WO2003023293A1

WO2003023293A1 - Soil heat exchanger for soft soil, like clay or sand

Info

Publication number: WO2003023293A1
Application number: PCT/SE2002/001562
Authority: WO
Inventors: Ove Platell
Original assignee: LOWTE AB
Current assignee: LOWTE AB
Priority date: 2001-09-13
Filing date: 2002-09-02
Publication date: 2003-03-20
Anticipated expiration: 2004-03-13
Also published as: SE0103038D0; SE523912C2; SE0103038L

Abstract

The invention relates to soil heat exchanger for soft soil, like and or clay, comprising a first long leg (1, 2) and in parallel with that leg a second long leg (5), which legs contain flow ways for a heat transferring liquid. The soil heat exchanger is designed to be pushed down into the soil with the bottom end foremost. To enable this with a soil heat exchanger, which fulfils high demands on thermal efficiency and which must not get damaged during the pushing down into the sand or clay, the soild heat exchanger according to the invention is designed with the first leg containing at least one heat-insulated pipe (1, 2) in a cover (31, 34) and with the second leg containing numerous narrow flow ways (6) in at least one wide, thin plate (5) that extends along the cover (31, 34) and is attached to it.

Description

SOIL HEAT EXCHANGER FOR SOFT SOIL, LIKE CLAY OR SAND.

The present invention relates to a soil heat exchanger for soft soil, like clay or sand, comprising a first long leg and in parallel with hat leg a second long leg, which legs contain flow ways for a heat transferring liquid, and at a bottom end a flow connection between the ends of the legs and at opposite end connecting means for connecting the legs to an exterior flow circuit, in addition to which the soil heat exchanger is designed to be pushed down into the soil with the bottom end foremost.

The arrangement of soil heat exchangers in soft soil, and especially then in clay, is associated with many difficulties. Attemts have been carried out to push down 35 m long double- folded plastic tubes in clay by using a pile-driving machine equipped with an iron pipe provided with a fork-shaped tool. This has proved to be possible if the plastic tube has a sufficient wall thickness and dimensioning in the typically sucking clay. At pulling upof the iron pipe a cavity is formed that automatically becomes filled with water and clay which is a good heat conductor and from a heat point of view more or less forms a short circuit between the two legs of the plastic tube. It is not possible to obtain an efficient soil heat exchanger in this way.

Efficient soil heat exchangers have up to now been realizable only by arranging a first leg consisting of a heavy pipe provided with a good heat-insulation and a second leg consisting of numerous thin plastic tubes in good thermal contact with surrounding soil, as shown for instance in US 5,477,914. A soil heat exchanger of this type, however, can be arranged only in a heavy bore hole in firm soil. In clay a lining has to be introduced in connection with the boring to prevent the clay from flowing back into the bore hole before the introducing of the soil heat exchanger in the bore hole. This is a complicated and costly operation. Pulling up of the lining after the introduction of the soil heat exchanger is not possible, which results in that the soil hole is filled up with water striving to lift the soil heat exchanger due to primarily the considerable buoyancy of the heat-insulation.

To push down a soil heat exchanger of said type in clay or sand in a similar way as is carried out with a double-folded plastic tube is not to be thought of, because the friction between the thin plastic tubes and the surrounding soil would be strong enough to thorn off the plastic tubes. The object of the invention is to achieve an uncomplicated and efficient solution of the problem to bring a soil heat exchanger, which has a tested, thermally efficient design, in place in soft soil, like clay or sand.

This is achieved according to the invention by the fact, that the first leg of the soil heat exchanger mentioned by way of introduction comprises at least one pipe that is heat-insulated in a cover, and the second leg contains numerous narrow flow ways, which are arranged in at least one wide, thin plate that extends along the cover of the first leg and is attached to i along essentially all the length of the cover. The two legs are kept together during the pushing down operation due to the arranging of the narrow flow ways of the second leg in a plate which adheres to the cover of the first leg, and, hence, the narrow flow ways need not be exposed to damage. The bottom end of the soil heat exchanger is, according to an embodiment of the invention, encased in a fixedly attached cap made of hard material, preferably metal, and provided with a sharp edge directed in the longitudinal direction of the soil heat exchanger, such that hard particles in the soil can be moved aside without damaging the soil heat exchanger.

The cap may with advantage be designed with at least one socket connected to the cap and designed to receive and hold a push rod dimensioned for pushing the cap down into the soft soil eith the sharp edge foremost.This design of the soil heat exchanger prevents the soil heat exchanger from beingfolded and damaged during the pushing down operation due to the fact that the push rod or rods exert a traction force instead of the compressive force that is followed by a pressure exerted to the upper parts of the legs.The push rods are suitably possible to detach from the corresponding sockets to be used again.

