AU2007299586B2

AU2007299586B2 - An inclined heat exchanger

Info

Publication number: AU2007299586B2
Application number: AU2007299586A
Authority: AU
Inventors: Brendan Vincent Bourke; Jeff Elliott; Mario Hatzioannou; Philip John Hopwood
Original assignee: Rheem Australia Pty Ltd
Current assignee: Rheem Australia Pty Ltd
Priority date: 2006-09-21
Filing date: 2007-09-20
Publication date: 2012-05-17
Anticipated expiration: 2027-09-20
Also published as: WO2008034185A1; AU2007299586A1; NZ575404A

Abstract

A heat exchange element having a first port and second port, the first port being connected to the second port via an intermediate ducting section oriented such that, in use, the second port is located at a height above the first port, and the intermediate ducting section is inclined at an angle to facilitate degassing the heat exchange element.

Description

07330 An inclined heat exchanger Field of the invention [001] This invention relates to a heat exchanger. [002] The invention is applicable to heat exchangers which use a heat transfer fluid to transfer heat from a heat source to a fluid to be heated. An example of such a heat exchanger is the rooftop heat exchange used in conjunction with a solar collector forming a heat transfer fluid circuit. The heat transfer fluid is added to the heat transfer fluid circuit when the solar water heating system has been installed on the roof. A difficulty in installing such solar water heaters is ensuring that the air is expelled from the heat transfer fluid circuit. (003] The amount of material used in the heat exchanger is a significant part of the cost of a heat exchanger. As the material must be resistant to corrosion from the heat transfer fluid and heated fluids, and from the atmosphere, stainless steel is often used for heat exchangers. In addition, the amount of energy used in manufacture of a heat exchanger depends on the amount of material used in the construction of a heat exchanger. [004] It is desirable to provide a heat exchanger arrangement with a low requirement for stainless steel. [005] It is also desirable to provide a heat exchanger arrangement which can be readily charged with heat transfer fluid in situ. Summary of the Invention [006] The present invention provides a water heater, including a tank for holding water to be heated, a heat exchange element immersed in said tank, a heat source to heat a heat transfer fluid, the tank having a cold water inlet and a hot water outlet, the heat exchange element having a first port and second port, the first port being connected to the second port via an intermediate section such that, in use, the second port is located at a height above the first port, the intermediate section being inclined at an angle to the horizontal, the intermediate section also including an outer tubular member and an inner 07330 2 tubular member, the inner tubular member being spaced from the outer tubular member to define an annular heat transfer fluid pathway therebetween, said annular pathway being closed at its ends, wherein said heat transfer fluid is circulated between the heat exchange element and said heat source by thermosyphoning. [007] The heat source can be a solar collector. [008] The first port can be located proximate the bottom of the tank. [009] The angle can facilitate expelling gas from the heat exchange element. [010] The angle can facilitate thermosyphoning of the fluid in the water heater heat exchange element. [011] The angle can be of the order of 3' or 4'. [012] The tank can be cylindrical. [013] The tank can be mounted with its axis in a substantially horizontal direction. [014] The heat exchange element can have or can be one or more of the following: a length of the heat exchange element that is greater than its width and its depth; the length of the heat exchange element that is oriented substantially in the same direction as the axis of the tank; mounted substantially parallel to the lower wall of the tank; mounted at an incline to the lower wall of the tank. [015] Between 50% and 80% of the water in the tank can be adapted to be below a top of the heat exchange element. [016] The intermediate section can surround an open ended path for the water, the heat exchange element further including an expansion chamber located within the open ended path and in fluid communication with the heat transfer fluid via an opening proximate the lower end of the expansion chamber. [017] The heat transfer fluid pathway of the heat exchange element can be in fluid communication with an expansion vessel, wherein the expansion vessel includes an expansion tank and an air lock.

