Heating appliance with pneumatic gas-air connection and method for operating a heating appliance

Description

[0001] The invention relates to a heating device with a pneumatic gas-air system and a method for operating a heating device.

[0002] Heating appliances for the combustion of a fuel gas, such as natural gas or hydrogen, generally create a combustion mixture of fuel gas and combustion air with a predetermined air-fuel ratio (also known as lambda or air-fuel ratio) and supply this mixture to a burner for combustion. Such heating appliances are also called premix burners. Various methods are known for determining the air-fuel ratio. Heating appliances with a pneumatic gas-air system detect a reference pressure in the area of ​​a throttling point, often called a Venturi, located in the combustion air supply, which allows conclusions to be drawn about the mass flow rate of combustion air supplied. Based on the reference pressure, the gas valve adds a mass flow rate of fuel gas corresponding to a predetermined air-fuel ratio. Such a heating appliance is described, for example, in EP 3 957 910 A1.The advantage of pneumatic mixture formation is that it does not require complex sensors and is therefore very robust in application and simple in design.

[0003] In such heaters, the heating output, or rather the activation of a modulation point, is controlled by the fan speed, which regulates the mass flow of combustion air supplied. Modern heaters have a wide modulation range to ensure high user comfort and to avoid frequent, wear-inducing on / off cycles. To enable robust operation at low outputs, the flow cross-section (diameter) of the Venturi nozzle must be small. The resulting high pressure drop across the Venturi nozzle can lead to high control pressures at the gas valve upstream of the Venturi nozzle (relative to the flow direction) and a correspondingly small pressure differential between the gas supply pressure and the control pressure.One consequence is a limitation of the maximum power output of the heating device, since above a certain limit a robust adjustment of the combustion air ratio (lambda) is not possible due to the low differential pressure, and thus a limitation of the possible modulation range.

[0004] German patent DE 295 04 706 U1 proposes a heating device in which a radial fan is arranged upstream of a Venturi nozzle. A differential pressure before and after the Venturi nozzle is measured to regulate the combustion air ratio. However, this arrangement also has the disadvantage of not being able to precisely adjust the combustion air ratio over a large modulation range at high power outputs.

[0005] FR 2 515 314 A1 describes a method for operating a gas boiler comprising an air scrubber for the incoming combustion air, in which the combustion air flow upstream of the scrubber and the supplied gas flow are measured, and flow control valves for gas and combustion air are provided by means of which an optimal lambda value can be set. A disadvantage of this method is its high complexity.

[0006] US Patent 5,630,408 A describes a control device for the air-fuel ratio that uses the absolute pressure of the airflow for adjustment. It also proposes using the differential pressure of a Venturi device. This control device is also complex and cannot react to fluctuations in gas pressure.

[0007] Based on this, the object of the invention is to propose a heating device with a pneumatic gas-air system that at least partially overcomes the problems of the prior art described above. In particular, an increase in the modulation range is to be achieved.

[0008] Furthermore, the invention should not significantly increase the complexity of a heating device, should require only minor structural changes to a heating device, and should allow for easy integration into an existing production process.

[0009] These problems are solved by the features of the independent claims. Further advantageous embodiments of the solution proposed here are specified in the independent claims. It should be noted that the features listed in the dependent claims can be combined with one another in any technologically meaningful way and define further embodiments of the invention. Furthermore, the features specified in the claims are further specified and explained in the description, which also presents further preferred embodiments of the invention.

[0010] This is achieved by a heating device comprising a conveying device for conveying combustion air to a burner, a Venturi device arranged downstream of the conveying device and a gas valve connected to a gas supply and a pressure control, wherein a control line downstream of the Venturi device is connected to the gas valve and the gas valve is configured to adjust a flow rate of fuel gas according to a differential pressure between a pressure of the control line and a pressure of the gas supply as well as a predetermined combustion air ratio.

[0011] The heating appliance can be a gas-fired heater with a pneumatic gas-air system. This system can include a delivery device, in particular a blower, capable of delivering a mass flow (or volume flow) of combustion air. The combustion air can be supplied via a combustion air inlet featuring a Venturi device (Venturi nozzle) as a throttling point, which can be located downstream of the delivery device. A gas valve is configured to add a mass flow of fuel gas corresponding to a predetermined combustion air ratio and the combustion air mass flow. Subsequently, the resulting combustion mixture can be fed via a mixture channel to a burner of the heating appliance and combusted there.A reference pressure (control pressure) is measured in a control line, allowing conclusions to be drawn about the effectively delivered mass flow of combustion air, and a differential pressure between the control line pressure and a gas supply pressure is transmitted to the gas valve. It is proposed to measure the control pressure downstream of the Venturi device. For this purpose, the control pressure line can be routed into the mixture channel downstream of the Venturi device.

