WO2006032084A1

WO2006032084A1 - Water heater jacket

Info

Publication number: WO2006032084A1
Application number: PCT/AU2005/001433
Authority: WO
Inventors: Michael Sandor Biczo; David Allan Lawson
Original assignee: Rheem Australia Pty Limited
Priority date: 2004-09-22
Filing date: 2005-09-20
Publication date: 2006-03-30

Abstract

A jacket type storage water heater includes a storage tank (802) and a jacket (804) surrounding at least part of the tank. The jacket is spaced from the tank by a jacket gap to define a jacket chamber. A heat transfer fluid inlet (806) and a heat transfer fluid outlet 808 permit heat transfer fluid to be circulated through the jacket chamber from a heat source. Fluid guides (810, 812, 814), (816) cause the heat transfer fluid to follow a meander path around the outside of the tank.

Description

WATER HEATER JACKET

Field of the invention

[001] The present invention relates to a jacket for use in the indirect heating of a water heater unit. It is particularly adapted for a jacket that receives heated fluid from a solar heating panel which is directed to indirectly heat hot water service for domestic or commercial usage. However it has potential application well beyond this use. The invention can be implemented in a heat exchanger.

Background of the invention

[002] Solar water heaters for domestic use may be of two general types: the thermosiphon type where the water storage container is held at a height slightly above that of the solar collection panels and split system where solar panels heated on a roof feed a water storage facility located below it, usually at ground or other level at which the water supply is being used. Thermosyphoning usually requires a negative temperature/height gradient. The present invention is particularly useful in relation to split systems.

[003] Split systems are also divided into two general categories: direct systems wherein the water circulating through the solar collection panels is transferred after being heated to the split water storage facility through piping; and indirect systems wherein a fluid is contained within a separate heat transfer fluid circulation system which incorporates the solar collection panels and passes through a heat exchanger by which heat energy from the circulated heat transfer fluid is transferred through the storage thank wall to the water in the hot water storage tank.

[004] Indirect split systems have been adopted principally to overcome the problem of water freezing within the solar collection panel. Where such panels are used in environments where the ambient temperature falls below freezing, there is a problem with direct systems that the water freezes within the solar panel and fractures the tubing leading to leakage. Where an indirect system is used, the circulating heat transfer fluid comprises an antifreeze mixture with a freezing point below that which is likely to be encountered. In addition indirect split systems also help to avoid the blockage of the energy collector or source by calcium deposits and sludge, resulting in longer component life and maintaining the efficiency and integrity of the system.

[005] In such indirect systems a range of heat exchangers have been tried. Such heat exchangers include: a coil of the recirculation system mounted inside the tank, and a jacket in contact with a portion of the water storage tank. [006] In the case of vertically oriented tanks, large gap jackets having a gap of the order of 35 mm have been used. The present invention relates to an improvement in the design of a jacket for a vertically oriented tank.

[007] Water storage tanks generally used are pressurised to withstand foil mains water pressure and for that reason are usually of cylindrical construction with a central axis of the cylinder oriented vertically. The jacket has generally been a cylindrical sheet surrounding the lower portion of the water storage tank where recirculating fluid enters the jacket at a high point of the jacket and exits the jacket at a low point on the opposed side of the jacket. While such a system has a number of advantages it has been found that heat transfer in such a system is imperfect as the flow is dominated by buoyancy, stagnant flow and complex re-circulation zones. The buoyancy zone occurs in the top 20% of the jacket and the large re-circulation zone in two thirds of the jacket and stagnant flow in the remaining section of the jacket in lower heat transfer.

[008] The applicant does not concede that the features described in the description of the art are within the common general knowledge of a person skilled in the field.

[009] Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application.

Summary of the invention

[010] The present invention provides jacket water heater for a vertically oriented tank including: a jacket surrounding at least a part of the exterior of a tank and forming a jacket gap between the exterior wall of the tank and the interior wall of the jacket, a heat transfer fluid inlet to admit heat transfer fluid into the jacket gap, and a heat transfer fluid outlet to permit heat transfer fluid to flow out of the jacket gap, wherein the jacket gap is less than 20 mm.

