AU2014203608A1

AU2014203608A1 - Swimming pool operation

Info

Publication number: AU2014203608A1
Application number: AU2014203608A
Authority: AU
Inventors: Peter Wallace
Original assignee: Astral Pool Australia Pty Ltd
Current assignee: Fluidra Group Australia Pty Ltd
Priority date: 2013-08-30
Filing date: 2014-07-01
Publication date: 2015-03-19
Anticipated expiration: 2034-07-01
Also published as: AU2014203608B2; NZ626977A; AU2018204660A1; NZ710952A; AU2018204660B2

Abstract

A control system 11 configured to control a swimming pool pump 2 to at the end of a period during which the pump is inactive, operate for a period at a treatment output to treat the swimming pool water and in response to an output from a sensor 8 at or 5 before the start of the period during which the pump is inactive vary at least one of the treatment output and a duration of the period during which the pump is operated at the treatment output. "' / 22 20 -4 x,21411r+ 'N N f eater @2Outlet Ilt 7 FigI1 6 110 t 9 -L o g ic M o d u le -------- tt 21 ' y I User hnterface..K 14 Fig 2 TimerA Cloockut i~OIOr 32 Chloride& Oupu SCdetyh ~Standby/Off1 / bpa~ 28/ Fig 3 30

Description

P1148AUAU 1 SWIMMING POOL OPERATION FIELD OF THE INVENTION The invention relates to the operation of swimming pools, and in particular to the treatment of the swimming pool water. 5 "Swimming pools" as used herein is used interchangeably with "pools" to refer to swimming pools, spas, Japanese hot tubs and like water containing structures for bathing. BACKGROUND TO THE INVENTION Existing swimming pools are equipped with a pump arranged to draw water from the 10 swimming pool and to drive that water through a filter and in turn through an electrolytic chlorinator before the water is returned to the pool. This arrangement of parts constitutes a water treatment system. The filter provides mechanical filtration separating leaves and debris from the water. The electrolytic chlorinator includes spaced electrodes between which the water is moved. The electrodes are energised to act on the water to generate 15 sanitiser. The sanitiser destroys undesirable biological species. When destroying the undesirable biological species the sanitiser is itself destroyed. Sunlight and other factors also destroy sanitiser. Thus in the operation of a swimming pool there is an ongoing balance between sanitiser production and the introduction of undesirable species. The oxidation reduction potential (ORP) of the pool water provides 20 an indication of this balance. Generally speaking a higher ORP corresponds to more sanitiser and less undesirable biological species. Most existing swimming pools incorporate a single speed pump set to run a selected number of hours per day. From time to time a pool attendant may check an ORP sensor (and/or other measures of the condition of the pool water) and adjust the length of the 25 daily operating period as required.