Both the legs are with advantage made of a flexible material, like plastic, that permits reeling of the soil heat exchanger of a necessary length on a bobbin after the manufactoring to enable an uncomplicated transport to the place for construction and a construction without joint demand.

The soil heat exchanger according to the invention may be designed in different ways. The first leg comprises, according to a suitable embodiment, two heat-insulated pipes attached each to a longitudinal edge portion of the thin plate of the second leg to enable winding up on a bobbin in spite of a big length, outside which pipes sockets for two push rods are attached to the cap. This prevents the heat exchanger from being twisted during the winding up on a bobbin. The thin, wide plate of the second leg may be curved in the latitudinal direction. This normally gives the soil heat exchanger a sufficient bending strenght to permit pushing down of the soil heat exchanger in the soil without use of any push rod. This is valid especially if the thin, wide plate of the second leg is curved like an arc of a circle in the latitudinal direction with the free longitudinal edge attached to the cover of the first leg, i.e. so that a cylindrical unit is formed. Such a unit can also be formed by said free, longitudinal edge as well as a longitudinal edge of the cover of the first leg being provided with attachment means, thus forming a heat exchanger section to be attached together with a number of further sections to form a cylindrical soil heat exchanger. A preferred embodiment of the invention is, according to an alternative, characterized in that said second leg is formed by two concentric sleeves, an inner sleeve and an outer sleeve, with the outer sleeve fitted with easy running fit outside the inner sleeve, with the flow ways formed between the sleeves, and with the first leg containing at least one heat-insulated pipe integrated with one of the sleeves.

When the soil heat exchanger is pushed down in the soil a correponding amount of soil is pushed up if it is not compressible. To facilitate this, the soil heat exchanger according to a preferred embodiment of the invention is provided with a device for injecting liquid, preferably water, possibly mixed with a friction reducing agent, adjacent to the outside of the bottom end of the soil heat exchanger. Thus, sand and clay, possibly in combination with a vibration of the soil heat exchanger, becomes fluidized adjacent the surface of the soil heat exchanger and is pushed upwards to make room for the downwards moving soil heat exchanger.

The invention is described in more detail in the following description taken in connection with the accompanying drawings which schematically show examples of different embodiments of soil heat exchangers according tothe invention. Figure 1 is a front view of a first embodiment of a soil heat exchanger according to the invention, partly in section, figure 2 is perspective view of a cap for enclosing the bottom part of a soil heat exchanger, figure 3 is a cross-sectional view along line iπ-ITI in fig.1, figure 4 and figure 5 are corresponding cross-sectional views of an embodiment with an arc-curved second leg and a V-curved second leg, respectively, figure 6 is a corresponding cross-sectional view of a second leg curved in the shape of a circular arc with one of its edges connected to the cover of a first leg, figure 7 shows the same embodiment as fig.6 but provided with attachment means and forming a section attached to two equivalent sections indicated by dot-dash lines, figure 8 is a cross-sectional view along line VLH-Viri in fig.9, and Figure 9 is a longitudinal sectional view along line IX-LX in fig.8 of an embodiment having a circular cross-section.

The soil heat exchanger shown in fig.1-3 of the drawings has a first leg consisting of two plastic pipes 1,2 surrounded by heat-insulation 3,4 and each a plastic cover 31,34. The pipes 1,2 together with the heat-insulation 3,4 are embedded in the covers, which are joined by a wide, thin plastic plate 5, in which narrow channels 6 are arranged in parallel with the pipes 1,2. The soil heat exchanger has a bottom end portion 7, which in a manner known per se is sealingly welded or in any other way joined to the bottom end part of the plate 5, and in which the channels 6 through a distribution channel 8 are arranged to communicate with the radially directed bottom end openings of the pipes 1,2, and an upper end portion 9 which in a manner known per se is sealingly welded or in any other way joined to the upper end part of the plate 5 and in which the upper ends of the channels 6 are arranged to communicate with each other through an upper distribution channel 10, which is connected to an outlet pipe 14 provided with a connection means 11. The upper ends of the pipes 1,2 are connected to each a connection means 12,13. The soil heat exchanger is intended to be connected by the connection means 11-13 to an exterior circuit (not shown) for circulating a heat transferring liquid down into the soil by one of the legs, e.g. pipes 1,2, and up from the soil by the other leg, e.g. the channels 6, or vice versa.

