DE102011008165A1 - Procedures for the performance-optimized operation of an electric motor-driven pump at low flow rates - Google Patents

Abstract

The invention relates to a method for the performance-optimized operation of an electric motor-driven pump in a hydraulic system with very low volume flows (Q), the desired delivery head (H) of the pump being regulated as a function of the volume flow (Q) along a preset characteristic curve (K). The nominal delivery head (H) is lowered compared to the preset characteristic curve (K) when the volume flow (Q) falls below a reference value (Q_ref), which is at most one tenth, preferably one twentieth, of the maximum volume flow (Q_max) on the characteristic curve (K), whereby the reduction takes place as long as the volume flow (Q) is below the volume flow reference value (Q_ref) and a minimum head value (H_min) has not yet been reached. Furthermore, the invention relates to an electromotive pump with control and regulating electronics, which is set up to carry out this method, and a computer program product with instructions for carrying out the method for operating an electromotively operated pump, if it is in a control and regulating electronics of the Pump is running.

Description

The present invention relates to a method for performance-optimized operation of an electric motor-driven pump in a hydraulic system at very low flow rates, wherein the target delivery height of the pump is controlled as a function of the volume flow along a characteristic curve. The invention further relates to an electric motor operated pump with a control and regulating electronics, which is adapted to carry out the inventive method. Finally, the invention relates to a computer program product with instructions for carrying out the method according to the invention, when it is executed in a control electronics of the pump.

The regulation of pumps along a predetermined characteristic is known. In this case, so-called Δp-c characteristics are used, in which the nominal delivery head of the pump is kept constant over the volume flow. Furthermore, so-called Δp-v characteristic curves are known in which the regulation of the pump takes place in accordance with a linear dependence of the nominal delivery height on the volume flow. Δp-v curves adjust the hydraulic power of the pump depending on the volumetric flow demand of the hydraulic system.

The disadvantage of such a characteristic control that the target delivery height of the pump with closed valves in the system, d. H. is not adjusted to the actual hydraulic demand of the system at a flow rate equal to zero. The control characteristic is rather defined for volume flows greater than zero and can only be used there. If, in addition, the control characteristic in the H / Q diagram is considered, there is an intersection with this axis in the case of geometric extension of the control characteristic to the H axis of the diagram, which results in a comparatively high nominal delivery height for the pump at a flow rate equal to zero. The pump therefore delivers against the closed valves in the system, which unnecessarily consumes power.

It is therefore an object of the present invention to provide a method for operating an electric motor-driven pump in a hydraulic system that allows for very low flow rates of the pump performance-optimized, energy-efficient operation of the pump.

This object is achieved by a method having the features of claim 1. Advantageous developments of the invention are given in the dependent claims.

According to the invention, for a performance-optimized operation of a pump driven by an electric motor in a hydraulic system at very low volume flows, wherein the nominal delivery height is regulated as a function of the volume flow along a preset characteristic curve, it is proposed to lower the nominal delivery height compared to the preset characteristic when the volume flow falls below a reference value, the maximum one tenth of the maximum volume flow on the characteristic curve, preferably one twentieth of this maximum value, wherein the lowering takes place as long as the volume flow is below the volume flow reference value and a minimum conveying height value has not yet been reached.

The basic idea of the method according to the invention is to make a reduction of the nominal delivery height of the pump at very low volume flows, d. H. to depart from the control on the originally set control characteristic at these low flow rates and instead to reduce the delivery rate of the pump targeted controlled, with a subordinate characteristic control can still be active. The lowering of the nominal delivery head of the pump can be carried out by reducing a pumping height setpoint directly specified by the pump. This can be done for example by reducing the pump speed, respectively the electric drive power. In this case, the pump motor is directly preset by the pump controller for a specific nominal delivery height. Alternatively, the lowering of the setpoint delivery height of the pump can take place by reducing a characteristic setpoint conveying height that determines the characteristic curve. The characteristic setpoint head specifies the position of the characteristic curve in the characteristic field of the pump. For example, the characteristic setpoint conveying height can be predetermined by the intersection of the characteristic curve with the curve describing the maximum speed. This means that, according to the invention, the lowering of the setpoint delivery height of the pump can also be achieved by shifting the position of the predetermined characteristic curve below the volume flow reference value. In this case, the pump motor is indirectly predetermined by the pump controller for a specific target delivery height, with a delivery rate set point for the pump coming directly from the subordinate characteristic control.

