Abstract:
The present invention relates to a storage system ( 1 ) for storing thermal energy for use in heating a building ( 6 ) or heating water, said system comprising—a cavity ( 11 ) with a bottom surface ( 12 ), at least one side surface ( 13 ) and a top surface ( 14 ),—at least one hose ( 7 ) for transporting a fluid, said hose ( 7 ) being placed inside said cavity ( 11 ) and being arranged to be connected to a heating assembly ( 2 ) for producing and/or using thermal energy, and wherein said cavity ( 11 ) comprises a stone dust material for covering said at least one hose ( 7 ) and only one of said top, side and bottom surfaces ( 14, 13, 12 ) is equipped with an insulating layer ( 15 ), namely said top surface ( 14 ). The invention also relates to a heating assembly ( 2 ) comprising a storage system ( 1 ) and a method for manufacturing a storage system ( 1 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a storage system for storing thermal energy for use in heating a building, said system comprising
       a cavity with a bottom surface, at least one side surface and a top surface,   at least one hose for transporting a fluid, said hose being placed inside said cavity and being arranged to be connected to a system for producing and/or using thermal energy,       
 
       BACKGROUND ART 
       [0004]    The manufacture and use of energy efficient buildings is increasing and provides a convenient and environmental friendly way of living. Often, thermal energy is produced by the use of solar panels on a roof of the building and the energy is transmitted to heating devices such as radiators, underfloor heating or a ventilation system to provide a suitable indoor climate. During some periods of warm and sunny weather, substantially more thermal energy than required can however be produced while during cold and overcast or snowy periods the solar panels produce very little energy that is not sufficient for heating the building. The need for an efficient storing system for storing thermal energy and retrieving it when required is therefore apparent. 
         [0005]    Such storing systems are for instance shown by U.S. Pat. No. 4,138,995 (Yuan), U.S. Pat. No. 4,184,477 (Yuan) and by JP 2004169977 (Taisei Corp.) where thermal energy can be directed into a layer of wet sand or earth and be retained there by insulation, or be directed into a tank placed in the ground. These systems have the drawbacks, however, that the stored energy can seep into surrounding or that the tanks used will require maintenance that is difficult to perform due to the fact that the equipment is buried in the ground. 
         [0006]    GB 1563076 discloses a storage system for storing thermal energy in a layer of a material, but the system is of a complicated construction with excessive insulation and requires energy dissipation within the layer for extracting energy, which is inefficient and potentially costly. 
         [0007]    U.S. Pat. No. 4,321,962 discloses a similar storage system but is only suitable for short time storage due to its limited dimension, and also has a risk of condensation forming on the hose transporting fluid, thus significantly reducing the capacity of the storage system. 
         [0008]    DE 2704938 discloses a system for storing energy, but requires massive insulation to prevent energy leakages, as does WO2010041961. 
         [0009]    Also, none of the systems above is suitable for use with a heat pump or air conditioning system, which significantly reduces their efficiency in heating or cooling a building. 
         [0010]    The requirement for a more efficient system for storing thermal energy without the need for maintenance is therefore apparent. 
       DISCLOSURE OF THE INVENTION 
       [0011]    The object of the present invention is to eliminate or at least to minimize the problems mentioned above. This is achieved through a storage system for storing thermal energy according to the appended claim  1 , wherein a cavity of the system comprises a stone dust material that is arranged to cover a hose for transporting a fluid. Thereby, thermal energy can be conveniently stored in the storage system and thanks to the properties of the stone dust material it can be retained inside the storage system without leaking into surrounding areas. Also, thanks to the configuration of the storage system, only the top surface of the cavity requires an insulating layer to prevent a leakage of thermal energy from the storage system. On the side and bottom surfaces, the heat retaining properties of the storage system keep the thermal energy safely inside the system without the need for a separate insulating layer. 
         [0012]    According to an aspect of the invention said at least one hose is placed in an essentially two-dimensional spiral pattern in said cavity. Thereby, the thermal energy can be concentrated to an area in the centre of the storage system and the risk for a leakage decreased. 
