WO2006120717A1

WO2006120717A1 - Heating plant with radiant tubes

Info

Publication number: WO2006120717A1
Application number: PCT/IT2006/000351
Authority: WO
Inventors: Oscar Pallaro
Original assignee: Systema S.P.A.
Priority date: 2005-05-11
Filing date: 2006-05-11
Publication date: 2006-11-16
Also published as: EP1880143A1; ITPD20050133A1; CN101198824B; CN101198824A

Abstract

A heating plant with radiant tubes comprising a burner of a gas - coitiburent air mixture suitable for generating high temperature combustion products which are introduced in a closed circuit with radiant tubes where they heat a carrier fluid circulated in depression by the action of a fan arranged upstream of the burner. There are provided regulation means comprising an regulation valve of the gas rate, whose modulation is directly controlled by at least one pressure value, detected into the combustion chamber, which at the same time determines the forced suction of the comburent air rate.

Description

"Heating plant with radiant tubes"

[0001] The present invention relates to a heating plant with radiant tubes . [0002] More in detail, this plant can be advantageously used for warming areas of any type, such as living and industrial buildings, and in particular large-sized buildings such as warehouses, factories, theatres, cinemas, supermarkets, greenhouses, swimming pools or else.

[0003] The plant is provided with a burner for the production of high temperature combustion products, hereinafter also referred to with the term of flue gases, which are made to circulate in a closed circuit consisting of radiant tubes capable of warming the areas by irradiation.

[0004] Radiant tubes, in the technical jargon of the field also referred to with the term of radiant tapes due to their shape and modularity, for example consist of annealed or coated aluminised steel ducts, to be arranged a little below the ceiling of the buildings to be warmed so as to irradiate heat towards the people or things underneath, preferably with thermal radiations in the infrared field. [0005] The burners used on such plants of the known type, are traditionally provided with a combustion chamber wherein the comburent mixture, consisting of primary air and gas, burns in a torch head, generating a flue gases carrier fluid that is brought in circulation into the radiant tubes along with the circulation flue gases already produced before, by a fan arranged upstream of the burner and operating in suction.

[0006] Old colder flue gases add in equicurrent to the new flue gases coming out of the burner and are all made to circulate by the fan that keeps the entire circuit in depression.

[0007] The plant thus configured is especially safe since the burner is usually placed outside the building to be warmed, and the radiant tubes are in depression so as to prevent any possibility of flue gases dispersion to the environment to be warmed.

[0008] In the practice, in the radiant tubes the fan circulates a rate of carrier fluid partly consisting of the new very hot burnt gases produced in the burner and partly of the old colder burnt gases that have already transmitted a portion of the heat to the radiant tubes during the circulation thereof.

[0009] To balance the masses involved, a portion of the cold circulation flue gases is discharged outside of the building through a special stack. [0010] Therefore, the fan is responsible for both the recirculation in depression of the carrier fluid and the ejection in pressure of a flue gases portion through the stack. [0011] The regulation of the thermal power expressed by the burner is usually obtained by varying the rate of the air/gas mixture introduced in the burner itself. [0012] The known burners of the so-called blown-air type use a blower that regulates the air inlet to the burner regulating the gas release valve opening accordingly.

[0013] Forced suction burners withdraw the comburent air by the effect of the depression that determines downstream of the combustion chamber in the proximity of the outlet point of the combustion products in the circuit of radiant tubes. In fact, in the proximity of the flue gases outlet point, the circuit exhibits a narrowing that causes a depression in the carrier fluid pushed by the fan. [0014] They normally envisage the use of a gate on the intake of the comburent air. Such gate regulates the inlet air rate moving between multiple fixed positions. A solenoid valve group, controlled by a microprocessor, allows the modulation of the gas quantity so as to keep the ratio thereof with the air constant and optimal. [0015] The European patent EP 647819 discloses a plant provided with an atmospheric pressure burner which envisages air suction partly due to the depression induced by the fan and partly to the negative pressure produced by the gas jets into special Venturi tubes. [0016] Of course, the quantity of new combustion gases produced, and thus of comburent air-gas mixture, must be in a mass equal to the quantity of flue gases ejected by the stack. [0017] To this end, there can be provided one or more regulation gates arranged for example on the suction duct of the primary air, that is, upstream of the flue gases stack for dividing the carrier fluid rate between a portion circulating in the circuit and a portion in ejection. [0018] At present, in accordance with the art known to date, as the set-point conditions are approached (that is, generally when ambient temperature conditions set are achieved) , the thermal power of the burner is usually decreased modulating the quantity of the air/gas comburent mixture.