In this case, the core aspect of the invention is to make a reduction in the pump power when the volume flow is equal to zero, since in this case actually no pump capacity of the pump is needed. However, if the pump is completely switched off, the system is no longer observable and can no longer respond to a change in the volume flow requirement. It is also due to measurement inaccuracies in volumetric flow determination as well as inadvertent leaks on the valves of the hydraulic system expedient, not only to take into account the operating case of a volume flow equal to zero, but rather to define a lowering range, within which the method according to the invention is carried out.

This lowering range is limited upwards by the volume flow reference value, which is a maximum of one tenth of the maximum volume flow that can be reached on the preset control characteristic. Preferably, a smaller volume flow reference value can also be used, for example a reference value which is one twentieth of the maximum volume flow defined by the characteristic curve. By determining a volumetric flow reference value, the delivery head is lowered not only at Q = 0 l / h but in a certain volumetric flow range 0 <Q <= Q _ref . This area is referred to below as the lowering area.

Preferably, the reference value is between 10 l / h and 250 l / h. Since the typical design mass flow of a radiator is between 30 and 50 l / h, a lower limit of the reference value of approx. 10 l / h ensures sufficient operation of a single heating circuit in small systems. In larger systems, a larger limit value for the reference value makes sense, since a simultaneous operation of several consumers leads to a higher minimum operation of approx. 250 l / h. H. a higher minimum volume flow, which ensures the minimum supply of simultaneously operating consumers.

If the volume flow required by the hydraulic system drops to a value below the reference value, according to the invention the nominal delivery height of the pump is lowered. This takes place as long as the volume flow is below the reference value and a minimum head is not yet reached. In the lowering range, either the setpoint of a subordinate characteristic control can be lowered or the speed of the pump can be reduced directly. In the latter case, the pump is operated purely controlled.

The minimum head height is determined by the pressure difference required on the valves in the hydraulic system for any flow to flow in the system at all. It should be noted that in the hydraulic system gravity brakes, in particular backflow preventer can be used, which require a certain opening pressure, so that the medium flows. Only when this opening pressure is exceeded, a gravity brake allows a corresponding volume flow. It is therefore advantageous to orient the minimum height of heights of the heights at what the delivery height of the pump must be at least in order to achieve the opening pressure of the valves in the hydraulic system. For example, the minimum head height is between 60 cm and 200 cm depending on the construction of the plant, in particular the non-return valve used.

The definition of such minimum head height is necessary in order to keep the volume flow in the hydraulic system observable. Because if the delivery height of the pump is below this minimum value, the opening pressure of the valves in the system is not reached and flows due to the hydraulic resistance inherently no flow, so that in such operation of the pump is not determined, if and when a control valve of the System opens. If the system is formed by a heating system, for example, opening a valve, for example a thermostatic valve, would not change the pump control because this valve opening would go undetected. The same happens if the system is a cooling air conditioning system.

If the nominal delivery height remains above the minimum height of the delivery height, it is ensured that an opening of at least one valve in the system can cause the volume flow to increase correspondingly and rise again above the volume flow reference value. According to the invention, the setpoint delivery height can then be increased again and the regulations along the characteristic curve can be changed, if the volume flow increases or increases above the volume flow reference value. Outside the Absenkbereichs the target delivery height of the pump is thus raised again, in particular continuously, until the original control characteristic is reached.

