FIELD OF THE INVENTION

The present invention relates to the technical field of combustible gas burners. In particular, the present invention relates to the technical field of methods and apparatuses for monitoring and controlling combustion in combustible gas burners used, for example, in apparatuses, such as boilers, heaters, fireplaces and the like. BACKGROUND ART

In the technical field of combustible gas burners, it is known that in order to maintain efficient combustion, it is necessary that, for all power supplied by the burner, the ratio between the amount of air and the amount of combustible gas introduced into the burner is kept at around a predetermined optimum value.

Efficient combustion allows obtaining and maintaining important benefits in time, such as reducing the dispersion of energy in flue gas and reducing the production of polluting gases, this latter parameter being required by regulations on emissions, which are in force in a growing number of countries.

In order to achieve the object of achieving and maintaining an optimum air/gas ratio, different methods and apparatuses have been developed in the technical field of combustible gas burners. Methods are known for monitoring and controlling combustion, and in particular, the ionization of gas in the combustion zone of the flame based on flame analyses, like the so-called SCOT method, an example of which is described in European patent EP770824.

The available state-of-the-art systems provide the use of an electrode arranged in the zone of the flame or close to the flame, connected to an electronic circuit, which applies, to the electrode, a fixed or varying electrical voltage and measures the current crossing said electrode when it is supplied by the aforesaid electrical voltage. Therefore, the estimate of one or more parameters correlated to the combustion is carried out by means of processing and analyzing the measured current signal measured. Various types of processing techniques are used, all of which are aimed at detecting an instability of the flame of the burner or sub-optimal combustion, so as to provide combustion process corrections adapted to bring it back to the required conditions (see, for example, the systems described in European patents EP1002997 and EP2901080).

The techniques in use have limitations and drawbacks related to different factors, including wear of the electrode, which is adapted to operate as a flame or ionization sensor, which can have repercussions on the precision and also reliability of the data analyzed by the current algorithms for processing the current signal detected. Other drawbacks are linked to the fact that the current systems always work with a single closed control loop, and command of the gas valve and fan strictly depends on the feedback of the signal received by the ionization or flame sensor. This results in two problems:

1 ) poor adjustment quality for high modulation ratios given that at the minimum operating mode the feedback signal used for closing the adjustment control loop may not suffice to perform the adjustment;

2) a certain slow response, which makes control ill-adapted to manage transients or brief disturbances.

The aforesaid limitations and drawbacks are more serious in so-called pneumatic systems, wherein the gas flow rate is directly determined by the air flow rate recalled by the system, but they can also still be found in the most recent control systems where the gas flow rate is directly regulated by an actuator regulating the degree of opening of an adjustment valve. In patent EP3751200, for example, a system is described for controlling a gas burner, wherein it is provided that a certain power value of the burner corresponds to a certain degree of opening of a valve for adjusting the flow rate of the combustible gas; the described adjustment occurs with the loop open at low powers and with the loop closed only for higher burner powers. Lastly, the following difficulties must be highlighted among the criticalities of the current systems, on the air side:

1 ) detecting, with precision, alterations in the passage of air inside the system for totally or partially obstructing the fume intake chimney;

2) identifying, during the installation process, modifications in the density of the air, due to the altitude or temperature, which can also significantly impact the development of the combustion.

Furthermore, given that the power of the gas burner is determined by the amount of air introduced, the aforesaid difficulties make the estimate of actual power of the burner imprecise in a given step.

Therefore, it is an object of the present invention to introduce an apparatus and method for monitoring and controlling the combustion of a burner of combustible gas apparatus - through a precise adjustment of the gas mixture and air carried to the burner - which allow overcoming the limitations and drawbacks related to the prior art.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to an apparatus, and a related method for monitoring and controlling the combustion of a burner of combustible gas apparatuses by means of adjusting the gas mixture carried to the burner. Said burners are used in numerous applications, including, for example, common domestic boilers for producing domestic hot water and/or hot water for feeding hydraulic circuits for the heating of environments.

The apparatus and method according to the present invention are adapted to adjust, in a combustible gas burner, a mixture of gas formed by a first gas and a second combustible gas, wherein the gas mixture is provided through the appropriate mixing of an amount of said first gas by means of a first adjustment element and an amount of said combustible gas by means of a second adjustment element. Said first or second adjustment elements are managed, during operation, by a controller, which processes the data coming from at least two sensors.