[0019] Operatively, the flow of carrier fluid has the purpose of distributing the thermal power produced by the burner along all the exchange surface of the radiant tubes and thus of assuring a thermal flow as even as possible in the areas served by the plant. [0020] Theoretically, from a point of view of the overall plant efficiency, the volumetric rate of the carrier fluid should vary according to the thermal power delivered in order to ensure optimum distribution of the thermal power in relation to the power used for the carrier fluid recirculation, that is, the fluid rate should increase as the thermal power delivered increases and decrease as the same decreases. [0021] Actually, on the other hand, known plants do not envisage the possibility of modulating the volumetric rate of carrier fluid as the thermal power delivered varies. The volumetric rate of carrier fluid is in fact maintained substantially constant in all the expected operating conditions. This translates into a constant fan speed and therefore in a substantially constant absorption of electrical power by the fan in all the operating conditions .

[0022] This negatively affects the overall efficiency of known plants . The fan speed and thus the carrier fluid rate are normally set to the maximum thermal power deliverable by the burner. Therefore, the rate of circulating carrier fluid is the same also with thermal powers must lower than the maximum expected one, with a useless power absorption by the fan. [0023] Moreover, the thermal powers of the burners and the electrical powers of the fans are usually selected based on the design conditions, keeping into account the specificity of the plant to be installed. In particular, the electrical powers of the fans are also selected on the basis of the load losses that can be envisaged for the radiant tube circuit .

[0024] In the practice, as known, it often happens that the design conditions are not fully observed during the installation. For example, it may be necessary to vary the circuit of the tubes by introducing elbows or differences in height and this determines unexpected and not envisaged load losses.

[0025] Known plants do not allow a modulation of the carrier fluid rate for making up for the differences between the design conditions and the actual operating conditions found during the regular plant operation. In particular, it is not possible to use the fans in a versatile manner, with the result that current plants often do not work in the ideal conditions and with the maximum efficiency.

[0026] The object of the present invention therefore is to obviate the disadvantages of known solutions. [0027] A particular object of the present invention is to provide a plant which should be easily regulated in a versatile manner for operating in accordance with the actual operating conditions, in particular once the plant radiant tubes have been installed.

[0028] A further purpose of the present invention is to provide a constructively simple and totally reliable plant .

[0029] The technical features of the invention, according to the above objects, are clearly found in the contents of the claims below and the advantages of the same will appear more clearly from the following detailed description, made with reference to the annexed drawings, which show a purely exemplifying and non-limiting embodiment thereof, wherein:

[0030] - figure 1 schematically shows a plan view of a heating plant with radiant tubes object of the present invention, with some parts removed to better show others; [0031] - figure 2 schematically shows a side section view of the plant of figure 1 with some parts removed to better show others; [0032] - figure 3 schematically shows a perspective view of a detail of the subject plant relating to a burner, with some parts removed to better show others; [0033] - figure 4a shows an operating diagram of the plant according to a first embodiment of the invention; [0034] - figure 4b shows an operating diagram of the plant according to a second embodiment of the invention; [0035] - figure 4c shows an operating diagram of the plant according to a third embodiment of the invention; and [0036] - figure 5 shows an operating diagram of the plant according to a fourth embodiment of the invention. [0037] With reference to the annexed drawings, reference numeral 1 globally denotes a heating plant with radiant tubes 2 according to the invention.

[0038] Plant 1 comprises a closed circuit consisting in an in se traditional manner by one or more radiant tubes 2 , preferably made of annealed or coated aluminised steel . The circuit is connected to a burner, generically indicated with reference numeral 3 , and to a fan 7. The latter is arranged upstream of burner 3 , with reference to the direction of circulation of the combustion products into the circuit.

[0039] Burner 3 is of an in se known type, preferably with forced suction, and comprises a combustion chamber 4 into which by a torch head 4' a mixture consisting of a comburent air rate A (or primary air) and of a gas air G burns .

[0040] As you can see in particular in Figures 1 and 2, high temperature combustion products are introduced in the above closed circuit where they are made to circulate by the above fan 7 along with the flue gases previously produced, which have already transmitted a part of the heat to the radiant tubes 2 during their circulation. [0041] To balance the masses involved, a portion of the cold circulation flue gases is discharged outside of the building through a special stack 13 arranged between fan 7 and the combustion chamber 4.

