Storage heater

Abstract

 A storage heater comprises an assembly of bricks defining horizontal passages (19) containing electrical heating elements. Air flows from an inlet (15) beneath a partition (24) and then upwardly along a duct (27) to the passages (19). Air leaving these passages passes below a partition (25) and then to an outlet (16).

Description

[0001] This invention relates to a dynamic storage heater, by which we mean a heater comprising a heat storage body through which one or more air passages extend, means for supplying heat to the heat storage body, an air inlet, an air outlet and ducts for conveying a mechanically propelled stream of air from the air inlet to the air passage or passages and to the air outlet from the air passage or passages. Whilst a dynamic storage heater usually further comprises air propelling means for causing air to flow from the inlet through the air passage or passages to the outlet, such means may be extraneous to the heater.

[0002] In a storage heater according to a first aspect of the present invention, none of the ducts extends beneath the heat storage body. With this arrangement, a heat storage body having a large mass can be supported in a simple manner without incurring the cost of a structural framework capable of supporting the heat storage body above one or more of the ducts. In a heater according to this aspect of the invention, a part of a duct may lie below the level of, but not directly underneath, the lowest part of the heat storage body.

[0003] In known storage heaters, the heat storage body is supported above at least one of the ducts and generally above other parts of the heater, for example a fan and control devices. This known arrangement requires the provision of a framework for supporting the heat storage body and the framework represents a significant part of the cost of a heater. This disadvantage becomes more pronounced with increasing mass of the heat storage body and the present invention is most useful in storage heaters having large heat storage bodies, for example having a weight in excess of one metric ton.

[0004] According to a second aspect of the invention, there is provided a storage heater wherein the heat storage body comprises a plurality of bricks defining main air passages and wherein there are subsidiary air passages defined between substantially flat surfaces of the bricks and communicating with the main air passages.

[0005] It is common to form the heat storage body of a storage heater by assembling a number of pre-formed bricks. Each brick usually has several nominally flat surfaces and these are butted against corresponding surfaces of adjacent bricks. Since the surfaces are not precisely flat, joints between juxtaposed bricks are not air-tight and, during use of a heater, air can leak from the air passages through the heat storage body across abutting surfaces of juxtaposed bricks. In contra distinction to this known arrangement, in a storage heater according to the second aspect of the invention, where it is intended that there should exist between a pair of juxtaposed bricks a subsidiary air passage, the bricks are deliberately spaced somewhat apart so that there is no contact between the bricks of the pair. In a storage heater in accordance with the second aspect of the invention, the width of the subsidiary air passages exceeds the width of any gaps which exists between abutting bricks in a well ordered arrangement of bricks in a known storage heater. Typically, the gap between a pair of bricks between which there is defined a subsidiary air passage may have a width of at least 2mm and more preferably a width exceeding 3mm.

[0006] An example of a storage heater embodying both aspects of the invention will now be described, with reference to the accompanying drawings, wherein:-

FIGURE 1 illustrates diagrammatically a storage heater partly in side elevation and partly in cross-section;

FIGURE 2 illustrates diagrammatically a partial cross-section on the line II-II of Figure 1;

FIGURE 3 illustrates diagrammatically on an enlarged scale certain parts of a heat storage body of the storage heater during construction and in plan view; and

FIGURE 4 illustrates diagrammatically a modification of the heater.

[0007] The storage heater shown in the accompanying drawings comprises a casing 10 which includes a pair of opposed side walls 11, a pair of opposed end walls 12, a top wall 13 and a bottom wall 14. The casing further defines an air inlet 15 and air outlet 16 which extend upwardly from the top wall 13 adjacent to respective end walls and communicate with the interior of the casing. The walls of the casing are joined to each other in a manner to provide an air-tight casing, with the exception of the inlet 15 and outlet 16. The walls of the casing are formed of sheet metal, at least the side walls and end walls preferably having a double-skin construction with ventilation of the cavity between the skins. As shown, the bottom wall 14 may rest on a series of bars 17 which assist with even distribution of the weight of the storage heater over the surface of a floor on which the bars rest.

[0008] The storage heater further comprises a heat storage body 18 disposed within the casing 10 and through which there extends in a direction from one end wall 12 to the other end wall a number of horizontal air passages 19. The body 18 rests on a layer 20 of thermally insulating material which, in turn, rests on the bottom wall 14. It will be noted that there are no substantial voids or air ducts in the heater beneath the heat storage body. The weight of the heat storage body is transmitted directly by the insulating layer 20 to the bottom wall 14 over the entire area occupied by the heat storage body, as viewed in plan. In contra distinction to known storage heaters, no supporting framework is required for the heat storage body. It will be appreciated that the heat storage body may have a large mass. The upper limit of this mass will generally be determined by the strength of the floor on which the storage heater stands.