In some embodiments of the invention, the first gas can be a gas for carrying the oxygen and the second gas can be a combustible gas to be mixed with the gas for carrying the oxygen. For example, the first gas can be air or a mixture of air and flue gas and the second gas can be a natural gas, such as methane or LPG.

Said combustible gas burners are characterized by the specific heat output range (e.g. from 3 kW to 30 kW) and in that said heat output is independent of the type of said second gas used.

Given that different combustible gases have different Wobbe indices (Wobbe Index = ^PowerHeat °f ^combustion ) this means that, with the same power, the volumetric flow rate of gas will be different depending on the type of combustible gas used. Furthermore, the Stoichiometric combustion of said second gas requires a supply of said first gas in an amount, which is, in the first approximation, independent of the type of said second gas used. Thus: with the same power, depending on which type of said second gas is used, the flow rate of the latter must be changed, but not the flow rate of said first gas (e.g., air).

Said burner must be able to operate with different types of said second gas and therefore, the control apparatus must be capable of manually (during the installation stage) or automatically adapting as said second gas changes.

In a preferred embodiment of the invention, said first adjustment element comprises a fan with a varying number of revs, which can be set by means of a first command and said second adjustment element comprises a valve, which is adjustable by means of a second command. For example, said valve can be provided with an actuator comprising a stepper motor, as described in international patent application WO201 91 16407A1 by the applicant.

Furthermore, in a preferred embodiment, said at least two sensors preferably comprise a first flame sensor arranged close to the flame of the burner and adapted to measure the electrical features of the flame of the burner including, for example, the resistance, Rei, or electrical conductivity, Gei, and a second sensor positioned in the fan and adapted to measure the number of revs of the fan, e.g. by means of a Hall sensor adapted to read the supply current of the fan or by means of another device or method adapted to read the number of revs of said fan.

In another preferred embodiment, said plurality of sensors preferably also comprises a third absolute pressure sensor, preferably placed at the entrance or exit of the fan. In a further preferred embodiment, said absolute pressure sensor is flanked by a sensor adapted to measure the temperature of the air, which is also preferably arranged at the entrance or exit of the fan. Advantageously, the temperature and pressure sensors can also be integrated into only one sensor.

Finally, the controller comprises a microprocessor, or an equivalent electronic processing element, and at least one associated memory unit. Said controller is adapted to carry out cyclic readings and process the signals coming from the aforesaid sensors and produce, based on said processing and, optionally, based on a comparison with values of reference stored in tables placed in the memory unit, appropriate drive signals for said fan and said adjustable valve.

For a correct combustion, the apparatus and method according to the present invention must supply the burner with an excess amount of air with respect to the stoichiometric amount.

The ratio between the amount of air provided for the combustion of a certain amount of combustible gas and the amount of air needed for the combustion of the same amount of gas in stoichiometric conditions is traditionally called “A” (air number). The value of A will be equal to 1 where the amount of air provided is equal to the amount of air for a stoichiometric combustion, while the combustion is usually considered optimal and safe where the A is kept, in normal burner operating conditions, between 1.2 and 1.6.

The amount of air supplied to the burner varies proportionately as the revs “n” of the fan vary and it is influenced by the load losses of the fume discharge pipe, which may differ for each installation.

The amount of gas is determined by the degree of opening of the valve operated by an actuator, e.g., by a stepper motor, so that a certain opening section of the valve, and therefore a certain gas flow rate, will correspond to a certain number of steps “s” of the actuator.

At a certain Power “W”, while the number of revs “n” of the fan is substantially constant, the degree of opening of the valve depends on the type of combustible gas used. Therefore, different (at least two in number) different degrees of opening of the valve must be provided and thus, different numbers “s” of steps of the actuator of the valve, generally comprising a stepper motor.

During the development step of the apparatus according to the present invention, different “standard” tables are stored in the aforesaid controller, each of which, for each type of gas and for each power between the minimum power Wmin and the maximum power Wmax of the burner, indicates the “n” and “s” values, which are adapted to ensure the desired value of A in installation conditions, which is, in fact, “standard”. At the site of installation, the person installing the burner can manually determine the type of gas and thus the table to be used among those stored or an automatic gas recognition method can be used based on the ionization sensor selected from the methods already known in the state-of-the-art. The controller needs these tables to generate the correct drives for the fan and actuator of the valve, which follow on from a certain request for power from the burner. Furthermore, said tables can be “dynamically” updated by the aforesaid controller with new values calculated according to the method of the invention, if these new values calculated are different to those stored in the aforesaid “standard” tables due to the fact that the installation conditions and/or contingent operating conditions, also after installation, are different to the “standard” ones considered during the factory testing of the boiler or burner.

