DE4221715A1 - Controlling electrode boiler with on=off switched heater - correcting calculated switching temps. in accordance with rate of change of actual water temp. - Google Patents

Abstract

The desired water temp. is determined by a set-point device (4) with a stored characteristic of e.g. water temp. against ambient temp. A calculator (5) works out the temps. (Tein, Taus) at which the heater is switched on and off. These temps. are corrected (6) by the output from a differentiator (7) of actual temp. (Tist), which latter is compared with the corrected switching temp. signals from deviation limiters (8A, 8B) in a two-point regulator (9). ADVANTAGE - Oscillation of water temp. is reduced and heater operating time optimised without load-dependent hysteresis changes in twopoint regulator.

Description

The invention relates to a method for controlling a Boiler with a non-modulating burner and on one Device for performing the method according to the Ober Concept of claims 1, 7, 9 and 10.

A method of the type mentioned in the preamble of claim 1 is known from DE-PS 25 49 562. The switch difference of a two-point controller depending on the respective performance requirement changed so that, based on the average boiler water temperature, both the switch-on and the switch-off point can also be changed. With great performance requirement the switching difference is small and with falling Power requirement, the switching differential is increased. As the size determining the performance requirement is the outside called temperature. The boiler water temperature setpoint is also depending on the outside temperature.

Typical for heating systems with a two-point controller for the Boiler is that the boiler water temperature overshoots. When the switch-off point is reached, the two-point controller switches the burner immediately, but the boiler water rises temperature due to the higher temperature in the combustion chamber and delayed heat transfer from the combustion chamber to the water chamber further on. As a result, when the switch-on point is reached the execution of the burner commissioning program (Pre-rinsing the combustion chamber, preheating the heating oil etc.) certain time until the burner really generates heat. While during this time the boiler water temperature continues to drop. As a result this is the actual fluctuation of the boiler water temperature considerably higher than the set one Switching differential.

The invention is based, the overshoot reduce the boiler water temperature.  

The stated object is achieved by the features of Claims 1 and 7 solved. Devices for carrying out the Processes are characterized in claims 9 and 10. Advantageous configurations result from the dependent ones Claims.

An exemplary embodiment of the invention is described below the drawing explained in more detail.

It shows

Fig. 1 is a diagram of a regulator,

Fig. 2 is a diagram of a heating system,

Fig. 3 is a diagram with typical temperature curves in a boiler and

Fig. 4 is a diagram with time curves of the boiler water temperature, the switch-on and the switch-off point.

In FIG. 1, 1 denotes a controller, whose output 2, an unillustrated burner for a boiler of a heating system is connected. An automatic burner control is normally connected between controller 1 and the burner, which controls the burner's commissioning process after the release of controller 1 and then monitors the operation. The controller 1 has an input 3 to which a boiler temperature sensor (not shown) is connected.

The controller 1 has a setpoint generator 4 . The setpoint of the boiler water temperature is determined by this. In this setpoint generator 4 may be a known Heizkurvengeber that generates a dependent for example on the outside temperature or of the desired value of the heating flow temperature setpoint of the boiler water temperature T _target, and outputting at an output of the setpoint generator. 4

The output of the setpoint generator 4 is connected to an input of a computing element 5 . The computing element 5 is calculated from the boiler water temperature setpoint T _set and an embedded and computing element 5 can be input in this, during operation of the controller 1 is not changeable size for switching differential SD in known manner, a switch-T _and a turn point T _of the Burner. These two values are available at separate outputs of the computing element 5 .

The outputs of the arithmetic element 5 are connected to inputs of a correction element 6 . This correction element 6 has a third input which is connected to an output of a differentiating element 7 .

The input of the differentiator 7 is connected to the input 3 of the controller 1 so that the actual boiler water temperature T _actual is present at its input. The differentiator 7 differentiates the actual boiler water temperature T _actual , thus forms the gradient of the boiler water temperature T _actual , which can also be referred to as the rate of change of the boiler water temperature T _actual . This gradient is positive during the heating up of the boiler and negative during the cooling down of the boiler.