07330 3 [018] The airlock can include a relief duct including an aperture located below the top of the expansion tank. [019] The expansion vessel can be a cylinder. [020] The expansion vessel can have a major axis which is upright. [021] The expansion vessel can have a major axis which is inclined. [022] The air lock can be connected to a pressure relief valve [023] The airlock can be located above the beat exchange element, [024] The expansion vessel can be connected to heat exchange element proximate the top thereof. [025] The heat exchange element can be connected to the tank via a shock load absorbing arrangement, Brief description of the drawings [026] An embodiment or embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings: [027] Figure 1 illustrates a heat exchange element; [028] Figure 2 is a cut away perspective view illustrating a heat exchanger such as shown in Figure 1 installed in a heat exchanger tank; [029] Figure 3 illustrates an end view of the arrangement shown in Figure 2; [030] Figure 4 illustrates a cutaway side view of another heat exchanger arrangement including a heat exchanger element; [031] Figure 5 shows detail of the heat exchanger element of Figure 4; [032] Figure 6 shows a combination heat exchanger element and expansion vessel; [033] Figure 7 shows a further heat exchanger; [034] Figure 8 schematically illustrates a portion of the heat exchanger element of figure 6; 07330 4 [035] Figure 9 schematically illustrates another portion of the heat exchanger element of figure 6, with a link to figure 8 showing an assembly method; and [036] Figure 10 illustrates another heat exchanger element. [037] Figure I I shows a further embodiment of the invention having an expansion chamber external to the heat exchanger. [038] Figure 12 illustrates an end view of the arrangement of Figure 11. [039] Figure 13 shows a further water heater arrangement embodying the invention. [040] Figure 14 shows a side view of an embodiment of heat exchanger arrangement adapted to provide improved mechanical reliability; [041] Figure 15 shows an end view of the arrangement of Figure 14. Detailed description of the embodiment or embodiments [042] Figure I shows a heat exchanger element 100, which in use, forms part of a heat transfer fluid path including a heat source such as a solar collector panel. The heat exchange element can be designed to facilitate thermosyphoning, or it can be part of a heat transfer fluid path including a pump. [043] A first port 102 and a second port 104 are connected via a heat transfer fluid duct in the form of a pipe. The pipe is formed in a serpentine layout, having first and second bends 108, 112, and three substantially linear sections 106, 110, 114 connected in series via the bends. [044] The segments of the pipe are formed so that, when a heat exchanger tank containing the heat exchanger element is installed in situ, the segments are inclined to the horizontal so that gas pockets will not be trapped in the pipe. Thus the section 106 is inclined at angle a, section 110 is inclined at angle D, and section 114 is inclined at angle 0. In one version, these three angles can be of the order of 3' above the horizontal. [045] The material of the pipe is preferably stainless steel, but other suitable materials can be used.

07330 5 [046] The dimensions and configuration of the heat exchanger element can be chosen to suit the size of the tank in which it is to be installed. For example, in a 1500 mm length tank, the heat exchanger element may have a length of about 1300 mm. [047] The design of the height of the heat exchanger element can likewise take into account the diameter of the tank. For example, in a tank with a 500 mm diameter, the height of the heat exchanger element can be of the order of 240 mm. [048] Preferably, the upper port 104 is arranged to exit the tank proximate to the mid line of the tank, so that the major part of the heat exchanger element is located in the lower portion of the tank. (049] The pipe can have a diameter of the order of 25.4 mm and a wall thickness of about 1.2 mm. [050) Figure 2 is a cutaway perspective view illustrating a heat exchanger element such as that describe with reference to Figure 1 installed in a tank 220. A first port 202 and a second port 204 are connected via a heat transfer fluid duct in the form of a pipe. The pipe is formed in a serpentine layout, having first and second bends 208, 212, and three substantially linear sections 206, 210, 214 connected in series via the bends. [051] The tank 220 is designed to be installed with its major axis substantially horizontal. The port 202 passes through the tank wall near the bottom of the tank. The port 204 passes through the tank wall near the longitudinal mid line. As in Figure 1, the segments of the pipe are inclined to the horizontal to facilitate the escape of gas bubbles in the pipe. [052] Figure 3 is an end view of the heat exchanger assembly of Figure 2. A first port 302 and a second port 304 are connected via a heat transfer fluid duct in the form of a pipe. The pipe is formed in a serpentine layout, having first and second bends 308, 312, and three substantially linear sections 306, 310, 314 connected in series via the bends. [053] The port 302 is off-set from the centre line of the tank 320, and the port 304 passes through the wall of the tank near its mid line.

