GB2042158A - Thermally insulated heat accumulator - Google Patents

Abstract

A heat accumulator for use in a space heating or hot water supply system comprises an insulated container containing a heat storage medium, e.g. water or wax, and having a radiant heat reflecting lining or coating. As shown, the container 1 comprises a cylinder 2 formed from a series of rigid urethane foam segments, a top 3 and a bottom 4 of the same material, and a watertight liner 15 of polished aluminised foil. The cylinder 2 holds a large volume of water 6 as a heat storage medium and this medium is heated either by a heat exchanger (not shown) which may be heated by water circulated through a boiler or solar collector, or by direct circulation of the medium through a boiler or solar collector. Heat is extracted from the medium either by another heat exchanger (not shown) in the cylinder 2 or by a direct circulation of the medium through external radiators. <IMAGE>

Description

SPECIFICATION Thermally insulated heat accumulator The present invention relates to thermally insulated heat accumulators for use in space heating systems or hot water supply systems.

Great efforts have recently been made to produce heat energy with the aid. of solar collectors and heat pumps. Nevertheless attempts are also being made to improve the efficiency of conventional coal, gas, and oil fired heating systems.

Where heat is produced by means of solar collectors, it is a disadvantage that in our latitudes exposure to sunshine is very irregular and moreover in winter is relatively weak, so that with solar collectors it is not possible to collect a great deal of heat continuously, particularly at times when considerable energy is required, that is to say in winter.

When sunshine occurs, and particularly in winter, it is therefore all the more important to collect and store as much heat as possible in order to survive lengthy periods when the sun does not shine. This generally fails because the storage capacity is inadequate. Hot water boilers heated by circulating solar collector liquid usually have a water capacity of only 300 to 500 litres, and with this amount of hot water very little can be done, particularly when it is desired to use the stored heat not only for providing a hot water supply but additionally, or even exclusively, for space heating purposes.

In the case of coal, gas, and oil-fired heating systems, particular efforts are being made to improve efficiency through control techniques with the aid of external thermostats, thermostats valves provided on radiators, time switches for boiler heating control, and the like. With such heating systems, however, and particularly in the case of gas and oil-fired boiler heating systems, there is still the disadvantage that because of the relatively small capacity of the boiler, the burner switches on and off at relatively short intervals of time, so that the burner always burns only for short periods at a time and consequently there is a great loss of energy.

Electric storage heaters utilize inexpensive night current and store the heat in heat accumulators of relatively small volume. These storage heaters however are heated to very high temperatures and this not only entails problems of thermal insulation, but also gives rise to problems in respect of rational and healthy discharge of the stored heat.

The object of the present invention is to provide a heat accumulator which is not harmful to the environment and which both permits the storage of heat which is produced from solar collectors, heat pumps or other sources with only relatively small rises in temperature in the heat accumulator, and also effectively enables the efficiency of coal, gas and oil-fired heating systems or other types of heaters to be improved.

To this, end, according to this invention, a thermally insulated heat accumulator for use in a space heating system or a hot water supply system comprises an insulated container containing a heat storage medium consisting of water and/or other liquid which is not environmentally harmful, or a readily melting substance, such as wax, the interior of the container having a radiant heat reflecting lining or coating, means for supplying heattothe medium, and separate means for extracting heat from the medium in the container.

Water is preferred as the heat storage medium as it is easily obtainable and particularly non-harmful to the environment. Instead of water, however, it is also possible to use other liquids, for example glycerine, optionally mixed with water, or oils, for example paraffin or silicone oil. It may also be advantageous for the heat storage medium to be a substance which, although solid under normal conditions, melts at relatively low temperatures.Substances of this kind include for example paraffin wax having melting points between 50 and 62"C, waxes, lowmolecular inert polymers, and also very low-melting alloys, such as for example Woods alloy (melting point 60 to 70"C). With such low-melting substances the heat storage effect is increased by the fact that additional energy is required to melt them. If for example heat is supplied to a paraffin wax, its temperature will rise steadily up to its melting point; for a long time its temperature will rise no further, since all the heat energy supplied is used for melting it. Only when all the paraffin wax has melted will its temperature rise further. This amount of heat required for melting is referred to as melting heat.