According to the method of the invention, the drive signals and the measurements of the sensors, which determined them, may therefore be stored in the memory unit associated with the microprocessor, so as to update and cyclically complete said tables containing the optimum settings of the fan and of the valve of the apparatus, as a function of the changed operating boundary conditions. Thereby, the present invention allows obtaining an apparatus for monitoring and controlling the combustion of a burner, and a method related to said apparatus, which is capable of self-learning and self-adjustment so as to reach the optimum working conditions of the burner in terms of efficiency, stability and safety for the user.

On varying the thermal power requested of the burner, or if, with the same thermal power requested of the burner, a change is detected in the operating conditions, based on the reading of the signals coming from the signals of the apparatus, the controller varies the drive signals of the fan and/or the valve so as to restore the optimum combustion conditions corresponding to a desired excess air value, A.

Advantageously, the controller, according to the invention, can be provided with a memory unit or with a plurality of memory units adapted to contain the drive signals for said fan and said adjustable valve and the corresponding measurements of the sensors, which determined them in known operating conditions. Thereby, a memory unit - and different corresponding setting value tables may be available, for use, for example, in different circumstances, such as the final testing or initial starting stage, or again a calibration or emergency operation stage to be set after a malfunctioning. The operation of the controller according to the present description provides different control routines, based on the type of operation and conditions of use of the burner, succeeding in distinguishing between start-up, first installation, calibration and normal operation, allowing adapting the operation of the burner to changed conditions so as to optimize the working, and signal any potential alarm states. In a preferred embodiment, the control method applied by the controller according to the present description further provides using different feedbacked control loops, each based on the detections made by the aforesaid sensors and characterized by different speeds so as to appropriately react both to transients and the needs for rapid adjustment as in the case of a change in thermal power requested of the burner, and to slow deviations in the conditions and operating parameters as in the case of changes in the composition of the combustible gas mixture.

BRIEF DESCRIPTION OF THE FIGURES

Further features and advantages of the invention will become apparent from the reading of the following detailed description, given by way of non-limiting example, with the aid of the figures shown in the accompanying tables, in which:

Fig. 1 shows a functional block diagram of an embodiment of the apparatus according to the present invention;

Fig. 2 shows a functional block diagram of an embodiment of the apparatus according to the present invention;

Fig. 3 shows a flow diagram of a preferred embodiment of a part of the method according to the present invention relative to the initial start-up procedure of the apparatus according to the present invention;

Fig. 4 shows a flow diagram of a preferred embodiment of a part of the method according to the present invention relative to the calibration procedure of the apparatus according to the present invention;

Fig. 5 shows a flow diagram of a preferred embodiment of a part of the method according to the present invention relative to a first control loop of the postcalibration operating procedure of the apparatus according to the present invention; Fig. 6 shows a flow diagram of a preferred embodiment of a part of the method according to the present invention relative to a second control loop of the postcalibration operating procedure of the apparatus according to the present invention; Fig. 7 shows a flow diagram of a preferred embodiment of a part of the method according to the present invention relative to a third control loop of the post- calibration operating procedure of the apparatus according to the present invention; Fig. 8 shows an example of a table containing the operating parameters of the apparatus according to the present invention;

Fig. 9 shows a graph of the trend of the resistance R of the burner flame as a function of the degree of opening of the valve for adjusting the combustible gas;

Fig. 10 shows a graph of the trend of the resistance R of the burner flame as a function of the rotation speed of the fan, after fixing the value of the air number A; Fig. 1 1 shows a graph of the degree of opening of the valve for adjusting the combustible gas as a function of the rotation speed of the fan, after fixing the value of the air number A, for a specific gas;

Fig. 12 shows a graph relating the power of the burner W with the number of revs n of the fan, the amount of air Qa supplied by the fan and the change in pressure AP, and

Fig. 13 shows a graph relating the number of revs n of the fan, the amount of air Qa supplied by the fan, the volumetric flow rate of the air supplied by the fan, Q and the air density p.

