Underground thermal energy storage

Abstract

Underground thermal energy storage in a cylindrical or n-gonal prism shape with a vertical axis, comprising an inner volume for holding a liquid, an outer wall, an inner wall around the inner volume, and a filling layer between the inner wall and the outer wall. The inner wall comprises a series of modular wall parts provided with a heat exchanger for exchanging thermal energy with the liquid. The modular wall parts, arranged in rings, contact the inner volume and have an elastic sealing limiting liquid flow between the inner volume and the filling layer and taking up thermal expansion of the modular wall parts. The filling layer comprises an insulating layer designed to keep the outer wall below 30 C. when the inner volume is at least 90 C., and a structural layer for maintaining the insulating layer and the inner wall's modular wall parts in position.

Claims

1. An underground thermal energy storage: having a shape selected from cylindrical and an n-gonal prism, having an axial direction that in use is vertical, and comprising an inner volume for holding a liquid, said underground thermal energy storage comprising: a peripheral outer wall that defines the shape, a peripheral inner wall around said inner volume, and a filling layer between said inner wall and said outer wall, said inner wall comprising modular wall parts arranged in a ring, each of the modular wall parts: provided with a heat exchanger for exchanging thermal energy with said liquid, having opposite radial surfaces that are in use vertical, an inner tangential surface contacting said inner volume, an outer tangential surface directed towards said outer wall, and opposite axial surfaces that are in use horizontal, and comprising an elastic sealing between a joint of adjacent radial surfaces that limits liquid flow between the inner volume and the filling layer and takes up thermal expansion of the modular wall parts, and said filling layer comprising: an insulating layer extending over at least part of a height of the underground thermal energy storage, having a thermal resistance R value where R=d/[m.sup.2K/W], in which d is a layer thickness of the insulating layer, and , the thermal conductivity of said insulating layer, wherein the thermal resistance R value is configured to keep said outer wall at a temperature of below 30 C. when said inner volume is at a temperature of at least 90 C., and a structural layer that maintains said insulating layer and said inner wall modular wall parts in position.

2. The underground thermal energy storage of claim 1, wherein said thermal resistance R value at an upper part of said underground thermal energy storage is at least 8 m.sup.2K/W.

3. The underground thermal energy storage of claim 1, wherein said elastic sealing comprises a vertical expansion joint, compressible in tangential direction, between the adjacent radial surfaces.

4. The underground thermal energy storage of claim 1, wherein said insulating layer has a pressure resistance of more than 500 kPa.

5. The underground thermal energy storage of claim 1, wherein said structural layer comprises a setting composition including concrete and/or bentonite that provides a pressure resistance of more than 550 kPa.

6. The underground thermal energy storage of claim 1, wherein said peripheral outer wall is an in-situ produced soil mix wall.

7. The underground thermal energy storage of claim 1, wherein said ring comprises two or more vertically stacked rings that are functionally thermally insulated.

8. The underground thermal energy storage of claim 1, wherein a first ring of the modular wall parts is stacked above a second ring of the modular wall parts, further comprising a horizontal thermally insulating layer between adjacent axial surfaces of the modular wall parts of the first ring and the modular wall parts of the second ring.

9. The underground thermal energy storage of claim 1, further comprising a bottom layer connected to said inner wall and/or said outer wall, and a lid above an upper level of the liquid, such that the lid is at, above, or below a ground level.

10. The underground thermal energy storage of claim 1, wherein in use the inner volume is at least partially filled with the liquid, wherein the liquid is a medium for allowing energy storage.

11. The underground thermal energy storage of claim 10, wherein a first ring of the modular wall parts is stacked above and thermally insulated from a second ring of the modular wall parts, and wherein the medium comprises a first layer having a first density and a second layer having a second density greater than the first density, and wherein the first layer is within the first ring and the second layer is within the second ring.

12. The underground thermal energy storage of claim 10, wherein the medium includes a lowest layer that can store energy at a temperature of the medium below a temperature outside said underground thermal energy storage, and wherein the medium does not solidify at a temperature of the medium below 5 C.

