GB2436582A

GB2436582A - Geothermal energy pile / foundation

Info

Publication number: GB2436582A
Application number: GB0606293A
Authority: GB
Inventors: Anthony William Amis
Original assignee: Cementation Foundations Skanska Ltd
Current assignee: Cementation Skanska Ltd
Priority date: 2006-03-29
Filing date: 2006-03-29
Publication date: 2007-10-03
Also published as: GB0606293D0; IE20070192A1

Abstract

A technique for installing geothermal pipe-work 7 in foundation elements such as piles involves the use of a coupling means 11 to couple said pipe-work 7 to a longitudinal installation member 8 . This allows said pipe-work 7 to be plunged into wet concrete so as to install the pipe-work 7 to a required depth upon which point the installation member 8 may be decoupled and retrieved. The technique is said to be useful in forming geothermal piles by continuous flight auger techniques.

Description

I

Geothermal Foundations The present invention relates to a geothermal system which utilises a foundation element, such as a concrete pile or diaphragm wall panel, as a means to facilitate the transportation and/or storage of geothermal energy for use in heating or cooling a building.

Geothermal systems which extract energy from the ground for heating or cooling the structure above, are known. The presence of such systems in many types of domestic and industrial structures is becoming more common due to the fact that geothermal systems offer an economic and environmentally friendly means to heat or cool a building. Indeed, calculations show that up to 50kW of equivalent cooling capacity can be generated using a single 1kW pump and that annual heating costs could be cut by up to two-thirds. The actual efficiency of the system will, of course, be dependent on the properties of the foundation element, the design of the above-ground structure and the conditions of the ground itself.

It is also known to utilise the foundation support structure of a building as a means to facilitate the transportation and storage of geothermal energy. In this respect, it is usual for a concrete foundation structure, such as a pile, to be provided with a reinforcement cage. It is therefore convenient to fit pipes, which act as a fluid circulation means, to the reinforcement cages to thereby construct a geothermal system comprising a plurality of pipes through which heat energy can be transported from the ground to, for example, a network of piping embedded in the floors and/or walls of the superstructure. In effect, the entire network of pipes works as a heat exchanger.

Most previous methods of installing a geothermal system as a part of a foundation structure have involved the construction of the so-called "energy piles", by means of rotary bored piling techniques. According to these methods, a bore hole is formed in the ground and a temporary casing is inserted which acts to seal the pile bore from water-logged strata or to support an unstable ground. A reinforcing cage having a fluid circulation means such as a pipe, for connection to a greater fluid circulation network which comprises, or forms part of, a geothermal system, is then placed in the bore and concrete is poured to the required level. The temporary casing can be withdrawn or left in situ.

However, rotary bored piling techniques are often unsuitable for particular construction projects where ground conditions are found to be too unstable or where the depth of the required pile is substantial. A further disadvantage of rotary bored techniques is that the required temporary casings and drilling fluids add complexity and considerable additional cost to the piling operation.

Continuous Flight Auger (CFA) techniques offer several important benefits over rotary bored techniques. Importantly, CFA piling is suitable for most construction projects and causes minimum disturbance to the surrounding strata which may be unstable. A CFA pile is formed by a hollow stemmed continuous flight auger which is rotated into the ground to the required depth. Concrete is then pumped down the stem of the auger as the tool is gradually withdrawn. An important benefit of CFA piling is that no temporary casing is required since the bore is either supported by the CFA tool itself or by concrete which replaces the tool as it is withdrawn. A reinforcement cage is then plunged into the wet concrete as quickly as possible. Due to the way in which the cage must necessarily be plunged into wet concrete, the depth which may be reached by the reinforcement cage is restricted.

