Electronic closed-loop control device for fireplaces comprising a lower combustion system

Abstract

The invention relates to a device that does not require operator intervention, operates without delay, does not require a mains connection, and meets the requirements of the regulations with respect to permissible pollutant emissions. The device consists of a control unit which is electrically connected to two temperature sensors and to a door contact switch and which actuates an actuator by means of an electric motor and transmission elements. The temperature is detected in the flue behind the outlet of the combustion chamber. The temperature sensors record the change in temperature over time and the speed of the change in temperature. The temperature target / actual evaluation is used to record the combustion state of the solid fuel. The degree of the outgassing process is determined by recording and evaluating the increase or decrease in temperature over time. The target / actual temperature over time compared to comparative values for optimising combustion is an adaptive system. Therefore, the composition of the solid fuel is taken into account for the optimum combustion process and the necessity of the new charging with solid fuel is determined by means of the programme and displayed by means of an optical signal transmitter. The device is used for electronic closed-loop control for a fireplace comprising a lower combustion system.

Description

Technical field

[0001] The invention relates to a device for electronic control of a low-emission wood-burning stove with two combustion chambers positioned one above the other in an optimized under-firing principle according to the preamble of the first claim. State of the art

[0002] There are now many different types of devices for regulating the air supply in order to optimize the combustion of solid fuels.

[0003] From DE 10 2009 012 905 B3, a method for controlling the output of a solid fuel stove and a stove with two combustion chambers, in particular arranged one above the other, are known. The combustion chambers are separated from each other by a bottom but are nevertheless connected to each other by a bottom opening. The lower combustion chamber is connected to a flue gas passage via an exhaust gas duct, and the upper combustion chamber is connected to the flue gas passage via a transition opening and can be partially closed by a flue gas damper. A temperature sensor is arranged in the exhaust gas duct, which controls the primary air volume flow depending on the temperature in the exhaust gas duct, while the secondary air volume flow is kept at least constant.

[0004] Although this disclosed device has a temperature sensor, it does not use an automatic electronic evaluation and control program that uses the temperature change over time and the rate of temperature change to assess the target vs. actual combustion, or to determine the outgassing process of the solid fuel, and to optimize combustion.

[0005] From AT 507 930 A4, a method for regulating the supply of combustion air to the firebox of a stove is known, in particular a wood-burning stove with primary air supplied to the grate from below, secondary air supplied to the firebox in the door area from above and / or the side, and nozzle air supplied to the firebox above the grate from the rear wall and / or the sides. The invention is characterized in that the sequence of air supply comprises at least a standstill state with a high primary air content, a start-up phase with a high primary air content, a main combustion phase with a low or no primary air content, and two burn-out phases, the first with a low or no primary air content and the second with a noticeable primary air content, and that the transition between the phases depends on the temperature of the firebox and / or the rate of change of this temperature.

[0006] The claimed control method relates to a solid fuel furnace with a combustion chamber, but regulates the air supply depending on the temperature of the combustion chamber and / or the rate of change of this temperature. A disadvantage of this method is that it does not determine the degree of degassing based on the flue gas temperatures, as claimed by the applicant.

[0007] DE 20200311 U1 discloses a low-emission wood-burning stove with an optimized bottom-firing principle. This stove has two combustion chambers, one above the other, separated by a grate / firebox that supports the solid fuel. The lower combustion chamber serves as an afterburner and ash pan. A handle regulates the combustion by actuating a flue gas vent, directing the combustion gases produced during the combustion of the solid fuel in the upper combustion chamber into the lower combustion chamber, thus enabling the most efficient and cleanest possible combustion.

[0008] The smoke is then extracted through an opening located in the lower combustion chamber.

[0009] This type of control has the disadvantage that all actions of the shut-off device are based on the operator's subjective judgment, experience, and intuition. Manual control is very time-consuming, as adjustments must be made repeatedly depending on the combustion process. Optimal operation of the shut-off device is not possible because the operator has no way of monitoring the temperature in the flue. Temperature monitoring is necessary to open or close the shut-off device at the optimal time, or to determine the optimal time to add more solid fuel.

