HK1241011B - Gas domestic premixed ventilated hob - Google Patents

Description

Ventilated hobs for domestic gas premix

The invention relates to a novel stove, in particular for domestic use, comprising a plurality of gas burners capable of producing an air-gas mixture in stoichiometric proportions or with a slight excess of air; the burners are thus capable of producing a fully premixed flame, possibly with excess air.

Hobs comprising a plurality of atmospheric burners are known, in which the air-gas mixture is obtained by the effect of the gas supply pressure using the Venturi ejector principle and without fan assistance.

Ejectors (see Figure 2) are very simple, economical and reliable devices, and for this reason they are used for air-gas mixing in the burners of stoves. Almost all domestic gas stoves currently on the market use atmospheric burners.

In a Venturi ejector (hereinafter referred to as the "ejector"), the pressure energy of a motive fluid with a nozzle flow rate _Qm and a nozzle pressure _Pm , available at a nozzle located at the inlet of the Venturi tube, is converted into kinetic energy; a high-speed jet exiting the nozzle generates and carries away the resulting fluid at a lower pressure _Pi and flowing at a flow rate _Qi ; both fluids are conveyed in a section _Athr of the tube (i.e., the Venturi tank), where they mix and recover some of their pressure; then, the mixing continues in a diverging section (i.e., the Venturi diffuser), where additional kinetic energy is recovered as static pressure.

In this case, the secondary pressure _Pi is the atmospheric pressure _Pa , the motive fluid with flow rate _Qm is the gas with flow rate _QGas and pressure _pGas , and the produced fluid with flow rate _Qi is the combustion air with flow rate _Qa and pressure _Pa ; due to the very modest pressure changes to which the gases undergo when passing through the venturi, they can be considered to be incompressible.

The ideal length of the Venturi slot is between 2 and 4 times its diameter D; the diffuser has a weakened opening to restore pressure and thus avoid flameout (typically half-open 2°-4°).

At the outlet of the diffuser, the gas and the combustion air are substantially completely mixed, wherein the mixture has a flow rate _Qmix = _Qgas + _Qa and a pressure _pmix .

A stoichiometric mixture is an air-gas mixture in which the mass ratio of air and gas (mixture titer) is equal to the exact stoichiometric ratio (STC) for complete combustion of the gas without residual oxygen. A mixture rich in gas, that is, one with a mixture ratio < STC, i.e., lacking air, is referred to herein as a "rich" mixture. A mixture lean in gas, that is, one with a mixture ratio > STC, i.e., with an excess of air, is referred to herein as a "lean" mixture. For complete combustion, in practice, a mixture with a slight excess of air is required compared to the theoretically sufficient STC ratio. However, hereinafter, a "stoichiometric" titer mixture or "STC mixture" refers to a mixture with the minimum slight excess of air necessary to ensure complete combustion.

The ejector efficiency _ηej is defined herein as the ratio of the kinetic energy per time unit of the mixture at the diffuser outlet, ie, _Emix = ( _Pmix - _Pi ) x _Qmix , to the kinetic energy at the nozzle, ie, _Egas = ( _pgas - _Pi ) x _Qgas .

That is, η _ej =E _mix /E _gas = [(P _mix −P _i ) × Q _mix ] / [(p _gas −P _i ) × Q _gas ].

The geometry of the Venturi tube is a decisive factor for the efficiency η _ej of the ejector.

The greater the efficiency η _ej of the ejector, the greater the combustion air flow Q _air that can be generated, and if this is sufficient to obtain a mixture with a slight excess of air, the ejector burner will not be dependent on any additional air supply.

If there are no overall size restrictions, it is in principle possible to precisely set the dimensions by the required thermal power, the diameter D and length L20 of the Venturi slot, and the length L30 and divergence angle _B2 of the diffuser.

However, for burners of hobs, especially household hobs, offering power ratings ranging from 600÷800 W to 3 kW, and in the case of "special burners" up to 5 kW (usually in numbers of 4, 5 or 6), the geometrical and dimensional limitations of the hobs, as well as the operating parameters of the burners, are absolutely incompatible with the ideal construction criteria of the injectors, resulting in a sharp drop in efficiency to only a few percentage points, since the combustion air generated, known as "primary air", is insufficient to obtain a mixture with an STC titer that allows complete combustion. The resulting disadvantages should now be highlighted.

The most widespread, generally accepted and traditional technical solution for producing a gas burner BRN for the hob 400 is a gas burner with a “vertical venturi” (see FIG. 3 ).

In this configuration, which may be considered the standard configuration and henceforth referred to as STD, the ejector is particularly inefficient, primarily due to leakage in the radial diffuser 115 and the reduced longitudinal extension of the venturi, which is far from the ideal shape and substantially coincides with the slot 114. Values of _ηej in the 1% range are common.

Essentially, a mixture excessively rich in fuel is obtained inside the injector, which draws in primary air AIR1, but still within the flammable range of the gas. The rich mixture, exiting vertically from the slot 114, is conveyed to the "slot" 117 via a radial diffuser 115. The mixture leaves the slot in a droplet size that already allows partial combustion and feeds the flame FLAME1; this is brought about by the buoyancy (i.e., by natural circulation caused by the density difference) of additional air AIR2, called "secondary" air, necessary for the chemical reaction to complete the combustion.

The need for the input of secondary air actually limits the power density of the flame which can consist only of a discontinuous crown of flames, or the inner surface of the same crown will be starved of oxygen. By making the slots 117 too thick, the flame will not develop a sufficient surface for interaction with the secondary air, resulting in an excessive production of carbon monoxide (CO), or at best an unacceptably high [CO]/[CO ₂ ] ratio in the flue gas.

The slots 117 are essentially dozens of radial channels made with radial cuts (or holes) on the body of the "flame spreader" 116 and closed at the top by a "cap" 118 (the actual cover); thus, the base of the flame spreads centrifugally and radially as it moves away from the perimeter of the burner, and the various "bubbles" of the crown of the flame FLAME1 deflect upwards in the direction of the bottom of the pot (not shown) due to floating.

With the same power rating, this type of STD architecture involves at least a size disadvantage that needs to be eliminated or at least alleviated.

Since the secondary air needs to flow smoothly inside the flame crown, the distance H01 between the base of the flame FLAME1 and the pot bottom 404 has a minimum limit.

Being able to reduce this parameter means improving the efficiency η _b of the burner, which refers to the ratio _of the heat effectively transferred to the pot to the heat generated by the burner.

Furthermore, due to the need to facilitate the entry of the primary air AIR1 into the injector, the distance H11 between the base of the flame FlAME1 and the exterior surface 401 of the hob (hereinafter referred to as “cover top 401 ”) has a minimum limit.

Therefore, it is not possible to reduce the distance H31 = H01 + H11 between the pan and the cover top as required; the pan support grid (not shown in the drawings) is quite far away from the bottom cover top 401, with severe restrictions on the freedom of product design.

Although there are STD burners capable of drawing in primary air AIR1 under the covering roof 401 in any case (with appropriate structure and mounting means of the same hob), the height H11 cannot be reduced below certain limits due to overheating of the same covering roof 401 caused by the presence of radial flames.

It should be noted that if such appearance limitations are rarely felt by the user, it is only because he considers them to be inherent and unavoidable functional requirements.

- the vertical space H21 of the mixing chamber 113 (called "cup" 113) required to place the nozzle 111 (which must be able to be tightened even after the furnace frame 400 is installed) and ensure the optimal value of the distance L01 between the nozzle 111 and the Venturi tube slot 114 and the sufficient length L21 of the Venturi tube slot 114 is high. In the STD configuration, mixing is basically completed in the sufficient length L21 of the Venturi tube slot 114.

Due to the technical overall dimensions of the gas supply pipe that must be added to the nozzle 111 , the minimum value of the height H41 of the compartment 405 covering the bottom of the top 401 is large and greater than H21 .

In summary, in the case of the STD configuration, the vertical space is considerable, not only due to the constituent elements of the burner, but also due to the inevitable empty space that must be left.

The modulation ratio Y, which is the ratio between the maximum power that can be delivered with conventional combustion and the minimum power, is obtained with an STD burner and depends on many factors, but first of all on the permissible range of the velocity of the mixture exiting the slot 117. In practice, this must be contained _between a minimum velocity _Vmin , below which there is _flashback , and a maximum velocity Vmax _{, above} which there is lift-off.

According to rules well known to those skilled in the art, _Vmin and _Vmax depend on the flame front speed _Vf , which in turn depends on the _drip of the mixture, which, as will be seen, is influenced by the burner geometry, among other factors. In summary, since the flame stability _Vf is indirectly determined by the gas flow rate _Qgas and the burner configuration, the achievable modulation ratio Y is strongly influenced by these factors.

Typically, for the STD construction, Y is comprised between 3.5 and 4.5.

"Special" burners are used for higher modulation ratios Y. "Special" burners are provided with more than one injector, each providing more than one concentric flame crown; although usually provided with a single special regulating valve that can open and modulate them in sequence, these burners have special geometrical features so that the secondary air flows also to the innermost flame crown. In fact, they are multiple burners.

Burners BRN with a horizontal or “linear” venturi configuration, referred to herein as “LIN” (see FIG. 4 ), have been commercially available since several years.

This configuration carries a Venturi with a completely linear development (Venturi slot 214 and diffuser 215 on the axis) arranged horizontally parallel to the coverage surface (it should be noted that in STD burners, the diffuser 115 is radial instead). The linear diffuser 215 opens into another mixing chamber 213, which occupies the entire internal volume of the burner and in which the mixing of the primary air AIR1 with the gas continues and is completed.

This solution allows to obtain a mixture that is still rich compared to the stoichiometric titer, i.e. a mixture that is poor in air, but significantly leaner than the mixture obtainable with the STD solution. Therefore, also in this case, the supply of secondary air AIR2 is necessary, but in a smaller amount than in the STD case (obviously with the same rated burner power and therefore the same injector nozzle diameter).

