EP4675197A1

EP4675197A1 - A protective device

Info

Publication number: EP4675197A1
Application number: EP25186130.8A
Authority: EP
Inventors: Asmund Buen; Ånond Jarand Rønjom; Are Biseth; Per Olve Tobiassen
Original assignee: Power By Nature Energi AS
Current assignee: Power By Nature Energi AS
Priority date: 2024-07-04
Filing date: 2025-06-30
Publication date: 2026-01-07

Abstract

The invention is related to a protective device for an expandable outer tube of a coaxial borehole energy exchanger; the protective device being configured to fit over and cover at least a section of an end piece and a section of the expandable outer tube. The expandable outer tube being configured to move between a folded configuration and an unfolded configuration. The protective device is an external device connectable to, and moveable relative to the end piece and the expandable outer tube. The protective device is slidable onto the end piece while the expandable outer tube is in the folded configuration, wherein the protective device is further configured to cover a transition zone between the expandable outer tube and the end piece so that pressure forces are distributed over a larger area to prevent tearing of the expandable outer tube when the expandable outer tube moves from the folded configuration to the unfolded configuration.

Description

The present invention is related to a protective device for protecting an expandable outer tube of a coaxial borehole energy exchanger. More detailed, the present invention is related to a protective device designed to protect the expandable outer tube of a coaxial borehole energy exchanger during its installation and operation in a geothermal borehole.

BACKGROUND

A coaxial borehole heat exchanger (CBHE) is a type of ground source heat exchanger used in geothermal energy systems for heating and cooling applications. The CBHE utilizes the stable temperatures of the earth to exchange heat with a working fluid circulated through a coaxial pipe system installed in a borehole. This general background technology outlines the key components, principles, and advancements related to coaxial borehole heat exchangers.
The borehole is a vertical or inclined hole drilled into the ground to accommodate the heat exchanger system. The depth and diameter of the borehole depend on the thermal properties of the ground and the heating/cooling requirements.
The coaxial pipe (also referred to as "tube") system is the core of the CBHE, comprising two concentric pipes; an inner pipe that carries the working fluid down to the bottom of the borehole and an outer pipe that guides the working fluid back up to the surface after it has absorbed or released heat in the borehole.
The term "pipe" and "tube" are used interchangeably throughout the application and is referring to the same feature.
The working fluid is a heat transfer fluid, typically water or a water-antifreeze mixture, that circulates through the coaxial pipes to transfer heat between the ground and the heat pump system. The borehole is often filled with a thermally conductive grout to enhance heat transfer and to seal the borehole, preventing groundwater contamination.
In principle, the working fluid absorbs heat from the ground in heating mode or releases heat to the ground in cooling mode. This heat exchange occurs as the fluid circulates through the coaxial pipe system. The CBHE is typically connected to a heat pump that facilitates the transfer of heat between the working fluid and the building's heating or cooling system. The heat exchanger may also be referred to as an energy exchanger.
The efficiency of the CBHE is influenced by the thermal conductivity of the ground, which varies with soil composition, moisture content, and other geological factors.
The coaxial design provides a larger surface area for heat exchange compared to traditional U-tube configurations, enhancing thermal efficiency. The coaxial configuration allows for a smaller borehole diameter, reducing drilling costs and environmental impact, and the design promotes a more uniform and controlled flow of the working fluid, improving heat transfer performance. The coaxial pipe system can be prefabricated and installed with relative ease, and it is accessible for maintenance and inspection.
An energy capsule typically refers to a modular unit or an embedded structure within the borehole that aids in optimizing heat transfer between the working fluid and the surrounding ground. The coaxial pipe comprising the inner pipe (tube) and the outer pipe (tube) constitute the energy capsule, where the inner pipe is situated inside the outer pipe.
Publication US 2015/0068740 A1 , discloses a coaxial ground heat exchanger and installation method, where the heat exchanger has a central core tube that can be provided with a thermally insulating casing and an outer tube that delimits an annular gap which extends radially outwards from the core tube. The core tube and the annular gap can be configured such that a flowable heat transfer medium can flow through. The outer tube is formed by a tubular expandable cover that directly adjoins a wall of a ground heat exchanger borehole when the heat exchanger is installed.
Publication WO 2021/094644 A1 , discloses an outer pipe formed from a crystallized plastic material for forming an outer jacket of a coaxial heat transfer piping. It has a first operating form in which, in a cross-section of the outer pipe, a main part of a wall of the outer pipe substantially follows a first circle. The wall of the outer pipe comprises an elongated recess extending in a longitudinal direction of the outer pipe, at which recess in the cross-section of the outer pipe in the first operating form of the outer pipe the wall of the outer pipe deviates inwardly from said perimeter of the first circle, such that the perimeter of the wall of the outer pipe is longer than the perimeter of said first circle and the outer pipe is forceable into an expanded operating form in which said main part of the wall of the outer pipe in the cross-section of the outer pipe substantially follows, as a result of straightening of the recess, a second circle which is larger than the first circle.
To optimize the energy capsule, it is crucial that this capsule is completely diffusion-tight under pressure, with the primary challenge being to seal the capsule at the end of the energy well. A further problem associated with coaxial geothermal systems, particularly those utilizing expandable or foldable outer jackets, is the risk of mechanical damage or malfunction during insertion, deployment, or operation within the borehole. Without adequate protection, components such as the expandable jacket may be subject to abrasion, puncture, deformation, or snagging due to contact with sharp rock surfaces, loose debris, or irregular borehole walls. Moreover, unprotected components may deploy prematurely or fail to unfold reliably, compromising the thermal efficiency or retrievability of the system.
There is therefore a need for a protective device that safeguards sensitive elements of the coaxial tube throughout handling, insertion, and operation, thereby ensuring reliable deployment and functional integrity.

