COMBUSTION CELL FOR A HEATING SYSTEM

Abstract

A combustion cell (1) for a heating system comprising: a fan unit (2), configured to supply a flow of premixed air-gas required for the combustion, a lid (3); a burner, (5) comprising a central perforated zone (501) and a peripheral zone (502) free of holes; a distributor (6), comprising a peripheral part provided with apertures (601) and positioned upstream of the burner (5) for feeding the flow of premixed air-gas to the burner (5), with its peripheral part facing towards the peripheral zone (502) of the burner (5); a flange (7) configured to connect the lid (3) to the burner (5); a coil (8) for exchanging heat, wherein the flange (7) has a receiving surface (701) which receives a first spiral (801) of the coil (8) to exchange heat in direct contact with the flange (7).

Claims

1. A combustion cell for a heating system, comprising: a fan assembly configured to supply a premixed air-gas flow required for combustion; a combustion chamber extending along a longitudinal axis from a first end to a second end; a lid for closing the first end of the combustion chamber; a burner having a convex profile and including a central region and a peripheral region, wherein the central region is perforated whilst the peripheral region is hole-free; a distributor having a convex profile and including a peripheral region provided with apertures, the distributor being located upstream the burner to feed the premixed air-gas flow to the burner and being arranged so that the peripheral region of the distributor faces the peripheral region of the burner; a flange configured for connecting the lid to the burner; a heat exchanger coil arranged around the longitudinal axis to surround the combustion chamber and provided with a plurality of wraps including a first wrap proximal to the burner and a last wrap distal to the burner, wherein the flange provides a receiving surface accommodating the first wrap of the heat exchanger coil in direct contact thereto.

2. The combustion cell according to claim 1, wherein a minimum overall distance between the heat exchanger coil and the burner varies with respect to the angular position around the longitudinal axis, between a minimum value and a maximum value, and wherein at least one the of the following conditions is met: i) the minimum value of the minimum overall distance is less than 15 mm; ii) the maximum value of the minimum overall distance is less than 25 mm.

3. The combustion cell (1) according to claim 2, wherein at least one the of the following conditions is met: i) the minimum value of the minimum overall distance is less than 8 mm; ii) the maximum value of the minimum overall distance is less than 18 mm.

4. The combustion cell according to claim 1 wherein a minimum axial distance between the heat exchanger coil and the burner along the longitudinal axis varies, between a minimum value and a maximum value, and wherein at least one the of the following conditions is met: i) the minimum value of the minimum axial distance is less than 20 mm; ii) the maximum value of the minimum axial distance is less than 30 mm.

5. The combustion cell according to claim 4 wherein, at least one the of the following conditions is met: i) the minimum value of the minimum axial distance is less than 12 mm; ii) the maximum value of the minimum axial distance is less than 22 mm.

6. The combustion cell according to claim 1, wherein a burner assembly formed by the burner and the distributor is attached to the flange through one or more connecting elements at a first connecting zone, and wherein the lid is attached to the flange at a second connecting zone, the second connecting zone being distinct and spaced apart with respect to the first connecting zone.

7. The combustion cell according to claim 1, further comprising a feeding chamber defined between the lid and the distributor, wherein the flange includes an ear extending radially with respect to the longitudinal axis, for receiving the fan assembly connected thereto.

8. The combustion cell according to claim 7, wherein the ear of the flange cooperates with the lid to delimit a feeding duct configured to feed the premixed air-gas flow supplied by the fan assembly to the feeding chamber.

9. The combustion cell according to claim 8, wherein the air-gas flows in the combustion chamber in a forward direction from the first end to the second end of the combustion chamber, and wherein the feeding duct has an inlet located at an outlet of the fan assembly an outlet open to the feeding chamber, wherein the flow of the premixed air-gas within the feeding duct, at the inlet of the feeding duct is oriented in an inlet direction having at least a component directed longitudinally in a backward direction opposite the forward direction.

10. The combustion cell according claim 9, wherein the flow of the premixed air-gas within the feeding duct, at the outlet of the feeding duct is oriented in an outlet direction having at least a component directed radially towards the longitudinal axis.

11. The combustion cell according to claim 10, wherein the lid has an inner surface delimiting the combustion chamber and is provided, at a central area of the inner surface, with a protrusion projecting into the feeding camber, thereby forming an annular shaped portion in the feeding chamber, and wherein the annular portion cooperates with the apertures provided at the peripheral region of the distributor to provide a manifold for delivering to the apertures of the peripheral region of the distributor the premixed air-gas supplied by the fan assembly.

12. The combustion cell according to claim 8, comprising a lid sealing gasket, provided between the lid and the flange, wherein the lid sealing gasket has a first portion (12A) and a second portion, wherein the first portion of the lid sealing gasket is ring shaped and is arranged around the longitudinal axis and the second portion is offset the longitudinal axis, in contact with the ear of the flange.

13. The combustion cell according to claim 1, wherein the distributor includes a plurality of holes on its central region, having different dimensions from those of the peripheral region, and wherein the apertures of the peripheral region form at least 60% of the total area of the holes of the distributor.

