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 of the Invention The invention relates to a device for the electronic control of a low-emission logburning fireplace with two combustion chambers positioned one above the other, using the lower combustion principle in an optimised form. State of the Art Many different types of devices now exist for regulating the air supply in order to optimise the combustion of solid fuels. For example, utility model publication DE 20200311 U1 discloses a low-emission logburning fireplace, using the lower combustion principle in an optimised form. This fireplace has two combustion chambers, positioned one above the other, which are separated by a firing support / grate as a support for the solid fuel, wherein the lower combustion chamber serves as an afterburner chamber and ash pan. Combustion is regulated here by a handle. This actuates a closure device for the flue in order to conduct the combustion gases, produced during the combustion of the solid fuel in the first, upper combustion chamber, into the second, lower combustion chamber and to enable combustion to be as pollution-free and effective as possible. The smoke is then extracted through an opening located in the lower combustion chamber. One disadvantage of this type of control system is that all operations of the closure device are carried out at the subjective discretion of the operator, based on their experience and assessment. Manual control can be very time-consuming because corrections have to be continually made depending on the state of combustion. The closure device cannot be operated optimally, as the operator has no means of measuring the temperature in the flue. Measurement of the temperature is required in 2021332942   27 May 2026 order to open or close the closure device at the optimal time or to determine the optimal time for adding more solid fuel. Furthermore, a control system for a low-emission log-burning fireplace using the lower combustion principle in an optimised form and a thermo-bimetal for actuating the closure device are known. The supply of fresh air is regulated depending on the temperature surrounding the thermo-bimetal. The disadvantage here is that the closure device can be opened only after the thermo-bimetal has cooled down if the thermo-bimetal closes the closure device and the temperature drop is subsequently too great, due, for example, to different conditions at the installation site and / or the composition of the solid fuel (log size, moisture content, etc.). During the cooling period, combustion is poor with an increase in the emission of pollutants. Optimal low-emission combustion cannot therefore be achieved. In addition, regulating the combustion air supply using a lambda sensor is known to those skilled in the art. This principle is used in most cases in boilers for central heating systems and wood gasifiers, where the oxygen content in the combustion chamber or the residual oxygen content of the exhaust gas is permanently measured by the Lambda sensor and compared with the oxygen content of the air surrounding the boiler. The signal from the Lambda sensor can then be used to determine the required speed of a fan that regulates the combustion air supply. Some disadvantages here are the need for a power connection, high purchase costs and a time-consuming installation. Ever greater importance is being placed on adapting the combustion process with solid fuel to ecological requirements and on continuing to optimise this process. Summary of the Invention The invention present herein addresses the problem of creating a simple solution in terms of design and manufacture for a device for the electronic control of a low-emission log-burning fireplace with two combustion chambers positioned one above the other, using the lower combustion principle in an optimised form, which regulates 2021332942   27 May 2026 reliably, precisely, without mains connection, independently, and without the intervention of the operator, and is at the same time adapted to the individual characteristics of the fireplace by means of a freely parameterisable program of the control unit, thereby meeting the latest requirements of the Ordinance on Firing Installations for reducing the emission of pollutants and additional provisions for obtaining the Blue Angel quality seal, as well as eliminating one or more of the disadvantages of the state of the art referenced above. The present invention provides a device for the electronic control of a low-emission log-burning fireplace comprising two combustion chambers positioned one above the other, separated by a support for solid fuel, with an outlet to the lower combustion chamber, a flue, an outlet in the upper combustion chamber to the flue with a flap that can close it, an outlet in the lower combustion chamber to the flue, a firebox door with a door lock / handle. The electronic control device comprises a firebox door contact switch, at least two temperature sensors, an electric motor arranged to actuate an actuator for selectively opening and closing the flap, and a control unit (controller) electrically connected to the at least two temperature sensors, the door contact switch, and the electric motor which actuates the actuator, preferably via transmission elements. The temperature in the flue downstream of the outlets of the respective combustion chambers is measured by a respective one of the temperature sensor in each case. The control unit is configured to detect the temperature change measured by the temperature sensors over time and the rate of the temperature change. An evaluation of the target / actual temperature is performed by the control device (controller) over parameterisable time periods and serves as an evaluation criterion for the combustion state of the solid fuel. A degree of the outgassing process (size and / or moisture content) of the solid fuel is determined by the control unit by measuring and evaluating the temperature rise and fall over time. A comparison of the target / actual temperature over time with comparative values stored in a program for combustion optimisation combustion is used as an adaptive system so that the respective properties of the solid fuel (moisture, type of wood, log size ...) are taken into account for optimising the combustion process and the necessity for reloading 2021332942   27 May 2026 with solid fuel is