67330 6 [054] Figure 4 shows a section view of a further heat exchanger assembly 400 including a heat exchanger element 402. The heat exchanger element 422 is a tubular member defining a central duct 424 through which the water to be heated can pass. [055] The heat exchanger element 422 defines an annular heat transfer fluid duct having an inner wall 428 and an outer wall 426 defining a heat transfer fluid jacket. In one arrangement, the external diameter is of the order of 75 mm and the internal diameter is of the order of 50 mm, (056] In the case where the heat transfer fluid is to be circulated through the heat transfer fluid path using thermosyphoning, the gap between the inner and outer walls can be between 6 mm and 15 mm. (057] The heat exchanger element 422 is a tubular member extending over a substantial part of the axial length of the tank 420, and inclined to the horizontal. The heat exchanger element can be inclined at an angle of about 4". [058] The heat exchanger element includes a first port 402, and a second port 404. [059] Water inlet pipe 442 is located near the bottom of the tank, and water outlet pipe 440 is arranged near the top of the tank. [060] Water in the tank is heated through both the outer and inner walls, 426, 428. The water duct 424 is inclined and the water in the duct 424 will thus rise up the duct via thermosyphoning. The water outlet 440 can be located proximate the outlet of the heat exchanger element's water duct 424 so that the hottest water is provided near the outlet 440. [061] The upper end of the heat exchanger element 426 can be located in the lower two thirds of the tank. Preferably, the upper end of the heat exchanger element is located vertically proximate the mid point of the tank so there is approximately at least half the water above the heat exchanger element. [062] As shown by the dotted pipe 443, the cold water inlet can be located near the lower inlet of the water duct 424.

'07330 7 [063] The water channel 424 through the heat exchange element produces a thermosyphoning effect, while the outer surface of the heat exchanger element also heats the water in the tank Preferably, the heat exchange element 422 is at an angle of the order of 40. [064] Figure 5 shows details of the heat exchanger element of Figure 4. The annular heat transfer fluid duct is formed by the annular space between the outer and inner walls 526, 528. The water duct 524 is enclosed by the inner wall 528. Annular end plates 525 close the ends of the concentric tubes to form the annular duct for the heat transfer fluid while leaving the centre of the inner tube clear to permit water to flow therethrough. [065] Figure 6 illustrates a heat exchanger element similar to that of Figure 5, but with the ends of the inner duct closed off to form an enclosed chamber, and an aperture from the heat transfer fluid duet to the enclosed chamber. [066] End plates 662, 664 close off the ends of the heat exchanger element 600 to form an enclosed chamber. The chamber 668 which is in fluid communication with the heat transfer fluid duct between outer and inner tubes 626, 626 via aperture 660. [067] When heat transfer fluid is first poured into the heat transfer fluid duct, some of the heat transfer fluid will enter the chamber 668, thus forming a gas lock, trapping gas in the chamber 668. As the filling of the heat transfer fluid circuit continues, the gas in chamber 668 is compressed until a pressure equilibrium is reached. This is illustrated by the dotted outline 666 indicating the heat transfer fluid level within the heat exchanger element. [068] When in use, the heat transfer fluid is heated in a solar panel, not shown, so that the volume of the heat transfer fluid expands. The heat transfer fluid circuit is fluid tight so that the fluid can only expand into the chamber 668, further compressing the gas in the chamber 668. This provides a pressure relief mechanism which is closed to the outside atmosphere. When the heat transfer fluid cools, for example at night, the heat transfer fluid contracts, and the gas pressure in the chamber 668 forces the additional heat transfer fluid back into the heat transfer fluid circuit.

