EP0387703B1 - Burner control for heating systems - Google Patents

Abstract

A method and device are described for control of a burner or other heat generator with automatic adaptation of the water temperature to the heat requirement and for protection of the burner against too frequent switching on and off. In order to reduce the number of starting operations and to make the system more environment-friendly, it is envisaged that, in the control circuit or the main circuit of the burner, there is a rest-time contact and a timing device for measuring the switch-on duration of the burner and for allocating a rest time which is dependent thereon and variable in the opposite direction.

Description

Frequently briefly switching on the burner of a heating system, due to the low heat requirement in the warmer seasons, not only leads to excessive wear on the burner, but also to severe contamination of the nozzles and other burned parts.

Above all, however, there is an extremely high pollutant emission with every start, which can reach more than 1000 times the normal emission value.

From OS-DE 33 45 705 A1 a device for burner control is known in which, depending on the state of a medium to be heated, a measurement of the burning time and the total cycle time, the burning power is controlled in order to operate the burner at the most favorable operating point .

The disadvantage of such a burner control is that a relatively high and cost-intensive installation effort has to be carried out, e.g. to be able to upgrade existing burners that are only controlled via a thermostat contact. Furthermore, burners with only one or two power levels cannot be retrofitted with such a device.

This is where the invention comes in, which makes it possible to reduce the number of times the burner is started in a simple manner, in order to protect the burner, increase its service life and, overall, make the system more environmentally friendly. According to the invention, burners can now also be retrofitted which, for example, have only one power level.

According to the invention it is proposed, depending on the on-time of the burner, to force a pause until the next switch-on by opening a pause contact, the actual on-time of the burner being measured by a time measuring device and the pause time being determined in a mutually variable manner, that is, the pause time has an externally adjustable, reciprocal ratio to the burner's duty cycle. The consequence of this is that a longer pause is provided for a short on-time, corresponding to a low heat requirement, whereas a shorter pause occurs for a longer on-time of the burner, correspondingly a higher heat requirement.

Such an oppositely variable pause time can be easily achieved by programming a maximum pause time that is a constant multiple of the respective burner on time is shortened. If the burner is switched on for a longer period of time, this even reduces the pause time to '0', which means that the burner's full heating output can be used.

According to the invention, it is proposed in multi-stage or controllable burner systems to control the burner output in a variable manner depending on the duty cycle.

This can e.g. B. according to the invention in that one or more presettable duty cycles are programmable in the control, when the burner is below its power is switched to a lower level.

Only when the pause reaches '0' in a cycle does the burner receive the command to switch back to higher output.

Depending on the size and location of the rooms, it can make sense to make the maximum break time and / or the multiplication constant adjustable in order to achieve optimal conditions.

In order to be able to intervene in the control program in extreme situations, e.g. B. when ventilating rooms in winter, it is recommended to provide a bridging contact to the break contact.

This bridging contact can also be a thermostat contact, which falls below a minimum temperature of z. B. 16 ° C closes.

A simple example of a regulation according to the invention is presented below, which describes the concept of the invention schematically. This example is not to be regarded as restrictive, but any equivalent solutions can be provided, since in view of the Today's possibilities with micro-processors can also be used for complex computer programs to determine the break times. The determination of the amount of heat required from the ratio of the burning time or pause remains essential.

Figure 1 shows the functional diagram of a previous temperature control between two fixed temperatures T₁ and T. As soon as the room temperature drops below the value T₁, the burner or the heater is switched on until the temperature T is reached. Then the thermostat switches off and so on.

This results in the temperature profile (14). The blocks entered in FIG. 1 show the respective switch-on state of the burner. If the conditions are otherwise constant, the switch-on times (12) and pause times (13) are approximately the same.

In warm weather, i.e. low heat requirement and restricted water circulation, the switch-on times can be very short and numerous.

Figure 2 is a corresponding functional diagram for a device according to the invention.

FIG. 3 shows the schematic circuit diagram of a break control according to the invention.

The burner (1) is switched on by the thermostat contact (2) via the normally closed break contact (4). At the same time, the time control (6) receives the information via line (7) that the burner (1) is switched on.