[0012] The gas valve can reduce the pressure of the fuel gas from the pressure in the gas supply (e.g., pressure of the gas network) to the reference pressure.

[0013] The gas valve introduces a mass flow of fuel gas corresponding to the differential pressure between the pressure of the control line and the pressure of the gas supply, as well as a predetermined combustion air ratio, and establishes a predetermined combustion air ratio. The heating appliance can, in particular, be a wall-mounted condensing boiler.

[0014] The terms "upstream" and "downstream" refer to the direction of airflow through the heating appliance from a combustion air supply to the exhaust system and thus to the direction of delivery of the conveying device.

[0015] A "flow rate" of fuel gas here refers to a mass or volume flow of fuel gas that is set by the gas valve and flows through.

[0016] Such a heating appliance can adjust its heating output to the heat demand, a process also known as modulation. This can occur within a modulation range specified for the appliance. To avoid frequent, wear-inducing switching on and off of the burner, modern heating appliances can operate within a wide modulation range, for example, 1:5 from 4.8 kW [kilowatts] to 24 kW. In the future, modulation ranges of 1:7 (for example, 3.4 kW to 24 kW) or even 1:10 (2.4 kW to 24 kW) are expected to be achieved.

[0017] The Venturi device (Venturi nozzle) can have a flow cross-section (diameter) that allows the heater to operate within a wide modulation range, for example, with a maximum to minimum power ratio of 5 or more. For instance, the modulation range can cover a range from a minimum power of 1 kW to 5 kW up to a maximum power of between 12 and 24 kW.

[0018] To enable or ensure operation at the minimum power output of the modulation range, the flow cross-section of the Venturi device can be reduced to such an extent that a significant pressure differential arises across the Venturi device. A significant pressure differential exists, in particular, when the two pressures differ by a factor of at least 1.5, or preferably at least 2.0. For example, a pressure of 1300 Pa [Pascal] upstream of the Venturi device may exist compared to a pressure of 500 Pa downstream of the Venturi device. Thus, the control pressure measured upstream of the Venturi device is high, and the differential pressure between the control pressure and the gas supply pressure, which is transmitted to the gas valve for control, decreases accordingly.This can lead to a limitation in the maximum power output that can be delivered by the heating device, and to a differential pressure that is too low at high power outputs (a high predetermined speed of the conveying device).

[0019] The invention is based on the idea of ​​lowering the reference pressure level by utilizing the area downstream of the Venturi device, thereby enabling trouble-free operation of the heating appliance at high power output. If a reference pressure were detected upstream of the Venturi device, it could rise so sharply at high power output that the gas valve would no longer be able to regulate the gas flow correctly. Thus, the invention allows for a lower limit to the modulation range without compromising safe operation at high power output.

[0020] Furthermore, a control pressure measured downstream of the Venturi device is independent of the flow cross-section of the Venturi device and thus enables more precise adjustment of combustion parameters. This is primarily because a reference pressure measured downstream of the Venturi device depends only on components or parts in the flow path downstream of the Venturi device.

[0021] According to one design, the gas line from the gas valve can terminate in the area of ​​the Venturi device. This can enable good mixing of the fuel gas with the combustion air.

[0022] In a further aspect, a method for operating a heating appliance is proposed in which a differential pressure between a control line pressure and a gas supply pressure, as well as a predetermined combustion air ratio, is used to adjust the flow rate of a gas valve in the heating appliance. The control line is connected to the gas valve downstream of a Venturi device in the heating appliance. A heating appliance proposed here is configured to execute the proposed method.

[0023] This proposal therefore suggests a heating device and the use of differential pressure that at least partially solve the problems described with reference to the state of the art. In particular, the heating device enables robust operation across a wide modulation range; in other words, it allows for the selection of a diameter for minimum modulation output without limiting the choice of maximum output. Furthermore, it enables a more precise selection of combustion parameters.

[0024] Furthermore, the invention can be implemented with only minor structural changes to a heating device and is therefore also ideally suited for retrofitting existing heating devices.

[0025] The invention and its technical context are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the situations described in the figures and combine them with other components and findings from the present description. It should be emphasized that the figures, and especially the depicted dimensions, are only schematic. They show: Fig. 1 : a heating device suggested here, and Fig. 2: und Fig. 3 : Parameter profiles that can occur when carrying out a procedure proposed here.