[011] The present invention also provides a jacket water heater for a vertically oriented tank including: a jacket surrounding at least a part of the exterior of a tank and forming a jacket gap between the exterior wall of the tank and the interior wall of the jacket, a heat transfer fluid inlet to admit heat transfer fluid into the jacket gap, and a heat transfer fluid outlet to permit heat transfer fluid to flow out of the jacket gap, including a fluid guide means within the jacket gap.

[012] The jacket gap can between 3 mm and 18 mm. [013] The jacket gap can be of the order of 5 mm. [014] Heat transfer fluid can be circulated in a heat transfer fluid circuit including the jacket by convection.

[Ol 5] The heat transfer fluid can be circulated by a pump.

[016] The fluid guide means can include at least one fluid diverter in the form of an elongate barrier having a thickness substantially equal to the jacket gap.

[017] The or each fluid diverter can provide at least one fluid path between the heat transfer fluid inlet and the heat transfer fluid outlet.

[018] The fluid guide can include at least one a partial circumferential ring in the jacket gap, having a gap through which the heat transfer fluid can flow.

[019] The jacket water heater can include two or more partial ring fluid guides, wherein the gaps in adjacent rings are staggered axially. •

[020] The gaps in adjacent rings can be diametrically opposed.

[021] The fluid guide can be in a form of a spiral extending from the heat transfer fluid inlet at least part way down the axial length of the jacket.

[022] The jacket water heater can include a flow divider causing the flow from the heat transfer fluid inlet to follow two or more paths.

[023] The flow diverter can be adapted, in use, to cause a first part of the heat transfer fluid to flow on one side of the spiral, and to cause a second part of the heat transfer fluid to flow on the other side of the spiral.

[024] The jacket water heater can include a fluid guide formed by a channel pressed into the jacket.

[025] The j acket water heater can include a fluid guide formed by a spacer member between the outer wall of the tank and the inner wall of the jacket.

[026] The invention further provides a method of increasing the contact area of a heat transfer fluid in a heat exchanger having a jacket and a heat transfer wall, there being a jacket gap between the jacket and the heat transfer wall, the method including providing a fluid guide within the jacket gap.

[027] The fluid guide can increase the length of the heat transfer fluid flow path between the heat transfer fluid inlet and the heat transfer fluid outlet. [028] The invention also provides a jacket adapted to be. applied to a storage water heater tank, the jacket including one or more spacers adapted to form one or more fluid guides which, in use, forms one or more fluid flow paths between the jacket and the and the wall of the tank.

[029] The invention further provides a water heater jacket and fluid guide adapted to be applied to a storage water heater, the jacket including a sheet adapted to form an annular jacket around a storage water heater tank and spaced from the tank by a jacket gap, the fluid guide including an elongate member having a width corresponding to the jacket gap, the fluid guide being adapted to be placed at least partly around the tank in the jacket gap.

[030] The jacket can include annular rims adapted to be sealed to the tank to define an enclosed annular chamber surrounding at least part of the tank. Accordingly, the invention resides in a hot water storage facility comprising an indirectly heated water storage tank having a water heater jacket, the water storage tank adapted to contain a reservoir for water and having a tank wall with an external surface, the jacket providing an enclosed space covering at least a portion of the external surface of the tank wall and having an inlet to provide fluid entry into the enclosed space and an outlet to provide fluid exit from the enclosed space, wherein at least one fluid guide is provided within the enclosed space in order, in use, to direct fluid flowing from the inlet to the outlet to travel in an extended path through the enclosed space.

[031 ] By the present invention there is also provided in a hot water storage facility including an indirectly heated water storage tank having a water heater jacket, the water storage tank adapted to contain a reservoir for water and having a tank wall with an external surface, the jacket providing an enclosed space covering at least a portion of the external surface of the tank wall and having an inlet to provide fluid entry into the enclosed space and an outlet to provide fluid exit from the enclosed space, wherein at least one fluid guide is provided within the enclosed space in order, in use, to direct fluid flowing from the inlet to the outlet to travel in an extended path through the enclosed space.

