DE102010055841A1 - Method for operating a double pump or multi-pump unit - Google Patents

Abstract

The invention relates to a pump unit (1) as well as a method and a computer program for operating the pump unit (1), which has at least one first pump (2a) serving a base load and at least one second pump (2b) serving a peak load, which is switched on if necessary and is operated in parallel to the at least one first pump (2a), the pump unit (1) being controlled on a predetermined control characteristic (19, 39) in such a way that the power consumed is minimal. The pump unit (1) is operated depending on an upper and a lower limit value (n_o, n_u) of an operating variable (n_sync) either with at least two pumps (2a, 2b) or with at least one pump (2b) that is switched off, starting from a synchronous one Operation (21) of the pumps (2a, 2b) at an operating point (11, 13), in which the pumps (2a, 2b) are operated at the same speed (n_sync) and / or power, in a first step (24a) Value of at least one operating variable (n_sync) of the pump unit (1) is stored as a reference value (n_ref), in a second step (25) the volume flow delivered by the second pump (2b) is reduced, in a third step (26, 27) in Depending on the reaction of the regulated first pump (2a), an assignment of the operating point (11, 13) to a load range (15, a) the upper or lower limit value (n_o, n_u) is replaced by the reference value (n_ref).

Description

The present invention relates to a method for operating a pump unit with at least one base load-operated first pump and at least one second peak-load pump, which is switched on as needed and operated in parallel to the at least one first pump, wherein the pump unit regulated in such a predetermined control characteristic will be that the recorded power is minimal. Furthermore, the invention relates to a computer program with instructions for carrying out this method and a pump unit of the type mentioned with an electronic control system, which is set up for carrying out the method according to the invention.

Pump units consisting of two parallel pumps are called double pumps. In contrast, pumps with more than two parallel pumping pumps are called multipumps or pressure stations. The pumps are usually driven by an electric motor. The fields of application of such pumps are, for example, in heating systems as circulating pumps or in the supply of fresh water for pressure generation. A double pump and a corresponding control thereof is for example from the European patent specification EP 0864755 B1 known. Further shows also the EP 2 161 455 A1 a double pump.

Two different control concepts can be used for the control of double or multi-pumps. According to a first control concept, the pumps of the unit are synchronized over the entire control range to cover the required flow rate, d. H. at the same speed, operated. In contrast, in a second control concept, initially only one of the pumps of the pump unit is used to cover a required delivery flow. This pump is called base load pump and is responsible for covering the flow rate in the so-called base load range. However, if a flow is required that is outside the base load range, d. H. which has an operating point beyond the maximum delivery speed of the base load pump, the second or a second pump is connected, then to deliver together with the base load pump the required flow rate. This second or further pump may be referred to as a peak load pump, which, with its additional hydraulic power, allows the double pump or multi-pump unit to operate beyond the maximum capacity of the base load pump, i. H. achieved in the so-called peak load range. It should be noted that in a multi-pump unit two or more pumps can be jointly responsible for covering the base load and therefore together form a base load pump to which a peak load pump is hinzuschaltbar. Subsequently, therefore, "base load pump" is used in the singular, knowing that for the purposes of this application, two or more pumps can be understood by it.

In the aforementioned second control concept, the base-load pump is operated at maximum speed, whereas the peak-load pump delivers only that hydraulic power contribution that is required to achieve the additionally required delivery flow. If the operating point can not be reached in a multi-pump unit with the second or further, connected pump at maximum speed, then another pump is connected. This is done until the required flow rate is reached.

The peak load range in a double pump and multi-pump unit includes all those operating points in the characteristic field that are not reachable by the base-load pump alone. In contrast, the base load range includes all those operating points that can basically be achieved by the base-load pump alone. There are operating points in the base load range in which a synchronous operation of the base-load and peak-load pump is more energy-efficient than operation of the base-load pump alone. Based on the characteristic field of the base-load pump, these operating points are approximately in the range of medium to high flow at low to medium discharge pressure. This area is called efficiency-optimized area. A performance-optimized operation in double pumps and multipumps is therefore achieved in that in the said characteristic range a peak load pump is connected and both or all pumps run synchronously. Such operation at a reduced speed is then energetically cheaper than a sole operation of the base load pump with a correspondingly high speed.

To determine the efficiency-optimized range, a high metrological effort is required, which is performed at the manufacturer of the generic pump units on the test bench before the pump unit comes on the market. The entire characteristic field of the pump set is measured operating point for operating point, the corresponding measured data is stored and subsequently evaluated. At least those operating points that lie below the maximum characteristic of the base-load pump are approached exclusively with the base-load pump and in synchronous operation of the base-load pump and the peak-load pump, wherein in each of the two cases the respective absorbed power of the pump unit is determined and the two services together be compared. From the comparison of the services can then be determined whether the pump unit is operated energetically cheaper, if only the base load pump is running or if the synchronous operation of base load and peak load pump leads to a lower power consumption. The measurement of the characteristic field and the performance of the comparative experiments to determine the efficiency-optimized range within the characteristic field require considerable human and temporal resources and thus make the double or multi-pump aggregate more expensive.

A boundary line, which characterizes the theoretical transition between the operation of the pump unit in the base load range with only the base load pump to the efficiency-optimized range with base load and peak load pump, is deposited according to the prior art in the control electronics of the pump unit. During operation of the pump unit can then be determined by measuring the differential pressure between the suction side and pressure side and estimating or measuring the flow, if an operating point of the unit is below the limit and thus only the base load pump should be operated, or if the operating point is above the limit line and The pump set should be operated with base load and peak load pump. The limit line therefore indicates for each delivery pressure at which volume flow the peak load pump should be connected for energy reasons.

The object of the present invention is to operate a double pump or multi-pump aggregate efficiency-optimized, without a prior metrological recording and evaluation of characteristics of the pump set is required to determine the limit for switching from base load operation in the peak load operation.

This object is solved by the features of claim 1. Advantageous developments of the method according to the invention are specified in the subclaims.

According to the invention, a method is proposed for operating a pump unit having at least one base load-operated first pump and at least one second-pump operating at peak load, which is activated as needed and operated in parallel to the at least one first pump, with the pump unit being regulated on a predetermined control characteristic in that the power consumed is minimal, wherein the pump unit is operated in dependence on an upper and a lower limit either with at least two pumps or with at least one pump switched off, starting from a synchronous operation of the pumps at an operating point in which the pumps with operated in the same speed and / or power, in a first step, the value of at least one operating variable of the pump unit is stored as a reference value, in a second step, the funded by the second pump flow is reduced in one third step, depending on the reactions of the controlled first pump, an assignment of the operating point to a load range is carried out and in a fourth step, the upper or lower limit value is replaced by the reference value.

The inventive method makes it possible to make do without the measurement of the characteristic area of the pump unit before its commissioning. Rather, the boundary line or the switching point for a set during operation of the pump set control characteristic during operation is determined as a kind of "limit band". This is done by determining at each current operating point whether this operating point lies in the peak load range, in the efficiency-optimized range or in the base load range of the pump set, the limit band being limited in its width by the lower and upper limit values. A measurement of the volume flow, the delivery head or the differential pressure for the determination of the switching point is no longer necessary by the proposed method.

