FIELD OF THE INVENTION

The invention relates to swimming pool pumps.

BACKGROUND TO THE INVENTION Swimming pool pumps are centrifugal pumps powered by electric motors. Decades ago a typical swimming pool pump was required to merely move fluid through a suitable filter, such as through a sand filter. As such single speed two pole induction motors became the norm.

To select a pump a swimming pool installer would settle on a flow rate and filter size necessary to service the pool. The flow rate was typically determined based on a desired number of turnovers. The filter was then sized based on desired flow velocities within the filter. From this filter selection the system curve of the filtration system (including the filter and the plumbing to take water to and from the pool) could be estimated. In Figure 1 a system curve for such a filter is illustrated as the curve Si . The installer would then turn to pump manufacturer's catalogues that would typically include sets of curves such as the curves 1 hp, 1 .5 hp and 2 hp setting out the performance characteristics (pump curves) for a particular range of pumps. The pumps were typically referred to by the horsepower rating of their electric motors but were also typically distinguished by the configuration of their impellers and impeller housings. Through conventional design processes the hydrodynamic components (impeller and housing) and the electric motor were co-operably configured to operate efficiently along system curves similar to the curve Si. Typically this entailed the motor operating at about 5% slip from its synchronous speed.

Australia has a 50 Hz mains supply and as such synchronous speed is 3000 rpm and 5% slip therefrom is about 2850 rpm. In the United States of America the mains supply has a frequency of 60 Hz and as such the synchronous speed is 3600 rpm and 5% slip therefrom is about 3400 rpm. Faced with the estimate of the system curve, a desired flow rate, say 420 L/min and the illustrated pump curves the installer would then calculate that the two-horsepower pump operating at the design point DP (i.e. the intersection of the curve Si and the curve 2 hp) would be suitable. The speed of a typical induction motor depends on the load on the motor which in turn, in this context, depends on the flow rate through the pump. Australian pumps were typically optimised for operation at about 2850 rpm at the design point. When faced with pressures higher than the design point (corresponding to the lower flow and to the left of the design point DP) the pump would speed up to approach synchronous speed (3000 rpm in Australia). When faced with lower pressures (corresponding to higher flows and to the right of the design point DP), the pump would slow down.

As time progressed, typical home swimming pools became more elaborate and pumps were required to do more than merely move water through a filter. Pumps became expected to service other aquatic applications such as operating spa jets and/or floor cleaning jets that could be user-selected to operate from time to time. Such aquatic applications typically require a similar flow rate as the routine filtration cycle but require the water to be delivered at much higher pressure. Thus pumps were required to work harder when these secondary applications were selected. With the advent of such secondary aquatic applications, a different pump selection logic became the norm. That newer logic is illustrated in Figure 1 . To enable us to reuse the same chart, the following discussion relates to a smaller hypothetical pool requiring about 270 L/min to achieve the desired number of turnovers.

According to this new logic, the starting point is the system curve S2 for the

secondary aquatic application. Following this logic, the installer would again select the two-horsepower pump even in the context of the smaller pool. Of the three pumps only the two-horsepower pump is capable of reaching the operating point OP2 at which the pump supplies the jets with the necessary 270 L/min and 18 m, H2O of pressure. With the pump so selected, the installer would then take an estimate of the system curve Si for the sand filter to calculate the flow to which the sand filter will be exposed. Typically a few sand filters will be considered to arrive at one that could be safely exposed to that flow rate. Sand filters entail a large barrel of sand through which water is upwardly driven. The sand per se should remain essentially stationary and the water should work its way around the sand. If exposed to too high a flow rate, the sand becomes agitated and in turn the filtering performance is dramatically reduced and in the longer term the sand is rounded off and damaged. Selecting a flow rate to protect the sand filter as the wording and similar wording is used herein refers to selecting a flow rate to avoid this undesirable agitation.

Following this new logic much larger sand filters than were necessary to filter the pool were selected. Sand filters are typically characterised by the diameter of their barrel. With the advent of the spa jets (and other secondary aquatic applications) not only were much larger pumps required but so were larger sand filters, e.g. often a 036" filter would be used where years before a 024" sand filter would have been used.

For a while, many pools were operated with the much larger pump operating at the design point DP and delivering large flow rates (420 L/min in this case) resulting in pumps consuming vastly more power than was required for adequate filtration. In recognition of this excessive power consumption multi-speed pumps became more common.