Slots 217 are formed from hundreds of small holes formed directly in cover 218, oriented in an angled manner toward the vertical direction of the pot. This results in a shorter, nearly vertical flame FLAME2 with increased power density and a circumferentially continuous crown that extends less radially than in the STD case. This improves heat transfer to the pot, prolongs the contact time of the flue gases with the pot surface, and shortens the distance between the base of FLAME2 and the pot bottom 404 (labeled H02 in FIG. 4 ).

All these considerations lead to a higher efficiency η _b of the burner BRN.

However, even LIN burners are not without flaws.

Despite this high adaptability, the maximum value of the modulation ratio for LIN is still limited to Y ≈ 3. This is due to the confluence of two factors, both related to the combustion dynamics: the fact that the droplet of the mixture obtained in the Venturi is closer to the droplet of the STC involves a greater flame speed V _f with a greater risk of flashback; at the same time, to simplify, the flame is shorter and therefore more unstable and more prone to flashover than in an STD burner, due to the fact that the combustion is completed more quickly the less secondary air it requires to be fed.

In an STD burner, since changing the cup 113 is impossible or always unnecessary for space reasons, changing the type of gas only requires changing the nozzle 111, which will result in a moderate improvement in the injector efficiency _ηej . In a LIN burner, in order to adapt to all types of gas, in addition to changing the injector-Venturi distance, it is also necessary to replace the injector and the flame disperser, since the dimensions of the Venturi and the morphology of the slots 217 in the cover 218 must be different for the different grades of gas, otherwise the flame will be unstable.

The solutions with linear venturis LIN currently on the market, although slightly reduced in size compared to STD burners, have all the limitations of non-stoichiometric mixtures (too rich) because, inside a domestic stove, there is not enough space to house an injector of optimal dimensions to produce primary air AIR1 at a stoichiometric droplet for the power required per burner. In any case, in addition to the space limitations, the linear extension of the diverging diffuser 215 must be shortened in order to connect to the mixing chamber 213, which in turn must be large enough to allow a complete mixing of the air and gas, otherwise the flame generated will be uneven and unstable.

As confirmation of the lack of gas stoves on the market with fully premixed atmospheric burners, it is noted that the few examples of products with active combustion air input, known as "ventilated hobs" (see, for example, the solution described in documents EP2072900, which provides a fan for each burner of the hob, and/or EP1016823) are practically limited to the input of only secondary air to complete the device for maintaining partially premixed combustion. The market is dominated by gas burners with partially premixed burners; to date, no fully premixed gas burners have been proposed.

In other fields, fully premixed burners have been known for a long time; for many years, for example, premixed burners characterized by simultaneous input via special fans have been installed in boilers for room heating and/or for producing clean hot water, the special fans (located upstream or downstream of the same burner) being arranged in series to an air-gas mixer which is connected to the metering, primary air, secondary air and excess air valves.

Without going into too much detail, as schematically represented in FIG5 , this boiler, of a solution well known to those skilled in the art, provides at least one fan V which supplies the mixture to the burners B preceded by a mixer MX comprising a “Venturi” 12 in a trough 14 section where openings 16 for the admission of the gases are obtained.

The tank section 14 is enclosed in a sealed chamber 17 where the gases coming from the metering valve VD accumulate; the fan V that extracts the combustion air from the venturi 12 creates a suitable low-pressure portion that allows the gases to pass from said sealed chamber 17 to the same tank 14 .

The electronic control board S controls the speed of the fan V and the operation of the pilot valve VD according to the thermal power required by the boiler.

The latter, for example of the pneumatic type, delivers a quantity of gas that depends on the low-pressure portion in the sealed chamber 17 and on the air pressure at the input to the Venturi 12; it thus behaves as a signal "follower", keeping the output pressure of the gas constantly aligned with the input pressure to the Venturi 12, whatever the required thermal output; the droplet density of the mixture is thus kept constant as a function of the variations in the thermal power of the burner B.

In order to achieve this result, which is a modulation ratio Y of 8 for burner B, the metering valve VD is equipped with a plurality of sealed chambers separated by a spring-loaded membrane. This spring has a preload that can be set externally in a variety of adjustment methods, which is essential for its adaptability to various systems. FIG6 schematically illustrates this metering valve VD, which thus appears to be extremely complex in construction and has large overall dimensions; see, for example, a comparison with the mixer MX.

If we compare the simplicity of the construction of STD and LIN burners, the solutions used in the field of premix boilers are extremely difficult to apply to domestic stoves; in fact, these solutions are characterized by:

- the large overall size is incompatible with the aesthetics of a home stove;

- Excessive costs, which can be attributed to the need for complex mixing valves and fans, which must be controlled by high-performance electronic control boards.

The main object of the present invention is to provide a hob, in particular for domestic use, comprising more novel burners which at least partially eliminate the above-mentioned drawbacks.

More precisely, the invention aims to provide hobs comprising active means for moving the combustion air so as to produce a fully premixed and/or excess air flame towards the burners.

More specifically, the object of the present invention is to obtain a substantially stoichiometric air-gas mixture as defined above in the burners of the hob, without requiring the introduction of external secondary air above the flame.

Another object of at least some variants of the invention is to obtain a higher modulation ratio Y than is currently possible for hobs comprising STD or LIN burners.

Another object of at least some variations of the present invention is to reduce the currently required distance between the base of the flame and the bottom of the overlying pot.

Other features and advantages of the invention will better emerge from the following description of a ventilated hob comprising a plurality of burners according to the independent claim and will become clear from the possible variants according to the dependent claims and illustrated by way of non-limiting examples with the aid of the accompanying drawings, in which:

FIG1 shows, by way of illustration, arrows representing air-gas mixtures of varying droplets and inflow rates, whereas in the other figures these arrows are used by way of example without any intention of providing quantitative data;

- Figure 2 schematically shows a cross-sectional view of a Venturi ejector;

- Figure 3 shows a vertical section through a STD burner;

- Figure 4 shows a vertical section through a LIN type burner;

- FIG5 schematically shows a premix boiler according to the prior art;

- FIG. 6 schematically shows a possible embodiment of a dosing valve for a premix boiler according to the prior art;

- FIG. 7 schematically shows a vertical cross-section of a ventilated hob according to the prior art;

- FIG8 schematically shows a vertical section through a ventilated hob according to a possible variant of the invention;

- FIG9 schematically shows a vertical section through a ventilated hob according to another variant of the invention;

- Figure 10 schematically shows a vertical cross-section of a ventilated hob according to another variant of the invention;

- Figures 11a and 11b show a cross-sectional view of a component of the hob shown in Figure 10 and a detail thereof, respectively;

- FIG12 schematically shows a vertical section through a furnace according to another variant of the invention;

- FIG. 13 shows a first graph illustrating correlations between certain operating characteristic parameters of a furnace according to at least some of the variants of the invention;

- FIG. 14 schematically shows a vertical section through a possible embodiment of a burner of a ventilated hob according to the invention;

- Figures 15a, 15b, 15c, 15d and 15e schematically show vertical cross-sections of further embodiments of burners for ventilated hobs according to the invention;

- Figure 16 shows an optimization of the embodiment of the burner shown in Figures 15a-15b;

- Figure 17 schematically shows a vertical cross-sectional view of a management and control system for a furnace according to the present invention;

FIG. 18 shows a second graph illustrating correlations between certain operating characteristic parameters of a furnace according to at least some of the variants of the invention;

FIG. 19 shows a third graph illustrating correlations between certain operating characteristic parameters of a furnace according to at least some of the variants of the invention;

FIG. 20 shows a fourth graph illustrating correlations between certain operating characteristic parameters of a furnace according to at least some of the variants of the invention;

- Figures 21a, 21b, 21c show a hob "configuration table" (also called "mapping") according to the invention, corresponding to the graphs of Figures 18, 19, 20 respectively;

- Figure 22 shows a horizontal section view of another variant of the burner for the ventilated hob of the invention;

- Figure 23 shows a horizontal section view of another variant of the burner for the ventilated hob of the invention;

- FIG. 24 shows a horizontal section through another alternative variant of a burner for a ventilated hob according to the invention;

- FIG. 25 shows a horizontal section view of another alternative variant of the burner for the ventilated hob of the invention;

- FIG. 26 shows a horizontal cross-sectional view of an operative embodiment of the construction of a ventilated hob according to the invention;

- Figure 27 shows a horizontal cross-sectional view of an alternative embodiment of a ventilated hob according to the invention;

- Figure 28 shows a horizontal cross-sectional view of another alternative embodiment of the ventilated hob of the present invention;

- Figure 29 schematically shows an alternative variant of the burner according to the previous figures.

Unless otherwise stated, any possible spatial references in this document such as vertical/horizontal or lower/upper terms refer to the position of the element in working condition, while spatial terms such as front/rear, upstream/downstream should be understood with reference to the circulation direction of the airform flow.

In Figure 1, arrows are drawn, each representing a mixture flow of different speed and droplet. These arrows are used in many subsequent figures to illustrate the actual state of air, gas and their mixture at various points upstream, downstream and inside the burner shown without any intention of providing any quantitative indication.

In the following examples, reference shall always be made to LIN type or “geometrically” and constructionally equivalent burners.

As it will be referred to several times in the following description, FIG. 2 shows schematically and not to scale a Venturi ejector 10 with a straight axis, which is the ideal shape for maximizing its performance η _ej .

The following represents the contents of the ejector 10: a venturi tube 12; a converging section (or simply, "converging portion") 13; a slot 14 having a diameter D; a diverging section 15 (also simply referred to as "diverging portion 15" or "diffuser 15"); and a nozzle 11 located near the inlet of the slot 14.

Figures 3 and 4, without requiring further explanation or further elaboration, respectively illustrate a burner BRN of the STD or LIN type, according to the prior art and widely described. Only some reference numerals are cited here that are useful for a complete understanding of the invention, thus: 400 denotes the hob as a whole; 401 is the aesthetically pleasing roof covering of the hob, which, however, also has a functional purpose in certain variants of the invention; 402 is the hob bottom, i.e., the surface that delimits the hob at the bottom; 404 is the pan bottom that rests on a grate above the burner BRN; this grate is not shown in these or subsequent figures for the sake of greater clarity.

