WO2010096858A1

WO2010096858A1 - Fluid heater

Info

Publication number: WO2010096858A1
Application number: PCT/AU2010/000150
Authority: WO
Inventors: Albert Massey Trihey
Original assignee: Hydox Pty Ltd
Priority date: 2009-02-13
Filing date: 2010-02-12
Publication date: 2010-09-02
Also published as: WO2010096858A8

Abstract

A fluid heater (1) including a chamber (2), a heating means (3), at least one heat exchanger (4), and a fluid inlet (9). The heating means (3) is disposed within the chamber (2). The at least one heat exchanger (4) is mounted within the chamber (2) below the heating means (3). The fluid inlet (9) supplies fluid to said at least one heat exchanger (4). The fluid heater (1) also includes a means (11) for drawing heat downwardly from the heating means (3) for heat exchange with the at least one heat exchanger (4) to heat the fluid within the at least one heat exchanger (4).

Description

Fluid Heater

Field of the Invention

The present invention relates to a fluid heater. The present invention has been developed particularly for use as an instantaneous water heater and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular use and may also be used to heat other fluids, such as oil.

Background of the Invention

Conventional instantaneous (continuous flow) water heaters use either a natural or forced draft combustion chamber in which burners are positioned at the bottom of the combustion chamber and finned water to air heat exchangers are positioned above the burners. This configuration allows the hot combustion products to rise thermally, or be driven by a fan which accelerates the thermal rise of the combustion products, towards the heat exchangers. As the combustion products pass through the heat exchangers, heat exchange occurs with the flowing mains (domestic) water passing through the heat exchanger.

The combustion efficiency of the primary heat exchanger in the combustion chamber is generally in the range of 80 to 85%. Any increase above this efficiency range can cause condensation to occur in the combustion chamber which can result in condensation droplets falling onto the burners. This is unacceptable for normal operation as condensation which falls onto the burner region can interfere with the combustion process and create steam. The steam passes through the heat exchanger and out of the heater as steam energy which creates a significant heat loss, offsetting the original energy saving made with the increase in efficiency.

In order to overcome this issue, it is known to use a second (separate) heat exchanging chamber from the primary combustion chamber. Secondary combustion products from the primary combustion chamber enter the second chamber via transfer conduits and ducting. The secondary combustion products flow through a second air to water heat exchanger which contains the incoming and flowing cold mains (domestic) water. The mains water is thus pre-heated in the second chamber prior to entering the primary chamber. The relative temperature differential between the secondary combustion products and the incoming flowing cold mains water is such that condensate forms on the second air to water heat exchanger outer surface. Upon forming, condensate droplets drop down by gravity into a trough which has a drain outlet for removal of the condensation. These preheating units create a slightly acidic condensation which is discharged into a neutralising device prior to exiting the heater.

This dual heat exchanging process, utilising two chambers, is common to conventional high efficiency water heaters and allows condensation to occur without any negative influence on the combustion chamber. However, a disadvantage of these water heaters is that the combustion products transfer conduits and ducting between the two heat exchanging chambers require the water heater to be larger and contain more components than a single combustion chamber water heater.

Object of the Invention It is the object of the present invention to substantially overcome or at least ameliorate one or more of the prior art disadvantages or at least provide a useful alternative.

Summary of the Invention Accordingly, in a first aspect, the present invention provides a fluid heater comprising: a chamber; a heating means disposed within the chamber, at least one heat exchanger mounted within the chamber below the heating means; a fluid inlet for supplying fluid to said at least one heat exchanger; and a means for drawing heat downwardly from the heating means for heat exchange with the at least one heat exchanger to heat the fluid within the at least one heat exchanger.

The heating means is preferably a burner, most preferably a gas burner, and the chamber is a combustion chamber. The heating means is preferably disposed at an upper portion of the combustion chamber. The at least one heat exchanger preferably comprises a first heat exchanger located below the heating means and a second heat exchanger located below the first heat exchanger.

The heater preferably defines a fluid path extending from the fluid inlet, to the at least one heat exchanger, and to a fluid outlet. In the above embodiment, the fluid path preferably extends from the fluid inlet, to the second heat exchanger, and then to the first heat exchanger, and then to the fluid outlet. The fluid inlet is preferably connectable to a mains water supply.

The first and second heat exchangers preferably each include an array of fins for absorbing heat from the heating means and transferring said heat to the fluid therewithin in use.

The first heat exchanger preferably comprises at least one first pipe having an array of fins extending therefrom. The second heat exchanger in one embodiment comprises a plurality of parallel second pipes each having an array of fins extending therefrom, a first manifold connecting first ends of the pipes to a fluid inlet and a second manifold connecting second ends of the pipes to the first heat exchanger. The free end of the first pipe preferably forms the outlet for the fluid.

The burner preferably includes a fuel valve for supplying fuel thereto and inlet vents for allowing air to enter the combustion chamber to mix with the fuel. The means for drawing heat is preferably a fan, most preferably a pull fan, having an inlet located below the at least one heat exchanger. The fan is preferably located external to the combustion chamber, preferably below the combustion chamber. The fan preferably includes a vertical tube extending therefrom, the tube extending through a bottom wall of the combustion chamber, with the tube having an open end located within the combustion chamber which forms the inlet for the fan. The fan inlet is preferably spaced from the bottom wall. The fan preferably includes an outlet located external to the combustion chamber for connection to a flue.