[0042] Hereinafter, for simplicity, the mixture of hot flue gases and cold flue gases - indicated in the annexed figures with an arrow 5 - shall be defined as carrier fluid. The rate of carrier fluid ejected by stack 13 is indicated in the annexed figures with reference numeral 5' , whereas the rate of recirculated flue gases is indicated with reference numeral 5" .

[0043] The closed circuit therefore defines the circulation of the carrier fluid 5 in the area to be warmed. The carrier fluid 5, thanks to the heating due to the mixing with the combustion products, is in turn capable of raising the temperature of the radiant tubes 2. The latter develop inside the areas to be warmed, thus causing the heating by irradiation with thermal emissions, in particular in the infrared field.

[0044] Usually, tubes 2 are supported by brackets below the ceiling of the buildings to be warmed and consist of at least a delivery branch 2' and of a return branch 2' ' . Preferably, tubes 2 are covered in the top zone by an insulating parabola that conveys the radiations downwards. [0045] As already said, the circulation of the carrier fluid 5 is obtained by fan 7 which, being arranged upstream of burner 3, thanks to the circuit shape, circulates the carrier fluid 5 in depression into the closed circuit itself.

[0046] Functionally, therefore, the fan is responsible for both the recirculation in depression of the carrier fluid into the circuit and the ejection in pressure of a flue gases portion through the stack. [0047] More in detail, the depression present into the circuit - responsible for the intake of the comburent air and of the gas in the combustion chamber 4 - is generated by a narrowing in the circuit itself in the proximity of the combustion product inlet point. [0048] As can be seen in particular in Figure 1, high temperature flue gases coming from the combustion chamber 4 are introduced in the closed circuit by a shaped post- combustion duct 40 arranged downstream of fan 7 and downstream of the ejection stack 13. [0049] More in detail, duct 40 extends coaxially into a portion of tube 2 of the closed circuit. The presence of this duct reduces the available section for the flow of the recirculated carrier fluid 5" , thus determining a narrowing of the circuit. The carrier fluid 5", propelled by the fan, therefore undergoes a lamination that determines a depression at the flue gases inlet zone, indicated with letter H in Figure 1. The depression zone H extends to the entire shaped duct 40 up to the combustion chamber 4. [0050] In the following description, the expression "pressure in the combustion chamber" is meant to refer not only to the actual pressure in the combustion chamber, but also in general to the pressure conditions in the proximity and at the hot flue gases inlet zone into the circuit .

[0051] In plant 1 according to the invention, there are further envisaged means for regulating the rate of the air/gas (comburent) mixture, which shall be specified in detail hereinafter, suitable for varying the thermal power produced by burner 3 based on the quantity of heat required by the ambinets .

[0052] According to the idea at the basis of the present invention, the above means for regulating the rate of the air/gas mixture comprise an regulation valve 8 of the gas rate G, whose modulation is directly controlled by the pressure value present into the combustion chamber 4 and responsible for the intake of the comburent air rate A and of the gas rate G in the combustion chamber 4. [0053] The term "pressure" refers to an absolute pressure, since the pressure in the combustion chamber 4 necessarily is - as already explained hereinbefore - a depression value or a value below the atmospheric pressure due to the effect of the suction produced by fan 7 and by the narrowing of the circuit at the hot flue gases inlet zone .

[0054] In accordance with a preferred embodiment illustrated in Figures 4a, 4b and 4c, the regulation valve 8 of the gas rate G consists of a pneumatic valve and is provided with a shutter 9, connected to the combustion chamber 4 by a duct 10.

[0055] As the pressure in the combustion chamber 4 varies, shutter 9 moves, opening or closing valve 8 and thus determining a greater or smaller gas rate G in inlet to the combustion chamber 4. [0056] More in detail, as the pressure in the combustion chamber 4 decreases, the shutter tends to open valve 8, thus increasing the inlet gas rate, whereas as the pressure increases, it tends to close it, thus decreasing the inlet gas rate . [0057] Preferably, as can be seen in Figures 2 and 4a-c, valve 8 is provided with a settable by-pass 20 arranged on duct 10, for setting the pressure on shutter 9 to different values than those of actual pressure present in the combustion chamber 4. [0058] Advantageously, the setting of valve 8 may also be obtained by directly acting on the return spring of shutter 9, for example by a screw 20' schematised in figures 2 and 4. [0059] In accordance with an alternative solution of the invention illustrated in Figure 5, the regulation valve 8 of the gas rate G consists of a solenoid valve controlled by a control unit 15 based on the pressure values present in the combustion chamber 4. The pressure values are detected by one or more pressure probes 100 arranged into or in the proximity of the combustion chamber 4.