The correction element 6 calculates _a as described later on from the switch-T and the switch-off point T _and taking into account the gradient of the boiler water temperature T _is a corrected switch-T _einkorr and _auskorr a corrected off point T, and provides these values to two outputs to jointing.

The outputs of the correction element 6 are connected to a first input of two limiting elements 8 A and 8 B, respectively. At a respective second input of the limiting members 8 A and 8 B of the originating from the reference value transmitter 4 boiler water temperature set value T is on _target. The function of the limiting elements 8 A and 8 B will be described later.

Each limiting element 8 A or 8 B has an output. Both outputs are connected to two inputs of a two-point switch 9 . The two-point switch 9 has a third input, which is connected to the input 3 of the controller 1 , so that the current actual boiler water temperature T _Ist is present at this input.

The two-point switch 9 compares the boiler water temperature actual value T _Ist with the values at the two other inputs for the calculated switch-on point and the calculated switch-off point and, based on the known function of such two-point switch, forms an actuating signal for the burner which only has the two values "on""and" Off "can assume. This control signal is transferred from the output of the two-point switch 9 to the output 2 of the controller 1 and from there via a burner control, not shown, to the burner, also not shown.

In FIG. 2, a heating system is shown, consisting of a boiler 21 having a boiler flow line in a known manner 22 and a boiler return line 23, a via a heating flow line 24 and a heating return line 25 connected load group 26, and an inserted between the boiler supply pipe 22 and heating flow line 24 Mixing valve 27 , which is connected by means of a bypass line 28 to the boiler return line 23 and heating return line 25 . For example, in the heating flow line 24 , a circulation pump 29 is installed. The mixing valve 27 is controlled by a controller in a known manner so that the actual temperature of the heating flow corresponds to a predetermined value, for example, by a weather and / or room management.

In Fig. 3 the time course of the boiler water temperature for three different load conditions of the boiler is shown. Curve M shows the temperature curve for medium boiler loads, curve K the curve for small boiler loads and curve G the curve for large boiler loads. The starting point of all three curves that the _switch-ta was once previously reached, so that the burner is turned on and produces heat.

According to curve M, the boiler water temperature rises moderately quickly with medium boiler load. Upon reaching the OFF point T _from the burner is switched off, however, is carried out from the above-mentioned reasons, a further increase in temperature before the boiler water temperature due to the present heat requirement middle back again. The boiler water temperature then drops moderately quickly. On reaching the activation point T _a, the burner is switched on again, however, the boiler water temperature from the above-mentioned reasons initially drops further, before it rises after the onset of heat production by the burner again. The overshoot of the boiler water temperature after switching off and after switching on the burner is relatively small at medium boiler load and is not a problem.

According to curve K, the boiler water temperature rises significantly faster with a small boiler load than with a medium boiler load. When the switch-off point T _out is reached, the burner is switched off, but for the reasons mentioned at the outset there is a further rapid temperature rise before the boiler water temperature drops again owing to the smaller heat requirement present. The overshoot of the boiler water temperature is considerably higher. The boiler water temperature then drops very slowly. Upon reaching the turn point T _a, the burner is switched on again, however, the boiler water temperature from the above-mentioned reasons initially drops further, before it rises after the onset of heat production by the burner again. The overshoot of the boiler water temperature after switching off is slightly less than with a medium boiler load.

According to curve G, the boiler water temperature rises considerably more slowly with a large boiler load than with a medium boiler load. Upon reaching the switch-off point T _from the burner is switched off, however, is carried out from the above-mentioned reasons, a further increase in temperature more slowly, before the boiler water temperature due to the present average heat back again needs. The overshoot of the boiler water temperature is considerably lower. The boiler water temperature then drops very quickly. Upon reaching the turn point T _a, the burner is turned on again, however, the boiler water temperature falls from the aforementioned reasons initially continued quickly, before production of the onset of heat rises again by the burner. The overshoot of the boiler water temperature after switching off is significantly greater than with a medium boiler load.

The strong overshoot of the boiler water temperature after the Switch off when the boiler load is low and after switching on with a large boiler load is due to the invention Procedure prevented.

