NL2030007B1 - Geothermal heat exchange system - Google Patents

Abstract

A geothermal heat exchange system, for exchanging heat between the ground and a circulation fluid, the system comprising: - a hollow pipe, installed in the ground below a surface thereof, for receiving a circulation fluid therein, the pipe preventing a direct contact between the fluid and the ground; - a pump, for pumping the circulation fluid through the pipe; characterised by: - a plurality of solid extension element, thermally coupled with an exterior surface of the hollow pipe and extending outwards from the pipe, the extension elements aiding the exchange of heat between the circulation fluid and the ground, thereby increasing the effective heat exchange volume between the circulation fluid and the ground.

Description

Title: Geothermal heat exchange system

BACKGROUND

The present invention relates to a geothermal heat exchange system. In particular, the present invention relates to a heat exchange system that is arranged below the surface and that is capable of both extracting energy from the ground as well as storing energy in the ground.

At present, several types of geothermal heat extraction systems are known.

When geothermal heat extraction systems that extract heat from the ground are concerned, and when considering the inventive concept behind the present invention, the two most relevant known types of heat extraction systems are the so-called vertical geothermal heat extraction system and the so-called horizontal geothermal heat extraction system. Alternatively, systems to attract heat from the water are known.

These are deemed irrelevant for the present invention.

A vertical geothermal heat extraction system, essentially relies on a tube that extends relatively deep into the ground, e.g. up to a depth of in between 40 and 160 m. A circulation fluid is guided into the ground and pumped up again, the circulation fluid extracting heat from the ground in its travel through the tube. The heated circulation fluid can, via a heat exchange system, e.g. be used to heat an indoors area of a residential building, an office building, a factory, or can be converted to other useful sources of heat. Vertical geothermal heat extraction systems of the open-loop type as well as of the closed-loop type are presently in use. Disadvantageously, to install such a vertical geothermal heat extraction system, a deep hole must be drilled inthe ground, resulting in high installation costs. Also, to pump up the circulation fluid from such depths requires a relatively large amount of energy, leading to low efficiencies being obtained with vertical geothermal heat extraction systems.

Furthermore disadvantageous is that vertical geothermal heat extraction systems cannot be installed at any location due to the risk of leakages in the soil when drilling such deep holes. Finally, some area of the ground, typically near the drilled hole, must be permanently reserved for the equipment that is needed to operate the system.

A horizontal geothermal heat extraction system essentially relies on a tube having a large length, typically of hundreds of meters, the tube arranged just below the surface of the ground and e.g. being arranged in spirals or loops. When a relatively cold circulation fluid flows through the tube, it extracts heat from the relatively warm ground and heats up. This process takes place at a very slow rate, as a result of which a long tubing length is required to obtain a noticeable temperature increase for the circulation fluid. This heated circulation fluid can be used to heat an indoors area of e.g. a residential building, an office building, a factory, or can be converted to other useful sources of heat. A disadvantage of a horizontal geothermal heat extraction system is that it requires a large area of the surface to be uncovered in order to install the system and, after installation of the heat extraction system, to be covered again.

Also, the low heat flux capacity between the circulation fluid and the ground leads to a low efficiency per square meter of available ground surface, hence the necessity of long tubes. Additionally, a system relying on large lengths of tubes is prone to leakages and requires large and heavy pumps. Furthermore disadvantageous is that present horizontal geothermal heat extraction systems are prone to weather conditions and depending on the geographical location the circulation fluid might freeze in winter such that no energy can be extracted from the ground when heat is required the most.

For both the horizontal and the vertical geothermal heat extraction systems, a large volume of the soil is interacted with to extract the heat stored therein with the circulation fluid. This in part results from the relatively low heat exchange properties between the soil, in particular dry soil, and the circulation fluid. This problem is solved, in known systems, by using long pipes — either extending deep into the ground or by distributing them over a large surface area.

It is an aim of the present invention to provide a more efficient heat exchange system, particularly in the sense that the system can be installed at a relatively low cost, and that it has a relatively high output per unit length of pipe.