[0026] Fig. 1 Figure 1 shows an exemplary and schematic representation of a heating appliance 1 proposed here. This appliance can have an air supply 4 for combustion air. A Venturi device 15 can be arranged in the air supply 4. Viewed in a flow direction 16 of the heating appliance 1, a conveying device 2 designed as a blower can be arranged upstream of the Venturi device 15, which can convey a mass flow of combustion air. A gas valve 5 can be located in the area of ​​the Venturi device 15, in particular in the Venturi device 15, to add a mass flow of fuel gas to the mass flow of combustion air conveyed by the conveying device 2. The mixture of fuel gas and combustion air can be supplied to a burner 3 via a mixture channel 12 and combusted there. A heat exchanger 13 can be arranged at the burner 3, which can transfer the heat generated during combustion to a heating circuit 14 with a supply line 6 and a return line 9.

[0027] Downstream of the burner 3, an exhaust pipe 10 can feed combustion products to an exhaust system 11. A control and regulating unit 7 of the heating appliance 1 can be electrically connected to at least the gas valve 5 and the conveying device 2.

[0028] Fig. 2 Figure 1 shows a schematic and illustrative representation of gas valve 5, the Venturi device 15, and the delivery device 2. The delivery device 2 can supply a mass flow of combustion air to the Venturi device 15. Downstream of the Venturi device 15, a control line 17 can transmit the pressure in the mixture channel 12 to the gas valve 5. This valve can create a pressure differential between the pressure in the control line 17 and the pressure in the gas supply 8 and direct this differential pressure via a gas line 18 to the Venturi device 15, adding the combustion air to the mass flow. The resulting mass flow of combustion mixture consisting of fuel gas and combustion air can then be supplied to the burner 3 via the mixture channel 12.

[0029] Fig. 3Figure 19, 20, 21, 22, and 23 show exemplary combustion air ratio (lambda) curves as they develop in relation to the output of the heating appliance 1. Due to tolerances (especially manufacturing tolerances) of the gas valves 5, the first curve 19, the second curve 20, and the third curve 21 show differing combustion air ratios. The control line 17 of the gas valves 5 is connected upstream of the Venturi device 15, according to the state of the art. It is clearly evident that adjusting the combustion air ratio (lambda) for higher outputs above 22 kW [kilowatts] is not possible.

[0030] In contrast, the fourth curve 22 and the fifth curve 23 show a settling combustion air ratio at a gas valve 5, whose control line 17 is connected downstream of the Venturi device 15. It is clearly visible that the combustion air ratio can be adjusted up to a power output of 27 kW.

[0031] It should be noted as a precaution that the numerical terms used here ("first", "second", etc.) primarily serve (only) to distinguish between several similar objects, quantities, or processes, and thus do not necessarily dictate any dependency and / or sequence between these objects, quantities, or processes. Should a dependency and / or sequence be required, this is explicitly stated here, or it will be obvious to a person skilled in the art upon studying the specific configuration described. Where a component can occur multiple times ("at least one"), the description of one of these components may apply equally to all or some of the multiple components, but this is not mandatory. Reference symbol list

[0032] 1 Heating unit 2 Conveyor 3 Burner 4 Air supply 5 Gas valve 6 Flow 7 Control and regulating unit 8 Gas supply 9 Return 10 Exhaust pipe 11 Exhaust system 12 Mixing channel 13 Heat exchanger 14 Heating circuit 15 Venturi device 16 Flow direction 17 Control line 18 Gas line 19 First path 20 Second path 21 Third path 22 Fourth path 23 Fifth path

Claims

1. Heating appliance (1) comprising a conveyor device (2) for conveying combustion air to a burner (3), a Venturi device (15) arranged downstream of the conveyor device (2) and a gas valve (5) connected to a gas supply (8), wherein a control line (17) is connected to the gas valve (5) downstream of the Venturi device (15) with respect to a flow direction (16) of the heating appliance (1) relative to a flow direction (16) of the heating device (1) and the gas valve (5) is designed to adjust a flow rate of fuel gas corresponding to a differential pressure between a pressure in the control line (17) and a pressure in the gas supply (8) and a predetermined combustion air ratio.

2. . Heating appliance (1) according to claim 1, wherein the conveying device (2) is a blower.

3. . Heating appliance (1) according to claim 1 or 2, wherein the Venturi device (15) is designed to enable a ratio of maximum to minimum output of the heating appliance (1) greater than 4.

4. . Heating appliance (1) according to one of the preceding claims, wherein the heating appliance (1) is a wall-mounted heating appliance (1).

5. . Heating appliance (1) according to one of the preceding claims, wherein a gas pipe (18) from the gas valve (5) opens into the area of the Venturi device (15).

6. . Method for operating a heating appliance (1) in which a differential pressure between a pressure of a control line (17) and a pressure of a gas supply (8) and is used to adjust a flow rate of a gas valve (5) of the heating appliance (1), wherein the control line (17) is connected downstream of a Venturi device (15) of the heating appliance to the gas valve (5).