Parallel circulation pump coordinating control assembly

Abstract

A circulation pump assembly (22) includes an electrical drive motor (10) and an electronic control device (12) controlling the drive motor (10). The control device (12) is configured for the speed control of the drive motor (10) according to a control schema (I, II, III). The control device (12) includes a detection function (42) which is configured to detect a condition variable representing an operating condition, from a parallel flow path (16, 18, 20) with a second circulation pump assembly (22). The control device (12) is also configured such that it can change the control schema (I, II, III) on the basis of a condition variable detected by the detection function (42). Further an arrangement of at least two such circulation pump assemblies (22) and a method for the control of such two circulation pump assemblies (22) are provided.

Claims

1. A circulation pump assembly comprising: an electrical drive motor; and an electronic control device for control of the drive motor, wherein the electronic control device is configured to regulate a speed of the drive motor according to a control schema and the electronic control device comprises a detection unit configured to detect a condition variable representing an operating condition, of a parallel flow path with a second circulation pump assembly associated with only a single individual hydraulic branch of a hydraulic system having a single hydraulic resistance active in the single hydraulic branch, and the electronic control device is configured to change the control schema on the basis of the condition variable detected by the detection unit such that a differential pressure across a hydraulic resistance in another individual hydraulic branch of the hydraulic system connected to an outlet side of the circulation pump assembly is retained on a predefined value.

2. A circulation pump assembly according to claim 1, wherein the detection unit is configured to detect, as the condition variable a signal which represents the switching-on and/or switching-off or a speed change at least of a second circulation pump assembly, and the electronic control device is configured to control the drive motor whilst taking into account this detected signal.

3. A circulation pump assembly according to claim 2, wherein the detection unit is configured to recognize a signal in a form of at least one predefined pattern of a hydraulic load acting upon the circulation pump assembly.

4. A circulation pump assembly according to claim 1, wherein the electronic control device comprises a communication interface connected to the detection unit such that the detection unit receives a signal via the communication interface.

5. A circulation pump assembly according to claim 1, wherein the electronic control device comprises a signal generating device configured to produce a signal which represents the switching-in and/or switching-off or a speed change of the drive motor.

6. A circulation pump assembly according to claim 5, wherein the signal generating device is configured to produce a hydraulic signal.

7. A circulation pump assembly according to claim 1, wherein the electronic control device comprises a communication interface which is connected to the signal generating device such that the signal generating device emits a signal or a value, via the communication interface.

8. A circulation pump assembly according to claim 7, wherein the signal generating device is configured to output a delivery rate value representing the current delivery rate of the circulation pump assembly, via the communication interface.

9. A circulation pump assembly according to claim 8, wherein the communication interface is configured for the communication connection with a communication interface of at least the second circulation pump assembly of the same type, the electronic control device is configured such that, via the communication interface and the detection function, the electronic control device receives the condition variable from at least the second circulation pump assembly of the same type via the communication interface of this second circulation pump assembly and that the electronic control device controls the drive motor whilst taking into account the condition variable received from the communication interface.

10. A circulation pump assembly according to claim 8, wherein the communication interface is designed for communication with several second circulation pump assemblies of the same type, and the electronic control device controls the drive motor whilst taking into account all condition variables received from the communication interface.

11. A circulation pump assembly according to claim 1, wherein the electronic control device is configured such that the control schema, according to which the drive motor is regulated, comprises a pump characteristic curve which is changed and shifted, in dependence on a signal which is recognized or received by the detection function, in dependence on a received condition variable.

12. A circulation pump assembly according to claim 11, wherein the electronic control device is configured such that the pump characteristic curve is shifted by a correction value which represents a function of a received or detected condition variable.

13. A circulation pump assembly according to claim 1, wherein the electronic control device is configured such that after receiving a signal from the detection function, the electronic control device automatically changes the control schema in dependence on the change of the hydraulic load and shifts a pump characteristic curve which forms the control schema.

