GB2120874A - Circulating pump - Google Patents

Abstract

A circulating pump for heating plants has a motor which may be adjusted 2,4 in stages by switching windings 1 to at least two preset speeds, the lowest value of which is intended for plant operation in an economy stage, and each higher value is co-ordinated with a different operating stage of the plant. Starting from one of the higher preset speeds, the motor speed may be governed steplessly 7,9,8 towards the next lower speed figure to an operating value which is matched to the prevailing plant conditions. <IMAGE>

Description

SPECIFICATION Circulating pump The present invention relates to a circulating pump for heating plants in which the motor may be adjusted in stages by switching windingsthereofto at least two preset speeds (n1,n2....n), of which the lowest speed (n1) is intended for plant operation in an economy stage and each higher speed (n2....ni) is co-ordinated with a different operating stage of the plant. Hereinafter such a pump will be referred to as "of the kind described".

In most cases, circulating pumps are operated at a constant speed notwithstanding the momentary power demand of the heating plant. This mode of operation represents a wastage of electrical power however, since the delivery flow could be reduced without any disadvantage under partial load of the heating plant, which is possible by simply lowering the speed of the pump. The fact that a considerable amount of electrical power may be saved by doing so becomes particularly apparent if it is considered that in the case of fluid flow machines, the driving power is proportional to the third power of the speed. Consequently, this means that for example by reducing the speed of the pump by 20% to 80%, it is possible to lower the electrical driving power to say 50%.

This power saving facility available in the case of a fluid flow machine can be utilised sensibly only by selecting an electrical drive of the speed of which may be varied with minimum losses. A drive of this kind is an electric motor, the speed of which is adjustable by switching windings to different fixedly preset values, but the disadvantage of which is that the speed may be switched by stages only and cannot be governed at will to a particular operating speed established as an optimum and lying between the fixed preset speed values.

Although there are infinitely variable electric motors, e.g. those comprising frequency changers, these drives are unusable however in the case of circulating pump assemblies making use of comparatively low motor outputs for economic reasons, particularly since their price amounts to a multiple of the pump price.

Phase control systems are known moreover for stepless governing of the speed of the motor, which are substantially better value as compared to speed control systems utilising frequency changers, but have the disadvantage that the efficiency of the drive deteriorates in step with the drop in speed, so that control systems of this kind cannot be applied directly for controlling a pump motor, in particular if a saving in electrical power is sought.

It is an object of the invention to provide a circulating pump for heating plants, the operating speed of which is adjustable steplessly throughout the predetermined range of speed and with satisfactory efficiency to the value which is an optimum in each case in accordance with the plant conditions.

To achieve this and other objects, the invention consists in a circulating pump for a heating plant, having a motor that is adjustable in stages by switching windings thereof to at least two preset speeds (n1,n2....n1), of which the lowest speed (n1) is intended for plant operation in an economy stage, and each higher speed (n2....n1) is co-ordinated with a different operating stage of the plant, wherein the speed of the motor is steplessly governable, starting from one of the higher preset speeds (n2....n1) towards the next lower speed (n1....n11) and to an operating speed of (nx) adapted to the prevailing plant conditions.

If, upon designing a circulating pump, the speed range is specified as extending from nO at the speed zero to the highest possible speed nj, this range is divided into particulr switching or speed of revolution stages, say into the ranges nO to nj, n1 to n2 nj~1 to nj, the higher speeds nl,n2..nl appertain- ing to these stages being adjustable in conventional manner with satisfactory efficiency by switching windings. Starting from such a preset speed, it should not be possible in accordance with the invention to perform a governing action in stepless manner in the direction towards the next lower speed until the operating speed nx lying in the appropriate range of speed is reached.

To this end, the stepless control operation is in each case applied only to overbridge a single switching or speed stage and thus a comparatively small speed range. This yields the advantage that it is possible on the one hand to make use of inexpensive electric motors with a winding switching means at satisfactory efficiency and that, on the other hand, that the unavoidable drop in efficiency during stepless governing in the one switching stage of the other is kept within limits since it is unnecessary to apply governing throughout the possible speed range from ni to n1 or no.