The fluid heater preferably includes a protective cowl located within the combustion chamber, and disposed above and spaced from the inlet, wherein the cowl substantially prevents condensation within the chamber in use from entering the inlet. A drain pipe preferably extends downwardly from the bottom wall.

The fluid heater preferably includes a plurality of temperature and flow sensors for sensing the temperature and flow of the fluid at various locations within the fluid heater. The fluid heater also preferably includes a controller responsive to the sensors for controlling the activation and deactivation of the heating means.

In a second aspect, the present invention provides a fluid heater comprising: a storage reservoir for storing heating fluid; a heating unit having: a chamber; a heating means disposed within the chamber, at least one heat exchanger mounted within the chamber below the heating means; and a means for drawing heat downwardly from the heating means for heat exchange with the at least one heat exchanger; a heating fluid circuit connecting the storage reservoir with the at least one heat exchanger for carrying heating fluid from the storage reservoir, through the at least one heat exchanger and back to the storage reservoir; and a mains fluid path connecting an inlet for mains fluid to an outlet for heated mains fluid via the at least one heat exchanger.

The heating means is preferably a gas burner provided at an upper portion of the chamber and the chamber is preferably a combustion chamber. The at least one heat exchanger preferably comprises a first heat exchanger located below the gas burner and a second heat exchanger located below the first heat exchanger. The mains fluid path preferably passes through the second heat exchanger only.

The means for drawing heat is preferably a fan having an inlet located within the combustion chamber below the at least one heat exchanger. The combustion chamber preferably includes a protective cowl disposed above and spaced from the fan inlet for substantially preventing condensation from entering the fan inlet.

The fluid heater preferably includes a third heat exchanger formed within the storage reservoir, wherein the mains fluid path passes through the third heat exchanger. The mains fluid path preferably connects an inlet for mains fluid to an outlet for heated mains fluid via the second heat exchanger and the third heat exchanger. The second heat exchanger is preferably configured as a pipe-in-pipe heat exchanger having a plurality of first thermally conductive pipes for containing the heating fluid which are each located substantially within a respective second thermally conductive pipes for containing the mains fluid. The second heat exchanger preferably includes an array of fins for absorbing heat from the heating means in use and transferring the absorbed heat to the fluid therewithin.

The heating fluid path is preferably formed by a heating fluid delivery pipe extending from the storage reservoir to the first conductive pipes and a return pipe extending from the first conductive pipes through the combustion chamber and back to the storage reservoir. The first heat exchanger is preferably formed by the portion of the return pipe extending through the combustion chamber. The first heat exchanger preferably includes an array of fins for absorbing heat from the heating means in use and transferring the heat to the heating fluid water therein. The return pipe preferably causes the returning heated heating fluid to mix with the heating fluid inside the storage reservoir. The third heat exchanger is preferably immersed in the heating fluid in the storage reservoir. The third heat exchanger is preferably conFig.d as a pipe-in-pipe heat exchanger and includes a series of third thermally conductive pipes for containing the mains water connected to the second conductive pipes downstream of the second heat exchanger, wherein the third conductive pipes are disposed within fourth thermally conductive pipes which contain heated heating fluid.

The fluid heater preferably further includes an outlet in the storage reservoir for supplying heated heating fluid to an external heating circuit, wherein a return inlet is provided in the delivery pipe for the return of heating fluid from the external heating circuit. The inlet preferably returns heating fluid into the heating fluid circuit upstream from the second heat exchanger.

In the above embodiment, the first heat exchanger heats the heating fluid (preferably deoxygenated water) passing therethrough with primary combustion products from the burner. The heating fluid is pre-heated within the second heat exchanger via secondary combustion products contacting same. The mains fluid (preferably water) is pre-heated in the second heat exchanger via heat exchange with the heated deoxygenated water and the secondary combustion products within the combustion chamber. The mains water is then further heated in the third heat exchanger via heat exchange with the heated deoxygenated water in the storage reservoir prior to delivery to the outlet. The heated deoxygenated water in the storage reservoir can also be circulated to an external heating circuit, which is preferably a hydronic heating circuit. In an alternative embodiment, the heating fluid delivery pipe extends from the storage reservoir, through the combustion chamber, and back to the storage reservoir, wherein the portion of the delivery pipe extending through the combustion chamber forms the first heat exchanger. In this embodiment, a first branch pipe extends from the delivery pipe, upstream from the first heat exchanger, and connects to the second heat exchanger and a return pipe extends from the second heat exchanger and connects to the delivery pipe between the first heat exchanger and the storage reservoir. Thus, in this embodiment, the heating fluid circuit carries deoxygenated water from the storage reservoir, simultaneously parallel through the first and second heat exchangers, and then back to the storage reservoir.

The above alternative fluid heater preferably further includes an outlet in the storage reservoir for supplying heated heating fluid to an external heating circuit, wherein a return inlet is provided in the branch pipe for the return of heating fluid from the external heating circuit. The inlet preferably returns heating fluid into the heating fluid circuit upstream from the first and second heat exchangers.