14. A circulation pump assembly according to claim 1, wherein the electronic control device is configured such that the electronic control device changes the control schema given a predefined condition variable which is detected by the detection function, such that the drive motor is switched off.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 is a schematic view of a circulation pump assembly according to the invention;

(3) FIG. 2 is a schematic view of a hydraulic system with an arrangement of three circulation pump assemblies according to the invention;

(4) FIG. 3 is a QH diagram for representing the interaction of several circulation pump assemblies;

(5) FIG. 4 is a schematic view of a hydraulic system with three circulation pump assemblies according to the invention, according to a second embodiment of the invention; and

(6) FIG. 5 is a schematic view of a hydraulic system according to FIG. 4, with an arrangement of three circulation pump assemblies according to the invention, according to a third embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

(7) Referring to the drawings, the circulation pump assembly according to the invention is a centrifugal pump assembly which as a circulation pump assembly can be applied for example in a heating system or air-conditioning system, for circulating a fluid heat transfer medium such as water. It comprises a pump housing 2 with an inlet 4 as well as an outlet 6 and at least one impeller 8 which rotates in the inside. The impeller 8 is rotatingly driven by an electrical drive motor 10. A control device 12 which controls or regulates the electrical drive motor 10, in particular controls or regulates it in its speed, is moreover present in the circulation pump assembly. I.e. the speed of the drive motor 10 can be changed via the control device 12, for adaption to the hydraulic conditions. In as much as this is concerned, the circulation pump assembly corresponds to the construction of known circulation pump assemblies.

(8) The control device 12 is configured such that it controls or regulates the drive motor 10 according to at least one control schema, i.e. for example according to a pump characteristic curve as is represented in FIG. 3. For example, it is known for example to apply proportional pressure curves as control schemas, according to which curves the pressure increases proportionally to the flow. Alternatively, for example control schemas with constant pressure curves can also be used, with which the drive motor is regulated such that the pressure retains a constant value independently of the flow. By way of example, FIG. 3 shows three proportional pressure curves I, II and III in a QH diagram, in which the pressure H is plotted against the flow Q. Moreover, three facility characteristic curves A, B and C are represented in the diagram according to FIG. 3, and these represent the pressure loss in the hydraulic circuit in a manner depending on the flow Q. On operation, an operating point at the interaction point of the pump characteristic curve with the facility characteristic curve sets in. For example, if the circulation pump assembly is operated at the pump characteristic curve I and the hydraulic facility, in which the circulation pump assembly is applied, has the facility characteristic curve A, then the operating point 14 at the intersection point of both characteristics curves sets in.

(9) FIG. 2 schematically shows a heating facility with three heating circuits or heating branches 16, 18 and 20. A circulation pump assembly 22a, 22b or 22c is arranged in each of the heating circuits 16, 18, 20 of the hydraulic system, and one or more consumers 24 such as for example a radiator or loops of a floor heating are present. The three heating circuits 16, 18, 20 moreover lead through a common flow path 26 which runs through a heat source 28 such as for example a heating boiler. The three heating circuits 16, 18, 20 branch away from one another in the flow direction s at the outlet side of the heat source 28 and run through the circulation pump assemblies 22a, 22b and 22c through the respective consumer 24 of the three heating circuits 16, 18, 20. At the exit side of the consumer 24, the three heating circuits again run out again into the common flow path 26, at the run-out point 30. The three heating circuits 16, 18, 20 for example can heat different parts of a building, and alternatively for example the heating circuit 16 can be a heating circuit for a floor heating, whereas the heating circuits 18 and 20 represent heating circuits with normal radiators.

(10) It is to be understood that concerning the arrangements shown in the FIGS. 2, 4 and 5, the flow direction s could also run in the opposite direction. I.e. in the shown examples, the hydraulic load or the hydraulic resistance which is formed by the consumers 24 lies downstream of the circulation pump assemblies 22. With an opposite flow direction, the consumers 24 would lie upstream of the circulation pump assemblies 22. This could be the case for example if the several heating circuits 16, 18, 20 heat different apartments and the circulation pump assemblies 22 are each part of an apartment station.

(11) The flow through the common flow part 26 and thus the pressure loss across the heat source 28 changes, depending on how many of the heating circuits are in operation. This results in the facility characterizes curve changing, as explained by way of FIG. 3. The facility characteristic curve A shown in FIG. 3 represents for example a facility characteristic curve when only one of the circulation pumps 22, for example the circulation pump 22a is in operation. If now the heating circuit 18 is brought into operation and for example the circulation pump 22b is also additionally brought into operation, then the complete delivery rate through the common flow path 26 and thus the pressure loss across the heat source 28 increases, so that the facility then has the facility characteristic curve B. If now the circulation pump assembly 22a is operated at the pump characteristic curve I, then the operating point would then move on this pump characteristics curve I from the operating point 14 into the operating point 32 which represents the intersection point between the pump characteristic curve I and the facility characteristic curve B. I.e. the circulation pump assembly 22 would reduce its speed, and the flow and the pressure would decrease. This would result in the heating circuit 16 and the consumer 24 no longer being adequately supplied, i.e., the flow through the consumer 24 would not be able to be kept constant.

