The present invention relates to the utilization of ground earth under building structures for storing and/or with¬ drawal of heat energy.

It is known to utilize the ground earth or soil for the withdrawal and the storage, if any, of heat energy by arranging at a small depth in the ground substantially horizontal fluid conduits over an area which usually is considerably larger than the building to be heated by the heat obtained by means of fluid circulated in said con- duits and fed to a heat pump. The earth layer with the conduits is directly heated by sun energy during the year's .warm periods. Since an earth layer having only a small depth is utilized this method is limited for storing large quantities of heat ^' . Another disadvantage with this known method is that the possibilities of using the ground area occupied by the conduits for other purposes are much limited. A further disadvantage is that the ground area occupied by the conduits , owing to the conduits being situated at a small depth cannot effecti- vely be used for storing heat fed through said conduits and originating from solar heat .collectors, for instance, since the major part of the heat thus supplied would escape by radiation and be diverted by the wind from said area.

The main object of the present invention is to utilize the layers under building structures supported by piles for storing and withdrawal of heat, especially cheap low tem¬ perature heat preferably originating from solar heat collectors.

This is achieved by designing the piles as tube profiles of metallic material and feeding and/or withdrawing energy to and from, respectively, the inner wall of the pile by means of at least one conduit or conductor which consti¬ tutes or occupies part of the cross section of the pile.

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A good heat transfer between the medium fed down in the pile and the surrounding ground is most important for the purpose according to the invention. In order to achieve this the pile is made substantially entirely of metal, e.g. steel which has a very good heat conductivity as compared with other pile materials, e.g. concrete. If the pile has a tubular profile it is possible to utilize also the internal space thereof directly for feeding and withdrawing the heat carrying medium, thus considerably facilitating the heat transfer. Metal piles can also be fabricated having less wall thickness than piles of other common material and this is advantageous from the point of view of heat transfer. Metal piles can generally be driven into the ground with lighter driving tools than what is required for other piles. Finally it should be* pointed out that metal piles can easily be provided with profiles, e.g. flanges, inter alia by welding.

Other advantages and features of the invention will appear from the following description and the accompanying draw- ing, illustrating an embodiment example, and from the claims.

The drawing shows schematically a building 3 with under¬ lying ground or earth layers 1 and 2 into which tubular, tight-walled piles have been driven. At their upper ends 5 the piles are connected to the sole structure 7 of the building and their- lower tip 6 is sealed for preventing liquid-or gas fluid from flowing in and out. The piles are made of steel and have been rendered rust-proof by applying a layer of a tough plastic material to the outer side thereof. The diameter of the tubes can be different according to the circumstances, suitably 50 to 200 milli¬ meters, e.g. about 75 millimeters. The poles are arranged in a screen pattern in a manner known per se. They can be driven to the rock ground or can be permitted to constitut ■ so called friction piles.

An inner tube or hose 8 for a gas or liquid fluid has been introduced into the piles, said tube extending from its upper end 9 connected to a circulation pump 11 down to near the tip 6 of the pile where the end 10 of the tube 8 is open.

By means of the tubes 8 heated fluid or cooled fluid is fed down to the lower end of the pile according to whether the pile is to be utilized for storing heat in or with¬ drawing heat from the surrounding ground layers 1 and 2.

At the left in the Figure there is shown how the circula¬ tion pump is connected to the hot fluid outlet of a solar heat collector 12 by means of a conduit 14, while the cold fluid inlet of the solar heat collector is connected to the upper end 4 of the tubular pile 5, said end being sealed in other respects. As soon as the temperature of the fluid of solar collector at the outlet exceeds the temperature of the ground layers 1 and 2, which can be sensed by means adapted to automatically control the drive motor of the circulation pump, the latter is star- ted and heated fluid flows down into the pile. When the fluid flows back in contact with, the inner wall of the pile heat from the fluid passes to the surrounding earth layers 1 and 2. This heat storing process can take place with daily or seasonal variations. As soon as the tempera- ture of the hot outlet of the solar collector has decrea¬ sed below a predetermined volume at which heat does not pass to the earth the circulation pump 11 is automatically stopped.

In some cases it can be worthwhile to "lift" the te pera- ture of the fluid by means of a heat pump before the fluid is fed down into the pile for storing the heat energy.

Instead of a solar heat collector other cheap heat source can be used, e.g. warm waste water etc., and also cheap electric power during night hours in which cas-e electrical

conductors and heating elements are introduced into the piles.

The tube 8 can consist of steel and can, if desired, be heat-insulated, especially at the upper portion thereof, for counteracting heat exchange between the fluid in the tube 8 and the fluid in the pile 4.

At the right in the Figure the pile and the innertube 8 are shown as connected to a heat pump 15 the hot side of which being connected to heat radiators 16. The heat pump comprises a circulation pump for a fluid, e.g. a water-glycol mixture or oil which is brought to flow down through the tube 8 and flow back through the pile 4 while withdrawing heat from the earth 1 and 2 surroun¬ ding the pile.

The piles by means of which heat is withdrawn from the earth can be other piles than the piles by means of which heat is stored in the earth, in which case the firs men- tioned piles can be preferably evenly distributed between the last-mentioned piles. But it is also possible to utilize one and the same pile both for heat storing and heat withdrawal, in which case suitable, for instance automatically controlled, valves are provided for swit¬ ching the pile 4 and the inner tube 8 between a heat delivering conduit, e.g. from a solar heat collector, and a heat consumer, e.g. the cold side of a heat pump.

In some cases the piles can be utilized only for with¬ drawing heat from the earth which heat has been supplied to the earth layers 1 and 2 in other ways than by means of the piles, e.g. by means of moving ground water.

When storing heat by means of the piles in the manner described above some heat leakage can occur. The major part thereof, however, returns automatically to the buil-

ding 3 through the sole plate 7 and will thus come to use. Other heat losses from the heat store can be reduced by means of a ground insulation 20 around the building.

By filling the lower heat transmitting portion of the pile by a highly permeable material 18 developing a tur¬ bulent flow of the fluid the heat exchange with the sur¬ rounding earth is increased as boundary layer flow is thereby avoided. In the cases where ground water flows in the friction earth 2 and the piles are to be utilized for storing heat the lower portion of the piles is sealed by pouring concrete 17 therinto for avoiding dissipation of heat through the flowing ground water.

The piles 4 can be jointed piles, e.g. so called steel- plastic piles known per se and jointed by means of hot- zinced steel sleeves which are fixed by fusion at the joint to form a bending and traction resistant connec¬ tion. Such piles composed of steel tubes having av length of about 75.millimeters can take loads up to about 14 tons

For increasing the heat transmitting capability of the piles visavi the surrounding earth the piles can be pro¬ vided with axial steel ribs or flanges, or the piles can be formed with a non-circular, e.g. square, rectangular cross-formed or star-formed cross section.

Drying-up effects in the earth material and thus a deterio¬ ration of the heat transmission and the heat storing can be prevented by diverting drain water to each pile as hinted at 19.

The length of the piles depends upon the ground conditions and the size of the building structure. Typically the length of the pile is about 5 to about 10 meters .

For avoiding corrosion the fluid circulation in the pile

can suitably take place in a closed system.

Since the heat storing according to the invention utilizes piles, already necessary or suitable for the foundation of the building, for transmitting heat from a cheap sourc of heat to the earth and ^" for withdrawing heat therefrom the extra costs for the heat storing will be so low that heat storing of, for instance, solar energy can be a realistic alternative already at the present price rela¬ tions on the energy market.