Abstract:
A pump control method for controlling at least one booster pump ( 4 ). The method includes switching on the booster pump when a booster pump outlet pressure ( 24 ) drops to a lower limit value ( 26 ), and switching off the booster pump when the booster pump outlet pressure ( 24 ) reaches an upper limit value ( 28 ). The lower limit value ( 26 ) is reduced in a case, in which the maximal outlet pressure ( 24   a ) which can be reached on operation of the booster pump ( 4 ) lies below the lower limit value ( 26 ). A pressure-boosting device is also provided with which the pump control method can be carried out.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of European patent application 15 190 085.9 filed Oct. 16, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a pump control method for the control of at least one booster pump and to a pressure-boosting device. 
       BACKGROUND OF THE INVENTION 
       [0003]    The starting point of the invention is formed by those devices, in which a fluid delivery medium at the exit side of the device is brought to a pressure level which is higher than the pressure level at the entry side of the device, by way of at least one booster pump. Such devices hereinafter indicated as pressure-boosting devices are applied for example in water supply mains in those cases, in which the mains pressure is not sufficient or is sufficient stable, in order to deliver the water to consumers which are situated at a high level, for example in high-rise flats or at locations on higher ground. 
         [0004]    These pressure-boosting devices are typically designed such that a pressure level which is demanded from them at the exit side of the pressure-boosting device can be maintained in a certain pressure range. Accordingly, the booster pumps which are applied in such pressure-boosting devices are dimensioned in a manner such that under the assumption of a defined inlet pressure, they can provide a delivery pressure, with which the pressure level demanded at the exit side of the pressure-boosting device can be realized and can be held between a lower and an upper limit value. For this purpose, the booster pumps are always switched on when the pressure level at the exit side of the pressure-boosting device drops below the lower limit value, and switched off again when reaching the upper limit value. In the case that the inlet pressure of the booster pumps however drops to a value, at which the lower limit value for the outlet pressure demanded at the exit side of the booster pumps cannot be reached even with a maximal pump-difference-pressure, then the result of this is that the pressure-boosting devices continue to run in a temporally unlimited manner at maximal pump power, entailing a correspondingly high energy consumption, pump wear and heating of the delivered medium, without achieving the effect which is necessary regarding the pressure level which is to be provided at the exit side of the pressure-boosting device. 
         [0005]    No significant advantages result even if, with this procedural manner, a maximal time duration for reaching the pressure level demanded at the exit side of the pressure-boosting device is set after switching on the booster pumps, and the booster pumps are switched off after completion of this time duration, since the booster pumps are immediately started anew when the pressure level demanded at the exit side of the booster pumps is not reached in the defined time duration, and the switch-on duration of the booster pumps is thus only insignificantly changed. 
       SUMMARY OF THE INVENTION 
       [0006]    Against this background, it is the object of the invention, to provide a pump control method for the control of at least one booster pump, and a pressure-boosting device with at least one booster pump, with which significantly lower switch-on times of the at least one booster pump can be realized, in particular with a too low inlet pressure 
         [0007]    The part of this object with regard to the method is achieved by a pump control method according to the invention, whereas a pressure-boosting device with the according to another aspect of the invention solves the part of the object concerning the device. Advantageous further developments of the pump control method deduced from this disclosure including the following description as well as from the attached drawing. 
         [0008]    The pump control method according to the invention serves for the control of at least one booster pump. Thus one or more booster pumps can be controlled with the pump control method, depending on the case of application, wherein hereinafter one only speaks of one booster pump, but this is also to be understood as several booster pumps interacting with one another and controlled by way of the pump control method. 
         [0009]    With the pump control method according to the invention, the booster pump is switched on when its outlet pressure drops to a lower limit value, and is switched off when its outlet pressure reaches an upper limit value. The outlet pressure is hereby to be understood as the pressure which prevails at the exit or delivery side of the booster pump, wherein this outlet pressure in the case of a switched-on booster pump typically corresponds to the inlet pressure added with the delivery pressure of the booster pump. The upper and lower limit value of the outlet pressure hereby preferably indicates the region, in which the pressure at the exit side of the booster pump should be adhered to where possible. 
