The present invention relates to a boiler comprising a tank unit and a heating unit.

The present invention also relates to a use of said boiler for heating water.

Different types of boiler for heating water are known in the art.

In accordance with a first known system, a water tank is heated by means of a burner outside said tank, with a bottom wall thereof being heated by the direct action of a flame of said external burner.

A drawback of this system is the low heat transfer efficiency, since a significant percentage of the heat generated by the burner is dissipated into the external environment without heating the water contained inside the tank.

According to a second known system, for example disclosed in the prior art document US4541410A, a burner is located inside the water tank and releases heat to the water via a metal wall - which separates said burner from the water storage compartment - and by means of a coil which is in fluid communication with a chamber of the burner inside which the burner fumes are conveyed. According to this system, the heat transfer mechanisms are the irradiation by the burner of the metal wall and condensation of the fumes inside the coil.

However, this system is also not satisfactory from the point of view of heat efficiency since it does not manage to transfer the intense heat of the burner to the water in an adequate manner.

The Applicant, after a long and in-depth R&D activity, has developed a boiler which is able to provide a suitable response to the existing limitations, drawbacks and problems.

In particular, the inventor of the present invention has found that the transfer of the heat from a burner to a liquid may be improved by providing a heat exchanger for the liquid in the proximity of the burner (at temperatures for example comprised from 750°C to 1200°C), and keeping the burner chamber in thermal contact with the heated liquid. In this way it is possible to transfer heat more efficiently in the region of the burner and exploit more fully a heat fraction which - in the systems of the prior art - is inevitably dispersed into the surrounding environment.

Further boilers are known from US 4,875,465 A, US 2008/223313 A1 and WO 2011/092332 A1.

Therefore, the present invention relates to a boiler comprising a tank unit and a heating unit, with the features as defined in the attached claims.

The present invention also relates to use of said boiler for heating water, having the features as defined in the attached claims.

Preferred embodiments of the present invention will be described hereinbelow by way of a non-limiting example with the aid of the drawings wherein:

Figure 1 : cross-sectioned side view of the heating unit according to a possible embodiment;

- Figure 2: heating unit viewed from above, according to a possible embodiment, without the burner;

- Figure 3: boiler viewed from above, according to a possible embodiment;

- Figures 4, 5: partially cross-sectioned side views, according to a possible embodiment, wherein said views differ owing to a different orientation about the prevailing development axis X.

The present invention therefore relates to a boiler 1 which comprises a tank unit 10 and a heating unit 20.

The tank unit 10 extends along a prevailing development axis X and delimits a tank compartment 2 configured to store a volume of liquid (preferably water, more preferably drinking water) up to a predefined level L. Said predefined level L is for example schematically shown in Figure 4 or Figure 5.

Preferably, the predefined level L is a maximum capacity level of the tank compartment 2, beyond which said liquid starts to overflow from said tank unit 10. In this connection, the tank compartment 2 is preferably filled up to the predefined level L via a cold liquid inlet opening 46 which passes through a thickness of the tank unit and preferably of a tank wall 44 of said tank unit 10.

More preferably, the predefined level L is such that air is substantially absent from the tank compartment 2 (since air could result in overpressures). In other words, the predefined level L is such that only said liquid is present inside the tank compartment 2. The tank unit 10 preferably comprises the tank wall 44 which circumscribes at least partially the tank compartment 2. Preferably, the tank wall 44 extends in a substantially tubular manner about the prevailing development axis X. Preferably, the prevailing development axis X is a substantially vertical axis.

It is pointed out that the expressions “radial” or “axial” are understood as being in relation to the prevailing development axis X, unless otherwise specified.

The tank unit 10 comprises preferably a support base 58 for supporting said tank unit 10. The heating unit 20 is preferably supported by the tank unit 10.

The tank compartment 2 is preferably delimited by the tank wall 44, by a first wall 56 and by a second wall 60, opposite to said first wall 56. More preferably, the first wall 56 and the second wall 60 are connected to the axial ends of the tank wall 44. Preferably, the first wall 56 and the second wall 60 delimit concave surfaces 72, 74 which are directed towards the tank compartment 2.

The first wall 56 is preferably at least partially inserted in the support base 58.

The second wall 60 is preferably provided with a neck 4.

A thickness of said tank unit 10 is preferably crossed by a hot liquid inlet opening 50, by a hot liquid outlet opening 62, and by a circulation opening 92.

It is pointed out that the terms “cold” and “hot” are to be understood as being expressed in relative terms in the sense that a so-called cold liquid has a temperature lower than a so-called hot liquid.