[0010] Furthermore, a control system for a low-emission log fireplace with an optimized bottom-firing principle is known, utilizing a thermobimetal to actuate the closing mechanism. The supply of fresh air is regulated depending on the temperature surrounding the thermobimetal. A disadvantage of this system is that if the thermobimetal closes the closing mechanism and the subsequent temperature drop is too great—for example, due to varying conditions at the installation site or the properties of the solid fuel (piece size, moisture content, etc.)—the closing mechanism cannot be opened until the thermobimetal has cooled down. During the cooling period, combustion is inefficient, resulting in increased pollutant emissions. Therefore, optimal low-emission combustion cannot be achieved.

[0011] Experts are also familiar with the method of regulating combustion air supply using a lambda sensor. This principle is most commonly used in central heating boilers and wood gasifiers. Here, the lambda sensor continuously measures the oxygen content in the combustion chamber or the residual oxygen content of the exhaust gas and compares it to the oxygen content of the air surrounding the boiler. The signal from the lambda sensor can then be used to determine the necessary speed of a fan that regulates the supply of combustion air.

[0012] The disadvantages here are the need for a power connection, high purchase costs and time-consuming installation.

[0013] It is becoming increasingly important to adapt and further optimize the combustion process with solid fuels to meet ecological requirements. Description of the invention

[0014] The invention addresses the problem of creating a simple solution in terms of design and manufacture for an electronic control device for a low-emission wood-burning stove with two combustion chambers positioned one above the other, using the optimized under-firing principle. This device regulates reliably, precisely, independently, and without operator intervention, without requiring a mains connection. Furthermore, it is adapted to the individual characteristics of the stove by means of a freely configurable control unit program, thereby meeting the latest requirements of the fire regulations for reducing pollutant emissions and other requirements for obtaining the Blue Angel quality seal, and eliminating the disadvantages of the prior art.

[0015] According to the invention, the problem is solved by the electronic control device for a low-emission wood-burning stove comprising two combustion chambers positioned one above the other, separated by a solid fuel storage area with an outlet to the lower combustion chamber, a flue, an outlet in the upper combustion chamber to the flue with a closable flap, an outlet in the lower combustion chamber to the flue, and a firebox door with a door lock / handle, wherein the device includes a control unit with a program, the control unit is electrically connected to at least two temperature sensors and a door contact switch, and the control unit actuates an electric motor which, via transmission elements or a direct connection, actuates a flap closing the outlet.wherein the device is set up for temperature measurement in the flue behind the outlet of the respective combustion chamber by at least one temperature sensor each, wherein the temperature sensors measure the temperature change over time and measure the rate of temperature change, the target / actual temperature evaluation by the control unit over parameterizable time periods serves as an evaluation criterion for the combustion state of the solid fuel, the degree of the outgassing process is recognized by measuring and evaluating the temperature rise and fall over time, and wherein the target / actual temperature over time is compared with the reference values ​​stored in the program for combustion optimization as an adaptive system so that the respective properties of the solid fuel, in particular moisture content, wood type and piece size, are taken into account for the optimal combustion process.and whereby the need for a new solid fuel feed is determined by the program and indicated by an optical signal that is clearly visible to the user.

[0016] This provided a solution that eliminates the aforementioned disadvantages of the state of the art.

[0017] Advantageous embodiments of the invention are set out in the dependent claims.

[0018] It proves to be a favorable design feature of the device that the opening or closing process of the flap initiated by the control unit can take place almost without delay due to the use of an electric motor.

[0019] Another possible design is that the regulation can optionally take place in battery or mains operation.

[0020] The signaling of the operating states "normal operation", "recharging" or "fault" with each its own color code via a single optical signal transmitter leads to a further advantageous design.