Furthermore, to reiterate, in the two known types of STD and LIN burners, mixtures too rich in fuel are obtained, these mixtures requiring a supply of additional air AIR2 (known as "secondary"), which is brought by floating in the vicinity of the slots 117, 217 of the burner and is necessary for the completion of the combustion chemical reaction.

On the other hand, it is known that there are technical, logistical and aesthetic advantages (to be mentioned below) offered by a flame that is fully or substantially premixed at a stoichiometric titration STC (or above) at the output from the slots 117, 217 of the burners of a household hob; for example, it is known that this leads to a minimization of the distance between the base of the flame and the upper pot bottom 404, thereby contributing to a high _ηb value (ratio of the heat transferred to the pot to the heat generated by the burner) and minimizing the distance between the base of the flame and the aesthetic surface 401 of the hob 400 in which the burner or burners are integrated; shortening the minimum distance between the pot and the hob 400 eliminates the negative aesthetic effects that are common with grilles and contributes to an innovative and modern design of said hob.

The complete air-gas premixing that cannot be achieved with conventional STD or LIN burners allows to obtain a greater power density by further limiting the radial extension of the "flame bed"; since the input of external secondary air near the slots 117, 217 of the cover 118, 218 of the burner BRN is no longer necessary, these can also be distributed or directed in many ways.

Without any limiting intention, this allows to significantly increase η _b in the case of small pots (typical example: coffee machines generally have a smaller base than the flame crown); allows to increase the contact time of the hot flue gases with the pot bottom (the pot being the same pot); allows to minimize the dilution and cooling effects of the flame caused by the external air, thanks to the reduction of the perimeter of the flame bed (in fact, the floatation brings about a centripetal vertical flow of secondary air which, however, does not participate in the combustion but reduces the temperature of the perimeter of the flame bed); allows to limit in advance the risks arising from the excess of [CO] (so that the [CO]/[CO ₂ ] ratio is always systematically kept below the minimum limit imposed by the regulation).

As has been seen, among the solutions that have been used to try to obtain a systematically premixed combustion (hereinafter, for simplicity of description, called "premixed" or "premixed") or with a controlled excess of secondary air, solutions are known that use means for moving the air that are integrated into the same hob.

In FIG7 , an example of the prior art just mentioned, which has not proven to be sufficiently practical and economically and constructively advantageous, is shown in a highly schematic manner, wherein to each BRNi burner of a domestic hob 400 there is associated:

- a gas regulating valve VG (mechanical or electrical) for supplying gas to the burners BRNi and the associated supply duct CG;

- a supply duct CA for combustion air, capable of mixing inside the cup 200 of the same burner BRNi;

- a motor-driven fan which, in the example shown in the figure, is located upstream of said duct CA.

The heating power of each burner BRNi (and thus of the hob 400 as a whole) is constantly regulated by the gas supply pressure regulating valve VG. More precisely, in the preferred embodiment, it is regulated according to the "opening degree α" of the pressure regulating valve VG selected or set by the user by acting on, for example, a rotary handle or a push-button panel (not shown). This "opening degree α" is then appropriately detected and processed by known means (e.g., by a control circuit (not shown)) to modulate the speed of the individual fans V associated with and dedicated to the individual burners BRNi. In FIG7 , this operating situation is symbolically represented by the connecting line between the gas valve VG and the fan V (see "dashed arrow").

Another construction solution that allows keeping the chemical equivalence of the air-gas mixture substantially constant (even if not without difficulty) by "blowing" air to the burners BRNi at a constant ratio to the delivered gas flow is functionally identical to the construction solution for the well-known "premix boiler" (air flow as a function of the metered gas).

The high structural, constructive and functional complexity of this hob 400, which in fact has greatly limited its spread on the market, becomes immediately clear if compared with conventional STD or LIN burners of the passive type; for example, it is necessary for the regulating valve to be able to transmit a signal corresponding to its "opening degree α" to the corresponding fan V, which necessitates the presence of at least one control and processing unit.

Furthermore, installing, supplying and backoperating (for example, via pressure sensors) a fan V for each burner 1 can be complex and economically disadvantageous from a construction point of view.

The excessive overall size of such hobs may also detract from the overall aesthetics and/or integration with other appliances and fixtures of the kitchen.

What has been seen so far basically relates to the prior art.

According to the invention (see, for example, Figures 8 and 9), a single fan V is used for a plurality of burners BRNi of a hob 400, which will hereinafter also be referred to as "ventilated hob 400".

Although nothing prevents providing the example possibility of implementing more hobs, for simplicity of description the example in question shows a hob 400 comprising two burners BRNi.

More precisely, according to the variant shown in FIG8 , the only fan V pressurizes, inside the compartment 405 of the hob 400 , the sealed circuit CA1 which supplies combustion air to all the burners 1 through appropriate air lines CA10 , CA11 , . . . CAn.

According to an alternative simplified variant (see FIG. 9 ), said sealed circuit CA1 may be constituted directly by said compartment 405 of the oven frame 400 made sealed, thereby practically eliminating the previously listed internal circuits defining the air lines CA10 , CA11 , . . . CAn.

The term "pressurized" thus means that the pressure of the combustion air provided by the fan V is greater than the ambient pressure (generally corresponding to atmospheric pressure).

In both variants, each burner 1 can carry a throttle valve VP regulating the inflow of combustion air (preferably after a corresponding shut-off valve, not shown in FIGS. 8 and 9 ).

Preferably, the throttle valve VP is mounted directly on the cup 200 of the burner 1 .

Obviously, in particular for the variant of FIG. 8 , nothing prevents the throttle valve VP from being mounted at any point between said fan V and the cup 200 of the burner 1 , for example along the relative air line CA10 , CA11 .

It is thus clear that, according to the general solution of the invention to be cited below, the presence of said throttle valve (or, as will be seen, of an equivalent "fine-tuning" mechanism) allows "local" regulation of _the air flow Qair supplied to the individual burners BRNi at a substantially constant and fixed pressure in the compartment 405 (also called "plenum" 405) of the hob 400 or in the corresponding sealed supply circuit CA1.

In other words, from here on, a “local regulation” of the combustion air flow is understood to mean a regulation substantially locally in the vicinity of each single burner BRNi, so as to keep the internal pressure of the compartment 405 or the associated sealed circuit CA1 substantially constant.

As will be seen later, according to an alternative general solution of the invention, said fan V may be able to adjust its speed so as to ensure a combustion air pressure inside the compartment 405 of the hob 400 or the associated sealed circuit CA1 that satisfies the air flow _Qair required locally for each single burner BRNi.

This type of regulation of the air flow _Qair will be referred to below as “centralized”.

In practice, in various preferred embodiments, there may also be a combination of said “localised” and “centralised” regulation of the air flow _Qair in order to appropriately supply the _air flow Qair to the plurality of burners BRNi of the hob 400 of the invention.

As will be seen, a stoichiometric or substantially stoichiometric air-gas mixture is obtained by both "local" and "central" regulation (or a combination thereof) without the need for external secondary air input.

Reference will be made in this description to these aspects which have been discussed so far in a very general manner.

In the following, reference will now be made to a "local" solution (see, for example, the structural solution of FIG. 9 ).

The combustion air flows through the throttle valve VP of each burner BRNi and passes directly from the pressurized compartment 405 of the hob 400 acting as a plenum chamber to a mixing zone with the gas (supplied as seen through the associated gas valve VG) inside the cup 200 situated in the same burner BRNi.

It is noted that, according to this variant, the throttle valve VP is not necessarily subject to the strict safety requirements of the corresponding gas valve VG; in fact, due to the presence of the pressurized compartment 405 (in which the fan V obviously functions), any poor sealing of the throttle valve VP does not involve any risk.

The air throttle valve VP receives its positioning "signal" solely from the corresponding gas regulating valve VG (or from the control unit of the gas regulating valve VG), without the need for a central control and regulation unit. In practice, since the type of gas supplied to the burner BRNi and the operating pressures of the air and this gas are known, it follows that:

a characteristic outflow curve of each throttle valve VP defining the air flow Qair _fed to the burner BRNi, this curve being a function of the angular position β of the control trim of said throttle valve VP (hereinafter referred to as “air valve opening degree”);

a characteristic outflow curve for each _gas regulating valve VG defining the gas flow Qgas fed to the burner BRNi, this curve being a function of the angular position α of the control trim of said gas valve VG (hereinafter referred to as “gas valve opening degree”);

- Ensure the air/gas drop ( _Qair / _Qgas ) to each burner BRNi,

These parameters are all provided by the manufacturer of the hob 400 , and a correlation can be established and determined between the opening degree α of each gas valve VG and the opening value β of the air passage section of the corresponding throttle valve VP.

This relationship is illustrated graphically in FIG13, which will now be briefly described.

In this figure, the first quadrant (i) is shown with the horizontal axis being the opening degree α of the above-mentioned gas valve VG and the vertical axis being the flow rate _Qgas ; the second quadrant (ii) is defined between the vertical axis _Qgas and the horizontal axis the air flow rate _Qair (through the throttle valve VP) required to ensure a predetermined desired value of the droplet of the mixture; the third quadrant (iii), in which the combustion air flow rate Qair is related to the opening degree β of _the throttle valve VP; and the fourth quadrant (iv), in which the vertical axis is defined by the said opening degree β of the air valve VP, and the vertical axis is opposite to the opening degree α of the gas valve VG in the horizontal axis.

In other words, in this first quadrant there is a defined single relationship between the degree of opening α of the gas valve VG and the gas flow Qgas that the _gas valve VG can deliver (indicated by the outflow curve represented as a "dashed line" in Figure 13); in the second quadrant there is a correlation curve between the gas flow Qgas required to ensure a certain droplet density of the _mixture and the air flow _Qair ; in the third quadrant there is one of the outflow curves of each air valve VP represented by a short dash line; in the fourth quadrant (iv) there is a correlation curve between the said degree of opening α of the gas valve VG and the said degree of opening β of the air valve VP.