(12) In order to compensate this, the control device 12 of the circulation pump assembly is configured such that its control schema can be changed in dependence on the operation of further circulation pump assemblies 22 in parallel branches 18, 20 of the hydraulic system. The control device 12 can therefore shift the pump characteristics curve I which is used as a control schema, for example such that the circulation pump assembly is operated according to the second pump characteristic curve II, whose intersection point with the facility characteristic curve B forms a new operating point 34 which lies at the same flow q.sub.1 as the operating point 14. The flow q.sub.1 through the consumer 24 of the heating circuit 16 can therefore be kept constant. The pressure H is simultaneously increased so that the higher pressure loss in the common flow path 26 is compensated and the differential pressure across the consumer 24 can also ideally be kept constant. For this, the circulation pump assembly 22a increases its speed and hence also its electrical power consumption. If the second circulation pump assembly 22b is switched off again, then the control schema is then changed back to the initial pump characteristic curve I and the circulation pump assembly 22a is again operated with the pump characteristic curve I at the operating point 14.

(13) If the third circulation pump assembly 22c in the third heating circuit 20 is also simultaneously brought into operation, then the pressure loss across the heat source 28 increases further and the facility characteristic curve assumes the form of the facility characteristic curve C in FIG. 3. In this case, the control schema of the circulation pump assembly 22a can then be changed such that it is operated according to the pump characteristic curve III in FIG. 3, so that the operation is effected at the operating point 36 which represents the intersection point between the facility characteristic curve C and the pump characteristic curve III. Here too, the flow q.sub.1 is held constant, but the pressure H increases so that the increased pressure loss in the common flow path 26 is compensated, and the heating circuit 16 continues to be supplied with an essentially constant flow. An adaptation of the control schemas of the circulation pump assemblies 22b and 22c in the heating circuits 18 and 20 is effected in the corresponding manner, depending on how many of the respective other heating circuits 16, 18, 20 are in operation. Here, it is to be understood that the circulation pump assembly 22a, 22b, and 22c does not necessarily need to be brought into operation in this sequence. For example, depending on the thermal requirement in the individual heating circuits 16, 18, 20, for example also only the circulation pump assembly 22c can be in operation and the circulation pump assembly 22a and 22b be subsequently taken into operation. Here, arbitrary combinations and sequences are conceivable.

(14) The necessary compensations can be computed from the hydraulic variables in the subsequently described manner. The consumers 24 in the heating circuits 16, 18, 20 have the hydraulic resistances R.sub.1, R.sub.2, and R.sub.3. The flows s.sub.1, s.sub.2 and s.sub.3 which are caused by the respective circulation pump assembly 22a, 22b, and 22c prevail in the three hydraulic circuits 16, 18, 20 which are shown in FIG. 2. The circulation pump assembly 22a produces a differential pressure h.sub.1, the circulation pump assembly 22b a differential pressure h.sub.2 and the circulation pump assembly 22c a differential pressure h.sub.3. A flow s prevails in the common branch or flow path 26 and the heat source 28 forms a hydraulic resistance R.sub.0. Here, it is to be understood that the hydraulic resistances R.sub.0, R.sub.1, R.sub.2, R.sub.3 not only represent the hydraulic resistance of the consumers or the heat source, but the complete hydraulic resistance in the respective branch, said resistance being formed by the conduit losses and the like. In a hydraulic heating system, the hydraulic resistances R.sub.1, R.sub.2 and R.sub.3 vary, for example in a manner depending on the opening degree of a thermostat valve in the respective heating circuit 16, 18, 20.

