GB2543527A

GB2543527A - A thermal ground loop installation device

Info

Publication number: GB2543527A
Application number: GB1518572.1A
Authority: GB
Inventors: Robin Bolwell Michael
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-10-20
Filing date: 2015-10-20
Publication date: 2017-04-26
Also published as: GB201518572D0

Abstract

A geothermal heat-pump system or solar thermal system can be installed using a spearhead -shaped drill bit 31. A percussion hammer may strike a shaft 32 to create a borehole. Pipes 35, which may be a single, continuous length of flexible tubing, can be attached to the spearhead, to be buried in the borehole. A resilient compliant coupling may attach pipes 35 to the spearhead. The spearhead may have an internal void for retention of the thermal loop 35. A third pipe (28, fig 3) may provide a thermal barrier between the first and second pipes 35, possibly backfilling the borehole with bentonite grout. A bulbous channel forming feature 39 may form a larger channel in the soil to prevent the driving tube from binding during insertion. The sacrificial spearhead 31 may be detachable from the shaft 32 using a releasable coupling 33. A series of ground loops may be installed in a radial formation (figures 8 and 9). Pipes 35 can act as a thermal transfer ground-loop for a ground source heat-pump system or a solar thermal system, e.g connecting a heat-exchange fluid to a heat pump.

Description

A Thermal Exchange Ground Loop Installation Device

Field of the Invention

This patent relates to a device and a method for the installation of thermal transport fluid pipes into the ground. Such pipes are typically used in combination with a heat pump as a means of pumping heat between an area of land and a building for space heating, water heating or for space cooling, depending on the operating mode of the heat pump. It also relates to the use of solar panels, both thermal and hybrid photovoltaic / thermal panels, where heat generated by the panels is transferred to the ground during the warmer months for utilisation by a ground coupled heat pump in the cooler months to heat a building.

Background of the Invention

In the quest for a sustainable, low carbon and energy efficient heating system, ground source heat pumps have proved to be an effective space and water heating solution. However, their popularity has been limited by the cost and disruption involved in installing the ground fluid loop. In a typical installation for a domestic property, a length of pipe is embedded in the garden and filled with a thermal transport fluid. Typically a solution of water and antifreeze is used in a closed loop system, where a heat pump chills the solution and a circulation pump moves the chilled solution through the underground pipe loop, thereby allowing heat to be drawn from the ground. It is necessary to embed around 100 to 300 metres length of pipe into the soil to extract enough heat for a typical dwelling. Where space allows, this length of pipework can be buried by excavating a large trench, laying a length of coiled pipe and backfilling the excavation. This method causes the greatest disruption to the garden and many properties do not have sufficient garden area to adequately heat the property.

Where outside space is limited, a set of vertical boreholes may be drilled to a depth of around 100 metres each, using specialised drilling equipment. A pair of parallel pipes joined together at one end by a compact 'U' bend is then inserted into the borehole. The drawbacks with this approach are that there is very little solar gain due to the depth of the borehole and the drilling operation is very costly. The lack of solar gain can result in 'ground freeze' over a number of years where the ground is primarily used as a heat source, rather than as an inter-seasonal thermal store. This results in a decrease in heat pump efficiency over time

Patent US 2012/0097448 describes a mechanical mole that can bore to a length of up to 100 metres, taking the two loop pipes with it. When the required depth is reached, the mole tunnelling mechanism is de-activated and a valve activates within the mole to form the 'U' bend loop, so connecting the two pipes. The mechanical complexity of the mole makes these devices fairly costly and this cost is left buried in the ground. Despite this, there is generally a cost benefit to using moles rather than drilling equipment. The use of moles also allows a ground loop to be installed in places where a drilling machine cannot be used, due to a restricted access, adverse slope or unstable ground conditions. The cost of the moles can make the installation of a ground loop uneconomic where a large number of shallow bores are required as in, for example a thermal bank for inter-seasonal heat storage.

Summary of the Invention

According to a first aspect of the present invention, there is provided an apparatus for inserting a thermal exchange ground loop for a ground coupled heat pump or a thermal storage system, comprising; a thermal ground spear with a spearhead that is suitably profiled to form a borehole wide enough to accommodate a pre-formed 'U' bend with a first and a second thermal exchange pipe, together with a first spear shaft, with a detachable first coupling to fasten the spearhead to the shaft; and a second coupling for the attachment of a ground loop with a pre-formed 'U' bend to the spearhead. The second coupling may incorporate a resilient compliant element to reduce shock transmission from the spearhead to the 'U' bend, thus avoiding damage to the pre-formed 'Ll' bend. In the art, it is common practise to form the ground loop from a first and a second High Density Polyethylene (HDPE) pipe, the first and second pipes being securely bonded to a pre-formed 'Ll' bend by a thermal fusion method. Typically in the art, the pre-formed 'U' bend will be provided with an eyelet below the base of the 'U', from which weights may be hung to assist the installation of the ground loop to a borehole.