[032] The fluid entry inlet can be positioned in the upper portion of the jacket. [033] The fluid exit outlet can be positioned in the lower portion of the jacket.

[034] Alternatively, the inlet can be located in the lower portion of the jacket and the outlet can be positioned in the upper portion of the jacket.

[035] The heat transfer fluid can be circulated by a pump.

[036] The heat transfer fluid can be circulated by thermosyphoning. [037] At least one fluid guide can comprise a wall extending between the external surface of the tank and the jacket, the wall dividing the enclosed space into a plurality of regions, a break being provided in the wall to permit fluid to flow between adjoining regions.

[038] The wall can include a baffle in the form of a broken ring positioned within the enclosed space.

[039] A single ring can be provided within the enclosed space, the ring dividing the enclosed space into two substantially equally size regions.

[040] A plurality of rings can be provided within the enclosed space. [041] The rings can be substantially equi-spaced.

[042] The position of each break in each wall, and the position of the outlet can be positioned relative to the inlet to extend the flow path between the inlet and the outlet.

[043] The wall also provides reinforcement to the jacket.

[044] The width of the enclosed space between the external surface of the tank and the jacket can be less than 15 mm.

[045] The width of the enclosed space between the external surface of the tank and the jacket can be in the range of 4mm to 10mm.

[046] The fluid guide can be adapted to produce a spiral path from the inlet to the outlet.

[047] The spiral can be configured to produce a longer contact time for the heat transfer fluid nearer the inlet than the heat transfer fluid nearer the outlet.

Brief description of the drawings

[048] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[049] Fig. 1 is a diagrammatic partially cut-away elevation of a conventional indirectly heated hot water storage facility of the prior art.

[050] Fig. 2 is a diagrammatic isometric view of the jacketed portion of a hot water storage tank according to the first embodiment.

[051] Fig. 3 is a diagrammatic elevation of the jacketed portion" of a hot water storage tank according to Figure 2. [052] Fig. 4 is a diagrammatic isometric view of the jacketed portion of a hot water storage tank according to the second embodiment.

[053] Fig. 5 is diagrammatic elevation of the jacket portion of a hot water storage tank according to Figure 4.

[054] Figure 6 shows a sheet for forming a jacket with a fluid guide.

[055] Figure 7 shows a partially formed jacket formed from the sheet of Figure 6.

[056] Figure 8 shows a tank with jacket and flow divider.

[057] Figure 9 shows detail of the flow divider.

[058] Figure 10 shows a jacket heater with spiral fluid guide.

[059] Figure 11 shows a flow divider for the arrangement of Figure 10.

Detailed description of the embodiment or embodiments

[060] In order to better understand the improvements made by the invention it will be helpful to first describe a conventional indirectly heated hot water storage tank. This description is given with reference to Figure 1.

[061] As shown in Figure 1, a conventional, indirectly heated, hot water storage facility 11 comprises a generally elongate substantially cylindrical storage tank 12 and is configured with withstand mans water pressure. In use, the tank 12 is usually oriented in an upright position, that is, with the central axis of the cylinder substantially vertical to promote temperature stratification within the tank 12. The tank 12 is usually constructed of sheet metal, preferably either of copper or stainless steel to resist corrosion, although protected steel or other materials might be used. The tank 12 has a cold water inlet 14 near the base and a hot water outlet 15 at the upper region. A pressure relief valve (not shown) is also provided.