         [0013]    According to another aspect of the invention, said system comprises at least two hoses, at least one of which is a storage hose that is arranged to transport thermal energy into the system and at least one other being a retrieval hose that is arranged to transport thermal energy from the system. Thereby, thermal energy can be loaded into the storage system at the same time as energy is also retrieved, making it possible to use the energy for heating a building without requiring interruption for storage. Dimensions of the hoses can also be adapted to what is beneficial for storing and retrieval, respectively. 
         [0014]    According to yet another aspect of the invention, said at least two hoses ( 71 ,  72 ) are placed at essentially the same distance from the top surface ( 14 ) of the cavity ( 11 ). Thereby, retrieval of thermal energy can be performed efficiently since the retrieval hose is located centrally in the storage system near the storage hose. 
         [0015]    A heating assembly for a building comprising a storage system according to the invention is also provided. Thereby, a complete system with energy production, storage, retrieval and use can be provided, keeping consumption of external energy from a grid, for instance, to a minimum. 
         [0016]    Many other advantages and aspects of the invention are described below and will become apparent to the person skilled in the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention will now be described in more detail with reference to the appended drawings, wherein: 
           [0018]      FIG. 1  shows a schematic view of a heating assembly for a building, comprising a storage system for storing thermal energy according to a preferred embodiment of the present invention; 
           [0019]      FIG. 2  shows a schematic view from the side of the storage system of  FIG. 1 ; 
           [0020]      FIG. 3  shows a schematic view from above of a preferred placement of hoses in the storage system of  FIG. 2 ; and 
           [0021]      FIG. 4  shows a hemispherical shape of a storage unit created inside the storage system of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    In  FIG. 1 , a heating assembly  2  for use in heating a building or similar structure can be seen. Through means for producing thermal energy  3  such as solar panels  3 , thermal energy can be captured and entered into a water storage unit  21  for short term storage or for direct use in a tap  5  for extraction of hot water for the benefit of a person present in the building. Means for distributing thermal energy  22 , such as a heat pump  22  is connected to the water storage unit  21  and also to a storage system  1 , preferably placed in the ground underneath the building. Further, the heat pump  22  is connected to a heating system  4  for heating the building through radiators, underfloor heating or ventilation, for instance. 
         [0023]      FIG. 2  shows a view from the side of the storage system  1  for storing thermal energy according to a preferred embodiment of the invention, where said storage system  1  is located in the ground beneath a building  6 . The storage system  1  comprises a cavity  11  with a bottom surface  12 , side surfaces  13  and top surface  14 , and the top surface  14  is covered by an insulating layer  15 . In the cavity  11 , at least one hose  7  connected to the heating assembly  2  described above is placed, with a heat storage conduit  73  that allows for thermal energy to be inserted into the storage system  1  and a retrieval conduit  74  that allows for said thermal energy to be removed and used in the heating assembly  2 . Surrounding the hose  7 , a stone dust material is placed and fills essentially all available space within the cavity  11  so that the hose  7  is embedded. Preferably, a plurality of hoses  7  are used with the invention, so that a separate storing hose  71  is used for storing thermal energy and another hose, a retrieving hose  72 , is used for retrieving said thermal energy. The storing hose  71  is in this embodiment connected to the heat storage conduit  73  and the retrieving hose  72  to the retrieval conduit  74 . 
         [0024]      FIG. 3  shows a view from above of a preferred placement of the hoses  71 ,  72 , where a double spiral pattern is created. The conduits  73 ,  74  are placed in a centre of the spiral in this preferred embodiment. 
         [0025]    A method of manufacturing the storage system  1  will now be described according to a preferred embodiment of the invention. 
