METHOD FOR CONTROLLING A CIRCULATION PUMP AND CIRCULATION PUMP

Description

[0001] The invention relates to a method for controlling a variable-speed circulation pump in a hydraulic system, in particular in a heating system, and to a circulation pump, in particular a heating circulation pump, for carrying out the method.

[0002] Older heating circulation pumps, especially those for small or medium-sized heating systems, are often unregulated, meaning their output must be manually adjusted to the specific heating system's requirements. The pump offers different output levels for manual selection. If the output level is not manually adjusted within the heating system, a sufficiently high output level must be selected to ensure adequate flow even during peak demand. Since these peak demands are only brief, the pump will predominantly operate at an energy-inefficient level.

[0003] Due to increasingly stringent energy efficiency requirements, modern circulation pumps are equipped with frequency converters and speed controllers that allow the speed to be adjusted according to a control curve. Using an estimation algorithm, the pump determines its current flow rate and head and adjusts the speed so that the operating point can only shift along the respective control curve.

[0004] EP 1 323 986 A1 discloses a method for controlling a speed-controlled heating circulator pump, in which the pump speed can be varied along a control curve. DE 195 25 887 A1 describes a method for adapting the hydraulic performance field of a centrifugal pump unit to the requirements of a heating system.

[0005] In Figur 1Control curves 3, 4, and 5 are shown for three different pump control strategies. With constant pressure control according to control curve 3, the pump regulates its speed independently of the flow rate to maintain a constant delivery head. With proportional pressure control according to control curve 4, the delivery head is always adjusted proportionally to the flow rate along a straight line. In Eco mode with control curve 5, the behavior is similar to proportional pressure control, except that the control curve here represents a quadratic function (parabola). Curve 1 indicates the maximum operating range of the pump.

[0006] The curve characteristics and the endpoint of the control curve selected for pump operation must usually be set by the user before operation begins. For energy-efficient operation, the control curve should always be set just above the minimum system characteristic curve 2 according to [reference to relevant data]. Figur 1The system characteristic curve corresponds to the pipe resistance of the hydraulic system and changes with the degree to which the thermostatic valves of the individual radiators are open. The minimum system characteristic curve is reached when all thermostatic valves are fully open. The current operating point of the pump is determined by the intersection between the applied control curve of the pump and the actual system characteristic curve. If the control curve lies below the actual minimum system characteristic curve, the radiators will not be able to adequately heat the room. Conversely, if the control curve lies significantly above the actual minimum system characteristic curve, the thermostatic valves will close, and the pump will consume more energy than necessary.

[0007] The difficulty with this approach lies in the fact that the actual minimum system characteristic curve is often unknown or can only be roughly estimated. In practice, therefore, a proportional or parabolic control characteristic curve is frequently used, which lies sufficiently or significantly above a minimum system characteristic curve estimated by the installer, in order to always have an adequate power buffer. However, this difference between the system characteristic curve and the control characteristic curve is a characteristic value for the pump's excess power and thus for the existing energy-saving potential of such pumps.

[0008] Therefore, a method for controlling the circulation pump is being sought that adequately addresses the problems mentioned above while still optimizing the energy efficiency of the pump.

[0009] This problem is solved by a method for controlling a circulation pump, in particular a heating circulation pump, according to the features of claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

[0010] According to the invention, it is proposed that the pump speed be controlled based on a control curve stored in the pump controller; that is, the pump speed of the pump drive is set depending on this selected control curve. For the initial start-up of the pump, an initially estimated minimum system characteristic curve is set or stored in the pump controller. For subsequent pump operation, it is proposed according to the invention that the pump independently determines a new expected minimum system characteristic curve during regular pump operation, which ideally represents the actual minimum system characteristic curve better than the initial or previously used expected minimum system characteristic curve. Hereinafter, the term "expected minimum system characteristic curve" will be used whenever this curve is determined by the pump itself during pump operation.Instead, the "real minimum system characteristic curve" should be understood as the actual, physically present system resistance with fully open valves.

[0011] If the newly determined expected minimum system characteristic curve lies predominantly below the initially estimated minimum system characteristic curve, the pump control system uses it as the new expected minimum system characteristic curve and adjusts the control curve accordingly. Conversely, if the new expected minimum system characteristic curve lies above the previous expected minimum system characteristic curve, it is preferably discarded, and the control curve remains unchanged. However, this is not mandatory. For correction purposes, the new expected minimum system characteristic curve may occasionally be used to adjust the control curve, even if it lies above the last used expected minimum system characteristic curve.