Thus, once a certain opening degree α of the gas valve VG, indicated by point 1 in FIG. 13 , has been set by the user of the hob 400 (by acting on a control handle or button of the hob 400 as already described), the corresponding gas flow _Qgas (point 2) supplied by the gas regulating valve VG to the burner BRNi is immediately and uniquely known; from this, the corresponding air flow _Qair (point 3) required to keep the titration STC of the mixture in the burner BRNi constant and the opening degree β of the throttle valve VP (indicated by point 4) can therefore be found.

In general, α and β represent geometric parameters associated with the degree of opening of the gas valve VG and the degree of opening of the air valve VP, respectively.

As a non-limiting example, more specifically, the geometric parameters α and β may be angular or linear parameters defining the rotation or sliding of the throttle valves of the respective gas valve VG and air valve VP. In the example shown in FIG11 , α is an angular geometric parameter defining the degree of rotation of the throttle valve VG1 of the gas valve VG from its "normally closed" position, while β represents a parameter defining the degree of opening of the throttle valve VP1 of the air valve VP from its "normally closed" position.

Several kinematic mechanisms can be used to mechanically establish the correct correspondence between the degree of opening α of the gas valve VG and the degree of opening β of the associated air valve VP.

According to a possible embodiment of the invention, as a non-limiting example, such a correlation between the opening angle α of the gas valve VG and the opening angle β of the combustion air throttle valve VP (β=β(α)) can be technically achieved by incorporating the air throttle valve VP and the gas regulating valve VG into a single valve body (usually metallic), wherein the inner part VG0 of the gas valve VG actuates the inner part VP0 of the air valve VP (which can be of linear type, for example spherical, also called "streamlined flow") via a cam CM (see details in Figure 11b) connected to the inner part VG0 of the gas valve VG and the inner part VP0 of the air valve VP.

As schematically shown in Figure 11a, the inner part VG0 of the gas valve VG has an axis that is preferably perpendicular to the inner part VP0 of the air valve VP. The two inner parts are respectively referred to as VG0 and VP0 and are mechanically connected to each other by adjusting the positions of the gas throttle VG1 and air throttle VP1 of the corresponding gas valve VG and air valve VP, respectively.

Obviously, there is nothing that prevents the possibility of electromagnetically or electronically controlling the correlation between the degree of opening α of the gas valve VG and the degree of opening β of the air valve VP; for example, a more complex system could be provided that uses electrical signals of the position of the throttle valve VG1 of the gas valve VG, these electrical signals being transmitted to an electronic positioner carried by the air throttle valve VP, which is able to receive these electrical signals and thereby set the position of the associated throttle valve VP1.

Furthermore, the air valve VP is not necessarily of the type shown in FIG. 11 merely as a non-limiting example (the air valve VP could for example be a known and simple “throttle valve”).

In Figures 10 and 12 is shown a "mechanical system" of choking the combustion air supplied by a single fan V to the burners BRNi of the hob 400 of the invention, instead of the valve VP described above.

It is useful to note that the alternative system facilitates the possibility of retrofitting or in any case converting/modifying conventional or already on the market/installed ventilated hobs 400 without requiring major disruption of the conventional production lines.

For example, FIG10 shows a conventional hob 400 comprising a plurality of burners BRNi (however, for simplicity of description only one burner BRNi is drawn, preferably of the linear LIN type) and an inner compartment 405 pressurized by a fan V (and in which the overpressure is kept substantially constant).

Once the burner BRNi is set to ensure a stoichiometric mixture (STC=100%) to the burner BRNi by reducing, for example, the required thermal power (and therefore the gas flow _QGas ), a systematically "leaner" mixture will be obtained, as has been widely seen, i.e. with an increasing redundant excess of combustion air.

Therefore, in order to maintain the chemical equivalent titration STC over the entire thermal power adjustment range of the burner BRNi, it is necessary to provide the combustion air blocking system that is able to vary the flow rate input to the Venturi injector 10 according to the opening degree α _i of the gas valve VG (the opening degree α _i of the gas valve VG is set by the user U by acting on the control handle/button panel).

This system of action for “fine regulation” of the power of the burner BRNi makes it possible to provide, at the convergent portion 13 of the injector 10 , movement means suitable for reducing and “blocking” the useful air passage section.

In more detail, such a moving device 101 may be constituted by a moving throttle 101 whose position may be mechanically linked as desired to the opening degree α _i of the throttle VG1 of the gas valve VG (ie to the gas flow Qgas input to the _burner BRNi).

According to this variant, the movement device 101 is then mechanically connected to the control inner part VG0 of the throttle valve VG1 of the gas valve VG via a known kinematic mechanism.

Alternatively, by way of non-limiting example only, such a mobile device 101 may be comprised of the following:

- means suitable for reducing the distance L02 between the injector 211 downstream of the gas valve VG and the slot of the Venturi injector 10 (see FIG10 ), for example by making the converging portion 13 to the slot 14 of the injector 10 telescopic so as to be gradually displaced towards said fixed injector 211;

- means suitable for reducing the section D02 of the groove 14 of the Venturi ejector 10 , for example by means of an iris (not shown) interposed between the converging portion 13 of said ejector 10 and the groove 14 and/or by means of a shutter.

It is also possible to provide a variant according to which the movement means is the same gas injector 211 which can be transferred to the convergent portion 13 of the Venturi injector 10 , thereby effectively reducing the useful section for the air supplied by the fan V to pass to the cup 200 of the burner BRNi.

In addition to the above-described mechanical solution for coupling the angular position αi of the inner part of the gas valve VG to the linear displacement of the air throttle 101 , a pneumatic variant can also be provided: according to this variant, the displacement of the air throttle 101 can also be achieved preferably by a pneumatic servo control 100 .

For example, as shown in FIG12 , the displacement of the air damper 101 can be achieved by connecting the air damper 101 to a thrust-moving element 103 of a “corrugated capsule 102”, which is anchored on an opposite surface 104 to a fixed element, such as the frame of the oven frame 400. The capsule 102 is free to deform elastically in the longitudinal direction (normal to the fixed and moving surfaces) according to the pressure difference between its inner compartment 105 and the external environment; in addition, a traction spring 106 is housed in the capsule 102, which tends to cause the capsule 102 to “implode”.

The inner compartment 105 of the capsule 102 is pneumatically connected, via a small tube 107, to a portion 202.a of the conduit for connecting the gas valve VG to the associated injector 211. In this way, the actual supply pressure of the injector 211 solely determines the position of the air throttle 101 by regulating the preload of the spring 106.

At this point, as anticipated, another mode called “centralized” for regulating the air flows that can be supplied to the various burners BRNi of the hob 400 in appropriate and specific quantities should be analyzed as an alternative to or in combination with the “localized” mode described just above in various embodiments.

It is therefore worthwhile to initially identify the advantages that may be derived from pressurizing the compartments (or plenums) 405 of the oven rack 400 .

It is known that, to work at too low a pressure (for example by providing the use of an axial fan V), the throttle valve VP should have a large nominal diameter to avoid producing excessive load losses; this gives rise to obvious problems in terms of overall size and weight; on the contrary, high pressures close to the gas supply pressure (for example from 20 to 30 mbar) (achieved for example by providing a centrifugal fan/blower V) will make it possible to install much more compact air throttle valves, but it will first be possible to replace them with air injectors that are completely similar in construction and function to the gas injectors (provided that preferably there are means, such as connecting rods, suitable for preventing the structure of the furnace frame 400 from temporarily deforming and/or bulging due to the pressures involved).

A first novel solution with forced air input is shown in FIG14 , in which a burner BRNi (also called “premix burner”) whose functional solution is suitably optimized to operate with active supply of combustion air and for generating a completely or essentially premixed flame is shown.

For the sake of simplicity, the figure shows only one of the burners BRNi of the hob 400 , while the graphic representation of the fan V pressurizing the compartment 405 is deliberately omitted.

According to this variant, what in a conventional burner is the "cup 200" can now become the actual mixing chamber 200; the nozzle 211 of the gas injector is actually constrained (for example, by screwing in without loss of generality) to the input seat 209 located in the first area 200.a of the side of said cup 200, allowing the user U to replace it as the type of gas supplied to the gas injector changes.

An inlet 208 for air pressurized by a fan V is provided on a second, opposite side region 200.b of the cup 200, facing a gas injector 211, the gas nozzle 211 and the air inlet 208 being positioned substantially opposite each other and on the same level. Due to this arrangement, a permeable screen 204 (or equivalent device) is interposed inside the cup 200 between the gas nozzle 211 and the combustion air inlet 208. The screen 204 has the task of slowing down and dispersing the gas jet, which is much faster than the air flow; in this way, the risk of gas entering or leaking into the pressurized compartment 405 of the hob 400 is avoided.

Thus, inside the cup 200, a first air-gas thrust mixing occurs (hence the fact that the cup 200 can be considered a real mixing chamber), which then continues vertically upwards to the vicinity of the slots 217 of the cover 218 of the burner BRNi 1. Preferably, according to the invention, one or more grilles 205 can be provided between the first mixing zone inside the cup 200 and the associated cover 218, these grilles 205 being optionally movable by the user U.

More precisely, Figure 14 shows a premix burner, inside which two perforated grids 205.a and 205.b can be arranged, one superimposed on the other, whose task is to improve and homogenize the air-gas mixture and stabilize the flow until a chemically equivalent mixture STC (or air-rich) is obtained, which mixture advances to the array of narrow slots 217 of the flame diffusion cover 218.

Preferably, without any limiting intention, the perforated grids 205.a and 205.b may differ from each other in the number of holes and in their shape and size.

These grids 205, 205.a and 205.b can be called "homogenizer baffles" due to the functions they perform and define multiple mixing stages inside the cup 200 of the burner BRNi; for example, for the burner shown in Figure 14, there is determined: a first mixing stage contained between the bottom 206 of the cup 200 and the first perforated grid 205.a; a second stage determined between the two grids 205.a and 205.b; and a final mixing stage that develops between the upper perforated grid 205.b and the flame diffusion cover 218.

By means of this solution, it is possible to obtain a premix burner BRNi with a cup 200 having a smaller vertical space compared to conventional burners and a resulting reduction in the minimum height of the pressurized inner compartment 405 of the hob 400 .