SUMMARY

As a perquisite, a borehole with unspecified diameter and length, capable of directional or free drilling for use with an energy capsule, must be established. The energy capsule, which is lowered into the borehole, is terminated using an end plug device.
As used herein, the terms "end plug" and "end piece" are used interchangeably and refer to the same device.
The terms "folded state" and "folded configuration" are used interchangeably throughout this application, as are the terms "unfolded state" and "unfolded configuration."
As used herein, the terms "protective device" and "pressure relief device" are used interchangeably and refer to the same component.
The present invention relates to a protective device designed to protect the expandable outer tube of a coaxial borehole energy exchanger during its installation and operation in a geothermal borehole. The coaxial borehole energy exchanger typically includes a central core tube and an expandable outer tube, which are configured to facilitate the flow of a heat transfer medium. The expandable outer tube is connected to an end piece adapted for termination of the distal end of the energy capsule which involves sealing and securing the end of the capsule to ensure efficient fluid flow, prevent leakage, and enhance thermal performance.
As used herein, the term "expandable" refers to a characteristic of the outer tube whereby the outer tube is capable of transitioning from a folded or compact configuration into an unfolded or expanded configuration. The expansion may occur in response to internal pressure, mechanical actuation, or other means. The term "expandable" does not require that the material undergo permanent (plastic) deformation, but may encompass: Elastically expandable configurations, wherein the jacket returns to its original folded state upon removal of the expansion force; Plastically expandable configurations, wherein the jacket retains its expanded shape even after the force is removed; or Hybrid configurations that include elements or regions exhibiting both elastic and plastic behaviour. The term is intended to encompass all such variations unless explicitly limited by the claims.
The outer tube is designed to move between a folded configuration for insertion into the borehole and an expanded configuration once deployed inside the borehole.
The protective device serves as a pressure relief mechanism and is specifically designed to cover at least a portion of an end piece of the energy capsule and a portion of the expandable outer tube.
The protective device is configured as an external component that is not part of the end piece, and it is positioned over the end piece and the folded portion of the expandable outer tube while the outer tube is in its folded configuration. The protective device is mounted externally to the energy capsule and is slid onto the end piece and outer tube from above or from below, ensuring secure coverage and protection of the critical connection points.
The protective device may slide or move relative to the end piece of the energy capsule and a section of the expandable outer tube. The protective device may be slidable along a length of the expandable outer tube and the end piece such that it can be placed in multiple positions.
An important feature of this invention is the flexibility of the protective device. Because it is an external device, it is not permanently integrated into the end piece and can be used with a variety of different end piece solutions, providing significant versatility. This flexibility allows the protective device to be adapted for various types of energy capsules, facilitating easy assembly during installation and simplifying maintenance or replacement.
The protective device is designed to cover the transition zone between the expandable outer tube and the end piece. This transition zone is particularly vulnerable to damage during the unfolding and expansion of the outer tube. The protective device is configured to distribute the forces that are applied during the expansion of the outer tube, reducing the localized pressure at the transition zone. By spreading these forces over a larger area, the protective device prevents tearing or other forms of damage at the critical connection point between the expandable outer tube and the end piece.
Once the protective device is mounted and in place, it ensures that the outer tube can move smoothly from the folded configuration to the expanded configuration without compromising the integrity of the outer tube or the end piece. This feature is particularly important in the context of geothermal applications, where the energy capsule is subjected to high pressures and temperatures that could otherwise lead to failures at the transition zone.
In essence, the protective device provides a simple, cost-effective, and flexible solution to enhance the durability and reliability of the coaxial borehole energy exchanger. Its external design allows for easy installation, making it compatible with various end piece solutions, while also ensuring protection at the critical transition zone. By offering protection during both the insertion process and the expansion process, the device helps to ensure that the energy capsule remains intact and functional, minimizing the risk of damage during installation and operation in harsh geothermal environments.