14. A method heating water in a heating system, comprising the following steps: providing a fan assembly, a lid, a convex shaped burner, and a convex shaped distributor; providing a heat exchanger coil, the heat exchanger coil extending around a longitudinal axis to surround a combustion chamber and having a plurality of wraps including a first wrap proximal to the burner and a last wrap distal to the burner; providing a lid for closing a first end of the combustion chamber; providing the burner with a central perforated region and with a peripheral hole-free region; providing the distributor with a peripheral region provided with apertures and arranging the distributor upstream the burner, so that the peripheral region of the distributor faces the peripheral region of the burner; providing a flange connected to the lid and to the burner, wherein the flange has a receiving surface and accommodates the first wrap of the heat exchanger coil in direct contact thereto; circulating water in the heat exchanger coil; supplying a premix of combustible gas and air to the burner, through the distributor.

15. The method according to claim 14, wherein a burner assembly formed by the burner and the distributor is directly attached to the flange.

16. The method according to claim 14, wherein the fan assembly is connected to the flange, so that the burner assembly formed by the burner and the distributor can be accessed by removing the lid, without removing the fan assembly.

17. The method according to claim 14, wherein a feeding chamber is provided between the lid and the distributor and wherein a premixed air-gas flow is conveyed from the fan assembly to the feeding chamber, through a feeding duct delimited by the flange and by the lid.

18. The method according to claim 17, wherein the premixed air-gas flow is conveyed to the feeding chamber with an orientation having a radial component directed towards the longitudinal axis, so as to generate within the feeding chamber an air-gas flow touching an inner surface of the lid.

19. A combustion cell for a heating system, comprising: a fan assembly, configured to supply a premixed air-gas flow required for combustion; a combustion chamber extending along a longitudinal axis from a first end to a second end; a lid, for closing the first end of the combustion chamber; a burner, including a perforated region; a distributor, including a region provided with apertures, the distributor being located upstream the burner to feed the premixed air-gas flow to the burner; a flange configured for connecting the lid to the burner; a heat exchanger coil arranged around the longitudinal axis to surround the combustion chamber and provided with a plurality of wraps including a first wrap proximal to the burner and a last wrap distal to the burner, wherein the flange provides a receiving surface accommodating the first wrap of the heat exchanger coil in direct contact thereto, wherein the fan assembly is connected to the flange, so that a burner assembly formed by the burner and the distributor can be accessed by removing the lid, without removing the fan assembly.

20. The combustion cell of claim 19, wherein the burner includes a central region and a peripheral region, wherein the central region is the perforated region whilst the peripheral region is hole-free, and wherein, in the distributor, the region provided with apertures is a peripheral region of the distributor, the distributor being arranged so that the peripheral region of the distributor faces the peripheral region of the burner.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0066] These and other features of the invention will become more apparent from the following detailed description of a preferred, non-limiting example of it, with reference to the accompanying drawings, in which:

[0067] FIG. 1 illustrates a combustion cell according to the invention;

[0068] FIG. 2 is an exploded perspective view of the combustion cell of FIG. 1;

[0069] FIG. 3 is a cross section of a burner unit, formed by the burner and the distributor;

[0070] FIGS. 4A and 4B are front views of the burner unit (distributer and burner, respectively);

[0071] FIG. 5 is a front view of the lid of the combustion cell;

[0072] FIG. 6 is a front view of the inner part and the outer part of the central zone of the burner;

[0073] FIG. 7 is a front view of the distributor;

[0074] FIGS. 8 and 9 are cross sections of the burner unit and distributor.

[0075] 30

DETAILED DESCRIPTION

[0076] With reference to the accompanying drawings, the numeral 1 denotes a combustion cell for a boiler. The combustion cell (that is to say, the cell) 1 comprises a fan unit 2. The fan unit 2 is configured to supply a flow of premixed air-gas required for the combustion. The cell 1 comprises a combustion chamber. The combustion chamber extends along a longitudinal axis L from a first end to a second end. The cell 1 comprises a lid 3. The lid 3 is configured for closing the first end of the combustion chamber. The cell includes a bottom element 4. The cell 1 is closed at its first end by the lid 3 and at its second end by the base element 4. The cell 1 comprises a burner 5. According to an example of the burner 5 has a convex shape. The burner may comprise a central zone 501 and a peripheral zone 502. The central zone 501 is perforated whilst the peripheral zone 502 is free of holes. The cell 1 also comprises a distributor 6. Preferably, the distributor 6 is convex in shape. The distributor 6 comprises a peripheral part provided with apertures 601. The distributor may also comprise a central part including a plurality of holes. According to an example, the central holes 602 of the plurality of holes of the central part of the distributor are smaller than the apertures 601 of the peripheral part of the distributor 6. According to an example, the apertures 601 of the peripheral part form at least 60% of the total surface of the holes of the distributor 6. The distributor 6 is positioned upstream of the burner 5 for feeding the flow of premixed air-gas to the burner 5.

[0077] The distributor 6 is positioned in such a way that the peripheral part of the distributor 6 faces towards the peripheral zone 502 of the burner 5. In this way, the flow of premixed air-gas enters into the apertures 601 of the peripheral part of the distributor 6 and comes into contact with the peripheral zone 502 of the burner 5; before the flow of air-gas passes through the central zone 501 of the burner 5, a circulation of the air-gas flow is generated between the peripheral zone of the burner 5 and the peripheral part of the distributor 6 which cools the burner 5. According to an example, the apertures 601 of the peripheral part of the distributor 6 form at least 60% of the total surface of the holes of the distributor 6. The cell 1 may comprise a flange 7. The flange 7 is configured to connect the lid 3 to the burner 5.