[0021] An additional feature is that a memory in the control unit, which cannot be erased by the user, records the operating hours, operating states, minimum and maximum temperatures for the purpose of traceability and can also be used, if necessary, to clarify warranty claims. Example of implementation

[0022] Exemplary embodiments of the device according to the invention are described in more detail below using one embodiment as an example. The figures show: Fig. 1 shows a device according to the invention mounted on a wood-burning stove with an optimized under-combustion principle, as an exemplary arrangement of the flap 5 closed (before commissioning). Fig. 2 shows a device according to the invention mounted on a wood-burning stove with an optimized under-combustion principle, as an exemplary arrangement of the flap 5 open (heating-up phase). Fig. 3 shows a device according to the invention mounted on a wood-burning stove with an optimized under-combustion principle, as an exemplary arrangement of the flap 5 closed (control mode / combustion). Fig. 4 shows a program flowchart of the control of the device according to the invention during the heating-up phase. Fig. 5 shows a program flowchart of the control of the device according to the invention in control mode. Fig. 6 shows a program flowchart of the control of the device according to the invention in refueling mode. Fig. 7 shows a program flowchart of the control of the device according to the invention during combustion.

[0023] In the Figure 1An exemplary setup incorporating the device according to the invention is shown, preferably intended for a low-emission wood-burning stove (1) with two combustion chambers (2 and 3) positioned one above the other, operating on an optimized bottom-fire principle. The device according to the invention enables the operation and monitoring of the combustion process of the solid fuel by controlling the combustion air supply. Operation by the user is limited to supplying the solid fuel and igniting the fire.

[0024] In this example, the wood-burning stove 1 consists of an upper combustion chamber 2 and a lower combustion chamber 3, separated by a shelf for the solid fuel 19. This shelf contains an outlet 4 to the lower combustion chamber 3. Both the upper and lower combustion chambers 2 and 3 each have an outlet 5 and 8 to the flue 7.

[0025] In the upper combustion chamber 2 there is a flap 5 which, if necessary, can close the outlet 6 to the flue vent 7, as in Fig 1The opening and closing of the flap 5 is effected via a transmission element 11, driven by an electric motor 12. The electric motor is electrically connected to the control unit 13. Both combustion chambers 2 and 3 are tightly sealed to the surrounding installation room by a firebox door 9 using a door lock (handle) 10. A door contact switch 14 is installed to provide information about the closure of the firebox door 9. The door contact switch 14 is electrically connected to the control unit 13. The temperature sensors 17 and 18 required for controlling the combustion air are positioned behind the respective outlets 6 and 8 of the two combustion chambers 2 and 3 in the flue gas outlet 7 and are electrically connected to the control unit 13. The control unit 13 is located at a point on the chimney that is easily visible to the operator, preferably in the front area, as shown in the diagram. Fig 1As shown, an optical signal generator 16 is located as an indicator to request the addition of solid fuel, to indicate the operating status (normal operation) or to signal a fault, which is also connected to the control unit 13.

[0026] The operating principle of the low-emission wood-burning stove 1 with two combustion chambers 2 and 3 positioned one above the other, using the optimized bottom-firing principle, is known to those skilled in the art. Therefore, a more detailed description and explanation of the specifics is omitted in this exemplary embodiment.

[0027] The description of the function of the device according to the invention follows the individual phases or modes of the combustion process. The individual process steps, characterized by reference numerals, are illustrated in the drawings. Fig. 4 , Fig. 5 , Fig. 6 and Fig. 7 Program flowchart shown. Heating phase (Program flowchart Fig.4)

