EP0481040A1 - A method of regulating a gas-fired heat-generating appliance, and the relative appliance - Google Patents

Abstract

The method consists in programming the temperature of the spaces to be heated and then in controlling the flow and return temperatures of the heated fluid, the flow rate and the indoor and outdoor ambient temperatures so as to obtain a heat output in relation to the effective capacity of the system. and thus achieve a constant and optimized thermal efficiency without producing harmful combustion emissions. The equipment consists of a battery of heat exchangers (8, 10, 63, 64), each of them comprising a combustion chamber (16, 17, 70, 71) housing a corresponding burner (1, 58 ) receiving gas from the chamber of a simple manifold (3, 60), by means of a respective valve aligned on the inlet axis of the burner; the combustion chamber ends at its upper part with a ventilation opening (22, 74 ') through which the hot gases rise towards the combustion duct; flexible membranes in thin and light material, placed on the outlets of each ventilation opening, are used to close the passage to the combustion duct in case the burner stops.

Description

A method of regulating a gas-fired heat-generating appliance, and the relative appliance.

The invention relates to a method of regulating a gas heat- generating appliance, and to the relative appliance, that is, a new procedure by means of which to regulate, within generous limits, and to pilot the operation of a heat generating appliance equipped with gas burners as used for domestic or communal central heating systems and in heating systems for fluids, industrial and otherwise, for swimming pools, muds, kilns and ovens, temperature controlled enclosures etc.; the appliance with its relative devices also constitutes subject matter of the application.

The prior art embraces systems utilizing heat generated, in most cases, by a single appliance; there are also applications, especially where the system is of considerable dimensions, in which use is made of two or more such appliances selected from production ranges designed and manufactured to power rat ings suitable for general sale ; the single appliances may be dissimilarly rated, installed in parallel, and caused to cut in as the system calls progressively for more heat, thereby enhancing the efficiency of the installation.

The heat output of such systems is regulated by the following methods:

-by interlocking combustion to either an "on-off" or a "modulating" control, in the latter instance through infinitely variable regulation of the supply of fuel (gas) to the burner;

-by thermostatic control of the heat exchange fluid temperature, effected manually or using a remote sensor;

-by regulating the temperature of the space to be heated utilizing a manually controlled thermostat or by programming temperature levels to a daily or weekly schedule.

Nevertheless, such methods are unable to maintain a steady, maximized thermal efficiency of the system during operation; neither are they able to minimize heat losses through the flue during "off" periods, nor to supply the system with an amount of heat matched to the effective requirement (not dependent exclusively on external temperature), nor, finally, to reduce harmful flue emissions to negligible values in all imaginable operating conditions.

Thus it happens, particularly (though by no means exclusively) in systems heated by one appliance, that with maximum output required only for short periods within the overall time span that heat is generated, and given that for some 80% of this span the maximum output required reflects perhaps 45% of the installed capacity, power effectively utilized is on average no more than 25% of total capacity; in consequence, the mean operating efficiency of the system is drastically reduced, resulting in a high cost to the user, energy is wasted at the expense of the community, and the environment is degraded.

In also happens, given the fall in efficiency of the appliance with the increase in temperature of the heated fluid, that the albeit brief periods of use at the highest temperatures are accompanied by reduced efficiency.

The prior art likewise affords more sophisticated methods, aimed at an automatic and continuous type of regulation which seeks to increase the overall efficiency of use afforded by the system, namely:

-by regulating the temperature of the heated fluid automatically, according to an external temperature value; -by modulating fuel combustion according to the temperature of the heated fluid;

-by reducing heat losses through the adoption of motorized valves which block the vents to the flue when the burners are shut off;

-by regulating the excess of air using pneumatically or mechanically operated valves, to ensure constant combustion efficiency.

Neither are these methods applied on a significant scale, however, whether by reason of the lower levels of reliability afforded by the more complex control devices required, or of the difficulties with servicing, which calls for skilled personnel, or again, of the expenditure on devices and other equipment needed for control purposes, remembering that this is not a cost proportional to the rated thermal capacity of the system, but essentially a fixed outlay that often renders the application prohibitive in those smaller heating installations accounting for the majority of gas-fired systems.