Preferably, the circulation opening 92 and the hot liquid outlet opening 62 are arranged on the tank wall 44. The hot liquid inlet opening 50 is preferably arranged in the region of the neck 4, more preferably along the second wall 60.

Preferably, the hot liquid outlet opening 62 is connected to a draw-off duct 64 (shown in broken lines in Figure 4) which is directed and arranged so as to convey to the hot liquid outlet opening 62 the liquid located in proximity of the heating unit 20 and which is preferably arranged in the space radially situated between said heating unit 20 and the tank unit 10, more precisely between a heat exchange wall 8 of said heating unit 20 and a wall 60 of said tank unit 10.

The hot liquid outlet opening 62 can be connected to an external user appliance.

In the embodiment shown in Figure 4, the draw-off duct 64 is preferably arranged with its inlet mouth 68 directed towards the top of the tank unit 10.

The draw-off duct 64 is preferably arranged with its inlet 68 directed vertically upwards, preferably in the vicinity of or in the region of the hot liquid inlet opening 50.

The tank unit 10 comprises the neck 4 delimiting an access opening 6 to the tank compartment 2. The heating unit 20 is at least partly inserted in the tank compartment 2 through the access opening 6.

Said neck 4 preferably comprises a fixing flange 38, more preferably an annular fixing flange 38 which extends radially with respect to the prevailing development axis X.

Said heating unit 20 comprises preferably a fixing counter-flange 40 fixed mechanically to the fixing flange 38.

Preferably, the fixing counter-flange 40 has a shape matching the fixing flange 38, for example an annular shape.

Said boiler 1 preferably comprises at least one sealing element 42 at least partially inserted between, and keeping spaced, said fixing flange 38 and said fixing counter-flange 40.

Said boiler preferably comprises mechanical fixing elements (for example threaded elements such as screws or the like) which are inserted in fixing openings 66, 70 formed respectively through a thickness of the fixing counterflange 40 and the fixing flange 38. Tightening of said mechanical fixing elements (not shown) causes the fixing flange 38 and the fixing counter-flange 40 to exert a compressive force against the sealing element 42.

Said heating unit 20 comprises at least one heat exchange wall 8 made of thermally conductive material, at least one heat exchanger 12 comprising a liquid inlet 14 and a liquid outlet 16 in fluid communication with the tank compartment 2, and at least one burner 18 for heating the liquid in the heat exchanger 12.

In the embodiment shown in Figure 5, the liquid inlet 14 (for example formed by a tube) passes through a thickness of the heat exchange wall 8.

The liquid inlet 14 is preferably in fluid communication with the tank compartment 2 and in particular with a vertically bottom portion of the tank unit 10.

More precisely, said fluid communication is achieved by means of an internal duct 48 - located at least partly inside the tank compartment 2 - which extends from the liquid inlet 14 to the circulation opening 92 and which is operationally connected to at least one pump or circulation device 90. The circulation opening 92 crosses the thickness of the tank unit 10 and more precisely the tank wall 44.

The pump or circulation device 50, which is preferably situated outside the tank compartment 2, displaces the cold liquid from the tank compartment 2, through the circulation opening 92 to the liquid inlet 14, and through the heat exchanger 12.

The liquid outlet 16 is in fluid communication with the tank compartment 2, preferably with the hot liquid opening 50, more preferably via an external duct 52 to the tank compartment 2. The external duct 52 is only schematically shown in Figure 5 by means of a broken line.

Preferably, the boiler 1 comprises at least the liquid pump or circulation device 90 (shown in Figure 5) for displacing the liquid at least through the heat exchanger 12, from the liquid inlet 14 to the liquid outlet 16 and, preferably, from the circulation opening 92 to the hot liquid inlet opening 50, so as to form a circuit.

The heat exchange wall 8 comprises preferably at least one portion (or immersed portion) 54 which is generally or substantially bowl-shaped.

The thermally conductive material of the heat exchange wall 8 is preferably selected from among polymer materials (preferably of the type which are heat- resistant up to a temperature of about 140°C, by way of example: poly(p- phenylene sulphide) (PPS), polytrimethylene terephthalate (PPT) or combinations thereof, and/or metallic materials. Said materials are preferably ferrous, more preferably carbon steel, even more preferably ferrous stainless steel or austenitic steel. Said ferrous metallic materials are preferably enamelled at least on the surface facing the tank compartment. Purely by way of example, ferrous metallic materials which can be used may be chosen from among AISI 414 steel, AISI 304 steel, or AISI 316L steel.