         [0026]    In a first step, a cavity  11  is created in the ground in a location where a building  6  is later to be built, or in the vicinity of an existing building. Said cavity  11  is in a preferred embodiment at least about 2 m deep and covers approximately the same area as the building  6  is intended to. If bedrock is encountered at a suitable depth, it can constitute a bottom surface  12  and can thereby provide an additional thermal storage volume, thanks to the good heat storage properties of bedrock. It also prevents ground water from seeping into the storage system  1 . If no bedrock is encountered, a bottom surface  12  is created from any materials encountered while making the cavity  11 , such as earth or sand. Side surfaces  13  are also created, essentially by digging the cavity  11  sharply downwards to that a wall is created from the earth in the vicinity of the cavity  11 . 
         [0027]    After the cavity  11  has thus been created, in a second step a stone dust material is placed into the cavity  11  to create a first stone dust layer of a depth of at least about  0 , 5  m. At a surface of this first stone dust layer, hoses  71 ,  72  are placed in a third step in the spiral pattern described above and shown by  FIG. 3 , with the conduits  73 ,  74  being attached to the hoses  71  and  72 , respectively, and extending vertically upwards towards. The hoses  71 ,  72  can be fixated by a metal net to keep them in a horizontal plane without the risk for vertical displacements that would cause bends in the hoses  71 ,  72  and increase a risk for wear and tear. Around and above the hoses  71 ,  72 , a second stone dust layer is placed in a fourth step to fill any space left in the cavity  11 , i.e. to a depth of  1 , 5  m of the second stone dust layer, to arrive at ground level. On top of the second stone dust layer, a top surface  14  of the cavity is created and a third layer  16  of crushed rock and an insulation layer such as 250-400 mm of Styrofoam is placed above the third layer in a fifth step. After the storage system  1  has thus been completed, the building  6  can be built on top of the insulation layer  15 . The conduits  73 ,  74  are allowed to protrude through all layers of material placed above the hoses  71 ,  72  and into the building  6  to be connected to the heating assembly  2 . Thanks to a small particle size of the stone dust, the hoses  71 ,  72  are held securely without movement in relation to the storage system  1  and thus wear and tear to the hoses  71 ,  72  can be kept at a minimum. The thermal energy stored in the stone dust can also be kept securely and stably with a very low risk for leakage to the surrounding earth. Even if movements should occur in the ground around the storage system  1 , such as vibrations from heavy vehicles passing nearby for instance, the stone dust will prevent any such vibrations from causing damage to the storage system  1 . 
         [0028]    The stone dust material used can be created from particles left over when crushing rock and stone for other purposes, such as road construction or gravel preparation, and can be an essentially dry material with particles having a diameter of 0-3 mm. The stone dust material has good heat retaining properties and will to a high degree prevent a leakage of thermal energy. Thanks to this very beneficial property, essentially no insulation is needed along the bottom surface  12  and side surfaces  13 . 
         [0029]    When the storage system  1  is charged with thermal energy, a storage unit of an essentially hemispherical shape is created in the stone dust material due to the energy spreading out in all directions from the storing hose  71 , where said hemisphere has a circular area approximately parallel with the top surface  14  and a radius extending vertically from the top surface  14  to the bottom surface  12 , as shown by the area  17  with dashed lines in  FIG. 4 . 
         [0030]    The insulation layer  15  and third layer  16  thus provide an insulation upwards to keep most of the thermal energy stored in the storage system  1  safely inside the system  1 . Any leakage through the layers  15 ,  16  will, however, seep up into the building  6  and serve to warm floors inside the building  6  to the benefit of its inhabitants. This will occur during periods of time when a large amount of energy is stored inside the storage system  1 , i.e. during warmer periods such as summer when a high amount of energy can be captured by the solar panels  3 . 
         [0031]    It is beneficial that the insulation layer  15  and third layer  16  extend over a larger area than that of the top surface  14  of the cavity  11 , to prevent any leakage around the edges of the top surface  14  during cold periods, i.e. to prevent that a winter&#39;s cold seeps into the storage system to decrease storage capacity. A distance of 1.5-2 m may be suitable for the preferred embodiment described here. 