[0012] As already described in the introduction, energy-efficient control always aims to adapt the control curve as closely as possible to the actual minimum system characteristic curve. The method according to the invention is intended to recalculate the expected minimum system characteristic curve one or more times during operation, with the aim of approximating it as closely as possible to the actual minimum system characteristic curve.

[0013] According to the invention, the new expected minimum system characteristic curve is determined by the following process steps. First, the pump is to detect a steady-state operating point of the circulation pump. Such a steady-state operating point is characterized by a substantially constant flow rate over a certain period of time. A steady-state operating point is assumed when the room temperature in the heated rooms remains substantially constant and, accordingly, a constant system resistance is also established. In this case, the pump should operate with a constant flow rate. However, since in practice certain fluctuations in the flow rate cannot be ruled out even in such a steady-state operating condition, a narrow tolerance range with an upper and lower limit for the flow rate is preferably defined.If the flow rate determined by the pump is within this tolerance range, a nearly constant flow rate is assumed and the pump operates from a steady-state operating point.

[0014] The duration for which the flow rate must remain nearly constant or within the tolerance range is preferably adjustable. Possible periods include between one and three hours, for example, approximately two hours.

[0015] If the pump control system detects a steady-state operating point, it initiates a continuous reduction in pump speed while simultaneously monitoring the pump flow rate. In a stationary system, this speed reduction would, in principle, lead to a decrease in the pump flow rate. However, in a system with variable system resistance, particularly a heating system with thermostatic radiator valves, this measure causes the thermostatic radiator valves to attempt to compensate for the reduced flow rate and the associated lower heat transfer by continuously increasing the valve opening in order to maintain the desired room temperature. For this reason, the flow rate initially remains constant.

[0016] However, as the pump speed is further reduced, the thermostatic valves are forced to open fully or as far as possible, ultimately reducing the system's piping resistance to a minimum and bringing the system state to the minimum characteristic curve. If the pump speed is further reduced in this state, the resulting reduction in flow rate can no longer be compensated for by the valve opening, and the flow rate supplied by the pump actually decreases. This decrease in flow rate shifts the pump's operating point downwards along the minimum characteristic curve. This effect is used to mathematically calculate the expected minimum characteristic curve. As soon as the pump detects a significant drop in flow rate, the flow rate and delivery head are simultaneously recorded over a specific period.From the recorded curves of the two parameters, the expected minimum system characteristic is then calculated, taking into account that this can naturally be described by a quadratic function. Using this information, the hydraulic resistance coefficient can be determined based on the recorded measured values ​​or estimates for flow rate and head. If the pump has corresponding sensors for measuring the flow rate and / or head, these can be measured directly for the process. Alternatively, a sensorless pump can also estimate its head and / or flow rate indirectly from system parameters, e.g., from the motor speed or power consumption, etc. However, for the process execution, it is irrelevant whether the values ​​are measured or estimated / calculated.

[0017] Ideally, the rotational speed is reduced only until the flow rate falls below a predefined limit, thus preventing an excessive drop in room temperature. For example, the speed reduction is reversed as soon as the flow rate falls outside the tolerance range described above.

[0018] If the presented procedure steps result in a new expected minimum system characteristic curve that lies below the previously used expected minimum system characteristic curve, this newly determined minimum system characteristic curve is then used to adjust the corresponding control curve. If, however, the newly determined system characteristic curve lies above the previously used minimum system characteristic curve, the latter can be discarded, and the previously applied control curve remains unchanged. However, this is not necessarily the case.

[0019] According to an advantageous embodiment, the expected minimum system characteristic curve is repeatedly determined during regular pump operation. This can occur periodically or randomly. A situation-triggered determination of the expected minimum system characteristic curve is also conceivable, for example, if the controller detects the actual operating conditions of the pump and deems them suitable for determining the minimum system characteristic curve. For instance, a meaningful determination of the minimum system characteristic curve is only possible during a heating season. The pump can detect the presence of a heating season, for example, based on the medium temperature, as this is known to be adjusted by the heating system depending on the outside temperature. The pump can detect the temperature independently or query it from the system controller.

