The present invention concerns a weighted pipe assembly according to the preamble of claim 1.

Such a pipe assembly comprises at least two pipes placed in parallel orientation and connected at one end with a U-shaped pipe fitting to allow for the formation of a liquid flow path from one pipe to the other. Further, there is a weight which is capable of weighting the pipe assembly when fitted inside a borehole.

The present invention also concerns a method of weighting collector pipes according to the preamble of claim 20.

Ground source heat pumps are used for providing heating of various buildings. They provide a clean and environmentally friendly means of collecting renewable energy stored in the ground. At present, they represent one of the most energy efficient ways of heating.

In this field of technology, heat energy is collected with U-shaped collector piping sunk into boreholes. Water, for example with some antifreeze agent such as ethanol, is circulated in a closed loop formed by the collector piping and a heat pump. The circulating water passes heat from the collector piping to the pump. Typically, the difference in temperature between the water leaving and re-entering, respectively, the pump is sufficient to pass through a compressor and be converted into useful heat. Borehole collectors are comprised of thermoplastic pipes with a U-bend and a weight. The depth of the borehole typically varies in the range from about 50 to 250 m.

Conventionally, the weight comprises a lump of hardened concrete surrounding the U- bend. The weight is difficult to install onto the U-bend on site, which means that the weight has to installed at the factory. This increases transportation costs. The problem of weighting the collector pipes is further aggravated when there is a need to install collector piping in a plurality of parallel boreholes, which means that each U-bend should be equipped with a weight. It is an aim of the present invention to eliminate at least a part of the problems of the art and to provide a novel solution for weighting collector pipe assemblies, in particular in connction with ground surface heat collection. The present invention is based on the idea of providing a weighted pipe assembly by joining the parallel ends of collector pipes with a pipe bend (a U-bend). To the bend there is coupled a weight which has an elongated, e.g. cylindrical, portion. The elongated portion of the weight typically has a first thickness (or, in the case of a cylindrical portion, first outer diameter) and, in a second region, a second thickness (outer diameter) which is greater than the first. The elongated portion is capable, in the region of the first outer thickness, of receiving a sleeve pipe surrounding the collector pipes. The sleeve pipe covers the coupling zone formed between the weight and the ends of the collector pipes. Thereby the sleeve prevents the weight from being deattached from the pipe bend, and keeps the collector pipes and the weight (axially) aligned.

More specifically, the present pipe assembly is characterized by what is stated in the characterizing part of claim 1.

The method according to the present invention is characterized by what is stated in the characterizing part of claim 20.

Considerable advantages are obtained with the invention. Thus, the present weighting solution is uncomplicated and can readily be carried adapted to any collector pipes. In one preferred embodiment, the sleeve pipe has an inner diameter which is generally at least somewhat smaller than the outer diameter of the first cylindrical portion and made of a thermoplastic material which can be stretched about the cylindrical portion so that it snugly fits about both the collector pipes and the weight, whereby it readily locks the ends of the collector pipes to the weight.

The weight can be assembled either at the installation site or beforehand. The sleeve pipe efficiently locks the weight in place, and stiffens the lower end which makes it easier to sink the collector pipes into deep boreholes. If necessary, the weight can be disengaged from the collector pipes. Next the invention will be examined more closely with the aid of a working example with reference to the attached drawings.

Figure 1 shows in perspective view of a bottom weight;

Figure 2 shows in perspective view of two parallel collector pipes provided with a U-bend; Figure 3 shows in perspective view a sleeve pipe fitted about two parallel collector pipes; Figure 4 shows in perspective view a bottom weight coupled with a hook to the nose ring of a U-bend;

Figure 5 shows in perspective view the coupling between a bottom weight and a U-bend covered by a sleeve pipe; and

Figures 6a and 6b show in sideview two alternative embodiments for bottom weights.