The essence of the method according to the invention is that the rate of change of the boiler water temperature is detected and that, depending on this rate of change, the switch-on and switch-off points are varied in accordance with the size of the rate of change. The switch-on point means the temperature T _{out of} the boiler water below which the burner is switched on. The actual switching on of the burner is delayed in a known manner by an automatic burner control. The switch-off point means the temperature T _{out of} the boiler water below which the burner is switched off immediately.

To regulate the burner a switch-T is _a given and a switch-off _of T. In practice, this happens, for example, by setting these switching points on a controller. However, the setting of the switching points can also be effected, for example, that the _switch-T, and to a differential SD are set and the controller calculates the switch-off point T _from a sum of switch-on and switch T _{is a} difference SD. In a similar way, a target value T _{target can be} specified and the switching points according to the formulas, taking into account the switching difference SD

T _a = T _target - SD / 2

and

T _off = T _target + SD / 2

be calculated. This predetermined or calculated switching points become faster according to the size of the change speed varies. The variation of the switching points can either continuously or in stages.

The variation is made so advantageous in the switch-on point for T _a and T off point _of a term

is added, where K is a constant factor adapted to the design of a boiler. From the fact that _both is added as well as to switch off T _from the same term to the switch-T, it follows that the distance between the turn point T _and switch-off point T remains unchanged _from any at all times and is determined by the size of the switching difference SD.

This can also be seen from FIG. 4, in which the time course of the boiler water temperature T _{actual is indicated for} the corrected switch-on point T _einkorr and the corrected switch-off point T _auskorr for a specific boiler _load . In accordance with the above formulas, the corrected turn-T are _einkorr and the corrected off point T _auskorr at rising boiler water temperature T _is lower than the uncorrected turn point T _on and the uncorrected off point _T, and on the falling boiler water temperature T _is higher. The magnitude of the differences between the corrected and uncorrected _einkorr switch-T switch on one hand and _a T corrected T _auskorr switch-off and switch-off of an uncorrected T _from the other are determined by the size of the change speed of the boiler water temperature T _Is. So of the boiler in Fig. 4 during the heating of the differences between the corrected turn-T _einkorr and uncorrected switch-T _a on the one hand and corrected OFF point T _auskorr and uncorrected off point T _of the other part is greater than during the cooling phase, since the rate of change of the boiler water temperature T _is in the example shown when heating is larger than when cooling.

In the moment when the boiler water temperature T _is not rising or falling - characterizes _Is by briefly horizontal course of the curve for boiler water temperature T - agree corrected switch-T _einkorr and uncorrected switch-T _just as consistent as corrected OFF point T _auskorr and uncorrected off point T _off It is advantageous if the calculation of the corrected switch-on point T _{einkorr is} suppressed when the burner is switched on. It is also advantageous if the calculation of the corrected switch-off point T _{auskorr is} suppressed when the burner is switched off. With these two measures, time can be saved in the program sequence, for example if the method is implemented by a digital controller.

It is also advantageous if the corrected switch-on point T _{einkorr is compared} with the setpoint of the boiler water temperature T _Soll and, if the corrected switch-on point T _{einkorr is} greater than the setpoint of the boiler water temperature T _Soll , the corrected switch-on point T _{einkorr is} equal to the setpoint of boiler water temperature T _target is set. It is also advantageous if the corrected switch-off point T _{auskorr is compared} with the setpoint of the boiler water temperature T _Soll and, if the corrected switch-off point T _{auskorr is} smaller than the setpoint of the boiler water temperature T _Soll , the corrected switch-off point T _{auskorr is} equal to the setpoint the boiler water temperature T _target is set. With these two measures it is achieved that the burner runtime is optimized in extreme load situations and the boiler water temperature is not too far from the specified setpoint, which could have negative effects on a downstream mixer control.

From the previously described formulas and also from FIG. 4, it can be derived directly that the simultaneous shifting of the switch-on and switch-off points by the same amount is completely identical to the shift of the setpoint. According to the invention it is therefore also possible that in dependence of the rate of change of the boiler water temperature actual value T _is the boiler water temperature setpoint T _set in accordance with the magnitude of the change speed is varied and the switch-T _and the OFF point T _and taking into account a constant switching difference SD from this varied set boiler water temperature value T _set .