[0060] Functionally, in plant 1 as described hereinbefore, a variation of the carrier fluid rate corresponds to a corresponding variation of the pressure value in the combustion chamber 4 of the burner. [0061] More in detail, an increase of the rate of carrier fluid 5 determines a pressure drop in the combustion chamber (or a higher depression) , and thus an increase of the gas rate G in inlet and in constant relation an increase of the rate of comburent air A. An increase of the thermal power delivered therefore occurs.

[0062] On the other hand, a decrease of the rate of carrier fluid 5 determines an increase of the pressure in the combustion chamber (or a smaller depression) , a decrease of the inlet gas rate G and therefore also a decrease of the thermal power delivered. [0063] In accordance with a first embodiment of the plant illustrated in Figure 4a, the regulation means of the comburent mixture rate comprise an inverter 11 associated to fan 7. Inverter 11 allows to vary the number of revolutions of the fan and therefore the volumetric rate of carrier fluid 5. In this way, it is possible to vary the pressure in the combustion chamber 4 and therefore the thermal power delivered by burner 3. [0064] As an alternative to inverter 11, the motor of the fan may be controlled by another actuation device, for example a Brushless or a direct current motor. [0065] The rate is increased by increasing the number of revolutions of the fan, and vice versa decreased by decreasing the number of revolutions. For example, inverter 11 may envisage a variation of the frequency to the motor of fan 7 comprised between 30 and 60 Hz. [0066] In accordance with a second and third embodiment of the plant respectively illustrated in Figures 4b and 4c, the regulation means of the rate of comburent air comprise an adjustable gate 12, 120 arranged in the circulation circuit of the carrier fluid. In this case, the rate of comburent mixture and therefore the thermal power delivered by the burner is regulated by varying the opening degree of the adjustable gate 12, 120. Operatively, in fact, by keeping the number of revolutions of the fan constant, the volumetric rate of carrier fluid 5 and therefore the pressure in the combustion chamber 4 are regulated. [0067] More specifically, in accordance with the second embodiment illustrated in Figure 4b, the gate - in this case indicated with reference numeral 12 - is advantageously arranged at the base of the flue gases ejection stack 13. Gate 12 serves for dividing the rate of carrier fluid 5 between an ejection rate 5' towards stack 13, equal in mass to the rate of incoming air-gas mixture, and a recirculation rate 5'' in the closed circuit sent to burner 3. Operatively, the rate of fluid 5 is increased by increasing the opening of gate 12 , vice versa it is decreased by decreasing the opening of gate 12.

[0068] In accordance with the third embodiment illustrated in Figure 4c, the gate - in this case indicated with reference numeral 120 - is advantageously arranged at the inlet duct of comburent air A. In this case, the rate of carrier fluid 5 is increased by increasing the opening of gate 120, and vice versa it is decreased by decreasing the opening of gate 120 itself.

[0069] In accordance with an embodiment, said regulation means comprise means for regulating the rate of carrier fluid 5. [0070] In accordance with the embodiment of the invention described in Figure 4a, such means for regulating the rate of carrier fluid 5 can comprise a device for regulating the speed of fan 7, such as for example an inverter 11 or another type of actuation device.

[0071] In accordance with the embodiments of the invention described in Figures 4b and 4c, such means for regulating the rate of carrier fluid 5 can comprise, or not, one or more adjustable gates 2, 120 arranged at the inlet of the flue gases ejection stack 13 and/or in the suction duct of the comburent air A.

[0072] In particular, each of said gates can be provided alone or in conjunction with other gates and in conjunction or separated to predetermined variable speed actuation means of the fan.

[0073] From an operating point of view, such means for regulating the rate of carrier fluid 5 - irrespective of the specific embodiment thereof - allow to regulate the pressure that sets in burner 3 and therefore, as explained hereinbefore, the rate of the comburent air/gas mixture and in conclusion, the thermal power delivered by burner 3.

[0074] Advantageously, the regulation of fan 7 through inverter 11 or the regulation of the position (opening) of gate 12, 120 is carried out on the basis of at least one of the following temperatures: the temperature of the carrier fluid 5 in the circuit, the temperature of the ejection flue gases 5' from stack 13, the temperature of the outer surface of the radiant tubes 2 or the ambient temperature. The temperature chosen for the regulation is detected by a special temperature probe 14. [0075] Preferably, the regulation of the rate of carrier fluid is carried out on the basis of the temperature of the area to be warmed and optionally on the basis of at least another between the temperatures listed above.