[0028] The control unit 13 is powered by a battery-operated voltage source 15. Alternatively, a mains connection can also be used as the voltage source 15. When voltage is applied to the control unit 13, either by inserting batteries into the voltage source or via the mains connection, the electric motor 12 performs a reference run to determine the position of the flap 5 and to test its function. The control unit 13 is now ready for operation in standby mode (procedure step 14A). When the firebox door 9 of the fireplace 1 is opened for the first time while cold, the control unit is activated from standby mode via the door contact switch 14 (procedure step 14B), and the electric motor 12 and the transmission element 11 switch the flap 5 to the open position. Fig. 2(Process step 5A). The solid fuel 20 is now placed on the support 19 of the fireplace 1 and ignited in a suitable manner. To achieve and make reproducible the optimal switching point for the ignition phase, namely the closing of the damper 5, the control system begins after a signal is sent to the control unit 13 via the door contact switch 14 by closing the firebox door 9 using the door lock 10 (process step 14C) and a temperature rise above 50°C has occurred. Simultaneously with the activation of the control unit 13, the temperature sensors 17 and 18 continuously measure the existing temperatures. After reaching a temperature of 50°C, measured by the temperature sensor 17 behind the outlet 6 to the flue 7 (process step 17A), a waiting time t w1 (sec) is activated by the control unit 13 (process step 13A) and the exhaust gas temperature TA (°C) is measured by the temperature sensor 17 in the flue 7.After the waiting time t w1 (sec) has elapsed and the flue gas temperature TA (°C) specified in the program has been exceeded (process step 17B), the flap 5 is closed by means of an electric motor 12 and transmission element 11 (process step 5B) and the combustion gases are directed through the outlet 4 into the lower combustion chamber 3, as in . Fig. 3As shown. After switching over, it may happen that the temperature for the outgassing process T AU (°C) is not yet sufficient or the wood-burning stove is not yet optimally heated. Consequently, the wood gas cannot be burned properly. The temperature sensor 17 detects this situation of a significant temperature drop in the flue gas and, by means of a control command from the control unit 13 (process step 17C), opens the flap 5 (process step 5A) by means of an electric motor 12 and transmission element 11. The control unit 13 thereby reactivates a waiting period t w2 (sec) (process step 13B) and the exhaust gas temperature in the flue 7 is measured by the temperature sensor 17 until the preset temperature T setpoint (°C) is reached again. This process is repeated, controlled by the control unit 13, until stable combustion is established. The system then switches to control mode. Rule mode (Program flowchart Fig.6)

[0029] Once stable combustion is achieved, the temperature sensor 18 (process step 18A) detects the maximum temperature T AU max in the lower combustion chamber 3. If the temperature falls below a defined temperature range (T AU max tolerance), the control unit 13 (process step 18B) then activates a refueling signal (process step 18C), which is indicated by an optical display 16, informing the operator of the correct time to refuel (process step 16A). Due to varying amounts of solid fuel 20 being refueled, the temperature range (T AU max tolerance) is fixed, but the temperature level (TN) is not. The control unit 13 detects and sets the temperature level after each refueling. Reload mode (Program flowchart Fig.5)

[0030] To add more fuel, the firebox door 9 is opened by actuating the door lock 10, and the door contact switch 14 is activated, sending a signal to the control unit 13 (process step 14D). This, in turn, controls the electric motor 12, which opens the damper 5 via the transmission element 11 (process step 5A). After the door closes (process step 14C), a parameterized waiting time t w3 (sec) is activated (process step 13C), and the exhaust gas temperature is measured by the temperature sensor 17 in the flue 7 (process step 17D). After the waiting time t w3 (sec) has elapsed and the flue gas temperature TA (°C) specified in the program has been exceeded, the damper 5 is closed via the actuators 11 and 12 (process step 5B), and the combustion gases are directed through the outlet 4 into the lower combustion chamber 3. After switching, the temperature T AU (°C) may change, e.g. due to excessively large pieces of wood or excessively wet wood, etc., which is not yet sufficient for the outgassing process. In this case, a significant temperature drop in the flue gas is measured by the temperature sensor 17 and detected by the control unit 13 (process step 17E), and the flap 5 (process step 5A) is opened. This reactivates a parameterized waiting time t w4 (sec) (process step 13D), and the exhaust gas temperature in the flue 7 is measured by the temperature sensor 17 until a preset temperature T set (°C) is reached again. This process is repeated, controlled by the control unit 13, until stable combustion is established. fire (Program flowchart Fig.7)

[0031] If the exhaust gas temperature TA (°C), measured by temperature sensor 17, falls below a defined value TA setpoint (process step 17F) and no more fuel is added, the damper 5 opens (process step 5A). The remaining solid fuel 20 burns down and the chimney cools down. If the temperature measured by temperature sensor 17 in the flue 7 falls below 50°C, the control unit 13 deactivates and enters standby mode.