P1148AUAU 2 The present inventor has recognised that the need for sanitiser production is highly variable and that operating a swimming pool pump at certain times can be problematic, for example operating a swimming pool pump late at night can upset the neighbours. The present invention aims to provide improvements in and for the treatment of 5 swimming pool water, or at least to provide alternatives for those concerned with the treatment of swimming pool water. SUMMARY OF THE INVENTION One aspect of the present invention provides a control system configured to control a swimming pool pump to, at the end of a period during which the pump is 10 inactive, operate for a period at a treatment output to treat the swimming pool water; and in response to a sensor output vary at least one of the treatment output and a duration of the period during which the pump is operated at the treatment output; wherein the sensor output is from a sensor, e.g. an ORP sensor, prior to a start of the period during which the pump is operated at the treatment output. 15 The sensor output is preferably from a sensor at or before the start of the period during which the pump is inactive. Preferably, the system is configured to in response to the sensor output vary the treatment output. The system may be configured to operate the pump in accordance with a repeating schedule, in which case at least a portion of the period during which the pump is inactive 20 may be a lockout period defined in the repeating schedule. Preferably the period, during which the pump is operated to deliver the treatment output, has a fixed duration; alternatively it may end in response to the sensor. A preferred form of the system is configured to after the period in which the pump is operated at the treatment output 25 reduce the output of the pump to a reduced output having a non-zero time averaged value, and P1148AUAU 3 in response to the sensor increase the output of the pump. Optionally the system may be configured to, after so increasing the output of the pump, in response to the sensor reduce the output of the pump. The reduced output is preferably substantially continuous, and is most preferably substantially constant. 5 The system may be configured to control an electrolytic chlorinator such that the chlorinator's electrodes are not energised whilst the pump is operating at its reduced output. Another aspect of the invention provides a control unit including a housing containing the control system, 10 a power inlet for connecting the system to, to receive power from, an electrical power supply; a power outlet for connecting the system to, to supply power to, electrodes of an or the electrolytic chlorinator to energise the electrodes; a data inlet for connecting the system to, to receive an output from, the sensor; and 15 a data outlet for connecting the system to, to send control signals to, the pump. Another aspect of the invention provides a swimming pool installation including at least one of the control systems and the control unit; a body of water in which a person may bathe, a defined flow path along which water flows 20 from an inlet for receiving the water from the body of water to an outlet for returning the water to the body of water; the pump; and the sensor; wherein P1148AUAU 4 the pump is arranged to drive water along the flow path; the sensor is along the flow path to sense at least one characteristic of the water flowing along the flow path; and the at least one of the system and the control unit is arranged to control the pump. 5 Another aspect of the invention provides a swimming pool installation including a body of water in which a person may bathe, a defined flow path along which water flows from an inlet for receiving the water from the body of water to an outlet for returning the water to the body of water; 10 a pump arranged to drive the water along the flow path; a sensor along the flow path to sense at least one characteristic of the water flowing along the flow path; and a control system configured to operate the pump at an output having a non-zero time averaged value; and 15 in response to the sensor increase the output of the pump. The installation may include an electrolytic chlorinator along the flow path to treat the water flowing along the flow path. Preferably the system is configured to de-energise electrodes of the electrolytic chlorinator such that the electrodes are 20 not energised whilst the pump is operated at the output having a non-zero time averaged value; and energise the electrodes when so increasing the output of the pump in response to the sensor.