The present invention may also relate to an end plug device for sealing off a distal end of an expandable outer tube of an energy capsule. The term "sealing off" is also referred to the task of "terminating" the energy capsule.
The end plug device may comprise an end piece having a recess and a wedge positioned within the recess, wherein the recess is adapted for receiving a folded end of the expandable outer tube at the distal end, with the wedge situated inside the fold. During pressurization of the expandable outer tube, the wedge is concurrently pressed against an inner surface of the recess, thereby sealing off the folded end of the expandable outer tube.
Terminating the distal end of the energy capsule in a Coaxial Borehole Heat Exchanger (CBHE) (or also referred to as a coaxial borehole energy exchanger) involves sealing and securing the end of the capsule to ensure efficient fluid flow, prevent leakage, and enhance thermal performance. The termination method of the present invention is robust and reliable to withstand the pressures and thermal conditions within the borehole. This allows for the use of alternative fluids within the energy capsule without the risk of contaminating the groundwater.
The end plug device may be made from durable, thermally conductive material (e.g., metal or high-strength polymer) and fitted to the distal end of the expandable outer tube of the energy capsule.
The end piece may comprise a threaded or snap-fit design in connection with the recess to ensure a secure connection to the distal folded end of the expandable outer tube. This arrangement ensures a tight seal and can be easily implemented in various capsule designs.
The fold of the expendable outer tube may be inserted into the recess, manually or using a tool to ensure it is driven in with adequate force to create a seal. It can be threaded, or it can be laid into the opening of the recess before the recess is clamped or tightened.
Thus, the energy capsule is terminated by a mechanical compression fitting comprising the wedge and the recess (fitting body). The recess is adapted to receive the fold of the expandable outer tube including the wedge, and wherein the wedge under pressurizing compresses around the folded tube material, creating a tight seal. This arrangement further allows for easy assembly and disassembly.
The arrangement according to the present invention accommodates thermal expansion and contraction of the expandable outer tube material without compromising the seal. The sealed end of the expandable outer tube is therefore arranged to withstand the pressure of the working fluid and any external pressures from the surrounding ground. Furthermore, the termination method is straightforward to implement in the field and requires minimal maintenance.
The recess or the fitting body for receiving the fold, may have a teardrop shape having an opening that gradually widens inwardly into at least a part of the recess. The gradual tapering of the teardrop shape contributes to the overall strength and durability of the fitting body, allowing it to withstand higher pressures and mechanical loads. Furthermore, the design allows for better pressure distribution, enhancing the seal's reliability and longevity.
The smooth contours of the teardrop design may further help distribute mechanical stresses uniformly across the structure, reducing the likelihood of stress concentrations that could lead to material fatigue or failure.
While the teardrop shape of the recess is highly effective for a range of applications due to its streamlined design and efficiency, other shapes are also applicable, like the elliptical, airfoil, bullet, streamlined oval, laminar flow body, fish body, and parabolic shapes also provide similar properties and benefits. The choice of shape may depend on the specific requirements of the application, such as the type of fluid flow, structural demands, and manufacturing considerations.
The wedge is a simple mechanical device characterized by its triangular or teardrop shape with a sharp edge tapering to a thicker, blunt edge. The wedge converts the force applied to its blunt end into forces perpendicular to its inclined surfaces. The wedge creates high localized pressure, ensuring a tight and reliable seal.
The wedge of the present invention may have a shape corresponding to the shape of the recess, and such that it can be received into the recess.
The wedge of the present invention may have a teardrop shape corresponding to the teardrop shape of the recess so that the wedge has a similar shape but smaller footprint than the recess, and wherein the wedge is moveable within the recess. The wedge has a gradual taper, allowing it to be inserted easily into the folded tube and gradually increasing the pressure.
The narrow end of the wedge may be essentially sharp, allowing it to press or squeeze the flexible outer tube material easily. Thus, the wedge compresses the tube material, increasing the contact pressure between the folded layers of the flexible outer tube and creating a seal. This pressure prevents liquid or gas from leaking through the folded section, and when the pressure on the wedge increases, the contact pressure increases concurrently.