The following description of exemplary embodiments relates to the accompanying drawings. The same reference numbers in the various drawings identify the same elements or similar elements. The following detailed description does not limit the invention. The scope of the invention is defined by the appended claims. DETAILED DESCRIPTION OF THE INVENTION

[Adjustment of the combustion with at least two sensors]

With reference to the attached Fig. 1 , in a preferred embodiment of the invention, the apparatus for monitoring and controlling the combustion of a burner for combustible gas apparatus comprises a first adjustment element 5 for adjusting a first gas 3, a second adjustment element 6 for adjusting a second combustible gas 4, a combustible gas burner 2 adapted to burn a mixture of gas formed by said first gas and by said second combustible gas, at least two sensors for detecting operating parameters of the apparatus, and a controller 9 adapted to manage said first adjustment element 5 and said second adjustment element 6 based on the processing of the signals from said at least two operating parameter sensors of the apparatus. Said adjustment element 5 can be placed upstream or downstream indifferently of the mixing point 11 between said first 3 and said second combustible gas 4.

Said first adjustment element 5 comprises a fan with a varying number of revs, which can be set by means of a first drive command and said second adjustment element 6 comprises a valve, which can be adjusted by means of a second drive command. In a preferred embodiment of the invention, said at least two sensors comprise a first sensor 12 adapted to measure the number of revs of the fan 5 and a second flame sensor 8 associated with the flame of the burner 2, as shown in Fig. 1 .

In further detail, said second flame sensor 8 is preferably arranged close to the flame of the burner and is adapted to measure the resistance Rei, or the electrical conductivity, Gei, or other electrical parameters of the flame of the burner 2; said first sensor 12 is preferably placed inside the fan 5 and is adapted to measure the rotation speed of the electric motor of said fan 5, for example, expressed in number of revs per minute.

In another preferred embodiment of the invention, said adjustment element 5 is associated with a third absolute pressure sensor, or absolute pressure and temperature sensor 7. Said sensor 7 is preferably placed at the entrance or exit of the fan 5, which, in turn, may be placed both upstream and downstream of the mixing point 1 1 .

Said controller 9 preferably comprises a microprocessor, or an equivalent electronic processing element, and at least one associated memory unit 13. Said controller 9 is adapted to carry out readings and cyclically process the signals coming from the aforesaid sensors 7, 8, 12 and produce, based on said processing and a comparison thereof with values of reference stored in tables allocated in the memory unit 13, appropriate drive signals for said fan 5 and said adjustable valve 6.

The drive signals and/or the measurements of the sensors, which determined them, and/or the various operating parameters, which are calculated to estimate the optimum operating point, may also be stored in the memory unit 13 associated with the microprocessor of the controller 9, so as to update and cyclically complete said tables containing the optimum settings of the fan 5 and of the valve 6 of the apparatus, as well as create and store new tables, as a function of the changed operating boundary conditions. Thereby, the present invention allows obtaining a method for monitoring and controlling the combustion of a burner, which is capable of self-learning and self-adjustment for achieving the optimum working conditions of the burner in terms of efficiency, stability and user safety.

The appended fig. 8 shows an example of the aforesaid tables and relative sizes reported therein, used in the operation of the method according to the present invention. In the development stage, the aforesaid tables can comprise a first table T 1 , stored in the memory unit 13, which, for each power value “W” that can be taken by the specific burner 2 used, identifies the drive values of the fan “n”, and of the valve, “s”, which are adapted to ensure the desired Avalue considering values deemed “standard” of air density and chimney length. In a preferred embodiment of the invention, for each type “x” of gas usable by the burner 2 there will be, in the memory unit 13, a first corresponding table T 1 x.

[Starting calibration on initial start-up]

With reference to the attached Fig. 3, on the first starting 30, thus, based on the starting power read W _acc 31 (usually set at a value between 1/3 and 2/3 of the maximum power), it is possible to read 32 from table T1 - stored in the memory unit 13 associated with the microprocessor of the controller 9 - the number of revs n _acc of the fan 5 and the positioning s _ac c of the actuator of the valve 6 (e.g. the pitch of the stepper motor) to be set 33 to start 34 the burner 2 and obtain the set thermal power. If the burner does not start, (a situation, that may be detected, for example, through the absence of an electrical signal from the sensor 8) act 35 on the s value to increase the amount of gas and try starting it again; such cycle is repeated until the burner actually starts and the correct value s _ac c is identified.

