DE19526793A1 - Fuzzy control of space heating installation - Google Patents

Abstract

Blocking and regulating valves (5,6) for fuel supply to the burner are operated by a fuzzy controller (22) with inputs representing desired and actual temps. (18,12) of forward flow of the hot water, burner exhaust gas and ambient temps. (14,19), a timing program status temp. (20), forward/return flow temp. difference (25), average burn duration (27) and burner switching frequency (28). Re-ignition of the burner is delayed by an amt. representing the demand for heat so that the delay is reduced as the setting of temp. of the forward flow is raised.

Description

The invention relates to a method for controlling a heater system according to the preamble of the independent patent saying.

The performance of a heating system, for example an order water heater, a gas or oil boiler, is becoming more normal so way to the heating needs of an apartment or a house adapted to the maximum output of the heating system is only required at very low outside temperatures.

In the rest of the time, the heating system has to draw less power give. In a heating system with a modular burner is that up to the minimum burner output without switching off the Brenners possible. For combination water heaters where the maximum device performance from that to domestic water heating necessary power is determined, the maximum necessary performance for heating the heating water mostly below the burner output adjustable minimally by modulation. Therefore must be used with modulating combination water heaters - as with non-modulating devices - the burner with low heat acceptance is operated in cycles.  

The ratio between switch-on time and switch-off time results derive from the ratio between the lei taken off and the minimum adjustable burner output. At one tiered boilers is the nominal output. If the heating system requires 1 kW of power, for example, the heater but can only deliver a minimum of 10 kW, the clock ratio consequently be 1:10, which means that with one burner run time of 1 minute or a period of 10 minutes a 9-minute burner lockout period that must.

The burner runtime is a generally customary one weather-dependent flow temperature control from this be Right. To regulate a specified flow target temperature the burner must exceed the set flow temperature be switched off. The burner runtime is also from Time constant of the heating system dependent. Because circulation water heaters can only have a small time constant burner runtimes are in the range of seconds. To extend Only the burner lockout can therefore reduce the burner runtime time to be adjusted.

Heat sources with a low time constant and thus low thermal inertia require a timing element to limit the number of operating cycles, which forces the burner to take predetermined breaks. Devices are known - for example according to DE-OS 37 18 653 - which have a timer which is set at the factory with a fixed blocking time of approximately 5 minutes. In such a device described in EP-PS 8 461 there is provided a control device with a timer, the fixed blocking time of which runs repeatedly in succession as long as no heat request occurs. This minimum blocking time has a disadvantage, in particular in systems with low water content and thus a low time constant, for example when using plate radiators, since the blocking time may then be too long. After turning on the burner, the temperature rises quickly and below the flow temperature set value VT _should. The burner switches off again after a short time, so that the system can be expected to cool down considerably in the subsequent blocking period. The consequences are very strong temperature fluctuations, which often trigger complaints. For this reason, the timer in a known circulating water heater is provided with a potentiometer for adjusting the blocking time. However, a position for a shorter lock-up time can only be carried out by customer service specialists, with the number of operating cycles of the device reducing the number of operating cycles. Increasing the number of switching cycles, i.e. the burner's switch-on and switch-off frequency, also results in an increase in start-up emissions in the burner's starting phase.

From DE-OS 39 08 136 and DE-PS 34 26 937 are Vorrich become known with the help of which the blocking period in Ab dependence on the length of the previous switch-on period or the number of heat consumers switched on is determinable. These devices are only suitable for be agreed heating systems. In addition, there are complex circuits with sensitive sensors required.

The invention has for its object a universal Ver drive to control a heating system of the above Specify the way in which the ease of use, the Number of operations and the starting emissions of the heating system ver be improved.

The object is achieved by the characterizing Features of the independent claim solved. Through the Introduction of a variable, using a fuzzy controller automatically optimizing reclosing time results an adaptation of the number of switching cycles to the time behavior of the Heating system and the respective heat demand situation. All Commonly applies that with high heat requirements, for example very low outside temperature, short blocking times and low high heat demand result in long blocking times. Thereby in a heater already existing sensors or Target values used.

The following rules specified in the dependent claims can be used individually or in any combination the.

Claim 2

If the flow target temperature is high, then the Bren lockout time be small. High flow target temperatures indicate a high heat requirement, with only a short burner block times are necessary.  