Regardless of what is alternatively shown in at least the schematic diagrams of the hob shown in Figures 7 to 9, there is nothing preventing, for example, the bottom of such a cup 200 from also being in direct contact with the bottom 206 of the compartment 405, also due to the absence of a gas supply pipe and its technical overall dimensions.

As schematically shown in Figures 15a and 15b, according to a preferred variant of the invention, the above-mentioned seat 208 of pressurized air inside the cup 200 of the burner BRNi of the hob 400 can serve as a seat for the calibration air nozzle UG.

Note that in this embodiment, which will now be examined in detail, the air nozzle UG with a calibrated and fixed opening replaces the air throttle valve VP with a variable opening (or an equivalent mechanical adjustment system shown in Figures 10 and 12).

An air (on/off) shut-off valve (not always in the drawings) should continue to be present (even if not always shown) and located upstream of the air nozzle UG (as is the case with the throttle valve VP).

According to this further variant of the invention, the air nozzle UG

- receiving pressurized air from compartment 405, the pressurized air being pressurized by a fan V driven by a motor;

As already foreseen, an inlet 208 constrained (for example by screwing) to the side wall 200 . b of said cup 200 of the burner BRNi and extending in the cup 200 (as seen, acting as a mixing chamber).

Fuel gas and combustion air can be supplied to the burner BRNi via respective injectors substantially at the same pressure, thereby mixing inside the cup 200 .

Furthermore, in this variant of the burner BRNi, the two gas nozzles 211 and the air nozzle UG face each other, and the presence of the permeable screen 204 previously described for the variant of FIG. 14 is no longer necessary, since the two flows of gas and combustion air, as described, have the same pressure, which is sufficiently high, and this pressure prevents the gas from leaking into the pressurized compartment 405.

Furthermore, the burner BRNi of Figures 15a-15b may alternatively comprise one or more perforated grids 205.a, 205.b inside the mixing chamber 200, suitable for promoting and homogenizing the air-gas mixture so as to obtain a substantially stoichiometric STC mixture.

To maximize this beneficial effect, it is possible and preferred to constrain the gas nozzle 211 and the air nozzle UG to respective opposite sides 200.a, 200.b of the cup 200 of the burner BRNi, so that the gas nozzle 211 and the air nozzle UG are offset relative to each other. FIG16 shows this further constructional variant of the burner BRNi according to the present invention. Since the offset of the gas nozzle 211 and the air nozzle UG generates a persistent vortex inside the mixing chamber 200 of the burner BRNi, which improves the air-gas mixing, according to this variant, it is possible to provide a first homogenizer baffle 205.a (or grid) with a single central opening 207, through which the air-gas mixture is forced to pass to improve its homogeneity (see FIG16).

The second homogenizer baffle 205.b may in turn be completely similar to the second homogenizer baffle 205.b described with reference to other variations of the present invention.

In Figures 15c, 15d and 15e further construction variants are shown, according to which both the air nozzle UG and the gas nozzle 211 are constrained to the same inlet 2008 of the side 200.a, 200.b of the cup 200 of the burner BRNi.

More precisely, said nozzles UG, 211, which may also constitute a single component (replaceable depending on the gas supplied), may be arranged concentrically to one another (see FIG. 15 c ) or adjacent to one another (see FIG. 15 d and 15 e ).

For example, in the variant with a "concentric injector" of Figure 15c, the air nozzle UG is arranged outside the gas injector 211 and can be supplied by corresponding air supply ducts 203 and gas supply ducts 202. According to a known construction scheme, the air supply duct 203 and the gas supply duct 202 are also concentric and are called "tube-in-tube".

In the “side-by-side injector” variant, both the air nozzles UG and the gas nozzles 211 can alternatively be supplied via the already mentioned pipe-in-pipe solution ( FIG. 15 e ) and via supply ducts 202 , 203 parallel to one another ( FIG. 15 d ).

Furthermore, in all these configurations of Figures 15a, 15b, 15c, 15d, 15e and 16, each calibrated air nozzle UG is preferably placed after a "normally closed" shut-off valve (not shown) which opens only at start-up of the burner BRNi.

Furthermore, the cross-sections of the air nozzles UG and the gas nozzles 211 are generally much smaller than the cross-section of the interior of the cup 200 of each burner BRNi acting as a mixing chamber (also called "plenum").

In the case where each such burner BRNi of the hob 400 (i.e. with integrated air and gas nozzles) is served by a corresponding and dedicated fan V, the power regulation system can be set up according to the graph shown in Figure 18, which provides an upper quadrant (I) and a lower quadrant (II), the upper quadrant (I) having the air flow _Qair that can be supplied by the air nozzle UG in the horizontal axis and the pressure drop DP across said air nozzle UG in the vertical axis (hereinafter referred to as the "operating pressure DP" inside the pressurized compartment 405 for the sake of simplicity), and the lower quadrant (II) also having said air flow _Qair in the horizontal axis, but having the degree of opening of the gas valve VG in the vertical axis (as can be seen, only the gas nozzle 211 of the gas valve VG is shown in the figure).

More precisely, the upper quadrant (I) shows at least one possible characteristic curve _Ki of the air injector UG of the burner BRNi selected by the manufacturer, which characteristic curve defines the relationship between the operating pressure DP and the air flow rate Qair flowing _therein , while the quadrant (II) shows the intrinsic characteristic curve of the gas valve VG, which intrinsic characteristic curve is known per se once the air/gas ratio ( _Qair / _Qgas ) to be ensured to the burner has been selected.

Thus, through this graph, the correlation between the air flow _Qair through the air injector/nozzle UG and the gas flow _Qgas as a function of the angular position _α determined by the inner part of the plug of the gas valve VG is defined.

The graph shown in FIG. 18 also shows characteristic curves (referred to as “performance”) of the fan V of the hob 400 , each characteristic curve corresponding to a constant number of revolutions “n”.

It should be noted that the thermal power regulation range of the burner BRNi extends from a minimum value corresponding to the minimum value of the degree of opening α _min of the gas valve VG ensured by the minimum value n _min of the speed of the fan V and the minimum value DP _min of the operating pressure of the pressurized compartment 405 of the hob 400, to a "rated" value obtainable by the maximum value α _max of the degree of opening of the gas valve VG, the maximum value DP _max of the operating pressure and the maximum value n _max of the speed of the fan V.

What may be appreciated from this graph is how relatively simple it is to ensure a substantially stoichiometric STC air-gas mixture and a perfectly premixed flame as the required thermal power of the burners BRNi varies, provided that each burner BRNi is served by a corresponding and dedicated fan V as described.

This "simplified" situation is shown in detail and "constructively" in FIG17 , which shows, among other things, a burner BRNi of the type described with reference to FIG15 b. Obviously, nothing prevents the possibility of using a burner BRNi already described, modified according to the variants shown in FIG15 c, 15 d, 15 e or 16.

In this case, in practice, each fan V regulates its speed according to the aforementioned characteristic curve. More precisely, the speed "n" of the fan V is regulated according to the value of the operating pressure DP to be reached in the pressurized compartment 405 of the hob 400, which in turn is a result of the thermal power required by the burner BRNi, i.e., the degree of opening α of the gas valve VG defined by the user U.

As a non-limiting example, the degree of opening α ₁ of the gas valve VG (point 1 in FIG. 18 ) corresponds uniquely to a “point 2” on a known and predetermined characteristic curve of the gas valve VG, with the result that a corresponding value of the air flow Q _air necessary to keep the droplet density of the air-gas mixture constant (represented by “point 3” on the abscissa).

This air flow _Qair to be supplied to the burner BRNi corresponds to "point 4" on the known characteristic curve K of the air injector UG; therefore, the speed of the fan V should be the speed of its characteristic curve passing through said "point 4", which defines the intersection with the characteristic curve of the fan V representing the predetermined speed "n".

This number of revolutions "n" of the fan V ( _n4 in the example) ultimately corresponds to a predetermined value for the operating pressure DP to be ensured to the air nozzles UG.

This simple example shows a first possible method of regulating a single burner BRNi of the hob 400 , so as to always ensure perfectly premixed combustion as the heating power required by the user U varies.

It is noted that, according to this configuration of the invention, the manufacturer, having available mappings of the characteristic curves of the gas valve VG and the air injector UG, does not need to use a pressure sensor to regulate the power of the burner 1; therefore, under these conditions, it is sufficient for the fan V to be able to provide a speed signal to the control unit CMD of the hob 400.

Furthermore, the degree of opening a of the gas valve VG can advantageously be transmitted to the same control unit CMD via a known transmitter TD integrated into said gas valve VG and an associated known transmission line L0.

There is no need to describe in detail the other wirings L1, L2, L3 shown in Figure 17, which are well known to those skilled in the art; it is sufficient to specify here that line L1 connects the motor V0 of the fan V to the control electronics CMD, while lines L2 and L3 respectively command the igniter IGN of the burner BRNi and the corresponding flame detector FD.

Finally, reference L4 denotes the power line of the fan V, which is also controlled by the control electronics CMD.

Much more complex is the logic underlying the thermal power regulation of each burner BRNi when a single fan V of the aforementioned compartment 405 inside the pressurized hob 400 supplies combustion air to all of said burners BRNi (after specific shut-off valves), which are usually different from one another.

In practice, the speed "n" of a single fan V may be excessive or unsuitable for some burners BRNi in the hob 400; these burners BRNi may thus move away from a substantially premixed operating condition with an STC drop of the mixture.

Thus, what is described below will be the “centralized” regulation solution previously discussed in a very general form, of the air flow _Qair to be supplied to each burner BRNi of the hob 400 .

Although everything that will be discussed can be made with reference to a hob 400 comprising any number of burners BRNi, for ease of understanding reference will be made to a hob 400 equipped with only four burners BRNi (Z=4); in the example considered, they are:

- are all different from each other,

- as already mentioned, served by a single fan V pressurizing the compartments 405 of the same oven 400 ,

- The air injectors UG are actually parallel to each other because they are subject to the same upstream-downstream pressure drop.