[0078] The cell 1 comprises a coil 8 for exchanging heat. The coil 8 is arranged around the longitudinal axis L to surround the combustion chamber. The coil 8 is provided with a plurality of spirals, including a first spiral 801 proximal to the burner 5 and a last spiral distal to the burner 5. The cell 1 also comprises an outer jacket 9 configured to house the coil 8. Preferably, the flange 7 has an internal diameter equal to or greater than the internal diameter of the coil 8. The flange 7 provides a receiving surface, which receives the first spiral 801 of the coil 8 to exchange heat in direct contact with it.

[0079] According to an example, an absolute distance D between the coil 8 to exchange heat and the burner 5 varies with respect to the angular position around the longitudinal axis L. The absolute distance D varies between a minimum value and a maximum value. According to an example, the minimum value of the minimum absolute distance D is less than 15 mm. Preferably, the minimum value of the absolute minimum distance D is less than 8 mm. The maximum value of the minimum absolute distance D is less than 25 mm. Preferably, the maximum value of the absolute minimum distance D is less than 18 mm. According to an example, a minimum axial distance A between the coil 8 to exchange heat and the burner 5 along the longitudinal axis L varies between a minimum value and a maximum value. According to an example, the minimum value of the minimum axial distance A is less than 20 mm. Preferably, the minimum value of the minimum axial distance A is less than 12 mm. According to an example, the maximum value of the minimum axial distance A is less than 30 mm. Preferably, the maximum value of the minimum axial distance A is less than 22 mm. The burner 5 and the distributor form a burner unit. According to an example, the burner unit is fixed to the flange by one or more screws 10° in a first connecting zone C. Preferably, the flange 7 has a part in the shape of a tooth 702 at the first connecting zone C. This solution makes it possible to directly connect a minimum portion of flange 7 to the burner unit and to prevent overheating of the flange 7. According to an example, the lid 3 is fixed to the flange 7 in a second connecting zone S. Preferably, the lid 3 is fixed to the flange 7 by a plurality of axial screws 10B. According to an example, the second connecting zone S is distinct and spaced from the first connecting zone C. The cell 1 also comprises a feeding chamber 11. The feeding chamber 11 is defined between the lid 3 and the distributor. The flange 7 includes an ear 701. The ear 701 extends radially with respect to the longitudinal axis L. The ear 701 is configured to receive the fan unit 2. The cell 1 comprises a feeding duct for feeding the flow of premixed air-gas supplied from the fan unit 2 to the feeding chamber 11. According to an example, the ear 701 of the flange acts in conjunction with the lid 3 to delimit the feeding duct. The feeding duct has an inlet situated in an outlet of the fan unit and an outlet open to the feeding chamber. According to an example, the flow of premixed air-gas flows in said combustion chamber 11 in a forwards direction F from the first end to the second end of the combustion chamber 11. Preferably, the flow of premixed air-gas inside the feeding duct, at the inlet of the feeding duct is oriented in an inlet direction having at least one component directed longitudinally in a backwards direction, opposite the forward direction F. Moreover, preferably, the flow of premixed air-gas inside the feeding duct, at the outlet of the feeding duct, is oriented in an outlet direction having at least one component directed radially towards the longitudinal axis L.

[0080] The lid 3 includes an inner surface which delimits the combustion chamber 11. According to an example, the lid 3 includes a projection in a central zone of the inner surface. The protrusion protrudes in the feeding chamber 11 and forms a shaped annular portion 301. According to an example, the annular portion 301 has a lid 302. The lid includes a hole. According to a preferred example, the annular portion 301 acts in conjunction with the apertures 601 provided in the peripheral part of the distributor 6 to provide a manifold for dispensing to the apertures 601 of the peripheral part of the distributor 6 the premixed air-gas supplied by the fan unit 2.

[0081] The cell 1 may also comprise a gasket 12 for sealing the lid 2. The gasket 12 is positioned between the lid 3 and the flange 7. According to an example, the gasket 12 for sealing the lid 2 has a first portion 12 A and a second portion 12B. The first portion 12A is annular and is positioned around the longitudinal axis L. The second portion 12B is offset with respect to the longitudinal axis L, in contact with the ear 701 of the flange.

[0082] According to an aspect of the invention, a method for heating water in a heating system is also provided. The method comprises a step of providing a fan unit 2 to provide a flow of premixed air-gas necessary for the combustion. The method comprises a step of providing a lid 3. The method comprises a step of providing a burner 5. The burner is preferably convex in shape. The method comprises a step of providing a distributor 6. The distributor is preferably convex in shape. The method also comprises a step of providing a coil 8 for exchanging heat. According to an example, the coil 8 for exchanging heat extends around a longitudinal axis L to surround a combustion chamber. The coil 8 has a plurality of spirals comprising a first spiral 801 proximal to the burner and a last spiral distal to the burner 5. The method comprises a step of providing a lid 3. The lid 3 is configured to close a first end of the combustion chamber. The method may comprise a step of providing the burner 5 with a central perforated zone 501 and a peripheral zone 502 without holes. The method may comprise a step of providing the distributor 6 with a peripheral part provided with apertures 601. The distributor is located upstream of the burner 5, in such a way that the peripheral part of the distributor 6 faces the peripheral zone 502 of the burner 5.

[0083] The method may comprise a step of providing a flange 7. According to an example, the flange 7 is connected to the lid 3 and to the burner 5. According to an example, the flange 7 has a receiving surface 701 and receives the first spiral 801 of the coil 8 to exchange heat in direct contact with it. The method comprises a step of circulating water in the coil 8 for exchanging heat. The method comprises a step of providing a mixture of fuel gas and air to the burner 5, through the distributor 6. According to an example, the fuel gas of the mixture of gas and air is natural gas.

