Method For Evaluating A Quasi-Stationary Pressure Difference Detectable By A Sensor At A Gas Boiler, And Associated Gas Boiler

Abstract

A method for evaluating a quasi-stationary pressure difference detectable by a sensor at a gas boiler. The gas boiler has a mixing device (4), a fan (5), a main flow regulator (3), .a control valve (2) and a safety valve (1). The sensor detects a differential pressure between a pressure (p2) at a measuring point upstream of the main flow regulator (3) and downstream of the control valve (2) and a reference pressure (p0, p1) at a reference measuring point. The sensor transmits a signal to an electronic evaluation system. The electronic evaluation system compares the differential pressure during a pre-purge phase, wherein the safety valve (1) is closed, with the differential pressure after the pre-purge phase and detects an error by the comparison.

Claims

1. A method for evaluating a quasi-stationary pressure difference detectable by a sensor at a gas boiler, the sensor is a differential pressure sensor or a mass flow sensor, the gas boiler has a mixing device, a fan, a main flow regulator, a control valve and a safety valve, the mixing device mixes a fuel flowing in from a fuel inlet and air flowing in from an air inlet to form a fuel-air mixture, the fan is for intake of the fuel and the air through the mixing device, the main flow regulator limits a mass flow of the fuel into the mixing device, the control valve, arranged upstream of the main flow regulator, controls a mass flow of the fuel into the mixing device, the safety valve, arranged upstream of the control valve, interrupts the mass flow of the fuel, the method comprising: detecting a differential pressure between a pressure at a measuring point upstream of the main flow regulator and downstream of the control valve and a reference pressure (p0, p1) at a reference measuring point; transmitting the differential pressure to an electronic evaluation system; comparing the differential pressure during a pre-purge phase where the safety valve is closed with the differential pressure after the pre-purge phase; and detecting an error by the comparison.

2. The method according to claim 1, wherein the error is an incorrect or incorrectly inserted main flow regulator and the method comprises the following steps: a. identifying a first differential pressure p(t.sub.pp), with the sensor at a time t.sub.pp during the pre-purge phase with the safety valve closed, a defined position of the control valve and a fan speed of the fan; b. identifying a second differential pressure p(t.sub.s), with the sensor at a time i.sub.s after the time t.sub.pp where the second differential pressure p(t.sub.s) is quasi-stationary, with the safety valve open, the defined position of the control valve and the fan speed of the fan; c. determining a pressure difference between the second differential pressure p(t.sub.s) and the first differential pressure p(t.sub.pp), in particular by subtracting the first differential pressure p(t.sub.pp) from the second differential pressure p(t.sub.s), and determining a fuel mass flow rate of the known fuel through the main flow regulator from the pressure difference and the defined position of the control valve by the electronic evaluation system; d. determining an actual pressure loss coefficient of the main flow regulator from the fuel mass flow and the pressure difference by the electronic evaluation system; e. matching the actual pressure loss coefficient by the electronic evaluation system with a target pressure loss coefficient of a provided main flow regulator stored in the electronic evaluation system; and in the event of a deviation of the actual pressure loss coefficient from the target pressure loss coefficient outside a predetermined tolerance, the electronic evaluation system detects that a main flow regulator used in the gas boiler does not correspond to the intended main flow regulator and that the main flow regulator used is therefore an incorrect or incorrectly inserted main flow regulator.

3. The method according to claim 1, wherein the error is an uncalibrated or incorrectly calibrated control valve and the method comprises the following steps: a. identifying a first differential pressure p(t.sub.pp), with the sensor at a time t.sub.pp during the pre-purge phase, with the safety valve closed, a defined position of the control valve and a predetermined or known fan speed of the fan; b. identifying a second differential pressure p(t.sub.s), with the sensor at a time i.sub.s at which the second differential pressure p(t.sub.s) is quasi-stationary, with the safety valve open, the defined position of the control valve and the fan speed of the fan; c. determining a pressure difference between the second differential pressure p(t.sub.s) and the first differential pressure p(t.sub.pp), in particular by subtracting the first differential pressure p(t.sub.pp) from the second differential pressure p(t.sub.s), and determining a fuel mass flow of the known fuel through the control valve from the pressure difference and a defined pressure loss characteristics of the main flow regulator by the electronic evaluation system, wherein the mass flow through the control valve and the defined position of the control valve form a pair of values belonging to an actual characteristic curve of the control valve; d. determining a deviation of the actual characteristic curve of the control valve from a target characteristic curve of the control valve by the electronic evaluation system by comparing the pair of values with the target characteristic curve of the control valve (2); and in the event of a deviation of the value pair from the target characteristic curve of the control valve outside of a predetermined tolerance, detecting an uncalibrated or incorrectly calibrated control valve.