The prior art thus outlined stands in need of considerable improvement with regard to overcoming the drawbacks mentioned above.

From the foregoing, there emerges the need for a method of regulating and monitoring the operation of a heat-generating appliance such as will permit of achieving a significantly constant and maximized level of efficiency in general utilization of the relative heating system, which can be maintained throughout operation and without occasioning the release of harmful emissions during combustion; also, to apply such a method to any type of gas and in any operation conditions.

Similarly, in carrying such a method into effect, the need emerges for a heat-generating appliance, especially for small and medium capacity systems, that is notably simple, inexpensive and dependable from the standpoint of construct ion.

According to the present invention, the features of such a method are that:

a) heat is generated by means of atmospheric gas burners, piloted individually between "full on" or "off" configurations in such a way that each burner will always operate in the best possible conditions, and the combustion obtained is free of harmful emissions;

b) combustion is distributed between a plurality of flames, advantageously bladed and arranged in an ordered manner whereby the flames of the single burner are masked optically one from another while capable of mutual ignition, in such a way as to maximize the absorption of radiated heat, in order to cool them;

c) the combustion chambers of adjacent burners are intercommunicating, in such a way as to allow mutual ignition between burners; d) secondary air is channelled to the base of the flames in such a way as to lap them and bring about combustion in an excess of air;

e) the heated fluid is kept at the minimum temperature possible commensurate with maximizing efficiency of the heat exchange, though without allowing the temperature of the fluid to fall below a critical level so that the temperature of the surface of the heat exchanger in contact with the flue gas is kept above the temperature of condensation of the steam contained in the flue gas, in the case of a hot gas/water exchange;

f) the temperature of heated spaces is programmed, and the external ambient and room temperatures both monitored, in order to reduce temperature fluctuations within the spaces to a minimum;

g) the upward movement of hot combustion gases is utilized to open the passages from each burner to the flue automatically, however orientated, by occasioning the movement and/or elastic deformation of flexible diaphragm shutters, thereby reducing heat losses through the flue to negligible values duri ng periods when the relat i ve burner is shut off;

h) regulation is effected by monitoring the flow and return temperatures of fluid passing through the appliance, and the rate of flow, to enable calculation of the heat output per unit of time; the value of the heat exchange and its variation over time, in conjunction with the room set point and external ambient temperature values, providing the variable parameters for operation of the appliance.

The method comprises the steps of:

A) programming or setting the temperature of the space to be heated, then verifying the flow temperature of the fluid, which is equal to the room temperature hence lower than the critical level;

B) fuelling and igniting a first burner, with flow rate of the heated fluid at minimum;

C) verifying both flow and return temperatures of the circulated fluid in order to establish the relative difference, which initially will be on the increase;

D) fuelling and igniting each of the remaining burners in turn, occasioning a swift rise in the flow temperature of the heated fluid beyond the critical value toward the maximum permissible;

E) regulating the flow rate of the heated fluid so as to obtain a minimum flow temperature, above the critical level;

F) continuing the gradual ignition of all burners until such time as the temperature of the heated space differs from the temperature initially programmed (or fixed) by a predetermined value, and thereupon shutting off one or more burners;

G) fuel l ing a number of burners, once steady state conditions are achieved whereby the temperature selected for the heated space can be maintained, such as will give output matched approximately to the heat called for by the system within a maximum margin of error equal to the output of one burner.

To advantage, the method according to the present invention is implemented adopting an appliance consisting in batteries of heat-generating units, each unit comprising at least two independently embodied and structurally interconnected exchangers each consisting of a combustion chamber accommodating a burner and connected with a vent passage above, each burner advantageously affording an ordered plurality of bladed flames, to prevent harmful flue emissions, and supplied with fuel independently of the remainder by way of a relative valve mounted internally of a transversely disposed hol low manifold, of which the moving element, associated at the forwardmost end with a tapered nozzle of cyl indrical -frustoconical -cy l indri ca l section and axially aligned with the Venturi tube into which the nozzle discharges, opens slowly and gradually.