According to a second aspect of the present invention, there is provided an apparatus for inserting a thermal exchange ground loop for a ground coupled heat pump or a thermal storage system, comprising; a durable, suitably profiled ground spear with an integral 180 degree 'U' bend in the spearhead, a first thermal transfer pipe fluidly coupled to a first end of the spearhead 'U' bend to convey a thermal transport fluid into the ground, a second thermal transfer pipe fluidly coupled to a second end of the spearhead 'U' bend to convey the thermal transport fluid out of the ground and a first detachable spear shaft to transmit the impact from a percussion tool to the spearhead. There is also provision for attaching an optional third pipe to the spearhead which may be used to provide a thermal break between the first and second pipes and may also be used for the injection of a thermally conductive grout.

This apparatus provides a very low cost and simple method for installing a thermal exchange ground loop while also providing a means for enhancing the performance of the ground loop by installing a thermal break between the first and second thermal transfer pipes to lessen the thermal short circuit that is normally present in a borehole ground loop installation. This allows a reduction in the ground loop length for a given system performance. The spearhead has a robust outer profile that allows it to form a borehole as the impact transmitted to the spear from a first spear shaft drives the spearhead through the soil by displacing and compacting the soil. The first and second ground loop pipes are securely fastened to the spearhead by a jointing method that ensures the ground loop will be durable and leak proof for the service life of the installation. As the spear is driven through the soil, the first and second loop pipes and an optional third pipe that may be used as a thermal break or a grout pipe are drawn into the channel formed by the spearhead. The spear may be driven into the ground by the use of any suitable percussion tool, such as a post hammer or a pneumatic, hydraulic or electric percussion tool with a suitable attachment that connects the tool to the first spear shaft, allowing the hammer action to be transmitted into the shaft. The shaft may be of any suitable profile that fits within the third pipe and effectively transmits the impact from the percussion tool to the spearhead. As the first percussion shaft follows the spear into the ground, the shaft may be extended by coupling a second spear shaft and connecting piece to the first shaft. As the second shaft travels into the ground, a third shaft may be coupled to the second shaft. Further extension shafts may be added as required as the spear travels further into the ground.

The spear shafts are preferably of a convenient length that allows the spear to be driven in with a hand held impact tool, without standing on a stool or similar and without an excessive number of couplings in the shaft. Each coupling of each extension shaft allows the percussion action to be transmitted through the shafts and couplings to the spearhead without damage to the shafts or couplings. Each coupling should lock together to allow withdrawal of all the shafts once the spearhead has been driven in to the required depth. The spearhead is connected to the first spear shaft by a detachable coupling that transmits the percussion impact from the first shaft to the spearhead but allows the shaft to be separated from the spearhead once the spearhead and ground loop have been driven in to the required depth. The percussion rod assembly can be withdrawn by simply lifting or pulling it out of the borehole. If necessary, a slide hammer may be used to uncouple the shaft from the spear. Once removed from the borehole, the spear shaft assembly may be disassembled and re-used.

According to a third aspect of the present invention, there is provided an apparatus for inserting a thermal exchange ground loop for a ground coupled heat pump or a solar thermal system, comprising; a durable, suitably profiled spearhead with a detachable coupling to a spear shaft and an internal void to accommodate a flexible fluid transport pipe and a pipe retaining insert. At the point of installation, a suitable length of flexible thermal transfer fluid pipe may have a 180° 'U' bend formed at the approximate centre of the length of pipe, using a pipe retaining insert as a pipe former to ensure the minimum bending radius of the pipe is not exceeded. The pipe length prior to bending should exceed twice the desired ground loop depth plus twice the distance to the installation it is to be connected to. This installation method allows the ground loop pipe to be installed in a continuous length with no pipe joins below ground and therefore, no risk of underground joint failure. The installed ground loop will have a first and a second pipe tails for connection to the heat exchange circuit of a heat pump or solar heat system after the ground spear has been driven into the soil to the required depth.

Preferably, the ground loop pipe diameter is small, so as to permit the formation of a small 'U' bend, thereby reducing the ground facing profile of the spearhead. This allows the ground loop and spear to be driven into the ground using a hand held percussion tool and a set of spear shafts as described hereinbefore. There is also provision for installing an optional third pipe which may be used to provide a thermal break between the first and second pipes and may also be used for the injection of a thermally conductive grout.