In mounting, the expandable outer tube may be folded back onto itself to create a doubled-over section. This fold provides a physical barrier to water flow. The wedge is inserted into the folded section of the tube and the assembly further positioned into the recess. As the wedge is driven into the fold and into the recess, it forces the walls of the expandable outer tube tightly against each other. Upon pressurizing, the wedge compresses the expandable outer tube material, increasing the contact pressure between the folded layers and creating a seal. This pressure prevents liquid or gas from leaking through the folded section.
The wedge may be made from a durable material that can withstand the pressure and environmental conditions (e.g., plastic, metal, or composite materials). A smooth surface finish is preferable since it reduces friction during insertion and ensures a tight seal.
The wedge is sized appropriately for the tube diameter and thickness. It is large enough to compress the tube fully but not so large that it damages the tube material. The length of the wedge may be at least the same as the cross-sectional length of the fold such that it covers the entire folded section, thereby ensuring uniform pressure across the seal.
The wedge may be inserted into the fold manually or using a tool to ensure it is driven in with adequate force to create a seal. The wedge may have features such as barbs or a locking mechanism to prevent it from slipping out once inserted.
This arrangement and method require minimal components and no complex machinery. Using a wedge is generally inexpensive compared to other sealing methods.
The end piece may be a solid end piece, or it may comprise a split clamp plate, or any combinations thereof. The recess in the end piece may be provided by milling, moulding, machine cut, made up from one or more parts, split clamp plates or any combinations thereof.
The split clamp plate may comprise a first clamp plate and a second clamp plate, arranged with surfaces facing each other. They may be arranged such that the recess is centred between the first and second clamp plate.
The split clamp plate may constitute a circular clamp plate equipped with through bolts, ensuring a secure and tight fit around the energy capsule. The segments of the split clamp plate may comprise bolt holes that align when the plate is closed, allowing bolts or screws to be used to tighten the clamp.
The split clamp plate, also referred to as a split plate clamp, is a mechanical device used to secure, hold, or clamp the fold (with the wedge) of the expandable outer tube in its position within the recess. It may comprise of two or more segments that can be tightened around the object to provide a firm grip. This split design is essential for applications where the object (end fold assembly) cannot be threaded into the recess.
The inner surface of the recess of the clamp plate may be curved to match the contour of the fold being clamped. This ensures a better fit and more even distribution of clamping forces.
The split clamp plates are easy to install and remove, requiring minimal tools. The split design simplifies the process of positioning and securing the clamp around the fold of the expandable outer tube.
A pressure relief device covering the expandable outer tube at a connection point may be provided to prevent the tube from tearing open due to excessive pressure. This device ensures the integrity and safety of the system by managing pressure levels and providing a controlled release when necessary.
According to an embodiment of the present invention, the end plug device may comprise a pressure relief device adapted to fit over and cover at least a section of the end piece and the expandable outer tube at the fold. The pressure relief device may also be referred to as a tension relief device. It distributes the forces from the expandable outer tube over a larger area so that it the expandable outer tube won't get teared at the connection point.
The pressure relief device may be a circular tube that partially fits over the circular clamp plates of the end piece, serving as a pressure relief mechanism. The circular tube has an inner diameter that is approximately equal to the width of the expandable outer tube of the energy capsule in its folded state (configuration). The function of the tube is to act as a pressure relief mechanism, thereby reducing the internal pressure against the clamp plates.
One or more pressure relief devices may be provided to control the pressure on the expandable outer tube at the fold (connection point) to the end piece. The one or more pressure relief devices may have different size, and they may be arranged one over another, to control and distribute the pressure forces.
To have a controlled and safe deployment of the distal end of the expandable outer tube towards the bottom of the borehole, the end plug device needs sufficient deadweight.
Therefore, the end piece may be designed with sufficient dead weight for lowering the expandable outer tube to the bottom of the borehole, or the end piece may comprise an attachment point for connecting a weight load. The purpose of the weight load is to provide necessary weight for pulling the expandable outer tube to the desired position at the bottom of the borehole.
Attaching a weight load to the end piece is a common requirement in various fields, such as construction, mechanical engineering, and manufacturing. The method chosen depends on the specific application, load requirements, material properties, and safety considerations, and are known from prior art. The method that are applicable may be:

Boted connections: using bolts, nuts, and washers to secure the weight load to the end piece.
Threaded inserts and screws: embedding threaded inserts into the end piece to accept screws or bolts.
Pin and hole connections: using pins inserted through aligned holes in the weight load and end piece.
Snap-fit or interlocking mechanism: using interlocking features that snap together to secure the weight load to the end piece.

The present invention may also relate to a coaxial borehole energy exchanger comprising an energy capsule and an end plug device for terminating the expandable outer tube of the energy capsule, as described above.
The energy capsule comprises an expandable outer tube moveable from a folded state (folded configuration) in which it is folded along its longitudinal direction for introduction into a borehole, to an unfolded state (unfolded configuration) in which it is pressurized such that it expands and lie against a wall surface of the borehole. The expandable outer tube comprises a distal end with an end fold having a wedge located inside the end fold, and wherein the end fold with the wedge is adapted to be inserted into the recess of the end piece so that during pressurization of the outer tube the wedge seals off the distal end of the expandable outer tube at the end fold.
The coaxial borehole energy exchanger may comprise an inner tube located inside the expandable outer tube, wherein the inner tube is arranged to transport a pressurizing medium to pressurize the expandable outer tube, such that it moves from the folded state to the unfolded state.
The inner tube may be preinstalled into the expandable outer tube in the folded state, for introduction into the borehole together. In the case, the energy capsule comprises the expandable outer tube and the inner tube and wherein the inner tube ends inside and before the end fold of the expandable outer tube, such that only the expandable outer tube is sealed off by the end plug device.
The coaxial borehole energy exchanger may comprise a fluid circulation tube, arranged to replace the inner tube after the expandable outer tube is in its unfolded state, whereby in the unfolded state the inner tube is extracted from the borehole and replaced by the fluid circulation tube. The fluid circulation tube may comprise an inlet fluid circulation tube extending from the top of the borehole towards the bottom section of the borehole for transport a circulation fluid to the bottom of the borehole, and an outlet fluid circulation tube located at a top section of the borehole for extracting the heated circulation fluid out from the borehole.
The flexible or expandable outer tube in the Coaxial Borehole Heat Exchanger (CBHE) system according to the present invention, is designed to facilitate ease of installation, adaptability to various borehole configurations, and enhanced thermal performance. This component plays a critical role in ensuring efficient heat transfer between the working fluid and the ground.
The expandable outer tube may be constructed from materials that provide a high degree of flexibility, allowing it to conform to the borehole's shape and accommodate any irregularities in the borehole wall. Common materials include high-density polyethylene (HDPE), crosslinked polyethylene (PEX), and other thermoplastic elastomers that offer a balance of flexibility and durability.
Despite its flexibility, the outer tube is engineered to withstand the mechanical stresses associated with installation and operation, such as ground pressure, thermal expansion and contraction, and fluid pressure. Reinforced or composite layers may be used to enhance strength.
The material of the outer tube is selected for its thermal conductivity properties to facilitate efficient heat exchange between the working fluid and the surrounding ground. Specialized coatings or additives may be incorporated to improve thermal performance.
The expandable outer tube may be resistant to chemicals present in the soil and groundwater, ensuring long-term durability and preventing degradation that could compromise system performance.