[0009] The insulating layer 20 is formed of material selected from known insulating materials to have high compressive strength and preferably comprises calcium silicate. Each of the upper and lower surfaces of the layer 20 and the lower surface of the heat storage body 18 is substantially flat and without substantial interruption.

[0010] There rests on the upper surface of the heat storage body 18 a further layer 21 of thermally insulating material which is spaced downwardly from the top wall 13 to define therewith a horizontal by-pass duct 22 through which air can be directed from the inlet 15 to the outlet 16. The insulating layer 21 may comprise panels of compressed vermiculite, together with a layer of mineral wool. The side walls 11 also may be lined with panels of compressed vermiculite and there may be interposed between these panels and the -sheet -metal walls a layer -of mineral wool.

[0011] Between each of the end walls 12 and the heat storage body 18 there is a respective vertical partition 24 and 25 joined at its upper end in a substantially air-tight manner with the upper insulating layer 21. The partitions are also joined in a substantially air-tight manner to the side walls 11. The partition 24 separates a first duct 26 disposed between the partition and one of the end walls 12 from a second duct 27 disposed between the partition and the heat storage body. Between a lower end of the partition and the bottom wall 14, there is a junction 28 between these ducts. The second duct 27 communicates with all of the air passages 19 and communication can be established between the first duct 26 at its upper end and the air inlet 15. Such communication and communication between _';be air inlet and the by-pass duct 22 is controlled by a diverter valve 29.

[0012] The partition 25 separates third and fourth ducts 3o and 3₁. The fourth duct 31 lies between the partition 25 and the heat storage body 18 and communicates with all of the air passages 19 at their ends remote from the second duct 27. The third duct 3o communicates with the fourth duct at a junction 32 beneath the partition 25 and extends upwardly from this junction to the air outlet 16.

[0013] It will be noted that the air passages ₁₉ are arranged in parallel with one another and, considered collectively, are in series with the first to fourth ducts 26,27,3o and 31 respectively.

[0014] Within each of the air passage 19, there is disposed a respective electrical heating element 38 shown only in Figure 3 which is of the form disclosed in British Patent Specification 1,273,6o2. When energised, these heating elements- impart heat to the heat storage body 18. Conveniently, devices for controlling energisation of the heating elements are mounted above the top wall 13 as indicated diagrammatically at 33.

[0015] The storage heater as thus far described may be connected with a warm air distribution system which includes means for establishing a flow of air through the storage heater itself. By way of example, there is illustrated in Figure 1 a fan 34 having an outlet communicating with the air inlet 15. Alternatively, the fan inlet may be connected with 15 so that 15 is an air outlet of the heater.

[0016] The heat storage body 18 comprises a large number of substantially identical bricks 37, each having the form of a rectangular prism across one face of which there is a channel 35. The bricks are arranged in pairs with the channels of the two bricks in a pair facing towards each other, together to define a part of one of the passages 19. Along opposite sides of the passage, the bricks of the pair are in face-to-face contact.

[0017] The bricks 37 of the heat storage body 18 are arranged in a number of layers with each brick spaced slightly from each adjacent brick in the same layer so that there are between adjacent bricks in the same layer narrow gaps 36 which form subsidiary air passages. These subsidiary passages communicate with the main air passages 19. If required, each brick may be spaced from some only adjacent bricks in the same layer and abutting one or more further bricks in the same layer. The width of each gap 36 is small, as compared with the width of an air passage 19. The width of the gaps 36 is preferably at least 2mm and may be somewhat greater than 3mm.

[0018] In order to provide a stable structure of bricks, the bricks in successive layers of the heat storage body 18 have their vertical faces inclined slightly to the side walls 11 and end walls 12 in opposite directions. All bricks of one layer have respective faces which are substantially parallel to one another but are inclined to corresponding faces of bricks of a superposed layer. Each brick overlaps a plurality of bricks in adjacent layers so that there is established a bond in the sense in which this term is used in the bricklaying art. It will be understood that the bricks are not bedded in a mortar and are not normally adhered to one another.

[0019] The partitions 24 and 25 are formed of panels of compressed vermiculite backed with layers of mineral wool. When the temperature of the heat storage body has been elevated, for example to 800°C, the heat is trapped in an insulating enclosure comprised by the upper and lower insulating layers 21 and 20, the partitions 24 and 25 and the insulated side walls 11. Heated air can escape from this enclosure only through the junctions 28 and 32 which are adjacent to the bottom wall 14 so that loss of heat from the heat storage body 18 by convection is severely restricted.

