CZ20013296A3 - Heating equipment and operation thereof - 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

HEATING EQUIPMENT AND METHOD OF OPERATION

Technical field

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a heating apparatus having a supply vessel with a heated fluid inlet and outlet, and to a supply for a heat transfer fluid having a supply line in which a valve is provided. temperature deviation from the setpoint. Furthermore, the invention relates to a method of operating a heating device in which the temperature of the heated fluid is determined and, depending on the deviation of this temperature from the set point, the supply of the heat transfer medium is controlled by a valve in the control circuit.

BACKGROUND OF THE INVENTION

The invention is further described on the basis of an apparatus for the preparation of hot service water. However, it can also be used for other heating systems in which the heating element or 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 a circulator in heating systems is known from DE 24 52 515 A1. Here too, a similar principle is used.

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

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The heated fluid extracts its heat from the heat transfer fluid. The heat transfer fluid can pass through a heat exchanger on the other side of which a 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.

However, it is common in all cases that the heat transfer fluid is controlled by a valve. If the temperature of the heated fluid drops, 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 if the valve is capable of controlling 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 determined in the storage vessel. It is also possible to measure this temperature in the supply line from the storage vessel to the actual heating circuit. In extreme cases, the storage vessel may be relatively small or even formed by a heating device.

With such devices, these conflicting phenomena now exist. On the one hand, the temperature of the heated fluid should be kept at the set value as best as possible. Thus, if there is a need for heat, for example, when hot water is drawn at the tapping point, the heat transfer fluid should return the removed heat as quickly as possible in order to heat the supplied cold water again. On the other hand, it has been found that very fast control circuits tend to oscillate. It has it with hot water systems

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PV 2001 - 3296 • The obvious consequences. Water temperature fluctuates. In a heating device that only supplies the heater or even only underfloor heating, the temperature oscillation is less critical. However, even in this case, the oscillation leads to a considerable load on the valve or the valve. an 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 low mechanical load.

This object is attained in the heating apparatus of the foregoing type by having a control circuit having a limit frequency detector which detects oscillations in temperature and increases the control circuit gain 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, the oscillation whose frequency exceeds the permissible level 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 completely avoiding temperature oscillations. The only thing is that the loads acting on the mechanical adjusting elements, such as the valve or actuator, must be kept low so as not to reduce the service life too strongly. The loop gain of the control loop can be changed relatively simply by changing the static gain of the controller. On the other hand, it is proportional to this static gain of the controller.

Preferably, the cut-off frequency detector has a critical cell

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PV 2001 - 3296 • Values and Values detects the frequency taking into account the output of the critical value cell. In other words, only frequency oscillations whose amplitude is greater than the critical value are detected in the frequency detection. This creates a corridor around a 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 oscillations that originate from this corridor.

Preferably, the temperature detector detects the oscillations at temperature indirectly from control signals or from valve movements. The control circuit should only operate the valve when necessary, in other words, if the temperature deviates from a predetermined value above a predetermined value. If there is such a deviation, 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, the existing information is used in the control circuit.

This object is solved in a method of the kind mentioned above by detecting the frequency of oscillations in temperature and the amplification in the loop decreases if the frequency is too high and increases if the frequency is too small.

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 oscillations. This results in a very fast reaction and at the same time saves in particular mechanical components such as actuators and valves. The adjustment of the amplification in the loop takes place adaptively. precisely adapted to the current situation. It can therefore vary from device to device and from one device to another.

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It is advantageous in this case that the frequency of only such deviations which exceed a predetermined difference from the set value is detected. Thus, a corridor is created around a set value, in which vibration at any frequency is allowed. These oscillations do not cause excessive stress on the adjusting members, since the resulting adjusting movements are very small. Also, for a potential hot water user, the oscillations within this corridor are hardly obvious and therefore acceptable.

Preferably, the frequency is determined indirectly based on valve movements and / or valve control signals. The control signals, respectively. the resulting valve movements are the immediate consequences of temperature deviations from the setpoint. Thus, the deviation information is available and presents relatively easily detectable signals. These can then be evaluated at 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 when the number exceeds the maximum value. Frequency detection may then be limited to a simple subtraction, naturally the subtraction may 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. Should there be more changes in the direction of movement than determined, then the system is observed to be unstable and the loop gain decreases.