As soon as the thermostat contact (2) opens again, the control ends (6) the time measurement of how long the burner (1) was on. At the same time, the timer (6) actuates the pause contact (4) via the relay (5), opens it and thus prevents the burner (1) from being switched on again.

arbeiten.
Dabei bedeutet

T_p =

Pausenzeit

Pm =

Max. Pausenzeit (Zykluszeit)

K =

Vervielfältigungskonstante

T_Br =

Einschaltzeit des Brenners

Diese Funktion kann aus Figur 4 abgelesen werden, wobei auf der horizontalen Achse die Zeit t in Minuten und auf der vertikalen Achse die Pausenzeit T_p ebenfalls in Minuten angegeben ist.The time control (6) can, for example, according to the formula $${\text{T}}_{\text{p}}{\text{= Pm - (K + 1) xt}}_{\text{Br}}$$

work.
Here means

T _p =

break time

Pm =

Max. Pause time (cycle time)

K =

Duplication constant

T _Br =

Burner on time

This function can be read from FIG. 4, the time t in minutes being indicated on the horizontal axis and the pause time T _p likewise being indicated in minutes on the vertical axis.

FIG. 4 shows the course of the burner's switch-on time and the pause time T _p derived therefrom. In the example in FIG. 4, it is assumed that the maximum pause time Pm is forty minutes and the reproduction constant K = 1, ie the pause is also shortened by one minute per minute of burner on time. That means from the max. In addition to the burning time for each minute of burning time, the pause time (cycle time) is also reduced by one minute of the pause time.

The point (11) in FIG. 4 at the intersection of the straight lines T _p and T _Br means that in this example the pause time T _p has shrunk to '0' after twenty minutes of burning time.

FIG. 6 schematically shows the structure of a digital time control which is able to implement the pause circuit shown in FIG. 1.

Such a timing can, for. B. from a digital time pulse generator (16) and a pulse counter (17).

The time pulse generator (16) is, for. B. designed so that you can select time pulses after 60,45,30 or 15 seconds to feed them to the pulse counter (17). The time pulse generator (16) is reset to '0' after the maximum time of 60 seconds.

If a shorter pulse time is set using the button (9), the time pulse generator (16) is reset prematurely via the reset line (23).

The maximum number of pulses at which the breaks can be ended and the burner can be switched on again by the thermostat (2) is set on the pulse counter (17) using the adjusting knob (8). The number of maximum pulses can be read off the display (19).

If desired, the current number of pulses which have elapsed in the respective cycle can also be read on a second display (18).

As soon as the thermostat (2) switches on, the relay (20) receives voltage via line (7) and switches the contact (22), which has the task of switching the cycle times, to line (25) and thus via the selector switch (9) to one of the shortened cycle times, for example as shown to a 30-second cycle, ie twice as fast as the basic cycle time 60 seconds.

If the thermostat (2) switches off when the upper temperature T is reached, the relay (20) no longer receives any voltage. It falls off and the contact (22) connects the pulse counter (17) via line (24) and (26) with the basic cycle time of 60 seconds. At the same time, the relay (5) picks up and opens the break contact (4).

Subsequently, the pulse counter (17) from the clock generator (16) is supplied with pulses every 60 seconds until the number of pulses shown on the display (19) (in this example '40') is reached. At this maximum number of pulses, the pulse counter (17) is also set to '0', the relay (5) is de-energized and the break contact (4) closes.

The burner (1) can only start operating again now, even if the thermostat (2) had previously closed.

If the contact (2) is not yet closed, the entire time control (6) remains in the "standby" waiting position until the next time the thermostat (2) is switched on, the relay (20) receives voltage again.

FIG. 5 shows the course of a control curve as can be achieved with the circuit of FIG. 6.

Time t is plotted again horizontally, the number of corresponding time pulses plotted vertically. In this example, too, a preselected maximum number of pulses of 40 pulses is assumed. The duplication constant K = 1 is also retained. This corresponds to a pulse sequence twice as fast during the burner's switch-on time, i.e. 1 pulse in 30 seconds.