Most CFA piles are provided with a nominal reinforcement cage length of between 4 to 6m. However, in order to maximise potential sources of geothermal energy, which may be natural or man-made, it is necessary to place fluid circulation means to the full depth, or near to the full depth, of the pile. In many instances there is therefore a need to install a fluid circulation means to a depth which is below the traditional 4-6m length of the cage. As such, if an energy pile is to be installed which may successfully tap into the source of geothermal energy, there is a need for the reinforcement cage to be plunged to a greater depth than is usually possible by CFA piling techniques in order to carry the fluid circulation means to the required depth. It is this feature of CFA piling which has deterred piling operators from using CFA techniques for the construction of an energy pile. Furthermore, there are concerns that the pipe-work connected to the cage which is intended to form part of a proposed geothermal system, may become damaged during the action of plunging the cage into the wet concrete. Such damage potentially being caused as a consequence of the attachment of the fluid circulation means thereto, or as a consequence of attempting to install the cage to greater depths than the cage can safely withstand without damage.

In order to alleviate these problems, it is known for the following principals to be adopted when reinforcement cages having geothermal pipe-work attached thereto must be plunged into the wet concrete: I) Cages should be as heavy and rigid as possible; ii) There should be sufficient space between reinforcement bars in order to allow concrete to flow more readily past the bars as the cage is plunged; and iii) The use of couplers as an alternative to splice joints is recommended and cages should not be spliced as part of the cage installation procedure.

The above measures add considerably to the overall cost of pile construction, especially in circumstances where only a nominal reinforcement cage is necessary.

There is therefore a need to find an alternative, more efficient and cost-effective, way of alleviating the problems associated with the use of CFA piling techniques for the installation of an energy pile. There is also a more general need to find an alternative method of installing geothermal piping in a volume of wet concrete which has been poured or pumped into a hole in the ground. It should be appreciated that the term "energy pile" within the context of the present application should be interpreted as meaning any foundation element (which may be a concrete column or panel etc) which is provided with a fluid circulation means to facilitate the transportation of thermal energy along a part of the foundation element. Usually, the thermal energy will be transported by means of pipe-work which, when the element is installed in the ground, will generally extend from an upper position to a lower position and back again.

According to a first aspect of the present invention, there is provided a method of installing a fluid circulation means in a foundation element, the fluid circulation means being for connection to a fluid network, the method comprising the steps of: i) coupling the fluid circulation means to an installation member by means of a coupling means; and ii) lowering the installation member having the fluid circulation means coupled thereto, to a predetermined depth, into a volume of wet concrete in the ground.

An advantage of embodiments of the present invention is that attachment to a reinforcement cage, which is intended to form part of the resultant foundation element, is not necessary. Therefore, the depth limitations associated with the use of a reinforcement cage to locate a fluid circulation means in a volume of wet concrete are alleviated. Moreover, since the installation member is provided specifically for the purposes of installing the fluid circulation means, methods of installing an energy pile which utilise CFA techniques and require the use of a reinforcement cage to be plunged into the wet concrete do not suffer from the risk that the cage may become damaged. It is envisaged that the installation member could be sacrificial, so that once the fluid circulation means has been installed to the required depth, the installation means could be left within the setting concrete. In such an embodiment, it is envisaged that the installation member will thereby provide some reinforcement to the foundation element. Alternatively, according to a more cost effective embodiment, the installation member may be de-coupled from the fluid circulation means and withdrawn from the wet concrete for possible future use. Thus, the coupling means is advantageously operable to release the installation member so that it may be withdrawn from the volume of wet concrete leaving the fluid circulation means and the coupling means behind. Alternatively, the coupling means is operable to release the fluid circulation means so that both the installation member and the coupling means can be withdrawn from the ground. An advantage of these embodiments is that the installation member (and the coupling means) can be re-used and the overall cost of the operation is therefore reduced.

Methods of the present invention can be advantageously employed in conjunction with other piling methods to construct a series of foundation elements wherein one in a particular number of elements is provided with a fluid circulation means for forming part of a geothermal system. For example, it is envisaged that one in every four piles installed in a pile wall may be energy piles formed according to embodiments of the present invention.

Preferably, the installation member comprises a longitudinal bar, such as a so-called "rider bar", which will benefit from minimal resistance by the wet concrete as the member is lowered into the ground. The installation member may be lowered into the ground by means of a downward crowd force or a vibrational force applied to the upper end of the member.