P1148AUAU 5 The output having a non-zero time averaged value is preferably low enough that gases would accumulate if the electrodes were energised whilst the pump is operated at this output. The installation may include 5 a control unit for controlling the electrolytic cell; the control unit including a housing containing the system, a power inlet for connecting the system to, to receive power from, an electrical power supply; 10 a power outlet for connecting the system to, to supply power to, electrodes of the cell; a data inlet for connecting the system to, to receive an output from, the sensor; and a data outlet for connecting the system to, to send control signals to, the pump. The control system is preferably configured to operate the pump for a period at a 15 treatment output to treat the swimming pool water then reduce the output of the pump to so operate the pump at an output having a non-zero time averaged value. The control system may be configured to, after so increasing the output of the pump, in response to the sensor reduce the output of the pump. Another aspect of the invention provides a control system configured to 20 control a swimming pool pump to operate the pump at an output having a non-zero time averaged value; de-energise electrodes of an electrolytic chlorinator though which the pumped water flows such that the electrodes are not energised whilst the pump is operated at the output having a non-zero time averaged value; and 25 in response to a sensor P1148AUAU 6 increase the output of the pump, and energise the electrodes; wherein the output having a non-zero time averaged value is low enough that gases would accumulate if the electrodes were energised whilst the pump is operated at this 5 output. A water treatment system including the control system, the pump and the electrolytic chorinator is also provided. Another aspect of the invention provides a method of treating water of a swimming pool; the swimming pool including a pump arranged to drive the water; 10 the method including at the end of a period during which the pump is inactive, operating the pump for a period at a treatment output to treat the water; and in response to a sensor output varying at least one of the treatment output and a duration of the period during which the pump is operated at the treatment output; 15 wherein the sensor output is from a sensor prior to a start of the period during which the pump is operated at the treatment output. Another aspect of the invention provides a method of treating water of a swimming pool; the swimming pool including a pump for pumping water; and 20 an electrolytic chlorinator through which the pumped water flows; the method including operating the pump at an output having a non-zero time averaged value whilst the electrodes of the electrolytic chlorinator are not energised; and in response to a sensor P1148AUAU 7 increasing the output of the pump, and energising the electrodes; wherein the output having a non-zero time averaged value is low enough that gases would accumulate if the electrodes were energised whilst the pump is operated at this 5 output. The method preferably includes, after so increasing and energising, in response to the sensor reducing the output of the pump; and de-energising the electrodes. 10 BRIEF DESCRIPTION OF THE DRAWINGS Various exemplary features are illustrated. Figure 1 is a schematic diagram of a pool filtration system with an electrolytic chlorinator control system according to an embodiment of the invention; Figure 2 is a schematic, block diagram illustrating the electrolytic chlorinator control 15 system used in the pool filtration system shown in Figure 1; and Figure 3 is a front view of a user interface on the electrolytic control system shown in Figure 2. DESCRIPTION OF AN EMBODIMENT The following examples are intended to illustrate the scope of the invention and to 20 enable reproduction and comparison. They are not intended to limit the scope of the disclosure in any way. Figure 1 illustrates a swimming pool filtration system 1. The system 1 includes a pump 2, a filter 3, a heater 4, and an electrolytic cell 5. Plumbing interconnects the pump, filter, heater, and cell and connects these elements with a swimming pool to define a fluid 25 circuit. The pump 2 drives water about the fluid circuit. Water is drawn from the pool via P1148AUAU 8 an inlet in the form of a skimmer box 6 and then driven in series through the filter 3, heater 4, and cell 5 before being returned to the pool via an outlet 7. An ORP sensor 8 may be mounted at any convenient location along the flow path from the inlet 6 to the outlet 7. In this example of the system the sensor 8 is mounted between the filter 3 and 5 the heater 4. The system 1 further includes a control unit 10 for controlling the pump 2 and the cell 5 in a coordinated manner. As illustrated in Figure 2, the control unit 10 includes a "control system" or "logic arrangement" in the form of module 11 within housing 12 containing suitable electronics (not illustrated explicitly). The control unit further includes an 10 incoming electrical connection (or "power inlet") in the form of a supply lead 14 for drawing power from an electrical supply (not shown). Preferably the supply lead 14 terminates in a simple plug cooperable with a conventional socket to draw power from a mains supply. In Australia such plugs typically include three pins (a positive, a negative and an earth).The lead 14 is adapted to receive and provide electrical power to the logic 15 module 11. Alternatively, the incoming electrical connection component could be a socket with electrical pins/prongs adapted to receive the female end of an extension cord. The control unit 10 further includes a second, output electrical connection (or "power outlet") in the form of a socket 18 adapted to connect the electronics of the control unit 20 10 to the cell 5 so as to provide energising electrical power to the electrodes of the cell 5. For example, a lead 16 could terminate in a plug cooperable with the socket 18 to connect the control unit 10 and the cell 5. The control unit 10 also includes a data outlet 22 in the form of a socket adapted to send control signals to the pump 2. A lead 20 could terminate in a plug cooperable with the 25 socket 22 to connect the control unit 10 and the pump 2. The control signal may take a variety of forms. Preferably a transformer (not shown) is interposed along the lead 20 and connected to the mains supply to supply a voltage of 24 volts to the lead 20, and the electronics of the module 10 receive this voltage and generate a signal by varying a milliamp current along the lead 20. Alternatively the P1148AUAU 9 electronics of the control unit 10 may supply a voltage to the lead 20. Indeed, power sufficient to power the pump 2 and data may be simultaneously transmitted along the line 20 in the manner of power line communication (PLC). The use of PLC could allow a conventional power socket to be both a power outlet and a data outlet. In a simple 5 implementation of the invention, the lead 20 and the socket 22 may define multiple conduction paths corresponding to separate speed windings within the pump motor, in which case the control signal would be the selective energisation of the conduction paths. In a preferred form of the invention the control unit 10 powers the pump 2 via a separate 10 power lead 21. A data inlet in the form of lead 23 connects the module 11 to the sensor 8. The control unit 10 includes logic module 11 for controlling the efficient operation of the pump 2 and of the cell 5, which logic module 11 could be implemented via hardware, software, or a combination of hardware and software. In the illustrated arrangement, the 15 logic module 11 includes a timing arrangement to operate the pump and the cell in accordance with a timetable 11 a. The control unit operates the pump and the cell in response to the sensor 8 (indicative of sanitiser concentration in the pool water) and optionally in response to other sensors such as sensor 15 located within the cell 5 (e.g., right by the cell's positive and negative electrodes, as schematically illustrated) to 20 provide an indication of sanitiser production levels in the cell 5. Preferably the timetable is structured for an operating period in the vicinity of four hours each morning and each evening to treat the pool water before and after the sun is out. Sunlight tends to destroy pool sanitiser. Treating the water outside of daylight hours is more efficient because the sanitiser lasts longer to destroy more undesirable biological species. 25 The described pump 2 incorporates an infinitely variable motor and a variable frequency drive (VFD). Optionally the VFD may be configured to deliver a plurality of discrete selectable outputs. Control signals from the control unit 10 tell the pump 2 at which output it should operate. The selectable outputs may include a low "detection" output merely sufficient for maintaining the accuracy of the sensor output, one or more outputs P1148AUAU 10 for effective filtration and chlorination, and one or more higher outputs for other operations such as operating a vacuum cleaning apparatus or more rapidly filtering and cleaning a cloudy pool. The control unit 10 preferably includes a user interface 24, illustrated in Figure 3, for 5 displaying information to and receiving input from a user. The interface 24 suitably includes: * a programming area 26 for setting the operating timetable; * a chlorine output control 28 which indicates the amount of chlorine being produced; 10 0 a user mode area 30 for controlling the pump and chlorinator, e.g. by selecting pre-set modes, e.g. a respective mode for pool and spa operation; * a warning display 32 for warning a user if there is no flow or if there is insufficient salt in the pool. Via the interface 24, a user can set the on-time for the cell 5 and the speed at which the 15 pump is to operate while the cell is on (e.g. high, medium, or low) and then select the time at which the chlorinator and pump should turn off. The described variant of the invention allows for up to four operating periods per day to be scheduled in the timetable. The operating periods may have different durations and pump operating speeds. The control unit 10 is desirably mounted remotely from the pool to permit 20 convenient access to its user interface 24, although it is also contemplated that the logic module might be integrated with one of the pump 2 and the cell 5. Preferably the logic module is configured to deliver a low pump output for most of the day and to periodically throughout the day increase the output of the pump. Operating at a low output is energy efficient but carries the risk of voids of uncirculated, or poorly 25 circulated, water in the pool. Periodically operating the pump at higher output desirably moves the water in these voids.