Accordingly, FIG. 5 shows a steep increase during this burner running time, which is assumed to be 15 minutes, up to 30 pulses corresponding to line 26. As soon as the burner is switched off, the time counting according to line 27 runs slowly with one pulse per minute during the remaining time (pause time T _p ), until the preselected maximum pause time Pm is reached at 40 pulses.

Figur 5 zeigt auch eine beispielsweise Möglichkeit bei einem zweistufigen Brenner mit veränderlicher Leistung zu fahren. z. B. volle und halbe Leistung.This function corresponds exactly to the specified formula $${\text{T}}_{\text{p}}{\text{= Pm - (K + 1) xt}}_{\text{Br}}$$

FIG. 5 also shows, for example, the possibility of driving a variable-capacity two-stage burner. e.g. B. full and half power.

According to the invention, the pulse counter (17) of the time control (6) has a further setting option. With the button (33) a number of pulses (31) can be set, at which the control checks whether the burner is still switched on, according to item 29 in FIG. 5. If this is not the case, this means that less than half Burner power is required in the control cycle and the time control (6) gives the command to switch over to half the power via the command line (32) (see circuit diagram in FIG. 6).

If, on the other hand, it is found when the set maximum number of pulses is reached that the burner is still switched on, i.e. H. the remaining pause time is '0', the burner receives the command to run with higher power via the command line (32).

With the button (33) you can adjust the number of pulses (31) to the different conditions, z. B. to check at half the number of cycle pulses or only at 3/4 of the maximum cycle pulses above which the burner should be switched.

The example described serves for a better understanding of the invention, but both the time measurement and the evaluation in the "cycle" can be varied as far as the task can be solved according to the invention.

Claims (10)

1. A device for the additional regulation of a burner or other heat producer, which by means of a thermostat (2) carry out an automatic adjustment of the water temperature to the heat requirement, in which the burner (1) is protected from too frequent switching on and off, as would take place by an exclusive thermostat regulation, characterised in that a time control- and time measurement device (6) is provided to measure the duration the burner (1) is switched on, which on switching off of the burner (1) via a relay (5) controls a pause contact (4) situated in the control- or main circuit of the burner (1) such that the pause time (Tp) of the pause contact is in an externally adjustable reciprocal relationship to the switched-on duration (TBr) of the burner.
2. A device according to Claim 1, characterised in that a maximum pause time is programmed in, which is shortened by a constant multiple of the respective switched-on duration of the burner.
3. A device according to Claim 1 or 2, characterised in that with multi-stage of controllable burner systems, dependent on the switched-on duration, the pause time and/or the burner power is able to be changed.
4. A device according to Claim 3, characterised in that one or more switched-on durations of the burner are provided which are able to be set in advance, on falling below which the burner is switched to a lower stage.
5. A device according to Claim 4, characterised in that on reaching a pause time '0' the burner is switched to a higher power.
6. A device according to Claim 2, characterised in that the maximum pause time and/or the multiplication constant is adjustable.
7. A device according to Claim 6, characterised in that the maximum pause time and/or the multiplication constant are able to be altered dependent on clock time or temperature.
8. A device according to Claim 1, 2 or 3, characterised in that a bridging contact to the pause contact is present.
9. A device according to Claim 8, characterised in that the bridging contact is controlled by a thermostat and/or a time switch clock.
10. A method for the additional regulation of a burner or other heat producer, which by means of a thermostat (2) carry out an automatic adjustment of the water temperature to the heat requirement, in which the burner (1) is protected from too frequent switching on and off, as would take place by an exclusive thermostat regulation, characterised in that whilst the burner (1) is switched on, its switched-on duration (TBr) is measured by a time control- and time measurement device (6), in which the thermostat contact (2) and the pause contact (4) are closed, whereupon on response of the thermostat (2) the burner (1) is switched off and hence the time measurement is ended, and the time control- and time measurement device (6) opens the pause contact (4) via a relay (5), and hence the burner (1), independently of the thermostat (2) is blocked from being switched on again over the duration of the pause time (Tp), in which the pause time (Tp) of the pause contact (4) is in an externally adjustable reciprocal relationship to the switched-on duration (TBr) of the burner (1).

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