It is particularly advantageous for the counting to be interrupted every time it is exceeded and the time interval starts again. This does

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achieves an even more steady state. The more unstable the system, the higher the frequency, ie. the more often the valve changes the direction of its movement. If a proofreading is performed when the criterion is met, then the entire time interval does not have to wait for the proofreading to be performed. 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 set value changes. Thus, not only the gain in the loop increases, but also the set value changes to determine whether the system, ie. control circuit, gets into oscillation. Also, in a non-oscillating system, increasing the loop gain would not automatically result in oscillation, so it is uncertain whether loop gain is appropriate. Changing the entered value, however, generates a jump that delivers the requested information.

Preferably, if the frequency gain is too large after the loop gain is increased, the loop gain value used prior to the increase is utilized. This reliably approaches the border. At the same load, we have information at which the loop gain is still stable and we know that the next time the loop is no longer stable. We can then return to the previous loop gain without having to perform a renewed iteration.

In a particularly advantageous embodiment, it is proposed that the gain in the loop is set depending on the load on the device. This is another possibility for the control system, respectively. the moving parts in it protected against the load by too much movement. If the demand for the device is small, for example if only a small amount of hot water is drawn, a small amplification is sufficient

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Ί

9 9 9 9 9 9

9 9 9 9 9 9 9 9 9 • • · · · · · ·

99998 9 99998 9 9

9 9 9

9 9 9 9 9 9 9 9 9 9 9 9 9. A quick reaction is also not necessary. The same is also true if most of the heater valves of the heater are throttled, for example, at night, so that little heat is consumed or dissipated. If, on the other hand, a need arises, i.e. if, for example, hot water is withdrawn or the radiator valves are turned, then a rapid reaction of the device is required. In this case, it can switch 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 steps.

Preferably, the load of the device is determined by the temperature of the heated fluid. This procedure is quite fast and does not require additional structural elements. If the equipment is burdened by, for example, hot water consumption, 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 vibrations immediately occurring. If, after some time, the oscillation occurs, it can be assumed that the load of the device is now terminated and we can return to the value of the free run of the gain in the loop.

BRIEF DESCRIPTION OF THE DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of a hot water heating device;

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PV 2001 - 3296 ·· · ·

giant. 2 schematic representation of the controller machines, giant. 3 different curves k loop gain, display reduction giant. 4 appropriate waveforms for loop amplification; and display increase giant. 5 schematic representation k system protection. explanation function

DETAILED DESCRIPTION OF THE INVENTION

Giant. 1 shows schematically a heating device 1 for the production of domestic hot water which can be withdrawn by taps 2 or other tapping points. The water taps 2 hang on a circuit 2 ^{with a} supply line 4 and a return line 5, which are connected to a storage vessel 6, for example a boiler. A circulating pump 7 is provided in the duct 2, which ensures that hot water is available without significant delay at the taps 2.

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

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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 to enter 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 vessel 6 through the supply line 16. The non-return valve 17 prevents water from the circuit 2 from flowing into the line 16. With the cold water supply the temperature drops naturally hot water, which is already in boiler 6. This temperature drop is detected by a temperature sensor 22. ^Based on this finding, the control device 14 controls the motor 12 which opens the valve 11. The parts thus form together a control circuit 18. The control device 14 forms its own regulator having a static gain X _P. The reciprocal of this static gain X _F is referred to as the loop gain V.

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 of the elements to which the control device 14 in FIG. 1 is connected.

The control device 14 has in particular a differential amplifier 23, to which the setpoint is supplied via input 15 and the actual temperature value by the temperature sensor 22 ^, depending on the difference

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44 9 9 99

9 9 9 9 9 9 9 9 9

99999 9,999 9 9 9

99999 9 9 99 99 9 between these two values, an appropriate adjustment signal for motor 12 is generated. However, the static gain of this differential amplifier 23 is variable. The limit frequency detector 19 is used for the change. The cut-off frequency detector 19 first receives the same signals that the motor 12 also receives. It also obtains the actual temperature and the desired temperature. These signals, respectively. values are fed to the preparation device 20, which, as explained below, under a predetermined condition, a critical value cell.

generuj e

Counter pulse counter and among other things has to supply counter 21.

it is connected to a timer 22 which indicates the start and end of a predetermined one

Impulses with time interval. The counter output 21 is connected to the reset input of the timer 22.