A particular advantage of the method according to the invention is that the position and width of the boundary strip are adapted and reduced during operation of the pump unit. This causes wear and wear on the pump set to require no change in the operating setting. Also, software and / or firmware updates remain unaffected. The pump set is always operated energy-optimized.

Preferably, the synchronous speed of the pump unit is used as the operating variable for determining the upper and lower limit values, and these are stored as a reference speed. The synchronous speed is that speed at which the base load pump and the peak load pump are synchronized, d. H. be operated at the same speed. The rotational speed can be determined in a simple manner, for example by calculation on the basis of current and voltage, which are determined metrologically or present numerically in a model (observer). Alternatively, the speed may be determined by means of a speed sensor well known in the art.

As an alternative to the synchronous speed, the operating quantity can also be that of the pump unit recorded electrical power can be used.

The volume flow delivered by the second pump can be reduced by reducing the speed of the second pump. This can be done in a simple manner by appropriate control of the pump. Alternatively, the volume flow of the second pump can also be reduced in that an arranged between the second pump and the confluence point of the flow rate of the second pump to the total volume flow of the pump unit valve is increasingly closed. However, this requires additional structural and control measures on the pump unit.

In addition to the synchronous speed, the power absorbed by the pump unit in synchronous operation can be determined and stored as a reference power. This makes it possible to carry out a performance comparison of the absorbed power of the pump unit for the assignment of the current operating point to a load range, in particular to the efficiency-optimized range. The comparison of the power is then carried out before the reduction of the volume flow of the second pump and after the reduction of this volume flow.

Preferably, the reference value, in particular the reference speed as an upper limit, in particular a speed limit can be stored if after the volume flow reduction at least a first condition is met, which is assigned to one of the load areas peak load range or efficiency-optimized range. Thus, if the first condition is satisfied, it can be determined that the current operating point is in the peak load range or the efficiency optimized range.

Furthermore, the reference value, in particular the reference speed can be stored as a lower limit, in particular speed limit, when at least one second condition is assigned, which is assigned to the base load range. If this second condition is satisfied, it can thus be determined that the current operating point of the pump set lies in the base load range.

After the evaluation of the first and the second condition can be determined in the rule in which load range of the current operating point of the pump set falls, d. h., whether the current operating point is in the peak load range, in the base load range or in the efficiency-optimized range. If it is in the base load range, the reference value is set as the lower limit value. On the other hand, if it is in the peak load range or efficiency-optimized range, the reference value is set as the upper limit value.

This procedure can be performed according to the invention for all operating points on a respectively set control characteristic of the pump unit on which the pump unit is operated according to a higher-level control, the upper and lower limit is dynamically adjusted during operation, if a new operating point is present closer to the theoretical limit line.

At the upper limit or above this upper limit, the pump unit according to the invention with at least two pumps, d. H. in the case of a double pump operated with both pumps. Further, the pump set will be at the lower limit or below the lower limit with at least one pump off, i. H. operated in the case of a double pump with only one pump. If the synchronous rotational speed of the pump assembly used by the process according to the invention always starts when a new operating point sets, it can be easily determined on the basis of a comparison of the current synchronous rotational speed with the stored upper rotational speed limit value and the stored lower rotational speed limit value whether the current operating point is equal to or above the upper limit value or equal to or below the lower limit value. In these cases no adjustment of the limit values takes place.

If the pump set is operated at an operating point with a synchronous speed between the upper limit and the lower limit, the above four steps are repeated starting from the synchronous operation of the running pumps. This causes both the upper limit and the lower limit to be dynamically adjusted during operation, and increasingly brought closer to the boundary line separating the base load range from the efficiency optimized range.

Preferably, the method according to the invention is carried out separately for each predetermined control characteristic. Thus, an upper and a lower limit of the operating variable, in particular the synchronous speed is set on each control characteristic on which a higher pressure regulator regulates the pump unit, between which the transition from the base load range to the efficiency-optimized range and depending on which the unit with at least one shut down pump or at least two pumps is operated.

The control characteristic may be such a characteristic in which the pressure generated by the pump unit is kept constant over the volume flow. Such a control characteristic is known as Δp-constant characteristic. Alternatively, control characteristics are known in which the pressure of the pump unit is adjusted proportionally to the volume flow. Such characteristics are known as Δp-variable. Since the transition from the base load range to the efficiency-optimized range for each control characteristic lies at a different operating point, it makes sense to store the determined limit values in a characteristic-specific manner, ie assigned to this last characteristic curve, when changing the current control characteristic. Thus, in the case that is changed back to a previous control characteristic, the limit values previously determined for this control characteristic can be reused.

Preferably, new limit values are used when changing the control characteristic. Like the limit values for the previous control characteristic, these new limits are set to initial values and then determined numerically based on the setting of operating points. In this case, the synchronous speed can be used again as a reference variable.

It is particularly advantageous in the method according to the invention that it can be carried out in the usual operation of the pump unit after its commissioning without the knowledge of characteristic curves, so that can be dispensed with a factory analysis of the family of characteristics of the pump unit before its commissioning.

As explained above, the reference value of the operating variable can be stored as an upper limit value if, after the volume flow reduction, in particular the speed reduction of the second pump, at least one first condition is met. This condition may be, for example, reaching or exceeding the maximum speed of the first pump. If this condition is met, it follows from the conclusion that the current operating point is in the peak load range, in which a flow is required, which can not be supplied by the at least one base load pump alone. Because by reducing the volume flow, in particular the speed of the second pump, the base-load pump must apply the missing volume flow of the second pump, d. H. be operated at a higher flow rate. If the speed of the base-load pump rises to or above the maximum speed with this volume flow transfer, the first condition would be met and the current operating point is in the peak load range.

Alternatively, a comparison with the stored reference power can be used as the first condition, wherein the current power consumption of the first pump, i. H. the base-load pump is compared with this reference power and is checked as the first condition exceeding this reference power. With this condition, it can be determined whether the current operating point of the pump set is in the efficiency-optimized range.

This finding is based on the finding that, in the case of a current operating point of the pump set, the first pump can achieve an assumption of the volume flow of the second pump below the maximum speed characteristic of the first pump. However, if the power consumption of the base-load pump is higher than the previously recorded in synchronous operation of the pump unit with base load pump and peak load pump power, it is energetically favorable to operate for this operating point, the base load pump and the peak load pump simultaneously, in particular synchronously. If the power consumption of the first pump after the volume flow reduction of the second pump thus rises above the stored reference power, it is determined that the current operating point is in the effective-wheel-optimized range of the characteristic field of the pump unit.

Of the two alternative conditions mentioned above, the comparison of the power consumption to the stored reference power represents the stricter criterion, because even in the case of an operating point in the peak load range, the power of the base-load pump will rise above the reference value.

However, the two aforementioned first conditions can also be applied in a commuative manner, whereby they are examined in a ranking order. Thus, first, the exceeding of the maximum speed of the first pump can be checked and, if this maximum speed is not reached or exceeded, the current power consumption of the first pump determined and compared with the stored reference power. The speed can be easily determined because the higher-level pressure regulator, which regulates the pump set to a predetermined control characteristic, outputs a speed setpoint, the amount of which can be easily determined. If this reaches a maximum value, the resource-intensive and more complex metrological and mathematical determination of the power consumption of the first pump or a numerical comparison of this value with the stored reference power can be saved.

