EP1161711B1 - Heating installation and method for operating the same - Google Patents

Abstract

The invention relates to a heating installation, comprising a supply vessel (6) with an inlet and an outlet (4, 5) for a heated fluid; and a feed system (9, 10) for a heat transfer fluid with a feed line in which a valve (11) is situated, a temperature probe (4) which detects the temperature of the heated fluid and a control circuit (18) which activates the valve in dependence on a deviation of the temperature from a predetermined value. The invention also relates to a method for operating this installation. The aim of the invention is to obtain a rapid reaction from the installation while exerting a minimal mechanical load on the parts that are moved. To this end, the control circuit (18) has a limit frequency detector (19) which determines fluctuations in the temperature (Tist) and reduces or increases the loop amplification (V) of the control circuit (18) when the frequency is too high or too low, respectively.

Description

The invention relates to a heating system with a Storage vessel with inlet and outlet for a heated fluid and a feed arrangement for a heat transfer fluid a feed line in which a valve is arranged, a temperature sensor that measures the temperature of the heated Fluids determined and a control loop that the valve depending on a deviation in temperature operated by a default value. The invention further relates to a method for operating a heating system, at which the temperature of a heated fluid is determined and depending on a deviation of this Temperature from a preset value the supply of a heat transfer fluid with the help of a valve in a control loop is controlled.

The invention is based on a system for Provision of hot domestic water described. she is also applicable to other heating systems those using the fluid radiator or underfloor heating should be supplied. An example of a The heating system, which even fulfills both purposes, is off DE 41 42 547 A1 known. From this revelation goes the present invention. A control of the circulation pump in heating systems is from DE 24 52 515 A1 known. A similar principle is also used here out.

The heat transfer fluid does not necessarily have to be water. It can also be heated air, the one Dining room or a room arrangement.

The heated fluid gets its heat from the heat transfer fluid. The heat transfer fluid can be one Flow through the heat exchanger on the other side the heated fluid is arranged. It is also possible that the heat transfer fluid directly from a Heating source, for example a burner, is heated, and then mixed with the heated fluid.

All cases have in common that the supply of Heat transfer fluid is controlled via a valve. If the temperature of the heated fluid drops, then must Heat to be tracked so that the influx of Thermal fluid control valve opens. If the Temperature then rises above the preset value, the valve must be closed again. In most In some cases the valve is in the feed line of the heat transfer fluid arranged. But this is not a requirement as long as the valve is able to to control the amount of heat supplied by the heat transfer fluid. The valve can also be arranged in the return line his.

The temperature of the heated fluid does not necessarily have to be either be determined in the storage vessel. It is also possible, this temperature in the supply line from the storage vessel to determine the actual heating circuit. In extreme cases, the storage vessel itself can be relative be small or even by the heating system itself be formed.

With systems of this type, the following contradicting one now Phenomena. On the one hand you want the temperature of the keep the heated fluid as good as possible on the default value. So if there is a need for heat, for example if hot water is drawn from a tap, then the heat transfer fluid should as quickly as possible Track the heat that has been removed again in order to warm up cold water again. On the other hand, you have found that with very fast control loops These circles tend to vibrate. With a hot water treatment system, this is certainly the case tangible consequences. The water temperature fluctuates. In a heating system that is only a radiator or even underfloor heating the oscillation in temperature is less critical. In this case, too, the vibration leads to a considerable stress on the valve or the valve actuating servomotor.

The invention has for its object a quick Response of the heating system with a low mechanical Achieve load.

This task is the beginning of a heating system mentioned type in that the control loop has a cutoff frequency detector that vibrates detects in temperature and a loop gain of the control loop when the frequency is too high if the frequency is too low.

With this configuration you get yourself adapting loop gain of the control loop, see above that one hand vibrations whose frequency is above goes beyond a permissible level, avoids, on the other hand but always a relatively quick response from the heating system can achieve a heat demand. in this connection it's not about having vibrations in temperature avoids at all. It’s just about that the loads on the mechanical actuators, like valve or actuator, keep it small would like to make the lifespan not too strong Reduce. The loop gain of the control loop can be done relatively easily by changing the change the static gain of the controller. she is in the first approximation inversely proportional to this static Reinforcement of the controller.