Claim 3

If the rate of change of the actual flow temperature during a start phase that is greater than the time constant of the Heater is large, then the burner blocking time must be long his.

During the start phase, the rate of change of the Actual flow temperature through the time constant of the heater and determines the water flow of the heating system. At a Small water flow will result in little power from the heater plant requested, that is, there are long burner blocking times sensible.

Claim 4

If the rate of change of the actual flow temperature after the start phase is large, then the burner must lockout time be small.

After the start-up phase, the change will be quick speed of the actual flow temperature by the time constant of Heating system determined. With a small time constant, that means rapid increase in the actual flow temperature, is with ge wrestle to count amounts of water in the heating system. Hey system with low water content cool down quickly and he therefore do not allow long burner blocking times.

The length of the start phase is in claim 5 is either predetermined in accordance with (for example 1 or 2 minutes) and constant or according to claim 6 with the difference in temperature history between the flow temperature VT _and the temperature T _WT in the area of a heat exchanger variable, wherein the start-up phase then T _WT - VT _is = const. is finished. By determining the actual length of the start phase, errors in the determination of the rate of increase of the actual flow temperature value VT _is avoided, which occur when the start phase is too short, and on the other hand, the determination period for the rate of increase is not unnecessarily extended, which with a very long start phase to be expected for safety reasons.

Claim 7

If the rate of change of the actual flow temperature is large and the change in the deviation between lead and Return temperature is low, then the burner blocking time be small.

If there is a difference between the flow and return temperatures barely changes, the time behavior of the actual Temperature only determined by the heating system. The The consequence is the same as described for claim 2.

Claim 8

If the rate of change of the actual flow temperature is large and the change in the deviation between lead and Return temperature is high, then the burner blocking time must be long his.

If there is a difference between the flow and return temperatures changes dramatically, the time behavior of the actual flow tem temperature only through the time constant of the heater and the Water throughput determined by the heating system. The consequence is the same as described for claim 3.  

Claim 9

If the deviation between the target flow temperature and the forward Current actual temperature when the burner is switched off and the Circulation pump is small, then the burner blocking time must be long. In this case, the heating system has only changed slightly cooled and therefore requires little power.

Claim 10

If the average burner runtime is short, then the burner lockout time should be long. Small burner runtimes indicate egg low heat loss.

Claim 11

If the average degree of modulation is small, then the Bren lockout time should be long. The burner runtimes and burner locking times averaged degree of modulation gives the removed Performance.

Claim 12

If the start-up frequency is high, then the burner must lockout time be large. The high switch-on frequency can be caused by longer burner blocking times can be reduced.

Claim 13

If the outside temperature is low, then the burner must lockout time be small. Signalize low outside temperatures a high heat requirement.  

Claim 14

While lowering the flow target temperature (for example Night reduction) the burner blocking time must be long. Disruptive Noises in the night phase can be avoided.

Claim 15

If the exhaust gas temperature is low, then the burner must lockout time be large. Low exhaust gas temperatures can increase indicate low energy requirements.

When implementing the fuzzy controller, of course, also the inverse of the rules listed above will. For example, the rule according to claim 2 must also be

• - If the flow target temperature is medium, then the Burner lockout time should be medium,

and

• - If the target flow temperature is low, then the Burner lockout time should be long

be specified.

A fuzzy controller is ideal for implementing the rules.

Advantageous developments of the invention are in the sub claims marked or are below  together with the description of preferred versions of the Er invention shown in more detail with reference to the figures.

Show it:

Fig. 1 is a schematic representation of a heating system and

Fig. 2 components of a controller.

