METHOD FOR EVALUATING A QUASI-STATIONARY PRESSURE DIFFERENCE DETECTED BY A SENSOR AT A GAS BATHROOM AND ASSOCIATE GAS BATHROOM

Description

[0001] The invention relates to a method for evaluating a quasi-stationary pressure difference detectable by a sensor at a gas boiler and to a gas boiler which is configured to carry out the method.

[0002] In the prior art, gas boilers are known in which a pressure difference upstream of a main flow throttle to a reference pressure is measured by a sensor designed as a differential pressure sensor and the fuel mass flow is regulated based on the pressure difference.

[0003] In general, a gas boiler typically includes, among other components, a mixing unit for blending fuel flowing from a fuel inlet with air flowing from an air inlet to create a fuel-air mixture; a blower for drawing the fuel and air through the mixing unit; a main flow restrictor to limit the mass flow of fuel into the mixing unit; a control valve located upstream of the main flow restrictor to regulate the mass flow of fuel into the mixing unit; and a safety valve located upstream of the control valve to interrupt the mass flow of fuel. The gas-air mixture can then be fed to a burner where it can be combusted.

[0004] To regulate the pressure of the incoming fuel, control valves in the prior art often operate as a mechanical-pneumatic gas valve, in which a pressure difference is detected by a control diaphragm and which is arranged between two areas of different pressure.

[0005] Alternatively, pressure sensors are also used in so-called "electronic control" systems. In these systems, the pressures are measured by separate sensors, and the pressure values ​​are electronically evaluated to determine the pressure difference. Depending on the evaluation, an electronically controlled control valve or gas valve is then controlled or regulated.

[0006] In a device for regulating the gas-air mixture of a gas boiler, for example, the pressure upstream of the main flow restrictor is measured with a differential pressure sensor, which measures the differential pressure or pressure difference between two pressure readings, relative to a reference pressure.

[0007] In this process, an electronic gas valve is usually controlled by a digital controller, which is implemented, for example, on a microcontroller or another control unit, and by which the determined offset pressure or pressure difference is to be regulated to the desired or specified setpoint.

[0008] Since the target value of the pressure or pressure difference is usually 0 Pa, it is often referred to as "electronic zero pressure control".

[0009] Regardless of whether it is an electronic or mechanical pneumatic control system, the function is limited to controlling the gas boiler based on the pressure difference without being able to provide additional functionalities.

[0010] However, it would be desirable to be able to monitor a gas boiler with regard to further parameters in order to detect errors in the gas boiler depending on the parameters and to control or regulate the boiler accordingly, as well as to take further measures, in particular to extend the service life of the boiler.

[0011] Insofar as additional parameters can be recorded or errors detected in the known gas boilers, this requires additional sensors and evaluation devices, which is complex and expensive.

[0012] Further methods for fault detection in gas boilers are also known from EP 2 966 354 A1, on which the two-part form of claim 1 is based. EP 3 404 326 A1 further teaches methods for fault detection in combustion engines in general.

[0013] The invention is therefore based on the objective of overcoming the aforementioned disadvantages and providing a method by which faults in a gas boiler can be detected and evaluated in a simple and cost-effective manner.

[0014] This problem is solved by the combination of features according to claim 1.

[0015] According to the invention, a method for evaluating a quasi-stationary pressure difference detectable by a sensor at a gas boiler is proposed. The sensor is either a differential pressure sensor or a mass flow sensor. Furthermore, the gas boiler is provided with a mixing device for mixing fuel flowing from a fuel inlet and air flowing from an air inlet to form a fuel-air mixture, a blower for drawing the fuel and air through the mixing device, a main flow restrictor for limiting the mass flow of fuel into the mixing device, a control valve arranged upstream of the main flow restrictor for regulating the mass flow of fuel into the mixing device, and a safety valve arranged upstream of the control valve for interrupting the mass flow of fuel.The sensor detects a differential pressure between a pressure at a measuring point located upstream of the main flow restrictor and downstream of the control valve, and a reference pressure at a reference measuring point, and transmits this data to an evaluation unit. The evaluation unit compares the differential pressure during a pre-purge phase, in which the safety valve is closed, with a differential pressure during an operating phase of the gas boiler after the pre-purge phase, and detects a fault by this comparison.