07330 8 [069] The gas in the chamber 668 can be selected to reduce corrosion. A gas such as nitrogen can be used for this purpose. [070] The assembly of the heat exchange element of Figure 6 will be described with reference to figures 8 & 9. In Figure 8, the outer tube 802 is attached to end plate 804 by welding around the first end 809 of the tube 802 to first end plate 804. Preferably, the diameter of the first end plate is at least as large as the outer diameter of the outer tube 802, [071] The inner tube 902 is closed by end plate 905 at the end having the aperture 910 and then closed by end plate 907 at end 909. the end plate has a diameter les than the inner diameter of the outer tube 802. Preferably, the diameter of the end plate 905 is at least as great as the diameter of the inner tube 902. [072] Then this inner tube sub-assembly assembly is inserted into tube 802, and the end 806 of tube 802 is welded to plate 907 around the dotted line 906. The end plate 907 has a diameter greater than the diameter of the inner tube 902, and is sufficiently great to close the end 806 of the outer tube 802. Preferably, the diameter of the third end plate 907 is greater than the diameter of the outer tube 802. [073] The length of the inner tube 902 with the end plate 905 attached is less than the length of the outer tube 802. [074] In an alternative assembly method, the inner tube can be attached to end plate 804 and the second end 909 of the inner tube can be closed by another end plate, and the outer tube can be closed by end plate 907, and the first end of the outer tube 802 can be closed by welding to end plate 804. [075] Alternatively, the outer tube can be attached to the end plate to which the inner tube is attached, and then the other end plate can be attached to the outer tube. This permits a support means, such as a resilient annular member or other suitable support member, to be inserted to support the free end of the inner tube before the outer tube is closed. the support member can include flow-through holes, or it can be located so as not to restrict the flow of heat transfer fluid.