Fuel is supplied to the nozzle through a passage of variable section which increases progressively to a maximum value during an opening movement of the valve that is obtained through axially slidable movement of the skirt of the valve element internally of the larger diameter cylindrical section of the nozzle, the internal surface of which affords at least one longitudinal forward tapering notch of cross section and shape specific to the type of fuel; the valve element is held in the closed position through the action of a cylindrical coil spring and connected by way of a stem, articulated with its rearwardmost end, to a unidirectionally cushioned solenoid actuator.

The bottom part of the combustion chamber flanking the burner on either side is encompassed externally by walls of profile complementary to that of the burner, in such a way as to afford a generous space through which secondary air is channelled to the base of the single flames, and merges immediately above the burner with a longitudinal central chamber flanked by upwardly converging walls and connecting above with the vent passage; the longitudinal central chamber communicates with at least one identical chamber relative to the adjacent exchanger by way of one or more transverse openings in the upwardly converging walls, located at least in the vicinity of and in alignment with the first flames to ignite in such a way as to promote interignit ion between adjacent burners, and is occupied by longitudinally distributed transverse projections serving to mask the flames optically one from another.

Finally, the passage through which hot gases are vented from each longitudinal chamber is opened and shut naturally by flexible diaphragms of especially lightweight and slender embodiment, arranged also in interlocking opposite sets, which rest initially under their own weight in a position whereby the passage to the flue is occluded, thereafter lifting when invested by the hot gases following ignition of the burner and freeing the passage; the thin diaphragms consist in sheets of flexible metallic material capable of withstanding corrosion, or in a lightweight fireproof fibre material such as glass fibre.

Advantages of the invention are: optimization both of the instantaneous efficiency of the appliance, and of the overall year on year efficiency of the system; development of combustion in predetermined conditions of maximum efficiency without harmful emissions; gradual delivery of heat output, commensurate with the demand of the system; elimination of heat loss via the flue stack with burners shut off; minimized temperature of the heat exchange fluid in any given operating condition; reduced cost of installation, by virtue of adopting simple, inexpensive devices capable of performing a variety of functions; lower running costs, enabled both by reduced consumption of fuel, and by the almost total elimination of servicing bills, due to the reliability of the components adopted; sharp reduction, if not almost total elimination, of fluctuations in temperature within the heated space, by virtue of the swift response of the regulation system; smooth ignition of each single burner, resulting in the elimination of noise and a marked reduction in noise-related vibration; the facility of adapting the appliance to burn different types of gas through the simple and inexpensive expedient of replacing the single burner nozzle, thereby retaining the advantages of gradual ignition without any need for complicated adjustments to the valve.

A preferred embodiment of the invention will now be described in detail, by way of example, with the aid of the eight accompanying sheets of drawings, in which:

-fig 1 is the perspective of a group of exchangers making up a heat-generating appliance, operating by hot gas/liquid heat exchange, fitted with devices for implementation of the method according to the invention;

-fig 2 is a vertical and longitudinal section of the appliance shown in fig 1, passing through the longitudinal axis of the burner and of the passage afforded to the rising hot gases;

-fig 3 is the vertical section through lll-lll in fig 2;

-fig 4 is a perspective showing the detail of an arrangement for securing flexible diaphragms by which to regulate the egress of hot gases, in an appliance with flue passages of horizontal section;

-fig 5 is a section identical to that of fig 3, relative in this instance to a hot gas/air type exchanger; -fig 6 is the vertical section through VI-VI, in fig 5;

-fig 7 is an axial section through the fuel valve associated with each burner;

-fig 8 is a partial and enlarged section through the nozzle outlet of a valve as in fig 7;

-fig 9 is a partial and enlarged plan view of a combustion chamber as in the appliance of fig 1, seen immediately above the burner;

-fig 10 is a perspective of the terminal part of a vertical flue pipe occluded by means of a flexible diaphragm, viewed in the position assumed when the relative burner is shut off;

-fig 11 is a view identical to that of fig 10, illustrating the position of the diaphragm with the relative burner alight.