Furthermore, the output of the counter is connected to a differential amplifier 23, more precisely to an input at which the amplification factor can be adjusted, i. static gain.

The operation of the control circuit 18 will be described with reference to FIG. 3.

Giant. 3a shows the curve _T13t , i. the temperature of the inlet pipe. The set value Tset, ie the setpoint of temperature, is indicated by dashed lines. Furthermore, the neutral zone N _{z is} indicated on both sides of the set point T _S et. Obviously, the temperature T _IST initially fluctuates relatively strongly. The differential amplifier 23 generates, at specified intervals, the pulses for controlling the motor 12 shown in FIG. 3b. If the actual temperature T _{IST is} less 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-). Naturally, this view is for example only. Other types of valve displacement 11 are naturally

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also possible.

In this heating device, it is assumed that the re-adjustment of the valve 11 is non-critical if it takes place in the same direction. We only want to prevent the direction of movement of the motor 12 and the valve 11 from changing too often.

Thus, the course of the adjustment direction shown in FIG. 3c is derived from the individual pulses shown in FIG. Giant. 3d now shows the default counter value 21, which increments by 1 each time the direction is changed. 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 during the time interval Z1 it becomes apparent that the counter 21 has exceeded a predetermined numerical value, then the amplification factor X _{p of the} differential amplifier 23 first increases, thereby decreasing the gain V in the loop. 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 completely. It takes advantage of the fact that there is no need to know at all how big a mistake itself is. It is enough to know that an error exists to correct it.

Giant. Fig. 3e shows that the gain V in the loop decreases each time the counter 21 has reached a given numerical value, in this case a value of 3, during the counting time interval Z, in this case 3. that real

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PV 2001 - 3296 the temperature Tist still oscillates, but the amplitude of this oscillation is usually within the neutral zone. In this case, only two direction changes occurred within the calculation interval Z3. Otherwise, the actual temperature Ti _ST satisfies the condition

Tset ^- 0.5 NZ <Tist <NZ + T SET ·

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

X _P = (1 + λ) x X _P , where λ> 0 a is constant. Also preferably, λ is 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 count interval Z1, Z2, ... _{Zn /,} then the static gain Xp, as described, again increases. If the numerical value of the direction changes has not reached a critical value, it is assumed that a steady state is achieved and this static gain is maintained.

In essence, the process is divided into two phases. In the first phase, it is ascertained whether there are critical oscillations, and at the output of the first phase, the gain in the loop changes accordingly. In the second stage, the stability check is carried out.

If no phase oscillation is detected in phase 1, the loop gain increases until an unstable count interval is observed, interrupting the adjustment sequence, and selecting the gain of the previous stable count interval. Giant. 4

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PV 2001-3296 illustrates a process for increasing loop gain. First, the static gain Xp, in which it is determined, for example, is reduced

X _P = (1 - σ) x X _p , 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 T _SE ? changes

Tset ^- Tset + sp.

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

Asp = Asp.

Changing the setpoint T _SET causes a jump to cancel the oscillation. Without such oscillation, instability cannot be detected even by changing the gain V in the loop. After the set point Tset has been changed, the dwell time At is expected. The cut-off frequency detector 19 is then started. When and if the cut-off frequency detector detects a stable behavior of the control circuit 18, this procedure is repeated, i.e., the control circuit 18 is repeated. the V gain in the loop increases.