13. The underground thermal energy storage of claim 1, wherein the heat exchanger comprises one or more conduit systems at or below an inner surface of the modular wall part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of a device will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

(2) FIG. 1 schematically an underground thermal energy storage in cross section;

(3) FIG. 2 schematically shows a building stage of the underground thermal energy storage;

(4) FIG. 3 schematically shows a part of a top of the underground energy storage during assembly of the inner wall;

(5) FIG. 4 shows a part of the underground energy storage at the building stage of FIG. 3 in top view;

(6) FIG. 5 schematically shows the inner wall of the underground thermal energy storage, at the building stage of FIG. 3;

(7) FIG. 6a schematically shows a column of wall parts of the inner wall of the thermal energy storage of FIG. 5, seen from the inside;

(8) FIG. 6b shows an exploded vies of the lowest wall parts of FIG. 6a, seem from the inside of the underground thermal energy storage;

(9) FIG. 6c shows the wall parts of FIG. 6b seem from the outside of the underground thermal energy storage;

(10) FIG. 7 schematically shows a part of a wall part, in cross section as indicated in FIG. 6a and showing a layout of the heat exchanger, and

(11) FIG. 8 a cross section through a wall part of FIGS. 6a-6c.

(12) The drawings are not necessarily on scale.

DESCRIPTION OF PREFERRED EMBODIMENTS

(13) FIG. 1 schematically depicts an underground thermal energy storage 1 in vertical cross section. In use, the underground thermal storage may be operated in such away that stratified thermal layers result. A thin layer in which temperature changes rapidly is also referred to as thermocline.

(14) In FIG. 1, the ground-level 2 is indicated. In an embodiment, the upper level of the medium inside an underground thermal energy storage 1 is provided at or below the ground water level. The energy storage 1 has an inner volume 3. In the inner volume 3, one or more media can be provided for storing thermal energy. In an embodiment, the energy storage may fill with groundwater. This groundwater may be heated (or cooled).

(15) The thermal storage 1 further comprises an inner wall 4 and an outer wall 5. Between the inner wall 4 and the outer wall 5 a spacing exists that may be filled with a filling layer 6. The filling layer 6 may completely or partially fill the space or gap between the inner wall 4 and the outer wall 5. It comprises her an insulating layer 17 and a structural layer 18.

(16) In the embodiment of FIG. 1, the inner wall 4 has rings 7 that are in this embodiment thermally isolated from one another and that each comprise a heat exchangers 8. Using these thermally isolated rings 7 and the heat exchangers 8, thermal energy can be added to a layer or can be retrieved from a layer. In this way, the medium in the inner volume 3 can be used in stratified, thermal layers. A lid 15 seals the thermal storage. Usually, an air space or air pocket remains between the upper level of the medium and the lower surface of the lid 15.

(17) In an embodiment, one or more of the layers may comprise another liquid, or may have a different temperature regime. Examples of possible layers and/or liquids are combining an increase in salt level in different layers, making one or more layers brine layers, using for instance glycol as a top layer, or in fact cooling the lower layer, using it as a storage for cold, thus de facto creating an ice cellar. Usually, separation between layers with different temperatures may occur and remain automatically. Using the different media, it is possible to make temperature differences between layers even bigger. It may even or additionally be possible to provide separation layers between layers. As an example, such a separation layer may be a just preventing diffusion of one or more components of the medium. Such a layer may comprise a foil or a membrane, for instance a polymer foil, a rubber foil, a polymer membrane, a rubber membrane, or a combination thereof. Such a layer may also have an insulating function. In such a case, the thickness of the layer may be adjusted. The material of the layer may be selected in a way to remain floating between medium layers. These medium layers may have a different densities. For instance, the medium may comprise a (lowest) layer of salt water or even brine, then a layer comprising mainly water, for instance originating from groundwater. The medium may further comprise an upper layer of water comprising for instance glycol. The density differences as well as their modified freezing and boiling points allow storage at different temperatures.

(18) In FIG. 2, an earlier stage of producing the underground thermal energy storage 1 is shown. The top soil layer is first removed. Here at this stage, the outer wall 5 is ready and encloses an inner space 9. The inner space 9 here filled with groundwater. The outer wall 5 comprises reinforcement beams 10 that are included in at least partially incorporate into the outer wall 5 and which are here substantially vertically aligned. Here the reinforcement beams extend only in part of the vertical or axial direction of the outer wall 5. The reinforcement beams 10 can in an embodiment extend in substantially the vertical or axial height of the outer wall 10.

(19) The outer wall is in this drawing substantially a circle, but in this embodiment fact has an n-gonal cross section. In FIG. 3, this indicated more clearly. This is due to the method of production. After the top soil layer is removed, first the outer wall is produced in-situ. A mix-cutter head having a length is each time lowered vertically while concrete is added to the loosened soil and part of the soil is removed. Thus, in fact each time a vertical wall slab is created in situ. This process as such is known as a soil mix process. In this way, here in fact an n-gonal right prism is created out of coupled vertical wall slabs. When the outer wall 5 has a closed circumference, the soil that is enclosed by the outer wall 5 can be removed. Usually, if the underground thermal energy storage 1 is constructed below ground water level, the inner volume 9 fills with groundwater.