FIGURES

The invention will now be described with reference to the attached figures, wherein:

Fig. 1: Shows a coaxial borehole energy exchanger comprising an energy capsule and an end plug device for terminating the energy capsule, according to an embodiment of the present invention.
Fig. 2: Shows the end plug device comprising an end piece having a recess and a wedge situated in a fold of the expandable outer tube.
Fig. 3: Shows the end plug device comprising an end piece with an attachment point for a weight load, and the expandable outer tube in the folded state.
Fig. 4: Shows the end plug device comprising an end piece and a pressure relief device adapted to fit over and cover at least a section of the end piece, and the expandable outer tube in the unfolded state.
Fig. 5: Shows the end plug device from above and the expandable outer tube folded along its longitudinal direction and with the inner tube located inside the expandable outer tube.
Fig. 6: Shows an exploded view of the end plug device comprises a first and a second clamp plate.

DETAILED DESCRIPTION OF THE FIGURES

In the following, embodiments of the invention will be discussed in detail with reference to the appended figures. It should be understood, however, that the figures are not intended to limit the invention to the subject-matter depicted in the figures.
Figure 1 shows a coaxial borehole energy exchanger 10, also referred to as a coaxial borehole heat exchanger 10, comprising an energy capsule 11 and an end plug device 20 for terminating the energy capsule 11.
The energy capsule 11 comprises an expandable outer tube 12 moveable from a folded state in which it is folded along its longitudinal direction for introduction into a borehole 19, to an unfolded state in which it is pressurized such that it expands and lie against a wall surface of the borehole 19. Figure 1 shows the expandable outer tube 12 in the unfolded state in which it is expanded such that it lies toward the wall surface of the borehole 19.
The expandable outer tube 12 has a fold 13 at its distal end towards the bottom of the borehole 19 and positioned inside a recess 22 of an end piece 21. A wedge 23 is located inside the fold 13, and wherein the wedge compresses around the folded expandable outer tube 12 material, creating a tight seal against an inner surface of the recess 22.
The coaxial borehole energy exchanger 10 may comprise an inner tube 14 (shown in figure 5) located inside the expandable outer tube 12, wherein the inner tube 14 is arranged to transport a pressurizing medium to pressurize the expandable outer tube 12, such that it moves from the folded state to the unfolded state.
The coaxial borehole heat exchanger 10 may comprises a fluid circulation tube 15, arranged to replace the inner tube 14 after the expandable outer tube 12 is in its unfolded state, whereby in the unfolded state the inner tube 14 is extracted from the borehole 19 and replaced by the fluid circulation tube 15. Figure 1 shows the fluid circulation tube in operation comprising an intake fluid circulation tube 15 for transporting fluid into the bottom of the borehole 19, and an outtake fluid circulation tube 15' at the top of the borehole 19 for extracting the heated or cooled fluid. Figure 2 shows an end plug device 20 for sealing off a distal end of an expandable outer tube 12 of an energy capsule 11. The energy capsule 11 comprises an expandable outer tube 12.
The end plug device 20 comprises an end piece 21 having a recess 22 and a wedge 23 positioned within the recess 22. The recess 22 is adapted for receiving the fold 13 of the expandable outer tube 12 with the wedge 23 positioned in the fold 13. The wedge 23 is moveable within the recess 22. During pressurization of the expandable outer tube 12, the wedge 23 is concurrently pressed against an inner surface of the recess 22, thereby sealing the fold 13 of the expandable outer tube 12. The length of the wedge 23 covers the entire folded section, ensuring uniform pressure across the seal.
The wedge 23 amplifies the force and create high localized pressure for sealing off the fold 13 of the expandable outer tube 12.
The teardrop shaped wedge 23 is placed in the fold 13 of expandable outer tube 12 of the energy capsule 11, and the arrangement further placed into a teardrop-shaped recess 22 arranged in the circular end piece 21. The recess may be made from milling into the end piece 21 (not shown), or it can be provided by at least a split clamp plate.
In the event the pressure inside the expandable outer tube 12 increases, some of the pressure is directed downward towards the fold 13 (bend) of the expandable outer tube 12. As the pressure attempts to pass through the tube bend, the force against the wedge 23 increases from below, enhancing the seal between the wedge 23, the expandable outer tube 12, and the upper part of the teardrop shape recess 22 in the end piece 21.
From figure 2 the recess 22 has a teardrop shape having an opening that gradually widens inwardly into at least a part of the recess 22. The gradual tapering of the teardrop shape recess contributes to the overall strength and durability of the recess 22, allowing it to withstand higher pressures and mechanical loads. Furthermore, the design allows for better pressure distribution, enhancing the seal's reliability and longevity.
Also shown in figure 2, the wedge 23 has a teardrop shape corresponding to the teardrop shape of the recess 22 and wherein the wedge 23 is moveable within the recess 22 such that it converts the force applied to its blunt end into forces perpendicular to its inclined surfaces. The wedge 23 creates high localized pressure, ensuring a tight and reliable seal at the end fold 13 of the expandable outer tube 12.
