WO2008017177A1

WO2008017177A1 - Method for controlling a burner

Info

Publication number: WO2008017177A1
Application number: PCT/CH2007/000364
Authority: WO
Inventors: Josef Wüest
Original assignee: Toby Ag
Priority date: 2006-08-10
Filing date: 2007-07-24
Publication date: 2008-02-14
Also published as: EP2052187A1; EP2052187B1

Abstract

The invention relates to a method for controlling a modulating burner, the power of which can be varied between a minimum power Qmin and a rated power QN, wherein the power can be controlled proportionally to the difference between a boiler water temperature actual value TKist and a boiler water temperature setpoint value TKsoll. According to the invention, when the burner is started, rather than the current difference between the boiler water temperature actual value TKist and the boiler water temperature setpoint value TKsoll, the variable used to determine the burner power is a modified parameter that is modified as a function of time in such a way that after a certain time the difference between the boiler water temperature actual value TKist and the boiler water temperature setpoint value TKsoll is the active variable determining the current burner power in each instance. This parameter is a corrected boiler water temperature setpoint value TKsollkorr which acts on the effective difference used to control the burner power. The invention results in longer burner run times.

Description

Method for controlling a burner

The invention relates to a method for controlling a burner according to the preamble of claim 1.

Such burners are advantageously used in boilers of residential buildings, with the combination burner / boiler heat for the heating of rooms and usually also for the preparation of domestic hot water is generated. Such boilers are advantageously designed as condensing boiler, through the design of which the exhaust gas is condensed, so that the heat of vaporization is used profitably.

Because at each start of a burner initially increased pollutant emissions occur and energy must be expended to pre-ventilate the combustion chamber, there is a long time the need to reduce the number of turn-on and to ensure the longest possible burner life.

State of the art

In order to achieve burner times as long as possible, it has therefore been provided according to DE-C3-25 49 561 to change the switching differential of the thermostat in function of the prevailing outside temperature. According to DE-C2-39 32 327 is also provided to make the switching differential also dependent on the setting of the heating curve for the heating circuit.

From DE-Cl- 34 26 937 a solution is known in which a hysteresis switch is provided to which an integrator is vorgschaltet. The difference between a reference temperature and a measurement temperature is integrated in the integrator.

EP-A1-0 909 922 discloses a gas-fired burner in which the ratio of gas to air is regulated by means of a microcontroller.

To regulate the power of a modulating burner is usually the difference between the boiler water temperature and the actual value

Used boiler water temperature setpoint, wherein the boiler water temperature setpoint for the heating operation is derived from the current outdoor temperature, as is known for example from DE-C3-25 49 561. If the difference between actual and setpoint is large, so the burner is operated at high power. If the difference between actual and setpoint is small, the burner is operated at low power. At the moment of turning on the burner, the difference has its maximum value. The burner runs with great power. If the burner generates heat, the boiler water is heated. As a result, the boiler water temperature actual value increases continuously. Thus, the difference between the actual and setpoint continuously decreases, with the result that the performance of the burner is further reduced.

It has been shown that this mode of operation is not optimal, because quite often very short burner runtimes occur.

Object of the invention

The invention has for its object to prevent these short burner life.

Description of the invention

The above object is achieved by the features of claim 1. Advantageous developments emerge from the dependent claims.

The use of the difference between the boiler water temperature actual value and the boiler water temperature setpoint as a determinant for the respective current burner output does not seem to be sufficient. According to the invention, the determination variable is additionally varied by initially not using the actual difference between the boiler water temperature actual value and the boiler water temperature setpoint as the determination variable for the current burner output at the burner start, but rather a modified parameter, and then this parameter is time-dependent is modified so that after a certain time, the difference between the actual boiler water temperature and the boiler water temperature setpoint becomes effective as a determinant for the current burner performance.