[Initial calibration and construction of table T2]

With reference to the attached Fig. 4, on completing the first starting after installing the boiler, a second table, T2, is generated, originating from said first table, T1 , updating the value of some parameters (for example, the value s _ac c) so as to make them more consistent with the boundary conditions of the environment, in which the boiler has been installed.

By using the first flame sensor 8 arranged close to the flame of the burner 2 and a second sensor 12 of the number of revs n of the fan 5, it is possible to update the values of the column R and s, as described below: after fixing the value of the number of revs of the fan 5, n, corresponding to a certain thermal power W, the R value is traced, so that the desired excess air value, A* is obtained, based on the following calibration sequence:

- a number of revs per minute, n, is set for the fan 5, and kept constant;

- the value of the gas flow rate is increased (or decreased) 40, by acting on the position s of the actuator of the adjustable valve 6, until a value s1 is identified, corresponding to the minimum of the value of the electrical flame resistance R (or another measured electrical flame parameter), corresponding, in turn, to an excess air value, A, equal to 1 , according to the trend of the curve shown in Fig. 9;

- the value of the gas flow rate is decreased 41 by acting on the position s of the actuator of the adjustable valve 6, until a value s* is reached, which corresponds to the desired excess air, A*; identification of A* is possible because we know, from the laboratory tests, (i) the section change of the flow rate adjuster on varying the position of the actuator, i.e., on varying the steps of the stepper motor, which regulates the opening of the adjustment valve 6, and, by virtue of the identification of the minimum value R stated above, we also know (ii) at which s value, and that is at which position of said stepper motor, we have A=1 ;

- the R* value is detected 42 corresponding to the value of required excess air, A* the value of which is replaced 43 in table T2;

- the procedure is repeated for other values of the number of revs n so as to collect a plurality of R* and s* values lying on the curves R = f(n) and s = f(n) shown in the attached Fig. 10 and Fig. 11 and which are used to populate the table T2;

- it is also possible to obtain 44, a plurality of values of the ratio AR/As = f(n) calculating the change of R with respect to the change of s in the passage of the excess air value, A, from 1 to A*. These values can also be stored in table T2.

After constructing and updating table T2, as described in the calibration stage, this will be stored in the memory unit 13 and will be constantly updated during the operation of the burner, as described below.

[Combustion control sequences - updating table T2]

The control sequence provides a first quick adjustment control loop and at least a second slow adjustment control loop.

[Quick control loop] With reference to the attached Fig. 5 and as described previously, an example of said first adjustment control loop is based on the setting of the number of revs n of said fan 5 and the degree of opening of the valve 6 determined by the position, s of the actuator of said valve 6. In fact, a certain number value of revs, n, of the fan 5 will correspond to the thermal power value W1 requested of the burner 2, and a certain degree of opening of the valve 6 determined by the position, s, of the actuator of said valve 6, according to table T2, in use.

Therefore, the fan 5 is driven 50 at a number of revs n1 corresponding to the amount of air needed for the required power W1 and, similarly, the actuator of the valve 6 will be brought 50 to the opening position s1. In table T2, in use, corresponding n and s values correspond to each thermal power value required of the burner in order to obtain, in the combustion A, the desired, A*.

[Slow control loop_ 1 -correct combustion verification and dynamic adjustment of valve opening ending]

With reference to the attached Fig. 6, an example of said second adjustment control loop is aimed at controlling the stability of the optimized combustion in progress and making a possible adjustment of system operation ending.

According to this second adjustment control loop, a first monitoring of the combustion is carried out cyclically, exploiting the detections of said first flame sensor 8, verifying that the current R value does not deviate from the R1 value, provided in table T2 for W1 and corresponding to n1 and s1 and to the desired excess air value A*.

If the measured R is equal, or sufficiently close to R1 in the table in use, for example, if the distance between the measured R and R1 is less than 10% of the original value of R1 , further actions are not carried out; whereas, if the measured R is not sufficiently close to R1 , for example, if the distance between the measured R and R1 is 10% greater than the original value of R1 , then, while the n value is kept constant, the actuator of the valve 6 is moved into different positions until it reaches an s1 _n value whereby there is correspondence between the measured R and the R1 value provided for said power. Therefore, the s1 n, value replaces the previous s1 value in the table.