P1148AUAU 11 It is desirable that the control unit be configured to de-energise the electrodes prior, say about five minutes prior, to deactivating the pump. This reduces the risk of sanitiser, such as chlorine, concentrations sitting in components of the pool water treatment system and in turn reduces the risk of accelerated corrosion of these components. In 5 particular, gas heaters are susceptible to corrosion caused by accumulated sanitiser. In a preferred configuration the module 11 is pre-programmed with a schedule that repeats on a daily basis, although it is also contemplated that the schedule might repeat on a weekly basis to deliver differing performance on Saturday and Sunday relative to the other days of the week. According to the preferred daily repeating schedule, there is 10 an overnight lock out window, e.g. from 10:00pm to 8:00am, in which the pump is turned off so that neighbours are not annoyed by the sound of the pump during these hours. At 8:00am the pump is routinely activated at a default treatment level equivalent to about 300 litres/minute. The output of the pump can be characterised in various possible ways. In a simple 15 implementation the output of the pump is determined by its rotational speed, for example the pump may be operated at a constant rotational speed known to be equivalent to about 300 litres/minute for a given system curve (although the system curve varies depending on the condition of the filter etc.). Alternatively, the pump may be controlled to deliver a constant flow rate or to consume a constant power, by way of example. 20 Desirably this initial period of operation may have a fixed duration selected to adequately treat the pool water on a typical day. Typically there are two key measures of treatment: 1. a sufficient number of turns of the water to provide adequate mechanical filtration to remove unsightly organic material; and 25 2. sufficient operation of the chlorinator to produce a quantity of sanitiser sufficient to address a typical input of undesirable biological species. By way of example an operating period of four hours (at 300 litres/minute) may be desirable in a 50,000 litre pool. This period of operation corresponds to about 1.5 turns.