[0084] The method may comprise a step wherein a burner unit formed by the burner 6 and by the distributor 5 is directly fixed to the flange 7. According to an example, the burner unit is fixed to the flange 7 in a first connecting zone C and the lid 8 is fixed to the flange 7 in a second connecting zone S. The second connecting zone S is distinct and spaced from the first connecting zone C. According to an example, the fan unit 2 is connected to the flange 7; consequently, it is possible to access said burner unit formed by the burner 5 and by the distributor 6, removing the lid 3, without removing the fan unit 2. The method may comprise a step of providing a feeding chamber 11 between the lid 3 and the distributor 6. The method may comprise a step of conveying the flow of premixed air-gas by the fan unit 2 to the feeding chamber 11, through a duct delimited by the flange 7 and by the lid 3. Preferably, the premixed air-gas flow is conveyed to the feeding chamber 11 with an orientation having a radial component directed towards the longitudinal axis L, so as to generate within the feeding chamber 11 an air-gas flow touching an inner surface of the lid 3.

[0085] According to an aspect of the invention, a premixed gas heating system is also provided. The heating system may comprise a combustion cell according to one or more aspects of the invention irrespective of the fuel used. The heating system comprises a fan unit 2. The fan unit 2 is configured to supply a flow of premixed air-gas required for the combustion.

[0086] According to an example, a fuel gas of the flow of premixed air-gas contains at least 20% by volume of hydrogen. Preferably, the fuel gas of the flow of premixed air-gas supplied to the burner contains at least 60% by volume of hydrogen. More preferably, the fuel gas of the flow of premixed air-gas supplied to the burner is 100% hydrogen. Alternatively, the heating system may use a mixture of air and natural gas. The heating system comprises a burner 5. The burner 5 has a plurality of holes. The plurality of holes provides a useful transit area defined as an area which allows the outflow of the flow of premixed air-gas from a feeding chamber 11 upstream of the burner 5 to a combustion chamber where combustion flames are generated. The heating system may comprise a load controller. The load controller is configured for adjusting an outlet load of the heating system in such a way that the heating system modulates between a minimum load and a maximum load. According to an example, the ratio between the maximum load and the minimum load is at least 4. Preferably, the ratio between the minimum load and the maximum load is equal to 8.

[0087] According to an example, the minimum load of the heating system is set in such a way that a combustion index is between 4 E06 and 6 E07. The combustion index is defined as the ratio between the minimum load and the useful transit area of the burner. The heating system may have different ranges for the value of the combustion index. An optimum range (that is to say, High Range) comprises the combustion index between 6 E07 and 2 E07. In this range the heating system has a high efficiency and a low modulation amplitude. The heating system may have a range for the combustion index of between 8 E06 and 2 E07. This range is a Balanced Range where there is an equilibrium between the efficiency of the heating system and its modulation amplitude.

[0088] The combustion index of the heating system may be in a third range (that is to say, Low Range) of between 4 E06 and 8 E06. In this range the heating system has a greater modulation amplitude and an efficiency less than the other two ranges. According to an example, the plurality of holes of the burner 5 includes a first group of holes and a second group of holes. The first group of holes has a first diameter. The second group of holes has a second diameter. According to an example, the first diameter is smaller than the second diameter.

[0089] According to an example, the second diameter is increased by at least 30% with respect to the first diameter. Preferably, an area covered by the second group of holes is less than 40% of the total useful transit area of the burner 5. The burner 5 of the heating system may comprise a central zone 501 and a peripheral zone 502. According to an example, the central zone 501 is perforated whilst the peripheral zone 502 is free of holes, the heating system also comprises a distributor 6. The distributor 6 has a peripheral part provided with apertures 601. The distributor 6 is located upstream of the burner for feeding the flow of premixed air-gas to the burner 5. Preferably, the distributor 6 is positioned in such a way that the peripheral part of the distributor 6 faces towards the peripheral zone 502 of the burner 5.

[0090] The distributor 6 may include a plurality of holes in its central part. The holes in the central part of the distributor are different in size from those of the peripheral part. According to an example, the apertures 601 of the peripheral part form at least 60% of the total area of the holes of the distributor 6. According to an example, the burner 5 has a convex shape. Alternatively, the burner 5 may have a cylindrical shape.

[0091] According to an example, the central zone 501 of the burner 5 includes an inner part 501A and an outer part 501B. According to an example, the inner part 501A of the central zone 501 of the burner 5 is free of holes. Moreover, according to an example, the outer part 501B of the central zone of the burner is perforated. The outer part 501B of the central zone of the burner may be an annular zone which surrounds the inner part 501A of the central zone of the burner. Moreover, the inner part of the burner faces a perforated zone of the distributor.

[0092] Moreover, according to an example, the central part of the distributor includes a central inner part 600A and a central outer part 600B. According to an example, the central inner part 600A and the central outer part 600B are both perforated and may be separated by a zone free of holes 600C. The zone of the distributor 6 without holes 600C may be an annular zone. According to an example, the central outer part 600B of the distributor faces the outer part 501B of the central zone of the burner, where there are the holes and, consequently, the flames. Moreover, the central inner part 600A of the distributor 6 faces the inner part 501A of the central zone of the burner 5.

[0093] Moreover, according to an example, the outer part 501B of the central zone 501 of the burner is more extended than the central outer part 600B of the distributor. In other words, the useful transit area of the burner is larger than that of the distributor.