[0076] To this end, plant 1 is provided with a temperature probe 14 for detecting the ambient temperature, to which it is optionally possible to associate at least another probe for detecting the temperature of the carrier fluid 5 into the circuit, or a probe for the flue gases temperature into stack 13 , or a probe for the temperature of the outer surface of the radiant tubes . [0077] Preferably, the regulation of the rate of carrier fluid 5 through the regulation of the inverter or of the gate position is controlled by a control unit 15 to which probe 14 and all the other temperature probes optionally associated to the latter are connected.

[0078] As already mentioned, in accordance with the fourth embodiment of the invention illustrated in Figure 5, the same control unit 15 may receive, besides a temperature signal, also one or more pressure signals by one or more pressure probes 100 that may be arranged into or in the proximity of the combustion chamber 4 for controlling the gas opening valve 8. [0079] Functionally, in plant 1 according to the invention, the thermal power delivered is regulated by controlling the quantity of air-gas mixture to burner 3 through a direct modulation of the rate of carrier fluid 5 that circulates in the circuit. [0080] One or more temperature probes 14 control the power required at burner 3 through the logics contained in the electronic control unit varying the rate of recirculation of carrier fluid 5 from which the rate of comburent mixture depends directly. [0081] Advantageously, in plant 1 according to the invention, the rate of the air gas mixture (A+G) therefore remains always optimised on the actual pressure present in the combustion chamber 4, even if the rate of carrier fluid 5 changes over time for a change of the atmospheric conditions, of load losses or else.

[0082] In this way, the overall energy performance of the plant itself is improved. This is essentially due to the fact that the thermal power delivered is calibrated on the actual heating requirements of the room. In fact, it is possible to fine-modulate the air and gas in inlet to the burner .

[0083] Moreover, if the regulation of the carrier fluid rate is carried out by acting on the speed of fan 7, as the set-point conditions for temperature are approached, there is a progressive reduction of the speed of fan 7 and consequently a considerable saving of electrical power absorbed as compared to traditional plants. In this way, even though an optimum distribution of the electrical power is ensured along the entire circuit, it is also possible to increase the overall efficiency of the plant considering, in this case, both the thermal power delivered by burner 3 and the electrical power absorbed by fan 7. [0084] In accordance with an embodiment, in synthesis, in any one of the plants described above there are provided, individually or in conjunction , regulation devices, such as fan actuation devices, suitable for varying the rotation speed thereof, actuation devices of the gas or other suitable fuel regulation valve shutter, actuation devices of the position of gates for cutting off the escape of flue gases, actuation devices of the position of gates for cutting off the incoming comburent air, as well as, in conjunction or separated with each or all of these devices, there are provided means for controlling the devices operating both in open loop, for example on the basis of predetermined calibration values, and in conjunction with or as an alternative to, in close loop, by actuating in feedback the control command with one or more signals coming from sensor means arranged internally and/or externally to the plant, such as one or more temperature probes arranged into the circuit, and/or in the flue gases outlet duct, and/or on the outer surface of the radiant tubes, and/or in the room to be warmed, and/or for detecting the temperature of the air introduced in the plant, so as to regulate the optimum operation of the plant on the basis of an environmental parameters and/or of a predetermined temperature changing program. [0085] In particular, in accordance with a further embodiment, any one of the plants described above may envisage the absence of gates for cutting off the escape of flue gases, entrusting the desired regulation to any one of the other regulation means described above. [0086] A further object of the present invention is a method for adjusting the thermal power delivered by a heating plant with radiant tubes, in particular of the type described above.

[0087] Such plant is intended for warming at least one room and at least comprises: [0088] - a sucked air burner, which can bed fed with a rate of comburent air A, and a gas rate G for generating high temperature combustion products in a combustion chamber; and

[0089] - a closed circuit of radiant tubes into which the above combustion products can circulate for defining a rate of a carrier fluid.

[0090] Preferably, the heating plant with radiant tubes comprises a fan suitable for circulating the carrier fluid in the closed circuit and an adjustable gate arranged in the circuit. The plant is further provided with a stack for ejecting at least a portion of the circulating gases .