As described above, the reference value of the operation quantity may be stored as a lower limit value when at least a second condition associated with the base load range is satisfied. As a second condition, the case may be used that the power consumption of the first pump in response to a volume flow reduction of the second pump, at least on average substantially no longer changed, ie in particular no longer increased. This condition is reached at an unchanged operating point in the base load range at some point. For this purpose, however, the volume flow reduction should be carried out continuously or successively stepwise such that the time period from the last to the next reduction is less than the time constant of the system response to the volume flow reduction. The following must be taken into account: starting from synchronous operation of the first and second pumps, these contribute 50% to the volume flow of the pump set. Since the pressure side of each pump of the pump unit, a check valve or a check valve is arranged, as for example in the European patent application EP 2 161 455 A1 If this is the case, a slight reduction in the second pump's flow rate of just a few percent already results in the pressure-side outlet of the second pump being largely closed. As a result, the first pump dominates the volume flow significantly. This means that a further reduction in the flow rate of the second pump will not affect the performance of the first pump. Against this background, a power consumption of the first pump that does not change significantly on average during the volume flow reduction of the second pump is the proof that the current operating point of the pump set lies in the base load range.

Alternatively to this criterion can be used as a second condition of the case that the volume flow or the speed of the second pump due to the reduction reaches or falls below a minimum value. This criterion can be used if the former criterion is not met, i. H. the power consumption of the first pump, in particular fluctuates on average, so that on the basis of this determination can not be made a clear statement about the operating point, unless in any case the power consumption does not rise above the stored reference power.

However, in this non-meaningful case, the volumetric flow of the second pump, in particular the rotational speed of the second pump, is gradually reduced to such an extent that the volumetric flow and / or the rotational speed reaches or falls below a minimum value and the power consumption of the first pump is still not exceeded the stored reference power has risen, this is a proof that the current operating point of the pump unit is in the base load range, the required flow can be provided by the base load pump alone and the operation of the base load pump alone requires a lower power consumption of the pump unit, as if base load - And peak load pump are operated synchronously.

It therefore makes sense if the second condition is only checked if the first condition is not met.

Preferably, at or immediately after the storage of the lower limit value, the value of an operating variable of the first pump is additionally stored as the base load reference value. This base load reference value represents a comparison value with which the current value of the considered operating variable of the first pump in the base load operation can be compared in order to detect a change in state of the first pump. The base load operation here is that operation in which only the at least one base load pump operates, d. H. in which at least one pump of the pump set is switched off.

From the base load operation, it is then possible to switch back to synchronous operation when the current value of the operating variable of the first pump rises above the stated base load reference value or becomes equal to or greater than a maximum value of this operating variable.

Preferably, its speed can be used as the operating variable of the first pump, since it can be determined in a simple manner on the basis of the speed information of the superordinate pressure regulator of the pump unit.

It is furthermore particularly advantageous if an offset is added to the base load reference value. As a result, a hysteresis is achieved when switching back to synchronous operation and a multiple, briefly in succession following switching between base load operation and synchronous operation prevented.

As already mentioned, the volume flow reduction of the second pump can take place stepwise or continuously. This has the advantage over an abrupt shutdown of the second pump that the higher-level pressure regulator is not affected in its control task and a sudden pressure drop in the hydraulic system is avoided. In addition, responding to a sudden volume flow request quickly by re-starting the second pump.

For example, a stepwise reduction can be made with values between 200 rpm and 50 rpm, in particular about 75 rpm to 150 rpm, preferably about 100 rpm. In the case of a continuous reduction of the speed, this can be done, for example, with a negative slope of 50-150 U / min per second, in particular 100 U / min per second.

In addition to the aforementioned measures, it is possible after the volumetric flow reduction to return to the synchronous operation of the pump unit when the power consumption of the first pump decreases. This can be used as a third condition that is applicable in addition to the other two conditions. It is then met when, during the implementation of the method steps according to the invention, in particular after the volume flow reduction, the required delivery rate drops, d. H. the operating point of the pump set changes in the direction of low volume flows. In this case, checking the first and second conditions would be negative. For this reason, it is advantageous in the case of a sinking power consumption of the first pump after the volume flow reduction of the second pump to return to the synchronous operation and continue from this operation, the method, d. H. repeat the assignment of the new operating point to one of the load ranges. The third condition is thus a fallback condition.

Preferably, it is checked only after a waiting period, if at least one of the conditions is met. This procedure takes into account the case that immediately after a volume flow reduction is still no statement about the assignment of the current operating point to a load range feasible because the system reaction has not yet done or ended, in particular a higher-level pressure control has not yet corrected.

Furthermore, it can be provided that the volume flow of the second pump is further reduced if none of the conditions is felt. In any case, this can be done as long as no minimum value for the volume flow, in particular the minimum speed of the second pump, has yet been reached.

Preferably, in each state of the method according to the invention can be converted into a synchronous operation, when the first pump reaches an inadmissible operating state, in particular when the speed of the first pump reaches or exceeds a maximum value. This procedure takes into account the fact that in the short term, an increased volume flow demand can be made of the pump unit, which can not be operated with the operation of one or more base-load pump alone. Accordingly, in this case, all pumps of the pump set are switched on again and operated synchronously, so that the method for the changed operating point can start anew.

Furthermore, it is advantageous if the first condition is immediately returned to the synchronous mode and the reference value is stored as the upper limit value only when the operating state before the volume flow reduction is restored after the return. This procedure represents a plausibility check and takes into account the case that changes during the review of the first condition of the operating point of the pump set. Because only in the case of no change in the operating point, the pump unit will return to the original operating state in the reversal of the volume flow reduction, in which the synchronous speed and / or power consumption of the pump unit again corresponds to / before the volume flow reduction. Only in this case is it possible to conclude that the operating state is in the peak load range or in the efficiency-optimized range, so that the reference value can be correctly stored as the upper limit value.

It is further advantageous if the lower limit is reset to a minimum value and is returned to the synchronous operation, when the first pump reaches an inadmissible operating state in the base load operation, in particular reaches or exceeds a maximum speed. With this procedure, a safety device is implemented, which applies in the event that the stored lower limit is incorrect. In order to avoid a malfunction of the pump unit, then a reset of the lower limit is performed and passed into synchronous operation when the first pump reaches an inadmissible operating state.

According to the invention, the above-described method can be implemented in a computer program, i. H. be formed by a computer program product containing instructions for carrying out the method according to the invention, and which is carried out when it is executed on a microcomputer of a control electronics. The method can be implemented both in a control electronics of the pump unit and in an external control device, in particular in a control computer.

Finally, the invention relates to a pump unit having at least one base load-carrying first pump and at least one second load pump serving a peak load, which is connected as needed and parallel to the at least a first pump is operable, wherein the pump unit is controllable on a predetermined control characteristic such that the power absorbed is minimal, and wherein it has a control electronics, which is adapted to carry out the method described above. In this case, the aforementioned computer program with the instructions for carrying out the method can be loaded onto a microcomputer of the control electronics.