P1148AUAU 12 One turn per day is considered a minimum rate for effective filtration. In contrast to merely controlling the pump in response to an ORP sensor to achieve 2, by controlling the pump to operate for a treatment period, the treatment period can advantageously be set to ensure that 1 is achieved. Optionally the module 11 may be programmed, or 5 otherwise configured, to ensure that a predetermined volume of water is pumped during the treatment period. At the end of this initial treatment period the output of the pump is reduced to a much lower level, e.g. about 50 litres/minute or less and the chlorinator deactivated. At this flow rate the pump is operating very quietly and consuming very little power. Shaft power 10 consumption varies in proportion to the cube of the flow rate. This flow rate is not considered sufficient to provide effective mechanical filtration (or to prevent the accumulation of gases within the chlorinator if the chlorinator was active). This is not its purpose. Rather the continuous flow of water from the inlet 6 to the outlet 7 serves to maintain the accuracy of the sensor 8. Without this flow the sensor would provide a false 15 reading, which reading would correspond to the ORP of the water within the flow path which may materially differ from the water in the pool as the ORP of the water in the pool drops throughout the day. The sensing arrangement is also considered superior to simply mounting an ORP sensor within the body of the pool. An ORP sensor within the body of the pool may well 20 similarly provide a false reading by being exposed to a "dead patch" of essentially static water which may have a materially different ORP to the bulk of the water within the pool. By operating the pump at a reduced output to move water over the ORP sensor a better ongoing indication of the ORP of the bulk of the pool water is obtained. Likewise, operating the pump at the treatment output for a morning treatment period 25 serves to better stir the pool relative to merely operating in response to an ORP sensor. This better stirring eliminates (or at least reduces) dead spots and stratification in the pool water, resulting in better mechanical filtration and more homogenous pool water. Improving the homogeneity of the pool water leads to a better indication, from the ORP sensor, of the ORP of the bulk of the pool water.

P1148AUAU 13 In the described exemplary systems the reduced pump output is substantially constant (e.g. constant RPM, flow rate or power consumption), although it is also contemplated that the reduced output may be achieved by periodically operating the pump. For example, the reduced output of described method could be achieved using a single 5 speed pump by operating that pump at a reduced duty cycle (e.g. operating for one minute out of every 10 minutes). Providing a more accurate ongoing indication of ORP allows for a more timely and appropriate reaction to changes in the ORP. By way of example if at some point during the day a pool is occupied by a large number of urinating infants and their pets the ORP 10 will drop dramatically. According to existing approaches in which the pump is operated at a fixed rate and for a fixed period each day it may take a few days for the treatment system to restore the ORP to a satisfactory level. During this time the pool may be less healthy than is desirable. According to preferred implementations of the described method, the ongoing flow of 15 water over the ORP sensor allows for that sensor to detect such as increase in the introduction of biological species and to activate the treatment system accordingly. The treatment system is activated by increasing the output of the pump, e.g. to the same output as in the morning treatment period, and by energising the electrodes of the electrolytic chlorinator. 20 During the latter portions of the day after the treatment system has been so activated, it is preferred that the treatment system be configured to be stood down, for example returning to the same reduced output that would customarily follow the treatment period, in response to the ORP sensor reading an ORP above a predetermined threshold set to correspond with a satisfactory concentration of sanitiser. 25 Pools are often heavily used in the evening when their owners' families return from work and school. The additional biological loading on the pool at this time presents an additional challenge in that despite this loading being detected and the treatment system activated manually by a diligent pool attendant or activated in accordance with the P1148AUAU 14 above method, the treatment system may not be able to adequately address this additional biological loading by the 10:00pm lockout. To address this challenge, preferred implementations of the described system vary the output of the pump during the 8:00am morning treatment period in response to the 5 sensed ORP level at 10:00pm the night before. In a simple implementation of this concept, if the ORP at 10:00pm is below a selected threshold that fact may be stored as a simple one bit ("true or false") value, then at 8:00am the next morning the pump operated at a higher output in response to that fact. Alternatively the value of the ORP sensor may be stored and the increased pump output determined as a function of that 10 value. Instead of or in addition to vary pump output during the morning treatment session, the duration of the morning treatment session may be varied. Whilst systems incorporating ORP sensors have been described, other types of sensors are possible. By way of example sensors may be arranged to read pH and/or chlorine 15 levels. It will be appreciated that various modifications to and departures from the exemplary disclosed embodiments will occur to those having skill in the art. What is deemed to be protected is set forth in the following claims.