[0020] According to a further advantageous embodiment of the invention, the adjustment or setting of the control curve is carried out depending on the expected minimum and maximum system characteristic curves. The expected maximum system characteristic curve can also be determined by the pump itself. To do this, the pump increases its speed to its maximum speed or a very high speed and simultaneously observes the resulting flow rate. Naturally, this will initially increase and eventually reach a nearly constant value. If this value remains essentially stable over a certain period, it can be assumed that all heating valves of the heating system are closed and the system is characterized by the maximum system characteristic curve. In this state, the pump determines the current flow rate and the corresponding delivery head.Using this pair of values ​​and knowing that the maximum system characteristic curve is also expressed by a quadratic function, the expected maximum system characteristic curve can now be determined with sufficient accuracy.

[0021] The control curve is determined or adjusted based on specific curve parameters and the expected minimum and, if applicable, maximum system characteristics. These curve parameters can either be permanently stored in the pump controller or optionally adjustable by the user.

[0022] A curve parameter preferably relates to the operating mode, i.e., the control strategy. This describes the basic curve characteristic, e.g., whether the control curve has a straight line with a proportional slope or, alternatively, a quadratic or exponentially increasing profile.

[0023] Further curve parameters that can be defined include the start and / or end point of the control curve. The end point of the control curve is preferably defined by the intersection of the pump curve at maximum speed with a user-configurable theoretical system characteristic curve. Consequently, the control curve is based on this theoretical system characteristic curve. The theoretical system characteristic curve is, in turn, determined based on the expected minimum and, if applicable, the expected maximum system characteristic curve. By using the theoretical system characteristic curve for pump control, an adjustable deviation from the expected minimum or maximum system characteristic curve can be enabled. In particular, a distance can be defined and adjustable by the user, specifying the desired deviation of the theoretical system characteristic curve from the expected minimum and / or maximum system characteristic curve. For example, if the user defines...If there is a minimal deviation from the expected minimum system characteristic curve, the determined expected minimum system characteristic curve is used as the theoretical system characteristic curve, and the control curve is adjusted to this expected minimum system characteristic curve. Consequently, the pump is operated with the smallest possible control curve. While this offers the highest possible pump efficiency, it is accompanied by a high risk of insufficient supply.

[0024] If the greatest possible distance to the minimum system characteristic curve is selected, the maximum control curve is set and the risk of undersupply is almost eliminated, naturally at the expense of energy efficiency.

[0025] It is conceivable that the user can specify the distance in relation to the expected minimum and expected maximum system curves, i.e. at 50% the theoretical system characteristic curve lies midway between the determined expected minimum and expected maximum system characteristic curves, while at 0% the theoretical system characteristic curve falls on the expected minimum system characteristic curve.

[0026] In a further advantageous development of the method, the endpoint is not determined by the aforementioned intersection of the two curves, but instead by a specific point on a user-adjustable theoretical system characteristic curve. Specifically, the endpoint is assumed to be the point on the curve within a certain flow rate range, namely the range of the maximum flow rate achievable in the hydraulic system.

[0027] Here too, the user can use the theoretical system characteristic curve to set the desired deviation from the determined expected minimum and / or expected maximum system characteristic curve. However, if the pump knows the maximum possible flow rate within the system, it is advisable to use this for defining the endpoint instead of starting with the pump characteristic curve. This allows for a better adaptation of the control curve to the set theoretical system characteristic curve. The maximum possible flow rate may be known to the pump, for example, through a previously performed hydraulic balancing of the heating system.

[0028] The starting point of the control curve can either be freely defined by the user or determined by the pump based on the previously defined endpoint. It is conceivable that the starting point corresponds to a defined fraction of the endpoint. For example, the starting point is approximately 0.5 of the endpoint for a linear control curve with a proportional slope and approximately 0.25 of the endpoint for a quadratic control curve.

[0029] A further aspect of the invention, besides the method according to the invention, relates to a circulation pump, in particular a heating circulation pump, with a pump controller configured to carry out the method according to the invention. This provides the pump with the same advantages and properties as those already discussed above with reference to the method according to the invention. Therefore, a repetitive description of these advantages is omitted below, and reference is made instead to the foregoing.