The heat exchanger 12, which is crossed by the liquid flowing in the direction from the liquid inlet 14 to the liquid outlet 16, is preferably formed by a serpentine duct or by a duct wound in the form of coils, more preferably cylindrical coils.

Preferably, the burner 18 is a gas burner. More preferably, said burner 18 is pre-mixed, namely is supplied with a pre-mixture of atmospheric air and fuel gas (for example natural gas, methane, butane, propane, LPG, or the like). In particular, the heating unit 20 comprises a fan (not shown) which may be placed in fluid communication with a fuel gas line. The fan is configured to draw in atmospheric air and to mix said air with the fuel gas in a ratio suitable for combustion. The combustion of the fuel gas generates a mixture of gases which below are referred to as “combustion gases”.

The burner 18 extends preferably along a burner axis Y. In the embodiments shown, the burner axis Y is preferably parallel to, or coincides with, the prevailing development axis X of the tank unit 10. In accordance with other embodiments (not shown), the burner axis Y is incident with or orthogonal to the prevailing development axis X.

The burner 18 preferably comprises a tubular portion 76 which extends around the burner axis Y. Preferably, the tubular portion 76 delimits radial passages 78 through its thickness. Said radial passages allow the combustion gases to be directed towards the heat exchanger 12.

The heat exchange wall 8 is arranged at least partially (preferably mainly or completely) below the predefined level L so as to be at least partially immersed in the liquid.

The heat exchange wall 8 circumscribes a heat exchange compartment 22 separated from the tank compartment 2, and delimits a gas outlet 24.

The heat exchange compartment 22 is preferably separated in a sealed manner from the tank compartment 2.

The gas outlet 24 is preferably connected to a gas outlet duct 84 which ends outside the boiler. More precisely, the gas outlet duct 84 is connected to a gas outlet hole 86 which passes through a thickness of the tank unit 10 and, more preferably, through a thickness of the tank wall 44. The gas outlet duct 84 is preferably arranged inside the tank compartment 2, in contact with the liquid.

Preferably, the heat exchange compartment 22 is circumscribed by the heat exchange wall 8 and by a closing element 80 of the burner unit 20. The closing element 80 is preferably provided with a through-hole 82 crossed by the burner 18. The closing element 80 preferably comprises at least one layer of heatinsulating material.

The burner 18 and the heat exchanger 12 are at least partially (for example mainly or completely) housed inside the heat exchange compartment 22.

As a result, according to an innovative aspect of the present invention, the burner 18 and the heat exchanger 12 are arranged inside the heat exchange compartment 22 and are therefore located inside a heated environment designed to transfer heat efficiently to the liquid circulating inside the heat exchanger 12. Furthermore, the heat exchange wall 8 - being located at least partially below the predefined level - is able to transfer heat to the liquid contained inside the tank compartment 2 via the heat exchange wall 8 made of thermally conductive material.

Preferably, the heat exchanger 12 extends in the form of cylindrical coils 26 around the burner axis Y. Preferably, the cylindrical coils 26 are arranged coaxially with respect to the burner axis Y.

The cylindrical coils 26 delimit preferably an exchanger compartment 28 wherein the burner 18 is at least partially (for example mainly or substantially completely) housed.

Preferably, pairs of adjacent cylindrical coils 26 delimit between them radial passages 30 for the combustion gases of said burner 18, said radial passages 30 being in fluid communication with the gas outlet 24.

Preferably, said boiler 1 comprises one or more separation elements at least partially inserted in the radial passages 30 so as to maintain a separation between said cylindrical coils 26 parallel to the burner axis Y. Said separation is preferably comprised from 0.1 mm to 3.0 mm, preferably comprised from 0.2 mm to 2.0 mm, more preferably comprised from 0.3 mm to 1.7 mm, even more preferably comprised from 0.4 mm to 1.2 mm, for example 0.7 mm, 0.8 mm or 0.9 mm.

Preferably, said one or more separation elements is/are substantially combshaped.

The heating unit 20 preferably comprises at least one first deviating element 32 and at least one second deviating element 34 which are spaced along the heat exchanger 12 so as to deviate the combustion gases of said burner 18 along a winding path through radial passages 30 delimited between pairs of cylindrical coils 26 adjacent to each other.

The winding path is for example schematically indicated by the arrows T1 , T2, T3 in Figure 1 .

The first deviating element 32 is preferably housed in the exchanger compartment 28.