If the current difference between the boiler water temperature actual value and the boiler water temperature setpoint is used as the nominal value for the current burner output at burner start, the burner starts with a high output. Regardless of the actual difference between the Boiler water temperature actual value and the boiler water temperature setpoint, the burner's operating time also depends on the actual energy requirement during heat generation. The difference between the boiler water temperature actual value and the boiler water temperature setpoint characterizes the actual heat requirement only insufficiently, because it also depends on which part of the produced heat is immediately removed from the heating circuit. If the heating circuit takes away a lot of heat, the boiler water temperature rises slowly when the burner is running. On the other hand, if the heating circuit absorbs little heat, then the boiler water temperature rises very quickly while the burner is running. This then leads to a quick shutdown of the burner, so a short burner runtime.

In order to avoid resulting in this way short burner run times, is now provided according to the invention that a corrected control difference Dkorr (Brstart) is used as the starting value for the control of the burner power, which is formed from a corrected boiler water temperature setpoint Tκsoiikorr (Brstart) at the moment of burner start and the current boiler water temperature actual value Tκact (BrStart) at the moment of burner start. Advantageously, the value of the boiler water temperature setpoint Tκ _s oiikorr (Brstart) is set lower than the real current value of the boiler water temperature setpoint Tκ _so that the corrected control difference Dkorτ (BrStart) is smaller than the real control deviation D _rea i, from the current boiler water temperature setpoint Tκ _S0 n and the current

Boiler water temperature actual value Tκi _{St is} formed, the burner starts with lower power.

Advantageously, the boiler water temperature setpoint Tκ _So iikorr at the burner start is equal to that boiler water temperature actual value Tκist (Brstart) _> prevails at the moment of burner start. The boiler water temperature setpoint Tκ _So ii _korr at the moment of burner start is referred to as kettle water temperature setpoint Tκ _S oiikorr (Brstart).

Thus, the corrected control deviation Dkorr (Brstart) automatically becomes zero at the moment of burner start. At the same time, if the controller is a PI controller, the integral component is set to zero. As a result, the burner starts in any case with a minimum power Q _m corresponding to its design; _n . This minimum power Q _ra j _n is considerably smaller than a nominal power QN of the burner. Modulating the burner thus takes place in the Limits Q _m j _n and QN. The ratio QN TO Q _m j _n is commonly referred to as the degree of modulation. A modulation factor of 3 means that the minimum power Q _m j _{n is} one third of the rated power Q _N.

Subsequently, the boiler water temperature setpoint Tκ is changed _so ii _korr time-dependent and indeed so that it approaches the boiler water temperature setpoint TK _SO II and finally reached this.

This advantageously takes place in such a way that the boiler water temperature setpoint Tksoiikorr is corrected according to a formula T _Ks oiikorr = T _K soiikorr (Brstart) + 1 * k, where t is the time in minutes and k is a factor representing a change constant in degrees indicates per minute. Then, as soon as the boiler water temperature setpoint Tκ _S oiikorr is equal to the boiler water temperature setpoint Tκsoii (BrStart) at burner start, the phase of the setpoint correction is completed and the control is now based on the current boiler water temperature setpoint TK _SO II and the current boiler water temperature setpoint Tκi _s t-

Because at any time, the control difference D _w ; _rk equals the difference between the actual and setpoint values, the control difference changes with the change of the actual and setpoint values. Thus, the control difference D _W j _rk starts with the value zero and is then varied.

The control difference D _w ; Thus, _rk changes automatically according to the respective values of boiler water temperature setpoint Tκ _S oiikorr and boiler water temperature setpoint Tκi _st - This controls the burner output.

The boiler water temperature actual value Tκi _St is subject to continuous changes. After the burner has heated the combustion chamber, then rises in the sequence and the actual boiler water temperature Tκi _S , whose current size is taken into account in the scheme.

Advantageously, the factor k in heating operation is about 2 degrees per minute, in operation for charging a hot water tank about 10 degrees per minute.

In an advantageous manner, the factor k can be variable in heating mode by adopting variable values as a function of an outside temperature TA. An example of this Type is the variation of the factor k according to a formula k = B + f * (TR _SO H - TA), where B is a base value, f is a multiplier and T _RSO I _{I is} the setpoint of the room temperature.