07330 9 [076] Figure 7 shows a further heat exchanger element 700 having a tubular heat transfer fluid duct 722 an internal water path 724 and an expansion chamber 770. [077] The expansion chamber 768 is supported within the water duct 724 so that the water can pass through the water duct and is in fluid communication with the heat transfer fluid circuit via stub pipe 760. However, the presence of the expansion chamber 768 in the water duct reduces the volume of water passing through the water duct and thus the water is heated more quickly. [078] Figure 10 shows a further heat exchanger element 1022, which is similar to that of Figure 4, except that the heat exchanger element 1022 is mounted approximately parallel to the bottom wall of the tank 1000. The tank 1000 is mounted at an incline to the horizontal so that the heat exchanger element 1022 is also inclined as in the other arrangements described above. The mounting angle can be achieved by the use of a mounting frame such as 1050. The mounting frame can be prefabricated. In this arrangement the depth of water between the heat exchanger element and the bottom wall of the tank 1022 is substantially uniform along the length of the heat exchanger element. [079] In a variation of the element of Figure 10, the heat exchanger element can be mounted at an incline to the bottom wall which can be less than the incline in the other elements described above. For example, the bottom wall of the tank can be at 20 to the horizontal and the heat exchanger element can be at a further 24 above the bottom wall of the tank so that the heat exchanger element is at 40 above the horizontal, while there is less water between the bottom of the tank and the heat exchanger element than in the arrangements where the tank is mounted horizontally. [080) Figure 11 shows a further embodiment of the invention in which a heat exchanger 1122 is located in a tank 1120. The tank has cold water inlet 1142 and hot water outlet 1140. Again, this embodiment of the heat exchanger 1122 has an annular heat transfer fluid jacket with inner tube 1128 having annular closures at the ends and through bore 1124 through which the water can flow. The heat transfer fluid enters the heat exchanger 1122 via pipe 1102 and exits pipe 1104. An expansion chamber 1180 which, in this embodiment, is a cylinder enclosing a through pipe 1186 connected to the heat exchanger. Through pipe 1186 is "blind" in that it terminates in a pressure relief 07330 10 valve 1184, which can be a Caleffi valve. An aperture 1182 is formed in the through pipe 1186 and is used to determine the fill level of the heat transfer fluid system by providing an air lock. The heat transfer fluid system is filled from the lowest point of the system with the relief valve 1184 open. The heat transfer fluid is added until the heat transfer fluid flows out the relief valve. As the heat transfer fluid rises in the system, the heat transfer fluid also flows out of the aperture 1182 into the expansion chamber 1180 and the pressure in the expansion chamber builds up when the heat transfer fluid in the expansion chamber covers the aperture 1182, limiting the amount of heat transfer fluid in the expansion chamber at installation. Thus the height of the aperture 1186 determines how much heat transfer fluid is "in reserve" in the expansion chamber. The relief valve 1184 effectively acts as the sealing cap for the heat transfer fluid system. The expansion chamber I180 connects at 1105 proximate the top of the heat exchanger 1120 to facilitate removal of air from the heat exchanger when it is being filled with heat transfer fluid. A drain hole 1183 is provided to permit the heat transfer fluid in the expansion vessel below the air lock aperture 1182 to drain back to the heat transfer fluid circuit. In an alternative design, the holes 1182 and 1183 can be co-located as a single hole. [081] Instead of a through pipe, a relief pipe extending part way through the expansion tank from the top can be used to form the air lock. The bottom of the relief pipe is open and serves a similar function to the aperture 1186. [082] An outer jacket 1160 encloses the water tank. A support 1170 is used for mounting the water heater on a sloping surface such as a roof In operation, as the temperature of the heat transfer fluid increases, the heat transfer fluid expands into the expansion chamber 1180 until the and compresses the trapped gas in the expansion eharnber. This pressure is then relieved as the heat transfer fluid cools and the gas expands as the level of heat transfer fluid in the expansion chamber falls [083] In this embodiment, the heat exchanger 1122 can be at an angle of about 2' or greater. In the embodiment of Figure 12, the heat exchanger 1122 is located in the lower portion of the tank 1220. so that most of the water to be heated is above the heat exchanger.