In Fig. 1, the typical structure of a heating system is Darge. Such a heating system consists essentially of a heat exchanger 1 , which is connected to a return line 2 and a flow line 3 and which is heated by a burner 4 , which is fed via a fuel supply line 7 provided with a shut-off valve 5 and a control valve 6 . The shut-off valve 5 and the control valve 6 are connected to a control device 8 , which opens or closes the shut-off valve 5 to enable or disable the fuel supply line 7 and acts on the control valve 6 in a modulating manner to set the desired output. The ignition and monitoring of the burner 4 takes place - as is generally customary - by means of a burner control (not shown) or a thermoelectric ignition fuse (not shown). For control and monitoring, a flow temperature sensor 9 , a return temperature sensor 10 and an exhaust gas temperature sensor 11 are available. The temperature sensors 9 , 10 and 11 can be designed, for example, as temperature-dependent resistors, so that lines 12 , 13 and 14 between the sensors 9 , 10 and 11 and the control device 8 with the respective temperatures have pending voltages on the associated connecting lines. Furthermore, the control device 8 is connected, for example, to a weather-compensated control device 15 installed in the living room, which is guided via a line 16 by an outside temperature sensor 17 and serves to regulate the flow temperature. Via a digital interface between the external controller 15 and the control device 8 can on signal lines 18, 19 and 20 in addition to the flow temperature set value _{is to} VT and the outside temperature T _Auss and status values of a time program, such a game is a reduced temperature t _abs , be transmitted. A circulation pump 21 is also integrated in the return line 2 .

In Fig. 2, the components of the control device 8 are Darge, which are necessary to determine and implement a burner lockout time. Further components of the control device 8 , for example for exhaust gas monitoring or regulation of the return temperature, are not shown for simplification. The individual control components can also be mapped as software programs in a microcomputer / processor.

The main component is a fuzzy controller 22 , which links the following input variables:

• - the pending on the signal line 18 set flow value _{is to} VT,
• the actual flow temperature pending on the connecting line 12 _is VT,
• - The existing exhaust gas temperature T _ab on the connecting line 14 ,
• the outside temperature T _outside present on the signal line 19 ,
• the lowering temperature T _abs present on the signal line 20 ,
• - the change of the surface zeitli formed via a first differentiating member 23 flow temperature actual value of d / dt VT _is
• - the member via an AND gate 24 and a second differentiator 25 from the flow temperature actual value VT _and the return temperature actual value RT _is temporal Än formed alteration d / dt _(VT - _RT) of the difference between flow - and return temperature as well
• - A signal proportional to the average burner running time via averaging 26 on the input line 27 and
• - A signal characterizing the number of burner cycles on line 28 .

The actual flow temperature value VT _is on the connecting line 12 and the desired flow temperature value VT _{should be} on the signal line 18 to form a control deviation on a subtractor 29 which is connected to a flow controller 30 . The output signal of the flow controller 30 on the line 31 is fed to a comparator 32 , the averaging 26 and the control valve 6 . The comparator 32 , the function of which is described below, generates the signal 28 which characterizes the number of burners and which, in addition to the fuzzy controller 22, is fed to an adjustable mono-flop 33 and an AND gate 34 . The second input of the AND gate 34 is formed by the output signal 35 of the mono-flop 33 . The time constant of the mono-flop 33 is controlled via a control line 36 from the output signal of the fuzzy controller 22 which specifies a burner blocking time. This affects the burner blocking time an input (signal 35 ) of the AND gate 34 , the output signal 37 from which the check valve 5 controls.

The burner blocking time formation works as follows:

Depending on the control deviation, which is formed by the second subtractor 29 , the flow controller 30 generates a modulation signal which is present on the line 31 . If this signal is above the minimum device power - for example 50% of the nominal power - the comparator 32 controls the shut-off valve 5 via the AND gate 34 , thereby putting the burner 4 into operation, and the control valve 6 is operated by the flow controller 30 according to the determined modulation signal on line 31 with a greater or lesser degree of opening. If the modulation signal falls below the minimum value after sufficient heating of the heat exchanger 1 , the comparator 32 switches off the shut-off valve 5 and triggers the fuzzy controller 22 with the falling edge via the burner cycle number signal 28 . However, the fuzzy controller 22 can also control the mono-flop 33 in the activated state, that is to say with a positive signal on the control line 36 , in such a way that its output signal 35 blocks the AND gate 34 and thus the shut-off valve 5 remains closed.