SUMMARY OF THE INVENTION

Accordingly, the invention relates to a geothermal heat exchange system, for exchanging heat between the ground and a circulation fluid, the system comprising: - a hollow pipe, installed in the ground below a surface thereof, for receiving a circulation fluid therein, the pipe preventing a direct contact between the fluid and the ground;

- a pump, for pumping the circulation fluid through the pipe; and - a plurality of solid extension element, thermally coupled with an exterior surface of the hollow pipe and extending outwards from the pipe, the extension elements aiding the exchange of heat between the circulation fluid and the ground, thereby increasing the effective heat exchange volume between the circulation fluid and the ground.

Advantageously, the solid extension elements that are thermally coupled with the exterior of the pipe and that extend from the pipe, allow the creation of a subsurface heat grid. Compared to solutions that contain only a pipe through which a circulation fluid flows, the extension elements allow a larger ground volume — per unit length of pipe — to act as a heat source. Whereas the heat flux between the ground and the circulation fluid itself is not improved per se with the system as disclosed herein, the extension elements, which can be in direct contact with the ground, on the one hand reach out and penetrate a larger ground volume, so the total effective heat exchange volume is increased, and on the other hand may allow heat to be transferred better from the ground to the extension element and therewith, indirectly, to the circulation fluid. Thus using the system as disclosed herein, it is not only the relatively thin ground layer directly around the pipe with which heat is exchanged, the total ground volume is significantly increased by the layer of ground around the extension elements as well, and with a higher heat exchange coefficient too.

Advantageously, this higher efficiency in energy exchange between the ground and the circulation fluid allows the system to be used not only for extracting heat from the ground, but also for storing heat in the ground, such that the geothermal system becomes a true heat exchange system that can both extract heat from the ground (as known systems can), but that can also store heat in the ground.

Further advantageously, when looking at the total system costs, the system as presented herein may be installed at significantly lower installation costs compared to known systems and doesn’t requiring large lengths of tubes such that leakage problems can be omitted to a great extent.

Further advantageously, the entire surface of the ground in which the system is installed may be used for another purpose after installation of the heat exchange system — without any space being required for the installation of operational equipment.

In accordance with the present invention, a geothermal heat exchange system is provided. As explained in the above, this exchange not only includes extracting heat from the ground to heat a circulation fluid, but advantageously it now also becomes possible to efficiently extract heat from a circulation fluid and store it in the ground.

For example, the circulation fluid may be heated as a result of heat exchange with waste water (e.g. rain water or domestic waste water). This heat may be stored locally in the ground, where it can (later) be regenerated again to heat a building. Possibly, two heat exchange systems as defined herein are arranged below the surface in a similar volume of the soil, one of the two systems for heating when excess heat is available the ground and the other system for extracting heat from the ground when heat is needed. One skilled in the art will understand that such moments may be at different points in time, requiring a buffer to temporarily store the available excess heat. Here, said buffer is formed by the ground, without needing any rare and/or unsustainable materials / metals. Alternatively, a single system may be configured to be operated in two ways, wherein when the circulation fluid is circulated in one direction it is heated and wherein when the circulation fluid is circulated in the other direction it is cooled. This may e.g. be useful in a system that is to heat a building in the winter and cool a building in the summer.

It is noted that the process of pumping a circulation fluid through a heat exchange area and regenerating the heat obtained therefrom, and all components generally associated with said process, are deemed known to one skilled in the art.

In accordance with the present invention, it is not required to treat the ground, that forms the energy buffer, in any way, besides possibly excavating it and re- installing it to install the system. The ground can e.g. be sand or clay, or any other soil material available at the installation position.