The cutoff frequency detector preferably has Threshold element and sets the frequency taking into account of the output of the threshold element firmly. In other words, only such vibrations determined when determining the frequency, its amplitude is greater than the threshold. So you generate around a default corridor in which any Vibrations can take place without this one Influence the frequency that the cutoff frequency detector determined. The cut-off frequency detector therefore provides only such vibrations stuck out of this corridor come out.

The cutoff frequency detector advantageously determines the vibration in temperature indirectly from actuation signals or from movements of the valve. The control loop should only operate the valve if it in other words, if the temperature is necessary deviates from the default value by a predetermined amount. If such a deviation took place then this difference is already available. It then manifests itself in the movement of the valve or, which is easier to determine in a signal that the Triggers movement of the valve. So you use in the control loop available information anyway.

The task is in a method of the aforementioned Art solved in that a frequency of Vibrations of the temperature is determined and the Loop gain is reduced when the frequency is too large, and is raised if the Frequency is small enough.

As already mentioned above, you get this way a control loop that is always with the highest possible Loop reinforcement works without being in an impermissible Swing to get. So you get a very quick reaction and gentle at the same time the mechanical components, such as the actuator and valves. The loop gain is adjusted adaptive, i.e. adapted exactly to the respective situation. So you can from plant to plant and in one Plant to be different from hour to hour.

It is preferred that the frequency is only from such deviations is determined that a predetermined Exceed the difference to the default value. It a corridor is created around the default value, in which vibrations are permitted at any frequency become. These vibrations have no effect excessive stress on the actuators because the the actuating movements occurring here are very small. Also for a potential user, the warm water there are vibrations within this corridor hardly noticeable and therefore acceptable.

The frequency is preferably determined indirectly on the basis of movements of the valve and / or control signals for the Valve detected. The control signals or those from them following movements of the valve are an immediate consequence of deviations in temperature from the specified value. The Information about the deviation is therefore available and is expressed in relatively easy to detect signals. These can then be done with relatively little effort be evaluated.

The number of changes of direction is advantageous the valve movement determined in a predetermined period and the loop gain is reduced, if the number exceeds a maximum value. you the frequency can then be determined simply by counting restrict, of course the counting in one predetermined period must be done. If you have this predetermined period of time, for example, 5 minutes then you can use a predefined number of, for example Allow 3 to 10 changes of direction of the valve, without recognizing instability. If there have been more changes of direction than planned, then the system is considered unstable and the loop gain reduced.

It is particularly preferred that the count at each exceeding is canceled and the period starts over. You can reach one even faster stable condition. The more unstable the system, the more the frequency is higher, i.e. the more often it changes Valve its direction of movement. If you already have then make a correction if the criterion is met then you don't have to wait for the entire period to make a correction. This reduces the load on the mechanical components and allows you to reach a much faster stable condition.

It is preferred if the frequency is small enough the loop gain is increased and the default value changed. So you not only increase the loop gain, but you change the default value to determine whether the system, i.e. the control loop, then starts to vibrate. With a non-vibrating one System would also increase the loop gain not yet automatically to a vibration lead so that one is not sure whether the loop gain fits. With the change of the default value but you create a jump that contains the information you want supplies.

It is preferably used when after an increase the frequency is too high for the loop gain, the loop gain value used before the increase. So you feel your way reliably "Border" approach. With the same load, you have the information at which loop gain the control loop is still stable and you have the information that the next time the control loop is not increased is more stable. You can then go back to the previous one Loop gain return without a new one Having to perform iteration.

In a particularly preferred embodiment, that the loop gain depending on the load on the system is specified. this is a further possibility to the control system or the one in it moving parts before loading due to frequent movement to protect. If the need of the facility is small is, e.g. only a little warm water is drawn, then you can get by with a small controller gain. A quick reaction is also not necessary. The same also applies if, for example, during a night setback most radiator valves in a heating system are throttled so that little heat is "consumed" or is discharged. However, if there is a need occurs, for example, warm water is removed or the radiator valves are turned on, then a quick response from the system is required. In this Case you can on a higher loop gain switch. In this case, where as an additional The criterion used can be part of the Skip iterative procedure with several levels.