In all aspects of the present invention, preferably the first and second thermal exchange pipes or pipe tails may be connected to a flow and a return manifold.

Further preferably, an array of thermal exchange ground loops may be installed at an inclined angle relative to horizontal and in a radial formation, whereby the lower blind ends of the ground loops are furthest from the centre of the radial formation. This allows the length of the first and second pipe tails from each ground loop to be kept to a minimum and to be of similar length when connected to the flow and return manifolds where they are located near or at the centre of the radial formation. This arrangement ensures a broadly equal distribution of thermal transport fluid to each and every ground loop in the radial formation and also minimises the length of interconnecting pipe and the resistance to the flow of thermal transport fluid.

Brief description of the drawings:

Figure 1 shows a first preferred form of the invention 10, which is comprised of a spearhead 11, a spear shaft 12, a shaft coupling 13, a thermal ground loop 14, comprised of; a first pipe 15 and a second pipe 16, a fluid 'U' bend 17 and a loop installation eyelet 18.

Figure 2 shows a plan view of the apparatus shown in figure 1. The same numbers refer to the same parts as in figure 1.

Figure 3 shows a second preferred form of the invention 20, comprised of a spearhead 21, a spear shaft 22, a shaft coupling 23, a first pipe 25, a second pipe 26, a 'U' bend 27 and a third pipe 28.

Figure 4 shows a plan view of the apparatus shown in figure 3. The same numbers refer to the same parts as in figure 3.

Figure 5 shows a third preferred form of the invention 30, comprised of a spearhead 31, a spear shaft 32, a shaft coupling 33, a first pipe 35 having first and second pipe tails and a 'Ll' bend, a 'U' bend retaining insert 34 and a third pipe fitting device 39.

Figure 6 shows a section view of the apparatus shown in figure 5 along the line X - X'. The same numbers are used for the same parts as in figure 5.

Figure 7 shows a section view of the apparatus shown in figure 5 along the line Y - Y'. The same numbers are used for the same parts as in figure 5.

Detailed description of the preferred embodiments:

Referring to figure 1 of the drawings, there is shown a first preferred form of the invention 10, which is comprised of a spearhead 11, a spear shaft 12 and a shaft coupling 13. The spear shaft 12 has a first end and a second end and is of sufficient strength and rigidity to transmit an impact from a percussion device striking the second end of the shaft to the spearhead 11 attached to the first end of the shaft by the coupling 13. When the point of the spearhead 11 is placed on soil or inserted into a pilot hole in the soil, it will travel into the soil as the action of the percussion device causes the spearhead to displace and compact the soil, thereby forming a borehole that is large enough to accommodate a thermal transfer ground loop 14. The thermal loop 14 is a device commonly used in the art for heat exchange in a borehole and is outlined in broken lines. The thermal loop comprises a first pipe 15 to convey thermal exchange fluid from a heat pump or solar thermal system into the ground, a second pipe 16 to convey thermal exchange fluid out of the ground and a pre-formed 'U' shaped channel 17, securely coupling the first and second pipes. There is typically a hole or eyelet 18 through the lowest point on the thermal loop to hang a weight from. This may be used to couple the thermal loop to the spear so that the thermal loop is drawn into the borehole formed by the spear.

Preferably, the spearhead 11 has an internal void for the insertion and retention of the thermal loop 14. The thermal loop may be retained within or behind the spearhead by a resilient compliant coupling means between the spear and the thermal loop to avoid the risk of damage to the thermal loop due to shock transmission from the percussion device.

Further preferably, the shaft coupling 13 securing the spearhead 11 to the spear shaft 12 is a releasable coupling that allows the spear shaft to be detached from the spearhead and withdrawn from the borehole for re-use after installation of the thermal loop.

Figure 2 shows a section view of the apparatus of figure 1, along the plane Y - Y', looking toward the 'U' bend. The same numbers are used for the same parts as in figure 1. The cross section profile of the spear shaft 12 is shown as an 'FI' section to fit between the first and second pipes as the pipes may be close together, depending on the design of the pre-fabricated 'U' bend.

Referring to figure 3 of the drawings, there is shown a second preferred form of the invention 20, which is comprised of a spearhead 21, a spear shaft 22 and a releasable shaft coupling 23. The spearhead 21 has an integral 'U' shaped fluid channel 27 and provision for the mechanically secure and fluid tight connection of a first thermal pipe 25 and a second thermal pipe 26 as well as provision for the connection of a third pipe 28 that may be used as a thermal barrier between the first and the second thermal pies or may be used to backfill the borehole with a material to improve the thermal contact of the first and second pipes with the ground, such as bentonite, once the thermal loop has reached the required depth.

