A METHOD OF STORING THERMAL ENERGY IN A GROUND STORAGE DEVICE

Abstract: In a method of storing thermal energy in aground storage device (1) of large volume, including a ground body for circulating water in a circuit comprising passages (2) in said body, there are used heat-absorbing and heat-emitting means. The heat-absorbing means has the form of a large, natural or artificial watermass, such as a lake, sea-inlet or the like (5), whose water - heated to above a given temperature during warm periods of the year - is charged to the ground storage device (1). The supply of water to said ground storage device (1) is interrupted when there is equilibrium between the temperature of the water supplied (5) and the temperature of the ground storage device (1).

Description: A METHOD OF STORING THERMAL ENERGY IN A GROUND STORAGE DEVICE The present invention relates to a method of storing thermal energy in a ground storage device of relatively large volume, preferably in a ground storage device which is in direct thermal connection with the surrounding earth and which includes a ground body provided with passages through which water can be circulated in a circuit which includes said passages and external heat-absorbing and heat-emitting devices. An example of such storage of thermal energy is given in Swedish Patent Application No. 7612143-3. The heat- absorbing device primarily considered is a solar energy collector, by means of which thermal energy can be stored during the warmer .periods of the year, to be then taken out during the colder periods. As disclosed in the description of the said Swedish Patent Application, thermal energy must be charged to the device over several years before the storage device can be used to the fullest extent with re¬ spect to its economic yield, despite the fact that the ground storage need only be heated to a temperature mode- rately above the ground temperature, which may be 8°C , for example. Temporary solar energy collectors or special energy sources are required for a number of years to effect this initial heating of the storage device, which must be con- sidered to constitute an additional investment for ensuring that the storage device can be utilized efficiently within a reasonable period of time. The same circumstances prevail in the arrangement of other, similar, large ground storage devices. For reasons of an economic and practical nature, there is a limit to the size and costs that heat-absorbing devices intended for initially heating grund storage devices and maintaining the level of said heat may have, in order to reduce the prepara¬ tory time or to increase the capacity of such devices. OMPI An object of the present invention is to provide a solution to the problem, such as to enable a large quantity of heat of limited temperature to be supplied to a ground storage device of the kind described over short periods during the summertime at relatively low costs. This object is achieved by means of the invention, in accordance with which the heat-absorbing device has the form of large or artificial collections of water, such as lakes, sea-inlets, creaks, rivers, canals etc., having a temperature above a given minimum value, said water being charged to said ground storage device until, at latest, equilibrium is reached between the temperature of said wate and said device. In principle, this type of heat-absorbing device is also a solar energy collector, although it has integrated factor, insomuch as - subsequent to a fair delay during spring - it is active twentyfour hours a day for int the autumn months with a temperature of from 18 to 22°C. By applying different, simple methods, the water of such natural or artificial water masses can be heated to much higher temperatures, e.g. by covering part of the surface of such a water-mass with a layer of heat-insulating materi and supplementing said layer with means for heating the water therebeneath by known solar-energy collecting systems. Thus, by means of the invention, the initial heating of a ground heat-storage device can be accomplished rapidly and cheaply, and the temperature of said device maintained during the warmer periods of the year in a very efficient a economic manner. The only limitation of the initial heatin source used in accordance with the invention vis-a-vis a mo conventional type of solar energy collector is the tempera¬ ture, which is normally limited. This has small importance, however, for initial-heating purposes, and is of no impor¬ tance at all when the ground heat-storage device is to be used in areas where only relatively low temperatures are re quired, i.e. normally water-temperatures of up to 15-20°C i said device. As an example of such areas can be mentioned roads, sidewalks, precincts, football pitches which it is desired to keep dry and free from snow, and the heating of buildings sufficiently to protect against frost. The tempe¬ ratures achieved--.are also sufficient to improve the cultiva¬ tion of crops, algas etc., during the cold periods. In accordance with one embodiment of the invention, the drop of a water-course, for example, incorporated in the water-mass used, or the difference in level to a water-mass situated above the level of the ground. Heat-storage device can be utilized to transport the water from said mass to said device, thereby obviating the need for pumps. So that the invention will be more readily understood and optional features thereof made apparent, an exemplary embodiment of the invention will now be described with refe¬ rence to the accompanying schematic drawing. In the single figure of the drawing there is illu- strated a ground heat-storeage device 1 of the kind described and illustrated in Swedish Patent Application No. 76121H3-3, said device including a plurality of vertically extending mutually parallel pipes 2 which are connected to a common outlet line 3. Each of the pipes 2 has extending coaxially therein a respective inner pipe which is open at the bottom thereof, said inner pipes being connected in parallel to an inlet line H. The inlet line communicates with a lake 5 which is located at a higher level than the device 1, while the outlet line 3 communicates with a lake 6 located at a lower level than said device. The flow of water through the device 1 is regulated by means of valves (not referenced), which may be thermostat controlled, and no pumps are required. If pumps are used, however, it will be possible, of course, to move the water to and from the lakes 5 and 6. It is also possible to connect the lines 3 and 4 to a water-course located between the lakes 5 and 6. If the temperature of the water in lake 5 is too low, part of the surface of the lake can be covered with a buoyant layer 7 of insulating material, such as a plastics material optionally supplemented with auxiliary means for heating the water by -means of solar energy. Such means are well known. The ground heat-storage device may be arranged, for example, beneath the surface of a football pitch, thereby to enable the surface of the pitch to be kept dry from ice by heat derived directly from said device, at least during a greater part of the winter months. The pitch can thus be used much earlier in the spring than is normally the ca As shown in the figure, water may be pumped, by mean of a pump 8, around a circuit which includes the device 1 and a footpath 10. The invention is not restricted to the described and illustrated embodiment, but can be modified within the sco of the claims.

Claims: CLAIMS:- 1. A method of storing thermal energy in ground storage devices of large volume, preferably in such a device which is in direct thermal contact with surrounding earth and which includes a ground body having passages for circulating water in a circuit which includes said passages and external heat- absorbing and heat-emitting means, characterized in that the heat-absorbing means has the form of a large water-mass, having a surface exposed to the sun, which water-mass may be a natural or artificial water-mass, and that water of a given minimum temperature is charged from said water-mass to said ground storage device until, at latest, equilibrium is reached between the water charged to said ground storage de¬ vice and said heat-absorbing means. 2. A method according to Claim 1, characterized in that at least part of the surface of said water-mass is covered by a layer of heat-insulating material, and that measures are taken to heat the water beneath said layer by solar energy. 3. A method according to Claim 1 or Claim 2, characterized in that the drop of a water-course forming part of the water-mass, or the difference in level between said water-mass and said device, is used to transport heated water to said ground storage device. O P

Inventors: LILLIEHOEOEK F, PLATELL O, WIKSTROEM H
Applicants: LILLIEHOEOEK F, PLATELL O, SUNROC ENERGY AB, WIKSTROEM H
Application year: 1979
Main classification: F24D11
IPC codes: F28D20