The characteristic curve along which the pump is controlled may be a pure Δp-c characteristic, a pure Δp-v characteristic or such a Δp-c or Δp-v characteristic that is changed in time, for example as a function of temperature. This means that the characteristic curve can describe a linear, quadratic or constant relationship between the volume flow and the delivery head and / or can be time-variable.

The lowering of the nominal conveying height can take place in continuous operation with a constant lowering speed. Also, the raising of the target conveying height after lowering can take place in continuous operation with a constant lifting speed. Preferably, the lowering speed and the lifting speed for the delivery height setpoint may be selected differently. It is particularly advantageous to set the lowering speed smaller than the lifting speed. At an increased Volumetric demand can then be served as quickly as possible.

If the volume flow remains below the reference value, the nominal delivery height is increasingly lowered. This is preferably done not by switching, but continuously, so that in the hydraulic system no non-linear effects, in particular a tearing off of the flow can occur.

Preferably, the lowering takes place at a constant lowering speed. This means that the longer the operating point of the system is in the lowering range of the characteristic field, the further the nominal delivery height is lowered. Illustrated, the operating point in the H / Q diagram moves downwards on the current piping parabola until after a certain time the minimum delivery height has been reached.

In an advantageous development of the method according to the invention, the pump is controlled in a clocked manner after reaching the minimum height of the delivery height. In this case, it alternates between a first delivery altitude value and a second delivery altitude value which is below the first delivery altitude value. By switching between the first and the second delivery height value, on average, a delivery height value is set below the first delivery height value.

The switching between the two delivery height values preferably takes place in a uniform cycle. In this case, the pump is operated for the first time on the first delivery height value as a setpoint. For the duration of a second period, however, the second delivery level value is set for the pump.

The second delivery height value may preferably correspond to the delivery height zero. This means that the pump is switched off for the duration of the second period. In this case, on the basis of the first delivery level value, a temporary switch-off (to zero cycles) or a cyclical switch-on of the pump takes place, whereby a discontinuous but energetically optimized operation is achieved. Alternatively, the second delivery altitude value may be any elevation value between the minimum altitude and the zero value.

The cyclical switching off of the pump has the advantage that a maximum energy saving can be achieved with the pump. In contrast, a second delivery level value at a level above the delivery head zero has the advantage of ensuring that sufficient pressure is available throughout the pipeline network to drive the volume flow. The system thus remains completely observable even below the minimum head. For when a clocking between the first and the second delivery height value above the delivery value zero can be prevented that the mass flow in parts of the system due to the very low pressures and possible non-linear effects, such as thermal rotation or closing the valve flaps in gravity brakes, breaks off.

As an alternative to a fixed second delivery altitude value, the second delivery altitude value may also be variable. According to the invention, therefore, the head of the pump after reaching the minimum head height can preferably be further reduced in average by clocking the pump between the minimum head height value as the first head height value and the second head height value, the second height value being gradually reduced.

It is particularly advantageous to use the delivery height minimum value as the first delivery height value, since switching off the pump from this minimum delivery value or switching to the second delivery level value from this minimum delivery height value causes a minimal noise development. Otherwise, the noise generated by switching on and off or switching over would be perceptible and would lead to corresponding complaints by the end user.

For the duration of the second period, d. H. if the pump is operated either at the second head level or off, the hydraulic system is not safely observable. This means that no system-relevant volume flow information can be obtained. Switching the pump back to the minimum level of the pump, or switching the pump to this value, ensures that the system becomes observable again and an increased volumetric flow requirement can be ascertained. It is therefore advantageous, at least during the period in which the pump is operated with the first delivery level value, to check whether the volume flow increases or increases above the volume flow reference value.

If it is determined during the check of the volumetric flow that it rises above the volumetric flow reference value or has risen, the nominal delivery height is raised again and the regulation along the characteristic curve is transferred. Preferably, a steady, d. H. stepless transition to the control characteristic in order to adapt the performance to the actual requirements of the plant.

Preferably, a switchover is made between the first delivery level value and the second delivery level value in a uniform cycle, wherein the pump is operated or switched off with the second delivery level value for a period between 10 and 120 seconds.