determined by the program and indicated by an optical signal transmitter that is clearly visible to the user. A solution has therefore been found that eliminates the disadvantages of the state of the art referred to above. An advantageous embodiment of the device has therefore proved to be where the opening or closing process of the actuator flap, initiated by the control unit, can take place almost without delay by using an electric drive (i.e., the electric motor). An additional advantageous embodiment of the device is where the electric drive (electric motor) is connected to the actuator flap, via the optional transmission elements or by direct means. Another possible embodiment is comprised in that the control process can be effected either by battery or mains operation. Signalling the operating states “Standard operation", “Reloading" or "Malfunction", each with its own colour code, via a single optical signal transmitter, leads to an additional advantageous embodiment. A supplementary embodiment is comprised in that a memory in the control unit that cannot be deleted by the user records the operating hours, operating states, and minimum and maximum temperatures for traceability purposes and can, if necessary, also be used to resolve warranty claims. Exemplary embodiments of the device according to the invention are described in more detail below using an exemplary embodiment as captured in the accompanying drawings. 2021332942   27 May 2026 Brief Description of the Drawings Fig. 1 schematically illustrates a device according to the invention mounted on a fireplace that uses the lower combustion principle in an optimised form, the exemplary arrangement shown with the actuator flap closed, (before commissioning); Fig. 2 schematically illustrates the device according to the invention mounted on the fireplace that uses the lower combustion principle in an optimised form, the exemplary arrangement shown with the actuator flap opened, (heating up phase); Fig. 3 schematically illustrates the device according to the invention mounted on the fireplace that uses the lower combustion principle in an optimised form, the exemplary arrangement shown with the actuator flap closed (control mode / combustion); Fig. 4 illustrates a program flow chart of the control process of the device according to the invention in the heating up phase; Fig. 5 illustrates the program flow chart of the control process of the device according to the invention in control mode; Fig. 6 illustrates the program flow chart of the control process of the device according to the invention in reloading mode; and Fig. 7 illustrates the program flow chart of the control process of the device according to the invention during burnout. Detailed Description of Embodiments of the Invention Figure 1 shows an exemplary construction including the device according to the invention, which is preferably intended for a low-emission log-burning fireplace (1) with two combustion chambers (2 and 3) positioned one above the other, using the lower combustion principle in an optimised form. The device according to the invention enables the combustion process of the solid fuel to be operated and monitored by regulating the combustion air supply. Operation by the user is restricted here only to the supply of solid fuel and its ignition. 2021332942   27 May 2026 In this example, the fireplace 1 comprises an upper combustion chamber 2 and a lower combustion chamber 3, separated by a tray for the solid fuel 19. There is an outlet 4 in this tray to the lower combustion chamber 3. An outlet 5 and 8 to the flue 7 are located respectively in the upper and lower combustion chamber 2 and 3. In the upper combustion chamber 2 there is a flap 5 acting as an actuator which can, if necessary, close the outlet 6 to the flue 7, as shown in Fig 1. The flap 5 is opened and closed 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 closed to the surrounding installation area by a firebox door 9 by means of a door lock (handle) 10. A door contact switch 14 is fitted in order to obtain 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 regulating the combustion air are positioned downstream of the respective outlets 6 and 8 of the two combustion chambers 2 and 3 for extracting the exhaust gas in the flue 7, and are electrically connected to the control unit 13. An optical signal transmitter 16, which is also connected to the control unit 13, is located at a point on the fireplace that can be easily seen by the operator, usefully in the front area as shown in Fig 1, as an indicator for requesting more solid fuel to be added, for indicating the operating status standard operation or for signalling a malfunction. The mode of operation of the low-emission log-burning fireplace 1 with two combustion chambers 2 and 3 positioned one above the other, using the lower combustion principle in an optimised form, is known to those skilled in the art. A more detailed description and explanation of the individual components has therefore not been provided in this exemplary embodiment. The description of the function of the device according to the invention relates to the individual phases or modes of the combustion process. The program flow chart shown in Figs.4, 5, 6 and 7 serves to illustrate the individual process steps denoted by reference characters. 2021332942   27 May 2026 Heating up phase (program flow chart Fig.4) The power supply required for the control unit 13 is provided by a battery-operated voltage source 15. Alternatively, a mains connection can serve as a 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, a reference run is performed by the electric motor 12 to locate the position of the actuator flap 5 and to check its function. The control unit 13 is now ready for operation in standby mode (process step 14A). When the firebox door 9 of the fireplace 1 is opened for the first time in the cold state, the control unit is actuated from the standby mode via the door contact switch 14 (process step 14B) and the actuator flap 5 is switched to the open position via the electric motor 12 and the transmission element 11 (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. In order to achieve the optimal switchover time for the heating up phase, for closing the actuator flap 5 and for ensuring reproducibility, the control process begins after a signal has been sent to the control unit 13 by the door