[062] The water heater jacket 21 comprises a second cylindrical skin of the same or similar material to that used for the water storage tank 12 and is slightly larger diameter to that of the water storage tank 12. The jacket is positioned around the lower portion of the water storage tank 12 and the upper 26 and lower edges 23 of the jacket 21 are inwardly formed to contact and be sealed to the water storage tank 12 by welding or other appropriate means. The jacket 21 thus provides a fully enclosed annular space 22 between the water storage tank 12 and the jacket. A fluid outlet 24 for the recirculating fluid is provided near the lower edge 23 of the jacket 21 and a fluid inlet 25 is provided near the upper edge 26 of the jacket 21 disposed 1800 relative to the fluid outlet 24 when seen from the plan view. The jacket usually covers about 50% of the external, cylindrical surface of the water storage tank 12, although this can be varied according to the particular design. The distance between the wall of the water storage tank 12 and the skin of the jacket is usually in the region of 15mm to 30mm.

[063] In use, heated fluid from the solar collection panel is piped to the fluid inlet 25 of the jacket 21. The heated fluid passes from the fluid inlet 25 to the fluid outlet 24 travelling around annular space 22 and transferring heat to the water storage tank 12 as it goes. The fluid passes through the fluid outlet 24 and returns to the solar collection panel for further heating.

[064] While the configuration described gives satisfactory performance when there is plenty of sunlight, it has been found that it is not as effective as expected when sunlight is limited or large quantities of hot water are required. A study by the applicant of the fluid flow within the jacket has revealed that fluid tends to flow in a rather direct and limited path between the inlet and the outlet as shown by flow lines 28 in Figure 1. As a result, there are relatively stagnant regions of fluid within the jacket, in particular proximate the lower edge 23 below the outlet (as indicated by A) and proximate the upper edge 26 above the inlet (as indicated by B). In these regions, the fluid is not caused to move and therefore rapidly cools to the temperature of the tank. The surface area of the tank wall though which heat is transmitted to the stored water is thereby considerably less than would be expected from the area covered by the jacket. This results in an overall reduced efficiency of the system.

[065] According to the invention, the fluid in the jacket is caused to flow in a manner whereby the regions of stagnant fluid are substantially eliminated or at least their area is significantly reduced.

[066] The invention is described by reference to several preferred embodiments of the invention described below. Where features of these embodiments are similar to features of the conventional, indirectly-heated, hot water storage tank previously described so in the drawings, like features are denoted with like numerals. The first embodiment is described with references to Figures 2 and 3.

[067] La the first embodiment a water storage tank for an indirectly heated solar hot water system includes a cylindrical tank 12 of the same form as that which has been described previously in relation to the prior art. The tank 12 is provided with a water heater jacket 21. However, in the embodiment, a fluid guide is provided in the jacket space to divert fluid from a direct path between the inlet and the outlet. The fluid guide can be formed by a wall or a baffle 31. This guide can take any suitable shape to adjust the flow path, such as in the form of a broken ring of metallic sheet material having an inner diameter substantially conforming to the outer diameter of the tank and an outer diameter corresponding to the inner diameter of the jacket. In the embodiment, the baffle 31 is located substantially midway between the upper 25 and lower edges 24 of the jacket and the break 32 in the ring is disposed 1800 around from the fluid inlet 23. The baffle 31 thus divides the jacket space into two sub-spaces, one above the other with an opening between the sub-spaces provided by the break 31 in the ring to thereby allow fluid to flow from the lower sub-space to the upper space.

[068] The fluid guide can be formed by pressing a channel of the required dimensions into the sheet material of the jacket before the jacket is applied to the tank.

[069] As shown in Figure 3, it can be seen by the flow lines 33 that, in use, by providing the baffle 31 according to the embodiment and also by locating the inlet 25 above the outlet 24, fluid will flow around the tank in the upper sub-space from the inlet 25 to the break in the baffle 31, and then around the tank in the lower sub-space to the outlet 25. It can be seen that the fluid is forced to travel a greater distance than in the conventional arrangement which has no baffle and in the process more completely cover the surface area of the tank. It will be appreciated that the proportion of the area of the tank which can be covered by stagnant water is significantly reduced and thus the area through which heat may be effectively transferred to the storage water significantly increased, thereby leading to increased efficiency of the system.