07330 11 [084] Figure 12 is an end view of the arrangement of Figure 11. The heat exchanger 1222 and the expansion chamber 1280 are aligned with the vertical centre line of the tank 1220, while the cold inlet 1242 is offset. The installation platform 1250 is shown inclined to match the slope of the installation surface, such as a roof. [085] When the heat exchanger element is installed in a solar hot water system, it is connected to solar collector panels to form a heat transfer fluid circuit in which the heat transfer fluid circulates between the solar collectors and the heat exchanger element. The heat transfer fluid can be circulated by a pump or by thermosyphoning. [086] In Figure 13, the numbering system of Figure 11 has been used to identify similar elements, with the change of the first two digits from "11" to "13". While the major axis of the expansion vessel of Figure 12 is upright, in an alternative embodiment, the heat exchanger can be located and angled so that at least part of the heat exchanger is located in the upper portion of the tank above the horizontal centre line of the tank as shown in Figure 13 and the expansion tank 1380 can be inclined. The aperture 1382 is located at an appropriate height for the air lock function. [087] Also shown in Figure 13 is an auxiliary electrical booster heater 1301. The heater element 1301 is controlled by temperature sensors and control electronics (not shown), The larger angle of inclination of the heat exchanger element 1322 in this embodiment results in the upper end of the heat exchanger element lying above the horizontal centre line of the tank 1320. In this embodiment, the heater element 1301 is located proximate the horizontal centre line of the tank 1320. The combination of the more steeply inclined heat exchanger element 1322 and the heater element 1301 can reduce the energy requirements auxiliary boost and improve overall efficiency, due to the temperature stratification of the water in the tank resulting from the inclination of the heat exchange element. For example, the inclination of the heat exchanger element may be such that a certain percentage, say, 60% of the water in the tank is below the top of the heart exchanger element. This results in the hottest water heated by the heat exchanger element forming a substantially isothermal layer in the upper portion of the tank above the top of the heat exchanger element, with a thermal gradient from the top of the heat exchanger element to the bottom of the heat exchanger element, and substantially 07330 12 isothermal water below the heat exchanger element. Thus the water heated by the electrical booster element is warmer than the average temperature of the water in the tank, so less energy is required from the booster to heat the water above the booster element. In various embodiments, the volume of water below the top of the heat exchanger element can be, for example, between 50% and 80%. [088] Figure 14 shows an alternative construction of the heat exchanger 1400. The arrangement of Figure 14 shows the heat exchange tube 1402 with its axis horizontal, but, in use it will be inclined at angle al, with the tank connection 1418 at approximately the same horizontal height as tank connector 1414. The connectors 1408, 1414, and 1418 form water-tight connections though the water tank wall (not shown). [089] The heat exchange tube 1402 has a doughnut cross-section, with an outer shell closed at both ends and in communication with the heat transfer fluid circuit via pipes 1412 and 1416, and an open-ended central tube 1404 through which the water passes. The riser 1406 acts as a pressurized expansion tank when the heat transfer fluid is heated. A pressure relief valve can be connected to the riser 1406 via pipe 1410 through connector 1408. The pipe 1410 connects to the riser 1406 at 1411. [090] Preferably the riser 1406 is located so that gasses dissolved in the heat transfer fluid when it is hot will return to the riser when the heat transfer fluid cools and the dissolved gasses are expressed by the heat transfer fluid. [091] The various components are inclined at the angles shown in the Table I shows exemplary angles for the corresponding components referred to the central axis of the heat exchanger: TABLE 1 - APPROXIMATE ANGLES ANGLE ITEM EXAMPLE al heat exchanger 1402 (installed 20 angle) 13 TABLE I - APPROXIMATE ANGLES ANGLE ITEM EXAMPLE a2 pipe 1410 900+30 930 a3 riser 1406 900 90* a4 connector 1408 901 + a 920 as connector 1418 900 - al 880 a6 pipe 1416 60 a7 pipe 1412 90* -90 810 a8 connector 1414 90 0 - al 20 [092] The pipes 1412/1512, 1416/1516, and 1410, 1510 have been formed with bends to permit mechanical loads to be at least partially absorbed in the pipes, thus reducing the load transferred to the heat exchanger/pipe joints 1420, 1422. Loads can be generated by the hydraulic forces involved in turning the water flow on and off and by thermal cycling. [093] The connections between pipes 1410, 1412, 1416 and the water tank wall indicated by the dashed lines 1440, 1442, are in the form of blind stubs 1408, 1414, and 1418, with the pipes joining substantially transverse to the corresponding stub axes. The tank wall is installed substantially horizontally in use. The pipe/stub connections need not be precise right angles, but can be at an incline as shown by thejunction between pipe 1416 and stub 1418. This provides a compact junction between the pipes and the tank wall. The stubs can be of larger diameter than the pipes, providing a larger junction over which the shock loads can be distributed. In addition, the curved nature of the pipes assists in diminishing the load transferred to the junctions. It is not necessary that all the pipes be curved, provided that the arrangement provides sufficient flexibility provided to reduce the shock loads to an acceptable level.

