Long Distance Heating Conduit in Particular for Hot Water Lines

The invention relates to a long-distance heating conduit, in particular for hot water lines, comprising one or more tubes conveying the heating medium, which tubes are supported on support means in the conduit, surrounded by a heat-insulating material, and covered so that they may be weighted from above.

In a known heating conduit of this type, the cavity between the tubes and the waterproof conduit walls made of concrete are filled up with for example an insulation material of light-weight concrete. In this heating conduit, the penetration of moisture has to be absolutely avoided, since moisture once penetrated can be removed from the insulation only in a very long drying time with the known conduit construction method being employed.

It is, however, impossible to keep the conduit impervious continuously, as it may be damaged for example by too great a mechanical load, by accidents, or other hazards. It may also happen that the tubes conveying the heating medium themselves become pervious. These leakages are mostly minute, but still they prevent the insulating materials impregnated by the hot water, for example, from drying again. By this process, not only a great portion of the insulating effect is being lost, but also favorable conditions are produced for damages caused by corrosion by chlorine ions affecting the tubes conveying the heating medium. Such damages may lead to the complete destruction of the lines, which can then be repaired only at a very high expense.

The object on which the present invention is based lies in preventing occurrences of such damages. According to the present invention the support for the tubes conveying the heating medium comprises an insulating material resistant to compression, and the heat-insulating material surrounding the tubes is also resistant to compression and is enclosed by cover foils having holes, which foils touch each other or cover each other on the top side of the insulation layer, but not on the bottom side where apertures or a gap are to be provided, and above the lining of the conduit bed, outside of the cover foils, drain pipes are provided.

The heating conduit according to the invention dries by itself. The hot water tubes are laid in an insulating material, and a waterproof cover foil is provided above the insulating material to prevent water from penetrating from above. However, the insulating material according to the invention is not surrounded by a completely tight waterproof shell, but by a cover foil having small holes. Said holes are so small that they allow the vapor to escape which is formed upon evaporation of water, but on the other hand, they prevent water from penetrating through the holes into the insulating material. Water runs off to the lining of the conduit bed at the sides and reaches there the drain pipes laid at this point. According to the invention, therefore a more or less tight space is formed containing the hot water tubes and the insulating material, a gauge pressure being generated which results in the aforementioned effect of the holes in the foil. The perforated cover foils are applied along the side walls down to the lining of the conduit bed, without, however, covering each other so that the water of condension formed on the inside of the foils, or other water having penetrated in cases of emergency, can run off freely and can be drained off by the drain pipes.

As an insulating material, balls of expanded clay have proved to be advantageous, which clay has become known under the names "Leca" (light-weight expanded clay aggregates) or "Porondur" (see for example pages 68 and 80 of the book "Leichtbeton", volume I, by Dr.-Ing. Siegfried Reinsdorf, published in 1961). This material combines a good mechanical strength and good insulating qualities against heat losses.

It is expedient to not have the cover foils meet at their ends beneath the tubes, but to leave apertures or a gap so that, upon a great amount of water breaking in, also the water penetrating into the balls of the insulating material may be drained off to the drain pipes.

In another embodiment, the perforated cover foils cover each other or are completely tight also at the bottom. In such a case, either cover foils are used having holes of different sizes, i.e. for example small holes according to the invention on the upper side and at the sides of the insulating material, and larger holes on the bottom side. In cases in which cover foils are used having small holes everywhere, the bottom side has to be provided with large holes, which may be achieved by cutting or punching out.

For example, in the case of inundations or thunder showers, water may penetrate into the insulating material. The embodiment of a heating conduit according to the invention brings about a rapid drying, i.e. only a short period of impregnation occurs, which is endured in particular by chromium steel, but a long period of impregnation as with the known heating conduits does not occur. For the latter, very long periods of drying are necessary in the course of which, as is well known, the attack by corrosion is especially favored.

The essential characteristic of the heating conduit according to the invention is the foil having minute holes. Advantageously, the foil according to the invention consists of a base layer of even thickness provided with minute holes having a diameter of more than 0.002 inches (0.05 mm), preferably, however, of about 0.008 inches (0.2 mm). Advantageously, the foil is provided with longitudinal and transverse reinforcement wires or ribs which, in particular, are only on the one side while the other is completely smooth. Usually, the foil is made of synthetics resistant to aging, but it may also consist of mineral or rock wool or of asbestos or of other fabrics produced of materials resistant in the earth, which fabrics are preferably impregnated, the voids in the fabric corresponding to the holes of the synthetic foil. As the task of said foil having holes consists in keeping dry by evaporation the space in which the tubes conveying the hot water are positioned, naturally every foil material may be used which resists to the attack of moisture and which is resistant to aging, as for example pure aluminium, titanium, silicon alloy steel and the like.