In the drawings, the following reference numerals are used: la, lb collector pipes

2 U-piece

3, 13, 23 bottom weight

3 ' , 13 ' , 23 ' conical part of weight

4, 14, 24 sleeve pipe

5 nose ring

6 hook

7 loop

8, 18 connector bolts As explained above, in the present technology, a stiffened and weighted pipe assembly is provided. It is formed basically from five components, namely a pair of parallel pipes (collector pipes), a U-shaped pipe bend which in the following is also called a "pipe fitting" as indicated by the drawings, a coupling assembly, a weight and a sleeve pipe. The pipe bend according to the present technology typically has two parallel openings which are opening in the same direction and which are capable of receiving the parallel ends of the pipes. Thus, it is generally U-shaped and in the following it will also be identified as a "U-piece". The pipe bend further has a first portion of the coupling means affixed to an end which is opposite to the end which is coupled to - or capable of being coupled to - the pipes. The weight has a first elongated portion and a second portion. The first elongated portion is typically cylindrical, e.g. a shaft. The first elongated portion has a thickness or, for a cylindrical shape, diameter which is smaller than the maximum or diameter, respectively, of the weight. The weight has a front end, i.e. an end which is opposite to the collector pipes, which preferably is conically shaped for ease of installation (to prevent the assembly from getting stuck to the sides of the borehole).

The sleeve pipe is rigid or substantially rigid and, in one embodiment, has an inner diameter equal to or smaller than the outer thickness or diameter of the elongated portion.

The length of the sleeve is sufficient to cover at least a part of the collector pipes, the pipe bend and a part of the weight when the pipe bend and weight are coupled via the coupling means. In a preferred embodiment, the coupling means between the weight and the pipe bend is a hook and a ring.

In a first embodiment, the surface of the first portion of the elongated part of the weight is smooth. In a preferred mode of this embodiment, the inner diameter of the sleeve pipe is equal to, or 0.1 to 20 %, in particular 0.1 to 10 % smaller than, the outer diameter in the first portion of the elongated or cylindrical part of the weight.

In a second embodiment, the surface of the first portion of the elongated part of the weight is roughened or provided with projections, such as tangential or axial ribs to increase friction between the sleeve pipe and the weight. In this embodiment, the inner diameter of the sleeve pipe is equal to, or 0.1 to 20 %, in particular 0.1 to 10 % smaller or greater than, the outer diameter of the first portion of the elongated or cylindrical part of the weight. The maximum radius at any point of the first portion of the elongated part of the weight shall in this embodiment be 0.1 to 20 % larger than the nominal inner diameter of the sleeve pipe divided by 2 (two).

In a third embodiment, the sleeve pipe is coupled to the elongated portion (shaft) of the weight by mechanical fastening means, such as locking bolts. In a fourth preferred embodiment, the sleeve pipe, which covers a portion of the pipes, all of the U-shaped pipe bend and at least a portion of the weight, has a length of at least 2 times, in particular at least 3 times, preferably 4 to 20 times, greater than its inner diameter. In a fifth preferred embodiment, which can be combined with any of the afore-mentioned embodiments, the sleeve pipe overlaps the weight to a length which is equal with at least 0.2 times DN/OD (nominal outside diameter) and preferably less than 2.0 times DN/OD.

When installed, the sleeve pipe should preferably reach at a minimum 2 cm, in particular at least 10 cm and preferably not more than 3 m, past the U-shaped pipe bend, whereby it also covers the weight. In a particularly preferred embodiment, the pipe should reach past the pipe bend with 20 to 50 cm.

Using the components mentioned above, the present method of weighting a collector pipe assembly preferably comprising the steps of

- arranging two collector pipes in parallel orientation,

- coupling to the parallel ends of the pipes a pipe bend, which joins the ends so as to form a continuous flow path,

- coupling to the pipe bend a weight which has a two successive elongated,

preferably cylindrical portions, the first portion which is adjacent to the pipe fitting having a thickness or diameter which is smaller than the thickness or diameter of the second portion, and

- at an optional point of time, however prior to the connection of the weight to the pipe bend, fitting about the collector pipes a sleeve pipe which locks the ends of the collector pipes to the weight.