Figure 2-6 shows the end piece 21 comprising a split clamp plate. The split clamp plate is used to secure, hold, and clamp the end fold of the expandable outer tube 12 in place inside the recess 22. It may comprise of two or more segments that can be tightened around the object to provide a firm grip.
Thus, the split clamp plate may comprise a first clamp plate 24 and a second clamp plate 25, arranged such that the recess 22 is centred between the first and second clamp plate 24,25.
The split clamp plate comprises openings for screws and bolts 26 for tensioning the first and second clamp plate 24,25 towards each other such that the end fold 13 including the wedge 23 is clamped inside the recess 22.
Fig. 3 shows the protective device 27 as an external device and slidable onto the end piece 21 from above and secured by friction while the expandable outer tube 12 is in the folded configuration. The protective device 27 has a shape of a circular tube and may move relative to the end piece 21 and the expandable outer tube 12. The expandable outer tube 12 being in the folded configuration.
Fig. 4 shows the protective device 27 as a circular tube in position covering the transition zone between the expandable outer tube 12 and the end piece 21. The figure3 shows the expandable outer tube 12 in the unfolded configuration in which it is expanded.
The pressure support 27' extends beyond the edge or the end of the protective device 27 and covers the entire end of the protective device 27 to ensure that the entire transition zone is protected from the edges of the protective device 27. The circular tube may be connected to the end piece and the folded portion of the expandable outer tube 12 by a friction fit.
The protective device 27 is also referred to as a pressure relief device 27.
The pressure relief device 27 may be circular tube that partially fits over the circular split clamp plates, serving as a pressure relief mechanism, thereby reducing the internal pressure against the first and second clamp plates 24,25. The inner diameter of the circular pressure relief device 27 may be approximately equal to the width of the expandable outer tube 12 in its folded state.
Figure 2-4 shows a pressure relief device 27 adapted to fit over and cover at least a section of the end piece 21. Figure 3 and 4 shows the pressure relief device 27 covering the recess 22 and the end fold 13 including the wedge 23.
The pressure relief device 27 covering the expandable outer tube 12 at a connection point is designed to prevent the tube 12 from tearing open due to excessive pressure. This pressure relief device 27 ensures the integrity and safety of the system by managing pressure levels and providing a controlled release when necessary.
Figure 3 shows the pressure relief device 27 in position, and with the expandable outer tube 12 in its folded state before pressurization. Figure 4 shows the pressure relief device 27 in operation in which it ensures the integrity and safety of the system in the event the expandable outer tube 12 is pressurized and expanded.
The pressure relief device 27 may comprise one or more layers of pressure supports 27' arranged between the energy capsule 11 and the pressure relief device 27. The pressure supports 27 main goal is to protect the energy capsule 11 and expandable outer tube 12 from mechanical stress when pressurized, and it may therefore be made from a softer material than the pressure relief device 27. Figure 3 and 4 shows the pressure support 27' having a size extending past (bigger footprint than) the pressure relief device 27 for protecting the expandable outer tube 12 against the abut edge of the pressure relief device 27. Figure 4 shows the pressure support 27' made from a flexible material that follows and controlling the shape of the expandable outer tube 12 when pressurized.
The end piece 21 may comprise an attachment point 28 for connecting a weight load 29. The weight load 29 provides necessary weight for pulling the expandable outer tube 12 to the desired position at the bottom of the borehole 19. This illustrated more clearly in figure 1.
Figure 5 shows how the expandable outer tube 12 can be folded along its longitudinal direction. The inner tube 14 may be located inside the longitudinal fold such that it can be assembled into the borehole 19 together with the expandable outer tube 12, wherein the inner tube 14 is unfolded and adapted to transport a pressure medium in form of liquid or gas, to pressurize the expandable outer tube 12 such that is moves from the folded state into the unfolded state.
Figure 6 shows an exploded view of the end plug device 20 together with the end fold of the expandable outer tube 12. The fold with the wedge 23 can be assembled into the recess 22 prior to mounting the first and second clamp plate 24,25, such that they are properly secured and clamped inside the recess 22.
The end piece 21 may comprise a centre block 21' arranged between the first and second clamp plate 24,25 and wherein a surface of the centre block 21', and the first and second clamp plates 24,25 defines the recess 22 when assembled. The centre block 21' may comprise one or more centre blocks, and the first and second clamp plate 24,25 may comprise one or more clamp plates.
Also shown in figure 6, the length of the wedge 23 covers the entire folded section of the expandable outer tube 12, ensuring uniform pressure across the seal.
Figure 6 also shows the protective device 27 mounted into or onto the folded expandable outer tube 12 before the entire end piece device 20 is mounted. When the entire end piece device 20 is mounted, the protective device 27 can slide into position such that it covers the transition area between the expandable outer tube 12 and the end piece device 20. The system will thereafter be ready to be deployed into the borehole 19.