[070] The provision of the baffle provides another advantage. Because the baffle 31 extends between the wall of the water storage tank and the skin of the jacket 21, it provides positive mechanical reinforcement to maintain the annular gap 22 between the tank 12 and the jacket 21. As a result, it has been found possible to reduce the width of the annular gap 22 to 10 mm or less and indeed gaps of around 5mm are practical. It has in turn been seen that the smaller annular gap itself improves the efficiency. It is believed that this results from the fact that a small gap requires a larger area of fluid to flow in order to transfer a given volume. This in itself broadens the flow path and therefore assists in reducing the regions of stagnant fluid. In addition, a small gap can provide better ort more complete contact between the heat transfer fluid and the wall of the tank.

[071] It will further be appreciated that that arrangement described in respect of the first embodiment can be further enhanced by the use of additional baffles. In the second embodiment, as shown in Figure 4 there is shown an indirectly heated water storage tank with a water heater jacket having three baffles 41, 42 and 43, substantially equi-spaced axially within the jacket 21. The baffles are of the same form as the baffle of the first embodiment but the break in one baffle is configured to be at a position 1800 relative to an adjacent baffle.

[072] It will be appreciated that any number of baffles might be used, and that where there are an add number of baffles it will be appropriate to position the fluid inlet 25 from the jacket directly above the fluid outlet 24 while, where there are an even number of baffles, it will be appropriate to position the fluid around 1800 relative to the fluid outlet 24. It will also be appreciated that it is possible to use more than three baffles. However, if too many baffles are used or the annular gap is reduced to a very small figure, increased impedance will be imposed upon the fluid flow through the jacket, which in turn will decrease the overall performance of the device.

[073] Figure 6 shows a sheet of material 602 for forming a jacket. A channel 604, having a depth corresponding to the width of the jacket/tank gap is formed in the sheet by pressing or other forming process. The channel does not run the full width of the sheet, but is dimensioned so that, when the jacket is formed around the tank, the channel will form a broken ring, rather than a continuous ring. In figure 6, an end profile of the sheet is shown at 614. This illustrates the depth of the channel 604. In addition, Figure 6 shows the stepped ends 612, 614 which are sealed to the tank to form the jacket chamber. The channel 604 and the stepped ends 612 can have the same depth. However, in one embodiment, the channel can be slightly deeper than the stepped ends to produce a tighter fit between the channel and the tank wall due to flexibility of the jacket material.

[074] As shown in Figure 7, the sheet can be curved and the ends overlapped (606, 608, 706, 708) or butt welded to form a jacket around a tank, m the case of an overlap join, the channel 704 has a length which is less than the width of the sheet minus the overlap. The channel can be formed by a single impression which does not intersect the edges of the sheet, or it can be formed by a pair of impressions which do intersect the edges and align or nest when the ends are joined.

[075] In Figure 7, the sealing rims (610, 612 in Figure 6) are omitted to simplify the drawing.

[076] Figure 8 shows an embodiment of the invention using a flow divider 818 to distribute the flow into at least two streams. The jacket 804 encloses part of the outside of the tank 802. The fluid guides provide a meander path 820 for the heat transfer fluid. There are in fact two such meander paths formed by the fluid guides, but only one is shown as the other is a mirror image on the reverse side of the tank. The flow divider 818 divides the flow of heat transfer fluid between the two paths. This is illustrated in Figure 9, where the flow divider 818 is shown as bisecting the inlet path vertically. This can assist in overcoming any flow resistance bias between the two flow paths.

[077] Figure 10 shows an embodiment of the invention using a spiral fluid guide. The jacket 1004 is applied to the tank 1002. The heat transfer fluid inlet 1006 and heat transfer fluid outlet 1008 permit the heat transfer fluid to enter and exit the jacket. A spiral fluid guide 1010 directs the heat transfer fluid in a spiral path around the tank.

[078] If the fluid guide 1010 is located below the inlet 1006, the heat transfer fluid will flow only on one side of the spiral. Thus in one embodiment, a flow divider 1018 is used to direct the flow to either side of the spiral fluid guide, so that the heat transfer fluid flows in a first path 1020, and a second path 1022.

[079] Figure 11 shows the flow divider 1018 transecting the inlet 1006 in a horizontal plane.