contact switch 14 by closing the firebox door 9 by means of the door lock 10 (process step 14C), and after the temperature has risen above 50°C. At the same time as the control unit 13 is actuated, the temperature sensors 17 and 18 permanently measure the existing temperatures. After a temperature of 50°C has been reached, measured by the temperature sensor 17 downstream of the outlet 6 to the flue 7 (process step 17A), a waiting time tw1 (sec) is actuated 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 tw1 (sec) has elapsed and the flue gas temperature Ta (°C) set in the program has been exceeded (process step 17B), the actuator flap 5 is closed by means of the electric motor 12 and transmission element 11 (process step 5B) and the combustion gases are conducted through the outlet 4 into the lower combustion chamber 3, as shown in Fig. 3. After the switchover, the temperature may not yet be sufficient for the outgassing process Tau (°C) or the fireplace may not yet be optimally heated. As a result, the wood gas cannot be burned properly. This situation of a sharp drop in the temperature of the flue gas is detected by the temperature sensor 17 and the actuator flap 5 (process step 5A) is opened by a 2021332942   27 May 2026 control command from the control unit 13 (process step 17C) by means of the electric motor 12 and transmission element 11. The control unit 13 thereby actuates a waiting time tw2 (sec) again (process step 13B) and the exhaust gas temperature in the flue 7 is measured by the temperature sensor 17 until the preset temperature TSoll (°C) is reached again. This process, controlled by the control unit 13, is repeated until stable combustion has been established. The change to control mode now takes place. Control mode (program flow chart Fig.6) After stable combustion has been achieved, the undershooting of the value of a defined temperature corridor (Tau max tolerance), detected by the maximum temperature Tau max by the temperature sensor 18 (process step 18A) in the lower combustion chamber 3, activates after evaluation in the control unit 13 (process step 18B) a reloading signal (process step 18C) which is signalled by a visual display 16, which indicates to the operator the correct time for reloading (process step 16A). Because different quantities of solid fuel 20 are loaded each time, the width of the temperature corridor (TAU max - tolerance)) is fixed, but not the temperature level (TN). This is detected and set by the control unit 13 after each reloading. Reloading mode (program flow chart Fig.5) To add more solid fuel, the firebox door 9 is opened by actuating the door lock 10 and the door contact switch 14 is actuated, a signal is sent to the control unit 13 (process step 14D), which in turn controls the electric motor 12 and opens the actuator flap 5 via the transmission element 11 (process step 5A). After the door has been closed (process step 14C), a parameterised waiting time tw3 (sec) is actuated (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 tw3 (sec) has elapsed and the flue gas temperature Ta (°C) set in the program has been exceeded, the actuator flap 5 is closed via the actuators 11 and 12 which are already known (process step 5B) and the combustion gases are conducted through the outlet 4 into the lower combustion chamber 3. After the switchover, the temperature Tau (°C) may 2021332942   27 May 2026 not yet be sufficient for the outgassing process, e.g. because of excessively large logs or wood that is too wet etc. In this case, a sharp 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 actuator flap 5 (process step 5A) is opened. A parameterised waiting time tw4 (sec) is thereby actuated again (process step 13D) and the exhaust gas temperature in the flue 7 is measured by the temperature sensor 17 until a preset temperature Tsoll (°C) is reached again. This process, controlled by the control unit 13, is repeated until stable combustion has been established. Burnout (program flow chart Fig.7) When the exhaust gas temperature Ta (°C), measured by the temperature sensor 17, falls below a set value TA Soll (process step 17F) and no more solid fuel is added, the actuator flap 5 is opened (process step 5A). The remaining solid fuel 20 burns down and the fireplace cools down. If, in the process, the temperature measured by the temperature sensor 17 in the flue 7 falls below 50°C, the control unit 13 de-actuates and goes into standby mode. The device according to the invention is, of course, not limited to the exemplary embodiment shown. On the contrary, modifications and variations are possible without departing from the scope of the invention. 2021332942   27 May 2026 List of reference characters 1 Fireplace 2 Upper combustion chamber 3 Lower combustion chamber 4 Outlet (to the lower combustion chamber) 5 Actuator flap 6 Upper outlet (to the flue) 7 Flue 8 Lower outlet (to the flue) 9 Firebox door 10 Door lock (handle) 11   Transmission element (for the actuator flap 5)) 12 Electric motor 13 Control unit (controller) 14 Door contact switch 15 Voltage source 16 Optical signal transmitter 17 Temperature sensor (upper combustion chamber) 18 Temperature sensor (lower combustion chamber) 19 Support for solid fuel 20 Solid fuel List of reference characters for the process steps 5A Open flap 5 5B Close flap 5 13A Waiting time tw1 13B Waiting time tw2 13C Waiting time tw3 13D Waiting time tw4 14A Firebox door 4 has been opened from the standby mode. 2021332942   27 May 2026 14B Firebox door 4 has been opened. 14C Firebox door 4 has been closed. 14D Firebox door 4 has been opened from the control or reloading mode. 16A Optical signal transmitter 16 Indicator for adding more solid fuel 17A Temperature sensor 17 upper combustion chamber 2 with Ta >50°C 17B Temperature sensor 17 upper combustion chamber 2 with TA > TASoll in heating up phase 17C Temperature drop dTa in upper combustion chamber 2 in heating up phase too great 17D Temperature sensor 17 with TA > TASoll in reloading mode 17E   Temperature drop dTa in upper combustion chamber 2 in reloading mode too great 17F Temperature sensor 17 with Ta < 50°C in burnout mode 18A Temperature sensor 18 Determination of maximum temperature Tau in the lower combustion chamber 3 18B Saving of maximum temperature Tau in the lower combustion chamber 3 18C Temperature sensor 18 Pause until temperature Tau. falls below the tolerance limit.