It is advantageous value T _desired is if the variation of switch-on and switch-off _a T T _of or boiler water temperature set only carried out when the magnitude of the rate of change of the boiler water temperature value T _Is exceeds a certain threshold.

The inventive device for performing the method works in the manner described below.

The function of the controller 1 according to FIG. 1 is described below. The setpoint generator 4 sets the boiler water temperature setpoint T _set, from which the computing element 5, taking account of the value contained in it for the switching SD difference _a the switch-T and the switch-off T calculated _from in accordance with the above formulas.

The differentiator 7 determines the rate of change of the boiler water temperature T _{actual from} the changes over time in the _actual boiler water temperature T _actual . Instead of a differential quotient, a difference quotient with a different time base can also be determined. If necessary, a subsequent filtering can also be advantageous.

The correction element 6 then corrects the turn point T _and the switch-off point T in accordance with the size of the rate of change of the boiler water temperature is _of value T _is, for example, by adding the term

The correction _element 6 thus forms the corrected switch-on point T _eiskorr and the switch-off point T _auskorr . In contrast to FIG. 1, these values can be passed on directly to the two-point switch 9 . However, it is advantageous to limit the variation of these values, as has already been stated.

The limiting _element 8 A compares the switch-off point T _auskorr with the setpoint T _Soll and sets the corrected switch-off point T _auskorr equal to the setpoint of the boiler water temperature T _Soll , if the corrected switch-off point T _{auskorr is} less than the setpoint of the boiler water temperature T _Soll . The limiting element 8 A thus carries out a limitation of the variation which corresponds to a minimum limitation.

Accordingly, the limiter 8 B compares the switch-on point T _einkorr with the target value T _Soll and sets the corrected switch-on point T _einkorr equal to the target value of the boiler water temperature T _Soll if the corrected switch-on point T _{einkorr is} greater than the target value of the boiler water temperature T _Soll . The limiting element 8 B thus carries out a limitation of the variation which corresponds to a maximum limitation.

The possibly limited switching points are evaluated by the two-point switch 9 together with the boiler water temperature actual value T _Ist and converted into an actuating signal for the burner in accordance with the known working method of such a two-point switch 9 .

In a further embodiment of such a controller 1 , the setpoint of the setpoint generator 4 can also be processed directly by a correction element 6 . Only the varied target value is then supplied to the computing element 5, which varied from the target value and the differential SD the corrected turn point T _einkorr and forms the switch-off corrected T _auskorr. Further processing is carried out as previously described.

Below is an example of which Perhaps the procedure described above and this Method implementing device in real heating systems acts particularly advantageous.

It is assumed that the heating system according to FIG. 2 has reached a steady state. For example, the nightly lowering of the heating controller is active. Now you switch to comfort mode. The setpoint for the heating flow is increased, with the result that the mixing valve 27 opens the passage from the boiler flow line 22 to the heating flow line 24 and shuts off the bypass line 28 . Characterized now arrives in accordance with the delivery rate of the circulation pump 29 cooled water from the heating return line 25 through the boiler return line 23 in the heating boiler 21 with the result that the temperature of the boiler water falls quickly. The strong negative temperature gradient of the boiler water now causes the controller 1 to the power on _a point T lifting.

In general, it can be stated that the mixing valve 27 causes the flow through the boiler 21 to vary depending on the position of the mixing valve 27 , although the delivery quantity of the circulation pump 29 remains constant. Any change in the flow rate in the boiler 21 causes a change in the temperature gradient in the boiler 21 regardless of whether the burner is currently on or off. That caused by the function of the mixing valve 27 change in the temperature gradient in the boiler 21 is now being implemented by the controller 1 in the manner previously described in a change of switch T _on and switch-off _from T.

Even if thermostatic radiator valves are used in the consumer group 26 , the circulating quantity of the heating water can change. Also in this case, the change caused by the temperature gradient in the boiler 21 in a change of switch T is _one or implemented OFF point t _off.

The method according to the invention makes it possible to dispense with the rigid change in the switching difference of the two-point controller as a function of the power requirement. It is thus achieved that the actual mean value of the boiler water temperature actual value T _actual largely corresponds to the boiler water temperature set point T _target specified by the setpoint generator 4 . At the same time, the burner runtime is optimized.