In particular, the sleeve pipe which has an inner diameter which is equal to or smaller than the outer diameter of the first cylindrical portion. The sleeve pipe is made of a

thermoplastic material which is capable of being stretched about the cylindrical portion so that it snugly fits about both the collector pipes and the weight.

In a preferred embodiment, the collector pipes are coiled during the assembly process, and the sleeve pipe is put in place before the weight is attached, either before or after the welding of the U-piece to the collector pipes. Turning now to the drawings which illustrate a particularly preferred embodiment, it can be noted that the pipes discussed above, in the example referred to as "collector pipes", are designated with reference numerals la and lb. There are at least two pipes of the indicated kind and they are capable of receiving heat from the surrounding and transferring it to the heat transfer medium flowing inside them.

The collector pipes are essentially linear pipes which are joined at their protruding ends with a separate collector pipe 2 fitting which forms a narrow bend. The collector pipes, thanks to the design of the U-shaped pipe bend, can be welded adjacent (in tangential connection) to each other, which enables the use of a shield pipe with a smaller diameter, and thus also a weight with a smaller diameter. This allows for either an easier installation, or the use of a smaller borehole. The collector pipes are typically manufactured from plastic materials allowing for heat transfer through the pipe wall. Examples of suitable materials include polyolefm materials, for example polyethylene or polypropylene. Other thermoplastic materials can also be used, such as polyesters, polyamides, polycarbonates and polyimides. In principle, in order to improve heat transfer, the polymer material can be modified for example by

incorporating components having higher heat conductivity than the polymer material.

However, the present collector pipes are made of pressure grade material. Due care needs to be taken to ensure pipe pressure properties even if fillers or additives are being used. The pipe bend, which in the drawings is shown generally in the shape of a U-piece, is designed for connecting the two collector pipes. It can be coupled to the pipes in various ways, a particularly preferred coupling comprising butt welding. Thus, it is preferred to manufacture the U-shaped pipe bend from a thermoplastic material which is compatible with the collector pipe material at least to the extent that butt welding is possible. In a particular preferred embodiment, basically the same polymer material is used for both the pipes and for the pipe bend.

With the U-shaped pipe bend in place a flow path is formed between the collector pipes which allows the liquid in the pipes to flow freely from one pipe to the other, preferably without significant flow resistance at the bend.

The pipe bend 2 features a geometrical feature, for example a nose ring 5 (as in the drawings) or a hook in the far end. The nose ring 5 can be provided by making an opening in a projecting lip which is formed at the apex of the pipe bend in order to stiffen the bend, as shown in the drawings.

In the drawings the weight (also called the "bottom weight") used for weighting the pipe assembly into the borehole has been given the reference numeral 3, with numeral 3' referring to the conical front end of the weight. This weight is made out of a high density material like cast iron, steel or concrete. Generally, the mass of the weight is selected such that it is capable of weighting the pipe assembly to the bottom of the borehole, in particular keeping in mind that the piping is generally manufactured from a material lighter than water, and the circulating medium inside the pipe generally has a lower density than the water in the borehole outside the collector pipes.

The weight features two areas with different diameters, viz. a smaller diameter designated Dl and a larger one (D2), and a cone shape 3' in the front end. The conical shape will help steering the weight into the borehole. At the same time, the conical shape minimizes the risk for the weight getting stuck at any irregularities in the borehole that might exist.

Typically, in one embodiment, Dl is slightly larger than the inside diameter of the sleeve pipe, to allow for a tight connection that will not come off easily. D2 is slightly larger than the outside diameter of the sleeve pipe, to make certain the sleeve pipe end will not prevent the installation of the collector into the borehole.