By activating the delivery height reduction, a small amount of liquid in the hydraulic system, in particular hot water, is always conveyed compared to a permanent shutdown of the pump. As a result, at the resumption of regular operation, a state is present, from which a continuous transition to the normal control operation along the characteristic curve is possible.

By reducing the nominal delivery head of the pump and the cyclical downshift to a lowest delivery level value, in particular the temporary shutdown of the pump, the system remains observable on the one hand and in a state in which the actuators of the hydraulic system independently react, for example, to a water temperature increased by a drinking water preparation can. The increased power introduced into the system by the increased water temperature is compensated for early by lowering it to the minimum head.

It is further proposed an electric motor driven pump with a control and regulating electronics, which is adapted to carry out the inventive method. Finally, a computer program product with instructions for carrying out the method according to the invention is proposed, when it is executed in a control electronics of the pump.

Further advantages, features and properties of the method according to the invention are explained below with reference to the attached figures. Show it:

1 : H / Q diagram with Δp-v characteristic curve and marked lowering range with reduction of the nominal delivery height

2 : H / Q diagram for the transition from the lowering range to the Δp-v characteristic

3 : Representation of the transition from a continuous to a pulsed operation of the pump with increasing reduction of the second delivery level value

1 shows a H / Q diagram 1 for a hydraulic system, here a heating system, with an electric motor driven pump. numeral 2 indicates the operating points on a characteristic curve at maximum speed of the pump. The pump is controlled in normal operation on a Δp-v curve K, according to which the target delivery height H is set in linear dependence on the volume flow demand Q of the system. At maximum speed of the pump, a maximum volume flow Q_max is reached on the characteristic curve K. The then applied setpoint conveying height H is marked H_soll and corresponds to the characteristic setpoint conveying height.

If the operating point of the heating system moves along the characteristic curve K in the direction of smaller volume flows Q and if the volume flow Q reaches a reference value Q_ref which is approximately 5% of the maximum volume flow Q_ref, for example 150 l / h, then the nominal delivery height H of the pump is opposite the characteristic curve K lowered. The operating point has then in the in 1 hatched lowering area 3 moved into it. The lowering takes place as long as the volume flow Q is below the volume flow reference value Q_ref and a minimum head H_min has not yet been reached.

The minimum head height value H_min is dimensioned such that, in its case, the opening pressure of the valves and gravity brakes present in the heating system is overcome, i. H. when the thermostatic valves are open, a volume flow is possible. For example, the minimum head H min is typically about 70 cm for pumps for a one- or two-family house and about 1 m for pumps for larger buildings.

After falling below the volume flow reference value Q_ref, the operating point of the heating system moves by lowering the nominal delivery height H along a not shown piping parabola in the direction of smaller volume flows Q to the minimum delivery height value H_min is reached. The lowering takes place continuously with a constant lowering speed, so that the setpoint conveying height H is lowered all the more, the longer the operating point in the lowering area 3 lingers.

The fact that in continuous operation no further than the minimum delivery head H_min is lowered has the advantage that the heating system remains observable, because always at least a minimum volume flow Q is possible with valves not completely closed. The lowering speed can be, for example, 10 rpm per minute.

If the setpoint conveying height H is lowered to such an extent that the minimum height of the delivery height H_min is reached, a pulsed activation of the heating-medium circulation pump is transferred according to the invention. H. to a discontinuous operation, wherein alternately between the minimum height of the conveyor height H_min and an underlying, second delivery level value is switched.

Depending on the clock ratio, d. H. time duration for which the minimum head H_min on the one hand and the second head value on the other hand is applied, can be set on the average any H height value H between the minimum height of the conveyor height H_min and the lower second head value. In comparatively sluggish heating systems such as underfloor heating, the pump can also be switched off for the second period. In this case, the heating system remains observable both when switching between the minimum head height H_min and the underlying head and the temporary shutdown of the pump, if at least during the period in which the pump is operated with the minimum head height H_min, it is checked whether the flow rate Q over the volume flow reference value Q_ref increases or has increased.

