WO2008014626A1

WO2008014626A1 - Method for the regulation of a burner

Info

Publication number: WO2008014626A1
Application number: PCT/CH2007/000363
Authority: WO
Inventors: Josef Wüest
Original assignee: Toby Ag
Priority date: 2006-08-02
Filing date: 2007-07-24
Publication date: 2008-02-07
Also published as: EP2049839B1; EP2049839A1

Abstract

The invention relates to a method for regulating a modulated burner having an output that is variable between a minimal output Qmin and a rated output QN, wherein the output is regulated to be proportional to the difference between the boiler water actual temperature value TKact, and the boiler water set temperature value TKset. According to the invention, there is a power output limit that is derived from the boiler water set temperature value TKset. In this way the burner remains in operation for longer with a low heating requirement, and hence the number of burner starts will be reduced.

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.

To regulate the power of a modulating burner usually the difference between the boiler water temperature and the boiler water temperature setpoint value is used, the boiler water temperature setpoint for the heating operation is derived from the current outside temperature, as known for example from DE-C3-25 49 561 is. If the difference between actual and setpoint is large, 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 is running great performance. 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.

EP-A1-0 781 965 discloses a gas-heated process water heating system and a method for controlling the process water temperature in such a system. This is about reacting to a fluctuating hot water tapping quantity so that the outlet temperature remains as constant as possible. Therefore, there is a means for measuring the flow of the extracted hot water. It is not apparent that a power limitation is provided for the burner, which could be prevented by the short burner run times.

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 limiting the current burner output by means of an additional parameter.

The difference between the boiler water temperature actual value and the boiler water temperature set point characterizes the actual heat requirement only insufficiently, because it depends also on which part of the respectively produced heat is taken off immediately 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. Does that take Heating circuit on the other hand, little heat from, then the boiler water temperature increases when the burner is running very fast. This then leads to a quick shutdown of the burner, so a short burner runtime.

According to the invention, a limitation of the maximum burner power allowed for the regular operation of the burner by the setpoint of the boiler water temperature as a further reference variable for the heat demand takes place. The effectively effective burner output is thus determined not only by the difference between the boiler water temperature actual value and the boiler water temperature setpoint alone, but additionally by the boiler water temperature setpoint.

An embodiment of the invention will be explained in more detail with reference to the drawing.

The sole figure shows a graph for the burner output in function of the boiler water temperature setpoint. On the abscissa axis, the boiler water temperature setpoint T _KSO II is plotted. For heating operation, the smallest possible value of room temperature corresponds to T _RSO H of 20 degrees. The largest possible value is the boiler water temperature maximum setpoint Tκ _so iiMax- This is determined by the design of the boiler and by the type of heating system and is for example 70 degrees. The boiler water temperature setpoint TK _SO II is in a known manner a function of the outside temperature.

On the ordinate axis, the burner power Q is plotted. A modulating burner has a maximum operating power, referred to as rated power QN. A burner can now not be operated with a power close to zero, but it has a certain design minimum performance Q _min . Modulating the burner thus takes place within the limits Q _min and QN. The ratio QN TO Q _min is usually referred to as the degree of modulation. A degree of modulation of the value 3 thus means that the minimum power Q _{min is} one third of the rated power QN.

For a better understanding of the invention, a relative degree of modulation M _re i is introduced here. This relative modulation degree M _re i is 0% when the burner is running at a power equal to the minimum power Q _mm , and it is 100% when the burner is running at its nominal power Q _N. According to the invention, the minimum power Q _m j _{n is} assigned to the boiler water temperature setpoint Tκ _S0 n ⁼ 20 degrees, and the rated power QN- to the boiler water temperature maximum setpoint Tκ _S oiiM _ax . These two points, labeled A and B in the diagram, are denoted by connected a straight line. Thus, there is a linear relationship between these two boundaries. This straight line is the maximum permissible modulation degree M _re i according to the invention.

It can be seen from the diagram that for a boiler water temperature setpoint T _KSO II ⁼ 45 degrees, the maximum permissible relative modulation degree M _re i is 50%. Thus, the maximum permissible burner output in normal operation is one

Boiler water temperature setpoint Tκ _s oii = 45 degrees, namely

Usually, a boiler water temperature setpoint TK _SOII ⁼ 20 degrees is assigned a room temperature setpoint TR _SO H = 20 degrees. Thus, the straight line AB ^{■ can} also be described as a function with the aid of which the degree of modulation M _re i can be calculated in percent:

That this leads to prevent short burner run times is illustrated by examples

T - T

M = ^{■ Ks0} "- Rsoll -x lOO

T ¹ KSoIl max - T Rsoll explained.