The soil heat exchanger is so far made of mainly flexible plastic material and is principally extruded in the shape of a continuous length corresponding to the depth to which the soil heat exchanger is intended to be pushed down. The bottom end of the soil heat exchanger is enclosed in a fixedly attached steel cap 15 which is formed in correspondance to the shape of the bottom end and which is provided with a downwards directed sharp edge 16 to enable such a pushing down operation. The ends of the cap 15 are provided with each a socket 17,18 for receiving the bottom ends of two push rods 19,20 which are detachably fixed in the sockets.

The soil heat exchanger is reeled on a bobbin (not shown) when it is positioned at a place with a deep layer of clay. The soil heat exchanger is unreeled at the same time as the bottom part with the cap 15 is pressed against the ground and is pushed with the sharp edge 16 foremost down into the clay by means of the push rods 19,20.The push rods cannot as a rule have the same length as the soil heat exchanger and, hence, have to be lengthened and detachably fixed, e.g. by bayonet joints, by adding further push rods one by one.When the intended deep is achieved is it possible to pull up the push rods 19,20 and use them again for next arrangement of a soil heat exchanger.

The sockets 17,18 may be open downwards such that the push rods may have the shape of pipes and may be used for injecting water down to tha cap 15 in order to fluidize present sand and/or clay and for smearing the surfaces of the soil heat exchanger in contact with surrounding clay during the pushing down of the soil heat exchanger. The bottom walls of the sockets 17,18 are for that purpose provided with an opening that communicates with each end of a distribution channel 21 in the cap 15, which is provided with outlet openings 22 from the channel 21 on both sides of the cap 15.

The soil heat exchanger can, in case of softer soil conditions, be pushed down into the soil by applying a pressure to its upper end. In such a case it is necessary to have provided the soil heat exchanger in advance with a strenghtening, e.g. by forming the second leg of the soil heat exchanger, i..e. the thin plate 5, with a curved shape like an arc of a circle in the latitudinal direction, as shown in Fig.4 for a soil heat exchanger of the type shown in Figs 1-3, but without the sockets 17,18 and the rods 19,20. The soil heat exchanger may, as an alternative, have the shape shown in Fig.5 with the second leg bent in V-shape and the first leg 1,3 and 2,4, respectively, arranged at the ends of the first leg 5.

Another alternative to the embodiment according to Figs. 1-3 is shown in Fig.6, where the first leg is arranged with the pipe 2 and the heat-insulation 4 in the cover 34 at one of the edges of the plate 5 of the second leg, which plate here is curved like an arc of a circle. At the upper part of the other edge of the plate 5 is the outlet pipe 14 from the channels 6 arranged.. This embodiment makes it possible to provide both the longitudinal edges of the soil heat exchanger with attachment means 23,24 of a type that permits attachment side by side of similar sections of the kind of soil heat exchangers shown in Fig.7. Here the soil heat exchanger shown in Fig.6 is a section - marked with 25 - with the cover 34 surrounding the pipe 2 and the heat-insulation 4 provided with a male attachment means 23, known per se, and the opposite edge of the soil heat exchanger 25 provided with a corresponding female attachment means 24. A second similar section 26, which is attached to the section 25, is marked with dot-dash lines, and a third similar section 27 marked with dot-dash lines is connected with the sections 25 and 26 and consequently form a cylindrical soil heat exchanger with large resistance to bending. A special advantage with this embodiment is that it can be dismounted during transport to form sections which can be piled in a very space-saving way. It may be desirable at all the embodiments with a reinforcement of the bottom part of the soil heat exchanger and with a fluidizing of the adjacent sand and/or clay by means of said injection of water. If this is the case is suitably all the different embodiments completed with a suitably adapted cap of the kind shown in Figs.l and 2.

An embodiment especially adapted for rational manufacturing is shown in figs. 8 and 9. Here the second leg of the soil heat exchanger comprises two main components, viz. an inner cylindrical sleeve 40 and one outer cylindrical sleeve 41 which latter is positioned outside the inner sleeve with a small interspace between the sleeves. The first leg is integrated with the inner sleeve 40 which on the inside is made in one piece with the cover of the first leg, e.g. the cover 34, in which, as described above, the pipe 2 of the first leg with its heat-insulation 4 is fitted with the bottom end of the pipe 2 opening at an opening 42 in the inner sleeve 40. Also the outlet pipe 14 of the soil heat exchanger is integrated with the inside of the inner sleeve 40 and communicates with an outlet opening 43 at the upper part of the inner sleeve 40. A cylindrical room between the sleeves 40 and 41 is formed by an upper gasket 44 and a bottom gasket 45 between the sleeves. Spacers 50 or cams are positioned in the interspace shaped to divide and distribute the liquid flowing in the interspace in numerous narrow flow ways.