[0016] During the pre-purge phase, the gas boiler is purged with air, as is known to experts, without adding any gas, which is made possible by the closed safety valve. The pre-purge phase is usually carried out at the beginning of operation or during initialization of the gas boiler.

[0017] According to the invention, the fault detection after the pre-purge phase relates to all further operating phases or types after the pre-purge of the gas boiler and in particular to a setup operation in which the gas boiler can be calibrated, and a continuous operation of the gas boiler.

[0018] A quasi-stationary pressure difference is defined as a pressure difference that does not fluctuate or only fluctuates within a predetermined tolerance range. For example, a pressure difference fluctuation of 1% around a mean pressure difference can be considered quasi-stationary.

[0019] Insofar as predetermined or previously known values ​​and / or ranges are mentioned, these can be stored or at least storable in the evaluation electronics.

[0020] Based on known data stored in the evaluation electronics, which can be determined during the calibration of the gas boiler or entered by a user, various system states and / or errors can be detected and / or validated. This state and error detection is achieved primarily through physical and logical analysis of the system's prevailing states and values. State detection using machine learning, for example, neural networks, is also possible. Furthermore, tolerance ranges or general tolerance values ​​can be generated or expanded using machine learning.

[0021] The proposed methods are based on the signal from the differential pressure sensor, which, for example, measures the offset pressure p2 during normal operation of the "electronic zero-pressure control". With a known gas type and a defined main flow restrictor, the gas valve characteristic curve can be calibrated using the offset pressure.

[0022] According to the invention, the fault is a missing or disconnected sensor and / or a poor or non-existent connection between the sensor and the measuring point and / or the reference measuring point. A pressure difference is determined between the pressure at the measuring point, located upstream of the main flow restrictor and downstream of the control valve, and a reference pressure at a reference measuring point. The evaluation electronics detect the sensor as missing or disconnected and / or 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.

[0023] In this context, an advantageous further development to prevent or at least minimize damage provides that the safety valve is closed if the sensor is missing or not connected and / or has a poor or non-existent connection to the measuring point and / or the reference measuring point.

[0024] Here too, the fuel used, the main flow restrictor, the characteristics of the mixing device, and the gas valve characteristic curve of the control valve are preferably known. These values ​​are determined beforehand and / or stored in the evaluation electronics.

[0025] Other advantageous embodiments of the invention are characterized in the dependent claim or are described in more detail below together with the description of the preferred embodiment of the invention with reference to the figure. It shows: Fig. 1 is an exemplary schematic representation of a gas boiler.

[0026] Figure 1 Figure 1 schematically shows a part or section of a gas boiler, where a Venturi mixer is depicted as mixing device 4, in which air at a pressure p0 is drawn from the environment through an air inlet L by a blower 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.

[0027] The fuel flowing in from the fuel supply G, which is in particular a gas, passes through a safety valve 1, a control valve 2, and the main flow restrictor 3. The safety valve 1 preferably has a flow-through position and a closed position, in which the flow of fuel through the safety valve 1 is blocked. The control valve 2 is designed to regulate the fuel flow rate, so that the fuel flow rate through the control valve 2 to the mixing device 4 can be adjusted. By adjusting or regulating the fuel flow rate via the control valve 2, the mixing ratio of the fuel-air mixture can thus be adjusted.

[0028] Furthermore, at least one differential pressure sensor is provided, which is configured to determine the differential pressure between the fuel pressure p2 upstream of the main flow restrictor 3 and downstream of the control valve 2, and a reference pressure, wherein the reference pressure is preferably the ambient pressure p0 or a pressure p1 of the air in an air-carrying supply line to the mixing device 4. For this purpose, the differential pressure sensor can, for example, have a pressure sensor or pressure transducer for detecting the respective pressures p0, p1, and p2. Furthermore, additional pressure sensors can be provided for detecting the further pressures pg, p3, and p4, which can serve as reference pressure sensors for detecting a reference pressure or for verifying the plausibility of the pressures p0, p1, and p2.