This is advantageous in particular in the known night-day switching. Here it is achieved that the room reaches the so-called comfort temperature faster after the night setback.

The base value B may be, for example, 1, the multiplier f 0.05. With these values, the factor k at -20 degrees outside temperature TA has a value of 3, at 0 degrees outside temperature TA a value of 2 and at 10 degrees outside temperature T _A a value of 1.5. Since the actual heat demand is related to the outdoor temperature T _A , so a longer burner run time is achieved even when the heat demand is small.

Also in the case of boilers, the heat demand can be different. A varying heat requirement due to the set boiler water temperature setpoint TK _SO II for the boiler load is taken into account anyway. But it also depends on the size of the hot water tank. Therefore, it may be advantageous to provide a value of the factor k that deviates from 10 degrees per minute for the boiler load, namely a smaller value than 10 for a smaller boiler.

Hereinafter, the essence of the invention will be explained with reference to the drawing.

1 shows a diagram of the time profile of the boiler water temperature setpoint T _KSO II and

Fig. 2 shows such a diagram in the event that during the

Correction phase of the boiler water temperature setpoint TK _SO II changes.

The diagram of FIG. 1 shows the time t in minutes on the abscissa axis and the temperature on the ordinate axis. Shown on the left is the boiler water temperature setpoint T _KSO II, as specified, for example, by the weather control of the heating system.

As soon as in a known manner at the time tl a command BURNER ON is given, the currently prevailing boiler water temperature setpoint T _KSO II as boiler water temperature setpoint Tκ _So ii (Brstart) and the currently prevailing Boiler water temperature actual value Tκi _S t is recorded as actual boiler water temperature Tκi _st ( _Br s _tar t).

Shown is the course of a corrected boiler water temperature setpoint Tκ _so ii _corr with solid line, which is varied time-dependent according to the aforementioned formula.

The curve of the boiler water temperature actual value Tκi _{St is also shown} . Before switching on the burner, it will decrease until the switch-on command for the burner is issued. However, after switching on the burner, this value does not increase immediately because it takes a while for the heat produced by the burner to pass to the boiler water.

At time t2 according to FIG. 1, the temporal variation of the boiler water temperature setpoint T _KSO II is terminated, and thus also the consequent temporal variation of the effective control difference D _W _{rk rk} . Now the usual control starts due to the measured actual control deviation.

It should also be noted that the time-limited variation by the corrected boiler water temperature setpoint Ttc _so iiko _π - is effective only in the context of power control, but does not affect the switching behavior with respect to turning off the burner. Here, the true boiler water temperature setpoint TK _SO II continues to be effective. This prevents the burner from switching off unnecessarily as long as the controller is not yet in its normal control mode with the formation of the control difference between the true boiler water temperature setpoint T _KSO II and the boiler water temperature actual value Tκi _s t.

In the example of FIG. 1, the assumption is made that the boiler water temperature setpoint Tκ _S0 n does not change in the period from t1 to t2. This is also true in most cases, because the period tl to t2 is not large and the boiler water temperature setpoint T _KSO II does not change rapidly especially if, as already mentioned, it is a function of the outside temperature TA, which is also usually only changes slowly.

However, there are cases in which the boiler water temperature setpoint TK _SO II changes during the period t1 to t2. He can go up, for example, when in a heating system in the morning of nocturnal lowering to the morning rapid heating is switched. Most, however, turning on the burner is because of the increase of the boiler water setpoint Tκ _so ii, SO that the setpoint step occurs before turning on the burner. However, it may happen that the boiler water temperature setpoint TK _SO II changes during the period tl to t2.

Conversely, it may also happen that in the period tl to t2, the boiler water temperature setpoint T _KSO II is smaller. There are also different causes for this.

In Fig. 2, these two cases are shown. This FIG. 2 largely corresponds to FIG. 1, so that the explanations for FIG. 1 also apply to FIG. 2.

