Device for optimizing the efficiency of a gas-fired heat generator

Abstract

 A device (1) for optimizing the efficiency of a gas-fired heat generator comprising a burner positioned within a combustion chamber provided with a fan for evacuating burnt gases, the fuel reaching said burner via a feed pipe in which there is positioned an electrically powered pressure regulator, said regulator being controlled to vary the gas flow rate to the burner by electrical signals generated by a control unit of the heat generator. The device comprises fan command and control means (2) which measure the electrical control signals (V_REF) of the pressure regulator, said signals (V_REF) being compared with a reference signal (V_R) to generate a control signal for the fan, the rotational speed of this latter being modified on the basis of the control signals (V_REF) which reach the pressure regulator.

Description

[0001] This invention relates to a device in accordance with the introduction to the main claim.

[0002] A modern gas-fired heat generator or boiler is known to comprise a fan used both as the device for evacuating burnt gases from the combustion chamber and as the combustion air feed member.

[0003] In a boiler of known type, as the required heat output varies, the heat output of the adjustable heat generator is regulated by the action of its control unit on the pressure regulator of the gas valve, but the rotational speed of the fan is left unaltered to give a constant volumetric throughput (optimized for maximum heat output). Hence in such a generator, combustion takes place with optimum combustion air throughput only for maximum heat output, the air throughput being excessive and increasing as the heat output decreases. As a result the thermal efficiency with respect to the water decreases in relation to the air excess.

[0004] To obviate this drawback it is known to control the fan speed and hence the combustion air throughput as a function of the fuel gas flow. This is achieved by providing in the feed pipe a pressure sensor connected to the control unit. By means of this sensor the unit measures the variation in gas throughput in the feed pipe and consequently acts on the fan to modify its rotational speed. Although this solution enables the air flow to be varied as a function of the fuel gas flow, it is very complicated to arrange and cannot be used on already operating boilers without modifying the gas feed pipe, with obvious drawbacks. In addition, the known solution does not enable an adequate combustion air throughput to be maintained (by maintaining a suitable fan rotational speed) if the electricity supply mains voltage falls.

[0005] An object of the present invention is therefore to provide an improved device for optimizing the efficiency of a gas-fired boiler.

[0006] A particular object of the invention is to provide a device of the stated type allowing the combustion air throughput to be substantially and instantaneously regulated for all operating ranges (ie for every possible required heat output) of the heat generator.

[0007] A further object is to provide a device of the stated type which, even if the mains voltage varies (rises or falls), enables optimum combustion air throughput to be maintained for any gas flow to the burner, in particular enabling a minimum air throughput corresponding to minimum heat output to be maintained even following a drop in mains voltage.

[0008] These and further objects which will be apparent to the expert of the art are attained by a device in accordance with the accompanying claims.

[0009] The present invention will be more apparent from the accompanying drawing, which is provided by way of non-limiting example and in which the only figure represents a block diagram of the invention.

[0010] Said figure shows the device 1 of the invention, comprising means 2 for controlling a motor 3 of a usual fan (not shown) positioned within the combustion chamber of a gas-fired heat generator (not shown). The means 2 measure the voltage across a usual electrically operated flow regulator (not shown), and on the basis of this (ie on the basis of the gas flow rate to the burner) they act on the fan motor 3 to modify the fan speed and hence modify the combustion air flow rate.

[0011] More specifically, a voltage V_REF is withdrawn from across the modulator of a gas valve (not shown) defining the said gas flow regulator. This voltage is fed to an amplifier 5 which amplifies the V_REF signal and constitutes a stage with a high impedance input. From the amplifier there leaves a signal V_C which is fed to a comparator 6 which compares this signal with a voltage signal V_R originating from a block 7 which measures the voltage of the electricity mains powering the heat generator. The block 7 in particular comprises a ramp generator 8 connected to a zero sensor 9 from which it receives a signal V_Z. This latter is formed from a sequence of pulses generated each time the mains voltage passes through zero. The block 7 is connected to the mains voltage V_A (symbolize by the block 10) via a voltage reducer 12.