Preferably, the load on the system over the Heated fluid temperature determined. This approach is fast enough and does not require any additional Components. If the system is loaded, for example by taking warm water, then the temperature in the storage vessel drops due to the supply a corresponding amount of cold water relative quickly. Accordingly, you can use the loop gain Set up relatively quickly without the danger there is an immediate vibration. If it vibrates after a certain time comes, one can assume that the burden of System is now finished and you can go back to the Jump back to "idle" value of loop gain.

Fig. 1

eine schematische Darstellung einer Heizungsanlage zur Bereitstellung von warmem Wasser,

Fig. 2

eine schematische Darstellung eines Steuergerätes,

Fig. 3

verschiedene Kurvenverläufe zur Darstellung der Verminderung der Schleifenverstärkung,

Fig. 4

entsprechende Kurvenverläufe zur Darstellung der Erhöhung der Schleifenverstärkung und

Fig. 5

eine schematische Darstellung zur Erläuterung einer Systemschutzfunktion.

The invention is described below with reference to a preferred embodiment in connection with the drawing. Show here:

Fig. 1

1 shows a schematic illustration of a heating system for providing hot water,

Fig. 2

1 shows a schematic illustration of a control device,

Fig. 3

different curves to show the reduction in loop gain,

Fig. 4

corresponding curves to show the increase in loop gain and

Fig. 5

a schematic representation to explain a system protection function.

Fig. 1 shows schematically a heating system 1 for provision of hot domestic water that flows through Taps 2 or other taps can be removed can. The taps 2 hang on a ring line 3 with a flow line 4 and a return line 5, with a storage vessel 6, for example a boiler, are connected. In the ring line 3 is a circulation pump 7 arranged, which ensures that warm Water without significant delays in the taps 2 is available.

The storage vessel 6 is designed as a heat exchanger, on the primary side 8 a supply line 9 and a drain line 10 for a heat transfer fluid or, more generally, a heat transfer fluid are. The heat transfer fluid can be water act that is already started by a boiler becomes. But it can also be a liquid act in a district heating system for heat transfer is used. The specific design of the Heating the heat transfer fluid does not play a major role Role.

A valve 11 is arranged in the supply line 9, that opened or closed with the help of a motor 12 can be. The motor 12 is for example designed as a stepper motor, so that different opening positions of the valve 11 can be adjusted.

A temperature sensor 13 is arranged on the flow line 4, which is the temperature of the warm water in the Flow line 4 determined. The temperature sensor 13 is connected to a control device 14, which in turn controls the motor 12. The control device 14 has an input 15 for specifying a default value for the temperature in the storage vessel 6. This default value is also referred to as the "setpoint".

If 2 warm water is now removed through a tap is then simultaneously via an inlet line 16 cold water in the reservoir 6 refilled. A check valve 17 prevents water flows out of the ring line 3 into line 16. With of course, the temperature drops when cold water is supplied of the warm water already present in the boiler 6. This temperature drop is caused by the temperature sensor 13 found. Because of this finding the control device 14 actuates the motor 12, which Valve 11 opens. The parts mentioned form together a control loop 18. The control device 14 forms the actual "controller" which is a static one Gain Xp has. The reciprocal of this static Gain Xp is referred to as loop gain V.

The detailed structure of the control device 14 is shown in FIG. 2 shown schematically. The inputs and outputs of the Control device 14 are with the reference numerals of the elements provided with which the control device 14 in Fig. 1 is connected.

The control device 14 initially has a differential amplifier 23 on which the specified value exceeds input 15 and the actual temperature value from the temperature sensor 13 is supplied. In dependence of the difference between these two values becomes a corresponding adjustment signal for the motor 12 is generated. However, the static gain of this differential amplifier is 23 changeable. To change a cut-off frequency detector 19 is used. The cutoff frequency detector 19 initially receives the same signals, which the engine 12 also receives. It also receives the actual temperature and the target temperature. These signals or Values are fed to a processing device 20 which, as explained below, are below predetermined Conditions generated an impulse and under other has a threshold. The impulses will be fed to a counter 21. The counter 21 is connected with a timer 22, the counter 21 the Indicates the beginning and end of a predetermined period. The output of counter 21 is with a reset input of the timer 22 connected. Furthermore, the Output of the counter 21 with the differential amplifier 23 connected, more precisely to an entrance at which the Gain factor, i.e. the static gain, can be adjusted.

The operation of the control circuit 18 is now to be based on 3 are described.