[0094] According to an example, the load controller has access to a memory. The memory contains a plurality of reference ranges for the value of the combustion index. Moreover, the load controller is programmed to provide a user with a plurality of operating modes, wherein each operating mode of the plurality of operating modes corresponds to a respective reference range corresponding to the operating mode selected by the user.

[0095] According to an aspect of the invention, a method is provided for operating a premixed gas heating system which is able to modulate between a minimum and a maximum load. The heating system may comprise a combustion cell according to one or more aspects of the invention. According to an example, the ratio between the maximum load and the minimum load is at least 4. According to another example, the ratio between the maximum load and the minimum load is equal to 8. The method comprises a step of providing a fan unit 2 configured to provide a flow of premixed air-gas necessary for the combustion. The method comprises a step of providing a flow of premixed air and fuel gas to the burner. According to an example, the fuel gas of said flow of premixed air-gas contains at least 20% by volume of hydrogen. The method comprises a step of providing a burner 5. The burner 5 comprises a plurality of holes on a central part 501 of the burner 5. The plurality of holes provides a useful transit area defined as an area which allows the outflow of the flow of premixed air-gas from an area upstream of the burner 5 to an area in which combustion flames are generated. The method may comprise a step of providing the burner 5 with a first group of holes and a second group of holes. According to an example, the second group of holes has a diameter at least 30% greater than the first group of holes. Preferably, an area covered by the second group of holes is less than 40% of the total useful transit area of the burner. The method may comprise a step of providing a load controller. The load controller is configured to adjust an outlet load of the heating system in such a way that the heating system modulates between the minimum load and the maximum load. The method may comprise a step of setting up a minimum load value such that a combustion index value is between 4 E06 and 6 E07. The combustion index is defined as the ratio between the minimum load and the useful transit area of the burner.

[0096] The method may also comprise a step of providing the burner 5 with a peripheral zone 502 free of holes. The method comprises a step of providing a distributor 6. The distributor comprises a peripheral part having apertures 601. The distributor has a central part having a plurality of holes. According to an example, the apertures 601 of the peripheral part constitute at least 60% of the total area of the holes of the distributor 6. Preferably, the method comprises a step of positioning the distributor 6 upstream of the burner 5 for feeding the premixed air-gas flow to the burner 5 and in such a way that the peripheral part of the distributor 6 faces towards the peripheral zone 502 of the burner 5.

[0097] The method may comprise a step of providing a plurality of operating modes to a user. Each operating mode of the plurality of operating modes corresponds to a respective range of the plurality of reference ranges. Each reference range includes a plurality of values for the combustion index. The method may comprise a step of selecting three ranges for the value of the combustion index: “optimum, balanced, low”. The optimum range allows a high efficiency and a low modulation amplitude to be achieved. The balanced range does not allow either high efficiency or an extremely large modulation amplitude. The low range allows the modulation amplitude to be increased as much as possible.

[0098] The method comprises a step of selecting a reference range for the combustion index, between a plurality of reference ranges for the value of the combustion index, as a function of the operating mode selected by the user. The method comprises a step of setting the minimum load to a value within the selected reference range.

[0099] According to an aspect of the invention, a method is provided for making a premixed gas heating system which is able to modulate between a minimum and a maximum load. The heating system may comprise a combustion cell according to one or more aspects of the invention irrespective of the fuel used. According to an example, the ratio between the maximum load and the minimum load is at least 4. The method comprises a step of providing a fan unit 2. The fan unit 2 is configured to supply a flow of premixed air-gas necessary for the combustion. The method comprises a step of providing a flow of premixed air and fuel gas to the burner. According to an example, the fuel gas of said flow of premixed air-gas contains at least 20% by volume of hydrogen. Alternatively, the fuel gas could be a flow of natural gas. The method may comprise a step of providing a burner 5. The burner 5 comprises a plurality of holes. The plurality of holes provides a useful transit area defined as an area which allows the outflow of the flow of premixed air-gas from an area upstream of the burner 5 to an area in which combustion flames are generated. The method may comprise a step of providing the burner with a peripheral zone 502 free of holes. The method may comprise a step of providing a distributor 6. The distributor has a central zone comprising the holes. The distributor 6 includes a plurality of apertures 601 in a peripheral part of it. According to an example, the method comprises a step of positioning the distributor upstream of the burner 5 for feeding the premixed air-gas flow to the burner 5 and in such a way that the peripheral part of the distributor is facing towards the peripheral zone 502 of the burner. The method may comprise a step of providing a load controller. The load controller is configured to adjust an outlet load of the heating system in such a way that the heating system modulates between the minimum load and the maximum load. The minimum load is set to a predetermined reference value. The useful transit area provided by the burner 5 is such that a combustion index value is between 4 E06 and 6 E07. The combustion index being defined as the ratio between the reference value of the minimum load and the useful transit area of the burner. The following paragraphs, listed with alphanumeric references, represent exemplary and non-limiting ways of describing the present invention.

[0100] A. A combustion cell (1) for a heating system, the combustion cell (1) comprising: [0101] a fan assembly (2) configured to supply a premixed air-gas flow required for combustion; [0102] a combustion chamber extending along a longitudinal axis (L) from a first end to a second end; [0103] a lid (3), for closing the first end of the combustion chamber; [0104] a burner (5); [0105] a flange (7), configured for connecting the cover (3) to the burner (5); [0106] a heat exchanger coil (8), arranged around the longitudinal axis (L) to surround the combustion chamber and provided with a plurality of wraps including a first wrap (801) proximal to the burner (5) and a last wrap distal to the burner. A1. The heat exchanger cell (1) according to paragraph A, wherein the burner (5) has a convex or flat profile.