When the substance cools this heat is liberated in the form of solidification heat in addition to the actual cooling.

The storage capacity of the heat accumulator depends on the one hand on the properties of the heat storage medium used, and on the other hand on the amount of the latter. The storage capacity should preferably be so great that the stored heat is sufficient, without additional heating, to supply a normal household with the usual amount of hot water for several days.

Since according to the invention water is particularly preferred as heat storage medium, the heat accumulator preferably has a storage capacity of at least 1,500 liters, particularly a storage capacity of about 5,000 to 15,000 liters, and preferably a columnlike shape, more particularly a cylindrical, vertically disposed shaped. The inside diameter of a hollow cylinder of this kind amounts for example to about 0.8 meterto 2.0 meters, with a height of about 3 to 5 meters.The wall of the cylinder, and also the bottom and top, may be of any suitable material which, if it is not itself already sufficiently insulated thermally, is additionally provided with a thermal insulating layer, the thickness of the insulating layer being dependent on the A value (coefficient of thermal conductivity) and being so great that practically no heat losses occur through the wall, bottom or top of the tank.

The thermal insulating layer preferably consists of a hard polyurethane foam and has a thickness of about 15 cm. The thermal insulating layer may either directly form the heat accumulator as a selfsupporting element, or may be applied externally or internally to the wall, bottom, and top of the tank or introduced between suitable shutterings. The walls of the heat accumulator may then be made of metal, plastics material, or concrete rings. The same applies to the shutterings. According to the invention, for example, it is advantageous to use concrete rings which are disposed one above the other and which are concentrically surrounded by concrete rings whose diameters are preferably 30 cm larger than the diameters of the inner concrete rings.The gap remaining between the concrete rings is then filled in situ with hard polyurethane foam, the foaming preferably being effected in stages, that is to say one or two inner concrete rings, depending on their height, and a corresponding number of outer concrete rings are laid in position, and the space between them is filled with foam before the next concrete rings are placed above them. Instead of outer rings of concrete it is obviously possible to use corresponding rings of metal or plastics material, or the outer rings may be of concrete and the inner rings of metal or plastics material. The inner and outer rings may of course also simultaneously be of metal or plastics material. Moreover, the filling with foam need not be effected in situ, but the heat accumulators may be delivered completely ready for use.

As already mentioned, the cylindrical wall, the bottom, and the top of the heat accumulator may however also be in the form of self-supporting elements, these elements optionally being held together by additional means. For example, the cylinder wall may consist solely of hard polyurethane foam and be in the form of a tube, or it may be composed of superimposed tubular rings corresponding in onstruction to the concrete rings, or it may consist of two half-shells or of a plurality of longitudinal cylindrical segments. The half-shells or longitudinally cylindrical segments either have a length which corresponds to the desired height of the heat accumulator, or they are so dimensioned that they form the desired height when additionally disposed one above the other.In order to enable them to be superimposed in such a manner that they cannot be displaced, the tubes, the tubular rings, and also the half-shells and longitudinal segments are provided at their bottom end, and optionally at their top end, with correspondingly shaped projections and depressions similar to tongue and grooving, such as are customary for concrete rings.

The longitudinal cylindrical segments are in addition preferably so shaped that the inside and outside surfaces have the same radius of curvature. Because of this the longitudinal cylindrical segments can be stacked one above the other during transport, in such a manner as to save space and to protect them against damage, without the corners being endangered in any way.

On their longitudinal edges the half-shells preferably also have tongues and grooves or corresponding projections and depressions, whereas for the longitudinal cylindrical segments this is not necessary because on their longitudinal edges they are so shaped that they come to lie against one another in accordance with the principle of arch stones. The position of the side surfaces of the longitudinal segments is so arranged that the theoretical extension of the side surfaces passes through the longitudinal axis of the cylinder.