FIG. 3a shows a curve T _ist , that _is , the course of the temperature in the flow line 4. The default value T _SET , ie the setpoint of the temperature, is shown in broken lines. Furthermore, a neutral zone Nz is shown on both sides of the setpoint T _SET . It can be seen that the temperature T _ist fluctuates relatively strongly at the beginning. The differential amplifier 23 generates pulses for actuating the motor 12 at predetermined time intervals, which are shown in FIG. 3b. As long as the actual temperature T _{ist is} lower than the set temperature T _SET , the motor is operated in one direction (on +). If the situation is reversed, the motor is operated in the other direction (on-). This representation is of course only an example. Other ways of adjusting the valve 11 are of course also possible.

In the present heating system it is assumed that a repeated adjustment of the valve 11 is not critical is as long as it goes in the same direction. You just want to prevent that Direction of movement of the motor 12 and the valve 11 to often changes to a greater extent.

In a manner not shown, the individual pulses, which are shown in FIG. 3b, a course of adjustment derived, which in Fig. 3c is shown. 3d now represents the initial value of the counter 21, which with every change of direction the value 1 is increased. The timer 22 now gives one predetermined time period before, which is entered in Fig. 3a is. The time periods Z1, Z2, Z3 are initially basically all the same length.

If it turns out Z1 within a period of time, that the counter 21 has a predetermined count has exceeded, then the gain factor Xp of the differential amplifier 23 up and thus the loop gain V is reduced. simultaneously the counter 21 is reset to zero and the Timer 22 reset. Accordingly, the begins second counting period Z2 before the first counting period Z1 has expired completely. Here you use the fact that you don't want to know how big is the error in and of itself. It is enough, if you know that there is a mistake to a Initiate correction.

3e shows that the loop gain V is reduced each time the counter 21 has reached a predetermined count value within a counting period z, in the present case the value 3. It can be seen that two corrections are necessary before the loop gain V has become so small that the actual temperature T _ist is still oscillating, but the amplitude of this oscillation is mostly still within the neutral zone. In this case, only two changes of direction occurred within the counting period Z3. Otherwise, the actual temperature T _{ist has met} the condition T SET - 0.5 Nz <T is <0.5 Nz + T SET ,

The loop gain V corresponds to the reciprocal of the static gain Xp of the differential amplifier 23. The following algorithm can now be run. First you bet Xp = (1 + λ) x Xp, where λ> 0 and constant. Preferably, λ is also less than 1. After the increase in the static gain Xp, which corresponds to a decrease in the loop gain V, the cutoff frequency detector 19 is started. If the cut-off frequency detector detects instability, for example a number of 3 or more changes in direction within a counting period Z1, Z2,... Zn, then the static gain Xp is increased once more, as described above. If the count of the direction changes does not reach the critical value, it is assumed that a stable state has been reached and this static gain is maintained.

Basically, the process is divided into two phases. In the first phase, it is determined whether "critical" Vibrations are present and at the exit of the The first phase is the loop gain accordingly changed the result. In the second phase there is a Monitoring stability.

If no limit oscillations are found in phase 1, the loop gain is increased until an unstable counting period is observed, the setting process being interrupted and the gain of the preceding stable counting period being selected. Fig. 4 shows the procedure for increasing the loop gain. The static gain Xp is first reduced, for example by setting Xp = (1 - σ) x Xp, where σ is constant, greater than zero and preferably less than 1. Σ can be the same value as λ, but it will usually be a different value.

The set temperature T _{SET is then} changed T SET = T SET + Δsp.

For this purpose, a fixed value transmitter 24 and a switchable reversing amplifier 25, which is connected to an addition point 26, are provided in the control device. Then the reversing amplifier is switched over, ie it is set Δsp = -Δsp.

The change in the setpoint T _SET causes a jump that should trigger an oscillation. Without such an oscillation, instability could not be determined even by changing the loop gain V. After changing the setpoint T _SET , a delay time Δt is waited for. Then the cut-off frequency detector 19 is started. If and as long as the limit frequency detector determines a stable behavior of the control circuit 18, this procedure is repeated, ie the loop gain V is increased.

At some point the loop gain V will be so great that the control loop 18 starts to oscillate. This is the case in the exemplary embodiment in FIG. 4 at time t3. In this case, the setpoint T _{SET is reset} to its original value and the static gain Xp is set Xp = 1 1 - σ Xp and the setting process is finished. The value of the loop gain V is thus reset to the value that allowed the last stable state.