A further characteristic of the present invention consists in that the tube joint connections which are inevitable and occur very often, are executed by means of gluing or welding, the gluing being preferred.

According to a further feature of the invention, the welding is most favorably executed by welding tube sections having a relatively thick wall and being annular in cross section on the ends of the tube (root face welding), the front surfaces being then worked mechanically so that a chamfer is formed which, upon joining together the tubes, makes a V-shaped welding groove then welded in known manner.

The gluing method is characterized in that the preformed tube ends according to the example which tube ends are to be joined, are prepared for gluing and are then protected against contamination by applying protective layers which are removed shortly prior to gluing, thereby guaranteeing a surface quality suitable for gluing. For example, this protective layer consists of a plastic layer pulled off prior to gluing.

The invention will be explained in detail with reference to two embodiments and with the aid of the attached Figures.

FIG. 1 shows a cross section of a heating conduit with two tubes conveying the heating medium positioned therein.

FIG. 2 shows a cross section of a heating conduit with a different arrangement of the insulating material, and

FIG. 3 shows a plan view of a cover foil.

At the bottom of a heating conduit 1 drain pipes 2 are laid. The tubes 3 conveying the heating medium lie upon a block 4 of insulating material, which may be continuous, but which also may consist of individual cubes into which the insulating material has been pressed. But also a loose fill of the insulating material 14 may be used. On all sides, the tubes 3 are surrounded by insulating material which is enclosed by two synthetic foils 5. On the top side, said foils meet like a roof and cover one another with their edges 6. The foils 5 leave a gap 15 between themselves and the side walls of the conduit 1 which gap is expediently kept open by ledges, laths or the like, and, with their bottom ends, the foils go beneath the block 4 where they do not, however, cover one another. The drain pipes 2 are positioned outside of the foils and may also be covered by insulating material 16. The space above the foils is filled up with excavation material up to ground level. It is also possible to cover the conduit with a highway surface, as the insulating layer may be weighted.

In the embodiment according to FIG. 2, the fill 14' of insulating material enclosed by the foils 5' comes up to only about the top edge of the tubes conveying the heating medium. In this case, a plate of heat insulating and water repellant or waterproof material 7 is positioned on top of the fill, which plate has a load capacity sufficient to endure the weights occurring.

Also in the embodiment according to FIG. 2, gaps 15' permeable to water are provided between the side walls of the conduit and the foils 5, through which gaps water may be drained off to the drain pipes 2 which may be covered with an insulating material 16', e.g. Leca balls.

The foils enclosing the heat insulating layer consist, as is shown in FIG. 3, of a base layer 8 advantageously of even thickness, which layer is provided with minute holes 9 of more than 0.002 inches (0.05 mm) diameter and with reinforcement ribs 10 net-like extending over the base layer. The side of the foils provided with the reinforcement ribs engages the insulating layer.

In the case of water breaking in, the water is led along the foils to the conduit walls and between said walls and the foil drawn downwardly to the drain pipes. Also, if water is penetrating from the outside of the conduit wall, the foil serves to drain off the water to the drain pipes. In the case of large amounts of water breaking in, for example upon sudden snow melts, cloudbursts, extensive periods of rain and the like, water may also penetrate the insulating material below the cover foils and come into contact with the warm tubes. Then, the water is evaporated and dissipates up to the foils through the holes of which the vapor may escape upward and to the outside. Thereby, a low gauge pressure is achieved within the covered area. As soon as the large supply of water stops, immediately the drying process starts whereby water coming into contact with the tubes is avoided and thus the precondition for an attack of corrosion. Simultaneously, the full insulation effect is restored. Also the amount of water penetrating in a case of emergency is drained off by the drain pipes.

Apart from the aforementioned advantages of the heating conduit according to the invention, the following is pointed out:

Laying of the tubes may be executed without any auxiliary means, for example cranes, as the tube sections may be laid manually. For handling the known heating conduits also having a good insulating quality, however, cranes have to be used, as the individual sections are very heavy. As a rule, they consist of the protective pipe, the insulating material, and the tube sections. The plant according to the invention is considerably less expensive to construct than the other heating conduits referred to. Conclusively, possible repair works may be executed more easily and more simply than with the known heating conduits.

Once more, it is to be repeated that the heating conduit according to the invention is the only one which may be readily "drowned".

The examples shown serve only to explain, not to limit the invention.

In the drawings and in the specification, there have been set forth preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined in the claims.