(15) If the differential pressures across the hydraulic resistances R.sub.1, R.sub.2, R.sub.3 are to be constant and regulated to a constant value, which is effected by the control device of the respective circulation pump assembly 22, then each branch has a differential pressure setpoint h* which is to be achieved across the hydraulic resistance R. In this case, the following results for the differential pressure h.sub.1, h.sub.2, h.sub.3 which is to be achieved by the respective pumps:
h.sub.1=h*+R.sub.0s.sup.2=h*+R.sub.0(s.sub.1+s.sub.2+s.sub.3).sup.2
h.sub.2=h*+R.sub.0s.sup.2=h*+R.sub.0(s.sub.1+s.sub.2+s.sub.3).sup.2
h.sub.3=h*+R.sub.0s.sup.2=h*+R.sub.0(s.sub.1+s.sub.2+s.sub.3).sup.2

(16) It is to be recognized that the pump differential pressure h.sub.1, h.sub.2 and h.sub.3 is dependent on the flow through all branches and on the hydraulic resistance R.sub.0 in the common branch.

(17) There can also be the case, in which the circulation pump assembly 22 is not to be regulated to a constant pressure but to a proportional pressure in a manner depending on the flow, in order to produce a proportional pressure curve. The pressure setpoint h* would then result as a value dependent on the flow, for the heating circuit 16 for example:
h*=as.sub.1.sup.2+b
In this equation, a and b represent parameters of the proportional pressure curve.

(18) In order to be able to take into account the pressure losses in the common flow path 26, it is therefore necessary to know and determine the hydraulic resistance R.sub.0 in this common flow path. The hydraulic resistances R.sub.1, R.sub.2 and R.sub.3 as a rule change very slowly on adjusting the thermostat valves in the heating circuits. This permits the hydraulic resistance R.sub.0 to be determined by way of switching the circulation pump assemblies 22 on and off in short time intervals, since the hydraulic resistances R.sub.1, R.sub.2 and R.sub.3 do not essentially change in these short time intervals.

(19) In order to determine the hydraulic resistance R.sub.0, firstly, preferably by way of a suitable communication via the subsequently described communication interfaces 40 and the data connections 38, the control devices 12 of the circulation pump assemblies are initiated into bringing all circulation pump assemblies 22a, 22b and 22c into operation. Thereby, the differential pressures h.sub.1, h.sub.2, h.sub.3 and the flows s.sub.1, s.sub.2 and s.sub.3 are each determined by the control devices 12 and are preferably exchanged amongst one another via the data connections 38. The detection of these values can be effected by way of suitable sensors in the circulation pump assemblies 22 and/or by way of computation on the basis of electrical variables drive motors of the respective circulation pump assembly 22. After these readings have been detected, the circulation pump assembly 22b for example can be switched off and the pressure values h.sub.1, h′.sub.2, h.sub.3 and flows s′.sub.1, s′.sub.2 and s′.sub.3 can be determined. The hydraulic resistance R.sub.0 in the common flow path 26 can be derived from these measurements, by way of solving the following equation system with two unknowns.

(20) A first example is based on the pressure h.sub.1 of the circulation pump assembly 22a:
h.sub.1=R.sub.0(s.sub.1+s.sub.2+s.sub.3).sup.2
h.sub.1=R.sub.1s′.sub.1.sup.2+R.sub.0(s′.sub.1+s′.sub.3).sup.2
R.sub.0 results from this:

(21) $R_0=\frac{s_1^{\mathrm{\prime 2}}{h}_1-s_1^2{h}_1}{{s_1^{\mathrm{\prime 2}}\left(s_1+s_2+s_3\right)}^2-{s_1^2\left(s_1^{\prime }+s_2^{\prime }\right)}^2}$
A second example is based on the pressure h.sub.2 of the circulation pump assembly 22b:
h.sub.2=R.sub.2s.sub.2.sup.2+R.sub.0(s.sub.1+s.sub.2s.sub.3).sup.2
h′.sub.2=R.sub.0(s′.sub.1+s′.sub.3).sup.2
R.sub.0 results from this:

(22) $R_0=\frac{h_2^{\prime }}{{\left(s_1^{\prime }+s_2^{\prime }\right)}^2}$
A third example is based on the pressure h.sub.3 of the circulation pump assembly 22c:
h.sub.3=R.sub.3s.sub.3.sup.2+R.sub.0(s.sub.1+s.sub.2+s.sub.3).sup.2
h.sub.3=R.sub.3s′.sub.3.sup.2+R.sub.0(s′.sub.1+s′.sub.3).sup.2

(23) A solution similar to the solution for the circulation pump assembly 22a results for this equation system.