The invention will be explained in more detail below with reference to an exemplary embodiment with reference to the accompanying figures. Show it:

1 : schematic representation of a double pump unit

2 : schematic representation of a multi-pump unit

3 : superordinate sequence of steps of the process sequence according to the invention

4 : Exemplary implementation of the inventive method for power control of the pump set with dynamic limit value adjustment as a program flowchart

5 : Characteristic field of a double pump unit

6 : Start of the procedure with an exemplary operating point in the base load range

7 : Representation of the characteristic field with newly set lower limit and new operating point in the peak load range

8th : Representation of the characteristic field with set upper and lower upper limit and new operating point in the efficiency-optimized range

9 : Illustration of the adaptation of the upper limit of the characteristic field

10 : Illustration of the adjustment of the lower limit on the characteristic field

11 : Illustration of the method after the selection of a new control characteristic Δp-c in the characteristic field with a new operating point in the base load range

12 : Illustration of a new control characteristic Δp-v in the characteristic field

13 : Representation of the time course of the power and the speed of the pumps and the pump set with gradual speed reduction of the second pump over time

1 shows a schematic representation of a double pump, ie a pump unit 1 with two identical pumps 2a . 2 B , which are connected hydraulically parallel to each other. They have a common suction line 4 to which the two pumps 2a . 2 B are connected with their suction side. On the pressure side, the pumps open 2a . 2 B in a common pressure line 5 , wherein in the transition region to the pressure line 5 a non-return valve 3a is arranged. This non-return valve prevents pumped fluid from entering one pump into the pressure side of the other pump, thus creating unnecessary hydraulic resistance. Rather, the check valve deflects 3a the flow of the two pumps 2a . 2 B in the pressure line 5 ,

Every pump 2a . 2 B is a pump electronics 6 associated with the electromotive drive unit of the pump 2a . 2 B controls. The pump electronics 6 is connected to an operating voltage and energizes the respective electric motor by means of a frequency converter. The frequency converter is controlled by a pulse width modulated (PWM) signal, which is generated by a microprocessor of the pump electronics in response to a speed reference. This speed setpoint is output by a controller, which is also part of the pump electronics, in particular implemented in the microprocessor of the electronics.

This controller is superior to the method according to the invention and regulates a pump 2a . 2 B according to a control characteristic that is connected to the respective pump electronics 6 can be specified. In each case, that of a pump 2a . 2 B regulated pressure, the pumps 2a . 2 B are metrologically set up to detect the differential pressure between the suction side and pressure side. Alternatively, the pump unit 1 also be pressure controlled, with only the control of one of the two pumps 2a . 2 B is needed.

In the exemplary embodiment according to 1 are the two pump electronics 6 the pumps 2a . 2 B via a control line 8th connected in parallel. The pump electronics 6 the second pump 2 B can over this control line 8th receive the same control signal for their frequency converter, that of the pump electronics 6 the first pump 2a is issued. The first pump 2a thus acts together with their control electronics 6 as a kind of master, whereas the second pump 2 B with their control electronics 6 is controlled as a kind of slave. According to this control engineering arrangement is a synchronous operation of the two electric motor drive units of the first pump 2a and the second pump 2 B reached. The pump electronics 6 the second pump 2 B However, it is completely identical to the pump electronics 6 the first pump 2a trained and may, if necessary, the second pump 2 B completely self-sufficient from the pump electronics 6 the first pump 2a Taxes.

2 shows an exemplary second embodiment of the pump unit according to the invention 1 with a large number of parallel pumps 2a . 2 B , Of this variety, however, only three pumps in the 2 shown. There are two pumps 2a as synchronously running base load pumps and a pump 2 B as a peak load pump. All pumps are connected to a common suction line 4 connected and open into a common pressure line 5 , Between each pump 2a . 2 B and the pressure line 5 is a check valve 3 arranged like the check valve 3a in 1 each prevents the pressurized fluid enters the pressure-side area of a pump that pumps or pumps out less.

Also in this embodiment according to 2 is every pump 2a . 2 B with a pump electronics 6 equipped with the appropriate pump 2a . 2 B can control completely self-sufficient, that can energize the electric motor drive unit such that the pump 2a . 2 B is regulated on a predetermined control characteristic. The pump electronics 6 according to 2 are therefore identical to the pump electronics 6 in 1 , In principle, the pump electronics can also in this second embodiment variant 6 Be connected to each other via control lines, not shown, and implement control technology, a master / slave arrangement. Alternatively to this variant is in 2 a higher-level central control unit 7 shown with which the individual pump electronics 6 via one control line each 9 are connected. About this central control unit 7 be the speeds of each pump 2a . 2 B of the pump set 1 in 2 specified.

The in the 1 and 2 illustrated pump units 1 are preferably used as circulation pumps in heating systems or as printing stations for fresh water delivery.

The method according to the invention will be described below with reference to a double pump unit 1 according to 1 illustrated. This is the first pump 2a to operate the base load and the second pump 2 B used to operate the peak load. According to this understanding, the first pump 2a referred to in the context of the invention as a base load pump, whereas the second pump 2 B is called peak load pump. The peak load pump 2 B On the one hand, it is needed to cover a flow requirement that can not be met by the basic load pump alone. However, it is also operated synchronously to the base load pump in an area of the characteristic field in which the synchronous operation of both pumps is energetically more favorable than the exclusive operation of the base-load pump.

The inventive method can easily on a multi-pump unit according to 2 be extended by the base load pump 2a and a connected peak load pump 2a control technology common as a base load pump 2a considered to be another pump 2 B namely, the new peak load pump 2 B is added.

3 shows the superordinate sequence of the method according to the invention. The process is immediately at the commissioning of the pump set 1 executed and learns to himself, when it is energetically cheaper to operate only the base load pump or when a synchronous operation of base load and peak load pump 2a . 2 B energetically cheaper.

Start of the procedure is according to 3 at the step marked with "Start" 10 , First, an upper limit n_o and a lower limit n_u are defined and in a step labeled "Reset" 12 given these limits values. In this case, the upper limit n_o is equal to the maximum speed n_max of the base load pump 2a and the lower limit n_u is equal to the minimum speed n_min of the base load pump 2a set. Because the two pumps 2a . 2 B are constructed identical, these limits also correspond to those of the peak load pump 2 B respectively the double pump unit 1 in synchronous operation.

When setting or resetting the limit values n_u, n_o, a further limit value n_u_GLP is additionally set, which defines a base load reference value of the rotational speed. This reference value will in the course of the procedure with the speed n_GLP of the base load pump 2a occupied by the base load pump 2a is applied when the base load operation, ie to the operation with only the base load pump 2a is passed. This speed value then serves as a reference to the current speed n_GLP of the base-load pump 2a , by means of which an abnormal increase in the speed of the base-load pump 2a can be determined. This will be explained in more detail below.

The essential steps of the process according to the invention are in 3 through the block labeled APL (Adaptive Peak Load) 20 summarized, its implementation 4 shows and explained below. APL 20 implemented a power control of the pump set 1 with dynamic limit adjustment.