[0107] A1.1. The combustion cell (1), according to paragraph A1, wherein the burner (5) includes a central region (501) and a peripheral region (502), wherein the central region (501) is perforated whilst the peripheral region (502) is hole-free.

[0108] A1.2. The combustion cell (1) according to any of paragraphs A1 to A1.1, wherein a plurality of holes of the burner (5) includes a first group of holes having a first diameter and a second group of holes having a second diameter, the first diameter being smaller than the second diameter.

[0109] A1.2.1. The combustion cell (1) according to paragraph A1.2, wherein the second diameter is increased by at least 30% with respect to the first diameter.

[0110] A1.2.2. The combustion cell (1) according to paragraph A1.2 or A1.2.1, wherein an area covered by the second group of holes is less than 40% of the total free passage area of the burner.

[0111] A2. The combustion cell (1) according to any of paragraphs A to A1.2.2, comprising a distributor (6), located upstream of the burner (5) to feed the premixed air-gas flow to the burner (5)

[0112] A2.1. The combustion cell (1) according to paragraph A2, wherein the distributor (6) has a convex or flat profile.

[0113] A2.2. The combustion cell (1) according to any of paragraphs A2 to A2.1, wherein the distributor (6) includes a peripheral region provided with apertures (601) and is arranged so that the peripheral region of the distributor (6) is facing the peripheral region (502) of the burner (5).

[0114] A2.3. The combustion cell (1) according to any of paragraphs A2 to A2.2, wherein the distributor (6) includes a plurality of holes on its central region, having different dimensions from those of the peripheral region, and wherein the apertures (601) of the peripheral region form at least 60% of the total area of the holes of the distributor (601).

[0115] A3. The combustion cell (1) according to any of paragraphs A to A2.3, in which the flange (7) has a receiving surface (701), which accommodates the first wrap (801) of the heat exchanger coil (8) in direct contact thereto.

[0116] A4. The combustion cell (1) according to any of paragraphs A to A3, wherein a minimum overall distance (D) between the heat exchanger coil (8) and the burner (5) varies with respect to the angular position around the longitudinal axis (L), between a minimum value and a maximum value, and wherein at least one the of the following conditions is met: [0117] i) the minimum value of the minimum overall distance (D) is less than 15 mm; ii) the maximum value of the minimum overall distance (D) is less than 25 mm.

[0118] A4.1. The combustion cell (1) according to paragraph A4, wherein at least one the of the following conditions is met: [0119] i) the minimum value of the minimum overall distance (D) is less than 8 mm; [0120] ii) the maximum value of the minimum overall distance (D) is less than 18 mm.

[0121] A5. The combustion cell (1) according to any of paragraphs A to A4.1, wherein [0122] a minimum axial distance (A) between the heat exchanger coil (8) and the burner (5) along the longitudinal axis (L) varies, between a minimum value and a maximum value, and wherein at least one the of the following conditions is met: [0123] i) the minimum value of the minimum axial distance (A) is less than 20 mm; [0124] ii) the maximum value of the minimum axial distance (A) is less than 30 mm.

[0125] A5.1. The combustion cell (1) according to paragraph A5, wherein, at least one the of the following conditions is met: [0126] i) the minimum value of the minimum axial distance (A) is less than 12 mm; [0127] ii) the maximum value of the minimum axial distance (A) is less than 22 mm.

[0128] A6. The combustion cell (1) according to any of paragraphs A to A5.1, wherein a burner assembly formed by the burner (5) and the distributor (6) is attached to the flange (7) through one or more connecting elements at a first connecting zone (C).

[0129] A6.1. The combustion cell (1) according to paragraph A6, wherein the lid (3) is attached to the flange (7) at a second connecting zone (S), the second connecting zone being distinct and spaced apart with respect to the first connecting zone.

[0130] A7. The combustion cell (1) according to any of paragraphs A to A6.1, further comprising a feeding chamber (11) defined between the lid (3) and the distributor (6), wherein the flange (7) includes an ear (703) extending radially with respect to the longitudinal axis (L), for receiving the fan assembly (2) connected thereto.

[0131] A7.1. The combustion cell (1) according to paragraph A7, wherein the ear (703) of the flange (7) cooperates with the lid (3) to delimit a feeding duct configured to feed the premixed air-gas flow supplied by the fan assembly (2) to the feeding chamber.

[0132] A7.1.1. The combustion cell (1) according to paragraph A7.1, wherein the air-gas flows in the combustion chamber (11) in a forward direction (F) from the first end to the second end of the combustion chamber, and wherein the feeding duct has an inlet located at an outlet of the fan assembly an outlet open to the feeding chamber, wherein the flow of the premixed air-gas within the feeding duct, at the inlet of the feeding duct is oriented in an inlet direction having at least a component directed longitudinally in a backward direction opposite the forward direction.

[0133] A7.1.2. The combustion cell (1) according to paragraph A7.1 or A7.1.1, wherein the flow of the premixed air-gas within the feeding duct, at the outlet of the feeding duct is oriented in an outlet direction having at least a component directed radially towards the longitudinal axis (L).

[0134] A8. The combustion cell (1) according to any of paragraphs A to A7.1.2, wherein the lid (3) has an inner surface delimiting the combustion chamber and is provided, at a central area of the inner surface, with a protrusion projecting into the feeding camber, thereby forming an annular shaped portion (301) in the feeding chamber (11).

