inside a mold; and- an outer surface of the insulation layer defines an outer surface of the thermal storage device.

15. Thermal storage device according to claim 14, wherein the insulation layer defines a substantially continuous insulation layer around the tank.

16. Thermal storage device according to claim 14 or 15, wherein the insulation layer also encloses further components of the thermal storage device.

17. Thermal storage device according to any of claims 14-16, wherein the expanded polymeric foam is an EPS or EPP foam that is enhanced with particles of an Infrared (IR) reflective material.

18. Thermal storage device according to any of claims 14-17, wherein the Infrared (IR) reflective material is a material out of the group of graphite, aluminum, titanium dioxide, silica or biopolymers.

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