[0029] The fuel-air mixture is conveyed by the blower 5 to a burner of the gas boiler (not shown), where the fuel-air mixture is burned.

[0030] Based on the in Figure 1 In the following example, errors or conditions in the system shown will be identified and, if necessary, values ​​will be determined or validated.

[0031] According to the invention, in a first case, for example, an installed main flow throttle 3 is to be detected by means of a differential pressure determined by the differential pressure sensor.

[0032] It is advantageous if the control pressure Venturi characteristic of the system, i.e., the gas boiler, is known. A Venturi mixer as a mixing device 4 is not strictly necessary; a pressure reduction element upstream of the mixing point of air and fuel (gas) with a known pressure reduction characteristic is sufficient. Furthermore, the type of gas (fuel type) should be known. The gas type can be stored by the installer or at the factory on the evaluation electronics, or a dedicated sensor can detect the gas composition, for example, at the gas inlet G.

[0033] With a preferably pre-calibrated control valve 2, the gas mass flow rate flowing through the control valve 2 in its installed state can be determined 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 that the mass flow rate through the control valve 2 does not depend on the inlet pressure pg. The offset pressure p2 upstream of the main flow restrictor 3 is measured, for example, with a pressure sensor as part of the differential pressure sensor.

[0034] The air density, which influences the control pressure of the mixing device 4 for a given air mass flow rate, can be manually entered beforehand by the installer. Alternatively, the air density can also be determined by a sensor. With a suitable geometric arrangement, this can also be done by the sensor that determines the gas type when the safety valve 1 is open.

[0035] In the pre-purge phase (time t=t pp ) of the gas boiler, in which the safety valve 1 is closed, a negative pressure pv, which is generated by the mixing device 4 at a speed N of the blower 5, is measured by means of a pressure sensor at point p2.

[0036] Because of the closed safety valve 1 during the pre-purge phase: p2(t pp )=p3(t pp )=p4(t pp )=pv(t pp ).

[0037] Using the measured pressure p2 or pv and a function or table stored in the evaluation electronics for this system consisting of mixing unit 4 and main flow throttle 3, an air mass flow rate is calculated. This calculation can be corrected for air density depending on the required accuracy.

[0038] After the pre-purge phase, at a constant rotational speed N, the desired pilot position of the actuator of control valve 2 is first reached, 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 ignites at the burner of the gas boiler, and the pressure p2 stabilizes from a certain time ts; a quasi-steady-state condition is reached.

[0039] The measured (or specifically adjusted) pressure p2(ts ) now results, together with the previously measured pressure p2(t pp ), in the driving pressure difference dp=p2(ts )-pv(ts ) across the series connection of flow resistances, consisting of the main flow restrictor 3 and further resistances in the mixing device 4. Further resistances can be, for example, deflections downstream of the main flow restrictor 3 as well as the openings at the point of air-gas mixing ("gas pockets").

[0040] If necessary, the speed N of the blower 5 can also be changed for the detection of the installed main flow throttle 3 in order to use multiple measuring points.

[0041] Using the gas mass flow rate determined via the gas valve characteristic curve and the pressure difference dp, the pressure loss coefficient of the main flow throttle 3 can be calculated.

[0042] The pressure loss of the other flow resistances should also be taken into account in this calculation. In particular, if the pressure loss across the main flow restrictor 3 is dominant compared to the total pressure loss dp, the installed main flow restrictor 3 (or the associated pressure loss coefficient) can be determined with sufficient accuracy.

[0043] If no ignitable mixture is present at the burner of the gas boiler at the time of ignition, further ignition attempts can be made, possibly with an adjusted pilot position of the control valve 2. The detection of the installed main flow restrictor 3 can also be carried out without combustion of the gas-air mixture in the burner. In this case, it must always be ensured that the potentially flammable gas-air mixture is removed from the gas boiler after a certain safety period by a safety purge (flushing) using the fan 5.

[0044] A further requirement is that the measured pressure p2(ts) reaches a quasi-steady state. If the measured pressure difference is completely outside a predetermined tolerance range, insufficient or no input pressure may also be responsible for the faulty ignition.