In accordance with the present invention, the hollow pipe is installed below a surface of the ground, such that it is not visible when the system is installed. This advantageously allows the use of said ground surface for other purposes. For example, a road may be load on the surface, a recreation space such as a playground, a sports field, a park or a garden may be laid over the subsurface system. Further alternatively, a house or other building may be built on top of the system, or any other use of the ground surface may be envisioned. Importantly, the surface of the ground used to install the system in can have another function when the system is installed, virtually without limitations. 5 In accordance with the present invention, the circulation fluid in the hollow pipe may remain in the hollow pipe — at least when it is in the subsurface part of the pipe system — and is not in direct contact with the ground. However, when the pipe is made of heat conductive material, (indirect) transfer of heat between the ground and the circulation fluid is possible and the soil is not polluted. Via the transfer of heat between the ground and the circulation fluid, one of the ground and the circulation fluid is heated, whereas the other of the circulation fluid and the ground is cooled.

Examples of suitable circulations fluids include water, brine, glycol, and mixtures thereof. In typical embodiments the circulation fluid will be a liquid. However, the circulation fluid may also be gaseous or partly be in the gaseous state.

In typical embodiments the pipe may for a closed-loop system. However, this is not required per se.

In accordance with the present invention, and in contrast with ‘conventional’ geothermal heat extraction systems, extension elements are thermally connected to the pipe and extend from the pipe, e.g. in a radial direction. As described, whereas in ‘conventional’ systems heat transfer it is only possible to exchange heat between the circulation fluid and a layer of ground directly adjacent the pipe (so that a long pipe length is required to obtain a sufficient heating / cooling of the circulation fluid), with the extension element also the layer of ground directly adjacent said extension elements can be used for the transfer of heat. Therefore, without increasing the diameter of the pipe, the volume of ground with which heat can actively be exchanged is drastically increased per unit length of pipe, allowing a larger temperature change for the circulation fluid per unit of pipe length.

In accordance with the present invention, the extension elements are solid, in the sense that no circulation fluid flows through them. Due to the thermal coupling between the extension elements and the pipe, even when no circulation fluid flows through the extension elements, the ground adjacent said extension elements can still effectively be used for the exchange of heat between the ground and the circulation fluid.

In accordance with the present invention, a thermal coupling between the extension elements and the pipe can e.g. be effected by making both of them of a heat-conductive metal, and physically connecting them to each other, e.g. by welding or bonding.

As such, in embodiments the extension elements are made of a heat conductive material, in particular a metal, e.g. steel, preferably stainless steel, especially when the system is installed in corrosive environments.

It is noted that the components of the system as described in the above are deemed sufficient — for one skilled in the art — to explain the inventive concept of the present invention. Of course, the person skilled in the art understands that more components may be required to come to a working heat exchange system. For example, there may be an additional heat exchange module in which the temperature of the circulation fluid is brought back into the original state — i.e. the temperature it had before exchanging heat with the ground — which may include both heating it and cooling it. The skilled person will further understand that the system may additionally include pressure vessels to increase and/or decrease the pressure of the circulation fluid, a buffer vessel and all kinds of monitoring and control elements, such as valves, sensors, etc. Such components of a heat exchange system are deemed common general knowledge and may be chosen among available components to come to a working system.

In an embodiment of the present invention, a maximum depth of the system in the ground is 15 meter, preferably 12 meter, more preferably 10 meter.

Advantageously, with such a maximum depth no drilling is required such that the system can be installed at relatively low costs. Further advantageously, when the system is installed as such depths, any energy that is extracted from the ground during the winter, will be replenished by natural resources — in particular sunlight — during the summer, as the ground is warmed up until approximately this depth by the sun; any deeper the temperature of the ground is relatively constant over the seasons (when considering one location) and draining energy from such deeper depths, in the long run, could lead to depleting the energy source — much like oil wells are depleted in the long run.

In an embodiment of the present invention, a minimum depth of the system is 20 cm, preferably 50 cm, more preferably 100 cm. Advantageously, this is considered deep enough to prevent an accidental exposure of the system to one excavating the ground without knowing the system is present. Also, this is considered deep enough to prevent exposure of the system to the upper surface when the ground is eroded over time. It is noted that although for the working of the heat exchange system its exposure to the surface would not be very disadvantageous as such, however the exposure of the heat exchange system — with in embodiments solid extension elements pointing upwards with respect to a deeper-laid pipe — could be dangerous to humans, and in particular playing kids.