In a hot-gas/liquid type of exchanger according to the invention, 1 denotes the barrel of the single burner, designed advantageously to produce bladed flames in order to avoid harmful emissions, which is cantilevered, secured with a clip fitting 2, from a manifold 3 of prismatic embodiment carried by the main supporting frame of the appliance (not illustrated); 4 denotes the fuel valve (see fig 7) through which gas is supplied to each burner, 5 a solenoid actuator by which the valve is opened to direct fuel to the nozzle, 6 a pressure governor, and 7 a safety valve.

8 denotes intermediate exchangers constituting the main body of the appliance, affording projections 9 that serve to increase the heat exchange surface offered to the hot gases; 10 denotes the exchanger located outermost, 11 and 12 the bulkheads of the intermediate exchangers, and 11'-12' the bulkheads of the outermost exchanger 10.

13 denotes one of a plurality of transverse webs projecting on either side from the hot gas surface of each exchanger, which serve to mask the flames optically from one another and at the same time to create transverse windows 14 enabling the mutual ignition of adjacent burners; 15 denotes the wall of the exchanger exposed to the passage of hot gases, 16 the lower part of the combustion chamber, and 17 (fig 3) the upper part of the chamber lying above the burner 1.

18 denotes a longitudinal channel afforded between the walls

19 of each two adjacent exchangers and the barrel 1 of the intervening burner; 20 denotes a flange associated with each web 13, constituting the bottom of the transverse window 14 on either side and merging on each flank with the relative exchanger wall 19 at a point projecting ultimately toward the axis of the burner alongside, beneath which secondary air is allowed to reach the base of the single flames.

21 denotes the fluid heated by the flames, and 22 the passages along which hot gases rise from each burner.

23 and 24 denote interlocking sets of thin flexible diaphragms, disposed transversely to the exchangers in mutual opposition and embodied as pluralities of tongues, projecting freely from a common support fashioned as a longitudinal strip 25 anchored over a central rib 26 passing along the top face 27 of the single exchanger; 28 denotes a longitudinally disposed flexible clamp (fig 5) affording teeth 29 by which the strip 25 is secured to the rib 26.

30 and 31 denote a Venturi tube (fig 2) with its relative inlet, inserted into the barrel 1 of each burner; 32 denotes the fuel valve nozzle, which is frustoconical with a cylindrical outlet, and 33 the oval flange of the nozzle, which is located between a pair of longitudinal grooves 34 created behind lips 35 extending along the front of the manifold 3 and rotated thus through 90C to secure the nozzle. 35' denotes a seal associated with the flange 33. 36 denotes a cylindrical hole afforded by the front wall 36' of the manifold, through which fuel passes to the nozzle; 37 denotes a longitudinal notch (see fig 8) let into the internal cylindrical surface of the nozzle 32 at its rear end, which tapers forward and combines with the external cylindrical surface of the skirt 39' of the valve element 39 to create a fuel passage of which the cross section varies according to the position of the element, thereby enabling a gradual and noiseless ignition of the burner. 38 denotes a seal located between the valve element 39 and the nozzle 32. 40 denotes a return spring against which the valve element 39 is loaded, 41 the valve stem, coupled with the element 39 by means of a ball and socket joint 42 so as to enable self- alignment with the nozzle 32, and 43 the rear end of the stem, which is rigidly associated with a ferromagnetic core 44 of cylindrical embodiment slidably accommodated in a cylindrical cap 45 ensheathed by the electrical winding 46 of the actuator 5.

47 denotes the annular front cover of the cap 45, which serves to guide the stem 41 whilst providing a seating for the rear end of the return spring 40, and 48 a seal offered to the oval flange 48' of the cap 45, which is retained by a pair of grooves 48'' afforded internally of the manifold 3 at the rear, between the rear wall 48 ' '''on the outside, and walls denoted 48''' on the inside. 49 denotes the fuel (gas) present within the manifold 3.

50 denotes an axially offset bore passing through the core 44 of the actuator, and 51 a flexible tongue serving to occlude the bore in one direction only, which affords a metering hole 51' positioned in alignment with the bore 50. 52 denotes the base of the cap 45, which affords a welded shank threaded to accept a nut by means of which to clamp the winding in the desired position. 54 denotes one of a plurality of sets of flame slots afforded by the burner (fig 9), 55 and 56 the front and rear chambers of the cap 45, and 57 the rear wall of the manifold 3.