         [0010]    The pump control method according to the invention is characterized in that the lower limit value for the outlet pressure is reduced in a case, in which the maximal outlet pressure which can be reached on operation of the booster pump lies below the lower limit value. Accordingly, the value for the lower limit value of the outlet pressure at the exit side of the booster pump is lowered, if per se, it is foreseeable that the maximal outlet pressure or delivery pressure of the pressure-boosting device which can be reached given a switched-on booster pump is not suitable for increasing the outlet pressure above this lower limit value. Although this measure does not affect the outlet pressure demanded at the exit side of the booster pump, however compared to the procedural manner which was common until now and with which a lower limit value for the outlet pressure is fixedly set, it has the advantage that the running time of the booster pump is significantly reduced compared to the methods which have been common until now, on account of the lowering of the lower limit value for the outlet pressure, which in turn entails a reduction of the energy consumption and wear of the booster pump as well as a reduced absorption of heat by the delivery medium in the booster pump. 
         [0011]    The lower limit value is reduced preferably in dependence on the maximal outlet pressure within can be reached on operation of the booster pump, when the maximal outlet pressure which can be reached on operation of the booster pump lies below the lower limit value for the outlet pressure. Accordingly, with the pump control method according to the invention, the decision as to the extent in which the lower limit value for the outlet pressure is to be reduced, is preferably made in a manner depending on the maximal outlet pressure which can presently be realized at all given a switched-on booster pump. 
         [0012]    In an advantageous further development of this procedural manner, i.e. with the reduction of the lower limit value, the lower limit value is reduced to a value which is lower than the maximal outlet pressure which can currently be achieved on operation of the booster pump, when the maximal outlet pressure which can be reached on operation of the booster pump lies below the lower limit value. The aim of this measure lies in the switching-on of the booster pump entailing an increase of the outlet pressure at all when the outlet pressure has dropped to the newly fixed lower limit value, at which increase the outlet pressure with the given conditions assumes the largest possible value, i.e. the maximal outlet pressure which can be achieved on operation of the booster pump. 
         [0013]    With the pump control method according to the invention, one further advantageously envisages the lower limit value being reduced to a value which is lower than the maximal outlet pressure which can be currently reached on operation of the booster pump, by a predefined difference value. The magnitude of the difference value can hereby usefully be directed to the inlet pressure which presently prevails at the booster pump. The difference value can thus be fixed such that the lower limit value for the outlet pressure which is then newly set assumes at least the value of the inlet pressure presently prevailing at the booster pump, but meaningfully does not lie below this inlet pressure. 
         [0014]    As soon as the inlet pressure of the booster pump is so large that the delivery pressure of the booster pump lies above the initially set lower limit value for the inlet pressure, a previously implemented lowering of this lower limit value is to be seen as disadvantageous, since this entails very large fluctuations of the outlet pressure due to the consumers. Above all, for this reason, with the pump control method according to the invention, one advantageously envisages resetting the lower limit value to a predefined starting value when the maximal outlet pressure which can be reached on operation of the booster pump lies above this predefined starting value and in particular lies above this predefined starting value by a predefined difference. 
         [0015]    According to a further preferred development of the pump control method according to the invention, the booster pump is switched off after a defined time duration, in a case, in which the maximal pressure which can be reached on operation of the booster pump lies below the upper limit value. This means that when the delivery pressure of the booster pump lies below the upper limit value of the outlet pressure, the booster pump is only taken into operation in a fixed time interval, by which means the operational duration of the booster pump can be further advantageously reduced compared to the procedural manner common until now. The setting of a time duration until switching off the booster pump is moreover particularly advantageous if the lower limit value for the starting pressure has already been reduced, and in the time interval until switching off the booster pump, it is ascertained that a higher outlet pressure can hereinafter be realized on operation of the booster pump, so that the lower limit value for the outlet pressure can be increased again in a comparatively rapid manner. 