In an embodiment of the present invention, a maximum temperature of the circulation fluid, in use, is about 30°C. As known to one skilled in the art, also at these relatively low temperatures the exchange of heat between the ground and a circulation fluid is possible. Depending on the geographic location on the Earth where the system is installed, a suitable installation depth and a suitable circulation fluid may be chosen to prevent the circulation fluid from being frozen — such a situation preventing the optimal working of the system. For example, simple water, brine, glycol or mixtures thereof may be used as circulation fluid. In embodiments, to prevent freezing of the circulation fluid, a back-up heating system may be provided. The back-up heating system may heat the circulation fluid when temperatures are extreme low — below or at the lower end of the design conditions. Advantageously, as the pipe is relatively short per unit of heat exchange volume, and as heat transfer from the ground to the circulation fluid takes place at a relatively high rate, freezing of the circulation fluid is prevented compared to heat exchange systems with much longer pipes and lower heat transfer coefficients.

In a particularly advantageous embodiment, the heat exchange system is combined with a sustainable energy generation module, the heat exchange system e.g. being configured for storing energy generated by the sustainable energy generation module in the ground. Sustainable energy is not always generated at the moment it is needed. For example, when the sustainable energy is derived from the sun, more energy can be generated in the summer whereas heat to heat buildings is needed more in the winter. As a result of transport capacity deficiencies on (inter)national energy grids, local storage of such energy is highly desired. With the present system, as described, it is not only possible to extract heat from the ground but it is also possible to store heat in the ground. As such, in the summer the system may be operated to locally store energy, and in the winter the same system may be operated to locally regain said energy again — locally, independent of a grid, and at relatively high efficiency rates.

In other embodiments, to be described in more detail in the below, a heat extraction system having the features as disclosed herein and a heat storage system having the features as described herein may be installed in the vicinity of each other — to extract energy from and store energy in generally the same volume of the ground.

In one such embodiment, the sustainable energy generation module e.g. extracts energy from water - including domestic waste water, surface water and/or rain water. Using a heat exchange system, heat can relatively easily be extracted from such waters in ways known to one skilled in the art. It is however not a priori known when such energy sources become available — when rain water and domestic waste water are concerned — as their “supply” is (semi-)random. Again, such a resource to extract sustainable energy from is not per se available when heat is required to heat a building. Accordingly, one heat exchange system having the characteristics as described herein may be installed subsurface to store the energy generated with the sustainable energy generation module in a volume of the ground, whereas an adjacent heat exchange system having the characteristics as described herein may be installed in generally the same volume of the ground, to extract said heat when the inhabitants of the building require the heat. Advantageously, in this way the local ground / soil acts as an energy buffer, without requiring external isolation, without relying on (increasingly rare) metals and while obtaining a satisfactory efficiency. It is expected that a system as described in the above can provide a fully functional year round heating system, without the need for additional heat sources, in particular without needing gas to heat the building — assuming isolation of the building is on par and that the heating system of the building is adapted to allow so-called low-temperature heating (e.g. with water at 35 degrees Celsius instead of the more conventional 60 — 80 degrees Celsius).

In an embodiment of the present invention a length of the extension elements exceeds a diameter of the pipe, preferably has a length of 5 — 25 times a diameter of the pipe. For example, the extension elements may protrude from the pipe in a radial direction thereof, and may e.g. be bar-shaped, although other shapes for the extension elements are certainly conceivable. Optionally, the extension elements may be linked / interconnected with each other to form a grid

In an embodiment of the present invention, a thickness of the extension elements is smaller than a diameter of the pipe, preferably is in between 0.02 — 0.25 times a diameter of the pipe. Both the pipe and the extension elements may e.g. be circular, but this is not required per se.