[080] While the spiral fluid guide is shown as extending from the inlet 1006 to the outlet 1008, it is not essential that it extend to the outlet 1008, and it can terminate short of the outlet 1008.

[081] The fluid guide can be formed by press forming the sheet. However, it is preferred to form the fluid guide 1010 using a stand-alone strip of a suitable material which can be, for example, a plastics material such as nylon or a suitable metal material.

[082] The heat transfer fluid can be circulated by the use of a pump. This can provide sufficient force to permit the inlet to be located in a lower position on the jacket than the outlet.

[083] The fluid guide can be integral with the jacket sheet.

[084] Alternatively, the fluid guide can be a separate element formed of a suitable material to be applied between the jacket and the tank wall. Such a fluid guide can be a meatal or plastics strip having a depth corresponding to the jacket gap.

[085] Various other path configurations can be used without departing from the inventive concept. The main purpose of the fluid guides is to produce a greater contact area between the tank and the heat transfer fluid flowing in the jacket Any fluid guide which produces this result can be considered to be within the scope of the invention.

[086] Where ever it is used, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words

"comprise", "comprised" and "comprises" where they appear.

[087] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. AU of these different combinations constitute various alternative aspects of the invention.

[088] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.

Claims

1. A jacket water heater for a vertically oriented tank including: a jacket surrounding at least a part of the exterior of a tank and forming a jacket gap between the exterior wall of the tank and the interior wall of the jacket, a heat transfer fluid inlet to admit heat transfer fluid into the jacket gap, and a heat transfer fluid outlet to permit heat transfer fluid to flow out of the jacket gap, wherein the jacket gap is less than 20 mm.

2. A jacket water heater for a vertically oriented tank including: a jacket surrounding at least a part of the exterior of a tank and forming a jacket gap between the exterior wall of the tank and the interior wall of the jacket, a heat transfer fluid inlet to admit heat transfer fluid into the jacket gap, and a heat transfer fluid outlet to permit heat transfer fluid to flow out of the jacket gap, including a fluid guide means within the jacket gap.

3. A jacket water heater as claimed in claim 1 or claim 2, wherein the jacket gap is between 3 mm and 15 mm.

4. A jacket water heater as claimed in any one of the preceding claims, wherein the jacket gap is of the order of 5 mm.

5.. A jacket water heater as claimed in any one of the preceding claims, wherein heat transfer fluid is circulated in a heat transfer fluid circuit including the jacket by convection.

6. A jacket water heater as claimed in any one of the preceding claims, wherein the heat transfer fluid is circulated by a pump.

7. A jacket water heater as claimed in any one of the preceding claims, including a fluid guide means which includes at least one fluid diverter in the form of an elongate barrier having a thickness substantially equal to the jacket gap.

8. A jacket water heater as claimed in claim 7, wherein the or each fluid diverter provides at least one fluid path between the heat transfer fluid inlet and the heat transfer fluid outlet.

9. A jacket water heater as claimed in any one of claims 7 or 8, wherein the fluid guide includes at least one a partial circumferential ring in the jacket gap, having a gap through which the heat transfer fluid can flow.

10. Aj acket water heater as claimed in claim 9, including two or more partial ring fluid guides, wherein the gaps in adjacent rings are staggered axially.

11. A jacket water heater as claimed in claim 10, wherein the gaps in adjacent rings are diametrically opposed.

12. A jacket water heater as claimed in any one of claims 1 to 8, wherein the fluid guide is in a form of a spiral extending from the heat transfer fluid inlet at least part way down the axial length of the jacket.

13. A jacket water heater as claimed in any one of the preceding claims including a flow divider causing the flow from the heat transfer fluid inlet to follow two or more paths.

14. A jacket water heater as claimed in claim 13 as appended to claim 12, wherein the flow diverter is adapted, in use, to cause a first part of the heat transfer fluid to flow on one side of the spiral, and to cause a second part of the heat transfer fluid to flow on the other side of the spiral.