[0030] Further advantages and features of the invention are explained in more detail below with reference to exemplary embodiments and drawings. These show: Figure 1: A QH diagram with an example pump curve, system characteristic curve, and different control curves shown; Figure 2: Two QH diagrams to illustrate the selection of the theoretical system characteristic curve depending on the minimum and maximum system characteristic curves; Figure 3: Schematic diagrams of the flow rate, pump speed, and thermostatic valve position over time during the process to determine the minimum system characteristic curve; Figure 4: Another QH diagram to illustrate the calculation of the minimum system characteristic curve; Figure 5: Another QH diagram to illustrate the adjustment of the control curve; and Figure 6: A diagram showing the measured QH profile (normalized) over time during the execution of the process in a real building.

[0031] The novel approach of this invention is that the user does not directly set the control curve, but rather defines how far the control curve is from the minimum (R min ) or the maximum system characteristic R max (see Figures 2a, 2b The curves Rth represent the theoretical system characteristics selected by the user, which are to be used for defining the control curve. In the exemplary embodiment of the Figur 2a The Eco mode is selected here as the operating mode, in which the control curve has a parabolic shape. However, the principle can be applied identically to a proportional pressure control ( Figur 2b ) or a constant pressure control system may be used.

[0032] In detail, it shows Figur 2aThe system defines the minimum system characteristic curve Rmin and the maximum system characteristic curve Rmax. The maximum system characteristic curve represents a system with all radiator valves closed, while the minimum system characteristic curve describes a system with all radiator valves fully open. Based on this concept, the user can set a target value, i.e., a theoretical system characteristic curve Rth, between 0% and 100%.

[0033] If the user selects 0%, the theoretical system characteristic curve lies on the minimum system characteristic curve R min, and the smallest possible control curve, which never falls below the minimum system characteristic curve R min, is selected. Theoretically, this would result in the lowest energy consumption; however, there is an increased risk of undersupply.

[0034] If the user selects 100%, the theoretical system characteristic curve falls to the maximum system characteristic curve Rmax, and the smallest possible control curve 10 is selected, which never falls below the maximum system characteristic curve Rmax. This would minimize the risk of undersupply, but would simultaneously result in very high energy consumption.

[0035] In Figur 2aThe diagram illustrates the case where the user sets the setpoint to 50%. In this case, the smallest possible control curve 10 is selected, which never falls below the 50% theoretical system characteristic Rth, i.e., the system characteristic that lies exactly between the minimum system characteristic Rmin and the maximum system characteristic Rmax. Specifically, the control curve is defined by the final value, which results from the intersection of the 50% theoretical system characteristic Rth with the pump characteristic curve (not shown here). The starting value of the control curve (flow rate = 0) is approximately 0.25 of the final value, and a parabolic curve shape is assumed.

[0036] In the variant of Figur 2b will be different than in Figur 2a Instead, a straight control curve with a proportional slope is assumed, whose final value is identical to Figur 2a is defined and its starting value is 0.5 (flow rate = 0) of the final value.

[0037] In practice, the pump control can initially start with a sensible value for the theoretical system characteristic curve Rth, for example, 20%. The user can then independently adjust the setpoint to a lower value if they wish to save energy. If they detect an insufficient supply, they can raise the setpoint again.

[0038] The difference to the previous method, where the control curve is directly set, is that this approach uses a building-specific setpoint rather than a pump-specific one. To implement this, the pump must independently determine the minimum and maximum system characteristics, Rmin and Rmax. The expected maximum system characteristic, Rmax, can be determined by briefly switching the pump to a high speed or its maximum speed. This results in an increase in the flow rate, Q. To prevent the room temperature from rising above the required level, the thermostatic radiator valves in the heating system will close, reducing the flow rate, Q. When all thermostatic radiator valves are closed, the maximum system characteristic, Rmax, is reached, and the flow rate will stabilize at a nearly constant value. The pump thus continuously monitors the flow rate.If this value remains essentially stable over a certain period, the pump control assumes that the maximum system characteristic curve is now present. By simultaneously measuring the current flow rate and the corresponding delivery head, the pump can then calculate the expected maximum system characteristic curve Rmax.

[0039] The system characteristic curve R always has a quadratic shape and can be mathematically defined as follows: Förderhöhe = ζ ⋅ Förderstrom 2 .

[0040] The curve can therefore be described by the parameter ζ, which denotes the hydraulic resistance coefficient of the system. The pump calculates this parameter ζ based on its determined values ​​for the flow rate and delivery head according to: ζ = Förderhöhe Förderstrom 2 .

[0041] Theoretically, it is sufficient to perform this procedure once after commissioning the pump to determine the expected maximum system characteristic curve Rmax. However, it can also be performed repeatedly during ongoing pump operation.