Claims (10)

1. A method for controlling a boiler with a non-modulating burner, in which the switch-on point and / or the switch-off point is varied depending on the power requirement, characterized in that the rate of change of the boiler water temperature (T _actual ) is detected and that depending on this rate of change of switch-on point (T _a) can be varied and the switch off point (T _off) in accordance with the size of the rate of change. 2. The method according to claim 1, characterized in that a corrected switch-on (T _einkorr) and a corrected switch off point (T _auskorr) are calculated by point (T _a) for turn-on and switch-off point for the (T _aus) is a term is added, where K is a constant factor adapted to the design of the boiler and T _{Actual is} the actual value of the boiler water temperature. 3. The method according to claim 2, characterized in that the calculation of the corrected switch-on point (T _einkorr ) is suppressed when the burner is switched on. 4. The method according to claim 2, characterized in that the calculation of the corrected switch-off point (T _auskorr ) is suppressed when the burner is switched off. 5. The method according to any one of claims 2 to 4, characterized in that the corrected switch-on point (T _einkorr ) is compared with the setpoint of the boiler water temperature (T _Soll ) and that if the corrected switch-on point (T _einkorr ) is greater than the setpoint the boiler water temperature (T _Soll ), the corrected switch-on point (T _einkorr ) is set equal to the setpoint of the boiler water temperature (T _Soll ). 6. The method according to any one of claims 2 to 4, characterized in that the corrected switch-off point (T _auskorr ) is compared with the setpoint of the boiler water temperature (T _Soll ) and that if the corrected switch-off point (T _auskorr ) is less than the setpoint the boiler water temperature (T _target ) the corrected switch-off point (T _offset ) is set equal to the target value of the boiler water temperature (T _target ). 7. A method for controlling a boiler with a non-modulating burner, in which the setpoint of the boiler water temperature is varied depending on the power requirement, characterized in that the rate of change of the boiler water temperature (T _actual ) is detected and that, depending on this rate of change, the boiler water be temperature setpoint (T _set) is varied according to the size of the rate of change and the turn point (T _a) and the switch off point (T _aus), taking into account a constant switching difference (SD) from that varied boiler water temperature set value (T _Soll) formed . 8. The method according to any one of claims 1 to 7, characterized in that the variation _(A T) of switch-on and switch-off (T _off) or boiler water temperature set is value (T _Soll) only carried out when the magnitude of the rate of change a exceeds a certain threshold. 9. A device for carrying out the method according to any one of claims 1 to 6 having a reference value transmitter (4), a rake member (5) _(a T) for calculating the switch-on and switch-off (T _off) from the boiler water temperature setpoint (T _Should ) and the switching difference (SD) and a two-point switch ( 9 ), characterized in that a differentiating member ( 7 ) is present, which determines the rate of change from the time profile of the _actual boiler water temperature (T _actual ), and that calculating means (5) member is a connected to the output of the differentiating element (7), correction (6) is connected, consisting of the switch-on point (T _a) and the switch off point (T _off) and the rate of change of the boiler water temperature actual value (T _actual) corrected a Switch-on point (T _einkorr ) and a corrected switch-off point (T _auskorr ) calculated, and that these corrected switching points (T _einkorr , T _auskorr ) on inputs d there two-point switch ( 9 ) are performed. 10. A device for carrying out the method according to claim 7 with a reference value transmitter (4), a computing element (5) for calculating _(a T) of the switch-on and the OFF point (T _off) from the boiler water temperature set value (T _Soll) and the differential (SD) and a two-point switch ( 9 ), characterized in that a differentiating element ( 7 ) is present which determines the rate of change of the _actual boiler water temperature (T _actual ) over time, and that the setpoint generator ( 4 ) has an output the differentiating element ( 7 ) connected correction element ( 6 ) is connected downstream, which calculates a corrected boiler water temperature setpoint from the boiler water temperature setpoint (T _setpoint ) and the rate of change of the actual boiler water temperature value (T _actual ), and that this corrected setpoint is via a Computing element ( 5 ) is guided to inputs of the two-point switch ( 9 ).