[0012] The ramp generator 8 is connected to a timer member 15 which receives mains voltage downstream of the voltage reducer and is connected in parallel with the zero sensor 9. The purpose of the member 15 is to enable the fan motor 3 to be powered to achieve maximum rotational speed (and hence maximum combustion air flow) for a predetermined time period each time the heat generator is started, independently of the value of V_REF, so as to achieve "scavenging" of the combustion chamber.

[0013] The comparator 6 compares the signals V_C and V_R, and generates an output signal V_U which is fed to an adder node 17 which also receives a signal V_K from a filter member 18 of compensator-limiter type which receives the mains voltage downstream of the reducer 12. The member 18 compensates for mains voltage variations which would otherwise influence the feed voltage of the motor 3. In particular, the member 18 ensures that the motor feed voltage never falls below a predetermined minimum value so as to set a minimum rotational speed of the motor 3 at which the air flow rate corresponds to the minimum heat output of the boiler.

[0014] A signal V_X leaves the adder node 17 to reach the control means 2. These latter can be an actual microprocessor unit (so as for example to allow automatic memorized control of the motor 3 on the basis of each value of V_REF measured or of the signal V_X) or a simple comparator member or other known control means. The unit 2 is connected to a galvanic separator 20 which ensures adequate electrical isolation between the mains voltage and the very low safety voltage present in the circuit. The signal from the unit 2 hence controls the closure and opening of a static switch (for example a TRIAC) 22 through which the mains power reaches the motor 3.

[0015] The use of the device is clear from the aforesaid description. During this use the control means or unit 2 measure the voltage V_REF corresponding to the state of gas flow to the burner, and hence by means of this signal measure the gas flow rate to said burner. This signal is compared with the signal V_R representative of the instantaneous mains voltage powering the motor 3. If this comparison shows that there is a preset difference between these two signals, the signal V_U is generated and, suitably treated with the signal V_K, reaches the means 2. Depending on said signal V_U representative of unbalance between the combustion air flow (measured by the signal powering the motor) and the gas flow to the burner, the means 2 operate to modify the duty cycle of the static switch, to hence vary the speed of the motor 3 and of the fan.

[0016] The device of the invention is reliable, is simple to construct and can be mounted in boilers already provided with an electrically controlled gas flow regulator, even after their installation.

[0017] With the device of the invention it is possible to optimize the efficency of a heat generator of the above cited kind because the combustion air throughput is regulated according to the gas flow to the burner.

Claims

1. A device (1) for optimizing the efficiency of a gas-fired heat generator comprising a burner positioned within a combustion chamber provided with a fan for evacuating burnt gases, the fuel reaching said burner via a feed pipe in which there is positioned an electrically powered pressure regulator, said regulator being controlled to vary the gas flow rate to the burner by electrical signals generated by a control unit of the heat generator, characterised by comprising command and control means (2) for the fan motor (3) which are arranged to modify the speed of said motor (3) and hence the rate of flow of combustion air to the combustion chamber on the basis of the measurement of a control signal (V_REF) of the pressure regulator.

2. A device as claimed in claim 1, characterised by comprising comparison means (6) arranged to compare the control signal (V_REF) of the pressure regulator with a reference signal (V_R) representative of the mains voltage powering said motor, said comparison means (6) generating an output signal (V_U) which is fed to the command and control means (2) for the fan motor (3).

3. A device as claimed in claim 1, characterised in that the command and control means (2) control switch means (22) through which the fan motor (3) receives mains power (10).

4. A device as claimed in claim 1, characterised by comprising timer means (15) enabling the fan motor (3) to be electrically powered such that, each time the heat generator is started, the fan generates maximum combustion air flow through the combustion chamber for a predetermined time period.

5. A device as claimed in claim 4, characterised in that the timer means (15) are connected to means generating the reference signal (V_R) representative of the mains voltage.

6. A device as claimed in claim 1, characterised by comprising means (18) for compensating mains voltage variation and for limiting the minimum feed voltage to the fan motor (3) so that the minimum combustion air flow rate corresponds to the minimum fuel gas flow rate.

7. A device as claimed in claim 6, characterised in that the compensator and limiter means (18) generate an output signal (V_K) fed to an adder node (17) to which the output signal (V_U) of the comparator means (6) are also fed, said node (17) generating an output signal (V_X) fed to the fan command and control means.

Drawing