Brief Description of the Drawings

Preferred embodiments of the present invention will now be described, by way of examples only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic sectional view of a first embodiment of a water heater, showing the water flow path in a mains (domestic) water heating mode;

Fig. 2 is a schematic sectional view of the water heater of Fig. 1 , showing the path of the combustion products in the mains (domestic) water heating mode, with the heat exchanger fins not shown for ease of description;

Fig. 3 is an enlarged view of the boxed lower portion of the heater of Fig. 2, showing the forced draft fan and the path of the combustion products in the mains (domestic) water heating mode;

Fig. 4 is an enlarged view of the boxed lower portion of the heater of Fig. 2, showing the condensation droplets path in the mains (domestic) water heating mode;

Fig. 5 is a schematic sectional view of a second embodiment of a water heater, showing the mains (domestic) water flow path in a mains (domestic) water heating mode; Fig. 6 is a schematic sectional view of the water heater of Fig. 5, showing the deoxygenated water flow path in the mains (domestic) water heating mode, with the mains (domestic) water flow path not shown for ease of description;

Fig. 7 is a schematic sectional view of the water heater of Fig. 5, showing the deoxygenated water flow paths in a hydronic heating mode;

Fig. 8 is a schematic sectional view of a third embodiment of a water heater, showing the mains (domestic) water flow path in a mains (domestic) water heating mode;

Fig. 9 is a schematic sectional view of the water heater of Fig. 8, showing an alternative deoxygenated water flow path in the mains (domestic) water heating mode, with the mains (domestic) water flow path removed for ease of description;

Fig. 10 is a schematic sectional view of the water heater shown in Fig. 9, showing the deoxygenated water flow path in a hydronic heating mode; and

Fig. 11 is a schematic sectional view of a fourth embodiment of a water heater, showing the deoxygenated and domestic water flow paths in the (domestic) water heating mode.

Detailed Description of the Preferred Embodiments

Figs. 1 to 4 show a water heater 1 according to a first preferred embodiment of the present invention. As shown in Fig.s 1 and 2, the water heater 1 comprises a combustion chamber 2 housing a gas burner 3 at an upper portion thereof, a first heat exchanger 4 located directly below the gas burner 3, and a second heat exchanger 6 located directly below the first heat exchanger 4.

The first heat exchanger 4 comprises a single pipe 21 having an array of fins 12 extending therefrom. The second heat exchanger 6 comprises a plurality of parallel pipes 22 each having an array of fins 12a extending therefrom. First ends of the pipes 22 are connected to a first manifold 23 which forms an inlet 9 for the mains (domestic) water.

Second ends of the pipes 22 are connected to a second manifold 24 which is connected to the pipe 21 of the first heat exchanger 4. The free end of the pipe 21 forms an outlet 10 for the mains (domestic) water. The pipes 21 to 24 form a fluid path 8 for the mains (domestic) water. The fluid path 8 extends from the inlet 9, passes through the second heat exchanger 6, and then through the first heat exchanger 4, and exits the heater 1 via the outlet 10. The gas burner 3 includes a fuel valve 14 for supplying fuel gas thereto and inlet vents 15 for allowing air to enter the combustion chamber 2. Fig.s 3 and 4 show the lower portion 2a of the water heater 1 located below the second heat exchanger 6 as indicated in Fig. 2. The lower portion 2a includes a bottom wall 29 of the combustion chamber 2 and a fan 11 located external and below the combustion chamber 2. A vertical tube 18 extends from the fan 11, through the bottom wall 29 and into the combustion chamber 2. The vertical tube 18 has an upper open end 25, spaced from the bottom wall 29, which serves as an inlet for the fan 11. The fan 11 includes an outlet 30, located external to the combustion chamber 2, for connection to a flue (not shown). A protective cowl 16 having a main panel 28 and a peripheral skirt 26 is located within the combustion chamber 2 and disposed above the inlet 25. The main panel 28 extends over and spaced from the inlet 25, and the peripheral skirt 26 extends downwardly from the main panel 28. The peripheral skirt 26 generally extends around the vertical tube 18. A distal edge 27 of the peripheral skirt 26 is spaced from both the inlet 25 and the bottom wall 29, and also located lower than the inlet 25. The protective cowl 16 is thus spaced from the inlet 25 and forms a space 28a therebetween. The lower portion 2a also includes an inclined lower end 13 of the side wall of the combustion chamber 2 connecting to the bottom wall 29. The bottom wall 29 includes a drain outlet 19a formed therein from which a drain pipe 19 extends downwardly. The water heater 1 includes a plurality of temperature and flow sensors (not shown) for sensing the temperature and flow of the mains (domestic) water at various locations within the water heater 1. The water heater 1 also includes a controller (not shown) which is responsive to the sensors for controlling the activation and deactivation of the gas burner 3. Further, the controller modulates the gas burner 3 fuel input rate to substantially provide maximum efficiency and temperature consistency in the hot mains (domestic water) which is flowing from the unit.

The operation of the water heater 1 will now be described.

As shown in Fig. 1 , in mains (domestic) water heating mode, mains water enters the water heater 1 via inlet 9. The mains water follows the fluid path 8 which extends from the inlet 9 to the second heat exchanger 6 and then to the first heat exchanger 4.

In response to a flow sensor (not shown) sensing flow of mains water, the controller (not shown) actuates the fan 11 to draw in air into the combustion chamber 2 via the inlet vents 15. The controller also opens the fuel valve 14 and ignites the burner 3. The air mixes with the gas from the fuel valve 14 to form a combustible mixture which ignites upon exiting the burner 3 ports.

As shown in Fig. 2, the flames (primary combustion products 5) from the gas burner 3 are directed/drawn generally vertically downwards by the fan 11 toward the first heat exchanger 4 to heat the first heat exchanger 4. The primary combustion products 5 contact the first heat exchanger 4 at a temperature in the range of approximately 100°C to 18O⁰C, depending on the water heater's temperature settings and gas burner 3 fuel input rate. The fins 12 of the first heat exchanger 4 assist in absorbing heat from the primary combustion products 5 and transferring the absorbed heat to the flowing mains (domestic) water in the first heat exchanger 4.