         [0016]    With regard to the pump control method according to the invention, it is particularly important to know the maximal outlet pressure which can be achieved on operation of the booster pump, above all with regard to a reduction of the lower limit of the outlet pressure, which is to be carried out as the case may be. In this context, one advantageously envisages that the maximal outlet pressure which can be reached on operation of the booster pump being detected or computed on operation. A computation of the maximal outlet pressure which can be achieved on operation of the booster pump can hereby be usefully effected on the basis of the power data of the booster pump as well as the inlet pressure prevailing at the booster pump or by way of extrapolating the pressure course at the exit side of the booster pump. Moreover, a pressure sensor, with which the outlet pressure of the booster pump is measured at least during the operational duration of the booster pump, can be advantageously provided at the exit side of the booster pump, for detecting the maximal outlet pressure which can be reached on operation of the booster pump. Usefully, such a pressure sensor is simultaneously used for the continuous pressure monitoring for switching the booster pump on and off. 
         [0017]    Apart from the previously described pump control method, a pressure-boosting device which is designed for carrying out the pump control method is also the subject-matter of the invention. This pressure-boosting device comprises at least one booster pump, with which it is preferably the case of a multi-stage centrifugal pump. Moreover, the pressure-boosting device has a control device. This control device comprises a memory, in which an upper and a lower limit value, which is to say an upper and a lower limit value for an outlet pressure prevailing at the exit side of the booster pump, are stored. The control device serves for the control of the booster pump, wherein it controls the booster pump in a manner such that it switches on the booster pump when its outlet pressure drops to the lower limit value, and switches it off when its outlet pressure reaches the upper limit value. With regard to the control device it is preferably the case of an electronic control device. 
         [0018]    What is special about the pressure-boosting device according to the invention is the fact that the control device comprises an adaptation module for adapting the lower limit value for the outlet pressure, said adaptation module being configured to reduce the lower limit value and store the reduced and store lower limit value in the memory, in a case, in which the maximal outlet pressure which can be reached on operation of the booster pump lies below the lower limit value for the outlet pressure. The adaptation module is thus provided and configured, in order, when required, to change the lower limit value for the outlet pressure and which is stored in the memory, on the basis of the maximal outlet pressure which can be reached on operation of the booster pump, and to further lead this changed lower value for the outlet pressure to the memory for storage, or to store this value itself in the memory. The memory is usefully a write-read memory, in which a previously stored lower value for the outlet pressure can be overwritten by a new lower value for the outlet pressure which is adapted by the adaptation module, in order to being able to store the changed value for the outlet pressure in the memory. 
         [0019]    The knowledge of the maximal outlet pressure which can be achieved on operation of the booster pump is a significant precondition for the lower value for the outlet pressure being able to be adapted by the adaptation module to the respectively prevailing operating conditions of the pressure-boosting device in a meaningful manner. Particularly for this purpose, the control device advantageously comprises a computation module which is configured to compute the maximal outlet pressure which can be reached on operation of the booster pump. With this computation module, it is the case of a part of the control device whose component architecture is of a nature such that at least the computation operations which are necessary for the computation of the maximal outlet pressure which can be reached on operation of the booster pump, can be carried out by it alone or in combination with suitable software. If these computation operations result in the fact that the maximal outlet pressure which can be achieved on operation of the booster pump will lie below the lower limit value for the outlet pressure and which is stored in the memory, then the adaptation module of the control device initiates the reduction of the lower limit value and accordingly its storage it in the memory. If the computation module however comes to the result that the maximal outlet pressure which can be achieved on operation of the booster pump lies above the lower limit for the outlet pressure and which is stored in the memory, then the lower limit value which is stored in the memory is retained or in a case, in which the lower limit value has already been lowered, the adaption module of the control device initiates the changing of the lower limit value again to the lower limit value initially stored in the memory. 
         [0020]    The pressure-boosting device according to the invention is further advantageously provided with at least one pressure sensor which is arranged at the exit side of the at least one booster pump, which detects the outlet pressure and is signal-connected to the control device. Hereby, the pressure sensor and the control device are usefully configured for the temporal, complete detection of the outlet pressure prevailing at the exit side of the booster pump, so that the booster pump can be switched off directly on reaching the upper limit value for the outlet pressure and be switched on directly on reaching the lower limit value for the outlet pressure. Moreover, the pressure values detected by the pressure sensor, as the case may be, can form a computation basis for the computation of the maximal outlet pressure which can be achieved on operation of the booster pump, or the actually achievable outlet pressure can be measured. 