In a hot-gas/air heat exchanger according to the invention, the parts of the gas/liquid exchanger denoted 1, 2, 3, 4, 5, 8, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 30, 31 and 32 become 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 74', 75, 76 and 77, respectively; additionally, 78 denotes the outer walls of the exchanger, in direct contact with the air to be heated, 79 the channel through which secondary air is induced to the bottom of the combustion chamber 70, and 79' the post-combust ion gases.

80 denotes an occluding diaphragm hinged to a lug 81 at the top of each exchanger 63, which serves to stop the relative passage whenever the burner shuts off. 83 denotes the outlet end of a flue pipe (see fig 10) through which hot gases are vented from the appliance, and 84 a flexible diaphragm placed over the outlet, by which heat losses through the flue are prevented when the appliance is off. 85 denotes one of a set of stays by which the diaphragm 84 is positioned and held in place during operation of the appliance (fig 11).

Operation of the appliance according to the method disclosed occurs in the following manner: with fuel supplied to the burners by way of the manifold 3, the corresponding solenoids excite, each drawing in the relative ferromagnetic core 44 and with it the valve element 39 and its respective skirt 39', to the point where the tapered passage 37 connecting with the nozzle 32 is fully open; the retracting movement of the core has the effect of compressing the fuelair mixture occupying the chamber 56 to the rear of the cap 45, thus cushioning the impact of the stroke. Similarly, the opening movement of the valve element causes the return spring 40 to compress, in readiness to shut off the passage at high speed once the electrical excitation signal to the coil 46 is deactivated at the moment when the relative burner is to shut down. With the upward stream of hot combustion gases from the burners thus discontinued, the flexible diaphragms 23, 24, 80, 84, hitherto raised, will regain their former position elastically and in so doing isolate the heat exchange surfaces of the appliance from the external environment.

The foregoing specification implies no limitation; in an alternative embodiment of the appliance, for example, the valve nozzle and solenoid cap might be screwed to the manifold rather than secured with the bayonet type arrangement illustrated; likewise, the manifold might be embodied in several parts and interconnected by sealed distance pieces.

Claims

1. A method of regulating a gas-fired heat generating appliance equipped with atmospheric gas burners disposed side by side and piloted between "full on" or "off" configurations, wherein combustion is brought about by a plurality of flames and the vent passages through which hot gases reach the flue are occluded whenever the burners shut down, characterized

a) in that the heat output from each single burner is controlled independently;

b) in that combustion is distributed between a plurality of flames, advantageously bladed and arranged in an ordered manner whereby the flames of the single burner are masked optically one from another while capable of mutual ignition, in such a way as to maximize the absorption of radiated heat, in order to cool them;

c) in that the combustion chambers of adjacent burners are intercommunicating, in such a way as to allow mutual ignition between burners;

d) in that secondary air is channelled to the base of the flames in such a way as to lap them and bring about combustion in an excess of air;

e) in that the heated fluid is kept at the minimum temperature possible commensurate with maximizing efficiency of the heat exchange, though without allowing the temperature of the fluid to fall below a critical level so that the temperature of the surface of the heat exchanger in contact with the flue gas is kept above the temperature of condensation of the steam contained in the flue gas, in the case of a hot gas/water exchange;

f) in that the temperature of heated spaces is programmed, and the external ambient and room temperatures both monitored, in order to reduce temperature fluctuations within the spaces to a minimum;

g) in that the vent passages are occluded by means of flexible diaphragms that shift and/or deform elastically to open up the passages, however oriented, when invested by the upward movement of the hot gases rising from each burner; h) in that regulation is effected by monitoring the flow and return temperatures of fluid passing through the appliance, and the rate of flow, to enable calculation of the heat output per unit of time; the value of the heat exchange and its variation over time, in conjunction with the room set point and external ambient temperature values, providing the variable parameters for operation of the appliance.