Multi-speed pumps included additional windings that enabled the pump to operate at higher rates of slip to deliver lower flow rates. In Figure 1 a potential low speed setting for the two-horsepower pump is illustrated as the dotted line 2 hpL. When switching from its high speed mode to its low speed mode the pump 2 hp slips from the design point DP down to an operating point OPi at which it is delivering only the necessary 270 L/min. In this context "speed" is of course a misnomer. Along the curve 2 hpL the motor would operate at shaft-speeds approaching synchronous speed (at zero flow) and falling to about 1500 rpm at the operating point OPi.

More recently, ranges of variable speed swimming pool pumps have hit the market. Early examples were triac controlled. Triac control entails a control arrangement (known as a triac) sitting between the mains supply and the electric motor. The triac simply drops outs a selected proportion of the voltage cycles whereby the voltage and frequencies supplied to the motor remains unchanged but the duty cycle of the electric drive reaching the motor is varied. This approach created a pump that was infinitely adjustable relative to the older discrete speed windings of the multi-speed motors.

Other forms of variable speed pump are known as Inverter Driven, such as Three Phase Inverter Driven, and Brushless DC. According to some variants the voltage delivered to the motor is maintained without changing the duty cycle and it is the frequency of the electrical drive that is varied to vary the performance of the pump. Following this approach a variable speed two-horsepower pump could be slowed to the operating point OPi by reducing the frequency supplied to the motor. Thus relative to a multi-speed pump, at the operating point OPi such variable speed pumps have less slip and in turn higher efficiency from their electric motors. The current pump-selection process is similar to the process in respect of multi- speed pumps:

• typically a pool installer will be presented with a set of curves similar to the curves 1 hp, 1 .5 hp and 2 hp corresponding to the performance of the pump at 2850 rpm (in Australia; 3400 rpm in the United States); · the pump would be selected based on the necessary flow rate and an estimate of the system curve S2; and

• then based on the selected pump curve, a suitable sand filter would be

selected to safely operate at the design point DP. In normal operation the pump might be slowed to the operating point OPi.

Preferred forms of the invention aim to provide a pump which is of lower cost to produce and/or to operate, or at least to provide an alternative for those concerned with swimming pool pumps. SUMMARY

The present inventors have recognised that by departing from the foregoing design principles (that are well established in their industry), significant efficiencies can be gained. More specifically, the present inventors have recognised that the design of hydrodynamic components has changed little over the years. Indeed many modern variable speed pumps incorporate hydrodynamic components substantially identical to their single speed ancestors. As such, these hydrodynamic components are optimized for operation at the design point DP and are therefore less efficient than they could be at the operating point OPi at which the pump is operated more commonly. Accordingly by modifying the hydrodynamic components to optimize their performance at the design point OPi significant efficiencies can be realised. Indeed a preferred form of the present invention would conventionally be rated as a 2.0 horsepower pump (based on the amount of active material in its motor, etc) but can be used where a 2.5, or even 3.0, horsepower pump would conventionally be specified. Further to these efficiencies in hydrodynamic performance, the present inventors have developed a range of improvements in motor control strategies which are particularly advantageous in the context of this pump but also may be

advantageously applied to other pumps.

One aspect of the invention provides a swimming pool pump to suit a first aquatic application and a second aquatic application; the second aquatic application being at least twice as restrictive as the first aquatic application; the pump including an impeller; a housing housing the impellor; an electric motor to mechanically drive the impeller; and a control arrangement to electrically drive the electric motor; the control arrangement being configured to supply a first electrical drive to drive the pump to a first operating point, at which a first- point flow rate is delivered, to suit the first aquatic application whilst the electric motor turns at a first speed, the electric motor draws a first current, and the pump operates at a first electromechanical efficiency; and a second electrical drive to drive the pump to a second operating point, at which a second-point flow rate is delivered, to suit the second aquatic application whilst the electric motor turns at a second speed, the electric motor draws a second current, and the pump operates at a second electromechanical efficiency; the second-point flow rate being within 20% of the first-point flow rate; the impeller, housing, electric motor and control arrangement being configured such that the first electromechanical efficiency is higher than the second electromechanical efficiency. Aquatic applications typically impose a parabolic system curve having the form P = Q ² where P represents pressure and Q represents flow. As the wording is used herein, an aquatic application having a system curve of P = 2Q ² is twice as restrictive as an application having the system curve P = Q ² .

The second-point flow rate is preferably within 10% of the first-point flow rate. The control arrangement may be configured to operate in accordance with a schedule more of which is occupied by operation at the first operating point than by operation at the second operating point.