[0042] To determine the control curve, it is also necessary to ascertain the minimum system characteristic curve Rmin with sufficient accuracy. It may be intended that the pump initially operates from an initial minimum system characteristic curve upon commissioning, which is either entered by the technician or stored in the pump control unit by the manufacturer. During operation, however, a more precise system characteristic curve for the operating system should be determined by the pump using a specific procedure to ascertain the expected minimum system characteristic curve. The procedure performed for this purpose can be clearly illustrated by the Figures 3a-3c explain.

[0043] After the pump is switched on at time t 0, a classic control curve is initially used (e.g., a control curve 3, 4, 5 according to Figur 1 Simultaneously, the pump monitors its flow rate Q and checks whether it remains within constant limits. In practice, the flow rate Q will never remain stable at a constant value, but will experience certain fluctuations, so a tolerance corridor Qtolerance is defined instead. If the flow rate Q remains within a certain timeframe, the pump will then... delayTime If the operating point remains constant, i.e., within the Q tolerance corridor, the pump considers it "stable". A reasonable value for the delayTime is approximately 2 hours. This decision is made at time t1.

[0044] The pump then begins to very slowly but permanently reduce its speed (see Figur 3b As a result, the thermostatic radiator valves in the system will open (see below). Figur 3c ), in order to prevent a drop in room temperature despite the reduced pump speed. This ensures that the flow rate will initially remain essentially constant or stable. However, as soon as the thermostatic valves are fully open, as occurs at time t 2, the flow rate Q will decrease (see Figur 3a The pump detects this and now records the time course of the flow rate Q and the delivery head H. At time t3, the current flow rate falls outside the tolerance range Q tolerance, and the pump control increases its speed to its original value and resumes normal operation according to the control curve. This ensures that no undersupply can occur in the room.

[0045] Considering in particular Figur 3cIt becomes clear that at time t2 the minimum system characteristic curve Rmin is present, because from this point onwards all thermostatic valves are fully open or as far open as possible. It is also clear that the pump's operating point moves along the minimum system characteristic curve from time t2 onwards. This is more clearly illustrated in Figure 4 , which follow the same procedure as in Figure 3 This is represented, however, not as a chronological sequence, but in the flow rate-head (QH) diagram. Additionally, the Figure 4The minimum system characteristic curve R min is plotted. The algorithm starts at point 1. As soon as a stable operating point is detected, the pump begins to reduce its speed. This forces the thermostatic valves to open further. While this keeps the flow rate Q constant, the resulting pump head H decreases. When the thermostatic valves reach their maximum opening degree, a further reduction in speed also reduces the flow rate Q. The pump's operating point thus moves to the left along the minimum system characteristic curve R min in section 2 until the flow rate Q falls outside the tolerance range Q tolerance.

[0046] Therefore, the pump cannot perform the calculation in this state. ζ = Förderhöhe Förderstrom 2 using the recorded values ​​for the delivery head H and the delivery rate Q in section 2, in order to obtain the hydraulic resistance coefficient with which the expected minimum system characteristic R min can be fully described.

[0047] Figure 6 This demonstrates the function of the process in a real building. For these investigations, the process was integrated into a sample pump, which was then used to supply a room in a real building with its own heating circuit. The diagram of the Figure 6The graph, which plots the normalized head H and flow rate Q against time, shows that the head H decreases very slowly by reducing the rotational speed, while the flow rate Q remains constant until the thermostatic valves are fully open after approximately 350 minutes. As the head H continues to decrease, the flow rate Q also decreases. The algorithm recognizes this and can determine the expected minimum system characteristic curve based on the curves of head H and flow rate Q. After 470 minutes, the rotational speed returns to its original value.

[0048] In Figure 5 A modification of the method is shown. The determination of the expected minimum and maximum system characteristic curves Rmin and Rmax is carried out analogously here; however, contrary to the explanations regarding... Figure 2a, 2bThe endpoint of the control curve is not defined by the intersection of the theoretical system characteristic curve with the pump characteristic curve, but by the maximum required flow rate q max,1 , q max,2, which is known to the pump.

[0049] Hydraulic balancing is frequently performed in new buildings. Once the necessary calculations have been carried out, the building occupants know the maximum flow rate qmax that can occur. With this knowledge, a further lowering of the control curve is possible. Figure 5 Curve 1 shows the theoretical system characteristic curve set by the user. Curve 2 shows the pump curve, thus indicating the maximum operating range of the pump.