In an embodiment of the present invention, a spacing between two neighbouring extension elements, when seen in a length direction of the pipe, exceeds a diameter of the pipe, e.g. is in between 2 — 25 times a diameter of the pipe.

These and other aspects of the present invention will be elucidated further in the below, with reference to the attached figures. In the figures, same or like elements are denominated with the same reference numerals.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 schematically shows a first embodiment of the geothermal heat exchange system according to the present invention — in isolation from the ground;

Figure 2A schematically shows a first alternative configuration of pipe and extension elements — when installed below the surface of the ground; and

Figure 2B schematically shows a second alternative configuration of pipe and extension elements.

DETAILED DESCRIPTION OF THE FIGURES

Starting with Figure 1 initially, shown is a first embodiment of the geothermal heat exchange system 1 according to the present invention. The system 1 includes a pump 31, for pumping a circulation fluid through a tube 11. The pump 31 can in principle be any type of pump, as long as it is capable of pumping the circulation fluid along the entire length of the pipe 11. Whereas the pipe 11 in an installed state will be below a surface of the ground, the pump 31 preferably remains above the ground, e.g. to allow easy inspection thereof. The pump 31 is preferably operable in two directions, to allow the fluid to be circulated in two directions.

The pipe 11 is hollow and receives a circulation fluid therein. The circulation fluid has a certain initial temperature when it enters the part of the pipe 11 that is installed below the ground, and has a different final temperature when it leaves the part of the pipe 11 that is installed below the ground. As such, the temperature of the circulation fluid is changed as it is transported through the ground, by exchanging heat with the ground.

On hot days, the circulation fluid may e.g. be heated — in parts of a circulation circuit not associated with the subsurface part thereof that is described herein — by cooling the hot components of an air conditioning system, or by being circulated through a building where it is heated by the air in the building. The circulation fluid enters the subsurface pipe 11 at a temperature higher than the ground layer around the pipe 11 and gives off this heat to the ground. The circulation fluid leaves the pipe 11 colder and can take up heat from the building and/or the air conditioning system again. Advantageously, by cooling the circulation fluid via a heat exchange with the relatively cold ground, this “waste” heat can be stored in the ground for re-use in colder times.

On cold days the reverse process may be applied, in which the circulation fluid extracts the same heat from the ground to heat the interior of a building. Such a heat extraction process includes heat exchangers and is known to one skilled in the art. As such, the “waste” heat that is available in the summer can be locally stored and re- used in the winter, in a highly efficient local process using the geothermal heat exchange system as disclosed herein. In this process, advantageously the available ground composition that is already available as a natural resource acts as an energy buffer.

It is noted that the heat stored in the energy buffer can alternatively come from many other sources, including the sun heating up the ground layer, heat extracted from the sewerage, and many other sources.

In exemplary embodiments a maximum temperature of the circulation fluid, in use, does not exceed 30 or 35 degrees Celsius. In principal a minimum temperature of the circulation fluid is not bound by a lower limit — although it is of course important that the circulation fluid does not freeze as then circulation is no longer possible. The minimum temperature the circulation fluid will experience, and thus the type of circulation fluid best used, will depend on the geographical location on Earth where the system is installed, and the depth at which it is installed.

For example the circulation fluid may be a liquid, more in particular water, glycol, brine and/or mixtures thereof. In principle any circulation fluid may however be used with the geothermal heat exchange system as disclosed herein. For example, the circulation may be a gas, or be in the gaseous state for a part of the circulation loop.

In embodiments, the geothermal heat exchange system 1 can be connected to a sustainable energy generation module, the heat exchange system e.g. being configured for storing the energy generated with the sustainable energy generation module locally, in the ground. In particular, thermal energy may be generated in a sustainable way from the sewerage system, in particular from domestic waste water and/or rain water.

The pipe 11, although shown here with a beginning and an end, will in reality typically be part of a closed-loop circulation system, wherein the fluid is pumped around in an endless piping system, through a heat exchanger, and typically will experience one or more step changes in pressure and be controlled by one or more control elements.

