SK12752001A3 - 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

Technical field

The invention relates to a heating device with a storage vessel with a supply and outlet for heated fluid and to a supply for a heat transfer fluid having a supply line in which a valve is provided, a temperature sensor which detects the temperature of the heated fluid and a control circuit which controls the valve temperature deviations from the setpoint. The invention further relates to a method of operating a heating device in which the temperature of the heated fluid is detected and, depending on the deviation of this temperature from the setpoint, the supply of the heat transfer medium is diluted by means of a valve in the control circuit.

BACKGROUND OF THE INVENTION

The invention is further described on the basis of hot water production systems. However, it is also applicable to other heating systems on which the heating element or the underfloor heating is to be supplied with fluid. An example for a heating device that even fulfills both purposes is known from DE 41 42 547 A1. The present invention is based on this application. The control of the circulation pump in heating systems is known from DE 24 52 515 A1. Here, too, it is based on a similar principle.

The heat transfer fluid does not necessarily have to be water. It may also be heated air that supplies a room or a certain space.

The heated fluid extracts its heat from the heat transfer fluid. The heat exchanger fluid can thereby pass through the heat exchanger, on the other hand of which the heated fluid is provided. However, it is also possible for the heat transfer fluid to be heated immediately by a heat source, such as a burner, and then mixed with the heated fluid.

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In all cases, however, it is common that the heat transfer fluid is controlled by a valve. If the temperature of the heated fluid decreases, heat must be supplied so that the valve controlling the heat transfer fluid is opened. If the temperature rises above the setpoint, the valve must be closed again. In most cases, the valve is provided in the heat transfer fluid supply line. However, this is not a condition as long as the valve is able to control the amount of heat supplied by the heat transfer fluid. The valve can also be provided in the return line.

Also, the temperature of the heated fluid need not necessarily be detected in the storage vessel. It is also possible to detect this temperature in the supply line from the storage vessel to the actual heating circuit. In extreme cases, the storage container may be relatively small or even formed by a heating device.

These contradictory phenomena now exist in such devices. On the one hand, the temperature of the heated fluid should be kept as close as possible to the set point. Thus, if there is a need for heat, for example when hot water is drawn at the tapping point, the heat transfer fluid should as soon as possible recover the recovered heat to heat the supplied cold water again. On the other hand, it has been found that in very fast control circuits these tend to oscillate. This has obvious consequences for hot water systems. Water temperature fluctuates. In a heating system that only supplies the radiator or even underfloor heating, the temperature oscillation is less critical. However, only in this case the oscillation leads to a considerable load on the valve or the adjustable motor controlling the valve

SUMMARY OF THE INVENTION

The object of the invention is to achieve a rapid reaction of the heating device under a slight mechanical load.

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This problem is solved in a heating device of the above type by having a control circuit having a cut-off frequency detector which detects temperature oscillations and decreases the gain of the control circuit in the loop at too high a frequency and increases at too low a frequency.

With this embodiment, an adaptable gain in the loop of the control circuit is obtained so that, on the one hand, an oscillation whose frequency exceeds the permissible degree is avoided, and on the other hand a relatively rapid reaction of the heating device to the heat demand can always be achieved. It is not a matter of preventing the vibration of the temperature completely. The only thing is that the load on the mechanical adjusters, such as the valve or actuator, must be kept low so as not to reduce the service life too strongly. The gain of the loop control loop can be relatively easily changed by changing the static gain of the controller. On the contrary, it is proportional to this static gain of the regulator.

Preferably, the cut-off frequency detector has a critical value member and detects the frequency taking into account the output of the critical value member. In other words, only frequency oscillations whose amplitude is greater than the critical value are detected in frequency detection. This creates a corridor around the set point at which arbitrary oscillations can occur without affecting the frequency detected by the cut-off frequency detector. Thus, the cut-off frequency detector detects only those vibrations that originate from this corridor.