         [0021]    According to a further preferred design of the pressure-boosting device according to the invention, the adaptation module is configured in a manner such that in the case, in which the maximal outlet pressure which can be reached on operation of the booster pump lies below the lower limit value, it reduces the lower limit value and in particular reduces it to a value lower than the achievable maximal outlet pressure. Hereby, the adaptation module via a signal connection between the adaptation module and the computation module usefully falls back on the value for the maximal outlet pressure which can be achieved on operation of the booster pump and which is determined by the computation module, or on a measured maximal outlet pressure. 
         [0022]    The adaptation module is moreover preferably configured in a manner such that it resets the lower limit value to a predefined starting value stored in the memory of the control device and stores it in the memory of the control device, when the maximal outlet pressure which can be reached on operation of the booster pump lies above this predefined starting value and in particular lies above this predefined starting value by a predefined difference. In this case too, the adaptation module advantageously communicates with the computation module which determines the value of the maximal outlet pressure which can be achieved on operation of the booster pump, or with a pressure sensor which detects the value. 
         [0023]    Apart from the lower and the upper limit value for the outlet pressure, preferably a maximal time duration for the operation of the booster pump without reaching the upper limit value is also stored in the memory of the control device. Hereby, the control device according to purpose is configured in a manner such that it switches off the booster pump after this maximal time duration, in a case, in which the maximal outlet pressure which can be reached on operation of the booster pump lies below the upper limit value. For this purpose, the control device favorably has a time switch which determines the point in time, at which the control device switches off the booster pump. 
         [0024]    The invention is hereinafter explained in more detail by way of one embodiment example represented in the drawing. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which the embodiment of the invention is illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    In the drawings: 
           [0026]      FIG. 1  is a schematic, simplified view of a pressure-boosting device according to the invention; and 
           [0027]      FIG. 2  is a diagram in three separate coordinate systems of the temporal course of the outlet and inlet pressure of a booster pump of the pressure-boosting device according to  FIG. 1 , as well as the switch-on duration of the booster pump. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Referring to the drawings, a supply conduit  2 , in which a booster pump  4  is integrated, is represented in  FIG. 1 . The booster pump  4  which is part of a pressure-boosting device, serves for delivering a fluid delivery medium led through the supply conduit  2 , from a pressure level prevailing in a region  2   a  of the supply conduit  2 , at the entry side of the booster pump  4 , to a higher pressure level prevailing in a region  2   b  of the supply conduit  2 , at the exit side of the booster pump  4 . A check valve  5  and a storage tank  6  as well as a shut-off valve  8  is arranged on the supply conduit  2 , at the exit side of the booster pump  4 . It is to be noted that the storage tank  6  is not essential to the invention and can be omitted as the case may be. For example instead flexible pipes can exist in the system. 
         [0029]    A control device  10  which via a lead  12  is signal-connected to the booster pump  4  is provided for the control of the booster pump  4 . As is the case with the booster pump  4 , the control device  10  is also part of a pressure-boosting device. The control device  10  is moreover signal-connected via a lead  14  to a pressure sensor  16  which detects the outlet pressure in the region of the supply conduit  2   b  and which prevails at the exit side of the booster pump  4 . The essential components of the control device  10  are a memory  18 , an adaptation module  20  as well as a computation module  22 , the significance of which with be dealt with in more detail hereinafter. 
         [0030]    The pressure-boosting device represented in  FIG. 1  serves for maintaining an outlet pressure  24  in the region  2   b  of the supply conduit  2  by way of the booster pump  4 , wherein this outlet pressure should lie between a lower limit value  26  and an upper limit value  28  and should not exceed the upper limit value  28 . This actual situation is clear from the upper coordinate system in  FIG. 2 , in which the outlet pressure  24  is plotted against time  30 . The lower limit value  26  (lower outlet pressure limit value  26 ) and the upper limit value  28  (upper outlet pressure limit value  28 ) for the outlet pressure  24  are stored in the memory  18  of the control device  10 . 
         [0031]    Normally, an outlet pressure  24  lying above the limit value  26  is realized by way of the control device  10  switching on the booster pump  4  when the outlet pressure  24  lies below the limit value  26 , and switching it off when the outlet pressure  24  reaches the upper limit value  28 . If now the outlet pressure  24  in the region  2   b  of the supply conduit  2  again falls to a value below the lower limit value  26  by way of opening the shut-off valve  8 , then the control device  10  initiates the renewed switching-on of the booster pump  4 . 