         [0032]    It is beneficial if the storage hose  71  comprises a plurality of hoses  711  placed close together in the spiral pattern, preferably 4-8 hoses  711 , since this facilitates an efficient storage of the thermal energy. Suitable dimensions for the storage hoses  711  may be 22-28 mm×100 m. Preferably, a closed loop is created for the storage hoses  711 , where a pump (not shown) can be used to pump a fluid contained inside said hoses  711 , such as water with an anti-freeze agent, from the heating assembly  2  where the fluid can be heated by the energy captured by the solar panels  3  and down through the storage conduit  73  and outwards in the spiral pattern. When confronted with the storage system  1 , the fluid will gradually cool while the area around the hoses  711  will be heated by thermal energy being transferred from the fluid and out into the stone dust material. The area at the centre of the storage system  1  will have the highest temperature, with the periphery of the storage system  1  being cooler. 
         [0033]    Similarly, the retrieval hose  72  can be a plurality of hoses but is in this preferred embodiment only one hose  72 , with dimensions 40 mm×400 m and containing a brine fluid. A pump can be used for pumping this fluid along a closed loop as well but from the periphery of the spirals and towards the centre, where the brine fluid will gradually be heated and transported into the building  6  by the retrieval conduit  74  for use with the heat pump  22 . 
         [0034]    The temperature inside the storage system  1  is kept relatively low, ranging in the interval 6-22° C. for a storage system  1  located underneath a building  6 . Thanks to this fact, a heating effect can be achieved even during cold winters as long as the sun is shining on the solar panels, since the fluid used for charging will only have to be warmed slightly to be able to transport thermal energy into the storage system  1 . The stone dust material, apart from preserving the thermal energy within the storage system  1 , also serves to prolong the life of the hoses  71 ,  72 ,  711  by providing a secure embedding with small particles that will prevent the wear and tear that would be caused by larger or pointed objects such as larger gravel, for instance. The temperature inside the building  6  is kept higher than the temperature inside the storage system  1 , which is very beneficial in preventing condensation to form on the conduits  73 ,  74  leading down into the storage system  1 . The minimum suitable temperature for underfloor heating, for instance, is thus 22° C., ensuring that this temperature is higher than that inside the storage system  1 . 
         [0035]    In the event that the storage system  1  is to be used with a pre-existing building, the beneficial effect of using any leakage of thermal energy for heating floors inside the building can of course not be utilized. Instead, a thicker insulation layer can be used along the top surface  14  of the cavity  11  to minimise leakage, and the temperature inside the storage system  1  can be allowed to be higher than the temperature inside the building. In this embodiment, conduits  73 ,  74  generally enter the building through a wall to reach the heat pump  22  rather than through a floor such as when the storage system  1  is placed directly below the building. 
         [0036]    The use of the storage system  1  and the heating assembly  2  will now be described in more detail. 
         [0037]    In order to provide heating for a building and for hot water used within said building, solar panels  3  are provided, preferably placed on a roof at a suitable angle to catch as much sun as possible. A slant of 20-40° may be suitable in a Nordic climate. The energy captured by the solar panels  3  is transferred to the water storage unit  21  and is used to heat an amount of water stored there. A suitable amount for a residential building can be 200-900 liters of water. Inhabitants of the house can use water from the water storage unit  21  for washing, showering or other regular water consuming activities. The water in the hot water tank is kept at a suitable temperature, for instance in the range of 55-90° C., and the tank is preferably insulated in such a way that the hot water can be kept hot for several days if no additional energy is added, such as for instance on several subsequent overcast winter days. As long as the sun is shining, however, the thermal energy is used to heat the hot water until a preset temperature has been reached, and any excess energy is stored as is described below. 
         [0038]    Any excess energy produces by the solar panels  3  is transferred into the storage system  1  and kept underground to be used for heating the house when such a need arises. The storage is effected by water heated by the solar panels  3  being led into the storage hose  71  of the storage system  1  along the storage conduit  73 , going down to a suitable depth in the storage system  1  and heat being transferred through a wall of the storage hose  71  into the stone dust material surrounding the hoses  71 ,  72 . Thanks to the spiral pattern, the water inside the storage hose  71  will gradually cool off as it travels outwards in the spiral, keeping a majority of the thermal energy in the stone dust placed centrally underneath the building  6 . Preferably, the storage hose  71  constitutes a closed loop with an outer end of the spiral being led back up into the building  6  and into contact with energy produced by the solar panels  3 . 