Preferably, the temperature oscillator detector detects temperature indirectly from control signals or valve movements. The control circuit should operate the valve only when necessary, in other words, if the temperature deviates to a predetermined amount from the set point. If such a deviation has occurred, this difference is already available. It is then manifested by the movement of the valve, which is easier to detect, or by a signal that causes the movement of the valve. Thus, existing information is still used in the control circuit.

This task is solved in a method of the above type by detecting the frequency of temperature oscillation and decreasing the gain in the loop if the frequency is

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As already mentioned, in this way a control circuit is obtained which always operates with the highest possible gain in the loop without causing undue oscillation. This results in a very fast reaction and at the same time saves in particular mechanical components such as actuator and valves. The adjustment of the gain in the loop is carried out adaptively, i. exactly tailored to the current situation. Thus, it can vary from device to device and from one device to another from hour to hour.

In this case, it is advantageous that the frequency is determined only by deviations which exceed a predetermined difference from the set value. Thus, a corridor is made around a set value, in which the oscillation at any frequency is allowed. These oscillations do not exert excessive stress on the displaceable members, since the displaceable movements produced are very small. Also, for a potential hot water user, the oscillations within this corridor are hardly obvious and thus acceptable.

Preferably, the frequency is detected indirectly based on valve movements and / or valve control signals. The control signals or the resulting valve movements are the immediate consequence of temperature deviations from the setpoint. Thus, the deviation information is available and manifests itself with relatively easily detectable signals. These can then be evaluated at a relatively low cost.

Preferably, the number of changes in the direction of movement of the valve is detected at a predetermined time interval and the gain in the loop decreases as the number exceeds the maximum value. Frequency detection can then be limited to a simple subtraction, and naturally the subtraction can take place at a predetermined time interval. If this predetermined time interval is determined, for example, 5 minutes, then a predetermined number of, for example, 3 to 10 valve direction changes can be allowed without detecting instability. If there were more changes in the direction of movement than specified, then the system is considered unstable and the loop gain

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It is particularly advantageous for the counting to be interrupted at each overshoot and the time interval is restarted. This achieves an even more stable steady state. The more unstable the system is, the higher the frequency, i. the more often the valve changes the direction of its movement. If a proofreading is performed just when the criterion is met, then the entire time interval need not be waited for the proofreading to take place. This reduces the load on the mechanical components and makes it possible to achieve a stable state substantially faster.

Preferably, if the frequency is too small, the gain in the loop increases and the input value changes. Thus, not only the loop gain is increased, but the input value also varies to determine if the system, i.e. the control circuit gets into oscillation. Also, with a non-oscillating system, increasing the loop gain would not automatically result in oscillation, so it is uncertain whether loop gain is appropriate. However, changing the entered value generates a jump that supplies the requested information.

Thus, preferably, if the frequency is too high after the loop gain is increased, the loop gain value used prior to the increase is utilized. This reliably approaches the “boundary”. Under the same load, we have information in which the loop gain is still stable and we know that the next time the control loop is no longer stable. We can then revert to the previous loop gain without having to perform a renewed iteration.

In a particularly advantageous embodiment, it is provided that the loop gain is set depending on the load on the device. This is a further possibility for the control system or the parts moving therein to be protected from the load by excessive movement. If the need for equipment is small, e.g. if only a small amount of hot water is removed, then a small gain of the regulator is sufficient. A rapid reaction is also not necessary. The same is also true if most of the heaters of the heaters of the heater are throttled, for example at night, so that little or no heat is consumed. If, on the other hand, a need arises, that is, for example, if hot water is taken or is removed

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• Turn the radiator valves on, then turn them on. • • • • • • • · · · · · · · · · · · · · · · · · · · rapid response of the device needed. In this case, it can link to a higher gain in the loop. In this case, where the need is used as an additional criterion, part of the iterative process can be skipped by several stages.

Preferably, the load of the device is determined by the temperature of the heated fluid. This process is quite fast and does not require additional structural elements. If a device loaded by, for example, hot water is loaded, then the temperature in the storage vessel drops relatively quickly by supplying an appropriate amount of cold water. Accordingly, the gain in the loop can be increased relatively quickly without the risk of oscillation immediately. If, after a certain period of time, the oscillation occurs, it may be assumed that the load on the device is now complete and we can return to the value of the free-running amplification in the loop.