(20) In FIG. 3, the top part of the underground thermal energy storage 1 is depicted during construction of the inner wall 4. At this stage, the inner wall 4 is placed, but alignment structures 12 that couple the inner wall 4 with outer wall 5 are still in place.

(21) In FIG. 3, it is further depicted that the inner wall 4 comprises a series of modular wall parts 11. Here, these modular wall parts 11 are in fact prefab elements. The modular wall parts 11 are here stacked into vertical cylinder segments, and also form the rings 7. The modular wall parts 11 are places inside the inner volume 9 enclosed by outer wall 5. This inner volume 9 usually is already filled with ground water. Alignment of the inner wall 4 in absolute sense and with respect to the outer wall 5 thus poses a problem. To that end, in an embodiment first the lowest cylinder of wall parts 11 is first placed in the inner volume 9, and provided with alignment poles 27, and with alignment frames 12 that connect the upper part of the alignment poles 27 and the outer wall. Furthermore, some additional alignment means are used which will be explained using the further drawings. Once all the wall parts are submerged into the inner volume 9 over the alignment poles 27 and rest on the lowest cylinder of wall parts 11 which are already properly aligned, additional alignment can be done using the alignment poles attaches via alignment frames 12 to the outer wall 5.

(22) FIG. 4 shows a top view of a part of the underground thermal energy storage 1, looking down in the gap between the inner wall 4 and outer wall 5. During construction, usually this gap is filled or fills with upcoming groundwater. FIG. 5 shows only the inner wall 4, for clarity without the surrounding outer wall 5. It shows parts of the additional alignment means 13 and 14 for aligning and subsequently fixing the position and orientation of the lowest ring 7. Alignment fixtures 13 are containers with flexible walls that are fixed to the lowest modular wall parts 11. In an embodiment, these alignment fixtures 13 are bags that can be filled and then set the position of the wall part. The alignment fixtures 13 may to that end, once its corresponding wall part 11 is properly positioned and aligned, be filled with for instance sand, concrete, or another, similar setting compound.

(23) The lowest modular wall parts 11 may in an embodiment further be provided with alignment actuators 14. In the current embodiment, to that end bags or bladders 14 are provided. These alignment actuators 14 can be filled for instance with water. By changing the water pressure inside, these alignment actuators are able to move the wall parts 11.

(24) FIGS. 6a-6c show the wall parts 11 and the various parts of the alignment and positioning means in more detail. After the outer wall 10 is constructed and the inner space 9 has been cleared by removing the earth inside, an important and delicate phase of constructing the inner wall 4 begins.

(25) First, an alignment structure 12 is provided. To this end, frame elements 12 are attached to the outer wall 5. These frame elements 12 comprise yokes. First the height of the frame elements 12 will be set, making the frame elements aligned in height. Attached to these frame elements 12 are vertical alignment beams 27. The alignment beam may comprise segments. Each time the lowest wall part 11 is lowered further, an additional segment is added. This to avoid manipulation of lengthy beams.

(26) In a further step, the lowest ring of wall parts will be placed. In FIG. 6a-6c it can be seen that these lowest wall parts differ from the further wall parts, as these wall parts have a lower reinforcement rib. Furthermore, an alignment fixture 13 is added. To each lowest wall part 11. Furthermore, an alignment actuator 14 is provided. The alignment fixture 13 at first is a flexible bag that is empty when the lowest wall parts 11 are sank into position. Furthermore, the alignment actuator 14 is also empty. First, alternating lowest wall parts 11 are placed. Thus, when numbering the lowest wall parts in transverse direction, first the odd numbered lowest wall parts 11 are lowered over the alignment beams 27. In an embodiment, the odd-numbered or first-placed lowest wall parts do not comprise the swell seal mastic bands 24. The height of these odd-numbered lowest wall parts 11 is set. Using for instance a laser height measuring device, the height is controlled. At this stage, the lowest wall parts 11 rest a little above the bottom of the inner space. Usually, the lowest wall parts 11 rest about 30-50 cm above the bottom of the inner space 9. This bottom is not equalised. Thus, all the odd-numbered lowest wall parts 11 are now aligned at a proper height. The lowest wall parts 11 are now fixed in position using ground pins 29 or ground anchors. In the current embodiment, ground pins 29 (FIG. 29) hang on wires inside the alignment beams 27. The wire are cut, and the ground pins 29 fall down and are further inserted into the bottom below the lowest wall parts 11, fixing the position of the odd-numbered lowest wall parts 11 in radial direction R and in transverse direction T. The height is maintained as the lowest wall parts 11 still hang on the alignment structure 12.