[0020] When heat is required to be extracted from the heat storage body, the fan 34 is energised and the diverter valve 29 is set to a position in which some air passes from the inlet 15 to the outlet 16 through the by-pass duct 22 whilst further air passes from the inlet to the outlet via the ducts 26, 27, the air passages 19 and the ducts 30 and 31. The valve 29 may be controlled by a signal provided by a temperature sensitive element 37 in the outlet 16. When the temperature of the heat storage body is high, the proportion of air directed via the passages 19 is small and most of this air flows through passages in a lower part of the heat storage body. Accordingly, the temperature of this lower part of the heat storage body falls somewhat more rapidly than does the temperature of a higher part of the storage body. If the temperature of the air leaving the storage heater through the outlet 16 is to be maintained, then as heat is extracted from the heat storage body, the proportion of incoming air which passes to the outlet through the air passages 19 is increased. This results in an increase in the pressure in the first duct 26 and the pressure in the second duct 27 so that the rate of flow of air through passages 19 in the upper part of the heat storage body is increased.

[0021] Whilst the main flow of air through the heat storage body takes place within the passages 19, there is also significant flow of air through the gaps 36 so that heat exchange between the air and the bricks is established at faces of the bricks other than those faces which define the passages 19. The total surface area of the bricks which is involved in heat transfer is large.

[0022] It will also be understood that, since the heat storage body 18 is large, the outer surface area per unit of volume of the heat storage body is small, as compared with the corresponding figure for known small storage heaters and the rate of heat loss per joule of stored energy can be maintained at a low level without elaborate and unduly expensive insulation.

[0023] The heater illustrated in Figures 1 to 3 may be modified as shown in Figure I by associating the fan with the outlet, not with the inlet. Except for the differences hereinafter mentioned, the modified heater of Figure 4 is as hereinbefore described and as shown in Figures 1, 2 and 3. In Figure 4, parts corresponding to those already described are indicated by like reference numerals with the prefix 1.

[0024] In the modified heater of Figure 4, the by-pass duct 22 is either omitted entirely or is closed off. The fan 134 is mounted in the air outlet to draw air from the fourth duct 30 and expel such air from the heater. In a wall of the outlet adjacent to the duct 30, there is provided an auxiliary air inlet 140. An electrically controlled valve l4l is provided for controlling the relative proportions of air which are drawn through the outlet from the fourth duct 130 and the auxiliary air inlet 140 respectively. The position of the valve 140 is adjusted automatically to maintain a substantially uniform temperature in the air leaving the fan 134. When the temperature of the heat storage body is high, a relatively large proportion of ambient air will be permitted to enter through the inlet 140. When the temperature of the heat storage body is low, the valve 140 will tend to close the inlet opening 140. In the modified heater of Figure 4, the main air inlet to the heater may simply be open to the ambient atmosphere or may be connected with an air circulation duct through which air is drawn to the heater.

[0025] It will be understood, in a case where the fan is provided in the position shown in Figure 1 but with its inlet connected to the passage 15, energization of the fan will cause air to flow from passage 16 through the by-pass duct 22 and also from the passage 16 through the ducts 31, 3o, the air passages 19 and the ducts 27 and 26 to the passage 15. The proportion of air which flows through the by-pass duct will be controlled by the valve 29.

Claims

1. A dynamic storage heater comprising a heat storage body through which one or more air passages extend, means for supplying heat to the heat storage body, an air inlet, an air outlet, ducts for conveying a mechanically propelled stream of air from the air inlet to the air passage or passages and for conveying air to the air outlet from the air passage or passages, wherein none of said ducts extends beneath the heat storage body.

2. A storage heater according to Claim 1 wherein the inlet and outlet are above the level of an upper boundary of the heat storage body.

3. A storage heater according to Claim 1 or Claim 2 wherein there are a plurality of said air passages at respective different levels, a first of said ducts extends from the inlet to a first junction adjacent to a bottom of the heat storage body, a second of said ducts extends upwardly from the first junction to communicate successively with the air passages, a third of said ducts extends from the air outlet to a second junction adjacent to the bottom of the heat storage body and a fourth of said ducts extends upwardly from the second junction to communicate successively with the air passages.

4. A storage heater according to any preceding claim wherein the air passages are substantially horizontal.

5. A storage heater according to Claim 3 or Claim 4 wherein said air passages are connected in parallel with one another.

6. A storage heater comprising a plurality of bricks defining main air passages and wherein there are subsidiary air passages defined between substantially flat surfaces of the bricks and communicating with the main air passages.

7. A storage heater according to Claim 6 wherein each of said bricks defines a channel and the bricks are arranged so that the main air passages are defined between juxtaposed bricks and comprise the channels.

8. A storage heater according to Claim 6 or Claim 7 wherein certain pairs of immediately adjacent bricks are spaced from each other horizontally to provide the subsidiary air passages, which subsidiary air passages extend vertically between said main air passages.

9. A storage heater according to any one of Claims 6 to 8 wherein the transverse cross-sectional area of each main air passage exceeds that of each subsidiary air passage.

10. A storage heater according to any one of Claims 6 to 9 wherein bricks in successive layers are mutually staggered to provide a bond.

Drawing