The half-shells or longitudinal cylindrical segments are preferably held together by steel bands, which for example are screwed together at their ends similarly to hose clips, or by concrete rings disposed one above the other.

The column shape, or in particular cylindrical shape, in a vertical arrangement is preferred because it is thereby ensured that the hot water will always collect in a relatively small space on the surface, from which it is either drawn off or the heat is given up to one or more heat exchangers in which the tapwater and/or heating water is heated.

The heat accumulator need not of course simply have a column or cylindrical shape and be disposed vertically, but it may also lie horizontally or have the shape of a pyramid, cone, right parallelepiped, or cube, in which case however a pyramidic or hemispherical or similarly shaped top portion should be disposed on the tank to ensure that the hot water can always collect in the relatively small space bounded by the said top portion.

The inner surfaces of the heat accumulator are preferably covered with aluminium foil, particularly a highly polished aluminium foil. According to the invention, for example, the half-shells or the longitudinal cylindrical segments can be produced continuously as sandwich elements, the outer layers consisting of aluminium foils and the core of hard polyurethane foam.At this point it may be observed that not only is protection claimed for the feature that the heat accumulator is provided internally with a complete or partial coating reflecting heat radiation orwith a reflecting foil lining, preferably a lining of aluminim foil or the like, in conjunction with the heat accumulator according to the invention, but that separate protection is also claimed for heat accumulators of other types, for example for smaller hot water boilers having a capacity of 300 to 500 litres.

In cases where the insulating casing of the heat accumulator is not watertight or is subject to corrosion, a foil bag is fastened in the heat accumulator, at the top end of the cylinder wall, this bag being of such dimensions that it rests on the bottom and bears against the inner wall of the cylinder. When a foil bag of this kind is used, it can also take over the function of the heat reflecting lining if the foil bag itself is coated or laminated with a heat reflecting layer.

In view of the size of the large heat accumulators preferred in accordance with the invention, they are preferably installed outside the house, preferably in the ground, for example in the case of detached or semi-detached houses. In many cases previously existing drainage pits can be "converted" into accumulators according to the invention.

In a preferred embodiment of the invention the wall, bottom, and top of the cylinder forming the heat accumulator therefore consist of hard polyurethane foams.

The accompanying drawings illustrate two examples of this preferred embodiment.

In the drawings: Figure lisa longitudinal section through the accumulator; Figure 2 is a longitudinal section througha part of the accumulator to a larger scale; Figure 3 is a longitudinal section through another part of the accumulator to a larger scale; Figure 4 is a cross-section through components of the accumulator before final assembly; Figure 5 is a cross-section similarto Figure 4, but showing a modification; Figure 6 is a perspective view of the components shown in Figure 4, but before initial assembly; and Figure 7 is an axial section through another component.

Figure lisa longitudinal section through a preferred heat accumulator according to the invention, the cylinder wall, bottom, and top of which are made of hard polyurethane foam, the cylinder wall 2 being composed of longitudinal cylinder segments 5, such as are shown in cross-section in Figures 4, 5, and 6. The longitudinal cylindrical segments 5 are laminated internally and externallywith aluminum foil (not shown in the drawings), so that the inner surfaces of the cylinder wall 2 can reflect heat. The inner surfaces of the bottom 3 and top 4 are preferably likewise laminated with aluminum foil.

The filling height of the heat accumulator is designated "h" and the inside diameter "i". The heat accumulator is filled with water 6. The heat exchangers, which are preferably disposed under the surface of the water and on the bottom of the heat accumulator, and their inlet and outlet pipes are not shown in the drawings. The inlet pipe ending with its inlet opening 8 in the air cushion 7 and the outlet pipe ending in the water with the suction opening 9 slightly above the bottom constitute the inlet and outlet pipes for a particular embodiment of the invention, to which reference will be made in rather greater detail later on in connection with a solar collector used as heat source.

Figure 2 is a longitudinal section on a larger scale, showing the top end 10 of the cylinder wall 2 with the edge 11 of the top 4, which by means of cover bolts 12 is joined to the top end 10 of the cylinder wall 2, hermetic sealing being achieved with the air of elastic sealing rings 13. The fastening 14 of the foil bag 15 is shown diagrammatically in longitudinal section at the top end of the longitudinal segment 2.