[0032] The device according to the invention is, of course, not limited to the illustrated embodiment. Rather, modifications and adaptations are possible without departing from the scope of the invention. List of reference symbols

[0033] 1 Wood-burning stove 2 Upper combustion chamber 3 Lower combustion chamber 4 Outlet (to lower combustion chamber) 5 Damper 6 Upper outlet (to flue) 7 Flue 8 Lower outlet (to flue) 9 Firebox door 10 Door lock (handle) 11 Transmission element (to damper (5)) 12 Electric motor 13 Control unit 14 Door contact switch 15 Power supply 16 Optical signal transmitter 17 Temperature sensor (upper combustion chamber) 18 Temperature sensor (lower combustion chamber) 19 Solid fuel support 20 Solid fuel List of reference symbols for the process steps

[0034] 5A Open flap 5 5B Close flap 5 13A Waiting time t w1 13B Waiting time t w2 13C Waiting time t w3 13D Waiting time t w4 14A Firebox door 4 was opened from standby mode 14B Firebox door 4 was opened 14C Firebox door 4 was closed 14D Firebox door 4 was opened from control or refueling mode 16A Optical signal transmitter 16 Refueling indicator 17A Temperature sensor 17 Upper combustion chamber 2 with TA > 50°C 17B Temperature sensor 17 Upper combustion chamber 2 with TA > T A setpoint in start-up phase 17C Temperature drop dT A in upper combustion chamber 2 in start-up phase too large 17D Temperature sensor 17 with TA > T A setpoint in refueling mode 17T Temperature drop dT A in upper combustion chamber 2 too large in refueling mode 17F Temperature sensor 17 with TA < 50°C in burnout mode 18A Temperature sensor 18 Determination of maximum temperature T AU in lower combustion chamber 3 18B Storage of maximum temperature T AU in lower combustion chamber 3 18C Temperature sensor 18 Wait until temperature T AU falls below the tolerance limit

Claims

1. Electronic closed-loop control device for fireplaces with a lower combustion system comprising two combustion chambers (2 and 3) positioned one above the other, separated by a support for solid fuel (19) with an outlet (4) to the lower combustion chamber (3), a flue (7), an outlet (6) in the upper combustion chamber (2) to the flue (7), an outlet (8) in the lower combustion chamber (3) to the flue (7), a firebox door (9) with a door lock / handle (10) wherein the device has • a control unit (13) with a program, the control unit is electrically connected to at least two temperature sensors (17;18) and a door contact switch (14), wherein the control unit controls an electric motor (12) which actuates a flap (5) closing the outlet (6) via transmission elements (11) or a direct connection, wherein the device is designed for • measuring the temperature in the flue (7) downstream of the outlet (6, 8) of the respective combustion chamber (2, 3) by at least one of the temperature sensors (17, 18) in each case, wherein the temperature sensors (17,18) measure the temperature change over time, and the temperature sensors (17,18) measure the rate of temperature change, • The evaluation of the target / actual temperature by the control unit (13) over parameterisable time periods serves as an evaluation criterion for the combustion state of the solid fuel (20), wherein the degree of the outgassing process is determined by recording and evaluating the temperature rise or fall over time, and wherein • the target / actual temperature over time is compared with the comparative values stored in the program for optimising combustion as an adaptive system so that the respective property of the solid fuel (20), especially moisture, type of wood and log size, is taken into account for optimising the combustion process, and wherein • the necessity for reloading with solid fuel (20) is determined via the program and indicated via an optical signal transmitter (16) that is clearly visible to the user.

2. Device for electronic control according to claim 1 wherein the opening or closing process of the flap (5), initiated by the control unit, (13), due to the use of the electric motor (12), can take place almost without delay.

3. Device for electronic control according to the previous claims, wherein the control process can take place optionally by battery or mains operation.

4. Device for electronic control according to the previous claims, wherein the operating states "Standard operation", "Reloading" or "Malfunction", each with its own colour code, are signalled by a single optical signal transmitter (16).

5. Device for electronic control according to the previous claims, wherein the operating hours, operating states and minimum and maximum temperatures are recorded for traceability purposes via a memory in the control unit (13) which cannot be deleted by the user.

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