BRIEF DESCRIPTION OF THE DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in more detail with reference to the drawings, in which: FIG. 1 shows a schematic illustration of a heating device for preparing hot water, FIG. 2 shows a schematic representation of a control apparatus, FIG. 3 shows different waveforms to show the gain reduction in the loop; FIG. 4 shows the corresponding waveforms to show the gain increase in the loop, and FIG. 5 is a schematic view to explain the system protection function.

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DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 shows schematically a heating device 1 for the production of domestic hot water which can be removed by taps 2 or other tapping points. The water taps 2 hang on a ring line 3 with a supply line 4 and a return line 5, which are connected to a storage vessel 6, for example a boiler. A circulation pump 7 is provided in the duct 3, which ensures that hot water is available in the taps 2 without significant delays.

The storage vessel 6 is designed as a heat exchanger, on the primary side 8 of which there is a supply line 9 and a discharge line 10 for heat transfer fluid or generally heat transfer fluid. The heat transfer medium can be water that is discharged from the boiler. However, it may also be a liquid that is used in a district heating device for heat transfer. In particular, the embodiment of heating the heat transfer fluid does not play a major role.

A valve 11 is provided in the supply line 9, which can be opened or closed by means of a motor 12. The motor 12 is designed, for example, as a stepper motor, so that the various opening positions of the valve 11 can be adjusted.

A temperature sensor 13 is provided on the supply line 4, which detects the temperature of the hot water in the supply line 4. The temperature sensor 13 is connected to a control device 14 which controls the motor 12 on its side. The control device 14 has an input 15 for entering a setpoint for temperature. 6. This setpoint is also referred to as the setpoint ”.

If hot water is now to be withdrawn from the water tap 2, then cold water is fed into the supply tank 6 via the supply line 16. The non-return valve 17 prevents the water from the circuit 3 from flowing into the line 16. With the cold water supply water already in boiler 6. This temperature drop is detected by a temperature sensor 13. Based on this finding, the control device 14 controls the motor 12,

31785Π · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · Thus, the portions 11 together form the control circuit 18. The control device 14 forms its own regulator 11, which has a static gain X _p . The reciprocal of this static gain X _p is referred to as loop V gain.

A more detailed construction of the control device 14 is shown schematically in FIG. 2. The inputs and outputs of the control device 14 are provided with reference numerals

marks of the elements to which the control device 14 in FIG. First

In particular, the control device 14 has a differential amplifier 23, to which the input value is supplied via input 15 and the actual temperature value by the temperature sensor 13. Depending on the difference between these two values, the respective adjustment signal for the motor 12 is generated. . The cut-off frequency detector 19 is used for the change. The cut-off frequency detector 19 first acquires the same signals that the motor 12 also obtains. Furthermore, it acquires the actual temperature and the desired temperature. These signals and / or values are supplied to a preparation device 20 which, as explained below, generates an impulse under predetermined conditions and, inter alia, has a critical value member. The pulses are fed to counter 21. Counter 21 is connected to a timer 22, which tells counter 21 the start and end of a predetermined time interval. The counter output 21 is connected to the reset input of the timer 22. Further, the counter output 21 is connected to the differential amplifier 23, more specifically to the input at which the amplification factor can be adjusted, i. static amplification.

The operation of the control circuit 18 will be described with reference to FIG. Third

Fig. 3a shows the curve T, _stl, i.e. the temperature curve in the supply line 4. The indicated value T _S et, hence the temperature set point, is indicated in dotted lines. Furthermore, the neutral zone N ^ is indicated on both sides of the set point T _SE t. Obviously, the temperature Tist initially fluctuates relatively strongly. The differential amplifier 13 generates, at specified intervals, the pulses for controlling the motor 12 shown in FIG. 3b. As long as the actual temperature is Tist

31785 / T less than setpoint T _S et. the motor is operated in one direction (on +). If the situation is reversed, the engine is operated in the other direction (on-). Naturally, this view is only an example. Other methods of adjusting the valve 11 are naturally also possible.