If you follow an adjustment process as shown in Fig. 3 or shown in Fig. 4, a stable state has reached, there is no further setting at first, the setting is finished. Only when one renewed instability is detected, for example due to a change in load resulting in a commute of the valve, a new setting process begins.

Fig. 5 shows another way how to Loop gain V can change. So that can implement a system protection function in which one at small loads near idle also vibrations can avoid.

A distinction is made between a high and one low loop gain, toggled between those can be. The purpose of this protective function is to stabilize the heating system 1 and to optimize depending on the load the plant.

The high loop gain V, which in Fig. 5 as V1 is the normal load Heating system 1 in operation. This loop reinforcement V1 can, for example, by the one described above automatic adjustment procedure has been found. Means not shown in detail can be provided to save this gain factor.

The small loop gain V2 will idle used.

The cut-off frequency detector 19 is now used for the determination used when consumption has ended. In this Case leads to the high loop gain V1 a vibration with too large an amplitude and too large Frequency. So if after a previous upgrade such a vibration of the loop gain is recognized, the gain from the high Value V1 switched to the lower value V2, after which the system stabilizes again.

The change in temperature that occurs during the change is used to determine the change from idling to consumption. This is the case, for example, at time t2 in FIG. 5. The removal takes place between times t2 and t3. A load, in the present case a water withdrawal, is determined when the actual temperature falls by a value Dz below the target temperature T _SET . In this case the loop gain is increased to the value V1. This gives the controller the necessary speed for normal consumption. The removal is complete at time t3. Since the loop gain is too high, an oscillation now takes place in the counting period Z2. This is recognized by the cutoff frequency detector and the loop gain is reset to the value V2 at time t4. The loop gain V2 in turn may have been found by a corresponding iteration when increasing the loop gain.

Claims (13)

1. Heating system having a storage tank with inlet and outlet for a heated fluid and a supply arrangement for a heat transfer medium with a supply line, in which is arranged a valve, a temperature sensor measuring the temperature of the heated fluid and a control loop, which activates the valve in dependence of a deviation of the temperature from a specified value, characterised in that the control loop (18) has a limit frequency detector (19), which determines oscillations of the temperature (T_ist), reducing a loop amplification (V) of the control loop (18) when the frequency is too high or increasing a loop amplification (V) of the control loop (18) when the frequency is too low.
2. System according to claim 1, characterised in that the limit frequency detector (19) has a threshold value element (20) and determines the frequency under consideration of the output of the threshold value element (20).
3. System according to claim 1 or 2, characterised in that the limit frequency detector (19) determines the oscillations of the temperature (T_ist) indirectly on the basis of activating signals or of movements of the valve (11).
4. System according to one of the claims 1 to 3, characterised in that the limit frequency detector (19) has a direction change counter (21), a comparator and a time-relay (22).
5. Method for operating a heating system, in which the temperature of a heated fluid is determined and the supply of a heat transfer medium is controlled by a valve in a control loop in dependence of a deviaiton of said temperature from a specified value, characterised in that a frequency of oscillations of the temperature is determined and the loop amplification is reduced, when the frequency is too high, and increased, when the frequency is low enough.
6. Method according to claim 5, characterised in that only the frequency of deviations exceeding a predetermined difference from the specified value is determined.
7. Method according to claim 5 or 6, characterised in that the frequency is determined indirectly on the basis of movements of the valve and/or activating signals for the valve.
8. Method according to claim 7, characterised in that the number of direction changes of the valve movement for a predetermined period is determined and the loop amplification is reduced, when the number exceeds a maximum value.
9. Method according to claim 8, characterised in that the counting is discontinued on each excess and the period starts over.
10. Method according to one of the claims 5 to 9, characterised in that, when the frequency is low enough, the loop amplification is increased and the specified value is changed.
11. Method according to one of the claims 5 to 10, characterised in that, when the frequency is too high after an increase of the loop amplification, the value of the loop amplification before the increase will be used again.
12. Method according to one of the claims 5 to 11, characterised in that the loop amplification is specified in dependence of the load of the system.
13. Method according to claim 12, characterised in that the load of the system is determined on the basis of the temperature of the heated fluid.

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