(24) It is likewise possible to carry out additional tests or measurements, for example by way of the circulation pump assembly 22b and the circulation pump assembly 22c being switched off. Thereby, the following three equations can result for example for the circulation pump assembly 22a:
h.sub.1=R.sub.1s.sub.1.sup.2+R.sub.0(s.sub.1+s.sub.2+s.sub.3).sup.2
h.sub.1=R.sub.1s′.sub.1.sup.2+R.sub.0(s′.sub.1+s′.sub.3).sup.2
h.sub.1=R.sub.1s′.sub.1.sup.2+R.sub.0s′.sub.1.sup.2
These equations can be solved by way of a linear regression.

(25) There can also be cases, in which it is not possible to switch off one of the circulation pump assemblies 22. In such a case, it can also possible to merely change the differential pressure h across the respective circulation pump assembly 22 by way of speed change. For example, the pressure of the circulation pump assembly 22b could be changed from h.sub.2 to h′.sub.2 by way of a speed change. The following equations for the three circulation pump assemblies 22a, 22b and 22c result from this:
h.sub.1=R.sub.1s.sub.1.sup.2+R.sub.0(s.sub.1+s.sub.2+s.sub.3).sup.2
h.sub.1=R.sub.1s′.sub.1.sup.2+R.sub.0(s′.sub.1+s′.sub.2+s′.sub.3).sup.2
h.sub.2=R.sub.2s.sub.2.sup.2+R.sub.0(s.sub.1+s.sub.2+s.sub.3).sup.2
h′.sub.2=R.sub.2s′.sub.2.sup.2+R.sub.0(s′.sub.1+s′.sub.2+s′.sub.3).sup.2
h.sub.3=R.sub.3s.sub.3.sup.2+R.sub.0(s.sub.1+s.sub.2+s.sub.3).sup.2
h.sub.3=R.sub.3s′.sub.3.sup.2+R.sub.0(s′.sub.1+s′.sub.2+s′.sub.3).sup.2

(26) The hydraulic resistance R.sub.0 can be determined from these. Once the hydraulic resistance R.sub.0 in the common branch 26 has been determined in this manner after an initial test, then later, given a flow change by way of connecting or speed change of one of the circulation pump assemblies 22, the change of the flow s in the common flow paths 26 can be taken into account for the adaptation of the pump characteristic curve in each individual circulation pump assembly 22. The pump characteristic curve I, II, III is thereby preferably shifted by an amount or a correction value which is proportional to the hydraulic resistance R.sub.0 in the common flow path 26 and is an increasing function of the sum of the flows, i.e. of the flow s in the common flow path 26.

(27) In order to achieve the described functionality of the adaptation of the control schemas in dependence on the operation of the circulation pump assemblies 22 in the parallel heating circuits 16, 18, 20, according to the invention, a communication is provided between the circulation pump assemblies 22a, 22b and 22c. According to a first embodiment example of the invention which is shown in FIG. 2, the circulation pump assemblies 22a, 22b, and 22c can be connected to one another in a direct manner via data connections 38. Here, the data connections 38 can be realized as a cable borne data bus or also in a wireless manner by way of radio connections. The control devices 12 of the circulation pump assemblies 22 comprise a communication interface 40 for this. In the inside of the control device 12, this interface cooperates with a detection module 42 which provides a detection function. The detection module 42 can be realized in the control device as a software module. The control devices 12 moreover each comprise a signal generating device 44 which according to a first embodiment example can likewise be connected to the communication interface 40, as is shown in FIG. 1. In as much as this is concerned, the communication interface 40 in this embodiment example therefore acts preferably bidirectionally. The signal generating device 44 can also be realized as a software module in the control device 12.

(28) On operation of the respective circulation pump assembly 22, the signal generating device 44 produces a signal which represents a condition variable and which is outputted to the further circulation pump assemblies 22 via the communication interface 40 and the data connection 38. In the simplest form, the condition variable can merely signalize that the respective circulation pump assembly 22 is or will be switched on or off. Alternatively, the condition variable can be a delivery rate value which represents the respective flow rate of the pump assembly 22. The delivery rate can either be measured in the circulation pump assembly 22 or be derived by the control device 12 from electrical variables.