This occurs during the execution of the steps of the APL block 20 a new setpoint specification 14 , ie a change of the control characteristic, the method is restarted and new limit values n_u, n_o, n_u_GLP are set for this control characteristic. In this case, the previously determined limit values relative to the original control characteristic, ie the original desired value specification, can be stored so that they can be reused when returning to the previous desired value specification. A new setpoint specification 14 does not mean deleting the previously determined limits. Rather, new limits n_u, n_o, n_u_GLP are only set if the pump set 1 a control characteristic is set, which has never been set before. If you change to a previously set characteristic, the limit values already determined for this characteristic will continue to be used. On the other hand, it occurs during the execution of the steps of the APL block 20 If there is no change in the control characteristic, these APL steps are repeated cyclically.

4 graphically illustrates the individual steps of the APL block 20 in 3 of the method according to the invention in a logical flowchart. The procedure starts with a synchronous operation 21 of the pump unit 1 in which the pump electronics 6 the base load pump 2a and the peak load pump 2 B These regulate such that the rotational speed of the base-load pump n_GLP and the rotational speed of the peak-load pump n_SLP are identical and correspond to a predetermined synchronous rotational speed n_sync. The synchronous operation is in 4 through the block 21 characterized. The synchronous speed n_sync is specified by the higher-level controller, which is the pump unit 1 adjusted so that it is at one of the hydraulic system in which the pump unit 1 is integrated, predetermined volume flow Q the differential pressure Ap or the delivery height H of the pump unit 1 holds according to the predetermined control characteristic.

Starting from this synchronous operation is first in one step 22 checked whether the synchronous speed n_sync is smaller than the lower limit n_u.

At the beginning of the procedure, this condition can not be fulfilled anyway, because the lower limit n_u is equal to the minimum speed n_min of the base-load pump 2a in step 12 has been set. In the course of the procedure, however, the lower limit n_u is dynamically raised and then indicates that each synchronous speed n_sync is below this lower limit n_u to one in the base load range 17 owned operating point belongs. If such a case occurs, in step 36 the peak load pump is switched off because in the base load range 17 the exclusive operation of the base load pump 2a sufficient to provide the required flow rate Q and also energy is cheaper than the synchronous operation of base load and peak load pump 2a . 2 B ,

If the lower limit n_u has been correct, the speed n_GLP of the basic load pump should be 2a increase only slightly, due to the elimination of the peak load pump 2 B to compensate for reduced volume flow. Should the speed n_GLP of the base load pump 2a but increase to the maximum speed n_max, which is subsequently in step 37 is checked, the lower limit n_u has been set incorrectly. It will therefore be in the subsequent step 38 to the initial value, ie to the minimum speed n_min reset. The peak load pump 2 B In this case, it is immediately reconnected and the pump set 1 in synchronous operation 21 operated.

The further method steps are described below with reference to FIGS 5 to 13 explained.

5 shows a schematic representation of the characteristic field of a double pump 1 according to 1 , The characteristic field is characterized by a variety of characteristics 44 constant speed and piping parabolas 43 formed, the slope is determined by the pipe network resistance of the hydraulic system, in which the pump unit 1 is integrated. The characteristic field is moved upwards by a maximum characteristic 41 of the pump unit 1 limited. This characteristic 41 corresponds to the operating points of the pump unit 1 , at maximum synchronous speed of the two individual pumps 2a . 2 B are reachable. In contrast, the reference number 18 characteristic curve shows the maximum characteristic of one of the pumps 2a . 2 B , in particular the base load pump 2a ,

This characteristic 18 identifies all operating points that are the sole operation of the base-load pump 2a can be reached at maximum speed n_max. Between the maximum characteristic 41 of the pump unit 1 and the maximum characteristic 18 the base load pump 2a lies the peak load area 15 , So that the pump set 1 an operating point within this peak load range 15 can reach, is the operation of base load pump 2a and peak load pump 2 B required.

At the bottom, the characteristic field becomes a minimum characteristic 42 the base load pump 2a limited. Between the minimum characteristic 42 and the maximum characteristic 18 can every operating point of the pump set 1 exclusively by the Base-load pump 2a be achieved. This intermediate area is divided into the base load range 17 , in which it is energetically cheaper, only the base load pump 2a operate and an efficiency-optimized range 16 in which the pump unit 1 absorbs less power when base load pump 2a and peak load pump 2 B be operated simultaneously, in particular synchronously, against an exclusive operation of the base load pump 2a , This efficiency-optimized range 16 is essentially in the range of low to medium volume flows Q at low to medium head H.

The transition between the base load range 17 and the efficiency-optimized range 16 is through a borderline 40 whose location has been found by measuring the characteristic field on the test bench according to the prior art. According to the invention, the position of this boundary line 14 However, with increasing accuracy during operation of the pump unit 1 found out.

To illustrate the method steps according to 4 will be on first 6 Referenced. The pump unit 1 is first according to a first control characteristic 19 regulated, on which the pressure Δp of the pump unit 1 respectively the delivery height H is kept constant over the volume flow Q. In 6 the lower limit value n_u and the upper limit value n_o are plotted. It is first assumed that after commissioning of the pump unit 1 and the set synchronous mode 21 first an operating point 11 sets in the base load range 17 lies. This is determined by the method as follows.

With reference to 4 was first in step 22 determined that the currently applied synchronous speed in the operating point 11 is not smaller than the lower limit n_u. It will then be in step 23 checks whether the current synchronous speed n_sync is smaller than the upper limit n_o. This is at the operating point 11 the case because the upper limit n_o is equal to the maximum speed n_max of the base load pump 2a has been set. In step 23 In addition, it is checked whether the synchronous speed n_sync is smaller than the maximum speed n_max. Since the method according to the invention has not yet set a new upper limit value n_o at this point, the aforementioned second condition is identical to the first one. It therefore only becomes significant if, in the course of the method, the upper limit n_o is set to a value below the maximum speed n_max.

For the operating point 11 in 6 are the ones in step 23 tested conditions. This is followed by a storage of the current synchronous speed n_sync as reference speed n_ref, step 24a , Subsequently, the total electric power P_Σ is determined and in step 24b stored as reference power P_ref. After that, in step 25 the speed n_SLP of the peak load pump 2 B reduced, for example, at 100 rev / min. As a result, the flow rate of the peak load pump 2 B reduced. The two pumps 2a . 2 B are no longer operated synchronously. It will now be the reaction of the pump unit 1 analyzed for this speed reduction.

The higher speed governor now controls the pressure drop of the pump set resulting from the speed reduction of the peak load pump 1 characterized in that the speed of the base load pump is increased. At the same time any existing valves in the hydraulic system, for example, thermostatic valves readjust. To wait for this system reaction, in step 35 waiting for a wait t_wait. This is between one and 20 s, preferably between 5 and 15 s, in particular about 10 s, and it can be chosen in particular as the product of the settling time of the pressure regulator and a factor which is preferably between two and five. A counter for the waiting time t_waiting may occur immediately after a speed reduction in step 25 set to zero and then counted up numerically. Only after expiry of the wait time t_wait is it checked how the pump set works 1 on the speed reduction of the peak load pump 2 B in step 25 responding.

It is first in step 26 checked, whether by the speed reduction of the peak load pump 2 B the speed n_GLP of the base load pump 2a reaches or exceeds its maximum value n_max. If this were the case, then the current operating point would be 11 in the peak load range 15 , However, this is not the case here.