In the case of four (Z=4) burners BRNi, there are 16 possible combinations C of burners C that are simultaneously active (indicated by the symbol "1") and/or deactivated (indicated by the symbol "0") and are summarized in the map in FIG. 21 a, which can be stored by the manufacturer in the control unit CMD of the hob 400.

Considering the portion of the pressurized compartment 405 defined between the inlet section of the fan V and the outlet section or sections constituting the open nozzle UG, it is possible, as is known from the laws of fluid dynamics of passive components, to define for each corresponding combination C a single corresponding "flow-pressure" characteristic curve KKn, which in the diagram shown in FIG19 is simplified by a parabolic relationship (of course, the typical characteristic curve in the case where all burners are closed is a degenerate parabola coinciding with the ordinate of the diagram).

Furthermore, for each burner BRNi, a stoichiometric titer STC can be attributed to its power level close to the rated power level, which power level will be referred to hereinafter as the “target” level TGT.

Preferably, the target power level TGT is 85% of the rated power of the burner BRNi. However, it can be provided that the droplet of the air-gas mixture to the burner BRNi is acceptably close to the stoichiometric ratio STC and thus close to the "substantially stoichiometric ratio STC" and also in the vicinity of this target power level TGT, i.e., even by narrowing its modulation range, for example by +/- 15% (although this inevitably corresponds to a reduction in the modulation ratio Y). In other words, it is possible to modulate the opening degree α of the gas valve VG of the burner BRNi between a minimum value α _min of 70% and a maximum value a _max of 100%, while at the same time ensuring a stoichiometric or "substantially stoichiometric" STC droplet of the air-gas mixture (and thus the premixed flame).

In this way, at each combination C there is also a unique value of the operating pressure DP(C), which ensures a precise supply of combustion air _Qair to all the burners BRNi that are simultaneously open in the furnace rack 400, and a single corresponding speed n(C) of the fan V, so that a chemically equivalent STC (or substantially chemically equivalent STC) drop is obtained, regardless of the adjustment of the opening degree α of the gas valve VG of each burner BRNi.

In general, if the combinations C are finite, ie if only a finite number of power levels are possible for each burner BRNi, all possible combinations C of an infinite number of simultaneously active burners BRNi can be stored in the aforementioned storage device.

Alternatively, when continuous variation of the power level is possible for one or more burners BRNi, the control unit CMD can be provided with the just-mentioned calculation means of said operating pressure DP(C).

In this way, it is ensured that the burner 1 always operates under premixed combustion conditions.

Such operation of the entire hob 400 is summarized in the graph shown in FIG19 , which is suitably and further simplified by making the burners BRNi identical to one another, thereby reducing the number of combinations C of four burners BRNi to five, i.e. from fully closed to fully open (thus reducing the number of characteristic curves that would render them substantially unrecognizable).

Thus, in this case (burners identical to one another), a single characteristic curve KKn=KKA is determined for all configurations involving only one active burner BRNi, and unique characteristic curves KKB and KKC are determined for all representative configurations of two or three simultaneously active burners BRNi; finally, a curve KKD is determined for a single combination of all active burners BRNi.

For simplicity, a mapping corresponding to this case has not been provided in the drawings; thus, reference should be made only to the graph shown in FIG. 19 as intended.

Thus, it has been found that, upon detection of the simultaneously active burners BRNi, the (e.g. electronic) control unit CMD of the hob 400 is able to determine the air flow _Qair and the associated operating pressure DP, ensuring a substantially stoichiometric or almost stoichiometric STC level for the air-gas mixture in each burner BRNi, regardless of the degree of opening _αmin <α< _amax of the gas valve VG.

For example, in FIG19 , the combination C=3 (corresponding to the characteristic curve KKB), which corresponds to the case in which only two of the four burners BRNi defining the hob 400 are open, would correspond to an air flow _Qair = _Q2 supplied to all active burners BRNi and a corresponding operating pressure DP2 ensured by the fan V operating at a speed _n2 .

Here, other evolutions and approaches to systems that can be defined as “almost premixed” should be analyzed.

It is known that by further extending the modulation range of the burner BRNi, the density of the air-gas mixture obtained varies according to the gas flow _Qgas provided by the gas valve VG, i.e. according to the power level required by the user U, as a function of the degree of opening α of the gas valve VG; below the target power level TGT, the mixture will become "leaner" (i.e. with a greater redundant excess of air), while above the target power level TGT the mixture will be richer in gas.

In order to extend the modulation ratio Y, the following variants can thus be provided.

Let us consider, without any limiting intention, a furnace stand 400 comprising three simultaneously active burners BRNi, all of which are different from one another and each of which is adjusted to its own thermal power, which is different from the target power TGT; this configuration can be achieved by setting a different opening degree α _i for the gas valve VG of each active burner BRNi, which is different from the defined target power level TGT and thus complies with the following relationship: α _{i min} < α _i < α _{i max} where α _i ≠ α _{i_TGT} (i=1; 2; 3).

As has already been seen with reference to the previous cases, each combination of simultaneously active burners BRNi corresponds to:

- a predetermined characteristic curve KKi of the associated air nozzle UG;

- the corresponding value of the operating pressure DP of the compartment 405 of the furnace stand 400, and

- the corresponding speed of the fan V pressurizing said compartment 405 .

In the Q _air - DP graph shown in FIG. 20 , for example, the burners BRN1 and BRN3 have been adjusted to a power higher than the target power TGT, whereas the burner BRN2 has been adjusted to a lower power.

This means that, by acting on the relevant handle/button panel, the user U has set:

the respective opening degrees _α1 and _α3 of the gas valves VG of the burners BRN1 and BRN3 are higher than _αtarget ( _α1 >_{α1_TGT}; _α3 > _{α3_TGT} ) suitable for ensuring the target power level TGT,

A lower opening degree α ₂ of the burner BRN2 (α ₂ <α _{2 — TGT} ).

That is, each burner BRNi will be operated under the influence of an appropriate and specific operating pressure DPα _i , which is obtained by the corresponding speed n(α _i ) of the individual fans V and is different from the "target" operating pressure _DPtarget , (corresponding to the "target" speed _ntarget of the _fan V and can be inferred from a mapping relationship that is completely similar to the mapping relationship shown in Figure 21a) which in turn will ensure premixed combustion as seen (for example, burner BRN1 should operate with pressure DPα ₁ , while fan V should operate with speed nα ₁ , and similarly for burners BRN2 and BRN3).

Thus, under these conditions, each burner BRNi (BRN1, BRN2, BRN3 in the example) does not ensure premixed combustion.

In this case, the control unit CMD of the hob 400 intervenes:

- by detecting the state of the shut-off valve (not shown in the drawing) upstream of the air nozzle UG, the configuration of the simultaneously active burners BRNi is known,

- knowing the angular positions α _i of the gas valves VG (the gas valves VG can thus communicate their position to said control CMD by means of appropriate electrical signals flowing through a particular and dedicated line L0, as a non-limiting example; see for example Figures 26 and/or 27 and/or 28),

- knowing the target speed _ntarget of the fan V (as already anticipated, the target speed _ntarget can be detected from the speed signal of said fan V and can be generated and sent via a dedicated data line; see, for example, reference L1 in Figures 26 and/or 27 and/or 28),

- a signal has been received from the flame detector FDi (line L3 in Figures 26 and/or 27 and/or 28),

A new operating pressure _DPaction is recalculated, _which corresponds solely to the new rotational speed _naction of the fan V and the resulting combustion air flow _Qaction .

More precisely, this pressure DP _action is the median value of the individual pressures DPα _i that each active burner BRNi should have; preferably, this pressure DP _action can advantageously be calculated as a weighted average:

DP _ACT =[(b1*DPα ₁ +b2*DPα ₂ +…+b _k *DPα _i +…+bC*DPα _C )/C]

The individual weights "b _k " can be freely selected and optimized by the manufacturer of the hob 400 , for example by determining an increased weight based on the size of the burner BRNi; in this way, the burners BRNi producing more power will also be those that are closer to fully premixed operation.

Although less precise and efficient, there is obviously nothing preventing the possibility of calculating said pressure DP _ACT as the arithmetic mean of the individual pressures DPα _i that each active burner BRNi should have.

It is clear that in all cases of single-acting burners BRNi, this control method ensures perfect premixed combustion.

Of course, the best results for an "almost premixed" system are achieved by adjusting the chemical equivalence titration STC of the air-gas mixture, wherein, as previously seen, the target power level TGT lies between 70% and 100% of the maximum power of the burner BRNi and wherein the individual burners are identical to one another.

It is noted that, by this regulation, the known risk of flashback is inherently eliminated, since the output speed from the slots 217 of each burner BRNi is systematically higher than the corresponding speed of the flame front.

Furthermore, a further consequence of this system is that the flame is systematically "disengaged" from the flame disperser 218, thereby avoiding the high operating temperatures typical of conventional burners throttled to minimum power.

Starting from the situation shown in the graph with reference to FIG20 , if one wishes to further extend the modulation range of the burners BRNi of the furnace 400, the modulation method of the “centralized” type just described would result in a proportional deviation from the premixed conditions and thus in greater inaccuracies in the control of the actual drop of the air-gas mixture for each burner BRNi.

In practice, as the modulation ratio Y increases, a corresponding premixing condition is obtained for each burner BRNi.

This problem is overcome at least according to the variant of the invention shown in FIG. 22 .

According to this variant, for each burner BRNi, the possible levels of air flow _Qair to be supplied according to the degree of opening α _i of the corresponding gas valve VG can be further discretized, thereby obtaining a “fine regulation” of its power.

This may be achieved by providing a separate combustion air inlet and/or more valves (or "multi-way" valves) providing one or more inlets for further supply air.

According to a variant, each burner BRNi may preferably be provided with, for example, a plurality of air injectors, each provided with an associated UGi and arranged after a respective solenoid shut-off valve (not shown).

Preferably, said air and/or gas valves are advantageously made by known valves of the "multi-way" type with sequential outlets (since these are well known to a person skilled in the art, no detailed description is required in this respect).