[Slow control loop_2 -correct combustion further verification] With reference to the attached Fig. 7, in a preferred embodiment of the method according to the invention, the following control step is present, which is adapted to correct the lack of sensitivity of the ionization current in cases of low exiting thermal power, or to correct the cases in which the R1 value might not be representative of the optimal A, e.g., due to a change in the composition of the combustible gas entering the system during operation. This control step may be implemented as the second adjustment control loop or as the third adjustment control loop in addition to the second adjustment control loop described previously and shown in the attached Fig. 6.

With reference to the attached Fig. 7, in order to verify the stability of the combustion of the burner 2 proceed as follows:

- at predetermined intervals of time, a change is commanded 70 in the degree of opening of the valve 6 by means of a change in the position s of the actuator of said valve 6 by an amount As;

- read 71 the information from said first flame sensor 8;

- process the information from said first sensor 8 to determine 72 the change in an electric parameter of the flame, AR, corresponding to the change As set previously;

- calculate 73 the ratio AR/As;

- compare 74 the ratio AR/As with the present value in table T2: if the two values are identical or the difference thereof is less than an acceptability threshold and there is a decrease in the electrical flame resistance on increasing the gas flow rate, then the degree of current opening, s is maintained 75; otherwise an anomaly is signaled or an alarm and a new calibration process is launched 76 to determine a new curve R = f(n) and a new curve s = f(n), or stop boiler 2 operations.

In further detail, the corresponding change AR in the electrical flame resistance is detected and compared with the corresponding values listed in table T2, checking that the AR/As ratio corresponds to the value and the sign listed in table T2 for the current value of the number of revs n. In fact, if the value of the ratio AR/As detected were of a different sign to that shown in table T2 then the excess air A would be < 1 and the boiler might have to work in a potentially dangerous situation producing excess CO.

The procedure described above can also be useful for verifying any blockages, also partial, of the chimney and consequently producing adequate alarm signals for the user. This can happen simply by controlling the congruity of the value of the number of revs per minute of the fan 5: if the current number of revs is greater than the number required, the cause might be a reduced draught in the chimney. With reference to the attached Fig. 9, AR/As represents the inclination of the curves shown, which, in turn, represent the trend of the flame resistance for a specific number of fan revs. If, for example, a AR/As value is detected at a certain number of revs, which is characteristic or very close to a value present on curves corresponding to a smaller number of revs, it means that less air than expected is arriving at the mixing of the gas and that there is probably a problem, such as a blockage of the chimney of the system, for example.

Should a recalibration be necessary:

- update table T2, in use, contained in said memory unit 13, associated with said controller 9.

- send appropriate drive signals to the valve 6, which are adapted to produce the previously calculated degree of opening of the valve 6, s.

Instead of the electrical flame resistance, R, other electrical parameters detected by said first sensor can be used, such as, the flame conductivity G or the flame capacity C, for example.

The method for monitoring and controlling the combustion of a burner for combustible gas apparatuses according to the invention allows continuously establishing the optimum working conditions of the burner, ensuring the thermal power required in a very wide range, from 100% of the nominal power value of the burner to about 5% of said nominal value. Furthermore, through the method according to the invention, it is possible to cause the burner to work with a desired excess air, A, which can be set from a minimum value equal to 1 to a maximum value, also greater than 2 and, in particular, it can be set at an optimum value of just over 1 , e.g., equal to 1 .25.

Furthermore, the method and apparatus for monitoring and controlling the combustion of a combustible gas burner according to the invention allows verifying the safety of the apparatus and, in particular, of the A, in particular, always ensuring that the A is greater than 1 over the whole spectrum of operation, through a direct measurement and not through an estimate or a plausibility test.

[Realization with third sensor - calibration value n]

In the case of a preferred embodiment of the invention using a first sensor 12 adapted to measure the number of revs per minute of the fan 5, a second flame sensor 8 arranged close to the flame of the burner 2 and a third absolute pressure sensor 7 associated with the gas mixture, the calibration can also provide updating the value of the parameter n in table T2.

With reference to the attached Fig. 13, given that, for a given desired value of the excess air A, the thermal power W of the burner 2 is a function of the mass of air and therefore of the number of revs n, of the fan 5, based on the data provided by the pressure sensor 7 (by means of which it is possible to determine, for example, the density of the air and the length of the chimney of the boiler housing the burner 2) it is possible to determine an updated value of the parameter n.