The above heat exchange cools the primary combustion products 5 down and forms the secondary combustion products 7. The secondary combustion products 7 are also directed/drawn generally vertically downwards by the fan 11 and contact the second heat exchanger 6. The fins 12a of the second heat exchanger 6 assists in absorbing heat from the secondary combustion products 7 and transferring the absorbed heat to the flowing mains (domestic) water in the second heat exchanger 6.

As shown in Fig. 3, after the secondary combustion products 7 contact the second heat exchanger 6 they are sucked downward by the fan 11 through the space 28a and into the fan inlet 25. The fan 11 then blows the combustion products 7 out of the combustion chamber 2 via the fan outlet 30 into a flue outlet (not shown) connected thereto.

When the secondary combustion products 7 contact the second heat exchanger 6, condensation forms and drops/flows downwards toward the heater lower portion 2a. As shown in Fig. 4, condensate droplets 17 that fall into the lower portion 2a cannot fall directly into the fan inlet 25 due to the protective cowl 16 and the vertical tube 18. After the condensate droplets 17 land on the bottom wall 29 of the combustion chamber 2, they drain out of the drain pipe 19. The inclined wall 13 assists in guiding the droplets 17 to the drain pipe 19.

In the water heater 1 , the controller also sets the gas rate to the required setting to ensure safe heating of the mains domestic water in relation to its flow rate through the heater 1. The water heater 1 provides an efficient heater for heating the mains (domestic) water present and flowing through the fluid path 8. The mains (domestic) water passes through the second heat exchanger 6 first where it is heated by exchanging heat with hot secondary combustion products 7 contacting the second heat exchanger 6. After the mains (domestic) water has passed through and been partially heated in the second heat exchanger 6 it then passes through the first heat exchanger 4 where it is heated by the primary combustion products 5. After the mains (domestic) water has passed through the first heat exchanger 4 it has completed its heating sequence and it exits the unit via outlet 10. When the mains domestic water has stopped flowing, the controller will respond to the temperature and flow sensors and will deactivate the burner 3 and shut down the heater 1.

The above described embodiment provides the following benefits:

• The combination of both the primary and secondary (condensing) heat exchangers mounted in the same chamber reduces the size of the heater and improves efficiency by reducing heat losses from connecting conduits and ducting fixtures which are common to conventional high efficiency condensing water heaters.

• In mains water heating mode, the large temperature differential between the flowing cold mains water and the secondary combustion products 7 in the second heat exchanger 6 provides a combustion efficiency of approximately 96-98%, dependent on the mains water inlet temperature.

• In mains water heating mode, the vertical downward direction of flow of the condensate droplets 17 and the secondary combustion products 7 is the same which enables the separation of the condensate droplets 7 for draining via the protective cowl 16 and the vertical tube 18 whilst substantially not entraining any of the condensate through the fan 11 with the exiting secondary combustion products 7.

It will be appreciated that many modifications can be made to the first embodiment. For example, the upper and lower limits of the various sensors can be adjusted based on the user's requirements and/or operating parameters of the water heater (e.g. desired hot water output temperature, cold mains water input temperature). The first heat exchanger 4 above is shown as a single pass finned heat exchanger but can alternatively be embodied as a multiple pass parallel or series version having multiple parallel pipes. Also, the second heat exchanger 6 is shown as a multiple pass in parallel finned heat exchanger but can alternatively be embodied as a multiple pass in series version. Also the bottom wall 29 of the combustion chamber 2 can be inclined to direct the condensation droplets to the area above and adjacent the drain outlet 19a. When a sufficient volume of condensate droplets has accumulated over the drain outlet 19a, the (head) pressure will be sufficient to overcome the suck pressure from the fan 11 and the condensate droplets will flow out of the combustion chamber 2 via the drain outlet pipe 19.

Figs. 5 to 7 show a second embodiment of a fluid heater 40 somewhat similar to that shown in Figs. 20 to 38 of International (PCT) Patent Application No. PCT/AU2008/001109 (published as WO/2009/015435), the entire contents of which are incorporated herein by cross-reference. The features of the fluid heater 40 are described in detail in WO/2009/015435. A short description thereof is however outlined below.

The fluid heater 40 comprises a heating unit 1 similar to that of the first embodiment described above and a storage reservoir 401 for storing deoxygenated water for use as a heating fluid. As in the first embodiment, the heating unit 1 comprises a combustion chamber 2 housing a gas burner 3 at an upper portion thereof, a first heat exchanger 41 located directly below the gas burner 3, and a second heat exchanger 42 located directly below the first heat exchanger 41.

The features of the heating unit 1 are essentially similar to that described in the first embodiment above, apart from the features of the first and second heat exchangers 41 and 42 as will be described below. As in the first embodiment, the gas burner 3 includes the fuel valve 14 and inlet vents 15. The heating unit 1 also includes the fan 11 located external and below the combustion chamber 2, the vertical tube 18, the protective cowl 16 and a drain pipe 19 (not shown). In the fluid heater 40, a third heat exchanger 409 is formed within the storage reservoir 401 as described below.