In this heating device, it is assumed that the re-adjustment of the valve 11 is non-critical when carried out in the same direction. We just want to prevent the direction of movement of the motor 12 and the valve 11 from changing too much.

Thus, from the individual pulses shown in FIG. 3b, derives the course of the adjustment direction shown in FIG. 3c. Fig. 3d now shows the default value of the counter 21, which increments by 1 for each change of direction. The timer 22 now enters a predetermined time interval, which is indicated in FIG. 3a. In particular, the time intervals Z1, Z2, Z3 are essentially all of the same length.

If it is shown during the time interval Z1 that the counter 21 has exceeded a predetermined numerical value, then the gain factor Xp of the differential amplifier 23 first increases and thus the gain V in the loop is reduced. At the same time, the counter 21 is reset to zero and the timer 22 is reset. Accordingly, the second time interval Z2 begins before the first time interval Z1 has passed. In doing so, it takes advantage of the fact that it is not necessary to know at all how big a mistake is. It is sufficient if the error is known to be corrected.

Fig. 3e shows that the gain V in the loop decreases each time the counter 21 has reached the entered numerical value, in this case the value 3, during the measured time interval Z. It is obvious that two corrections are necessary before the gain V in the loop was so small that the actual temperature T | Although the _ST is still oscillating, the amplitude of this oscillation is usually still within the neutral zone. In this case, only two direction changes occurred within the measured interval Z3. Otherwise, the actual temperature T | _S t satisfies the condition

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Tset- No.5 NZ <Tist ^< NZ + Tset.

The gain V in the loop corresponds to the inverse of the static gain X _{P of the} differential amplifier 23. The following algorithm can now be run. To be determined first

Xp = (1 + λ) x X _P , where λ> 0 a is constant. It is also preferably λ less than 1. After increasing the static gain X _P , which corresponds to a decrease in the gain V in the loop, the cut-off frequency detector 19 is started. When the cut-off frequency detector detects instability, for example the number of 3 or more direction changes during the measured interval Z1. Z2, ... Z _n , then the static gain X _P as described above again increases. If the numerical value of the direction changes has not reached the critical value, it is assumed that a steady state is reached and this static amplification is maintained.

Essentially, the process is therefore divided into two phases. In the first phase, it is ascertained whether there are critical oscillations, and the output of the first phase changes the loop gain accordingly. In the second stage, a stability check is performed.

If no phase vibration is detected in phase 1, the loop gain is increased until an unstable measurement interval is observed, while the adjustment sequence is interrupted, and the previous stable measurement interval gain is selected. 4 illustrates a process for increasing loop gain. First, the static amplification X _P1 is reduced, for example, as determined

X _P = (1 - σ) x Xp, where σ is constant, greater than zero and preferably less than 1. For σ, it may be the same value as λ, but usually it will be a different value.

Then the set temperature Tset changes

Tset - T _S et + Δ sp.

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For this purpose, a fixed value number 24 and a switchable inverting amplifier 25, which is connected to the addition point 26, are provided in the control device. Thereafter, the inverting amplifier is switched, i. to be determined

Δ sp = - Δ sp

Changing the setpoint T _S et causes a jump to interrupt the vibration. Without such oscillation, instability cannot be detected by changing the gain

In the loop. After a change in the set point T _S et, the delay time At is expected. The cut-off frequency detector 19 is then started. When and if the cut-off frequency detector detects stable behavior of the control circuit 18, this process is repeated, i.e., the gain V in the loop increases.

Sometimes the gain V in the loop is so great that the control circuit 18 begins to oscillate. This is in the embodiment of FIG. 4 case at time t3.

In this case, the setpoint T _S et returns to its original value and the static gain X _p is determined _.

Xp = -Xp

- σ and the setup process is complete. Thus, the gain value V in the loop returns to the value that allowed the last stable state.