The first deviating element 32 is preferably screwed between the cylindrical coils 26 into a desired axial position with respect to the burner axis Y. In other words, the first deviating element 32 is slid along the cylindrical coils 26 by means of a screwing action which is performed with the same pitch between said cylindrical coils 26.

The first deviating element 32 is preferably in the form of a plate.

The second deviating element 34 extends from the heat exchanger 12 to the heat exchange wall 8, outside the exchanger compartment 28.

The second deviating element 34 is preferably arranged so as to abut axially at least partially - with respect to the burner axis Y - against the heat exchanger 12, in particular against a bottom surface 88 of said heat exchanger 12.

The second deviating element 34 is preferably in the form of a ring.

The heat exchanger 12 preferably comprises - axially adjacent with respect to the burner axis Y - first cylindrical coils 26 between the burner 18 and the first deviating element 32, and second cylindrical coils 26 between the first deviating element 32 and the gas outlet 24.

The first deviating element 32 is configured to deviate said combustion gases from the exchanger compartment 28 towards an interspace 36 delimited between the heat exchanger 12 and the heat exchange wall 8 (arrow T1 in Figure 1 ). The second deviating element 34 is configured to deviate said combustion gases from the interspace 36 towards the exchanger compartment 28 in a position fluidically downstream to the first deviating element 32 (arrow T2). Finally, the combustion gases pass through to the gas outlet 24 (arrow T3).

The present invention also relates to use of said boiler 1 for heating drinking water or industrial water, or water for a domestic or commercial heating plant.

The operating principle of the boiler shown in the figures will be summarised here below.

The tank compartment 2 is pre-filled with liquid up to the predefined level L through the cold liquid inlet opening 46.

When the circulation device 90 is activated, a flow of liquid (preferably water) - initially cold - supplied via the circulation opening 92 flows inside the cylindrical coils 26 of the heat exchanger 12. Said liquid, flowing across the heat exchanger 12 from the liquid inlet 14 to the liquid outlet 16, increases in temperature owing to the heat exchange with the burner 18 and combustion gases thereof. Following said increase in temperature, the heated liquid exiting the liquid outlet 16 is introduced into the tank compartment 2 through the external duct 52 which terminates in the hot liquid inlet opening 50, thus forming a circuit.

The combustion gases generated by the burner 18 flow on the outside of the cylindrical coils 26 of the heat exchanger 12, passing through the radial passages 30 (preferably along a winding path defined by the deviating elements 32, 34) and flowing through the gas outlet 24. From there, the combustion gases are then discharged outside the boiler 1 via the gas outlet duct 84 which terminates in the gas outlet hole 86.

Advantageously, the fixing flange and the fixing counter-flange may be made of different metal materials, without undergoing corrosion.

Advantageously, the boiler according to the present invention has a compact and efficient exchanger structure.

Advantageously, the boiler according to the present invention has been designed to reduce the external dimensions of the boiler compared to the other solutions known in the prior art, for the same capacity of the tank compartment and the burner power.

Advantageously, the boiler according to the present invention is able to generate hot liquid - available for a user appliance - already during the first stages of activation of the burner. Advantageously, the throughflow cross-section of the radial passages inside the boiler according to the present invention is maintained despite the temperature variations and consequent expansion and deformation affecting the heat exchanger. With regard to the aforementioned embodiments of the boiler and use thereof, a person skilled in the art may replace or modify the features described, as required. These embodiments are also to be regarded as being included within the scope of protection formally defined in the claims below.

Moreover, it is pointed out that any embodiment may be implemented independently of the other embodiments described.

LIST OF REFERENCE NUMBERS boiler tank compartment neck access opening heat exchange wall tank unit heat exchanger liquid inlet liquid outlet burner heating unit heat exchange compartment gas outlet cylindrical coil exchanger compartment radial passage first deviating element second deviating element interspace fixing flange, preferably annular fixing flange fixing counter-flange, preferably annular fixing counter-flange sealing element tank wall or side wall cold water inlet opening internal duct hot liquid inlet opening external duct bowl-shaped portion or immersed portion first wall, preferably bottom wall support base second wall, preferably top wall hot liquid outlet opening draw-off duct fixing opening draw-off duct inlet mouth fixing opening concave surface concave surface tubular portion radial passage closing element through-hole gas outlet duct gas outlet hole bottom surface pump or circulation device circulation opening L predefined level

T1 winding path

T2 winding path

T3 winding path X prevailing development axis

Y burner axis