As shown in Fig. 5, a mains water path 410 connects an inlet 47 for mains water to an outlet 48 for heated mains water via the second heat exchanger 42 and the third heat exchanger 409. The second heat exchanger 42 is conFig.d as a pipe-in-pipe heat exchanger having a plurality of first thermally conductive pipes 414a for containing the deoxygenated water which are each located substantially within a respective second thermally conductive pipe 414b for containing the mains water. The first thermally conductive pipes 414a are connected in parallel and the second thermally conductive pipes 414b loop backward and forward through the second heat exchanger 42. The second thermally conductive pipes 414b include a first (upper) group of pipes 51a connected in parallel to a second (lower) group of pipes 51b. The second heat exchanger 42 includes an array of fins 415 for absorbing heat from the burner combustion products and transferring the absorbed heat to the mains water and/or deoxygenated water in the second heat exchanger 42. A mains inlet pipe 53 connects the mains inlet 47 to the pipes 414b of the second heat exchanger 42. A connecting pipe 54 connects the pipes 414b to third thermally conductive pipes 409a of the third heat exchanger 409 as further described below. The pipes 409a are joined to an outlet pipe 55 which forms the heated water outlet 48.

A deoxygenated water delivery pipe 52 extends from the storage reservoir 401 to the pipes 414a. A return pipe 407 extends from the pipes 414a, through the combustion chamber 2 and back to the storage reservoir 401. The portion of the return pipe 407 extending through the combustion chamber 2 forms the first heat exchanger 41. The first heat exchanger 41 includes an array of fins 417 for absorbing heat from the burner combustion products and transferring the heat to the deoxygenated water therein.

As shown in Fig. 6, the pipes 52, 414a and 407 define a heating fluid circuit 406 which carries deoxygenated water from the storage reservoir 401, through the second heat exchanger 42, and then through the first heat exchanger 41, and back to the storage reservoir 401. The return pipe 407 causes the returning deoxygenated water to mix with the deoxygenated water inside the storage reservoir 401. The deoxygenated water within the heating fluid circuit 406 is recycled during operation of the fluid heater 40.

The third heat exchanger 409 is immersed in the deoxygenated water in the storage reservoir 401. The third heat exchanger 409 is also conFig.d as a pipe-in-pipe heat exchanger and includes a series of third thermally conductive pipes 409a for containing the mains water connected to the pipes 414b downstream of the second heat exchanger 42 and upstream of the heated water outlet 48. The third thermally conductive pipes 409a are located within two fourth thermally conductive pipes 409b, which contain hot deoxygenated water. The hot deoxygenated water in the pipes 409b is drawn directly from the storage reservoir 401, via inlet bleed holes 408 and inlets 420. The third heat exchanger 409 is adapted to exchange heat between the deoxygenated water and the mains water.

As shown in Fig. 5, a first pump 44 is provided for pumping deoxygenated water through the heating fluid circuit 406. An expansion valve 46 is provided between the mains water path 410 and the heating fluid circuit 406 to allow mains water to pass from the mains water path 410 into the heating fluid circuit 406 when pressure within the mains water path 410 increases to a predetermined level. As shown in Fig. 7, a pipe 425 having an outlet 50 is provided in the storage reservoir 401 to allow for supply of the heated deoxygenated water to a hydronic heating circuit (not shown). A return inlet 49 is provided in the delivery pipe 52 to allow for the return of deoxygenated water from the hydronic heating circuit. The inlet 49 returns deoxygenated water into the heating fluid circuit 406 upstream from the second heat exchanger 42. The pipe 425 thus forms part of a hydronic heating fluid circuit 426, for providing heated deoxygenated water to an external hydronic heating circuit (not shown).

As in the first embodiment, temperature and flow sensors (not shown) are provided at various locations within the fluid heater 40, with a controller (not shown) being responsive to the flow and temperature of mains water and deoxygenated water in the fluid heater 40 for activating and de-activating the gas burner 3. Further details regarding the sensors and thermostats and operation thereof, as well as other features of the fluid heater 40, are described in WO/2009/015435.

The operation of the fluid heater 40 is also described in detail in WO/2009/015435. As with the first embodiment above, the controller actuates the fan 11 as required to create a downward draft for the combustion products of the gas burner 3 within the combustion chamber 2. The first and second heat exchangers 41 and 42 in the fluid heater 40 heat the deoxygenated water passing therethrough. The mains water is preheated in the second heat exchanger 42 via heat exchange with the heated deoxygenated water and the secondary combustion products 7 and then further heated in the third heat exchanger 409 via heat exchange with the heated deoxygenated water in the storage reservoir 401 prior to delivery to the outlet 48. The heated deoxygenated water in the storage reservoir 401 can also be circulated to an external hydronic heating circuit via outlet 50. As in the first embodiment, any condensation formed in the second heat exchanger

42 drops/flows downwards and is substantially prevented from entering the fan inlet 25 via the protective cowl 16 and the vertical tube 18. Condensate can drain out via the drain pipe (not shown).

Figs. 8 to 10 show a third embodiment of a fluid heater 50 which similar to the fluid heater 40 described above, apart from an alternative heating fluid flow path 406 as described below. Similar features to the fluid heater 40 are numbered with the same reference numerals. As shown in Fig. 8, the fluid heater 50 also comprises the heating unit 1, the storage reservoir 401 and the combustion chamber 2 housing the gas burner 3, the first heat exchanger 41 below the gas burner 3 and the second heat exchanger 42 below the first heat exchanger 41. The heating unit 1 also includes the fan 11, the vertical tube 18 and the protective cowl 16. The fluid heater 50 also includes the third heat exchanger 409 formed within the storage reservoir 401.