4. The method according to claim 3, shifting the target characteristic curve of the control valve by the deviation and thus approximated to the actual characteristic curve.

5. The method according to claim 1, wherein the error is an incorrect fuel and the method comprises the following steps: a. identifying a first differential pressure p(t.sub.pp) with the sensor at a time t.sub.pp during the pre-purge phase, with the safety valve closed, a defined position of the control valve and a fan speed of the fan; b. identifying a second differential pressure p(t.sub.s), with the sensor at a time i.sub.s where the second differential pressure p(t.sub.s) is quasi-stationary, with the safety valve open, the defined position of the control valve and the fan speed of the fan; c. determining a pressure difference between the second differential pressure p(t.sub.s) and the first differential pressure p(t.sub.pp), in particular by subtracting the first differential pressure p(t.sub.pp) from the second differential pressure p(t.sub.s); d. determining an actual fuel flowing in from the fuel inlet from the pressure difference, the defined position of the control valve and the predetermined mass flow delivered by the fan through the mixing device as well as a defined pressure loss characteristics of the main flow regulator; e. comparing the actual fuel with a predetermined target fuel; and detecting an incorrect fuel if the actual fuel does not correspond to the target fuel.

6. The method according to claim 1, wherein the error is a missing or too low fuel pressure pg of the fuel flowing in through the fuel inlet and/or an incorrectly installed or not installed main flow regulator, and the method comprises the following steps: a. opening the safety valve; b. igniting a burner of the gas boiler; c. identifying whether the burner has been ignited; d. if the burner has not been ignited, identifying a differential pressure curve with the sensor and the electronic evaluation system with the safety valve open for a predetermined time; comparing, via the electronic evaluation system, the differential pressure curve with a predetermined tolerance field and detecting the error if the pressure curve lies outside the tolerance field, whereby a differential pressure which does not increase over the predetermined time and detecting a missing or too low fuel pressure pg and/or an incorrectly installed or not installed main flow regulator.

7. The method according to claim 6, wherein a maximum permissible heating output of the gas boiler and/or a maximum permissible fan speed of the fan are/is reduced to a respective predetermined value if the fuel pressure pg is missing or too low.

8. The method according to claim 1, wherein the error is a non-existent or unconnected sensor and/or a poor or non-existent connection of the sensor to the measuring point and/or the reference measuring point, detecting a pressure difference between the pressure (p2) at the measuring point, which is located upstream of the main flow regulator and downstream of the control valve, and a reference pressure (p0, p1) at a reference measuring point; and recognizing, via the electronic evaluation system, the sensor as not present or not connected and/or as having a poor or non-existent connection to the measuring point and/or the reference measuring point if the differential pressure is outside a predetermined tolerance range.

9. The method according to claim 8, wherein the safety valve is closed in the event of a sensor not being present or not being connected and/or having a poor or non-existent connection with the measuring point and/or the reference measuring point.

10. The method according to claim 1, wherein the error is a defective safety valve or a defective control valve, and the method comprises the following steps: a. identifying an actual differential pressure, with the sensor, with the safety valve open, a defined position of the control valve and a predetermined mass flow delivered by the fan through the mixing device; b. determining a target differential pressure by the electronic evaluation system and a defined position of the control valve; c. determining a deviation of the actual differential pressure from the target differential pressure; and determining the electronic evaluation system, an error if the deviation is greater than a predetermined tolerance value.

11. A gas boiler designed to carry out a method according to claim 1.

Description

DRAWINGS

[0067] Other advantageous refinements of the disclosure are indicated in the subclaims or are illustrated in more detail below together with the description of the preferred embodiment of the disclosure with reference to the figure. In the figure:

[0068] FIG. 1 is an exemplary schematic illustration of a gas boiler.