[0045] Not according to the invention, in a second case, for example, a faulty calibrated control valve 2 should be detected and the control valve 2 should be able to be calibrated in operation (in-situ) if necessary.

[0046] It is again advantageous if the system's control pressure Venturi characteristic is known. Here too, a Venturi mixer is not strictly necessary as mixing device 4; a pressure reduction element upstream of the air-fuel mixing point with a known pressure reduction characteristic is sufficient. Furthermore, the type of gas (fuel type) should be known. The gas type can be stored by the installer or at the factory on the evaluation electronics, or it can be detected by a suitable sensor.

[0047] In addition to the aforementioned data, a known system of flow resistances downstream of the main flow restrictor 3 (deflections and gas pockets) and a main flow restrictor 3 with a known pressure loss characteristic are advantageous for the in-situ calibration of the control valve 2. The installed main flow restrictor 3 can be stored on the evaluation electronics by the installer or at the factory, or the main flow restrictor 3 can be mechanically / electronically / color-coded by the manufacturer so that the evaluation electronics, which evaluates the measurement data, recognizes the main flow restrictor 3.

[0048] As in the first case described, a pressure difference pv is determined during a pre-purge phase as well as a differential pressure with the flame ignited and in a quasi-stationary state.

[0049] The speed N of the blower 5 can also be changed here, if necessary, to determine multiple measuring points. In practice, however, often only one measuring point is required to determine the offset pressure of the characteristic curve of the control valve 2.

[0050] With the pressure difference dp determined in this way and a known overall pressure loss characteristic of main flow throttle 3 and, if applicable, downstream flow resistances, the flow rate (mass flow rate) through the control valve 2 can be calculated.

[0051] If no ignitable mixture is present in the burner of the gas boiler at the time of ignition, further ignition attempts can be made, possibly also with an adjusted pilot position of control valve 2. If these ignition attempts are also unsuccessful, the detection of control valve 2 and / or the in-situ calibration of control valve 2 can also be carried out without combustion of the gas-air mixture.

[0052] Furthermore, the calibration of control valve 2 during commissioning of the gas boiler can also be carried out without combustion of the gas-air mixture. However, it must be ensured at all times that the potentially flammable gas-air mixture is removed from the gas boiler after a certain safety period by means of a safety purge (flushing) using blower 5.

[0053] As before, the pressure difference p2(ts ) should be in a quasi-stationary state.

[0054] The described procedure for calibrating control valve 2 can also be used to calibrate control valve 2 at the factory during production, rather than in-situ during commissioning of the gas boiler. This calibration process can also be performed using air flowing through control valve 2. If the in-situ calibration is performed during production, the calibration parameters can be stored directly on the electronics of control valve 2 without direct communication between the production equipment and the electronics of the gas boiler.

[0055] In a third case, according to the invention, a gas used as fuel is to be made plausible or a defective gas is to be detected.

[0056] Preferably, the control pressure Venturi characteristic of the system is known. Here too, a Venturi mixer is not strictly necessary as the mixing device 5. A pressure reduction element upstream of the mixing point of air and fuel as the mixing device 5 with a known pressure reduction characteristic is sufficient.

[0057] For the plausibility check of the gas used as fuel, or for fault detection in this regard, it is advantageous if the system of flow resistances downstream of the main flow restrictor 3 (deflections and gas pockets) is known and a main flow restrictor 3 with a known pressure loss characteristic is used. The installed main flow restrictor 3 can be stored on the evaluation electronics by the installer or at the factory. Alternatively, the main flow restrictor 3 can also be mechanically / electronically / color-coded so that the evaluation electronics, which analyzes the measurement data, recognize the main flow restrictor 3.

[0058] As in the two previously described cases, for example, with a factory-calibrated electronic control valve 2, the gas mass flow rate flowing through the control valve 2 in its installed state can be determined for a given position of the control valve's actuator. In this case, it is assumed that the control valve 2's upstream pressure regulator operates ideally and that the mass flow rate through the control valve 2 does not depend on the gas inlet pressure pg. The offset pressure p2 upstream of the main flow restrictor 3 is measured with a pressure sensor, which can be part of the differential pressure sensor. The pressure sensor can either be installed upstream of the main flow restrictor 3 or mounted on an electronic circuit board of other components and connected via hoses / tubes to a representative pressure measurement point upstream of the main flow restrictor 3.