As an alternative, the interspace may be formed by a recess on the outside of the sleeve 40 or on the inside of the sleeve 41 or, altenatively, in both said outside and inside, in which case the upper ends and the bottom ends of the sleeves 40 and 41 are in contact with each other and are sealingly joined.

Also here it is suitable to have the bottom end of the cylindrical soil heat exchanger reinforced in a way similar to that described above. Hence, the bottom end is provided with a ring-shaped, hollow steel cap 46. The cap is provided with outlet openings 47 for water which is supplied under pressure through a pipe 48 on the inside of the sleeve 40, which pipe extends down to an opening 49 on the inside of the cap 46 to achieve the above mentioned injection of water into the soil.

The soil heat exchanger according to the invention is suitably prefabricated in the shape of easily handled lengths, 10 to 15 meters, and are adapted for lengthening with specially adapted upper parts with connecting means fitting the connecting means for an exterior circuit shown on the drawings. Pipes for water injection under pressure normally need not be lengthened, however, because such pipes may be unreeled from a supply reeled on a bobbin. The invention is of course not restricted to the examples of embodiments here shown and described but can be modified in different ways within the scope of the invention defined in the claims. This holds especially for short soil heat exchangers which need not be reeled on a bobbin. In such cases the two pipes 1,2 together with heat- insulation 3,4 may be replaced by a single pipe with heat-insulation positioned along the middle of the plate 5. It is also possible to manufacture the soil heat exchanger in the shape of lenghts made of metal which are lenghtened one by one till the required deep is achieved.

Claims

P A TE N T C L AI M S

1. Soil heat exchanger for soft soil, like clay or sand, comprising a first long leg (1,2) and in parallel with that leg a second long leg (5), which legs contain flow ways for a heat transferring liquid, and at a bottom end a flow connection (8;42) between the ends of the legs and at the opposite end connecting means (12,13,14) for connecting the legs to an exterior flow circuit, in addition to which the soil heat exchanger is designed to be pushed down into the soil with the bottom end foremost, characterized in that the first leg comprises at least one pipe (1,2) that is heat-insulated in a cover, and the second leg contains numerous narrow flow ways (6), which are arranged in at least one wide, thin plate (5) that extends along the cover (31,34) of the first leg and is attached to it along essentially all the length of the cover.

2. Soil heat exchanger according to claim 1, characterized in that the bottom end (7) of the soil heat exchanger is encased in a fixedly attached cap (15) made of a hard material, preferably metal, and provided with a sharp edge (16) directed in the longitudinal direction of the soil heat exchanger

3. Soil heat exchanger according to claim 2, characterized in that the cap is provided with at least one socket (17,18) connected to the cap (15) and designed to receive and hold a push rod (19,20) dimensioned for pushing the cap down into the soft soil with the sharp edge foremost.

4. Soil heat exchanger according to any of claims 1-3, characterized in that the two legs (1,2;5) are made of a flexible material that permits reeling of the soil heat exchanger on a bobbin before use.

5. Soil heat exchanger according to any of claims 1-4, characterized in that the first leg comprises two heat-insulated pipes (1,2) in covers (31,34) attached each to a longitudinal edge portion of the thin plate (5) of the second leg.

6. Soil heat exchanger according to any of claims 1-5, charcterized in that the thin, wide plate (5) of the second leg is curved in the latitudinal direction.

7. Soil heat exchanger according to any of claims 1-6, characterized in that the thin, wide plate (5) of the second leg is curved like an arc of a circle in the latitudinal direction with one of its longitudinal edge portions attached to the cover (34, Fig.6) of the heat-insulated pipe (2) of the first leg.

8. Soil heat exchanger according to claim 7, characterized in that the other longitudinal edge portion of the second leg (5) as well as the cover (34,Fig.7) of the heat-insulated pipe (2) of the first leg are provided with attachment means (23,24) operable essentially along all the length of the soil heat exchanger and forming a heat exchanger section (25) to be attached to a number of similar sections (26,27) to form a cylindrical soil heat exchanger.

9. Soil heat exchanger according to claim 1 or 2, characterized in that the second leg (5) is formed by two concentric sleeves, an inner sleeve (40) and an outer sleeve (41), with the outer sleeve fitted with easy lαinning fit outside the inner sleeve, with the flow ways formed between the sleeves (40,41) guided by studs or corresponding spacer means (50), and with the first leg (2,4,34) integrated with one of the sleeves (40)

10. Soil heat exchanger according to any of claims 1-9, charcterized in that it is provided with a device (46,47,48) for injecting liquid, preferably water, adjacent to the outside of the bottom end of the soil heat exchanger during the pushing down of the soil heat exchanger in the soil.