15. Aj acket water heater as claimed in any one of the preceding claims, including a fluid guide formed by a channel pressed into the jacket.

16. A jacket water heater as claimed in any one of claims 1 to 14, including a fluid guide formed by a spacer member between the outer wall of the tank and the inner wall of the jacket.

17. A method of increasing the contact area of a heat transfer fluid in a heat exchanger having a jacket and a heat transfer wall, there being a jacket gap between the jacket and the heat transfer wall, the method including providing a fluid guide within the jacket gap.

18. A method as claimed in claim 17, wherein the fluid guide increases the length of the heat transfer fluid flow apt between the heat transfer fluid inlet and the heat transfer fluid outlet.

19. Aj acket adapted to be applied to a storage water heater tank, the j acket including one or more spacers adapted to form one or more fluid guides which, in use, forms one or more fluid flow paths between the jacket and the and the wall of the tank.

20. A water heater jacket and fluid guide adapted to be applied to a storage water heater, the jacket including a sheet adapted to form an annular jacket around a storage water heater tank and spaced from the tank by a jacket gap, the fluid guide including an elongate member having a width corresponding to the jacket gap, the fluid guide being adapted to be placed at least partly around the tank in the jacket gap.

21. A jacket as claimed in claim 19 or claim 20, including annular rims adapted to be sealed to the tank to define an enclosed annular chamber surrounding at least part of the tank.

22. A water heater jacket and fluid guide adapted to be applied to a storage water heater, the jacket including a sheet adapted to form an annular jacket around a storage water heater tank and spaced from the tank by a jacket gap, the fluid guide including an elongate member having a width corresponding to the jacket gap, the fluid guide being adapted to be placed at least partly around the tank in the jacket gap.

23. A jacket as claimed in claim 22, including annular rims adapted to be sealed to the tank to define an enclosed annular chamber surrounding at least part of the tank.

24. A hot water storage facility including an indirectly heated water storage tank having a water heater jacket, the water storage tank adapted to contain a reservoir for water and having a tank wall with an external surface, the jacket providing an enclosed space covering at least a portion of the external surface of the tank wall and having an inlet to provide fluid entry into the enclosed space and an outlet to provide fluid exit from the enclosed space, wherein at least one fluid guide is provided within the enclosed space in order, in use, to direct fluid flowing from the inlet to the outlet to travel in an extended path through the enclosed space.

25. A hot water storage facility as claimed in claim 24, wherein the fluid entry inlet is positioned in the upper portion of the jacket.

26. A hot water storage facility as claimed in claim 24 or claim 25, wherein the fluid outlet is positioned in the lower portion of the jacket.

27. A hot water storage facility as claimed in claim 24, wherein the inlet can be located in the lower portion of the jacket and the outlet can be positioned in the upper portion of the jacket.

28. A hot water storage facility as claimed in any one of claims 24 to 27, wherein at least one fluid guide includes a wall extending between the external surface of the tank and the jacket, the wall dividing the enclosed space into a plurality of regions, a break being provided in the wall to permit fluid to flow between adjoining regions.

29. A hot water storage facility as claimed in claim 28, wherein the wall includes a baffle in the form of a broken ring positioned within the enclosed space.

30. A hot water storage facility, wherein a single ring is provided within the enclosed space, the ring dividing the enclosed space into two substantially equally size regions.

31. A hot water storage facility as claimed in any one of claims 24 to 29, wherein a plurality of rings are provided within the enclosed space.

32. A hot water storage facility as claimed in claim 31 , wherein the rings are substantially equi-spaced.

33. A hot water storage facility as claimed in claim 31 or 32, wherein the position of each break in each wall, and the position of the outlet are positioned relative to the inlet to extend the flow path between the inlet and the outlet.

34. A hot water storage facility as claimed in any one of claims 24 to 33, wherein the wall provides reinforcement to the jacket.

35. A hot water storage facility as claimed in any one of claims 24 to 34, wherein the width of the enclosed space between the external surface of the tank and the jacket can be in the range of 4mm to 10mm..