Figure 3 shows in longitudinal section on a larger scale the bottom end 16 of the cylinder wall 2, provided with a tongue 18 which extends around it and which engages in the groove 17 extending around the bottom plate 4.

Figure 4 shows in cross-section the longitudinal cylindrical segments 5 which are joined together to form a cylinder wall and whose inner surfaces have a smaller radius of curvature than the outer surfaces, the radius of curvature of the inner surfaces being adjusted to the desired inside diameter i of the heat accumulator and the radius of curvature of the outer surfaces being adjusted to the desired wall thickness of the cylinder wall 2 and also forming in section a circle on the outside.

Figure 5 shows in cross-section the longitudinal cylindrical segments 5 which are joined together to form a cylinder wall 2 and whose inner faces form a circular cross-section, while the outer faces form an undulating arc of a circle, since the radius of curvature of the inner faces is equal to the radius of curvature of the outer faces.

Figure 6 shows in perspective longitudinal segments 5 according to Figure 5, which are stacked one on the other.

Figure 7 shows a longitudinal section through a known concrete ring, with the diagrammatically shown projection 21 extending around it and with the corresponding depression 22 also extending around it, the projection and depression enabling the concrete rings to be disposed one above the other without risk of displacement.

The features described below in greater detail are also applicable to the various possible embodiments of the invention.

Above the heat storage medium 6 is. preferably provided a gas cushion 7, which preferably consists of air or an inert gas, for example nitrogen. The gas cushion is in the usual way sealed hermetically against the outside atmosphere and is of such dimensions that under normal conditions its volume is able to cushion the increase in pressure occurring on heating the heat storage medium 6. On the other hand, it may also be advantageous for the gas cushion not tote hermetically sealed in relation to the outside atmosphere, but to be in communication with the latter. In this way a simple equalization of pressure can be achieved in the system, provided that the connection to the outside atmosphere is such that large evaporation losses are avoided. The specialist will know how to make such a connectior.

to the outside atmosphere. In a special embodiment of the invention it is of course also possible to disperse entirely with the gas cushion, although in that case it is advisabie to provide elsewhere a pressure equalization vessel of the type customary in heating technique. In addition, it is possible for the heat storage medium 6, for example water which is preferably used, to be under a pressure which corresponds to the pressure prevailing in the water pipe. On the other hand it is naturally also possible to connect the heat accumulator to the water pipe by way of a suitable pressure reduction valve. This embodiment will in particular be selected when it is desired to use the water heated in the heat accumulator direct as the hot water.

The devices for the supply of heat are preferably disposed slightly above the bottom of the heat accumulator, since in this way it is ensured that the hot water will collect in the upper part of the heat accumulator and that the cold water collecting on the bottom of the heat accumulator will always be heated. The heat supply device is for example a heat exchanger, which is disposed on the bottom of the heat accumulator and which is fed with circulating water heated, for example, in solar collectors or in the heat pumps. In a particularly preferred embodiment of the invention the water contained in the heat accumulator can be pumped off at the bottom, passed directly through the solar collector or through the boiler of an oil, gas, or coal burner, and returned to the heat accumulator at the top.An embodiment of this kind will be described more fully below in connection with the use of a solar collector.

In many cases, however, it may be more advantageous for the medium contained in the heat accumulator to be heated by means of electric energy, which is available at low cost, particularly during the night. For this purpose an electrically heated heat source, for example one comparable with a large immersion heater, is then provided on the bottom ofthe heat accumulator.

Under the surface of the heat storage medium 6 are preferably disposed the devices for heat discharge, that is to say suitable heat exchangers through which the tapwater and/or heating water is passed and in which the said water is heated. An expedient arrangement provides for two suitable heat exchangers to be disposed one above the other or side by side, water intended for use being passed through one heat exchanger and water intended for heating purposes through the other.