If, after adjustment, as shown in FIG. 3 or FIG. 4, to achieve a stable state, there is no further adjustment at first, the setting is complete. Only when a renewed instability is detected, for example due to a load change that leads to a valve oscillation, does a new course of settings begin.

Fig. 5 illustrates another possibility for the gain V in the loop to be varied. In this way, a system protection function can be implemented in which the vibration can also be prevented at low loads near idling.

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There is a distinction between high and low loop gain, which can be switched between. The purpose of this protection function is to stabilize and optimize the heating system, depending on the load on the system.

The high gain Y in the loop shown in FIG. 5 denotes as V1, it is in operation under normal load of the heating device 1. This gain VI in the loop could be found, for example, by the automatic adjustment procedure described above. The means not shown in detail can be adapted to store this amplification factor.

The small V2 gain in the loop is used in idle mode.

The cut-off frequency detector 19 is now used to detect when power is complete. In this case, a high amplification of V1 in the loop results in a high amplitude oscillation and a high frequency. Thus, when such an oscillation is detected after a previous increase in gain in the loop, the gain switches from a high value V1 to a lower value V2, and then the system stabilizes again.

To detect the change from idle to consumption, the return temperature is used, followed by the replacement. This is the case, for example, at time t2 in FIG. 5. The sampling is performed between times t2 and t3. The load, in this case water withdrawal, is determined if the actual temperature drops by the value Dz below the set temperature Tset. In this case, the loop gain increases to V1. This gives the controller the necessary speed for normal consumption. At t3 the subscription is complete. Since the gain in the loop is too high, the oscillation is now performed in the measured interval Z2. This is recognized by the cut-off frequency detector and at time t4 the loop gain returns to V2. Loop gain could be found by iteration of the loop to increase loop gain

Claims (13)

PATENT CLAIMS 1. A heating device with a hot-water supply and discharge tank and a heat-transfer fluid supply arrangement with a supply line in which a valve is provided, a temperature sensor to detect the temperature of the heated fluid and a control circuit which controls the valve temperature deviations from the set point, characterized in that the control circuit (18) has a cut-off frequency detector (19) which detects the oscillation at temperature (Tist) and decreases the gain (V) of the control circuit (18) in the loop at high frequency low frequency increases. Device according to claim 1, characterized in that the cut-off frequency detector (19) has a critical value member (20) and the frequency is determined taking into account the output of the critical value member (20). Device according to claim 1 or 2, characterized in that the cut-off frequency detector (19) detects the temperature oscillation (Tist) indirectly from the control signals or from the movements of the valve (11). Apparatus according to one of claims 1 to 3, characterized in that the cut-off frequency detector (19) has a direction change counter (21), a comparator and a time element (22). 5. A method of operating a heating device which detects the temperature of the heated fluid and, depending on the deviation of this temperature from the set point, regulates the flow of heat transfer fluid by means of a valve in the control circuit. if the frequency is too high and increases, the frequency is too small. 31785 / T •·· ······················· Method according to claim 5, characterized in that the frequency of only such deviations is detected that exceed a predetermined difference from the set value. Method according to claim 5 or 6, characterized in that the frequency is detected indirectly based on the movement of the valve and / or the control signals for the valve. Apparatus according to claim 7, characterized in that the number of changes in the direction of movement of the valve is detected at a predetermined time interval and the gain in the loop is reduced if the number exceeds the maximum value. Method according to claim 8, characterized in that the counting is interrupted at each exceedance and the time interval is restarted. Method according to one of Claims 5 to 9, characterized in that, if the frequency is quite small, the gain in the loop is increased and the entered value changes. Method according to one of Claims 5 to 10, characterized in that if the frequency is too high after the gain in the loop is increased, the loop gain value used before the increase is again used. Method according to any one of claims 5 to 11, characterized in that the gain in the loop is set as a function of the load on the device. Method according to claim 12, characterized in that the load on the device by the temperature of the heated fluid is detected.