(29) If now, for example in the embodiment example according to FIG. 2, as described above, firstly only the circulation pump assembly 22a is in operation and the circulation pump assembly 22b is later connected, then the signal generating device 44 of the circulation pump assembly 22b produces for example a delivery rate value which specifies the delivery rate of the second circulation pump assembly 22b. This delivery rate value is transferred to the first circulation pump assembly 22a via the communication interface 40 and the data connection 38. The control device 12 of the first circulation pump assembly process this signal in the detection module 42 in a manner such that it now recognizes the change of the facility characteristic curve from the facility characteristic curve A to the facility characteristic curve B and accordingly changes the control schema of its control device 12, e.g. from the pump characteristic curve I to the pump characteristic curve II. This is effected in the corresponding manner on connecting the third circulation pump assembly 22c, by way of the circulation pump assembly 22c also transferring its delivery rate value to the circulation pump assembly 22b and circulation pump assembly 22a via the data connection 38, so that these two circulation pump assemblies can then again accordingly change their pump characteristic curve as a control schema. Conversely, the circulation pump assembly 22c also receives the delivery rate values from the circulation pump assemblies 22a and 22b, so that directly on starting operation, it can accordingly adapt its control schema to the hydraulic condition of the system which results from the simultaneous operation of the other circulation pump assemblies 22a and 22b.

(30) Instead of transferring the delivery rate values via the data connection 38 in a direct manner, as described, a signal which merely signalizes the switching-on and switching-off can also be transferred. If only the switching-on or the operation of the second circulation pump assembly 22b is communicated to the control device 12 of the first pump assembly 22a, then via the detection module 42 and from the change of the electrical variables and possibly hydraulic variables measured directly in the circulation pump assembly 22a, the control device 12 can automatically recognize how the facility characteristic curve changes and carry out a corresponding adaptation of the pump characteristic curve. This can be effected in the other two circulation pump assemblies 22b and 22c in a corresponding manner.

(31) In an alternative manner, the networking or linking for communication between the circulation pump assemblies 22a, 22b and 22c can also be effected as is shown for example in FIG. 4. There, the linking is effected via a central control appliance 46. The control appliance 46 is connected to the circulation pump assemblies 22 in each case via individual data connections 38′. Thereby, the data connections 38′ can again configured wire-connected or also configured wireless, for example as radio connections. The central control appliance 46 can therefore be configured such that it assumes the complete function of the control devices 12 in the manner such that it specifies the respective speed for the drive motor 10 to the circulation pump assemblies 22a, 22b, 22c, for example via a PWM signal input of the circulation pump assemblies 22a, 22b and 22c. Alternatively, the control appliance 46 can also merely assume the function of transferring the condition variables or signals between the circulation pump assemblies 22, as has been described above. In particular, this can be useful if the communication interfaces 40 of the control devices 12 are galvanically separated from the remaining parts of the control device, so that the communications connections 38′ require an external energy supply via the control appliance 46.

(32) According to a third possible embodiment which is described by way of FIG. 5, the communication between the circulation pump assemblies 22a, 22b and 22c is effected hydraulically. I.e., in this embodiment example, the circulation pump assemblies 22a, 22b, 22c require no communication interface 40. In contrast, the signal generating device 44 produces a hydraulic signal on starting operation of the respective circulation pump assembly 22, by way of the drive motor 10 being brought into operation according to a defined pattern, for example being briefly switched on and off several times in a certain pattern before being put into permanent operation. This leads to pressure fluctuations in the complete hydraulic system, said fluctuations being able to be detected by the other circulation pump assemblies 22 on the basis of a brief change of the hydraulic condition, for which the detection module 42 of the circulation pump assembly 22 is configured accordingly. If a circulation pump assembly 22 in the system recognizes the pattern which signalizes the starting operation of a further circulation pump assembly 22, then it can recognize the change of the facility characteristic curve A, B, C from its electrical variables or internal sensor signals and adapt the pump characteristic curve I, II, III accordingly, as has been described above. Such a hydraulic signal which signalizes the operation of a pump assembly can possibly also be produced in a recurring manner in regular intervals by the signal generating device 44, so that the circulation pump assemblies 22 via their detection devices or detection modules 42 can continuously monitor whether further circulation pump assemblies 22 are in operation in the same hydraulic system.

(33) While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.