In a similar way to that in which the water serving as heat storage medium can be heated direct in solar collectors, the stored water may also be passed directly through the radiators of the heating system or through the floor heaters. Exactly the same is true in the case already mentioned where it is desired to use the hot water stored in the heat accumulator direct as hot tapwater.

A particularly interesting application of the heat accumulator according to the invention is to be seen in a special combination with a solar collector, whereby a solar collector heating system is obtained which consists essentially of a solar collector, the heat accumulator of the invention, the recirculation pipes which enable the collector liquid to be pumped in a closed circuit through the solar collector and the heat accumulator, and the actual radiator or hot water system.This combination is characterized in that: (a) the thermally insulated heat accumulator 1 has a capacity of at least 1500 liters and the whole or part of its interior has a coating reflecting heat radiation or a reflecting foil lining, preferably a lining of aluminum foil orthe like; (b) the collector liquid is passed not through the heat exchangers contained in the heat accumulator 1, but through the heat accumulator 1 itself, and the water serving to heat the radiators or the hot tapwater is passed through a heat exchanger which is contained in the heat accumulator 1 and whose capacity is varied in dependence on its purpose; (c) a gas cushion 7 is disposed in the heat accumulator 1, above the collector liquid which is to be circulated;; (d) the heat accumulator is so shaped that the gas cushion 7 is situated above the heat exchanger, which is disposed in the heat accumulator 1 in such a manner that during the operation of the solar collector it lies slightly under the water surface 6; (e) a suction opening 9 is provided in the lower part of the heat accumulator 1, preferably on the bottom, and an inlet opening 8 is provided in the top part of the heat accumulator 1 for the collector liquid, the inlet opening 8 ending in the top part of the gas cushion 7; (f) the solar collector is so disposed that during its operation the collector liquid contained therein can, after the circulating pump pumping the collector liquid has been switched off, pass out of the solar collector and the corresponding recirculation pipes by way of the inlet opening 8 and suction opening 9 respectively and into the heat accumulator 1.

In this solar collector heating system therefore the feature essential to the invention can be seen in the combination of the heat accumulator, the air cushion, and the draining of the solar collector when the pump is out of operation, this draining of the collector when the pump is out of operation being possible only by working with the abovementioned air cushion. This air cushion has to fulfil two functions in this case: to permit the draining of the collector when the pump is not in operation on the one hand, and to act as a pressure buffer on the other hand, since not inconsiderable differences in pressure occur in the heating of the internal water from a temperature of 20 to 25"C to a temperature of 60"C.

The gas cushion 7 contained in the heat accumulator 1 is preferably connected by a pipe to the duct lying at the highest level in the solar collector, by way of a valve contained in the solar collector and opening when the circulating pump is switched off, that is to say when the internal pressure ceases to exist, whereby the draining of the collector liquid from the solar collector is assisted. As already indicated, the gas cushion 7 is an air cushion or an inert gas cushion, for example a nitrogen cushion, whose volume under normal conditions is so selected that on the one hand it is able to cushion the rise in pressure which occurs in the system when the collector liquid is heated, and on the other hand is at least so large that it can take the place of the collector liquid contained in the solar collector and recirculation pipes during pumping. The ducts in the solar collector through which the collector liquid circulates are preferably disposed with a slope such that when the circulating pump is switched off the collector liquid can flow back into the heat accumulator 1 not only through the inlet opening 8 but also through the suction opening 9.

Claims (32)

1. Athermally insulated heat accumulatorfor use in a space heating system or a hot water supply system, the accumulator comprising an insulated container containing a heat storage medium consisting of water andíor other liquid which is not environmentally harmful, or a readily melting substance, such as wax, the interior of the container having a radiant heat reflecting lining or coating, means for supplying heat to the medium, and separate means for extracting heat from the medium in the container.