As the circulation fluid is received in the pipe 11, the circulation fluid is not in direct contact with the ground. Any exchange of heat between the circulation fluid and the ground is indirect. Although a direct heat transfer might be more efficient, in the present case such a direct heat transfer would remove any controllability and could lead to a contamination of the soil. Advantageously, these negative effects are mitigated by circulating the circulation fluid in pipe 11.

Attached to the pipe 11 are a number of solid extension elements 22, here mainly protruding downwards and thermally coupled to the side surface of the pipe 11.

Effectively, the solid extension elements 22 increase the heat exchange surface of the pipe 11. As explained in the above, it is via the pipe 11 that heat is exchanged between the ground, arranged at the outside of the pipe 11, and the circulation fluid, arranged at the inside of the pipe 11. In conventional heat exchange systems, this is a rather slow process, at least in part due to the low heat conductivity of the ground itself, especially when the ground is dry. The solid extension elements 22, when thermally coupled with the exterior of the pipe 11, will experience the same heat exchange effect as the pipe 11 material itself, thus aiding the exchange of heat between the circulation fluid and the ground and thereby increasing the effective heat exchange volume between the circulation fluid and the ground. This all is achieved without lengthening the flow path of the circulation fluid in the pipe 11, such that pump requirements and risks of leakages can be minimized.

Looking at Figure 1, extension elements 22 are shown that are curved around the pipe 11 and extend mainly downwards from the pipe 11. As will be clear from

Figures 2A and 2B, to be discussed in more detail in the below, this is not the only configuration in which the extension elements can be arranged. The extension elements are here generally U-shaped, and extend generally downwards from the pipe 11. Seen with respect to the centre axis of the pipe 11, the extension elements 22 extend radially away from the pipe 11. These radially extending extension elements 22 are interconnected by a pair of extension elements 21 that generally extends parallel to a centre axis of the pipe 11. The extension elements 21 are not directly attached to the pipe 11, but are nonetheless thermally coupled via extension elements 22. The longitudinally extending extension elements 21 provide some more rigidity to the individual radially extending extension elements 22 and also help to increase the effective heat exchange volume between the circulation fluid and the ground.

It is noted that although only a single pipe 11 is shown in Figure 1, a person skilled in the art understands that another pipe, with extension elements thermally coupled to it, may be arranged above, under, or to the side of shown pipe. The skilled person will also understand that although only a single row of longitudinally extending extension elements 21 is shown, these may be left out entirely, or more rows of longitudinally extending extension elements may be provided. The skilled person will further understand that the material of the pipe 11 and the extension elements 21, 22 is preferably chosen to allow an optimal heat exchange between circulation fluid and ground, while having a long lifetime and being cost-effective. An obvious example of such a material is steel, in particular stainless steel. Other materials may however also be chosen.

Shown in Figure 1 is that the length | of the radially extending extension elements 22 may be longer than the diameter of the pipe 11. For example, the length of the radially extending extension elements 22 may be 5 — 25 times the diameter D of the pipe 11. The length of the longitudinally extending extension elements 21 may in principle almost infinitely longer than the diameter D of the pipe 11, e.g. up to 100 or even 1000 times the diameter D of the pipe 11 — or even more.

Shown in Figure 1 is that the spacing s between two individual solid extension elements 22 may also be larger than a diameter D of the pipe 11, although this is in principle not required and the spacing s may be smaller than the diameter D of the pipe 11. In the shown embodiment however, the spacing s is approximately 4 times the pipe diameter D, the spacing s e.g. varying between 0,5 — 25 times the diameter

D of the pipe 11, in particular varying between 1 and 15 times the diameter D of the pipe 11, more in particular between 2 and 5 times the diameter D of the pipe 11.