[0091] According to the invention, the method comprises an operating step of detecting the pressure inside the combustion chamber of the burner. Such pressure - to be intended in absolute terms - is less than the atmospheric pressure and directly depends on the value of the carrier fluid rate. As the rate of carrier fluid decreases, the pressure in the combustion chamber decreases (or, there is a higher depression) . On the other hand, as the rate decreases, the pressure in the combustion chamber increases (that is, there is a lower depression) . [0092] Therefore, there is envisaged an operating step of regulating the gas rate G that enters the combustion chamber based on the above pressure value detected. [0093] In this step, the rate of gas G is made to vary with the pressure present in the combustion chamber: by increasing the pressure (and thus creating a lower depression in the system than the atmospheric pressure) the rate of inlet gas decreases correspondingly, and vice versa by decreasing the pressure (and thus a higher depression relative to the atmospheric pressure) the gas rate increases . [0094] The method further envisages a step of regulating the rate of carrier fluid having the purpose of varying the pressure in the combustion chamber and thus of indirectly regulating the inlet gas rate G and therefore the thermal power delivered by the burner. [0095] In accordance with a preferred embodiment of the method according to the invention, the step of regulating the rate of carrier fluid is carried out by varying the number of revolutions of said fan.

[0096] As already mentioned above, this allows to improve the overall efficiency of the plant, thanks to a reduction of the electrical power absorbed by the fan.

[0097] In accordance with an alternative embodiment of the method according to the invention, the step of regulating the rate of carrier fluid is carried out by varying the opening of the gate. [0098] Advantageously, the step of regulating the rate of carrier fluid is preferably carried out on the basis of the temperature of the room to be warmed. In any case it is possible to keep into account in the regulation of the rate of carrier fluid, also the carrier fluid temperature, the temperature of the ejection flue gases and/or the temperature of the outer surface of the radiant tubes. [0099] A further object of the present invention is a process of installation of a plant with radiant tubes as described above . [00100] Advantageously, the plant with radiant tubes 1 according to the invention can be calibrated in the actual operating conditions in a quicker and easier manner as compared to similar plants of the known type. [00101] In fact, in the plants of known type the calibration must be carried out after bringing the plant to steady conditions. This requires a long time and is not always easy since the value of the comburent mixture rate A + G is not directly related to the value of the rate of carrier fluid 5. [00102] On the other hand, in plant 1 according to the invention, since the gas rate is directly related to the rate of carrier fluid 5, it is possible to carry out the calibration operations immediately after installing the plant without having to bring it to steady conditions. Functionally, in fact, the relation between the rate of gas G and the pressure value in the combustion chamber 4 and therefore with the rate of carrier fluid 5 is maintained as the operating conditions change.

[00103] More in detail, the installation process according to the invention envisages the following operating conditions :

[00104] - a step of setting up plant 1 in the building to be warmed;

[00105] - a step of setting the maximum useful rate of carrier fluid 5;

[00106] - a step of calibrating the regulation valve 8 of the gas rate G to the maximum rate of carrier fluid

5;

[00107] - a step of controlling the thermal power in the operation produced by burner 3 with carrier fluid rate lower than or equal to the above maximum useful rate of carrier fluid 5.

[00108] In the setup step, the heating plant 1 with radiant tubes 2 of the type described above is installed into the building to be warmed and in particular, the radiant tubes 2 are secured to the ceiling.

[00109] The step of setting the maximum useful rate of carrier fluid 5 in the closed circuit of the plant thus installed follows. [00110] This value of maximum rate of carrier fluid 5 corresponds to a minimum pressure (maximum depression) in the combustion chamber 4 and a corresponding maximum rate of comburent air A sucked. [00111] If in the operation it is envisaged that the regulation of the rate of carrier fluid 5 is carried out by varying the number of revolutions of fan 7, in this setup step the maximum rate of comburent air A is calibrated by suitably regulating the opening of the flue gases ejecting gate 12 and of gate 120 arranged on the inlet duct of primary air A.

[00112] If in the operation it is envisaged that the regulation of the rate of carrier fluid 5 is carried out by regulating the opening of one of the two gates 12, 120, in this setting step the maximum rate of comburent air A is calibrated by conveniently fixing the number of revolutions of fan 7 according to the actual load losses in the circuit .

[00113] After the above setting step, the calibration of the regulation valve 8 of the gas rate G is carried out. In this calibration step, the maximum rate of gas G is fixed relative to the maximum rate of comburent air G on the basis of, a predetermined ratio.