[0135] A8.1. The combustion cell (1) according to paragraph A8, wherein the annular portion (301) cooperates with the apertures (601) provided at the peripheral region of the distributor (6) to provide a manifold for delivering to the apertures of the peripheral region of the distributor the premixed air-gas supplied by the fan assembly (2).

[0136] A9. The combustion cell (1) according to any of paragraphs A to A8.1, comprising a lid sealing gasket (12), provided between the lid (3) and the flange (7), wherein the lid sealing gasket (12) has a first portion (12A) and a second portion (12B), wherein the first portion of the lid sealing gasket is ring shaped and is arranged around the longitudinal axis (L) and the second portion (12B) is offset the longitudinal axis, in contact with the ear (703) of the flange (7).

[0137] B. A premixed gas heating system, comprising: [0138] a fan assembly (2) configured to supply a premixed air-gas flow required for combustion, wherein a combustible gas of the premix air-gas flow contains at least 20% by volume of hydrogen; [0139] a burner (5) including a plurality of holes, wherein the plurality of holes provides a free passage area defined as an area that allows the outflow of the premixed air-gas flow from a feeding chamber (11) upstream the burner (5) to a combustion chamber where combustion flames are generated; [0140] a load controller, configured to regulate an output load of the heating system such that the heating system modulates between a minimum load and a maximum load, wherein a ratio between the maximum load and the minimum load is at least 4.

[0141] B1. The heating system according to paragraph B, wherein the minimum load of the heating system is set such that a combustion index ranges between 4 E06 and 6 E07, the combustion index being defined as the ratio of the minimum load over the free passage area of the burner.

[0142] B1.1. The heating system according to paragraph B1, wherein combustion index ranges between 8 E06 and 2 E07.

[0143] B2. The heating system according to any of paragraphs B to B1.1, wherein the load controller [0144] has access to a memory containing a plurality of reference ranges for the value of the combustion index, [0145] is programmed to provide a user with a plurality of operating modes, wherein each operating mode of the plurality of operating modes corresponds to a respective range of the plurality of reference ranges and, [0146] is programmed to set the minimum load to a value within the reference range corresponding to the operating mode selected by the user.

[0147] B2.1. The heating system according to paragraph B2, wherein the memory contains: [0148] a first reference interval for the combustion index value, between 4 E06 and 8 E06; [0149] a second reference interval for the combustion index value, between 8 E06 and 2 E07; [0150] a third reference interval for the combustion index value, between 2 E07 and 6 E07.

[0151] B3. The heating system according to any of paragraphs B to B2.1, ratio between the maximum load and the minimum load is preferably 8.

[0152] B4. The heating system according to any of paragraphs B to B3, wherein combustible gas of the premix air-gas flow supplied to the burner contains at least 60% by volume of hydrogen.

[0153] B4.1. The heating system according to paragraph B4, wherein combustible gas of the premix air-gas flow supplied to the burner is 100% hydrogen.

[0154] B5. The heating system according to any of the paragraphs from B to B4.1, wherein the burner (5) has the features described in one or more of the paragraphs from A1 to A1.2.2.

[0155] B6. The heating system according to any of paragraphs from B to B4.1, wherein the burner (5) has a cylindrical or flat profile.

[0156] B7. The heating system according to any of paragraphs from B to B6, comprising a distributor (6) located upstream of the burner (5).

[0157] B7.1. The heating system according to paragraph B7, wherein the distributor (6) has the features described in one or more of paragraphs A2 to A2.3.

[0158] B8. The heating system according to any of paragraphs B to B7.1, wherein the burner (5) comprises a central region (501) and a peripheral region (502), wherein the central region (501) of the burner includes an internal part (501A) and an external part (502B), wherein the internal part is hole-free and the external part of the central region of the burner is perforated, the external part of the central region of the burner being an annular zone that surrounds the internal part of the central region.

[0159] B8.1. The heating system according to paragraph B8, further comprising a distributor (6) located upstream of the burner to feed the pre-mixed air-gas flow to the burner, wherein the internal part of the central region of the burner faces a perforated area of the distributor (6).

[0160] B8.1.1. The heating system according to paragraph B8.1, wherein the distributor (6) includes: [0161] a peripheral region (preferably annular shaped) provided with apertures; [0162] an external central part (preferably annular shaped, preferably coaxial to and positioned inside the peripheral region) provided with holes; [0163] an internal central part (preferably annular or disc in shaped, preferably coaxial to and positioned inside the external central part) provided with holes, [0164] wherein the internal part of the central region of the burner faces the internal central part of the distributor (6), while the perforated area of the burner (external part of the central region of the burner) faces the external central part of the distributor (6).

[0165] C. A method for heating water in a heating system, comprising the following steps: [0166] providing a fan assembly (2), and a burner (5); [0167] providing a heat exchanger coil (8), the heat exchanger coil extending around a longitudinal axis (L) to surround a combustion chamber and having a plurality of wraps including a first wrap (801) proximal to the burner (5) and a last wrap distal to the burner [0168] providing a lid (3) for closing a first end of the combustion chamber; [0169] providing a flange (7), connected to the lid (3) and to the burner (5); [0170] circulating water in the heat exchanger coil (8); [0171] supplying a premix of combustible gas and air to the burner, through a distributor.

[0172] C1. The method according to paragraph C, wherein the flange has a receiving surface (701) and accommodates the first wrap (801) of the heat exchanger coil (8) in direct contact thereto.