The correlation between thermal power W and number of revs n of the fan 5 must be precise otherwise there is the risk of having less air than necessary and therefore excess gas and combustion characterized by a sub-optimal air number A. Therefore, the product between the density p and the volumetric flow rate of the air Q must be kept constant so that if the density of the air decreases, the volume of air must be increased to ensure that the mass of air introduced into the burner 2 is always correct.

Again, with reference to the appended Fig. 13, in the first quadrant the graph expresses the load curve, i.e., the relationship between the number of revs n of the fan 5 and the volumetric flow rate of the air, Q. The graph in the third quadrant expresses the relationship between the atmospheric pressure (for a specific temperature t1 measured by the sensor) and the density of the air p, while the graphs in the fourth quadrant express the relationship between the density of the air p and the volumetric flow rate of the air, Q, when the mass flow rate, equal to the product pQ and proportionate to the power W, is kept constant.

In table T2, in order to control and update the value of the parameter n, it is possible, for example, to carry out a first reading of the pressure sensor 7 to measure the atmospheric pressure P0 and the ambient temperature TO with the fan at a standstill, and a second reading of the pressure sensor 7 to measure the pressure Pn1 , after switching on the fan 5, at a constant speed n1 and thus, evaluate the change in pressure AP = Pni - Po representative of the initial boiler installation conditions. Thereby, the ratio between P and n, is stably fixed, starting from the assumption that an amount of air Qa1 (independently of the gas) will always correspond to a certain power W1 , substantially tracing the correct load curve with boiler installed and thus the corresponding value n1 .

If this procedure is repeated periodically, it may also be useful for verifying possible blockages, also partial, of the chimney and consequently producing adequate alarm signals for the user.

In summary, if the system possesses said pressure sensor 7, the air temperature and density are checked with every start-up, as well as any blockage of the chimney, updating, if necessary, in table T2 in use, the figure relative to the number of revs of the fan 5, n, thus also updating the trend of the curve binding the thermal power of the burner to the number of revs of the fan 5, W = f(Qa) = f(n).

If the system is provided with a flame sensor 8 and with a rotation speed sensor 12 of the fan 5, then, with every start-up and with every new request for thermal power W1 , a number of revs of the fan 5, n1 is determined by means of a quick control loop referring to the current table T2 and a degree of opening of the valve 6, s1 , to which both the requested thermal power should correspond and an electrical flame resistance value R1 corresponding to an optimum excess air value.

If a first slow control loop based on the measurement of the electrical flame resistance R = f(n) detects that, at the opening of the valve 6, s1 , in table T2 an R1 ’ value is present, different to the one expected, then the degree of opening s of the valve 6 is modified until a value s1 ’, which allows reaching the desired value R1 and table T2 is updated, replacing the s1 ’ value with the previous one s1 . If the difference between s1 and s1 ’ is greater than a certain threshold, a new calibration of the system can be provided, given that the operating conditions have probably changed, or the burner can be stopped, given that the current combustion conditions are deemed to be dangerous.

Furthermore, a second slow control loop, at predetermined intervals of time, further verifies that the combustion is proceeding optimally by controlling the ratio AR/As through the following sequence: - slightly decrease ( or increase) the amount of gas by setting a variation in the degree of opening of the valve 6, As;

- detect the corresponding variation AR of the electrical flame resistance and compare with the corresponding values listed in T2, verifying that the ratio AR/As corresponds to the value and to the sign listed in T2 for the current value of the number of revs n. If the value of the ratio AR/As detected was also only of a sign different to that shown in table T2 then the excess air A would be < 1 and the boiler might have to work in a potentially dangerous state, producing excess CO. The determining advantage of the second control loop is that it operates reliably, also with minimum powers, where the first control loop is imprecise, or the correct detection of the electrical flame parameters is practically impossible.

The method according to the present invention, in each of the embodiments thereof, can be used, with some possible variations, in each step of burner operation: in the initial calibration stage, in the first start-up stage after implementation, as well as during the normal operation stage.

The method according to the present invention in each of the embodiments thereof, is further adapted to be used for monitoring the current operating conditions and updating the tables containing the optimum settings of the fan 5 and the valve 6 of the apparatus as a function of the changed operating boundary conditions, so as to ensure the optimized working of the burner in an increasing number of situations, succeeding in preventing malfunctioning, which is potentially harmful both for the burner and the users.