[00114] These conditions of maximum circulation rate of the carrier fluid 5 correspond to the maximum thermal power that can be generated by burner 3. [00115] At this point, the step of controlling the thermal power in the operation produced by burner 3 is carried out by circulating carrier fluid rates 5 lower than or equal to the above maximum useful rate of carrier fluid 5.

[00116] In the normal operation of plant 1, the temperature probe 14 or the electronic control unit 15, to which probe 14 is connected, controls the thermal power required by burner 3 varying the rate of carrier fluid 5 through the regulation of the number of revolutions of fan 7 or of the opening of gate 12, 120. [00117] As already mentioned before, a variation of the rate of carrier fluid 5 corresponds to a variation of the pressure in the combustion chamber 4 of burner 3. Such pressure variation determines a consequent and direct regulation of the rate of air gas mixture (A+G) by the effect of the forced suction of the air rate, depending on pressure, and by the effect of the emission of the gas rate G through valve 8, also depending on pressure. [00118] In the practical embodiment thereof, the present invention may take shapes and configurations differing from those illustrated above without departing from the present scope of protection. [00119] Moreover, all the parts may be replaced by technically equivalent ones and the sizes, shapes and materials used may be whatever according to the requirements .

Claims

1. A heating plant with radiant tubes, comprising:

- a burner (3) provided with a combustion chamber (4) and intended for burning a comburent mixture, obtained with at least an air rate (A) and with at least a gas rate (G) , for generating high temperature combustion products;

- a closed circuit provided with radiant tubes (2) for heating the rooms by irradiation, capable of conveying a carrier fluid (5) , which is heated by the introduction of said combustion products therein;

- at least one fan (7) arranged upstream of said burner (3) for circulating said carrier fluid (5) in depression into said closed circuit (2) ;

- means for regulating the rate of said comburent mixture (A+G) for varying the thermal power produced by said burner (3) ; characterised in that said regulation means comprise at least one regulation valve (8) of the gas rate (G) , the opening of which is controlled in modulation directly by at least one pressure value, detected into said combustion chamber (4) and lower than the atmospheric pressure, said pressure value determining the forced suction of said comburent air rate (G) into said burner

(3) .

2. A plant according to claim 1, wherein said 6 000351

29

regulation valve (8) of the gas rate is provided with a shutter (9) communicating through a duct (10) with said combustion chamber (4) for modifying the position thereof based on the pressure value in the combustion chamber itself (4) .

3. A plant according to claim 1, wherein said regulation valve (8) of the gas rate (G) is settable to different calibration values.

4. A plant according to claims 2 and 3 , wherein said regulation valve (8) of the gas rate (G) is provided with a screw (20') for adjusting the spring of the shutter (9) of the valve (8), said screw (20') allowing the calibration of said regulation valve (8) .

5. A plant according to claims 2 and 3 or claim 4 , wherein said duct (10) is provided with an adjustable bypass (20) suitable for changing the pressure on the shutter (9) relative to the pressure value in the combustion chamber itself (4) .

6. A plant according to claim 1, wherein said regulation valve (8) of the gas rate is a solenoid valve controlled by a control unit (15) based on the pressure detected in said combustion chamber (4) through at least one pressure probe (100) arranged inside or in the proximity of said combustion chamber (4) .

7. A plant according to any one of the previous claims, wherein said means for regulating the rate of said comburent mixture (A+G) comprise an actuation device or an inverter (11) for controlling the number of revolutions of the motor of the fan (7) , said actuation device or inverter (11) being controlled by at least one temperature probe (14) .

8. A plant according to any one of the previous claims, wherein said means for regulating the rate of said comburent mixture (A+G) comprise an adjustable gate (12; 120) capable of changing the rate of carrier fluid (5) that circulates in the circuit and therefore the pressure value in said combustion chamber (4) , the position of said adjustable gate (12; 120) being controlled by at least one temperature probe (14) .

9. A plant according to any one of claims 1 to 6 , wherein said means for regulating the rate of said comburent mixture (A+G) comprise means for regulating the rate of carrier fluid (5) , which allow to regulate indirectly the pressure into the combustion chamber (4) .

10. A plant according to claim 9, wherein said means for regulating the rate of carrier fluid (5) comprise an actuation device or an inverter (11) for controlling the number of revolutions of the motor of the fan (7) , said actuation device or inverter (11) being controlled by at least one temperature probe (14) . 1

31

11. A plant according to claim 9 or 10, wherein said means for regulating the rate of carrier fluid (5) comprise an adjustable gate (12; 120) capable of changing the rate of carrier fluid (5) that circulates in the circuit and therefore the pressure value in said combustion chamber (4) , the position of said adjustable gate (12; 120) being controlled by at least one temperature probe (14) .