         [0032]    An outlet pressure  24  above the lower limit value  26  however is only possible from a certain inlet pressure  32  of the booster pump  4  which prevails in the region  2   a  of the supply conduit  2 . Such an inlet pressure  32   b  is to be deduced from the middle coordinate system of  FIG. 2 , in which a possible course of the inlet pressure  32  is plotted against time  30 . The outlet pressure  24  cannot be increased to a value above the lower limit value  26  if the inlet pressure  32  lies below the value  32   b,  as is represented in the middle coordinate system of  FIG. 2  by way of the value  32   a . This situation is now explained by way of  FIGS. 1 and 2 . 
         [0033]    As is represented in  FIG. 2 , the booster pump  4  is switched on by the control device  10  at a point in time  34 . Hereby, the inlet pressure  32   a  prevails in the region  2   a  of the supply conduit  2 , at the entry side of the booster pump  4 . The booster pump  4  is now operated only for a set time interval  36  which is likewise stored in the memory  18  of the control device  10 , and is switched off again after completion of the maximal time interval  36  at a point in time  38 , since the upper limit value  28  is not reached. This is deduced from the lower coordinate system of  FIG. 2 , in which the switching-on  40  of the booster pump  4  is represented over time  30 . The outlet pressure  24   a  which can be maximally achieved at the present inlet pressure  32   a  and which lies below the lower limit value  26  is computed in the computation module  22  of the control device  10  during the time interval  36 . An outlet pressure  24  which lies between the limit values  26  and  28  thus cannot be presently realized. For this reason, the adaptation module  20  initiates a reduction of the lower limit value  26  to the limit value  42  (adapted lower outlet pressure limit value) which is lower than the current maximally achievable outlet pressure  24   a . This new lower limit value  42  is now stored in the memory  18  of the control device  10 . 
         [0034]    The booster pump  4  thus remains switched off for so long, until the outlet pressure  24  has dropped to a new lower limit value  42 . This is the case at the point in time  44 . The booster pump  4  is switched-on again at this point in time  44  and remains in operation for a further maximal time interval  36 , since the upper limit value  28  is again not reached. The inlet pressure  32  during this time interval  36 , at a point in time  46  increases from a value  32   a  to the value  32   b . The outlet pressure  24  can again increase to above the initial lower limit value  26  on account of this, so that an outlet pressure  24   b  which is computed beforehand by the computation module  22  results after the completion of the time interval  36  at a point in time  48 . 
         [0035]    The adaptation module  20  of the control device  10  now initiates the changing of the lower limit value  42  again to the initial lower limit value  26  and its storage, in the memory  18  of the control device  10 . The booster pump  4  now remains switched off for so long, until the outlet pressure  24  has dropped to the lower limit value  26 . This is the case at the point in time  50 , at which the booster pump  4  is switched on again by the control device  10 . After a time interval  52  which is shorter than the time interval  36  stored in the memory  18 , the outlet pressure  24  reaches the upper limit value  28 , so that the control device  10  then initiates the basically envisaged switching-off of the booster pump  4 . The booster pump  4  remains switched off for so long until the outlet pressure  24  has dropped to the lower limit value  26 . The booster pump  4  is switched on again by the control device  10 , on reaching the lower limit value  26 , wherein the previously described procedures then repeat themselves 
         [0036]    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. 
       APPENDIX 
     List of Reference Numerals 
       [0000]    
       
           2  supply conduit  32   a,    32   b  value, inlet pressure value 
           2   a,    2   b  region  34  point in time 
           4  booster pump  36  maximal time interval 
           5  check valve  38  point in time 
           6  storage tank  40  switching-on 
           8  shut-off valve  42  limit value, adapted 
           10  control device lower pressure limit value 
           12  lead  44  point in time 
           14  lead  46  point in time 
           16  pressure sensor  48  point in time 
           18  memory  50  point in time 
           20  adaptation module  52  time interval 
           2  computation module 
           24 ,  24   a,    24   b  outlet pressure 
           26  limit value, lower 
       
     
         [0052]    outlet pressure limit value
     28  limit value, upper   
 
         [0054]    outlet pressure limit value
     30  time     32  inlet pressure