2. An accumulator according to Claim 1, in which the container has a lining which is of polished aluminium foil.

3. An accumulator according to Claim 1 or Claim 2, in which the volume of the medium is at least 1500 litres.

4. An accumulator according to any one of Claims 1 to 3, in which the container has a vertical column-like shape.

5. An accumulator according to Claim 4, in which the container is cylindrical.

6. An accumulator according to Claim 5, in which the cylinder has an internal diameter of from 0.8 to 2 metres and an internal peripheral wall height of from 3 to 5 metres.

7. An accumulator according to any one of the preceding Claims, in which the peripheral wall and also the top and bottom of the container are made of a thermal insulating material.

8. An accumulator according to Claim 7, in which the thermal insulating material is a foamed plastics material.

9. An accumulator according to Claim 8, in which the foamed plastics material is a rigid polyurethane foam.

10. An accumulator according to Claim 9, in which the wall thickness of the container is at least 15 cm, and the inner face of the wall, and of the top, and bottom are lined with a highly polished aluminium foil.

11. An accumulator according to Claim 7 when dependent on Claim 5 or Claim 6, in which the cylinder wall of the container consists of a tube, or of rings disposed one above the other, or of two semi-cylinders, or of a plurality of cylindrical segments.

12. An accumulator according to claim 11, in which the cylinder wall consists of a plurality of segments the inner faces and the outer faces of which have the same radius of curvature as each other.

13. An accumulator according to Claim 11, in which the cylinder wall consists of rings or segments which are joined together by means of tongues and grooves.

14. An accumulator according to Claim 11, in which the cylinderwall consists of semi-cylinders or segments which are held toegether by steel bands, or by concrete rings disposed one above the other.

15. An accumulator according to Claim 7, in which the peripheral wall and the top and bottom are made of the same material and have the same thickness as each other.

16. An accumulator according to any one of the preceding Claims in which the medium is held in a foil bag which bears against walls of the heat accumulator, the bag being provided internally with a heat reflecting layer.

17. An accumulator according to Claim 16, in which the foil bag consists of a plastics foil iaminated internally with a highly polished aluminium foil.

18. An accumulator according to any one of the preceding Claims, in which a gas cushion is situated in the container above the heat storage medium.

19. An accumulator according to Claim 18, in which the cushion is of nitrogen or other inert gas.

20. An accumulator according to Claim 18 or Claim 19, in which the container is hermetically sealed and also the volume of the gas cushion under normal conditions is able to cushion the increase in pressure occurring on the heating of the heat storage medium.

21. An accumulator according to Claim 18 or Claim 19, in which the gas cushion is vented to atmosphere.

22. An accumulator according to any one of Claims 1 to 20, in which the heat storage medium is under a pressure of from 1 to 2 atmospheres or under a pressure equal to that prevailing in an inlet pipe.

23. An accumulator according to any one of the preceding Claims, in which the means for supplying heat to the medium is a heat exchanger within and just above the bottom of the container.

24. An accumulator according to Claim 23, further comprising a solar collector or a heat pump and means for circulating water from the collector or pump through the heat exchanger.

25. An accumulator according to any one of Claims 1 to 22, in which the medium is pumped from the bottom of the container, and is passed directly through a solar collector or through an oil, gas, or coal-fired boiler, which forms the heating means and is returned to the top of the container.

26. An accumulator according to any one of Claims 1 to 22, in which the means for supplying heat is an electrically heated heating device.

27. An accumulator according to any one of the preceding Claims, in which the means for extracting heat is disposed just under the surface of the heat storage medium in the container.

28. An accumulator according to Claim 27, in which the means for extracting heat is a heat exchanger through which water to be heated flows.

29. An accumulator according to Claim 27, in which the means for extracting heat comprises two heat exchangers side by side, one for heating water for a hot water supply and one for heating water for space heating.

30. An accumulator according to any one of Claims 1 to 27 in which the means for extracting heat comprises means for circulating the heating medium through the radiators of a heating system or through a floor heating system.

31. An accumulator according to any one of the preceding Claims, in which the heating medium is water which is used directly as a hot water supply.

32. An accumulator according to Claim 1, substantially as described with reference to Figures 1 to 4 and 6, or as modified with reference to Figure 5 or Figure 7 of the accompanying drawings.