Sometimes the loop gain V is so large that the control circuit 18 begins to oscillate. This is the case at time t3 in the embodiment of FIG. In this case the setpoint T _SE 16 82554 (82554a)

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In 9 9 9 9 9 9 9 9 9 f 9 9 9 9 9 9

9 9 9 9 9 9

9 · 9 ·· · «9 9 9 9 9 returns to its original value and the static gain is determined

X _P

Xp = ---- Xp

- σ and the setup process is complete. The value of V gain in the loop

therefore state. returns on value, which enabled last stable Has- li se AFTER progress setup how is shown on Fig. 3 or giant 4, to achieve stable condition, does not occur

no other settings first, the setting is complete. Only when a renewed instability is detected, for example, due to a change in load that leads to valve oscillation, does a new adjustment sequence begin.

Giant. 5 illustrates another possibility for the V gain in the loop to be varied. As a result, a system protection function can be implemented, in which, at low loads near idling, vibration can also be avoided.

Here we distinguish between high and low loop gain, which can be switched between. The purpose of this protective function is to stabilize and optimize the heating device 1, depending on the load on the device.

The high gain V in the loop, which is referred to in FIG. 5 as VI, is in operation under normal load of the heating device 7. This loop gain VI could be found, for example, by the automatic adjustment procedure described above. The means (not shown) may be adjusted to store this amplification factor.

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PV 2001 - 3296 • 4 · »* 4 * · ··· 444 · 4 4 ·

4 4 · 4 4 · 4 · 4 04 44440

A small V2 loop gain is used in idle mode.

The cut-off frequency detector 19 is now used to detect when the power consumption is complete. In this case, the high gain VI in the loop leads to high amplitude and high frequency oscillations. Thus, when such an oscillation is detected after a previous increase in loop gain, the gain switches from a high value V1 to a lower value V2, whereupon 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. In this case, a take-off takes place between times t2 and t3. The load, in this case water abstraction, is determined if the actual temperature drops by the value D ₂ below the set temperature T _EET . In this case, the loop gain increases to a value of VI. This gives the controller the necessary speed for normal consumption. At t3, the subscription is terminated. Since the amplification in the loop is too high, the oscillation takes place now in the calculation 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 its appropriate iteration to increase loop gain.

Claims (12)

PATENT CLAIMS 1. A heating device with a hot-water supply and discharge tank and a heat-carrying fluid supply 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 a temperature deviation from the set point, characterized in that the control circuit (18) has a limit frequency detector (19) which detects the temperature oscillation (Tist) and 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 cell (20) and the frequency is determined taking into account the output of the critical value cell (20). Device according to claim 1 or 2, characterized in that the cut-off frequency detector (19) detects oscillations at temperature (Tist) indirectly from control signals or from movements of the valve (11). Device according to one of Claims 1 to 3, characterized in that the cut-off frequency detector (19) has a direction counter (21), a comparator and a time cell (22). 5. A method of operating a heating device in which the temperature of the heated fluid is determined and in dependence on the deviation 16 82554 PV 2001 - 3296 • 9 9 · 99 99 »9 O 9 999 ··· · ··· 99 99 ·· 9 This temperature from the set point is controlled by the supply of heat transfer fluid by means of a valve in the control circuit, characterized by detecting the frequency of temperature oscillations and gain high, in the loop decreases if the frequency increases if the frequency is too small. too much 6. Method according to claim 5, characterized in that the frequency of only such deviations is detected, exceeding a predetermined difference from the set value. which Method according to claim 5 or 6, characterized in that the frequency is determined indirectly on the basis of valve movements and / or valve control signals. by advance Apparatus according to claim 7, characterized in that the number of changes in the direction of movement determined by the time interval is determined and the gain in the valve in the loop decreases when the number exceeds the maximum value. Method according to claim 8, characterized in that the counting is interrupted at each exceedance by the time interval restarting. Method according to one of claims 5, characterized in that, if up to 9, the frequency is rather low, the amplification in the loop increases and the set value changes. Method according to one of claims 10 to 10, characterized in that, if the gain in the frequency loop is too high, the value of the gain in the loop used again before the increase is again. PO increase used 16 82554 PV 2001-3296 Method according to one of Claims 5 to 11, characterized in that the gain in the loop is set in dependence on the load on the device. Method according to claim 12, characterized in that the loading of the device by the temperature of the heated fluid is detected.