Furthermore, in step 26 checked as an alternative condition, whether the now adjusting electrical power consumption P_GLP the base load pump 2a rises above the stored power reference value P_ref. If this were at the operating point 11 the case, he would be either in the efficiency-optimized range 16 or in the peak load range 15 , If the speed condition n_GLP ≥ n_max before the power condition P_GLP> P_ref is checked and the speed condition is not satisfied, it would be established after checking the power condition that the operating point in the efficiency-optimized range 16 lies.

A hierarchical check of the two conditions in step 26 However, it is not absolutely necessary because both in the case of performance of the condition and in case of performance of the Speed condition is in each case transferred to a synchronous operation, step 29 , The procedural reaction to the occurrence of one of these conditions is therefore the same.

For the operating point 11 in 6 gives the verification of the mentioned conditions in step 26 a negative result. It is therefore already clear at this point that the operating point 11 in the base load range 17 lies.

It will then be in step 27 checked if the base load pump 2a has reached a stationary, ie stable state, that is, the recorded electric power P_GLP is substantially constant. This is checked by whether the derivative of the absorbed electric power of the base load pump P_GLP is substantially zero. Instead of the derivative, the difference quotient ΔP_GLP / Δt can also be used for the numerical calculation of the variables on a microprocessor, with which the power consumption change ΔP_GLP per waiting time Δt = t_waiting is determined. Furthermore, a moving averaging can be applied to the measured or calculated values to filter out disturbances from the measured current and voltage values for calculating the power.

The power P_GLP of the base load pump changes 2a after the speed reduction still, no concrete statement can be made about whether or not the operating point 11 in the base load range 17 lies. It is then by step 27 in the next step 28 passed. A special case exists when, contrary to the expectation of a speed increase of the base load pump 2a to compensate for the missing volumetric flow rate of the peak load pump 2 B , the power consumption of the base load pump 2a sinks. This may be the case if, in the meantime, a lower flow rate Q than before the speed reduction of the peak load pump 2 B is required and the higher-level pressure regulator of the pump unit 1 this down in performance. Since the peak load pump 2 B a specific speed is predetermined by the method according to the invention, only the base load pump remains 2a under the controlled influence of the superordinate pressure regulator, so that this the performance of the base load pump 2a turns down. Whether this is the case will be in step 28 checked. If this case occurs, then the operating point has 11 changed and a statement about its original position can not be made at this point. From step 28 Therefore, the method according to the invention goes back into synchronous operation 21 from where it starts anew with the changed operating point.

Is the condition in step 28 however, not met, the performance of the base load pump increases 2a due to the volume flow transfer either still on or fluctuates, so that no concrete statement about the operating point can be made.

It then becomes a further speed reduction of the peak load pump 2 B in step 25 performed and again waited for the system response. Then the conditions 26 . 27 and 28 checked again.

In the case of the operating point 11 in 6 A time of about 10 seconds is required until the power consumption of the base-load pump is reached 2a to a steady state, see in 13 the curve P1_MA.

In this case, by step 27 in 4 on step 32a passed over and the previously stored reference speed r_ref, the operating point 11 is assigned, is stored as the lower limit n_u, since now it is clear that the operating point 11 in the base load range 17 lies. The peak load pump 2 B is then turned off, step 32b , As a result, the speed n_GLP of the base load pump 2a change again, it makes sense to provide here another waiting time, which in 4 but not taken into account. After switching off the peak load pump 2 B becomes the current speed n_GLP of the base load pump 2a with an added offset stored as a base load reference value n_u_GLP, step 32c ,

The pump unit 1 is now in base load operation 33 operated in which the peak load pump 2 B is off, ie their speed n_SLP is zero, whereas the base load pump 2a is still operated regulated with a non-zero speed n_GLP. This is in block 33 in 4 shown.

During base load operation 33 the speed n_GLP of the basic load pump becomes permanent 2a checked. If it rises above the stored base load reference value n_u_GLP, it immediately becomes synchronous operation 21 returned. For safety reasons, it is in condition 34 for the case of an incorrectly set base load reference value n_u_GLP also checked whether the speed of the base-load pump n_GLP increases beyond its maximum speed n_max. If this is the case, it will also be in synchronous mode 21 passed.

7 shows that the lower limit n_u is now set to the speed value, that at the first operating point 11 before the volume flow reduction of the second pump 2 B present. This means that every other operating point with a Speed below the new lower limit n_u also in the base load range 17 lies. The area below the lower limit n_u is in 7 therefore marked hatched.

Furthermore, in 7 assumed that as a second operating point 13 an operating point in the peak load range 15 established. Starting from the previous base load operation 33 in 4 As a result, the speed n_GLP of the base-load pump will increase considerably compared to the base-load reference value n_u_GLP, in particular increase above the maximum speed n_max. The in step 34 in 4 mentioned and constantly checked conditions are therefore met and it is in the synchronous mode 21 passed.

The then adjusting synchronous speed n_sync must inevitably above that previously in the operating point 11 stored synchronous speed are such that the condition 22 in 4 is not fulfilled. Since the upper limit n_o still corresponds to the maximum synchronous speed value n_max, the in step 23 the condition checked, respectively, meets the two conditions specified therein. The current synchronous speed n_sync is therefore stored again as speed reference value n_ref, step 24a , and the electrical power P_Σ received by the pump set is determined and stored as reference power P_ref, step 24b , Subsequently, the speed n_SLP of the peak load pump 2 B reduced, step 25 , and the reaction of the pump set 1 Waited for this speed reduction, step 35 , and analyzed.

The reduction of the speed n_SLP will cause the speed n_GLP of the base load pump 2a reaches its maximum value n_max because of the operating point 13 conditionally a volume flow Q, which is beyond the maximum characteristic 18 the base load pump 2a lies. For this reason, the condition in step 26 be satisfied after a certain time, so that is returned to the synchronous mode, step 29 in 4 ,

It is thus stated that the new operating point 13 in the peak load range 15 is, so that the reference speed n_ref stored synchronous speed n_sync can be set as the upper limit n_o, step 31 , Before that, however, it is checked if after returning to the synchronous mode in step 29 the speed of the base-load pump n_GLP returns to its original value, namely to the original synchronous speed n_sync. This condition will be in step 30 in 4 checked. Only if this is the case, the reference value n_ref is set as upper limit n_o. Otherwise, the current operating point has changed again, so that a clear statement about its location is not possible. The procedure is then synchronous 21 continued. For the case illustrated purely by way of example, the operating point remains 13 but unchanged, so that the reference value n_ref is set as upper limit n_o. This is in 8th shown.

In 8th FIG. 11 further illustrates that synchronous speeds above the upper limit n_o belong to operating points in which both the base load pump 2a as well as the peak load pump 2 B should or should be operated. Furthermore, in 8th a third operating point 45 by way of example, which is now in the efficiency-optimized range 16 lies.