In this case it is thus possible simply to revert to the comparatively inexpensive phase control system for stepless r.p.m. governing, since the efficiency losses of the drive may be kept within limits as the r.p.m. decreases, provided that the r.p.m. ranges which are to be governed are designed appropriately, meaning that these r.p.m. ranges should not be selected excessively wide For example, starting from a fixedly preset r.p.m.

n2, the operating r.m.p. nx may be adjusted manually and/or automatically as well, by lowering the speed towards n1 until the working r. p. m. is reached. The r.p.m. which is selected amongst the fixedly preset speeds as the initial value for stepless governing action, and the amount of r.p.m. reduction towards the next lower fixedly preset r.p.m. until nx is reached, are determined by the prevailing plant conditions, operating parameters, extraneous influences by weather and the like.

For example, the stepless r.p.m. governing action may be determined by the external air temperature, by the feed temperature or by the delivery flow volume of the water within the heating loop, by the pressure conditions across the circulating pump, and the like. If the ambient temperature say were to drop or the delivery flow quantity were to rise, the control system will set a higher value for the operating r.p.m. nx and if required also switch to a higher one of the fixedly preset r.p.m. values, so that this r.p.m. may then form the starting point for stepless adjusting of the operating r.p.m. nx. Conversely, it would also be possible to set out immedimately from a lower one of the fixedly preset r.p.m.

values, provided that this appears to be appropriate, e.g. because of a rise in the feed temperature or in the pressure differential across the pump.

Finally flow noises within the heating plant may finally also be largely eliminated by means of control system according to the invention. Noises of this kind frequently arise if particular pressure differentials prevail at particular r.p.m. values say at heating element valves or other control fittings, and the heating water flows at correspondingiy high speed of said points, with the consequence of flow noises are engendered. It will be understood that, in the case of circulating pumps the r.p.m. of which may be varied by stages only, there is correspondingly little leeway for detection and setting up of the r.p.-in. at which no flow noises occur on the one hand, and the pump can nevertheless provide the required power, on the other hand.An optimum r.p.m. figure of this kind may now however easily be established and set up by means of a stepless control system.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which show certain embodiments thereof by way of example and in which: Figure 1 shows a longitudinal cross-section through a circulating pump, Figure 2 shows a graph with pump characteristics for two fixed r.p.m. stages and a steplessly adjustable operating r.p.m, Figure 3 shows a block wiring diagram for stepless control of a circulating pump within a range between two fixed r.p.m. values, Figure 4 shows a graph with pump characteristics forthree preset r.p.m. values, and Figure 5 shows a block wiring diagram for stepless modulation of a circulating pump in several ranges between fixedly preset r.p.m. values.

Referring now to the drawings the circulating pump shown in Figure 2 is commonly known as regards its fundamental structure and function.

Pumps of this nature were illustrated and described, for example in German Offenlegungs specifications Nos. 25 16 575, 25 29 399 and 2639 541. This is why only some components of this pump which are of significance in conjunction with the invention, are to be described herein.

The windings 1 of the pump motor are joined at their ends to contacts which are situated within a fixedly installed half or sockets 2 of an electrical plug and sockets coupling apart from other contacts to which are connected the ends of the conductors of the mains lead 3.

The other half or plug 4 of this plug and socket coupling forms part of a regulator module 5 and comprises plug contacts which are arranged in a particular pattern with respect to the contacts of the socket 2 and are connected to a bridge combination 6 appertaining to the module 4, in such manner that in dependence upon the position in which the plug 4 is inserted into the socket 2, the motorwindings are wired up and connected in different ways, that is for example in a star or delta connection. In this manner, the r.p.m. is set by stages to the fixedly preset r.p.m.

values n1,n2....n. The module 5 is thus fixedly pre-programmed by the pattern of the contacts within the plug 4 with respect to the contacts of the socket 2 and by the wiring of the bridge combination 6to particular r.p.m. values, the finally set r.p.m.

then depending on which position the module 5 or its plug is pushed into the socket 2. An analogous solution is known from the German Offelegungs specification No. 27 00 116, to which reference is made at this juncture to avoid repetition.

The electronic control system 7 for stepless r.p.m.

adjustment also appertains to the regulator module 5. As has already been stated, a phase control circuit tuned to the characteristics of the pump motor should appropriately be applied as the control system 7. This control system may be driven by means of a conventional nominal value emitter or r.p.m. setter 8, for manual or automatic adjustment of the operating r.p.m. nx. As an alternative thereof, an external nominal value emitter 9 may also be connected via a separate input terminal to the module 5 or the control system 7.

Figure 2 shows two pump characteristics, namely the mutual dependence of the delivery head H and delivery volume Q at the two r.p.m. values n1 and n2, the lower r.p.m. value n1 being appropriate, for example, for night-time or summer-time operation of the heating plant. The corresponding connection of the motor windings 1 via the plug and socket coupling 2,4 and the bridge combination 6, is indicated in the upper part of Figure 3. The three pairs of windings are in this case arranged as a "Dahlander" circuit, for example.