Another aspect of the invention provides a swimming pool pump to suit a first aquatic application and a second aquatic application; the second aquatic application being at least twice as restrictive as the first aquatic application; the pump including an impeller; a housing housing the impellor; an electric motor to mechanically drive the impeller; and a control arrangement to electrically drive the electric motor; the impeller, housing and electric motor being electromechanically capable of receiving a design-point electrical drive to reach a design operating point for the first aquatic application whilst the electric motor turns at a design-point speed and the electric motor draws a design-point current; the control arrangement being configured to supply a second electrical drive to drive the pump to a second operating point, at which a second-point flow rate is delivered, to suit the second aquatic application whilst the electric motor turns at a second speed and the electric motor draws a second current; the second electrical drive being harder than the design-point electrical drive such that the second-point speed is at least 10% higher than the design-point speed and the second-point current is not less than 90% of the design-point current. Preferably the design-point speed is within 6% of 2850 rpm. A design-point speed within 6% of 3400 rpm may also be convenient, e.g. to suit the US market.

Preferably the impeller, housing and electric motor are electromechanically capable of operating at the design operating point more efficiently than at the second operating point. The second current may be higher than the design-point current. Preferably the second-point speed is at least 20% higher than the design-point speed.

The control arrangement preferably has a selectable-mode for the first aquatic application and another selectable-mode for the second aquatic application.

The first aquatic application may be sand filtration. The second aquatic application may be jetting. The second aquatic application may be at least five times as restrictive as the first aquatic application.

The control arrangement is preferably configured to, over at least some of the operating range of the pump, limit the electrical drive to limit a flow rate of the pump to a flow rate limit. Preferably the flow rate limit is not more than 125% of the first- point flow rate.

Another aspect of the invention provides a swimming pool pump including an impeller; a housing housing the impellor; an electric motor to mechanically drive the impeller; and a control arrangement to electrically drive the electric motor; wherein the control arrangement is configured to, over at least some of the operating range of the pump, limit the electrical drive to limit a flow rate of the pump to a flow rate limit.

The control arrangement may be configured to so limit the electrical drive based on feedback from the electric motor. The flow rate limit may be selected to protect a sand filter.

The control arrangement is preferably configured to, over at least some of an operating range of the pump, vary the electrical drive to achieve a desired parameter of the electric motor. Another aspect of the invention provides a swimming pool pump including an impeller; an electric motor to mechanically drive the impeller; and a control arrangement configured to supply an electrical drive to the electric motor; monitor the electrical-parameter of the electric motor; and over at least some of an operating range of the pump, vary the electrical drive to achieve a desired value for the electrical-parameter of the electric motor.

The desired electrical-parameter may be current draw. Preferably the desired electrical-parameter is selected to protect the electric-motor from overloading. The control arrangement is preferably configured to, over at least some of an operating range of the pump, vary the electrical drive to limit a speed of the pump to a speed limit. Preferably the speed limit is not more than 3650 rpm.

Another aspect of the invention provides a swimming pool pump including an impeller; an electric motor to mechanically drive the impeller; and a control arrangement configured to upon activation of the pump supply an electrical drive to the electric motor; monitor a parameter of the electric motor; and upon the parameter of the electric motor crossing a threshold reduce the electrical drive.

The desired parameter may be current draw.

The control arrangement is preferably configured to upon activation of the pump drive the pump to a priming speed. The priming speed is preferably at least 3200 rpm, or more preferably at least 3500 rpm.

Another aspect of the invention provides a filtration system including a pump and a sand filter.

Another aspect of the invention provides a method of moving water of a swimming pool including utilising a pump whilst the pump is fluidly connected to the pool. The method preferably includes operating the pump at the second operating point. Most preferably the method includes operating the pump at the first operating point for one or more first-point periods; and operating the pump at the second operating point for one or more second-point periods; wherein over a 24 hour period a summation of the first-point periods is greater than a summation of the second-point periods.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 charts pump and system curves for conventional swimming pool equipment;

Figure 2 charts pump and system curves in accordance with a preferred form of the invention; Figure 3 schematically illustrates a pump; Figure 4 is a side view of a conventional impeller; Figure 5 is a cross-section view corresponding to the line A-A in Figure 4; Figure 6 is a front view of an improved impeller; Figure 7 is a cross-section view corresponding to the line F-F in Figure 6; Figure 8 is a side view of a pump;

Figure 9 is a cross-section view corresponding to the line E-E in Figure 8; Figure 10 is a rear view an outer housing;

Figure 1 1 is cross-section view corresponding to the line D-D in Figure 10; Figure 12 is a rear view of a diffuser; and

Figure 13 is a cross-section view corresponding to the line C-C in Figure 12. DETAILED DESCRIPTION OF THE INVENTION

Figure 3 shows a pump 1 according to a preferred form of the invention, which pump incorporates an impeller 10, a housing 20, an electric motor 30 and a control arrangement 40.