In general, the blocking can be achieved by providing for each burner BRNi an alternative use of:

- a plurality of air nozzles UGI, each air nozzle UGI having a different diameter;

-Multi-way valve.

Without any limiting intention, in the example shown in FIG. 22 , each burner BRNi of the hob 400 may preferably comprise two air nozzles UG1 , UG2 (and a single gas injector) of different sizes.

For the sake of continuity of description and to make it possible to see a comparison between the various variants of the invention, reference will again be made to a hob 400 comprising only four burners BRNi.

By successively increasing the thermal power of each burner BRNi, i.e. by varying the degree of opening α _i of the associated gas valve VG between a minimum value α _imin and a maximum value α _imax , the control unit CMD (for example of electronic type) will act so as to be able to sequentially: first (i.e. at low power), enable a smaller air injector; as the required thermal power increases, this air injector will be disabled to allow the actuation of a (larger) second injector; finally, when approaching the maximum thermal power of the burner BRNi, a first air injector will also be added by enabling it again.

In this way, the adjustment range of the opening degree α _i of the gas valve VG of each burner BRNi can be divided into three sections (or “stages”), which can be defined as follows:

α _{i_minimum} <α _i <α _{i_low} ;

α _{i_low} <α _i <α _{i_medium}

α _{i_中}<α _i <α _{i_max}

As a result, the mapping of the configuration of the hob 400 that can be preloaded and controlled by the control unit CMD changes as shown in Figure 21b; in practice, if reference is made to a hob 400 comprising a plurality of burners BRNi and provided with only one gas valve VG and air nozzle UG (see, for example, Figures 15, 16), then sixteen different combinations C of simultaneously active and/or switched-off burners are determined, which obviously become 256 in the case of the configuration of the burners BRNi that has just been described.

Thus, in this case as well, each configuration C describing the combustion of the simultaneously active burners BRNi of the furnace 400 and the required thermal power (which can be estimated based on the opening degrees α _i of the individual gas valves VG) should uniquely correspond to a combination of enabled air nozzles UGi, characteristic curves KK(C), optimal operating pressure DP(C) and corresponding rotational speed n(C), said configuration C being detectable by the control unit CMD of the furnace 400 essentially in the manner already described above with reference to the other construction variants.

According to another variant of the invention, the concept of discrete blockage of the combustion air described above can be applied to the regulation of the gas flow; that is, a variant can be provided according to which the burners BRNi of the hob 400 are systematically operated in the premixed combustion regime by means of discrete regulation steps of their thermal power.

An example of such a burner BRNi is shown in FIG. 23 .

Without any limiting intention, said burner BRNi comprises two air nozzles UG1 , UG2 and two gas injectors 211 a , 211 b , each gas injector being typically arranged after its on/off shutoff solenoid valve (not shown).

In FIG. 23 , the gas injectors 211 a, 211 b are preferably shown constrained (for example by screwing) to the cup 200 of the burner BRN1, one gas injector being orthogonal to the other, according to a configuration that optimizes mixing with the combustion air; without minimizing the generality of the invention, it is clear that nothing prevents the gas injectors 211 a, 211 b from being arranged and directed in a different manner, for example opposite each other.

Although not clearly visible in the figure, the two gas injectors 211a, 211b (like the air nozzles) have appropriately different diameters, thereby enabling the gas supply to the burner BRNi to be regulated via its three possible opening combinations (enables); this makes it possible to eliminate the gas regulating valve VG (necessary for the continuous regulation shown with reference to the previous variant), thus facilitating a perfectly premixed burner BRNi with four power states.

More precisely, the burner BRNi can be switched, by action on a specific selector (which can replace a standard rotary valve), from the off position when both injectors are disabled, to a minimum power level (P _min ) when only one gas injector of smaller diameter is enabled, to a mean power level (P _Med ) corresponding to the activation of only the gas injector with larger diameter, and to a maximum power level (P _Max ) when both gas injectors are in operation simultaneously.

Since each combination C of enabled gas nozzles 211a, 211b corresponds to one and only one combination of open air injectors UGi, the mapping of the configuration of the various states of the hob 400 schematically shown in Figure 21c can be considered to be essentially unchanged compared to the mapping associated with the burners BRNi in Figure 22 discussed previously (and referred to for further explanation and details).

Thus, even in this case, once the mapping is known and it has been detected which burner BRNi has been enabled by the user U and at what power, the control unit CMD is able to regulate the speed n _i of the fan V accordingly, by defining the pressure DP of the pressurized compartment 405 of the hob 400 and _the air flow rate Qair to be supplied, thus ensuring a substantially premixed combustion to each burner BRNi.

It is clear that in the practical embodiment of the invention several variants can be provided, all falling within the same inventive concept.

For example, nothing prevents the possibility of implementing a "chemically equivalent mixer MS" of the type shown in FIG29 , based on a similar solution used in the field of domestic boilers, in a ventilated hob 400. That is, _according to this configuration, the mixing chamber inside the cup 200 of the burner BRNi can be replaced by a primary gas injector EJ _p directly bonded to the mixing Venturi 10 through which the combustion air passes from a fan V that pressurizes the compartment 405 (not shown in FIG29 ) of the hob 400; thus, the gas and air supplied to the Venturi can be modulated by a single valve body.

In this way, the formation of the air-gas mixture proceeds through two successive steps; when the gas flows through the nozzle 211 of the gas injector (not explicitly shown) in the primary ejector EJ _p , it brings in a certain air flow rate, shown as AIR A in FIG. 29 , thereby forming a rich gas mixture flow (shown as MIX A), which then expands around the Venturi slot in the sealed chamber 17, where it is carried away by the low-pressure portion retained therein.

At this point, the mixture MIX A is appropriately diluted by the air flow AIR B entering the input of the mixing venturi, thereby ensuring a stoichiometric (or substantially stoichiometric) titer STC to the homogenized mixture MIX B in the output from the device.

Although not shown in reference figure 28, the outlet section 150 of the mixture MIX B of the stoichiometric mixer MS can be connected directly to the cup of the burner BRNi, which therefore does not require those internal mixing and homogenization grids 205.

Further variations can be made to the burner BRNi version, including (for example as shown in Figures 15, 22, 23) one or more air nozzles UG and/or gas nozzles 211 presented as removable parts (for example simply screwed to the cup 200 of the same burner BRNi).

As shown in Figure 24, calibrated openings 201.a, 201.b (of different diameters) are then located directly on the body of the cup (200) of the burner BRNi, each opening being supplied by a dedicated gas or combustion air duct 202, 203, which are equipped with relative shut-off solenoid valves _EV1 , _EV2 (the solenoid valves _EV1 , _EV2 can be positioned anywhere between the cup 200 and the gas and air supply manifold (not shown)).

According to the variant of Figure 25, the body of the cup 200 of the burner BRNi can also include external chambers 204, 205 (for example two in number) that supply combustion air and gas to the calibrated openings 201 obtained directly on the same cup 200 as described.

For simplicity of description and to distinguish the chambers 204 , 205 , the chambers 204 , 205 will be referred to as “air chamber 204 ” and “gas chamber 205 ”, respectively.

The shutoff solenoid valves may be bonded directly to the chambers 204 , 205 , thereby directly enabling the air injectors UGI and the gas injectors 211 .

Reference numerals 202, 203 again denote fuel gas and combustion air supply ducts, respectively.

This variant allows simplifying the construction of the air and gas supply circuits, thereby reducing the number of ducts required.

FIG. 25 also shows control lines LC for the gas and air solenoid valves, the enabling and/or disabling of which are controlled by an analog or digital electromechanical/electronic push button panel (as shown).

With reference to FIG. 26 , there is shown a possible structural configuration for a ventilated hob 400 comprising a plurality of burners BRNi of the type described above.

According to this model, the following facts should be noted:

- a single air channel 407 pressurized by a fan V located upstream, supplies all the supply ducts 203 of the air chamber 204 of each burner BRNi;

- a single gas channel 408 supplies the supply ducts 202 of all associated gas chambers 205 of the same burner BRNi;

Therefore, the air passage 407 and the gas passage 408 are different and separate components from each other.

Of course, it is preferred that the cross-sections of the air passage 407 and the gas passage 408 are greater than the cross-sections of the single supply ducts 202 and 203 , so as to minimize load loss.

Of course, there is nothing to prevent providing other variants of the hob 400 just described, by providing a gas and combustion air supply system of the "pipe in a pipe" type (not necessarily coaxial), the inner pipe 408 being able to supply gas directly to each supply duct 202 of the gas chamber 205 of each burner BRNi, and the outer pipe 407 supplying combustion air to the corresponding air duct 203 of the aforementioned air chamber 204 (see FIG. 27 ).

As they are well known to those skilled in the art and/or covered by other patent applications under the same applicant, there is no need to elaborate on the features or functions of the various wiring of the button panel and/or safety valve in any case shown and classified in the described variations of Figures 26 and 27.

It is clear that, according to these variants, the air-gas mixing is carried out and completed inside the cup 200 of each burner BRNi.

Obviously, nothing prevents the possibility of carrying out this mixing upstream of each burner BRNi as shown in FIG. 28 .

According to this variant, the (premixed or substantially premixed) air-gas mixture is actually obtained inside the mixing compartment 409, which is directly connected at the bottom to the air channel 407 and the gas channel 408 of the above-mentioned sealed circuit (CA1, 405, 407) and is then supplied to the burner BRNi through appropriate pipes 410.

More precisely, air injectors UG communicating with the air channel 407 and at least one gas injector 211 and, in turn, with the associated gas channel 408 are placed on the mixing compartment 409, the actuation of these air injectors UG allowing the input of the combustion air and gas for producing the mixture for the burner BRNi.

Thus, such a structural solution can be achieved simply by providing the channels 407, 408 substantially close to each other.

According to a structural variant not shown in the figures, said channels 407 , 408 may for example be substantially adjacent to each other and parallel.

However, as shown in FIG. 28 , preferably, the channels 407 , 408 are concentric (not necessarily coaxial) so as to define an air-gas supply system of the “tube-in-tube” type as has been seen.