Starting from synchronous operation 21 , in which the procedure because of the previous operating point 13 still located, will be with the new operating point 45 again set a synchronous speed n_sync above the lower limit n_u, so that the condition in step 22 in 4 is not fulfilled. In contrast, both are in step 23 to be tested conditions satisfied, so that the current synchronous speed n_sync can be stored again as a reference value n_ref, step 24 , Furthermore, the current electrical power P_Σ of the pump unit is again recorded 1 stored as reference power P_ref, step 24b , After these storage steps, the speed n_SLP of the peak load pump 2 B again reduced, step 25 , and waited until the superordinate pressure regulator adjusted.

The reduction of the speed n_SLP of the peak load pump 2 B will lead to the fact that the speed n_GLP the base load pump 2a does not run to its speed limit n_max, since the operating point 45 below the maximum characteristic 18 lies. However, it will happen that of the base load pump 2a absorbed power P_GLP due to the volume flow transfer by the base load pump 2a via the stored reference power P_ref increases. This will be in step 26 in 4 detected. It will then return to the pump unit 1 energetically better synchronous operation 29 set. Subsequently, it is again checked whether the speed n_GLP the base load pump 2a returns to the reference speed n_ref again. If this is the case, the reference speed is stored as a new upper limit n_o, step 31 , The adjustment of the upper limit is in 9 illustrated.

According to 10 It is now assumed that a fourth operating point 47 which is again in the base load range 17 is and on the set control characteristic 19 requires a volumetric flow Q, which causes a synchronous speed n_sync above the lower limit n_u. Therefore will the condition in step 22 in 4 again not fulfilled. By contrast, both are in step 23 satisfies to be tested conditions, so that the current synchronous speed n_sync is stored again as a reference speed n_ref, step 24a , the current power P_Σ as reference power P_ref is stored, step 24b , and then the speed of the peak load pump n_SLP is reduced, step 25 ,

Because the new operating point 47 in the base load range 17 is none of the steps in step 26 be fulfilled. This means that the base load pump 2a by the speed reduction of the peak load pump 2 B neither reaches its maximum speed n_max nor reaches a power consumption that is above the reference power P_ref. The speed reduction of the peak load pump 2 B will cause that from the base load pump 2a absorbed power P_GLP initially increases, but then reaches a saturation value when the base load pump 2a almost completely the volume flow of the peak load pump 2 B take over. Since the power P_GLP of the base-load pump no longer changes significantly in this case, the condition in step 27 Fulfills. The reference speed n_ref is then set as the new lower limit n_u, step 32a , the peak load pump 2 B off, step 32b and then applied current speed n_GLP the base load pump 2a plus an offset set as the new base load reference value n_u_GLP, step 32c ,

The pump unit 1 will then be in base load operation 33 operated in which the peak load pump 2a is off and the pump set 1 exclusively with the base load pump 2a on the set control characteristic 19 is regulated.

The increase of the lower limit n_u to the new operating point 47 is in 10 illustrated. It becomes clear that the distance between the upper limit n_o and the lower limit n_u becomes lower in the current process, in particular when there is a new operating point which is closer to the theoretical limit line 40 lies.

In 11 is now the change to a new constant control characteristic 40 illustrated. A new lower limit n_u and a new upper limit n_o are set, which are assigned a minimum value or maximum value for the rotational speeds. In 11 is again a new, fifth operating point 48 drawn in the base load range 17 lies. The method will now be described in accordance with the above-described steps in 4 as before on the basis of 6 - 10 explained. Based on 11 it becomes even clearer that for the previous control characteristic 19 determined limit values n_u, n_o persist, so that in case of a return to the original control characteristic 19 these limits n_u, n_o can be used again.

12 illustrates the application of the method according to the invention with a further control characteristic 39 , According to the delivery pressure .DELTA.p of the pump unit 1 is controlled linearly via the volume flow Q. In 12 are already shown adjusted values for the lower limit n_u and the upper limit n_o, which have been determined during operation. Between the two limits, the boundary line runs 40 ,

13 illustrates the graph of the readings for the peak load pump 2 B predetermined speed n_soll, for the total power P1_Sum of the pump set, for the power P1_MA the base load pump and for the power P1_SL the peak load pump, with a head H of 15 m and a flow Q of 55 m ³ / h.

Starting from the stationary state of the pump set 1 becomes the speed n_set of the peak load pump 2 B reduced by 100 rpm. In this case, the power consumption P1_SL of the peak load pump decreases 2 B considerably, whereas the power P1_MA of the base load pump 2a increases by a higher level. After about 10 seconds, the power P1_MA has the base load pump 2a reached a value of about 4000 watts. A subsequent further speed reduction of 100 rev / min has indeed a reduction of the peak load pump 2 B absorbed power P1_SL, but does not change the power consumption P1_MA the base load pump 2a , This is because the check valve 3a in the pump unit 1 This leads to a slight shift of the delivery rate contributions towards the base load pump 2a clearly dominate them. So already a speed reduction of about 5% of the rated operating speed of the peak load pump leads 2 B to that the volume flow Q almost exclusively from the base load pump 2a is delivered. The peak load pump 2 B Therefore, it can be switched off already after the first speed reduction, since it does not provide any noteworthy contribution.

The consideration of the pump unit 1 recorded total output P1_Sum in 13 shows that this total power always above the curve of the power P1_MA the base load pump 2a lies. This means that the operating point from which in 13 is assumed before the speed reduction, in the base load range 17 lies in which the power consumption of the base load pump 2a not above the previously in synchronous operation 21 The power P1_Sum of the entire aggregate taken up before the speed reduction increases. 13 therefore illustrates the physical quantities on the pump set 1 if an operating case according to 6 is present.

LIST OF REFERENCE NUMBERS

1

pump unit

2a

first pump, base load pump

2 B

second pump, spike load pump

3

check valve

3a

check valve

4

suction

5

pressure line

6

pump electronics

7

central control unit

8th

control line

9

control lines

10

commencement of proceedings

11

first operating point

12

Resetting the limits / Reset

13

second operating point

14

new setpoint specification

15

Peak load

16

efficiency-optimized range

17

Base load

18

Maximum characteristic of the base load pump

19

Control characteristic Δp-c

20

Power control of the pump set with dynamic limit value adjustment

21

synchronous operation

22

Query operating point in the base load range

23

Query operating point in peak load range

24a

Storage reference speed

24b

Storage reference performance

25

Speed reduction

26

Checking a first condition

27

Check a second condition

28

Review of a third condition

29

synchronous operation

30

Operating point change check

31

Adjust the upper limit

32a

Adjust the lower limit

32b

Transition to base load operation

32c

Storage of a base load reference value

33

Base load operation

34

Checking the operating state of the base load pump

35

Checking a waiting time

36

Transition to base load operation

37

Checking the operating state of the base load pump

38

Reset the lower limit

39

Control characteristic Δp-v

40

boundary line

41

Maximum characteristic of the pump set

42

Minimum characteristic of the basic load pump

43

Pipe network parables

44

Characteristic curves of constant speed

45

third operating point

46

new control characteristic Δp-c

47

fourth operating point

48

fifth operating point

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0864755 B1 [0002]
• EP 2161455 A1 [0002, 0032]

Claims (28)