07330 14 [094] In Figure 15, the pipe 1510 corresponds with pipe 1410 of Figure 14 and pipes 1512 and 1516 correspond with pipes 1412 and 1416 respectively. Figure 15 illustrates the bends in pipes 1510, 1512 and 1516 from an end view. The bends in the pipes adds flexibility so that mechanical loads can be absorbed by the pipes, reducing the mechanical load transmitted to the pipe connectors. [095] The arrangement of Figures 14 & 15 can raise the position of the heat exchanger in the water tank due to the increased height afforded by the pipes 1412, 1416. For example, the pipes can be of 16 mm OD and can result in an increase of the height of the heat exchanger within the tank by 60 mm. [096] 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. (097] 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. All of these different combinations constitute various alternative aspects of the invention. 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 water heater, including a tank for holding water to be heated, a heat exchange element immersed in said tank, a heat source to heat a heat transfer fluid, the tank having a cold water inlet and a hot water outlet, the heat exchange element having a first poll and second port, the first port being connected to the second port via an intermediate section such that, in use, the second port is located at a height above the first port, the intermediate section being inclined at an angle to the horizontal, the intermediate section also including an outer tubular member and an inner tubular member, the inner tubular member being spaced from the outer tubular member to define an annular heat transfer fluid pathway therebetween, said annular pathway being closed at its ends, wherein said heat transfer fluid is circulated between the heat exchange element and said heat source by thermosyphoning.

2. A water heater as claimed in claim 1, wherein the heat source is a solar collector,

3. A water heater as claimed in claims I or 2, wherein the first port is located proximate the bottom of the tank.

4. A water heater as claimed in any one of claims I to 2, wherein the angle will facilitate expelling gas from the heat exchange element.

5. A water heater as claimed in any one of claims I to 4, wherein the angle will facilitate thermosyphoning of the fluid in the water heater heat exchange element.

6. A water heater as claimed in claims 4 or 5, wherein the angle is of the order of 3* or 4*.

7. A water heater as claimed in any one of claims I to 6, wherein the tank is cylindrical.

8. A water heater as claimed in claim 7, wherein, in use, the tank is mounted with its axis in a substantially horizontal direction.

9. A water heater as claimed in any one of claims I to 8, wherein the heat exchange element has or is one or more of the following: 07330 16 a length of the heat exchange element that is greater than its width and its depth; the length of the heat exchange element that is oriented substantially in the same direction as the axis of the tank.; mounted substantially parallel to the lower wall of the tank; mounted at an incline to the lower wall of the tank.

10. A water heater as claimed in any one of claims I to 9, wherein between 50% and 80% of the water in the tank is adapted to be below a top of the heat exchange element.

11. A water heater as claimed in any one of claims I to 10, wherein the intermediate section surrounds an open ended path for the water, the heat exchange element further including an expansion chamber located within the open ended path and in fluid communication with the heat transfer fluid via an opening proximate the lower end of the expansion chamber.

12. A water heater as claimed in any one of claims 1 to L1, wherein the heat transfer fluid pathway of the heat exchange element is in fluid communication with an expansion vessel, wherein the expansion vessel includes an expansion tank and an air lock.

13. A water heater as claimed in claim 12, wherein the airlock includes a relief duct including an aperture located below the top of the expansion tank.

14. A water heater as claimed in claim 12 or claim 13, wherein the expansion vessel is a cylinder.

15. A water heater as claimed in any one of claims 12 to 14, wherein the expansion vessel has a major axis which is upright.

16. A water heater as claimed in any one of claims 12 to 14, wherein the expansion vessel has a major axis which is inclined.

17. A water heater as claimed in any one of claims 12 to 16, wherein the air lock is connected to a pressure relief valve.

18. A water heater as claimed in any one of claims 12 to 17, wherein the airlock is located above the heat exchange element. 07330 17

19, A water heater as claimed in claim 18, wherein the expansion vessel is connected to heat exchange element proximate the top thereof.

20. A water heater as claimed in any one of claims I to 19, wherein the heat exchange element is connected to the tank via a shock load absorbing arrangement.