Usually, the burner output, as mentioned above, derived from the difference between the boiler water temperature value Tκi _St and the boiler water temperature setpoint T _KSOII . Suppose that at a burner start this difference is 20 degrees. In burner controls of the prior art, only this value is used for the determination of the instantaneous power of the burner. Now there are two possible cases:

In the first case, the boiler water temperature actual value Tκi _St = 50 degrees and the boiler water temperature setpoint T _KSOII = 70 degrees. It is easily recognizable that this case occurs when very cold weather prevails. From the diagram can now be read, in the case of a boiler water temperature setpoint TK _SO H ⁼ 70 degrees, the permissible degree of modulation M _re i is 100%. The burner will start at full power. When heat is then generated, the difference between the boiler water temperature actual value Tκi _St and the boiler water temperature setpoint T _{KSOH will} decrease as a result, which then leads to a reduction of the burner output.

In the second case, the boiler water temperature actual value Tjci _st = 20 degrees and the boiler water temperature setpoint TK _SO H - 40 degrees, so that again usually used to control the burner power difference between the boiler water temperature Tκi _St and the boiler water temperature setpoint Tκ _S0 n 20 degrees. However, it is clear that this case occurs when there is no very cold weather. According to the invention, however, the difference of 20 degrees is now not used to control the burner power, but there is a power limitation according to the diagram of the figure. At a boiler water temperature setpoint Tκ _so n ⁼ 40 degrees, the burner output is limited to 40%. It follows, therefore, that due to the power limitation of the invention, the duration of the burner is extended.

The temperature difference of 20 degrees was taken as an example to illustrate the effect of the invention. In practice, of course, it depends on the switching difference, which is effective in the controller. These can be values of the order of 8 or 10 degrees, for example. But much higher differences occur regularly, for example, the transition from a working in the heating night reduction to normal operation, often carried out in a so-called rapid heating, thus ensuring that the occurred overnight cooling of rooms and walls is compensated as quickly as possible. Especially with such a rapid heating prevents the inventive limitation of the burner power frequent switching on and off of the burner with all its adverse effects.

The lower the effective heat requirement, the more the power limitation affects the longer the burner runtime. Thus, the number of burner starts is reduced. In particular, in the case of evaporator burners, this also has the effect that the additional energy requirement for the burner startup by pre-venting the combustion chamber and by electrical heating of the evaporator chamber is significantly smaller overall.

The connecting line between points A and B in the diagram does not necessarily have to be a straight line. Also possible is a hyperbolic line, which is shown in dotted lines in the diagram. This leads to a stronger one

Power limitation, which has a strong effect especially at lower than the maximum heat demand.

The effective modulation factor M _at , _s in percent corresponding to the true burner power can be calculated from the relative modulation degree M _re i by means of the relationship QN to Q _min as follows:

The power control for the burner is carried out in the known manner by a ratio controller for the fuel / air mixture. Thus, the amount of fuel per unit time is regulated and the amount of air tracked.

Since usually the boiler water temperature setpoint T _{KSOII is varied} only in heating mode, while when charging the hot water tank basically the

Boiler water temperature maximum setpoint Tκ _so ii _{Max is} effective, it does not need to switch between heating and hot water storage _to control the burner power.

Claims

claims

A method of controlling a modulating burner whose power is between a minimum power Q _m ; _n and a rated power QN is variable, the power proportional to the difference between a boiler water temperature value Tκi _St and a boiler water temperature setpoint T _{KSOÜ is} regulated, characterized in that a power limitation takes place, which is derived from the boiler water temperature setpoint Tκ _S0 n ,

2. The method according to claim 1, characterized in that a maximum controllable power of the burner is determined by a maximum permissible relative modulation _degree M _re i, which is derived from the boiler water temperature setpoint T _KSOI I.

3. The method according to claim 2, characterized in that the relative modulation degree M _re i decreases with decreasing boiler water temperature setpoint Tκ _So ii.

4. The method according to claim 3, characterized in that the boiler water temperature setpoint T _KSO II ⁼ 20 degrees a minimum power Q _m i _n and the boiler water temperature maximum setpoint TκsoiiMax a rated power Q _{N are} assigned and that between these two limits a linear relationship consists.

5. The method according to claim 4, characterized in that the relative modulation degree M _re i is calculated according to the formula

T ¹ Ksoll - 17 R "soll

M ^ι _n el, = - -xlOO,

- T ¹ KSoII max -T ^x Rsoll in which T _{RSOH is} the setpoint of the room temperature.