(27) Next, the even numbered lowest wall parts 11 are lowered, each time an even-numbered lowest wall part 11, filling the space between two odd-numbered lowest wall parts 11. Again, the height is checked and set. Next, the position of the even-numbered lowest wall parts 11 is fixed in the same way as the odd-numbered wall parts using ground pins 29. The order of placement of the wall parts 11 distributes tolerances evenly.

(28) Next, the alignment actuators 14 are activated. These alignment actuators press the wall parts 11 together in radial direction R with a force directed to the centre. Here, the alignment actuators 14 comprise balloons that are in fluid communication with a common reservoir. The reservoir is located above surface level 2. By setting the height of the reservoir, the pressure inside the balloons is regulated in a simple manner. The common reservoir distributes the pressure evenly around the perimeter of the storage.

(29) In a next step, the alignment fixtures 13 are activated. As mentioned, in this embodiment empty bags are fixed to the lowest wall parts 11 as they are lowered. When all the lowest wall parts 11 are in place and aligned to fixed, the empty bags are filled. Here, the empty bags are slowly filled with a setting composition. An example of such a composition is a mortar. In particular cement mortar. It can be selected according to the need. When filled, the alignment fixture 13 fills the space below the lowest wall parts and the bottom of the inner space, and further fixes the position of the lowest wall parts 11. Furthermore, the alignment fixture 13 in this embodiment comprises a part that fills a space between the outer wall 5 and the insulation layer 17. It thus additionally provides a radial alignment and radial fixation. In particular in combination with wall parts 11 that are shaped as cylinder segments.

(30) After the composition of the alignment fixtures is set, a bottom 16 may be created in the inner volume 3 (FIG. 1). This can be done using known methods for underwater constructing. The bottom 16 can be used in particular when the medium differs from groundwater, or if additional insulation is needed.

(31) Next, the alignment actuators 14 are deactivated. Here, the balloons are emptied. This allows the alignment actuator to be removes for re-use, or it may be used for the next ring of wall parts 11.

(32) As the lowest ring is now positioned, aligned and fixed, the alignment structure 12 may be removed. Next wall parts 11 are lowered over the alignment beams 27. After the last ring of wall parts 11 is placed, the alignment beams 27 are removed. The alignment beams can be re-used.

(33) When all the wall parts for the inner wall are positioned, a remaining space or gap between the insulating layer 17 and the outer wall 5 can be filled with setting material for forming the structural layer 18. This will keep the wall parts 11 in place, but will allow the wall parts to be dynamically coupled, not to be mechanically fixed to one another. In this way, changes in volume, thermal expansion and contraction, end the like, can be absorbed. The structural layer 18 may comprise concrete or mortar that is poured into the gap. Additionally of in combination, other solid material may be combined, like pebbles or the like.

(34) In a next step, a lid is provided to cover the inner volume 3. Here, first an inner lid is constructed. In operation, an air pocket is left between the upper surface of the medium and the lower surface of the lid. The inner lid can for instance be made using channel plates/hollow core slabs. Next, the heat exchangers 8 can be connected. Here, the conduits of the heat exchanges 8 are coupled. The heat exchangers 8 are coupled according to the Tichelmann principle. Next, the channels or piping duct 25 may also be filled with a setting composition, like concrete or mortar or the like.

(35) Each inner wall part 11 may be provided with a heat exchanger 8. In FIG. 7, showing a part of a modular wall part 11, an embodiment of the heat exchanger 8 of a modular wall part 11 is shown. The heat exchanger 8 here comprise a conduit that is indicated in a striped line and that runs just below the inner tangential surface of a modular wall part 11. The conduit of the heat exchanger 8 here has one end that connects into one piping duct 25 and another end that connects to another piping duct 25 of the modular wall part 25 (not shown).

(36) In FIGS. 7 and 8, a horizontal cross section through a modular wall part 11 is shown as indicated in FIG. 6a. It shows the piping duct 25, the conduits of its heat exchanger 8, and the insulating layer 17 that is attached to the concrete outer tangential surface. The insulating layer 17 is here held to the concrete surface via a flexible adhesive layer 28.