On the right in FIG. 2, in addition to FIG. 1, a higher boiler water temperature setpoint ik _is shown, which occurs sometime after the time t1, and a lower boiler water temperature setpoint Tjc _{is also} effective, which also takes effect after the time t1.

It is advantageous in such cases that for detecting the end of the correction phase for the boiler water temperature setpoint T _KSO II according to the formula given not the boiler water temperature setpoint Tκ _So ii (Brs _tart ) is used at the burner start, as shown in FIG is shown, but that the actual boiler water temperature setpoint Tκ _S0 π, ie the boiler water temperature setpoint Tκ _so ii _neuA in one case and the boiler water temperature setpoint Tκ _so ii _new B in the other case, determines the end of the correction phase. Thus, in the case of the higher boiler water temperature setpoint Tksoiineu _A , the end of the correction phase shifts to the later time t2A and in the case of the lower boiler water temperature setpoint Tκ _So ii _new B to earlier time t2B. In this way, caused by set point jumps discontinuities in the operation of the burner can be avoided.

In the case of FIG. 1, the end of the correction phase determines the boiler water temperature setpoint Tκ _S oii (Brsta _rt ) at the burner start, while in the case of FIG. 2 the comparison value is a boiler water temperature setpoint Tκsoiineu which has been changed after the burner start. The invention achieves a greater burner running time. Very short burner run times are avoided. This reduces the number of burner starts.

Claims

claims

1. A method for controlling a modulating burner whose power is variable between a minimum power Q _m j _n and a rated power Q _N , wherein the power is proportional to the difference between a boiler water temperature value Tκi _St and a boiler water temperature setpoint Tκ _So ii controllable characterized in that at the burner start instead of the actual difference between the

Boiler water temperature value Tκi _S t and the boiler water temperature setpoint Tκ _S0 n a modified parameter is used, which is subsequently modified in function of time so as a determinant for the burner output, that after some time the difference between the boiler water temperature value _st Tκi and the current

Boiler water temperature setpoint Tκ _S0 n is effective as a determinant for the current burner performance.

2. The method according to claim 1, characterized in that the parameter is a corrected boiler water temperature setpoint Tκs _o iikorr, which is smaller than the true boiler water temperature setpoint Tκ _so ii at burner start and then increases until it is equal to the true boiler water temperature Setpoint T _KSO II-

3. Method according to. Claim 2, characterized in that the

Boiler water temperature setpoint Ik _so ii _koπ - when _starting the burner is the same as a boiler water temperature actual value Tκi _st (Br s _ta rt) measured at burner start

4. The method according to claim 3, characterized in that the

Boiler water temperature setpoint Tκsoiikorr is then varied according to a formula Tκsoiikorr = T _K soiikorr (Brstart) + 1 * k, where T _Ks oiikorr (BrStart) the boiler water temperature setpoint Tjc _so iik _o π- i∞ moment of the burner start, t is the time in Minutes and k is a factor indicating a change constant in degrees per minute, and that the variation of the boiler water temperature setpoint Iksoiikorr ends when the boiler water temperature setpoint Tjc is _as equal to iikorr as a comparison value.

5. The method according to claim 4, characterized in that the comparison value of the boiler water temperature setpoint Tκsoii (Brstart) is at the burner start.

6. The method according to claim 4, characterized in that the comparison value is a changed after the burner start boiler water temperature setpoint Tκ _so ii _new .

7. The method according to claim 4, characterized in that the factor k in the heating operation has a size of about 2 degrees per minute.

8. The method according to claim 4, characterized in that the factor k in the loading mode for a service water storage has a size of about 10 degrees per minute.

9. The method according to spoke 4, characterized in that the factor k is varied according to a formula k = B + f * (T _RSO II - TA), where B is a base value, f is a multiplier and T _RSO II is the setpoint of Room temperature is.

10. The method according to spoke 7, characterized in that the base value B has the value 1 and that the multiplier f has the value 0.05.