The switching in steps to the higher r.p.m. value n2 may as described be performed by replugging the module 5 in such manner that the wiring of the bridge combination 6 and the control system 7 comprising the r.p.m. setter 8 are coupled as shown at the bottom in Figure 3.

In this case, the pump then runs at the higher r.p.m. value n2 and may as already stated be adjusted starting from this r.p.m. value towards the lower r.p.m. value n1 as well as in the opposed direction by means of the r.p.m. setter 8, to the operating r.p.m. nx advantageous for the control case in question. The possible course of the stepless r.p.m. variation is denoted by an arrow in Figure 2.

The governing an wiring example illustrated in Figures 4and 5 relates to a three-stage circulating pump having the three fixedly preset r.p.m. values n1,n2 and n3. The graph in Figure 4 shows the corresponding characteristics and by means of the arrows shown indicates the possible stepless control ranges.

In this case, the fixedly preset r.p.m. values n"n2 and n3 may also be set by appropriate insertion of the module 5 in the lower plug and socket coupling half 2, so that the motor winding 1 may be connected as a function of the correspondingly prepared layout of the bridge combination 6, as illustrated for two r.p.m. values in Figure 5. The delta connection, shown at the top in Figure 5, is in action for the motor windings 1 at the lowest r.p.m. value n.

The module 5 has to be replugged appropriately to establish the next higher r.p.m. value n2. For the r.p.m. value n3, the bridge combination 6 then connects the feed lines to the motor windings 1 as shown at the bottom in Figure 5, in which the box 6 (n3) drawn dash-dotted encloses the connections decisive for this case. The motor windings are then connected in a star (or Y) circuit. The exemplifying connections for other r.p.m. values n4...ni which are to be preset fixedly, have not been shown in Figure 5. Circuits of this kind are generally known moreover and need not be described in particular, therefore.

Reference is made to the German Offenlegungs Specification No. 13 164 regarding the prior art decisive in this respect.

If it is assumed, in the case of the embodiment shown in Figures 4 and 5, that the r.p.m. value n2 has been established by Dahlander connection of the motor windings 1,the r.p.m. may be varied by means of the phase control circuit 7 and the nominal r.p.m. value emitter 9 towards the r.p.m. value n1 and back from the same to reach the operating r.p.m.

value nx, the control range specified being apt to encompass all the values lying between n1 and n2. In corresponding manner, the r.p.m. value may also be acted upon within the range lying between n3 and n2, after the fixedly preset r.p.m. value n3 had been established beforehand. Finally, stepless adjustment from the r.p.m. value n1 towards the r.p.m. value zero is also possible in corresponding manner.

Even if it has to be accepted that particular losses occur as regards the efficiency in a control system of this nature, and that such losses become the greater the closer one gets from one of the preset r.p.m.

values to the next-lower r.p.m. value, the essential advantage will be decisive nevertheless, being that it is possible on the one hand to govern the whole r.p.m. range steplessly, without on the other hand having to accept the high efficiency losses which would be incurred if this entire r.p.m. range had to be governed steplessly in one passage, for example by means of a phase control circuit.

The arrangement according to the invention also offers the means of operating with other known control systems for r.p.m. governing, which would not otherwise be absolutely appropriate to modulate the circulating pump throughout the r.p.m. range specified, without substantial efficiency losses.

Claims (4)

1. A circulating pump for a heating plant, having a motor that is adjustable in stages by switching windings thereof to at least two preset speeds (n1,n2....n1), of which the lowest speed (n) is intended for plant operation in an economy stage, and each higher speed (n2....nj) is co-ordinated with a different operating stage of the plant, wherein the speed of the motor is steplessly governable, starting from one of the higher preset speeds (n2....n1) towards the next lower speed (nl....i~l) and to an operating speed of (nx) adapted to the prevailing plant conditions.

2. Acirculating pump as claimed in claim 1, wherein the operating speed (nx) in question is adjustable optionally by hand and/or automatically as a function of fluctuating plant conditions or control parameters, such as ambient temperature, feed temperature, pressure conditions and delivery flow volume.

3. A circulating pump as claimed in claim 2, wherein said operating speed (nx) is adjustable by means of a phase control circuit.

4. A circulating pump substantially as hereinbefore described with reference to the accompanying drawings.