2. A method as in claim 1, comprising the steps of:

A) programming or setting the temperature of the space to be heated, then verifying the flow temperature of the heated fluid;

B) fue l l ing and igniting a first burner, with flow rate of the heated fluid at minimum;

C) verifying flow and return temperatures of the heated fluid;

D) fuelling and igniting each of the remaining burners in turn;

E) regulating the flow rate of the heated fluid in such a way as to achieve a minimum temperature in the flow direction that remains above the critical level;

F) continuing the gradual ignition of all burners until such time as the temperature of the heated space differs from the temperature initially programmed, or fixed, by a predetermined value, and thereupon shutting off one or more burners;

G) fuelling a number of burners, once steady state conditions are achieved whereby the temperature selected for the heated space can be maintained, such as will give output matched approximately to the heat called for by the system within a margin equivalent to the output of one burner.

3. A heat-generating appliance for implementation of the method of claim 2, comprising a battery of at least two heat exchangers, an atmospheric burner fuelled by a solenoid operated valve, and a vent passage for hot gases positioned above the burner which can be occluded whenever the appliance is deactivated, characterized

-in that the heat exchangers (8, 10, 63, 64) are embodied independently and structurally inter-connected, encompassing a combustion chamber (16, 17, 70, 71) that accommodates a relative burner (1, 58) and connects with the vent passage (22, 74') standing above;

-in that each burner (1, 58) produces an ordered plurality of advantageously bladed flames and is supplied with fuel by a relative valve (4, 61) mounted transversely at the inside of a single transversely disposed inlet manifold (3, 60) and in axial alignment with, and upstream, the Venturi tube;

-in that the bottom part of the combustion chamber (16, 18, 70, 72) flanking the burner barrel (1) is encompassed externally by walls (19, 73) of profile complementary to the profile of the barrel, in such a way as to afford a generous space through which secondary air is channelled to the base of the single flames, and merges immediately above the burner with a longitudinal central chamber (17,71) flanked by upwardly converging walls and connecting with the vent passage (22, 69'); and

-in that the outlet sections (82, 83) of the vent passages are occupied and controlled by flexible diaphragms (23, 24, 80, 84).

4. A combustion chamber as in claim 3, wherein the longitudinal central chamber (17, 71) communicates with at least one identical chamber relative to the adjacent exchanger by way of one or more transverse openings (14, 68) formed in the upwardly extending walls, located at least in the vicinity of and in alignment with the first flames to ignite, and is occupied by longitudinally distributed transverse projections (13, 67) set apart at longitudinal distances whereby the f lames are masked optically one from another by their interposition.

5. A valve as in claim 3, comprising a moving element (39) held in the closed position through the action of a cylindrical coil spring (40) and connected by way of a stem (41), articulated with its rear end, to a unidirectionally cushioned solenoid actuator (5, 62), wherein the forwardmost end of the valve element (39) is associated with a tapered nozzle (32) of cylindrical-frustoconical-cylindrical axial section of which the internal cylindrical surface of the rear end affords at least one longitudinal forward tapering notch (37) and is coupled axially and slidably with the outer cylindrical wall of an internal skirt (39') afforded by the valve element.

6. Flexible diaphragms as in claim 3, of notably lightweight and slender embodiment, fashioned in elastically deformable material and positioned in such a way as to occlude the outlet section of a vent passage whenever the relative burner (1, 58) is shut off, and to lift when invested by the hot gases which rise from the burner when ignited.

7. Flexible diaphragms as in claim 6 , occluding vent passages of which the outlet sections are disposed in a horizontal plane, consisting in sets of interlocking tongues (23, 24) rigidly associated with and projecting from common central supports anchored to the structure of the heat exchanger.

8. Flexible diaphragms as in claim 6, occluding vent passages of which the outlet sections are disposed in a horizontal plane, consisting in sheets (84) of material anchored to the structure of the heat exchanger and held thus in position by means of stays (85).

9. Flexible diaphragms as in claim 6, occluding vent passages of which the outlet sections are disposed in a vertical plane, consisting in flaps (80) top hinged to the structure of the heat exchanger .