The housing 20 houses the impeller 10 and is sometimes referred to as a volute. The electric motor 30 mechanically drives the impeller 10. The control arrangement 40 receives power from a mains supply MS and electrically drives the electric motor 30.

In this example the motor 30 is a 220V three phase induction motor and the controller 40 is an inverter configured to take Australia's single phase 240 V, 50 Hz supply and supply the motor with three phase 240 V over a wide range of frequencies. The motor 30 has a nominal input rating of 1800 watts and has power factor correction which enables sufficient performance to be achieved without drawing more than 8 amps. A 1 hp (1070 watts nominal input, PFC) version is also contemplated. The housing 20 includes an inlet 21 and an outlet 22. Rotating impeller 10 drives fluid from the inlet to the outlet. Figures 4 and 5 illustrate the impeller 10' of a conventional 2.0 horsepower pump. Figures 6 and 7 illustrate an impeller 10 of a pump in accordance with a preferred embodiment of the invention. The impeller 10 includes an inlet 10a into which water is axially drawn and a circumferential outlet 10b through which the water is radially expelled from the impeller. At the rear of the impeller 10 is a shaft receiving socket 10c for receiving the shaft of the electric motor 30. The impeller is mechanically driven by this coupling arrangement. Other coupling arrangements are possible.

The impeller has been optimised to suit operation at the point OPi rather than at the point DP or the point OP2. Principally this entails (relative to the impeller 10') reducing the diameter of the impeller whilst at the same time increasing its length. Optimising the design of an impeller to a desired operating point is well within the ordinary skill of one in the art. It entails trial and error with a variety of impellers and/or may entail computational fluid dynamics. In this example the diameter of the impeller (dimension B in Figure 6) has been reduced from 128.8 mm to 120 mm whilst the axial length of the outlet (dimension A in Figure 7) has grown from 9.8 mm to 15.5 mm. Turning to Figure 8 to 13, the housing 20 is a two-part housing incorporating an outer housing 21 and a diffuser 23. The outer housing 21 defines a filter-inlet 25, a filter basket cavity 26, a volute inlet 27 and an outlet 29. As suggested by the arrows A, B, C water flows in sequence through the inlet 25, filter basket cavity 26, inlet 27 and outlet 29. The diffuser 23 is mounted along the fluid path from the inlet 27 to the outlet 29.

Diffuser 23 includes a conical inlet 23a and an arrangement of stator blades 23b. The inlet 23a sits in register with, to receive water from, the inlet 27. The stator blades circumferentially surround the impeller 10. Figure 2 illustrates the performance of a pump in accordance with a preferred form of the invention. The curve 2.0 hp illustrates the performance of the pump in its preferred configuration. The curve 2.0 hp' illustrates the performance of the pump when its motor is supplied with a 50 Hz supply in line with conventional thinking. In this example, the operating point OPi corresponds to 1121 rpm, 150 L/min, 2.5 m, H2O and about 0.94 amp. This impeller design corresponds to a conventional design point DP of 2850 rpm, 380 L/min, 14 m, H2O and about 8 amp when driving fluid through the sand filter Si.

The system curve S2 corresponds to cleaning jets that are about 10 times as restrictive as the sand filter Si and require 20 m, H2O pressure. It will be observed from the curve 2.0 hp' that when operated conventionally, the pump cannot reach the operating point OP2 on the curve S2. Indeed the inventors' modifications to the impeller reduce performance along the curve S2. When operating at about 2850 rpm in accordance with conventional thinking, the pump 1 when delivering 150 L/min would be operating at the operating point OP2' whereat it delivers only 17 m, H2O, well short of the necessary 20 m, H2O. According to conventional thinking, this is cause to select a larger pump, however the present inventors have recognised that at the point OP2' the motor is not working as hard as it might as indicated by its reduced current draw relative to the design point DP. Accordingly the inventors propose to work the electric motor harder by increasing the frequency of the drive signal from the controller 40. In other variants of the invention the motor 30 might be driven harder by increasing the voltage supplied to it and/or by increasing the duty cycle of the drive signal. By speeding the pump beyond the conventional 2850 rpm to about 3550 rpm the desired operating point OP2 (for spa jets and/or cleaning jets, etc) can be reached. At that operating point the pump is delivery about 150 L/min at about 22 m, H2O and drawing about 7 amp.