Method for operating a pump set ( 1 ) with at least one base load-operated first pump ( 2a ) and at least one peak-load second pump ( 2 B ), which are switched on as needed and parallel to the at least one first pump ( 2a ), the pump unit ( 1 ) so on a predetermined control characteristic ( 19 . 39 ) that the power consumed is minimal, characterized in that the pump unit ( 1 ) in dependence on an upper and a lower limit value (n_o, n_u) of an operating variable (n_sync) either with at least two pumps ( 2a . 2 B ) or with at least one switched-off pump ( 2 B ), starting from a synchronous operation ( 21 ) of the pumps ( 2a . 2 B ) at an operating point ( 11 . 13 ), in which the pumps ( 2a . 2 B ) are operated at the same speed (n_sync) and / or power, a. in a first step ( 24a ) the value of at least one operating variable (n_sync) of the pump set ( 1 ) is stored as reference value (n_ref), b. in a second step ( 25 ) of the second pump ( 2 B ) is reduced, c. in a third step ( 26 . 27 ) in response to the response of the regulated first pump ( 2a ) an assignment of the operating point ( 11 . 13 ) to a load range ( 15 . 16 . 17 ) and d. in a fourth step ( 31 . 32a ) the upper or lower limit value (n_o, n_u) is replaced by the reference value (n_ref). Method according to Claim 1, characterized in that the operating variable is the synchronous rotational speed (n_sync) of the pump unit ( 1 ), which is stored as reference speed (n_ref). Method according to claim 1 or 2, characterized in that that of the pump unit ( 1 ) in synchronous operation ( 21 ) recorded power (P_Σ) and stored as a reference power (P_ref) ( 24 ). Method according to one of the preceding claims, characterized in that that of the second pump ( 2 B ) is reduced by reducing their speed (n_SLP). Method according to one of the preceding claims, characterized in that the reference value (n_ref), in particular the reference rotational speed (n_ref), as an upper limit value (n_o), in particular a speed limit value (n_o) is stored ( 31 ), if after volume flow reduction ( 25 ) at least one first condition ( 26 ) satisfying one of the load ranges ( 15 . 16 ) Peak load range ( 15 ) or efficiency-optimized range ( 16 ) assigned. Method according to one of the preceding claims, characterized in that the reference value (n_ref), in particular the reference speed (n_ref), as a lower limit value (n_u), in particular speed limit (n_u) is stored ( 32a ) if at least one second condition ( 27 ), which corresponds to the base load range ( 17 ) assigned. Process according to claims 5 and 6, characterized in that the pump unit ( 1 ) at an operating point ( 11 ) at a synchronous speed (n_sync) equal to or above the upper limit (n_o) with at least two pumps ( 2a . 2 B ) and equal to or below the lower limit (n_u) with at least one deactivated pump ( 2 B ) is operated. Process according to claims 5 and 6 or claim 7, characterized in that the pump unit ( 1 ) at an operating point ( 13 ) with a synchronous speed (n_sync) between the upper limit (n_o) and the lower limit (n_u) the steps a. to d. starting from a synchronous operation ( 21 ) of the pumps ( 2a . 2 B ) be repeated. Method according to one of the preceding claims, characterized in that for each predetermined control characteristic ( 19 . 39 ) is carried out. Method according to one of the preceding claims 5 to 9, characterized in that the limit values (n_o, n_u) at a change of the control characteristic ( 19 . 39 . 46 ) of this characteristic ( 19 . 39 . 46 ) are stored assigned. Method according to one of the preceding claims 5 to 10, characterized in that when changing the control characteristic ( 19 . 39 . 46 ) a new upper and lower limit (n_o, n_u) are used. Method according to one of claims 5 to 11, characterized in that the first condition ( 26 ) is satisfied when the speed (n_GLP) of the first pump (n_GLP) 2a ) reaches or exceeds a maximum speed (n_max) or when the power consumption (P_GLP) of the first pump ( 2a ) exceeds the reference power (P_ref). Method according to one of claims 6 to 12, characterized in that the second condition ( 26 ) is satisfied when the power consumption (P_GLP) of the first pump ( 2a ) remains substantially the same on average, or when the speed (n_SLP) of the second pump ( 2 B ) reaches or falls below a minimum value. Method according to one of claims 6 to 13, characterized in that the second condition ( 27 ) is only checked if the first condition ( 26 ) is not fulfilled. Method according to one of claims 6 to 14, characterized in that during the storage ( 32a ) of the lower limit value (n_u) the value of an operating variable (n_GLP) of the first pump ( 2a ) is stored as a base load reference value (n_u_GLP) ( 32c ). Method according to claim 15, characterized in that the operation ( 33 ) with at least one pump switched off ( 2 B ) into synchronous operation ( 21 ) with at least two pumps ( 2a . 2 B ) ( 34 ), if the current value of the operating quantity (n_GLP) of the first pump ( 2a ) rises above the base load reference value (n_u_GLP) or becomes equal to or greater than a maximum value (n_max) of this operation quantity (n_GLP). Method according to claim 15 or 16, characterized in that the operating variable of the first pump ( 2a ) Their speed (n_GLP) is used. Method according to claim 15, 16 or 17, characterized in that an offset is added to the base load reference value (n_u) ( 32c ). Method according to one of the preceding claims, characterized in that the volume flow reduction takes place stepwise. A method according to claim 19, characterized in that the step size between 200 U / min and 50 U / min, in particular about 100 U / min. Method according to one of the preceding claims, characterized in that after the volume flow reduction ( 25 ) back into synchronous operation ( 21 ), if as a third condition ( 28 ) the power consumption (P_GLP) of the first pump ( 2a ) sinks. Method according to one of the preceding claims 5 to 21, characterized in that only after a waiting time (t_waiting) is checked whether at least one of the conditions ( 26 . 27 . 28 ) is satisfied. Method according to one of the preceding claims 5 to 22, characterized in that the volume flow of the second pump ( 2 B ) is further reduced ( 25 ), if none of the conditions ( 26 . 27 . 28 ) is satisfied. Method according to one of the preceding claims, characterized in that in a synchronous operation ( 21 ), when the speed (n_GLP) of the first pump ( 2a ) exceeds a maximum value (n_max) exceeded. Method according to one of the preceding claims 5 to 23, characterized in that when fulfilling the first condition ( 26 ) immediately into synchronous operation ( 29 ) is returned and the reference value (n_ref) is only stored as the upper limit value (n_o) ( 31 ), when the operating state before the volume flow reduction is restored after the return ( 30 ). Method according to one of the preceding claims, characterized in that the lower limit value (n_u) is reset to a minimum value ( 38 ) and synchronous operation ( 21 ) is returned when the first pump ( 2a ) reaches an inadmissible operating state, in particular reaches or exceeds a maximum speed (n_max). Computer program with instructions for carrying out the method according to one of the preceding claims, when it is mounted on a microcomputer of an electronic control system ( 6 . 6a . 6b ) is performed. Pump unit ( 1 ) with at least one base load-operated first pump ( 2a ) and at least one peak-load second pump ( 2 B ), which are switched on as needed and parallel to the at least one first pump ( 2a ) is operable, wherein the pump unit ( 1 ) so on a predetermined control characteristic ( 19 . 39 ) that the power consumed is minimal, characterized in that it has control electronics ( 6 . 6a . 6b ), which is adapted to carry out the method according to one of claims 1 to 25.

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