DETAILED DESCRIPTION

[0069] FIG. 1 shows schematically a part or a detail of a gas boiler. A Venturi mixer is shown as a mixing device 4 where air from the environment with an air pressure p0 is sucked through an air inlet L by a fan 5. In the mixing device 4, the incoming air and a fuel (gas) flowing in through the fuel supply G are mixed to form a fuel-air mixture.

[0070] The fuel, in particular a gas, flowing in from the fuel supply G, flows through a safety valve 1, a control valve 2 and the main flow regulator 3. The safety valve 1 preferably has an open position and a closed position where the flow of the fuel through the safety valve 1 is blocked. The control valve 2 is designed to control the volume flow of the fuel so that the volume flow of the fuel through the control valve 2 to the mixing device 4 is adjustable. By adjusting or controlling the volumetric flow of the fuel through the control valve 2, the mixing ratio of the fuel-air mixture can be adjusted.

[0071] Furthermore, at least one differential pressure sensor is provided. It is designed to determine the differential pressure between the pressure p2 of the fuel upstream of the main flow regulator 3 and downstream of the control valve 2 and a reference pressure. The reference pressure is preferably the ambient pressure p0 or a pressure p1 of the air in an air-carrying feed line to the mixing device 4. For this purpose, the differential pressure sensor can have, for example, a respective pressure sensor or pressure transducer to detect a respective pressure p0, p1, p2. Moreover, further pressure sensors can be provided to detect the further pressures pg, p3 and p4, which can serve as reference pressure sensors to detect a reference pressure or to check the plausibility of the pressures p0, p1, p2.

[0072] The fuel-air mixture is conveyed by the fan 5 to a burner of the gas boiler, which is not shown, where the fuel-air mixture is combusted.

[0073] In the following, the system illustrated in FIG. 1 is used as an example to detect errors or conditions and, if necessary, to determine or check the plausibility of values.

[0074] In a first case, for example, an installed main flow regulator 3 is to be detected by a differential pressure determined by the differential pressure sensor.

[0075] It is advantageous here if the control pressure-venturi characteristics of the system, i.e., the gas boiler, is known. A venturi mixer as a mixing device 4 is not absolutely necessary, a pressure reduction element upstream of the mixing point of air and fuel (gas) with known pressure reduction characteristics is sufficient. In addition, the gas type (fuel type) should be known. The gas type can be stored on the electronic evaluation system by the installer or at the factory, or a sensor provided for this purpose detects the composition of the gas, for example, at the gas inlet G.

[0076] With the control valve 2 preferably already being calibrated and a defined position of the actuator of the control valve 2, the gas mass flow that flows through the control valve 2 in the installed state can be inferred. In this case, it is assumed that the upstream pressure regulator of control valve 2 operates ideally and the mass flow through control valve 2 does not depend on the inlet pressure pg. The offset pressure p2 upstream of the main flow regulator 3 is measured, for example, with a pressure sensor as part of the differential pressure sensor.

[0077] The air density, which affects the control pressure of the mixing device 4 for a given air mass flow, can be entered manually beforehand by the installer. Alternatively, the air density can be detected by a sensor. With an appropriate geometric arrangement, this can also be done by the sensor, which can be used to determine the type of gas when the safety valve 1 is open.

[0078] In the pre-purge phase (time t=t.sub.pp) of the gas boiler, where the safety valve 1 is closed, a negative pressure pv, generated by the mixing device 4 at a speed N of the fan 5, is measured by a pressure sensor at the point p2.

[0079] Due to the closed safety valve 1 during the pre-purge phase, it holds: p2(t.sub.pp)=p3(t.sub.pp)=p4(t.sub.pp)=pv(t.sub.pp).

[0080] With the measured pressure p2 and pv, respectively, and a function or table stored in the electronic evaluation system for this system including the mixing device 4 and main flow regulator 3, an air mass flow is calculated. Depending on the requirement for accuracy, this calculation can be corrected with the air density.

[0081] After the pre-purge phase, at a constant speed N, the desired pilot position of the actuator of the control valve 2 is first approached and the ignition of the gas boiler is activated and subsequently the safety valve 1 is opened. As soon as a combustible mixture is present at the ignition electrode of the gas boiler, the fuel-air mixture burns at the burner of the gas boiler and the pressure p2 stabilizes from a point in time t.sub.s, i.e., a quasi-stationary state is present.