The fluid circulation means may comprise one or more pipes which are preferably shaped so as to facilitate fluid flow in a first direction and a second direction. Where the first and second directions are substantially opposite, as will usually be the case where fluid (which may be a gas or a liquid) must be circulated along the length of a pile or diaphragm wall installed vertically in the ground, this may be achieved by a pipe which is generally "U" shaped at one end. Alternatively, the fluid circulation means may comprises one or more pairs of pipes, which are operable to be in fluid communication, a first one of a pair of pipes being for facilitating fluid flow in a first direction, the other pipe of the pair of pipes being for fluid flow in a second direction. When the fluid circulation means is to be installed in a longitudinal pile or wall panel, the first and second directions of fluid flow will be substantially along the length of the pile.

Preferably, the fluid circulation means is provided with one or more valves which are operable to control fluid flow within the fluid circulation means.

According to a second aspect of the present invention there is provided a coupling means comprising fluid circulation attachment means for attaching a fluid circulation means thereto, and an installation member attachment means for attaching an installation member thereto.

Preferably, the installation member attachment means is operable to allow the installation member to be releasably attached to the coupling means. Preferably, the installation member attachment means allows the installation member to be released from attachment to the coupling means upon rotation of the installation member. For example, it is envisaged that the installation member attachment means may comprise a bayonet type fitting. The installation member could then be provided with one or more lugs which are engageable with corresponding slots provided on the bayonet fitting, the installation member being coupled to the fluid circulation means by rotation of the installation member in a first direction, and being releasable by rotation of the installation member in a second direction.

Embodiments of the present invention may be usefully employed in conjunction with soil displacement techniques in a similar manner to CFA, in that reinforcement and geothermal piping is plunged into wet concrete. Embodiments may also be used in conjunction with rotary bored piling techniques to place geothermal pipes to the full pile depth prior to concreting. This is particularly advantageous where the length of the reinforcement cage to be placed at the top of the pile is limited to 6m.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 shows a coupling means according to an embodiment of the present invention in use; and Figure 2 shows the coupling means of Figure 2, in use, from the side; Figure 3 shows plan and elevation views of the coupling means of Figure 2; Figure 4 shows a coupling means according to another embodiment of the present invention; Figure 1 shows a coupling plate 11 of a coupling means, generally designated 10, having a bayonet type attachment means 9. The attachment means is suitable for receiving one end of an installation member which comprises a reinforcement bar 8, also known as a "thermal rider bar". In this particular example, the attachment means is welded to the top of the plate. Fluid circulation means, comprising a pipe 7, is attached to the coupling means by means of two holes 3a and 3b (shown more clearly in Figure 3). The pipe 7 is threaded through the holes 3a and 3b and is secured in place as a result of the bend in the pipe. Figure 2 shows the coupling means from the side in order to illustrate the bayonet type fitting of the installation member attachment means 9. Specifically, the installation member 8, or thermal rider bar, is provided with a pair of diametrically opposed lugs which cooperate with the slot 5 provided on the bayonet attachment means 9. The installation member is coupled to the fluid circulation means by rotation of the installation member in a first direction, and is releasable by rotation of the installation member in a second, substantially opposite, direction.

It will be appreciated that the coupling means may be formed of metal or plastic or any other suitable material. Furthermore, although not shown in the accompanying drawings, it is convenient to tie the pipe 7 to the reinforcement bar at regular intervals therealong. The ties may be plastic cable ties or similar and can be removed one by one as the reinforcement bar is plunged into the concrete.

A method of constructing an energy pile according to an embodiment of the present invention comprises: i) A continuous flight auger is applied to the ground and is caused to penetrate the ground to a required depth in order to form a bore hole; ii) concrete is pumped to the base of the bore as the tool is gradually withdrawn to ground level; iii) the reinforcement bar having a fluid circulation means attached thereto by means of a coupling means embodying the present invention, is plunged into the volume of wet concrete to a required depth, removing any tie clips or similar; iv) the reinforcement bar is rotated approximately 45 degrees in a clockwise direction to release the bar from the coupling means; v) the reinforcement bar is lifted from the volume of concrete taking care to check for any movement in the fluid circulation means; and vi) a socalled "flush test" is performed to the circulation means in order to verify that it is in working condition.

