METHOD FOR REGULATING A CIRCULATING PUMP AND CIRCULATING PUMP

Description

[0001] The invention relates to a method for controlling a variable-speed circulating pump in a hydraulic system, in particular in a heating system, wherein the pump control sets the target delivery head and adjusts the speed of the pump to achieve the target delivery head.

[0002] Older heating circulation pumps, especially those used in small or medium-sized heating systems, are often unregulated. The pump speed must be manually adjusted to the heating system's specific power requirements, and the pump typically offers different speed settings for manual selection. The appropriate speed setting should be chosen to ensure sufficient flow for space heating, even during peak loads. Since these peak loads are usually irregular and short-lived, such pumps predominantly operate at an energy-inefficient speed.

[0003] Modern circulating pumps are equipped with frequency converters and speed controllers, enabling them to reduce their power consumption by adjusting their speed. This speed adjustment is based on a specific control curve. During operation, the pump uses sensors or an estimation algorithm to determine the current flow rate and actual head, and adjusts the speed so that the operating point only shifts along the defined control curve. The type of control curve thus defines the underlying control strategy. For example, with constant pressure control, the speed is always regulated to maintain a constant head, regardless of the flow rate. In contrast, with proportional pressure control, the head is regulated along a linearly increasing curve; that is, the target head is proportional to the actual flow rate.

[0004] WO 2018 / 162555 A1 discloses a method for controlling the speed of a centrifugal pump operated in an open hydraulic circuit, wherein the pump control controller calculates a target speed of the pump drive taking into account a target and actual delivery head as well as the actual speed, and wherein the controller considers a correction parameter for describing the geodetic head when calculating the target speed. DE 10 2014 018020 A1 discloses another method for operating a centrifugal pump.

[0005] The present application focuses on proportional pressure control and seeks optimization possibilities in order to further reduce the resulting power consumption of the pump.

[0006] This problem is solved by a method according to the features of claim 1. Advantageous embodiments of the method are the subject of the dependent claims.

[0007] According to the invention, for the generic method for controlling a circulating pump, it is proposed to adjust the dynamics of the speed adjustment. The dynamics of the speed adjustment, or speed control, here refers to the rate of such speed adjustment to bring the pump from the actual delivery head to the target delivery head specified by the control curve. According to the invention, the dynamics of the speed control are to be varied depending on the difference between the actual and target delivery heads, specifically depending on whether the target delivery head is greater or less than the current actual delivery head.

[0008] The pump control can operate based on constant pressure control or proportional pressure control. Alternatively, the pump control can also use the Eco-Mode developed by the applicant. The method is also applicable to temperature-controlled pumps.

[0009] In the pump control system used to set the target delivery head, the pump drive speed is not changed abruptly, but rather continuously increased or decreased. The dynamics of the speed control therefore correspond to the rate of change of speed. A key aspect of the invention is that the rate of change of speed when the actual delivery head (H) is less than the target head (H) differs from the rate of change of speed when H is greater than the target head (H). This dynamic adjustment of the rate of change of speed for the two control scenarios reduces the average power consumption of the circulation pump.

[0010] Ideally, a higher rate of speed change is selected when the target delivery head (Htarget) is lower than the current actual delivery head (Hactual) than when the required target delivery head (Htarget) is higher than the current actual delivery head (Hactual). Consequently, the speed is changed more quickly when a reduction is necessary than when an increase is required. This comparatively rapid reduction in pump speed results in lower average power consumption. Conversely, when increasing the actual delivery head and thus requiring a corresponding increase in speed, a comparatively slower speed adjustment is achieved, meaning the desired target delivery head is reached only after a certain delay. While this delay may lead to a temporary undersupply of heat to the rooms being heated, this is hardly noticeable to the occupants due to thermal inertia.

[0011] According to a preferred embodiment of the invention, the rotational speed is increased or decreased according to a definable time-dependent speed ramp until the required target delivery head is reached. From a control engineering perspective, such a speed control therefore corresponds to a first-order delay element, and the speed ramp behaves like a first-order low-pass filter. By adjusting the time constant, the steepness of the ramp, and thus the rate of change of the rotational speed, can be varied.