Figure 4 shows a section view of the apparatus 20 of figure 3, along the plane Y - Y', looking toward the 'U' bend. The same numbers are used for the same parts as in figure 3. The cross section profile of the spear shaft 22 is shown as a round section tube, which is located coaxially within the third pipe 28.

Referring to figure 5 of the drawings, there is shown a thermal ground spear 30, which is comprised of a spearhead 31, a spear shaft 32 and a releasable coupling 33 to secure a first end of the spear shaft to the spearhead. The spearhead has a cavity to accommodate a thermal exchange fluid pipe 35 and a pipe retainer 34. The pipe 35 is preferably a single, continuous length of flexible tube that is formed into a 'U' shaped loop by bending it around the pipe retaining insert 34, prior to insertion of the pipe 35 and retainer 34 to the spearhead as part of the thermal loop on-site installation process. The pipe 35 is made of a corrosion resistant and durable material and is secured within the spearhead by the pipe retainer 34 such that the pipe is protected from damage or distortion as the spearhead 31 is driven into the ground by the percussion device acting on a second end of the spear shaft. The use of a single, continuous length of pipe avoids the risk of a thermal fluid leak through joint failure. The size of the spearhead is determined by the diameter and minimum bending radius of the thermal transport tube. Preferably, the tube diameter should be minimised to keep the overall size of the spearhead small while still achieving sufficient thermal fluid throughput for efficient heat exchange. The spearhead 31 incorporates a channel forming feature 39. This acts on the soil to create an enlarged bore to provide a clearance in the borehole around the spear shaft 32. This can also provide additional strength to the spearhead 31 as well as facilitating withdrawal of the spear shaft from the borehole after installation of the thermal loop.

Figure 6 shows a section view of figure 1 through the line X - X'. The same numbers refer to the same parts as in figure 1. The pipe retainer 34 is shown as solid but could also be partly hollow. Preferably the retainer 34 is made of a material that will retain its integrity and form during installation of the thermal ground loop and for the service life of the system. Further preferably, all parts of the spearhead will be resistant to rot, corrosion, crushing and the extremes of temperature likely to be seen in service. The channel forming feature 39 forms a channel in the soil to prevent the driving tube from binding in the soil during insertion. This channel may also be used to fit a tube to aid backfilling of the ground loop with thermally conductive grout to improve thermal contact between the thermal transport fluid and the ground. The tube could also contain insulation so as to reduce thermal conduction between the thermal fluid flow and return tubes. This reduces the thermal short circuit path. The tube may also combine the roles of a thermal break and grout backfilling by suitable design, for example a coaxial design comprising a grout filling tube within an insulating sheath.

Figure 7 shows a section view of figure 1 through the line Y - Y'. The same numbers refer to the same parts as in figure 5. The spear driving tube 32 shown in dashed line is fitted over the coupling tongue which is not visible in this figure. The tube is of square section but may take any form that provides the necessary stiffness.

The ground spear and thermal fluid loop may be driven vertically into the ground. To obtain the required thermal exchange length, a series of ground loops may be installed in an array of regularly spaced loops, with the flow and return tubes connected to flow and return manifolds.

Referring to figure 8, the thermal ground spear 30 may be installed at an inclined angle. A shallow pit 40 may be used as an insertion point for one or more thermal spears as well as providing a location for a pair of flow and return manifolds. This can allow greater utilisation of solar gain as a greater length of the loop is close to the ground surface. Where the thermal loop is installed beneath a building as part of a solar thermal bank installation, the resultant higher ground temperature reduces the requirement to thermally insulate the internal floors from the ground. It also utilises some of the natural heat loss from the thermal bank for building space heating.

Figure 9 shows a radial form of thermal spear installation. A shallow pit 40 may be dug as a starting point for the array and also provide a location for the flow and return manifolds. This minimises the amount of groundwork and the length of thermal loop interconnecting pipework required. In figures 8 and 9, one of each pair of manifolds and one of each pair of thermal loop pipe tails is shown as broken lines for clarity.

The ground spear method of installing ground loops is well suited to the construction of an earth thermal bank or inter-seasonal thermal store, where heat from a solar thermal or solar hybrid panel is stored during the warmer months for utilisation during the winter months. A radial array of ground loops may be installed below the property to be heated, avoiding the need for an insulation blanket at ground level to keep the heat in. Any escaping heat will reach floor level of the property weeks or months after being piped into the ground depending on the soil type and depth of the pipes. This escaped heat will contribute to keeping the property warm in the autumn and winter months, even while heat is being extracted from the thermal store using a heat pump.