Without any limiting intent, in this latter preferred variant, said at least one air and gas injector may be concentric with each other, with the second being located inside the first, thereby defining a single component (hereinafter referred to as "concentric injector") which:

- preferably by obtaining it directly on the outer wall of said "pipe-in-pipe" supply system;

A single throttle valve is provided, actuatable, for example, by an electromechanical actuator, to allow the simultaneous introduction of air and gas into the interior of the mixing chamber.

It should be noted that in Figure 28, by way of non-limiting example and without any restrictive intention, the mixing compartment is shown as comprising two of said "concentric air-gas injectors", thereby essentially (with reference to Figure 23) reproducing the situation (and the associated advantages and results) already described for burner BRNi with reference to Figure 23.

Thus, it should be noted that for each burner BRNi, the two "concentric injectors" have different sizes (one with smaller air inlet section d _Li and gas inlet section DA _Li , the other with oversized sections d _Hi and DA _Hi ), each being provided with its throttle.

Thus, by selectively combining the openings of the throttle valves of the pair of "concentric injectors" of the burner BRNi, different power levels can be obtained as already broadly described.

It is thus clear that with the aid of the hob 400 and the associated burner BRNi according to the various variants of the invention, all the stated objectives are achieved and further advantages are also ensured.

More precisely, in addition to those mentioned from time to time in this description, there may be provided means for moving and supplying the combustion air (such as a fan V) which, according to the method described above, ensure a completely premixed flame and/or excess air to the burners BRNi of the hob 400 without the need for the input of secondary air, thus achieving modulation ratios Y higher than those currently achievable.

The need to replace the gas injectors to manage different gases is also avoided, i.e., it is sufficient to change the regulation "map" of the fan V to take into account the different density and calorific value of the new gas, for example, switching from methane (20 mbar) to liquefied petroleum gas (30 mbar), thereby keeping the gas and air openings unchanged, which would require a significant increase in the air supply, resulting in a consequent increase in the rated power of all BRNi (more than 50%). In the worst case, it would only be necessary to replace the "flame spreader" 218 of the burner BRNi according to the different outflow rate of the air-gas mixture from the corresponding "slot" 217.

Thus, the many variations of the inventive hob 400 described in this specification can thus be summarized and generalized.

Each burner BRNi of the hob 400 comprises means suitable for regulating the air flow _Qair in a suitable manner to ensure a quantity sufficient for the air-gas mixture to have a substantially constant, in particular substantially stoichiometric STC, drop, whatever the power set in the burner BRNi itself.

This means that one or more fans V are provided, which ensure an air pressure Q _air which is above the ambient pressure.

In a first general variant, the fan V ensures an overpressure in the plenum 405 of the hob 400 that, taking into account the thermal power set by the user on each burner BRNi, ensures an air flow to each of them substantially equal to that required to ensure an air-gas mixture with a stoichiometric or substantially stoichiometric ratio STC.

To this can be added the fact that at the air inlet section in each burner BRNi there is also a device for “fine regulation” of the air flow.

According to another basic variant, when providing said “fine regulation” for each burner BRNi, the fan V ensures a pressure that is substantially constant and exceeds the required maximum value.

Finally, according to this last variant, the fan V can also vary the operating pressure according to the maximum pressure currently provided in the respective burner BRNi.

Finally, it should be noted that some of the variants described in the present specification (for example, the mechanical air flow regulation devices of Figures 10 and/or 12) can be advantageously used even in hobs comprising only one burner or hobs with burners each supplied by its own dedicated fan, and therefore also constitute the specific object of parallel and concurrent patent applications.

Claims (18)

1. A ventilated furnace rack (400) comprising a motor-driven fan (V) adapted to supply high-pressure air to two or more burners (BRNi) of the furnace rack, each of the two or more burners (BRNi) comprising at least: —A device for supplying and regulating the gas flow (Q _gas ) to the input of each of the two or more burners (BRNi), the device being supplied by a gas passage (408), the device comprising at least one gas injector, - A means for supplying combustion air flow rate (Q _air ) to the input of each of the two or more burners (BRNi), the combustion air being supplied by a sealed circuit (CA1) and capable of mixing with the fuel gas. - An electronic unit (CMD) for controlling the airflow (Q _air ), Its features are, The electronic unit is configured such that the air flow rate ( _{Q_air} ) varies according to the gas flow rate ( _{Q_gas} ) in the input of each of the two or more burners (BRNi), thereby ensuring a gas-air mixture with a stoichiometric or substantially stoichiometric ratio without the need for external secondary air input. The change in the airflow rate ( _{Q_air} ) is achieved by altering the pressure of the combustion air in the sealed circuit (CA1) inside the furnace frame (400), and the fan (V) is configured to adjust its speed to determine the required air pressure. The regulation of the airflow ( _{Q_air} ) is referred to as "centralized". Furthermore, its characteristics also lie in, The control unit (CMD): - A configuration set to detect simultaneously operating burners (BRNi), - The gas valve (VG) of the burner (BRNi) is configured to detect the opening degree ( _αi ) of each of the aforementioned actions, each opening degree ( _αi ) corresponding to a specific operating pressure ( _DPαi ), also taking into account the characteristic curve of the device for supplying the combustion air flow rate (Q _air ), the device consisting of at least one air nozzle (UG) with a calibrated and fixed opening. The operating pressure (DP_action) is set to determine the intermediate value of a single pressure ( _{DP_i} ) that the burner (BRNi) should have for each action, the intermediate operating pressure ( _{DP_action} ) corresponding solely to the speed ( _{n_action} ) of the fan ( _V ). The intermediate pressure (DP _action ) is determined by a “map” loaded into the storage device of the control unit (CMD), which has all possible combinations (C) of simultaneously acting burners (BRNi) based on all possible power levels of the burner. 2. The ventilated furnace frame (400) according to claim 1, Its features are, The two or more burners (BRNi) also include shut-off valves for the flow of combustion air. 3. The ventilated furnace frame (400) according to claim 1 or 2, Its features are, The value of the intermediate pressure (DP _action ) is the weighted average of the individual pressures (DPα _i ) that the burner (BRNi) should have for each action. 4. The ventilated furnace frame (400) according to claim 1 or 2, Its features are, The at least one air nozzle (UG) consists of two air nozzles (UG1, UG2), which have different diameters. The two nozzles (UG1, UG2) discretize the level of air flow (Q _air ) to be supplied to each of the two or more burners (BRNi) according to the opening degree ( _αi ) of the corresponding gas valve (VG). 5. The ventilated furnace frame (400) according to claim 4, Its features are, The apparatus for supplying and regulating the gas flow (Q _gas ) associated with each of the two or more burners (BRNi) may include two gas injectors (211a, 211b) having different diameters, which discretize the thermal power rating of each burner (BRNi). 6. The ventilated furnace frame (400) according to claim 1 or 2, Its features are, The at least one air nozzle (UG) and the at least one corresponding gas injector (211a, 211b) are constrained on the cup (200) of each of the two or more burners (BRNi) as an air-gas mixing chamber (200). 7. The ventilated furnace frame (400) according to claim 6, Its features are, The at least one air nozzle (UG) and the at least one corresponding gas injector (211a, 211b) are constrained to the cup (200) facing each other, and the air nozzle (UG; UG1, UG2) and the gas injector (211a, 211b) are respectively constrained to opposite sides (200.b) and (200.a) of the cup (200). 8. The ventilated furnace frame (400) according to claim 7, Its features are, The at least one air nozzle (UG) and the at least one corresponding gas injector (211a, 211b) facing each other are misaligned. 9. The ventilated furnace frame (400) according to claim 7, Its features are, The at least one air nozzle (UG) and the at least one corresponding gas injector (211a, 211b) are concentrically constrained on the same side (200.a, 200.b) of the cup (200), and the at least one air nozzle (UG) is arranged outside the at least one corresponding gas injector (211a, 211b). 10. The ventilated furnace frame (400) according to claim 9, Its features are, The at least one air nozzle (UG) and the at least one corresponding gas injector (211a, 211b) that are concentric with each other may be coaxial. 11. The ventilated furnace frame (400) according to claim 7, Its features are, The at least one air nozzle (UG) and the at least one corresponding gas injector (211a, 211b) are constrained side by side on the same side (200.a, 200.b) of the cup (200). 12. The ventilated furnace frame (400) according to claim 6, Its features are, At least two perforated grilles (205.a; 205.b) located on top of one other may be disposed inside the cup (200) to improve and homogenize the air-fuel mixture, the at least two perforated grilles (205.a; 205.b) being distinguishable from each other by the number and/or shape and/or size of their holes. 13. The ventilated furnace frame (400) according to claim 7, characterized in that, The at least one air nozzle (UG) and the at least one corresponding gas injector (211a, 211b) are formed by a calibrated opening (201) obtained on the side (200.a, 200.b) of the cup (200) of each of the two or more burners (BRNi). 14. The ventilated furnace frame (400) according to claim 13, Its features are, The body of the cup (200) may externally include an air chamber (204) for the combustion air and a gas chamber (205) for the gas. 15. The ventilated furnace frame (400) according to claim 1 or 2, characterized in that, The at least one air nozzle (UG) and the at least one corresponding gas injector (211a, 211b) are constrained to a compartment (409), which serves as an air-gas mixing chamber and is located upstream of each of the two or more burners (BRNi) of the furnace frame (400), the mixing compartment (409): - The lower part communicates with the air supply passage (407) and the gas supply passage (408) of the sealed circuit (CA1), the passages (407) and (408) being substantially close to each other. - Connected to each of the two or more burners (BRNi) via appropriate conduit (410). 16. The ventilated furnace frame (400) according to claim 2, Its features are, The "centralized" regulation of the combustion air flow rate ( _{Q_air} ) can also be associated with "local" _regulation , which can be adjusted by changing the channel cross-section of the combustion air supply device. 17. The ventilated furnace frame (400) according to claim 2, Its features are, The shut-off valve is located upstream of the combustion air regulating device. 18. The ventilated furnace frame (400) according to claim 1 or 2, Its features are, The air supply channel (407) and the gas supply channel (408) are concentric with each other according to the pipe-in-pipe structure.