As in 2 In this case, the setpoint conveying height H is continuously raised, the control being transferred along the characteristic curve K. The lifting speed is greater than the lowering speed chosen to quickly adjust the pump power to the requested volume flow Q.

3 shows the temporal transition from a continuous to a pulsed operation of the pump with increasing reduction of the second delivery height value. The achievement of the volumetric flow reference value Q_ref is assumed at the time t = 0. The delivery head H of the pump is then continuously reduced to the minimum delivery height value H_min. If the minimum head height H_min is reached at the time t1, a discontinuous operation is started and clocked between a first head value and a second head value, ie periodically switched over. The switching times are chosen identical.

The first delivery height value corresponds to the previously reached minimum delivery altitude value H_min. The second delivery altitude value is below this minimum travel altitude value and is gradually reduced until a second minimum travel altitude value H_min2 is reached. In the example below 3 At each new cycle, the second delivery level value is reduced as long as the second minimum delivery level is not reached. Alternatively, a certain second delivery altitude value can also be maintained over several cycles. The embodiment according to 3 has the advantage that the hydraulic system always remains observable regardless of whether backflow preventer is present in the system.

Claims (17)

Method for performance-optimized operation of an electric motor-driven pump in a hydraulic system at very low volume flows (Q), wherein the nominal delivery height (H) of the pump is regulated as a function of the volume flow (Q) along a preset characteristic (K), characterized in that the Sollförderhöhe (H) compared to the preset characteristic (K) is lowered when the flow rate (Q) below a reference value (Q_ref), which is a maximum of one tenth, preferably one twentieth of the maximum volume flow (Q_max) on the characteristic (K), the Lowering takes place as long as the volume flow (Q) is below the volume flow reference value (Q_ref) and a minimum value of delivery height (H_min) has not yet been reached. A method according to claim 1, characterized in that the lowering takes place continuously. A method according to claim 1 or 2, characterized in that the lowering takes place at a constant lowering speed. Method according to one of the preceding claims, characterized in that the pump is controlled clocked after reaching the minimum height of the conveyor height, wherein alternately between a first delivery altitude value and a second delivery altitude value, which is below the first delivery altitude value, is switched. A method according to claim 4, characterized in that the first conveying height value corresponds to the minimum conveying height value (H_min). A method according to claim 4 or 5, characterized in that the second delivery height value is zero. A method according to claim 4, 5 or 6, characterized in that the second delivery level value is gradually reduced. Method according to one of claims 4 to 7, characterized in that at least during the period in which the pump is operated with the first delivery altitude value, it is checked whether the volume flow (Q) above the volume flow reference value (Q_ref) increases or has risen. Method according to one of claims 4 to 8, characterized in that between the first delivery level value and the second delivery level value is switched in a uniform cycle, wherein the pump is operated for a period of between 10 and 120 seconds with the second delivery height value. Method according to one of the preceding claims, characterized in that the nominal delivery height (H) is raised again and the regulation along the characteristic curve (K) is transitioned when the volume flow (Q) above the volume flow reference value (Q_ref) increases or has risen. A method according to claim 10, characterized in that the lifting of the nominal conveying height (H) takes place continuously. A method according to claim 10 or 11, characterized in that the lifting speed is greater than the lowering speed. Method according to one of the preceding claims, characterized in that the characteristic curve (K) is time-variable. Method according to one of the preceding claims, characterized in that it is used to control a heating circulation pump. Method according to one of the preceding claims, characterized in that the lowering of the nominal delivery height of the pump is effected by reducing a pumping height set point directly predetermined by the pump or by reducing a characteristic setpoint conveying height determining the characteristic curve. Electromotive pump having a control and regulating electronics, which is adapted to carry out the method according to one of claims 1 to 15. Computer program product with instructions for carrying out the method for operating an electric motor-operated pump according to one of claims 1 to 15, when it is executed in a control electronics of the pump.

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