The concepts described in this patent are applicable to any of the preferred embodiments. It will be appreciated by those skilled in the art that the thermal ground spear concept and installation method may take a variety of forms without deviating from the principles described in the patent.

Claims

A Thermal Exchange Ground Loop Installation Device Claims:

1. An apparatus for facilitating the installation of a thermal transfer ground-loop for a ground source heat-pump system or a solar thermal system, comprising: a spearhead with a first spear shaft, the shaft having a first and a second end, the first end being fastened to the spearhead by a first coupling means so as to transmit the impact from a percussion tool striking the second end of the shaft to the spearhead, causing the spearhead to displace and compact the soil, thereby forming a borehole that can accommodate a thermal transfer ground loop.

2. The apparatus of claim 1, where the spearhead has a second coupling means for attaching a preformed 'U' bend of a thermal transfer ground loop, thus causing the ground loop to be drawn into the borehole created by the spearhead as the spear is driven into the ground.

3. The apparatus of claim 2, where the second coupling means incorporates a resilient compliant coupling to the pre-formed 'U' bend.

4. An apparatus for inserting a thermal transfer ground-loop for a ground source heat-pump system or a solar thermal system, comprising: a thermal ground spear, having a spearhead and a first spear shaft; a first fluid pipe, fluidly coupled to the spearhead, for conveying a heat-exchange fluid from the heat-pump or solar thermal system into the ground; a second fluid pipe, fluidly coupled to the spearhead, for returning the heat-exchange fluid to the heat-pump or solar thermal system; and a first spear shaft with a first and a second end, the first end being fastened to the spearhead by a first coupling means so as to transmit the impact from a percussion tool striking the second end of the shaft to the spearhead, thereby driving the spear and thermal transfer loop into the ground.

5. The apparatus of claim 4, where the first and second pipes are connected to a 'U' bend fluid passage that is integral with the spearhead.

6. An apparatus for inserting a thermal transfer ground-loop for a ground source heat-pump system or a solar thermal system, comprising; a thermal ground spear having a spearhead and a first spear shaft, with a cavity within the spearhead for the insertion of a 'U' bend of a thermal transfer fluid pipe and a pipe retaining insert for the formation and retention of a 'U' bend in said pipe within the spearhead cavity, thus providing the ground spear with a first pipe for conveying a heat-exchange fluid from the heat-pump or solar thermal system into the ground, and a second pipe for returning the heat-exchange fluid to the heat-pump or solar thermal system; and a first spear shaft with a first end and a second end, the first end being fastened to the spearhead by a first coupling means so as to transmit the impact from a percussion tool striking the second end of the shaft to the spearhead, thereby driving the spear and thermal transfer loop into the ground.

7. The apparatus described in any previous claim, wherein the first coupling means is a releasable coupling that allows the first spear shaft to be uncoupled from the spearhead and withdrawn from the borehole after installation of the ground loop.

8. The apparatus described in any previous claim, wherein the second end of the first spear shaft may be coupled to a first end of a second spear shaft by a coupling that allows the first and second spear shafts and any number of subsequent shafts to be withdrawn from the spearhead and removed from the borehole after installation of the ground loop.

9. The apparatus described in any previous claim, wherein a third pipe may be attached to the spearhead between the first and second pipes prior to insertion of the spear into the ground, such that the third pipe is drawn into the ground channel formed by the spear, alongside and between the first and second pipes.

10. The apparatus of claim 9, whereby the third pipe provides a thermal barrier between the first and second pipes.

11. The apparatus of claim 9, whereby the third pipe facilitates the introduction of bentonite or a similar thermally conductive backfill material into the ground loop borehole.

12. The apparatus of claim 9, whereby the third pipe both provides a thermal barrier between the first and second pipes and facilitates the introduction of bentonite or a similar thermally conductive backfill material into the ground loop borehole.

13. An installation method for the apparatus in any previous claim, whereby two or more thermal transfer bores are installed at an inclined angle, having the lower blind ends of the boreholes furthest from each other and the open ends of the boreholes closest to each other, the boreholes being arranged in a fan or a radial formation to facilitate the connection of each and every first pipe to a flow manifold and each and every second pipe to a return manifold, ensuring a broadly equal distribution of thermal transfer fluid flow to each first pipe in a thermal transfer borehole.

14. An apparatus substantially as hereinbefore described with reference to the accompanying drawings.