The length of the burner blocking time is determined by the fuzzy controller as a function of the following input variables and is given to the meno-flop 33 functioning as the burner blocking time element:

• - actual flow temperature VT _ist (line 12 ),
• - change the flow actual temperature (about ferenzierglied is first formed Dif 23) d / dt _is VT,
• - Flow set point temperature _to VT (line 18),
• - Change in the deviation between the flow and return actual temperature (is formed by subtractor 24 and second differential element 25 ) d / dt (VT _ist - RT _ist ),
• Exhaust gas temperature T _ab (line 14 ),
• - outside temperature T _outside , indirectly via weather-compensated control device 15 (line 19 ),
• - Status of the time program (heating phase, lowering phase) T _abs (line 20 ),
• averaged modulation signal, ie integration of the modulation signal by averaging 26 over a fixed period (line 27 ),
• Time since burner start (not shown in FIG. 2): when implemented with a software program, it can simply be determined by a software counter and made available to the fuzzy controller 22 implemented in software,
• - Average burner runtime (not shown in Fig. 2): can easily be determined by a software algorithm when implemented with a software program, e.g. B. storage of the last 10 burner runtimes and formation of the mean value,
• - Switch-on frequency (not shown in Fig. 2): can be calculated in a implementation with a software program simply by counting the burner starts in a predetermined time window (e.g. every hour).

The input variables are processed according to predetermined rules by the fuzzy controller 22 or linked together. These rules have already been discussed in detail above, so that repetition is unnecessary here.

The embodiment of the invention is not limited to preferred exemplary embodiments specified above. A lot a number of variants are conceivable, which of the represent  provided solution even with fundamentally different types of out make use of guides. In particular, the Er not finding the realization with discrete logical construction groups, but can be advantageous with programmed logic - preferably using a microprocessor - reali sieren.

Claims (15)

1. A method for controlling a heating system with a burner-operated heat source, egg ner circulation pump and a control device with which a reclosing lockout time of the burner can be predetermined after it has been switched off due to its heat requirements, characterized in that the reclosing lockout time of at least one parameter representing the heat requirement can be varied by means of a fuzzy controller ( 22 ) in such a way that the blocking time of the burner ( 4 ) decreases with increasing parameter value. 2. The method according to claim 1, characterized in that the parameter is a Vorlauftempe temperature target value VT _should . 3. The method according to any one of the preceding claims, characterized in that the parameter is an inverse change of the actual flow temperature value VT _is during the shutdown preceding the start-up phase of the burner ( 4 ), the change d / dt VT _{is determined} during a start-up phase of the burner ( 4 ) comprising a period of time t 1. 4. claims method according to any of the preceding An, characterized in that the Pa d parameters a change / dt VT _is the flow temperature actual value of _VT is during the previous disconnection start-up phase of the burner (4), wherein the change by From the start of a period t 1 comprising the burner ( 4 ) is determined. 5. The method according to any one of claims 3 or 4, characterized in that the period t₁ the start phase (for example 1 or 2 minutes) and is constant. 6. The method according to any one of claims 3 or 4, characterized in that the period of the start phase with the temperature difference curve _and the temperature T _WT varies in the range of a heat exchanger (1) between the flow Tempera ture VT, wherein the time period t₁ T _WT - _VT = const. is finished. 7. The method according to any one of the preceding claims, characterized in that the parameter d it ste a change / dt VT _is the flow temperature actual value of VT _is the second parameter and an inverse change the difference between the flow temperature actual value VT _and the return temperature actual value _RT is. 8. The method according to any one of the preceding claims, characterized in that the first parameter is an inverse change the flow temperature actual value _VT, and the second parameter d, a change / dt _(VT - _RT) of the difference between the flow temperature actual value VT _and the return temperature actual value _RT is. 9. The method according to any one of the preceding claims, characterized in that the parameters a change Pa d / dt (VT _should - _VT) the difference between the set flow value _{is to} VT and the outlet temperature actual value VT _is at is switched off burner ( 4 ) and running circulation pump ( 21 ). 10. The method according to any one of the preceding claims, characterized in that the parameter is a previous switch-off, averaged duty cycle of the burner ( 4 ) within a time window, for example an hour. 11. The method according to any one of the preceding claims, characterized in that the parameter is a modulation degree of the burner ( 4 ) averaged within a time window, for example an hour, as a measure of the power consumed. 12. Method according to one of the preceding An sayings, characterized in that the Pa parameter is an inverse frequency of switching on. 13. The method according to any one of the preceding claims, characterized in that the parameter is an inverse outside temperature 1 / t _outside . 14. A method according to any one of the preceding claims, characterized in that the Pa parameters an inverse difference 1 / (VT _should - VT _abs) between the flow Tempera ture target value VT _to and decreased during egg ner lowering phase flow Tempera ture target -Value is VT _abs . 15. The method according to any one of the preceding claims, characterized in that the parameters Pa, an exhaust gas temperature T is _ABG.