[0059] The air density, which can influence the control pressure of the mixing device 4 for a given air mass flow rate, can be manually entered beforehand by a user. Alternatively, the air density can also be determined by a sensor.

[0060] As before, during a pre-purge phase (time t = t pp) or when purging the gas boiler, the negative pressure pv, which is generated by the mixing device 5 at a speed N of the blower 5, can be measured at point p2 using a pressure sensor. Because the safety valve 1 is closed during the pre-purge phase, the following again applies: p2(t pp) = p3(t pp) = p4(t pp) = pv(t pp). Using the measured pressure p2 and a function or stored table in the evaluation unit, an air mass flow rate can be calculated for this system consisting of the mixing device 4 and the main flow restrictor 3. This calculation can be corrected for the required accuracy using the air density of the air flowing through the air inlet L.

[0061] After the pre-purge phase, at a constant rotational speed N, the desired pilot position of the actuator of control valve 2 is first reached, 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 gas-air mixture ignites at the burner of the gas boiler, and the pressure p2 stabilizes from time ts onwards, resulting in a quasi-steady-state pressure p2 or differential pressure. The measured (or specifically adjusted) pressure p2(ts) now, together with the previously measured pressure p2(t pp), yields the driving pressure difference dp = p2(ts) - pv(ts) across the series connection of flow resistances, consisting of the main flow restrictor 3 and any further resistances in the mixing device 4. Further resistances can be, for example,There are deflections downstream of the main flow throttle 3 and openings in the mixing device 4 at the point of air-gas mixing ("gas pockets").

[0062] Here too, the rotational speed N can be changed if necessary to use multiple measuring points.

[0063] With the measured pressure difference dp, the known mass flow rate at a fixed or unchanged position of the control valve 2 and the known overall pressure loss characteristic of the main flow restrictor 3 and downstream flow resistances, the type or composition of the gas flowing through the gas inlet G can be verified.

Claims

1. A method for evaluating a virtually stationary pressure difference at a gas boiler detectable by a sensor, wherein the sensor is a differential pressure sensor or a mass flow sensor, wherein the gas boiler has a mixing apparatus (4) for mixing a fuel flowing in from a fuel inlet (G) and an air flowing in from an air inlet (L) into a fuel-air mixture, a fan (5) for sucking the fuel and the air through the mixing apparatus (4), a main amount throttle (3) for limiting a mass flow of the fuel into the mixing apparatus (4), a regulating valve (2) arranged upstream of the main amount throttle (3) for regulating a mass flow of the fuel into the mixing apparatus (4) as well as a safety valve (1) arranged upstream of the regulating valve (2) for interrupting the mass flow of the fuel, wherein the sensor detects a differential pressure between a pressure (p2) at a measurement point upstream of the main amount throttle (3) and downstream of the regulating valve (2) and a reference pressure (p0, p1) at a reference measurement point and transmits it to an evaluation electronics, characterised in that the evaluation electronics compares the differential pressure during a pre-purge phase, in which the safety valve (1) is closed, with a differential pressure in an operating phase of the gas boiler after the pre-purge phase and recognises an error through the comparison, that the error is a non-present or non-connected sensor and / or a bad or non-present connection of the sensor to the measurement point and / or the reference measurement point, that a pressure difference between the pressure (p2) at the measurement point upstream of the main amount throttle (3) and downstream of the regulating valve (2) and a reference pressure (p0, p1) at a reference measurement point is determined, and that the sensor is recognised as non-present or non-connected and / or as having a bad or non-present connection to the measurement point and / or the reference measurement point by the evaluation electronics if the differential pressure is outside a predetermined tolerance range.

2. The method according to the preceding claim, wherein the safety valve (1) is closed in case of a non-present or non-connected sensor and / or a sensor having a bad or non-present connection to the measurement point and / or the reference measurement point.

3. A gas boiler which is formed to perform a method according to any one of the preceding claims.