[0173] C2. The method according to any of paragraphs C to C1, wherein the burner (5) has the features described in one or more of paragraphs A1 to A1.2.2.

[0174] C3. The method according to any of paragraphs C to C1, wherein the burner (5) has a cylindrical or flat profile.

[0175] C4. The method according to any of paragraphs from C to C3, comprising a step of locating the distributor (6) upstream of the burner (5).

[0176] C4.1. The method according to paragraph C4, wherein the distributor (6) has the features described in one or more of paragraphs A2 to A2.3.

[0177] C5. The method according to any of paragraphs C to C4.1, a burner assembly formed by the burner (5) and the distributor (6) is directly attached to the flange.

[0178] C6. The method according to any of paragraphs C to C5, the fan assembly (2) is connected to the flange (7), so that the burner assembly formed by the burner (5) and the distributor (6) can be accessed by removing the lid, without removing the fan assembly.

[0179] C7. The method according to any of paragraphs C to C6, wherein a feeding chamber (11) is provided between the lid and the distributor and wherein a premixed air-gas flow is conveyed from the fan assembly to the feeding chamber, through a feeding duct delimited by the flange and by the lid.

[0180] C7.1. The method according to paragraph C7, wherein the premixed air-gas flow is conveyed to the feeding chamber (11) with an orientation having a radial component directed towards the longitudinal axis (L), so as to generate within the feeding chamber an air-gas flow touching an inner surface of the lid.

[0181] D. A method for operating a premixed gas heating system capable of modulating between a minimum and a maximum load, wherein the ratio of the maximum load over the minimum load is at least 4, the method comprising the following steps: [0182] providing a fan assembly (2) configured to supply a premixed air-gas flow required for combustion; [0183] supplying a premix of combustible gas and air to the burner, wherein combustible gas of said premixed air-gas flow contains at least 20% by volume of hydrogen; [0184] providing a burner (5) including a plurality of holes, wherein the plurality of holes provides a free passage area defined as an area that allows the outflow of the premixed air-gas flow from an area upstream the burner to an area where combustion flames are generated; [0185] providing a load controller, configured to regulate an output load of the heating system such that the heating system modulates between the minimum load and the maximum load.

[0186] D1. The method according to paragraph D, where the minimum load is set to a value of minimum load such that a combustion index value is within the range between 4 E06 and 6 E07, the combustion index being defined as the ratio of the minimum load over the free passage area of the burner.

[0187] D2. The method according to any of paragraphs D to D.1, wherein the burner (5) has the features described in one or more of paragraphs A1 to A1.2.2.

[0188] D3. The method according to any one of paragraphs D to D.2 wherein the burner (5) has a cylindrical or flat profile.

[0189] D4. The method according to any of paragraphs D to D3, comprising a distributor (6) located upstream of the burner (5).

[0190] D4.1. The method according to paragraph D4, wherein the distributor (6) has the features described in one or more of paragraphs A2 to A2.3.

[0191] D5. The method according to any of paragraphs D to D4.1, further comprising the following steps: [0192] providing a user with a plurality of operating modes, wherein each operating mode of the plurality of operating modes corresponds to a respective range of the plurality of reference ranges; [0193] selecting a reference range for the value of combustion index, from a plurality of reference ranges for the value of the combustion index, responsive to the operating mode selected by the user; [0194] setting the minimum load to a value within the selected reference range.

[0195] D5.1. The method according to paragraph D5, wherein there are three operating modes, with three corresponding reference intervals as follows: [0196] a first reference range for the value of combustion index, between 4 E06 and 8 E06; [0197] a second reference range for the value of combustion index, between 8 E06 and 2 E07; [0198] a third reference range for the value of combustion index, between 2 E07 and 6 E07.

[0199] E. A method for manufacturing a premixed gas heating system capable of modulating between a minimum and a maximum load, wherein the ratio of the maximum load over the minimum load is at least 4, the method comprising the following steps: [0200] providing a fan assembly (2) configured to supply a premixed air-gas flow required for combustion; [0201] providing a premix of combustible gas and air to the burner, wherein combustible gas of said premixed air-gas flow contains at least 20% by volume of hydrogen; [0202] providing a burner including a plurality of holes, wherein the plurality of holes provides a free passage area defined as an area that allows the outflow of the premixed air-gas flow from an area upstream the burner to an area where combustion flames are generated; [0203] providing a load controller, configured to regulate an output load of the heating system such that the heating system modulates between the minimum load and the maximum load, wherein the minimum load is set to a predetermined reference value.

[0204] E1. The method according to paragraph E, the free passage area provided by the burner is such that a combustion index value is within the range between 4 E06 and 6 E07, the combustion index being defined as the ratio of the minimum load reference value over the free passage area of the burner.

[0205] E2. The method according to paragraph E or E1, including the features described in one or more of paragraphs D2 to D5.1.

[0206] F. A burner assembly, comprising: [0207] a burner (5) including a plurality of holes, wherein the plurality of holes provides a free passage area defined as an area that allows the outflow of the premixed air-gas flow from a feeding chamber (11) upstream the burner (5) to a combustion chamber where combustion flames are generated; [0208] a distributor (6) located upstream of the burner (5) to feed the premixed air-gas flow to the burner (5).

[0209] F1. The burner assembly according to paragraph F, wherein the burner has the features of one or more of the following paragraphs: from A1 to A1.2.2 and B8.

[0210] F2. The burner assembly according to paragraph F or F1, wherein the distributor has the features of one or more of the following paragraphs: from A2.1 to A2.3 and from B8.1 to B8.1.1.