Claims

A protective device (27) for an expandable outer tube (12) of a coaxial borehole energy exchanger (10), the protective device (27) being configured to fit over and cover at least a section of an end piece (21) and a section of the expandable outer tube (12), the expandable outer tube (12) being configured to move between a folded configuration and an unfolded configuration,
characterized in that the protective device (27) is an external device connectable to, and moveable relative to the end piece (21) and the expandable outer tube (12), wherein the protective device (27) is slidable onto the end piece (21) while the expandable outer tube (12) is in the folded configuration, wherein the protective device (27) is further configured to cover a transition zone between the expandable outer tube (12) and the end piece (21) so that pressure forces are distributed over a larger area to prevent tearing of the expandable outer tube (12) when the expandable outer tube (12) moves from the folded configuration to the unfolded configuration.
The protective device (27) according to claim 1, wherein the protective device (27) is a removeable device adapted for flexibility in use with different end piece (21) solutions.
The protective device (27) according to claim 1 or 2, wherein the protective device (27) is slidable along a length of the expandable outer tube (12) and the end piece (21) such that it can be placed in multiple positions relative to the end piece (21).
The protective device (27) according to any one of the preceding claims, wherein the protective device (27) is a circular tube with a hollow body.
The protective device (27) according to claim 4, wherein the circular tube has an inner opening, defined by the hollow body, approximately matching the size of an outside surface of the expandable outer tube (12) in its unfolded configuration.
The protective device (27) according to claim 5, wherein the circular tube is connected to the end piece (21) and the expandable outer tube (12) by a friction fit.
The protective device (27) according to any one of the preceding claims, wherein the protective device (27) further comprising a pressure support (27') arranged at an end of the circular tube, between the protective device (27) and the expandable outer tube (12), the pressure support (27') being configured to protect the expandable outer tube from an edge of the circular tube.
The protective device (27) according to claim 7, wherein the pressure support (27') extends beyond the edge of the circular tube, covering the entire end of the circular tube to ensure that the entire transition zone is protected from the edge of the circular tube.
The protective device (27) according to claim 7 or 8, wherein the pressure support (27') is made of a reinforced material, such as a composite material, rubber, metal, or any combinations thereof, providing enhanced durability and strength to the protective support.
A method for installing a protective device (27) according to any one of claims 1-9, on an expandable outer tube (12) of a coaxial borehole energy exchanger (10), the method comprising the steps of:
a) mounting the protective device (27) onto the expandable outer tube (12) while the expandable outer tube (12) is in a folded configuration;

b) connecting the expandable outer tube (12) to the end piece (21);

c) sliding the protective device onto the end piece (21) from above, such that the protective device (27) covers a transition zone between the expandable outer tube (12) and the end piece (21);

d) lowering the expandable outer tube (12) and the end piece (21) into a borehole (19);

e) applying pressure to the expandable outer tube (12) to move it from the folded configuration to the unfolded configuration, wherein the protective device (21) distributes forces over a larger area to prevent tearing of the expandable outer tube (12) during expansion.