The Dl surface of the weight can be equipped with geometrical features enhancing the locking mechanism (roughened surface, ribs, etc.), as discussed above, even if the particular embodiment shown in the drawings has a smooth surface at Dl .

The bottom weight also features a hook 6 in the upper end capable of engaging the nose ring 5 of the pipe fitting 2. Further it may also feature a loop 7 in the lower end, as shown in the drawings. The two features, the hook and the loop 6, 7 are made of metal, preferably ductile steel. The purpose of the loop 7 is to allow for the attachment of additional weights, should such weights be needed. When the weight is installed in the factory, the hook also provides a mean for attaching the assembled weight securely to the coil, using, for instance, a rope. Numeral 4 refers to a sleeve pipe which is used for covering the lower, protruding ends of the pipes of the assembly, and for securing the coupling of the weight to the nose cone during sinking of the pipe assembly during and after installation. The inner diameter of the pipe is at least somewhat smaller than the smallest diameter of the bottom weight, to allow for a tight fit.

A further function of the sleeve pipe 4 is to stiffen and straightening of the pipe assembly from the lower end of the pipes towards the weight. This facilitates the installation of the assembly into the borehole. The rigidity of the sleeve is sufficient to stiffen the pipe assembly and for this reason the sleeve is made of a material having a rigidity greater than typical elastic and flexible materials, such as rubbery materials. In practice, Young's Modulus of the material should be 100 MPa or higher.

In a particularly preferred embodiment, the collector pipes, the U-piece and the locking pipe (sleeve pipe) are all made of PE-HD material.

Figures 6 A and 6B show alternative embodiments for the weight 13, 23 having a nose cone and an elongated portion, optionally connected by a cylindrical portion, as shown in Fig. 6A. The embodiments of Figures 6 A and 6B also comprise connector bolts 8, 18 for connecting the sleeve pipes 14, 24 to the elongated portions of the weights 13, 23.

The present pipe arrangement is readily assembled. On one embodiment, the following steps are taken to weight two collector pipes for a ground source heat system.

In the first step of the assembling method, the two collector pipes and the U-piece are prepared for the welding process using common practice. In the second step, the collector pipes and the U-piece are welded together using butt fusion to form an integral, leak-proof conduit of the two collector and the U-piece.

In the third step, the locking pipe is pushed over the collector pipes, and the U-piece is attached to the bottom weight by mounting the hole of the U-piece onto the hook of the bottom weight.

Next, the locking pipe is pushed back over the bottom weight. This secures the connection between the U-piece and the bottom weight. It also keeps the collector pipe ends straight which facilitates the installation, i.e. pushing down the collector pipes in the ground heating borehole.

Finally, after coiling of the collector pipe, the bottom weight is fixed to the coil by a rope or similar through the loop in the front end of the weight.

Normally, the pipes are coiled directly after the production of them. When the pipes are ready, the ends of the coiled pipes, normally having a length of a few meters, are then released from the coil and the assembling of the bottom weight, as explained here, is started.

The opposite ends of the collector pipes are coupled to the remaining portion of the ground source heat system, e.g. one of the pipes is typically coupled to a heat exchanger.

As discussed above, a particularly interesting feature of the above arrangement is that the sleeve pipe locks the assembly, i.e. prevents the weight from coming off the U-piece or dangle. Since the weight does not dangle facilitates the installation of the assembly into the borehole as it cannot get stuck provided the end of the weight is conical. In other words, the whole assembly stays straight enough during installation to prevent it from happening. As the collector pipes are coiled and made of a viscoelastic, not perfectly elastic, material, they will not become perfectly straight instantly when uncoiled, meaning the pipes will be slightly bent and thus provide some degree of resistance when pushed into the borehole. The ends of the pipes will during installation strive to be in contact with the sides of the borehole, and the conical shape of the weight effectively prevents the assembly from getting stuck to the sides of the borehole.