[0012] The speed ramps used for the aforementioned case distinction H are intended to<H ist oder H soll > H differs in terms of its slope or its time constant. Therefore, the first case (H should be) is preferred. <H ist ) eine sehr steile Drehzahlrampe eingestellt, d. h. die Rampe für H soll <H ist zeichnet sich durch eine niedrigere Zeitkonstante aus als die zweite Drehzahlrampe, wodurch es zu einer raschen Drehzahländerung der Pumpe kommt und die Sollförderhöhe deutlich schneller erreicht wird. Die mittlere Leistungsaufnahme der Pumpe wird dadurch reduziert.

[0013] According to an exemplary embodiment of the invention, a first and second speed ramp can be stored in the pump control system. The pump controller estimates or detects the current flow rate and the current delivery head and compares the latter with the target delivery head defined according to the proportional pressure characteristic curve. If the current actual delivery head is higher than the target delivery head, a necessary speed change is executed according to the first speed ramp to adjust the target delivery head. Conversely, if the target delivery head is higher than the actual delivery head, the second speed ramp is used for the speed change.

[0014] As explained above, increasing the actual delivery head necessitates a corresponding increase in pump speed, resulting in a comparatively slower speed adjustment. This means the desired target delivery head is only reached after a certain delay. This delayed speed increase creates a necessary condition for monitoring the heating system for potential over- or undersupply, as it ensures that the thermostatic valves react faster than the pump control.

[0015] This initially enables the monitoring of the flow rate during speed control. According to the invention, the pump continuously monitors the flow rate during speed adjustment, particularly during an increase in speed due to Htarget > Hactual. Furthermore, the invention provides that if the flow rate remains nearly constant during speed control, the applied speed change rate is further reduced, particularly to a minimum value that is only slightly greater than zero.

[0016] It is conceivable, for example, that in addition to the second speed ramp used here, a third minimum speed ramp is available, to which the pump switches when the speed is controlled according to the second speed ramp, provided the actual flow rate remains at a nearly constant level. If the flow rate remains constant despite an increase in the pump speed, it can be assumed that the thermostatic valves in the heating circuit will close simultaneously to prevent overheating of the rooms. In such a case, it makes energy sense to also reduce the speed increase rate to a minimum, i.e., the speed is only increased with a minimal, very shallow ramp. It is advisable to continue monitoring the flow rate during this process to ensure an adequate supply to the rooms being heated. If, for example, a change in the flow rate occurs, i.e.,An increase in the flow rate indicates that the heating valves are opening, so the speed control should also be switched from the minimum rate of change or minimum speed ramp back to the original rate of change, i.e., the second speed ramp.

[0017] In addition to the method according to the invention, the present invention also relates to a circulation pump, in particular a heating circulation pump, with a pump control for carrying out the method according to the present invention or an advantageous embodiment of the invention. The circulation pump is therefore characterized by the same advantages and properties as the method according to the invention, which is why a repetitive description will be omitted here to avoid repetition.

[0018] In addition to the circulation pump, the present invention also relates to a heating system with a circulation pump according to the invention. The same advantages and properties arise in this respect as well.

[0019] Further advantages and features of the invention will be explained in more detail below with reference to an exemplary embodiment shown in the figures. The figures show: Figure 1: an example diagram to illustrate the behavior of a low-pass filter and Figure 2: a functional diagram to describe the principle of the method according to the invention with adaptive ramp

[0020] The invention will be described below with reference to a heating circulation pump used within a heating circuit with a boiler and one or more radiators. The radiators are equipped with thermostatic valves that control the flow through the radiators depending on the room temperature.

[0021] The heating circulation pump includes a variable-speed inverter that operates according to a proportional pressure control curve, setting the target head proportionally to the actual flow rate. While this method can also be used if the pump control employs an alternative control strategy, for the sake of simplicity, the following explanation refers to a proportional pressure control curve. To achieve the target head, the pump control increases or decreases the pump drive speed according to an adjustable speed ramp until the target head is reached. Functionally, this speed ramp behaves like a first-order low-pass filter with adjustable time constants.