The mains water path 410 in the fluid heater 50 is the same as in the fluid heater 40 described above, as is the features of the pipe-in-pipe heat second heat exchanger 42 and the third heat exchanger 409. As shown in Fig. 9, the fluid heater 50 includes an alternative heating fluid flow path 406. The deoxygenated water delivery pipe 52 in this embodiment extends from the storage reservoir 401, through the combustion chamber 2, and back to the storage reservoir 401. The portion of the delivery pipe 52 extending through the combustion chamber 2 forms the first heat exchanger 41. A first branch pipe 427 extends from the delivery pipe 52, upstream from the first heat exchanger 41, and connects to the pipes 414a of the second heat exchanger 42. A return pipe 407 extends from the pipes 414a, downstream from the second heat exchanger 42, and connects to the delivery pipe 52 between the first heat exchanger 41 and the storage reservoir 401.

The pipes 52, 427, 414a and 407 define a heating fluid circuit 406 which carries deoxygenated water from the storage reservoir 401 , simultaneously in parallel through the first and second heat exchangers 41 and 42, and then back to the storage reservoir 401.

The fluid heater 50 also includes the pump 44 for pumping deoxygenated water through the heating fluid circuit 406 and a mains water expansion valve 46.

As shown in Fig. 10, the pipe 425 having an outlet 50 is provided in the storage reservoir 401 to allow for supply of the heated deoxygenated water to a hydronic heating circuit (not shown). The return inlet 49 is provided in the branch pipe 427 to return deoxygenated water into the heating fluid circuit 406 upstream from the first and second heat exchangers 41 and 42. The returning deoxygenated water from the hydronic heating system entering branch pipe 427 is at a pump pressure equal to the pump pressure created by pump 44. The deoxygenated water flowing from pump 44 (in the circuit 406) and the returning deoxygenated water from a hydronic heating pump (not shown) converge at a junction 428 upstream of the second heat exchanger 42 but past the entry to the pipes 414a and upstream of the first heat exchanger 41. Because the junction 428 is past the entry to the pipes 414a, the flow through the second heat exchanger 42 is only from the cooler returning deoxygenated water from the hydronic heating system. This ensures the highest possible temperature differential and consequently combustion efficiency between the secondary combustion gases 7 and the cooled returning deoxygenated water. At the junction 428, a mixing of the two converging deoxygenated flow paths occurs in which only a small volume of the cooler hydronic heating water is entrained into the already flowing deoxygenated water in the circuit 406 which is being pumped by pump 44 into the first heat exchanger 41.

Configuration of the branch pipe 427 to the fluid circuit 406 can assist in the prioritisation of the cooler deoxygenated water returning from the hydronic heating system into the secondary heat exchanger 42. hi this embodiment, the return inlet 49 can alternatively be provided in the delivery pipe 52 upstream from, and simultaneously to, the first and second heat exchangers 41 and 42. Fig. 11 shows a fourth embodiment of a fluid heater 60 which is similar to the fluid heater 50 described above. Similar features to the fluid heater 50 are numbered with the same reference numerals. However, in the water heater 60, a mains water path 410 connects an inlet 47 for mains water to an outlet 48 for heated mains water via the second heat exchanger 42 and the third heat exchanger 409. In this embodiment, the third heat exchanger 409 is a plate heat exchanger. The second heat exchanger 42 is configured as a pipe-in-pipe heat exchanger, simialr to that shown in Fig. 5. A mains inlet pipe 53 connects the mains inlet 47 to pipes 414b of the second heat exchanger 42. A connecting pipe 54 connects the pipes 414b to the third plate heat exchanger 409, which is immersed in the storage reservoir 401. The plate heat exchanger 409 is connected to an outlet pipe 55 which forms the (domestic) heated water outlet 48.

A deoxygenated water delivery pipe 52 extends from the immersed third plate heat exchanger 409 through the storage reservoir 401 to the circulation pump 44. The pump 44 pumps the cooled deoxygenated water through pipes 414a via connecting pipe 600 and the first heat exchanger 41 via pipe 601. A return pipe 602 extends from the pipes 414a back to the bottom of the storage reservoir 401. A return pipe 603 returns the deoxygenated water from the first heat exchanger 41 back to the top of the storage reservoir 401. The portion of the return pipe 601, 603 extending through the combustion chamber 2 forms the first heat exchanger 41. The first heat exchanger 41 includes an array of fins 417 for absorbing heat from the burner 10 combustion products and transferring the heat to the deoxygenated water therein.

A first temperature sensor 604 is positioned on return pipe 603, and controls the unit's thermostat which sets the temperature of the storage reservoir 401. A second temperature sensor 605 is positioned on pipes 52 and 54 so that the sensor is influenced by the temperatures of both pipes. The sensor 605 activates and deactivates the circulation pump 44 during certain operational modes of the water heater.

Pipe 425 has an outlet 50 and is provided in the storage reservoir 401 to allow for supply of the heated deoxygenated water to a hydronic heating 25 circuit (not shown). A return inlet 49 is provided in branch pipe 600 to return deoxygenated water into the heating fluid circuit 406 upstream from the second heat exchangers 42.

The fan 11 in the water heater 60 can function adequately without the protective cowl 16 described in Fig. 3.