Furthermore shown in Figure 1 is how the thickness t of the solid extension elements 21, 22 — through which no circulation fluid flows — is smaller than a diameter

D of the pipe 11 — through which circulation fluid does flow. For example, the thickness t of the extension elements 21, 22 may be about 0,02 — 0,25 times the diameter D of the pipe 11, here about 0,1 times said diameter D.

Shown in Figure 2A is a pipe 11 with solid extension elements 24 thermally coupled to it, the extension elements 24 arranged in a star-like pattern, all having approximately the same radial spacing from each other. The pipe 11 is installed below a surface of the ground G, as are all extension elements 24 such that from the surface, after installation, the components of the heat exchange system are not visible. In particular, a minimum distance d1 between the uppermost part of the heat exchange system and the surface may be at least 20 cm, e.g. at least 50 cm, preferably at least 1 meter. In particular, a maximum distance d2 between the lowermost part of the heat exchange system and the surface may be at most 15 meter, e.g. at most 12 meter, in particular at most 10 meter. Hence, the individual extension elements 24 as shown here may e.g. have a length of about 4 — 8 meter.

Turning now to Figure 2B, a further alternative configuration for the extension elements 25 is shown. Again, the extension elements 25 are thermally coupled with the pipe 11, to improve the heat exchange between the circulation fluid in the pipe 11 and the ground in which the heat exchange system 1 is to be installed. Here the extension elements 25 are mounted to sides of the pipe 11, extending in opposite radial direction with respect to a centre of the pipe 11.

Claims (11)

CONCLUSIONS A geothermal heat exchanger system (1), for exchanging heat between the ground (G) and a circulating fluid, the system comprising: - a hollow tube (11), installed in the ground (G) under a surface thereof, for receiving a circulating fluid therein, the tube (11) preventing direct contact between the fluid and the ground (G); - a pump (31), for pumping the circulating fluid through the tube (11); characterized by : - a plurality of fixed extension members (21, 22, 24, 25) thermally coupled to an outer surface of the hollow tube (11) and extending outwardly from the tube (11), the extension members (21, 22, 24, 25) aid in the exchange of heat between the circulating fluid and the ground (G), thereby increasing the effective heat exchange volume between the circulating fluid and the ground (G). The geothermal heat exchanger system according to claim 1, wherein a maximum depth (d2) of the system is 15 metres, preferably 12 metres, more preferably 10 metres. The geothermal heat exchanger system according to any one of the preceding claims, wherein a minimum depth (d1) of the system is 20 cm, preferably 50 cm, more preferably 100 cm. The geothermal heat exchanger system according to any of the preceding claims, wherein, in use, a maximum temperature of the circulating fluid is about 30°C. The geothermal heat exchanger system according to any one of the preceding claims, wherein, in use, the circulating fluid is adapted to extract heat from the ground (G). The geothermal heat exchanger system according to any of the preceding claims, wherein, in use, the circulating fluid is adapted to store heat in the ground (G). The geothermal heat exchanger system according to claim 6, wherein the heat exchanger system (1) is connected to a renewable energy generation module, wherein the heat exchanger system (1) is arranged for storing energy generated by the renewable energy in the ground (G). - generation module. 8. The geothermal heat exchanger system according to claim 7, wherein the sustainable energy generation module extracts energy from residual heat of e.g. domestic wastewater, spring water or rainwater. The geothermal heat exchanger system according to any one of the preceding claims, wherein a length (I) of the extension elements (21, 22, 24, 25) exceeds a diameter (D) of the tube (11), preferably a length (I) has from 5 — 25 times the diameter (D) of the tube (11). The geothermal heat exchanger system according to any one of the preceding claims, wherein a thickness (t) of the extension elements (21, 22, 24, 25) is smaller than a diameter (D) of the tube (11), preferably between 0, 02 — 0.25 times a diameter (D) of the tube (21, 22, 24, 25). The geothermal heat exchanger system according to any one of the preceding claims, wherein a space (s) between two adjacent extension elements (21, 22, 24, 25) exceeds a diameter (D) of the tube (11), e.g. is between 2 — 25 times a diameter (D) of the tube (11).