Claims

1. A control system configured to control a swimming pool pump to, at the end of a period during which the pump is inactive, operate for a period at a treatment output to treat the swimming pool water; and 5 in response to a sensor output vary at least one of the treatment output and a duration of the period during which the pump is operated at the treatment output; wherein the sensor output is from a sensor prior to a start of the period during which the pump is operated at the treatment output.

2. The system of claim 1 wherein the sensor output is from a sensor at or before the 10 start of the period during which the pump is inactive.

3. The system of claim 2 configured to in response to the sensor output vary the treatment output.

4. The system of claim 1, 2 or 3 being configured to operate the pump in accordance with a repeating schedule, at least a portion of the period during which the pump is 15 inactive being a lockout period defined in the repeating schedule.

5. The system of any one of claims 1, 2, 3 or 4 wherein the period, during which the pump is operated to deliver the treatment output, has a fixed duration.

6. The system of claim 1 to 5 wherein the period, during which the pump is operated to deliver the treatment output, ends in response to the sensor. 20

7. A system of any one of claims 1 to 6 being configured to after the period in which the pump is operated at the treatment output reduce the output of the pump to a reduced output having a non-zero time averaged value, and in response to the sensor increase the output of the pump. P1148AUAU 16

8. The system of claim 7 configured to, after so increasing the output of the pump, in response to the sensor reduce the output of the pump.

9. The system of claim 7 or 8 wherein the reduced output is substantially continuous.

10. The system of claim 7 or 8 wherein the reduced output is substantially constant. 5

11. The system of any one of claims 7 to 10 configured to control an electrolytic chlorinator such that the chlorinator's electrodes are not energised whilst the pump is operating at its reduced output.

12. The system of any one of claims 1 to 11 wherein the sensor is an ORP sensor.

13. A control unit including 10 a housing containing the system of any one of claims 1 to 12, a power inlet for connecting the system to, to receive power from, an electrical power supply; a power outlet for connecting the system to, to supply power to, electrodes of an or the electrolytic chlorinator to energise the electrodes; 15 a data inlet for connecting the system to, to receive an output from, the sensor; and a data outlet for connecting the system to, to send control signals to, the pump.

14. A swimming pool installation including at least one of the system of any one of claims 1 to 12 and the control unit of claim 13; a body of water in which a person may bathe, 20 a defined flow path along which water flows from an inlet for receiving the water from the body of water to an outlet for returning the water to the body of water; the pump; and P1148AUAU 17 the sensor; wherein the pump is arranged to drive water along the flow path; the sensor is along the flow path to sense at least one characteristic of the water 5 flowing along the flow path; and the at least one of the system and the control unit is arranged to control the pump.

15. A swimming pool installation including a body of water in which a person may bathe, a defined flow path along which water flows 10 from an inlet for receiving the water from the body of water to an outlet for returning the water to the body of water; a pump arranged to drive the water along the flow path; a sensor along the flow path to sense at least one characteristic of the water flowing along the flow path; and 15 a control system configured to operate the pump at an output having a non-zero time averaged value; and in response to the sensor increase the output of the pump.