All embodiments of water heater described above can use an electronic controller (not shown) which can be programmed so that if the second temperature sensor 605 does not sense any domestic water flow for a period of time it can program the unit to a hibernation mode, whereby the unit drops the temperature of the deoxygenated water in the storage reservoir 401 down to within a range of 5C to 25C to save energy. Upon the second temperature sensor 605 sensing water flowing, the unit's controller reactivates the unit which returns the temperaure of the deoxygenated water in the storage reservoir 401 to its normal operational temperature setting. This function is automatically activated and deactivated without any initiation required by the user. Considerable energy savings are achieved by the unit during hibernation mode when the unit is not being used for periods of inactivity.

Although preferred embodiments of the present invention have been described, it will be apparent to skilled persons that modifications can be made to the above embodiments and to the operation thereof. For example, it is possible in the water heater 1 to have a single heat exchanger only. The efficiency of the heat exchanger can be increased and condensation can be allowed to occur, as the condensation will substantially not affect the gas burners 3. Also the fan 11 can be positioned as desired as long as its inlet 25 is disposed beneath the heat exchangers. In another possible modification, the pull fan in the above embodiments can be replaced with a push fan disposed adjacent or above the gas burners for directing the combustion products downwardly.

Claims

1. A fluid heater including: a chamber; a heating means disposed within the chamber, at least one heat exchanger mounted within the chamber below the heating means; a fluid inlet for supplying fluid to said at least one heat exchanger; and a means for drawing heat downwardly from the heating means for heat exchange with the at least one heat exchanger to heat the fluid within the at least one heat exchanger.

2. The fluid heater as claimed in claim 1, wherein the heating means is a burner and the chamber is a combustion chamber.

3. The fluid heater as claimed in claim 2, wherein the burner is a gas burner.

4. The fluid heater as claimed in claim 1, 2 or 3, wherein the heating means is disposed at an upper portion of the combustion chamber.

5. The fluid heater as claimed in any one of the preceding claims, wherein the at least one heat exchanger comprises a first heat exchanger located below the heating means and a second heat exchanger located below the first heat exchanger.

6. The fluid heater as claimed in any one of the preceding claims, wherein the fluid heater defines a fluid path extending from the fluid inlet, to the at least one heat exchanger, and to a fluid outlet.

7. The fluid heater as claimed in claim 6, wherein the fluid path extends from the fluid inlet, to the second heat exchanger, and then to the first heat exchanger, and then to the fluid outlet.

8. The fluid heater as claimed in any one of the preceding claims, wherein the fluid inlet is connectable to a mains water supply.

9. The fluid heater as claimed in any one of claims 5 to 8, wherein the first and second heat exchangers each include an array of fins for absorbing heat from the heating means and transferring said heat to the fluid therewithin in use.

10. The fluid heater as claimed in claim 9, wherein the first heat exchanger comprises at least one first pipe having an array of fins extending therefrom.

11. The fluid heater as claimed in claim 9 or 10, wherein the second heat exchanger comprises a plurality of parallel second pipes each having an array of fins extending therefrom, a first manifold connecting first ends of the second pipes to a fluid inlet and a second manifold connecting second ends of the second pipes to the first heat exchanger.

12. The fluid heater as claimed in claim 11, wherein a free end of the first pipe forms the outlet for the fluid.

13. The fluid heater as claimed in any one of the preceding claims 2 to 12, wherein the burner includes a fuel valve for supplying fuel thereto and inlet vents for allowing air to enter the combustion chamber to mix with the fuel.

14. The fluid heater as claimed in any one of the preceding claims, wherein the means for drawing heat is a fan having an inlet located below the at least one heat exchanger.

15. The fluid heater as claimed in claim 14, wherein the fan is a pull fan.

16. The fluid heater as claimed in claim 14 or 15, wherein the fan is located external to the combustion chamber

17. The fluid heater as claimed in claim 16, wherein the fan is located below the combustion chamber.

18. The fluid heater as claimed in claim 17, wherein the fan includes a vertical tube extending therefrom, the tube extending through a bottom wall of the combustion chamber, with the tube having an open end located within the combustion chamber which forms the inlet for the fan.

19. The fluid heater as claimed in claim 18, wherein the fan inlet is spaced from the bottom wall.

20. The fluid heater as claimed in claim 19, wherein the fan includes an outlet located external to the combustion chamber for connection to a flue.

21. The fluid heater as claimed in claim 18, 19 or 20, wherein a drain pipe extends downwardly from the bottom wall.

22. The fluid heater as claimed in any one of the preceding claims, wherein the fluid heater includes a protective cowl located within the combustion chamber and disposed above and spaced from the inlet, wherein the cowl substantially prevents condensation within the chamber in use from entering the inlet.

23. The fluid heater as claimed in any one of the preceding claims, wherein the fluid heater includes a plurality of temperature and flow sensors for sensing the temperature and flow of the fluid at various locations within the fluid heater.

24. The fluid heater as claimed in claim 23, wherein the fluid heater also includes a controller responsive to the sensors for controlling the activation and deactivation of the heating means.

25. A fluid heater comprising: a storage reservoir for storing heating fluid; a heating unit having: a chamber; a heating means disposed within the chamber, at least one heat exchanger mounted within the chamber below the heating means; and a means for drawing heat downwardly from the heating means for heat exchange with the at least one heat exchanger;

5 a heating fluid circuit connecting the storage reservoir with the at least one heat exchanger for carrying heating fluid from the storage reservoir, through the at least one heat exchanger and back to the storage reservoir; and a mains fluid path connecting an inlet for mains fluid to an outlet for heated mains fluid via the at least one heat exchanger. 0

26. The fluid heater as claimed in claim 25, wherein the heating means is a gas burner provided at an upper portion of the chamber and the chamber is a combustion chamber.