[0050] If the control curve is set up in the conventional way with proportional pressure control mode (according to Figur 2bIf the endpoint of the control curve is defined as the intersection of the theoretical system characteristic curve 1 with the pump characteristic curve 2, then control curve 3 is obtained. However, if the pump knows that the maximum possible flow rate through the heating system is qmax,2, this value can instead be used to define the endpoint of the control curve. The control curve thus ends on the theoretical system characteristic curve 1 at the value qmax,2, resulting in control curve 4, which is clearly below control curve 3 and therefore closer to the system characteristic curve 1. If the maximum flow rate is qmax,1, this leads to control curve 5. The modification shown thus enables further energy savings.

[0051] The method according to the invention is explained using the example of a heating circuit, but it can be used equally for refrigeration applications. It should also be mentioned that this application always refers to a minimum and maximum system characteristic curve. However, in practice, the pump will never actually see the exact minimum or maximum characteristic curve, since thermostatic valves will never be completely open or closed. This is not relevant for this method, though. It is sufficient if a relatively very high or very low system resistance can be observed and determined.

Claims

1. Method for controlling a circulation pump with variable speed in a hydraulic system, in particular in a heating system, having the method steps: - adjusting the pump speed as a function of a control curve, - establishing a new expected minimum system characteristic during regular pump operation and - adapting the control curve as a function of the new expected minimum system characteristic, characterized in that the initial control curve is determined as a function of an initial minimum system characteristic, and in that the new expected minimum system characteristic is established by the following steps: - identifying a steady-state operating point with a substantially constant delivery rate, - in the case of an identified steady-state operating point, continuously lowering the pump speed while the delivery rate of the pump is simultaneously monitored and, - as soon as a decline in the delivery rate is identified, recording the time profile of the delivery rate and the delivery head over a specific period and / or until the delivery rate is below a defined limit value, and calculating the expected minimum system characteristic from the recorded course of the delivery rate and the delivery head of the circulation pump.

2. Method according to Claim 1, characterized in that a steady-state operating point with a substantially constant delivery rate is assumed when the delivery rate remains within a tolerance range, in particular over a definable time interval.

3. Method according to one of the preceding claims, characterized in that the expected minimum system characteristic is established repeatedly, in particular periodically or randomly, and / or on a situational basis during pump operation and the control curve is adapted when the new expected minimum system characteristic is below the initial or expected minimum system characteristic previously used for setting the control curve.

4. Method according to Claim 3, characterized in that establishment of the expected minimum system characteristic is initiated on a situational basis taking account of a suitable temperature of the delivery medium, in particular at relatively high temperatures of the delivery medium, which are indicative of a current heating period.

5. Method according to one of the preceding claims, characterized in that the control curve is determined as a function of the expected minimum and an expected maximum system characteristic.

6. Method according to Claim 5, characterized in that the pump establishes the expected maximum system characteristic by the pump being operated at the maximum or a definable high speed while the pump's delivery rate is observed, the pump checking whether the monitored current delivery rate remains constant or virtually constant over a period of time and, in the event of a constant delivery rate, calculating the expected maximum system characteristic from the current delivery rate and the current delivery head.

7. Method according to one of the preceding claims, characterized in that the control curve is defined by a selectable operating mode and a starting point and an end point, the end point being determined by the intersection of the pump curve at maximum speed and a theoretical system characteristic settable by the user, and the user being able to set the theoretical system characteristic by the desired distance from the expected minimum and / or expected maximum system characteristic.

8. Method according to one of the preceding claims, characterized in that the control curve is defined by a selectable operating mode and a starting point and an end point, the end point being located on a theoretical system characteristic settable by the user in the region of a maximum delivery rate of the hydraulic system known to the pump, and the user being able to set the theoretical system characteristic by the desired distance from the expected minimum and / or expected maximum system characteristic.

9. Method according to Claim 7 or 8, characterized in that the selectable operating mode defines whether the control curve has a proportionally rising, constant or quadratic curve profile.

10. Method according to Claim 7, 8 or 9, characterized in that the starting point corresponds to a definable fraction of the end value, for example 0.5 in the case of a proportionally rising control curve and 0.25 in the case of a quadratically rising control curve.

11. Circulation pump, in particular heating circulation pump, with a pump controller which is designed for carrying out the method according to one of the preceding claims.