12. A plant according to claim 8 or 11, characterised in that said adjustable gate (12) is arranged at the base of an ejection stack (13) of a fraction of said carrier fluid (5) and is suitable for dividing the rate of said carrier fluid between an ejection rate (5") from said stack (13) and a recirculation rate (5') in said circuit.

13. A plant according to claim 8 or 11, characterised in that said adjustable gate (120) is arranged at the inlet suction duct of the comburent air (A) .

14. A plant according to any one of claims 7 to 13 , wherein said temperature probe (14) is suitable for detecting the temperature of said carrier fluid (5) .

15. A plant according to any one of claims 7 to 13 , wherein said temperature probe (14) is suitable for detecting the temperature of the ejection flue gases (5').

16. A plant according to any one of claims 7 to 13, wherein said temperature probe (14) is suitable for 6 000351

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detecting the temperature of the outer surface of said radiant tubes (2) .

17. A plant according to any one of claims 7 to 13 , wherein said temperature probe (14) is suitable for detecting the ambient temperature.

18. A plant according to any one of claims 7 to 13, wherein said temperature probe (14) is suitable for detecting the ambient temperature and can be associated to at least a second temperature probe suitable for detecting the temperature of said carrier fluid (5) , the temperature of the ejection flue gases (5') or the temperature of said radiant tubes (2) .

19. A method for regulating the thermal power delivered by a heating plant with radiant tubes, which is intended for heating at least one room and comprises:

- a sucked air burner, which can bed fed with a rate of comburent air (A) , and a gas rate (G) for generating high temperature combustion products in a combustion chamber; and - a closed circuit of radiant tubes into which said combustion products can circulate, defining a rate of a carrier fluid; said method being characterized in that it comprises the following operating steps : - a step of detecting the pressure inside the combustion chamber of said burner, said pressure being lower than the atmospheric one and depending on the value of said rate of carrier fluid;

- a step of regulating said gas rate (G) based on said pressure; and a step of regulating said carrier fluid rate for varying said pressure, and consequently said gas rate (G) and thus said thermal power.

20. A method according to claim 19, wherein said plant comprises a fan suitable for circulating said carrier fluid in said circuit and wherein said step of regulating the rate of carrier fluid envisages varying the number of revolutions of said fan.

21. A method according to claim 19, wherein said plant comprises an adjustable gate arranged in said circuit and wherein said step of regulating the rate of carrier fluid envisages varying the opening of said gate.

22. A method according to any one of claims 19 to 21, wherein said step of regulating the rate of carrier fluid is carried out on the basis of the temperature of the room to be warmed.

23. A method according to claim 22, wherein said plant is provided with an ejection stack of a portion of flue gases, and wherein said step of regulating the rate of carrier fluid is carried out also on the basis of the temperature of said ejection flue gases.

24. A method according to claim 22, wherein said step of regulating the rate of carrier fluid is carried out also on the basis of the temperature of the outer surface of said radiant tubes.

25. A method according to claim 22, wherein said step of regulating the rate of carrier fluid is carried out also on the basis of the temperature of said carrier fluid.

26. A process of installing a heating plant with radiant tubes according to any one of claims 1 to 18, characterised in that it comprises:

- a step of setting up the plant in the building to be warmed;

- a step of setting the maximum useful rate of carrier fluid in the closed circuit of the installed plant, which determines a minimum pressure in said combustion chamber and a consequent maximum rate of the comburent air sucked;

- a step of calibrating the gas rate to the maximum rate with predetermined ratio relative to said maximum rate of comburent air determining a calibration of maximum thermal power of the burner; a step of controlling the thermal power in the operation produced by said burner with rates of carrier fluid that are lower than and/or equal to said maximum 1

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useful rate, by means of the regulation of said carrier fluid rate and consequent regulation of said pressure in combustion chamber responsible for determining the gas rate by said regulation valve and the comburent air rate by forced suction.

27. A process according to claim 26, characterised in that the regulation of said rate of carrier fluid is controlled by a temperature probe that acts on an actuation device or inverter for controlling the number of revolutions of the fan motor.

28. A process according to claim 27, characterised in that said regulation of said rate of carrier fluid is obtained through the regulation of a gate controlled by at least one temperature probe .