Of course it is not essential that the flow rate at OP1 and OP2 be identical although in practice similar flow rates within about 20% of each other, or more preferably within about 10% of each other, are desirable. Relative to the conventional 50 Hz approach illustrated by the line 1.5 hp', the present arrangement can be thought of as an over-speed mode in which a small pump is used where a larger pump would conventionally be selected. This comes from the inventors recognition of the "head space" afforded by the drop off in current that would usually be observed when switching from the first aquatic application Si to the second aquatic application S2 at 2850 rpm (i.e. moving from the design point DP to the operating point OP2").

According to a preferred form of the invention the control arrangement has a respective mode for each application which mode is selectable by a user and/or by a scheduling mechanism. By way of example, the control arrangement might incorporate a scheduling system by which the pool is filtering along the curve Si for most of the day and then periodically the pump turns to operating floor jets to clean the floor of the pool and upon so turning to that application selects the over-speed mode. In addition or as an alternative to reconfiguring the hydrodynamic components (e.g. reconfiguring the impeller) other changes could be made to achieve differing electromechanical efficiencies. Some implementations of the invention may entail an unconventional motor, e.g. the motor may be wound to switch from 2 pole operation for restrictive applications to more efficient 4 pole operation for less restrictive applications.

In a preferred implementation of the over-speed mode the control arrangement maximises the drive frequency within a range limited by (a) 60 Hz corresponding to 3600 rpm; and (b) a current draw of 8 amps.

3600 rpm is selected to protect bearings of the motor. This is a convenient figure since it corresponds to the speed of conventional pumps in the US market and therefore there are many cost-effective bearings that can be used with confidence. Of course other speed limits might be applied whether to protect the bearings or for another purpose such as to prevent cavitation. Preferably a minimum drive is also imposed. In this example the minimum drive frequency is 10 Hz. In our discussion of the over-speed mode thus far we have focused on current. Of course, the disclosed principle is readily generalised to other parameters of the electric motor such as power draw.

Furthermore, the present inventors have recognised that the over-speed mode may be advantageously applied to prime the pump. The skilled person would appreciate that moving to a smaller diameter impeller reduces a pump's ability to prime and this is another reason why a pump might not be optimised for the point OPi.

Accordingly, preferred forms of the invention are configured to upon activation operate in the over-speed mode. Since pumps are typically not primed when they are first activated, this usually entails 10 seconds or so of operation at 60 Hz. In the unprimed state there is very little load on the impeller and as such the motor is likely to be very close to 3600 rpm. The present inventors have recognised that there is very little current draw at this point and that upon priming of the pump there is a rapid increase in the current draw. Accordingly preferred forms of the control arrangement 40 are configured to revert to a preset operating mode, e.g. revert to suit routine filtration, upon the current exceeding a predetermined threshold. Of course, there is likely to be some noise in the signal indicative of current and accordingly any reference to a current passing a threshold herein includes a time averaged (or otherwise smoothed) indication of the current passing a threshold. This smoothing operation might entail a counter or the like.

This method of priming detection may be implemented based as on other parameters of the motor such as input power.

The present inventors have recognised that since the introduction of spa jets and the like the design point DP has become a largely theoretical point at which the pump should spend little or no time operating. Nonetheless it is standard practice in the swimming pool industry to select a sand filter that can safely tolerate the design point flow rate and as such this results in dramatically larger sand filters being selected than is necessary to filter the pool. Accordingly, whilst it is convenient to think of the design point DP that the impeller housing and motor are electromechanically capable of reaching, the control arrangement 40 of some variants may be configured to impose a flow rate limit FL to prevent the pump reaching that point. In this example the flow limit FL is 220 L/min. By imposing such a limit a smaller sand filter can be safely employed. The control arrangement may be configured to enable a user to select the flow limit, e.g. select the flow limit to protect a filter. As such a method of protecting a filter is also disclosed.

"Electromechanically capable" and similar wording as used herein is to be understood in its context. A person of skill in the art would have no difficulty assessing the electromechanical capability of a motor, impeller and housing combination. Even if a pump's control arrangement locked out the design point, the electromechanical capability could be assessed by bypassing that motor's control arrangement and energising the electric motor using standard testing equipment routinely used by those of skill in the art.

The invention is not limited to the described examples. Rather, the invention is defined by the claims.