27. The fluid heater as claimed in claim 26, wherein the at least one heat exchangers comprises a first heat exchanger located below the gas burner and a second heat exchanger located below the first heat exchanger.

28. The fluid heater as claimed in claim 27, wherein the mains fluid path passes through the second heat exchanger only. 0

29. The fluid heater as claimed in any one of claim 25 to 28, wherein the means for drawing heat is a fan having an inlet located within the combustion chamber below the at least one heat exchanger. S

30. The fluid heater as claimed in claim 29, wherein the combustion chamber includes a protective cowl disposed above and spaced from the fan inlet for substantially preventing condensation from entering the fan inlet.

31. The fluid heater as claimed in any one of claim 27 to 30, wherein the fluid heater0 includes a third heat exchanger formed within the storage reservoir, wherein the mains fluid path passes through the third heat exchanger.

32. The fluid heater as claimed in claim 31, wherein the mains fluid path connects an inlet for mains fluid to an outlet for heated mains fluid via the second heat exchanger and the third heat exchanger.

33. The fluid heater as claimed in any one of claims 27 to 32, wherein the second heat exchanger is configured as a pipe-in-pipe heat exchanger having a plurality of first thermally conductive pipes for containing the heating fluid which are each located substantially within a respective second thermally conductive pipes for containing the mains fluid.

34. The fluid heater as claimed in any one of claims 27 to 33, wherein the second heat exchanger includes an array of fins for absorbing heat from the heating means in use and transferring the absorbed heat to the fluid therewithin.

35. The fluid heater as claimed in claim 27 to 34, wherein the heating fluid circuit is formed by a heating fluid delivery pipe extending from the storage reservoir to the first conductive pipes and a return pipe extending from the first conductive pipes through the combustion chamber and back to the storage reservoir.

36. The fluid heater as claimed in claim 35, wherein the first heat exchanger is formed by the portion of the return pipe extending through the combustion chamber.

37. The fluid heater as claimed in claim 36, wherein the first heat exchanger includes an array of fins for absorbing heat from the heating means in use and transferring the heat to the heating fluid water therein.

38. The fluid heater as claimed in any one of claims 35 to 37, wherein the return pipe causes the returning heated heating fluid to mix with the heating fluid inside the storage reservoir.

39. The fluid heater as claimed in any one of claims 31 to 38, wherein the third heat exchanger is immersed in the heating fluid in the storage reservoir.

40. The fluid heater as claimed in claim 39, wherein the third heat exchanger is configured as a pipe-in-pipe heat exchanger and includes a series of third thermally conductive pipes for containing the mains water connected to the second conductive pipes downstream of the second heat exchanger, wherein the third conductive pipes are disposed within fourth thermally conductive pipes which contain heated heating fluid.

41. The fluid heater as claimed in any one of claim 25 to 40, wherein the fluid heater further includes an outlet in the storage reservoir for supplying heated heating fluid to an external heating circuit, wherein a return inlet is provided in the delivery pipe for the return of heating fluid from the external heating circuit.

42. The fluid heater as claimed in claim 41, wherein the return inlet returns heating fluid into the heating fluid circuit upstream from the second heat exchanger.

43. The fluid heater as claimed in claim 41 or 42, wherein the first heat exchanger heats the heating fluid passing therethrough with primary combustion products from the burner.

44. The fluid heater as claimed in claim 41, 42 or 43, wherein the heating fluid is preheated within the second heat exchanger via secondary combustion products contacting same.

45. The fluid heater as claimed in any one of claim 41 to 44, wherein the mains fluid is pre-heated in the second heat exchanger via heat exchange with the heated deoxygenated water and the secondary combustion products within the combustion chamber.

46. The fluid heater as claimed in claim 45, wherein the mains water is further heated in the third heat exchanger via heat exchange with the heated deoxygenated water in the storage reservoir prior to delivery to the outlet.

47. The fluid heater as claimed in claim 45 or 46, wherein the heated deoxygenated water in the storage reservoir is circulated to an external heating circuit.

48. The fluid heater is claimed in claim 47, wherein the external heating circuit is a hydronic heating circuit.

49. The fluid heater as claimed in any one of claims 25 to 34, wherein the heating circuit path is formed by a heating fluid delivery pipe extending from the storage reservoir, through the combustion chamber, and back to the storage reservoir, wherein the portion of the delivery pipe extending through the combustion chamber forms the first heat exchanger.

50. The fluid heater as claimed in claim 49, wherein a first branch pipe extends from the delivery pipe, upstream from the first heat exchanger, and connects to the second heat exchanger and a return pipe extends from the second heat exchanger and connects to the delivery pipe between the first heat exchanger and the storage reservoir.

51. The fluid heater as claimed in claim 49, wherein the heating fluid circuit carries deoxygenated water from the storage reservoir, simultaneously parallel through the first and second heat exchangers, and then back to the storage reservoir.

52. The fluid heater as claimed in claim 49, 50 or 51, wherein the fluid heater further includes an outlet in the storage reservoir for supplying heated heating fluid to an external heating circuit, wherein a return inlet is provided in the branch pipe for the return of heating fluid from the external heating circuit.

53. The fluid heater as claimed in claim 52, wherein the return inlet returns heating fluid into the heating fluid circuit upstream from the first and second heat exchangers.