[0082] The measured (or specifically adjusted) pressure p2(t.sub.s) together with the previously measured pressure p2(t.sub.pp) now results in the driving pressure difference dp=p2(t.sub.s)-pv(t.sub.s) via the series connection of flow resistors including the main flow regulator 3 and further resistors in the mixing device 4. Further resistors can be, for example, deflectors downstream of the main flow regulator 3 as well as the openings at the point of the air-gas mixture (“gas pockets”).

[0083] If necessary, the speed N of the fan 5, for detecting the installed main flow regulator 3, can also be changed to use multiple measuring points.

[0084] With the gas mass flow determined via the gas valve characteristic curve and the pressure difference dp, the pressure loss coefficient of the main flow regulator 3 can be calculated.

[0085] The pressure loss of the further flow resistors should also be considered in this calculation. In particular, if the pressure loss across the main flow regulator 3 is dominant with respect the total pressure loss dp, the installed main flow regulator 3 (or the associated pressure loss coefficient) can be determined with sufficient accuracy.

[0086] If there is no ignitable mixture at the burner of the gas boiler at the time of ignition, further ignition attempts can be made, possibly also with the adapted pilot position of the control valve 2.

[0087] In principle, the detection of the installed main flow regulator 3 can also be carried out without combustion of the gas-air mixture in the burner. In this case, it must be ensured at all times that the potentially combustible gas-air mixture is conveyed out of the gas boiler after a certain safety time by a safety purge (purging) by the fan 5.

[0088] It is also a prerequisite that the measured pressure p2(t.sub.s) reaches a quasi-stationary state. If the measured pressure difference is completely outside a predetermined tolerance range, too low or missing inlet pressure may also be responsible for the faulty ignition.

[0089] In a second case, for example, it should be possible to detect an incorrectly calibrated control valve 2. If necessary, the control valve 2 can be calibrated during operation (in-situ).

[0090] It is again advantageous if a control pressure-venturi characteristics of the system is known. Here too, a venturi mixer as mixing device 4 is not necessarily required, a pressure reduction element upstream of the mixing point of air and fuel with known pressure reduction characteristics is sufficient as mixing device 4. In addition, the gas type (fuel type) should be known. The gas type can be stored on the evaluation electronics by the installer or at the factory, or it can be detected by an appropriate sensor.

[0091] In addition to the aforementioned data, a known system of flow resistors downstream of the main flow regulator 3 (baffles and gas pockets) as well as a main flow regulator 3, with known pressure loss characteristics, is advantageous for the in-situ calibration of the control valve 2. The installed main flow regulator 3 can be stored on the electronic evaluation system by the installer or at the factory, or the main flow regulator 3 is mechanically/electronically/color-coded by the manufacturer in such a manner that the electronic evaluation system, which evaluates the measurement data, recognizes the main flow regulator 3.

[0092] As in the first case described, a pressure difference pv is identified during a pre-purge phase. A differential pressure is identified when the flame is ignited and in a quasi-stationary state.

[0093] Here too, the speed N of the fan 5 can be changed if necessary in order to be able to identify several measurement points. In the application, however, often only one measuring point is required to determine the offset pressure of the characteristic curve of the control valve 2.

[0094] With the pressure difference dp determined in this manner and a known total pressure loss characteristics of main flow regulator 3 and any flow resistors possibly arranged downstream, the flow rate (mass flow) through control valve 2 can be calculated.

[0095] If there is no ignitable mixture in the burner of the gas boiler at the time of ignition, further ignition attempts can be made, possibly also with an adapted pilot position of the control valve 2. If these ignition attempts are also unsuccessful, the detection of the control valve 2 and/or the in-situ calibration of the control valve 2 can be carried out without combustion of the gas-air mixture.

[0096] Furthermore, the calibration of the control valve 2, during commissioning of the gas boiler, can in principle also be carried out without combustion of the gas-air mixture. In this case, it has to be ensured at all times that the potentially combustible gas-air mixture is conveyed out of the gas boiler after a certain safety time by a safety purge (purging) with the aid of the fan 5.

[0097] As before, the pressure difference p2(t.sub.s) should be in a quasi-stationary state.