[0022] For example, in Figure 1 The temporal behavior of a known first-order low-pass filter was shown. Figure 1Figure 1 shows a setpoint step 1 and the corresponding step response 3 of the system. The intersection point between the tangent 2 of the step response 3 and the final value is the time constant T. As a rule of thumb, the step response reaches its final value after a duration six times the time constant T.

[0023] To save energy, two speed ramps are used. If the target head (Htarget) is less than the actual head (Hactual), the speed decreases. In this case, a steep speed ramp (low time constant) is set so that the speed drops quickly and the pump's power consumption is reduced. If the target head (Htarget) is greater than the actual head (Hactual), a very slow speed ramp (high time constant) is used instead, so that the speed increases only slowly and the actual head (Hactual) is reached with a delay. In this case, the delay can briefly lead to an undersupply of heat to the room being heated, but this is not noticeable to the occupants due to the room's typical thermal inertia. However, the pump's average power consumption has been reduced.

[0024] In addition to reduced power consumption, this method according to the invention can also determine whether the room is actually undersupplied with heat or whether a delivery head lower than the target delivery head is sufficient for heating the rooms. For this to work, the pump's speed control must be slower than the response of the radiator thermostatic valves. Experience has shown that radiator thermostatic valves react very quickly to changes in speed. If the pump speed increases very slowly, the valves close relatively faster (given sufficient heat supply to the room) and compensate for an oversupply. In such a case, the flow rate remains constant despite the increasing speed of the circulation pump.

[0025] The pump continuously monitors its flow rate as the speed ramps down. If the pump detects a constant flow rate, it can stop increasing its speed without causing a drop in room temperature. To further monitor whether the room is still adequately supplied, the pump can continue to increase its speed with a minimal ramp (just above zero) and check for changes in the flow rate. This allows for continuous monitoring to detect any insufficient supply. This principle is used in Figure 2 clarifies.

Claims

1. Method for controlling a circulation pump with variable rotational speed in a hydraulic system, in particular in a heating system, wherein the pump controller predefines a target delivery head and adapts the rotational speed of the pump in order to reach the target delivery head, wherein the rate of change in rotational speed is defined dynamically in a manner dependent on whether the target delivery head is greater than or less than the actual delivery head, characterized in that the delivery flow rate is monitored during the changing of the rotational speed, in particular an increasing of the rotational speed, and in that, with constant delivery flow rate, the rate of change in rotational speed is decreased, in particular is set to a minimum value greater than zero.

2. Method according to Claim 1, characterized in that rotational speed is increased or decreased according to a temporal rotational speed ramp until the target delivery head is reached, wherein the slope of the ramp is defined dynamically in a manner dependent on whether the target delivery head is greater than or less than the actual delivery head.

3. Method according to Claim 2, characterized in that, in terms of control, the rotational speed ramp acts like a first-order low-pass filter, the slope of it being described by the time constant of the low-pass filter.

4. Method according to one of the preceding claims, characterized in that, if Htarget < Hactual, a higher rate of change in rotational speed or a smaller time constant is selected than in the case of Htarget > Hactual.

5. Method according to one of Claims 2 to 4, characterized in that a first rotational speed ramp and a second rotational speed ramp are stored in the pump controller, wherein, if Htarget < Hactual, the first rotational speed ramp is used for the change in rotational speed and, if Htarget > Hactual, the second rotational speed ramp is used for the change in rotational speed, and wherein the first rotational speed ramp is steeper than the second rotational speed ramp, that is to say has a smaller time constant.

6. Method according to one of the preceding claims, characterized in that the rate of change in rotational speed is increased again, in particular is reset to the original rate of change in rotational speed, if a change in the delivery flow rate is determined.

7. Circulation pump, in particular a heating circulation pump, having a pump controller which is configured for carrying out the method according to one of the preceding claims.

8. Heating system having a circulation pump according to Claim 7.