Claims

1. An electronic closed-loop control device for fireplaces with a lower combustionsystem comprising two combustion chambers positioned one above the other, the two combustion chambers separated by a support for solid fuel with an outlet from the upper to the lower combustion chamber, a flue, a first outlet in an upper one of the two combustion chambers to the flue, with a flap arranged to selectively open and close the first outlet, a second outlet in a lower one of the two combustion chambers to the flue, a firebox door, and a door lock / handle for the firebox door, the control device comprising:- a door contact switch for detecting a state of the firebox door;- at least two temperature sensors, with a first of the temperature sensors located to measure temperature in the flue downstream of the first outlet of the upper combustion chamber and a second of the temperature sensors located to measure temperature in the flue downstream of the second outlet of the lower combustion chamber;- an electric motor connected to a flap actuator such as to selectively move the flap into positions between which the first outlet in the upper combustion chamber is closed and open; and- a control unit electrically connected to the at least two temperature sensors, the door contact switch, and the electric motor for controlling a positional state of the flap vis the associated first outlet, the control unit configured to:detect a respective temperature measured by the firstand second temperature sensors in the flue downstream of the first outlet and of the second outlet from the respective upper and lower combustion chambers,detect a temperature change over time in the temperatures measured by the first and second temperature sensors, detect a rate of the temperature change, perform an evaluation of a target / actual temperature over parameterisable time periods to serve as an evaluation criterion for a combustion state of the solid fuel being consumed,2021332942   27 May 2026determine a degree of an outgassing process of the solid fuel by recording and evaluating the temperature rise or fall over time,compare the target / actual temperature over time with comparative values stored in a program for combustion optimisation as an adaptive system such that a respective nature of the solid fuel, including one or more of moisture content, type of wood, log size, is also taken into account for optimising the combustion process,determine a need for reloading with solid fuel using the combustion optimisation program, anddisplaying the need via an optical signalling device that is clearly visible to a user.

2. The device for electronic control according to claim 1, wherein an opening or closing process of the flap actuator initiated by the control unit takes place almost without delay by using the electric motor.

3. The device for electronic control according claim 1 or 2, wherein the electric motor is connected to the actuator flap via transmission elements or directly.

4. The device for electronic control according to any one of the previous claims, wherein the control process is carried out either in battery or mains operation.

5. The device for electronic control according to any one of the previous claims, wherein the control unit is configured to signal operating states “Standard operation", “Reloading" or “Malfunction”, each with its own colour code, to the user through optical signalling device.

6. The device for electronic control according to any one of the previous claims, wherein the control unit is configured to detect operating hours, operating states and minimum and maximum temperatures and record these for traceability purposes onto a memory of the control unit that cannot be deleted by the user.

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