The fluid circulation means is provided with suitable means which render it suitable for connection to a fluid circulation network of the structure. For example, it is usual for a fluid circulation pipe installed in a given pile or wall panel to be connected to other fluid circulation pipes of the network using electrostatically welded joints. Thus, a fluid circulation network is created that circulates fluid to a heat pump for the purposes of either heating or cooling a building, and then circulates it back to the pile or panel.

The above sequence can be performed to install energy piles to significant depths such as 30 to 70 m.

According to a preferred embodiment, the circulation means is filled with water during installation to prevent floatation of the pipe. The weight of the installation member is selected bearing in mind the speed of operation needed and depth required for the installation of the fluid circulation means whilst concrete remains sufficiently wet.

Figure 4 shows a coupling means according to a further embodiment of the present invention. In this embodiment, the coupling means comprises a plate 12 having two pairs of holes 13 for receiving a fluid circulation means, the fluid circulation means comprising two looped pipes. The installation member attachment means 9 is similar to that shown in Figure 3.

Claims

CLAIMS

1. A method of installing a fluid circulation means in a foundation or wall element, the fluid circulation means being for connection to a fluid network, the method comprising the steps of: i) coupling the fluid circulation means to an installation member by means of a coupling means; and ii) lowering the installation member having the fluid circulation means coupled thereto, to a predetermined depth, into a volume of wet concrete in the ground.

2. A method as claimed in claim 1, further comprising the step of de-coupling the installation member from the fluid circulation means and withdrawing it, once at said predetermined depth, from the volume of wet concrete.

3. A method as claimed in claim 2, wherein the step of decoupling the installation member from the fluid circulation means comprises rotation of the installation member.

4. A method as claimed in claim 2 or 3, wherein the installation member is coupled to the fluid circulation means by rotation of the installation member in a first direction, and is de-coupled from the fluid circulation member by rotation of the installation member in a second, substantially opposite, direction.

5. A method as claimed in any preceding claim, wherein the installation member comprises a longitudinal bar.

6. A method as claimed in any preceding claim, wherein the step of lowering the installation member into the ground comprises applying a downward crowd force or a vibrational force to the trailing end of the installation member.

7. A method as claimed in any preceding claim, wherein the fluid circulation means comprises one or more pipes each of which are shaped so as to facilitate fluid flow in a first direction and a second direction.

8. A method as claimed in claim 7, wherein said pipe is generally "U" shaped at one end.

9. A method as claimed in any preceding claim, wherein the fluid circulation means comprises one or more pairs of pipes, which are operable to be in fluid communication, a first one of a pair of pipes being for facilitating fluid flow in a first direction, the other pipe of a pair of pipes being for fluid flow in a second direction.

10. A method as claimed in any one of claims 7, 8 and 9, wherein said first direction is substantially opposite to said second direction.

11. A method as claimed in any preceding claim, wherein said foundation element comprises a longitudinal pile or panel.

12. A method as claimed in claim 11 when appended to any one of claims 7 to 10, wherein the first and second directions of fluid flow will be substantially along the length of the pile.

13. A method as claimed in any preceding claim, wherein the fluid circulation means is provided with one or more valves which are operable to control fluid flow within the fluid circulation means.

14. A method as claimed in any preceding claim, wherein said method comprises the preceding steps of: i) applying a continuous flight auger to the ground and causing said auger to penetrate the ground to a predetermined depth; ii) withdrawing said auger from the ground whilst supplying concrete to the tip of said auger, to thereby create said volume of wet concrete in the ground.

15. A coupling means for use with methods of installing a fluid circulation means in a foundation element by means of an installation member, the coupling means comprising fluid circulation attachment means for attaching a fluid circulation means thereto, and an installation member attachment means for attaching an installation member thereto.

16. A coupling means as claimed in claim 15, wherein, in use, the installation member attachment means allows an installation member to be de-coupled from a fluid circulation means upon rotation of the installation member.

17. A coupling means as claimed in claim 15 or 16, wherein the installation member attachment means comprises a bayonet type fitting.

18. A method/apparatus/coupling means substantially as hereinbefore described with reference to the accompanying drawings.