         [0039]    For retrieving the energy stored in the storage system  1 , one or more retrieval hoses  72  are distributed in a similar spiral pattern as the storage hose  71  and on approximately the same depth. The flow is directed from a perimeter of the spiral towards the centre, where the retrieval conduit  74  is located. Thanks to this preferred placement, a fluid contained within the retrieval hoses  72  can be successively heated by the passage through the storage system  1  to arrive at a maximum temperature at the centre of the spirals. The retrieval conduit  74  is connected to the heat pump  22  that serves to heat the building  6  through underfloor heating, radiators or the like, and also serves to heat the water in the water storage tank  21 , if needed. 
         [0040]    Thus, the thermal energy captured by the solar panels  3  is continuously transferred to the storage system  1  for storage unless it is used for heating the hot water inside the water storage tank  21 , and at the same time thermal energy is continuously being retrieved by the heating assembly from the storage system  1 . The process of storing energy and the process of retrieving said energy can be performed at the same time. 
         [0041]    In the event that the water inside the hot water tank is too cold, the heating assembly in a first step attempts to heat the hot water to the desired temperature. If this cannot be performed, for instance because not enough solar energy is available to the solar panels  3 , the storage system  1  can instead be used for heating water placed in a smaller tank placed in conjunction with the heat pump  22  and using that hot water for regular use in the building  6 . 
         [0042]    The heat pump  22  is continuously operated to retrieve thermal energy from the storage system  1  unless the temperature inside the building  6  is higher than a preset maximum temperature that can be determined by a control system or manually by a person in the building  6 . 
         [0043]    Also located at the heat pump  22  is a retrieval system to retrieve thermal energy from heated air leaving the building  6  through ventilation. This retrieved energy is used by the heat pump to in the same way that the thermal energy from the storage system  1 . 
         [0044]    The operation of the storage system  1  and the heating assembly  2  can be controlled by a control unit (not shown) that strives to keep a preset indoor temperature in the building  6  and that controls the storage and retrieval of energy as well as the operation of the heat pump  22 , the solar panels  3  and the other components of the heating assembly  2 . The control unit can also be two separate control units, one controlling the heat pump and maintaining a desired temperature inside the building  6  and the other controlling the storing of thermal energy into the storage system  1 , or can be another number of control units as deemed suitable. 
         [0045]    In the preferred embodiment described above, it is assumed that thermal energy is used for heating a building  6  to a desired temperature. It would, however, be possible in a warmer climate to use the same storage system  1  and heating assembly  2  for cooling a building  6  to a desired temperature. The heat pump  22  could then be used for operating an air conditioning assembly, and any excess heat produced by that process could be retrieved for further storage by the storage system  1 . 
         [0046]    In an especially beneficial embodiment of the invention for cooling a building  6 , a cooling system can be used for cooling the storage system  1  to about 15° C. during a day period and for cooling the building  6  using a battery operated circulation pump with the storage system  1  during a night period. This is a very suitable embodiment for hot climates, especially desert climates, where a cooling of the building  6  during both day and night can be required for a portion of the year. Thus, during the day, the system is used for cooling the building as well as cooling the storage system  1 . During the night, a battery driven system with a circulation pump can cool the building using the storage system  1  and thereby achieve a reliable cooling effect inside the building  6  even where electrical energy is not delivered through the power grid during the night. This aspect of the invention may also be the subject of a separate patent application based on the storage system  1  for use in cooling a building. 
         [0047]    Of course, a combination of heating and air conditioning could also be effected by the present invention, for instance by using the thermal energy from the storage system to heat the building  6  during a cold season and cooling the air inside the building during a hot season. 
         [0048]    The invention is not to be seen as limited by the preferred embodiments described above, but can be varied within the scope of the appended claims, as will become readily apparent to the person skilled in the art.