[0098] The described procedure for calibrating the control valve 2 can also be used to calibrate the control valve 2 at the factory during manufacturing, rather than in-situ during commissioning of the gas boiler. This calibration procedure can also be performed with air flowing through the control valve 2. If the in-situ calibration is performed in manufacturing, the calibration parameters can be stored directly on an electronic circuit of the control valve 2 without direct communication of the manufacturing equipment with an electronic circuit of the gas boiler.

[0099] In a third case, a gas used as fuel is to be checked for plausibility or a faulty gas is to be detected.

[0100] Once again, a control pressure-venturi characteristics of the system is preferably known. Here too, a venturi mixer is not necessarily required as the mixing device 5. A pressure reduction element upstream of the mixing point of air and fuel as mixing device 5 with a known pressure reduction characteristics is sufficient.

[0101] For the plausibility check of the gas used as fuel or a fault detection to that effect, it is advantageous if the system of flow resistors downstream of the main flow regulator 3 (baffles and gas pockets) is known. A main flow regulator 3 with known pressure drop characteristics is used. The installed main flow regulator 3 can be stored, i.e. saved, on the electronic evaluation system by the installer or at the factory. Alternatively, the main flow regulator 3 can also be mechanically/electronically/color-coded in such a manner that the electronic evaluation system, which evaluates the measurement data, recognizes the main flow regulator 3.

[0102] As in the two previously explained cases, in the case of an electronic control valve 2 calibrated, for example, at the factory, it is possible to infer the gas mass flow that flows through the control valve 2 in the installed state for a given position of the actuator of the control valve 2. In this case, it is assumed that the upstream pressure regulator of the control valve 2 operates ideally and the mass flow through the control valve 2 does not depend on the inlet pressure pg of the gas. The offset pressure p2 upstream of the main flow regulator 3 is measured by a pressure sensor that can be part of the differential pressure sensor. The pressure sensor can either be installed upstream of the main flow regulator 3 or installed on an electronic board of other components. The sensor is connected to a representative pressure measuring point upstream of the main flow regulator 3 by hoses/pipes.

[0103] The air density, which can influence the control pressure of the mixing device 4 for a given air mass flow, can be entered manually beforehand by a user. Alternatively, the air density can also be identified by a sensor.

[0104] As before, in a pre-purge phase (time t=t.sub.pp) or during a purging of the gas boiler, the negative pressure pv, which is generated by the mixing device 5 at a speed N of the fan 5, can be measured by a pressure sensor at the point p2. Due to the closed safety valve 1 during the pre-purge phase, it holds again: p2(t.sub.pp)=p3(t.sub.pp)=p4(t.sub.pp)=pv(t.sub.pp). With the measured pressure p2 and a function or table stored in the evaluation unit, an air mass flow can be calculated for this system including the mixing device 4 and main flow regulator 3. Depending on the requirement for accuracy, this calculation can be corrected with the air density of the air flowing through the air inlet L.

[0105] After the pre-purge phase, at a constant speed N, the desired pilot position of the actuator of the control valve 2 is first approached and the ignition of the gas boiler is activated. Subsequently, the safety valve 1 is opened. As soon as a combustible mixture is present at the ignition electrode of the gas boiler, the gas-air mixture burns at the burner of the gas boiler. The pressure p2 stabilizes from the point in time ts, so that a quasi-stationary state of the pressure p2 or the differential pressure exists. The measured (or specifically adjusted) pressure p2(t.sub.s) together with the previously measured pressure p2(t.sub.pp) now results in the driving pressure difference dp=p2(t.sub.s)-pv(t.sub.s) via the series connection of flow resistors including the main flow regulator 3 and possible further resistors in the mixing device 4. Further resistors can be, e.g., baffles downstream of the main flow regulator 3 and openings in the mixing device 4 at the point of air-gas mixing (“gas pockets”).

[0106] Here too, if necessary, the speed N can be changed to use multiple measurement points.

[0107] With the measured pressure difference dp, the known mass flow at a fixed or unchanged position of the control valve 2 and the known total pressure loss characteristics of the main flow regulator 3 and downstream flow resistors, the gas type or composition of the gas flowing through gas inlet G can be checked for plausibility.

[0108] The disclosure is not limited in its embodiment to the preferred exemplary embodiments indicated above. Rather, a number of variants is conceivable, which make use of the presented solution even in fundamentally different embodiments.