(37) As explained above, the modular wall parts 11 rest on top of one another, with in this embodiment an insulating layer 19 between the radial surfaces of the modular wall parts 11. Furthermore, the modular wall parts 11 are placed against one another, connected at their axial surfaces via a sealing 21. The sealing 21 prevents liquid communication between the inner volume 3 and the outside of the storage via a space between the inner wall 4 and the outer wall 5. The modular wall parts 11 rest freely against one another. The sealing 21 is elastically compressible in tangential direction T. A column of stacked wall parts 11 in fact provide staves of a barrel. Between the (vertical) radial surfaces of neighbouring staves, the sealing 21 is provided. In the embodiment shown in FIG. 8, the sealing 21 at the left can be compressed when pressure is exerted towards the right. The sealing 21 at the right can be compressed when pressure is exerted to the left in the drawing. Thus, pressure with a component in plane of the wall parts 11 and compressed the sealing. In this way, the sealing 21 can take up dimensional changes in the modular wall part 11. For instance, it was realized that when the medium in the storage expands 2% in volume when heated, the circumference changes less than 1%. When the width of a modular wall part 11 is 1 meter, this means that a sealing needs to take up less than 1 cm. The sealing 21 here comprises a flexible, resilient layer 22. Here, a strip of rubber material like (natural) rubber or an elastomeric material is used. The thickness is at least 1 cm. In an embodiment, the thickness of the layer is below 3 cm. The sealing 21 here further comprises a wedge 23. Here, the wedge is made from an form-stable material, like wood, polymer material, or the like. The wedge 23 allows forming of the circular of polygonal rings 7. Additionally, here a band of hydrophilic expansive strips 24 are provided for additional sealing. These strips 24 can be swell seal mastic, for instance composed of bentonite. In an embodiment, the odd-numbered lowest wall parts 11 may not be provided with these strips 24 to avoid swelling when positioning takes more time then estimated. In the current embodiment, both sides of a wall part 11 comprise the strips 24. It may also be possible to have only one side of each wall part 11 be provided with these strips 24.

(38) A structural layer 18, here between the insulating layer and the inner surface of the outer wall 5, is provided. In fact, the structural layer 18 fills the remaining space or gap between the outer wall 5 and the outer surface of the insulating layer 17. For instance, a setting composition may be used. An example of a setting composition is concrete. The outer surface or outer transverse surface T of the wall parts 11 can be provided with a reinforcement, like wired mesh, for concrete. Thus, the structural layer 18 can be even more solid.

Example of Medium

(39) An example of a density-stratified medium is the following.

(40) The lowest layer of medium is a layer of water with salt added. In an example, for instance salt comprising at least 50% by wt. of NaCl is used. The density of salt water is larger than the density of water. When for instance more than 250 gram of salt per liter water is used, a temperature of below 15 C. is possible while maintaining a liquid medium layer.

(41) On top of the salt water, a layer of rubber granulate may be provided. For instance granulate having a specific density of 1150 kg/m.sup.3. The material has a lambda value of 0.29, and a layer thickness of 1.0 mm.

(42) The next layer is substantially composed of groundwater. This layer allows a temperature range of between 5 C. tot 95 C.

(43) On top of the groundwater layer, a film of (natural) oil may be provided as a separation layer.

(44) The top layer of the medium can comprise a water-glycol mixture that has a boiling temperature of above 130 C., and has a density of about 950-970 kg/m.sup.3, more in particular about 966 kg/m.sup.3.

(45) It will also be clear that the above description and drawings are included to illustrate some embodiments of the invention, and not to limit the scope of protection. Starting from this disclosure, many more embodiments will be evident to a skilled person. These embodiments are within the scope of protection and the essence of this invention and are obvious combinations of prior art techniques and the disclosure of this patent.

REFERENCE NUMBERS

(46) 1 underground thermal energy storage 2 surface level 3 inner volume 4 inner wall 5 outer wall 6 filling layer 7 ring 8 heat exchanger 9 inner space 10 outer wall reinforcement 11 modular inner wall part 12 alignment structure 13 alignment fixture 14 alignment actuator 15 lid 16 bottom 17 insulating layer 18 structural layer 19 ring insulating layer 20 vertical inner wall part gap 21 vertical elastic sealing 22 resilient elastic sealing strip 23 sealing beam 24 sealing band 25 piping duct/conduit 26 heat exchanger coupling conduit 27 vertical alignment beam 28 adhesive layer 29 anchoring pin A Axial R Radial T tangential