16. The installation of claim 15 including an electrolytic chlorinator along the flow path to treat the water flowing along the flow path. 20

17. The installation of claim 16 wherein the system is configured to de-energise electrodes of the electrolytic chlorinator such that the electrodes are not energised whilst the pump is operated at the output having a non-zero time averaged value; and P1148AUAU 18 energise the electrodes when so increasing the output of the pump in response to the sensor.

18. The installation of claim 17 wherein the output having a non-zero time averaged value is low enough that gases would accumulate if the electrodes were energised 5 whilst the pump is operated at this output.

19. The installation of claim 16, 17 or 18 including a control unit for controlling the electrolytic cell; the control unit including a housing containing the system, 10 a power inlet for connecting the system to, to receive power from, an electrical power supply; a power outlet for connecting the system to, to supply power to, electrodes of the cell; a data inlet for connecting the system to, to receive an output from, the sensor; and 15 a data outlet for connecting the system to, to send control signals to, the pump.

20. The installation of any one of claims 15 to 19 wherein the control system is configured to operate the pump for a period at a treatment output to treat the swimming pool water then reduce the output of the pump to so operate the pump at an output having a non-zero time averaged value. 20

21. The installation of any one of claims 15 to 20 wherein the control system is configured to, after so increasing the output of the pump, in response to the sensor reduce the output of the pump.

22. The installation of any one of claims 15 to 21 wherein the output having a non-zero time averaged value is substantially continuous. P1148AUAU 19

23. The installation of any one of claims 15 to 21 wherein the output having a non-zero time averaged value is substantially constant.

24. The installation of any one of claims 15 to 21 wherein the sensor is an ORP sensor. 5

25. A control system configured to control a swimming pool pump to operate the pump at an output having a non-zero time averaged value; de-energise electrodes of an electrolytic chlorinator though which the pumped water flows such that the electrodes are not energised whilst the pump is operated at the 10 output having a non-zero time averaged value; and in response to a sensor increase the output of the pump, and energise the electrodes; wherein the output having a non-zero time averaged value is low enough that gases 15 would accumulate if the electrodes were energised whilst the pump is operated at this output.

26. The system of claim 25 wherein the control system is configured to operate the pump for a period at a treatment output to treat the swimming pool water then reduce the output of the pump to so operate the pump at the output having a non-zero time 20 averaged value.

27. The system of claim 25 or 26 wherein the control system is configured to, after so increasing the output of the pump, in response to the sensor reduce the output of the pump.

28. The system claim 25, 26 or 27 wherein the output having a non-zero time averaged 25 value is substantially continuous. P1148AUAU 20

29. The system of any one of claims 25 to 28 wherein the output having a non-zero time averaged value is substantially constant.

30. The system of any one of claims 25 to 29 wherein the sensor is an ORP sensor.

31. A control unit for controlling an electrolytic cell; 5 the control unit including a housing containing the system of any one of claims 25 to 30; a power inlet for connecting the system to, to receive power from, an electrical power supply; a power outlet for connecting the system to, to supply power to, electrodes of the 10 cell; a data inlet for connecting the system to, to receive an output from, the sensor; and a data outlet for connecting the system to, to send control signals to, the pump.

32. A water treatment system including at least one of the system of any one of claims 25 to 30 and the control unit of claim 31; 15 the pump; and the electrolytic chlorinator.

33. A method of treating water of a swimming pool; the swimming pool including a pump arranged to drive the water; the method including 20 at the end of a period during which the pump is inactive, operating the pump for a period at a treatment output to treat the water; and in response to a sensor output varying at least one of the treatment output and a duration of the period during which the pump is operated at the treatment output; P1148AUAU 21 wherein the sensor output is from a sensor prior to a start of the period during which the pump is operated at the treatment output.

34. The method of claim 33 wherein the sensor output is from a sensor at or before the start of the period during which the pump is inactive. 5

35. The method of claim 33 or 34 wherein the varying is varying the treatment output.

36. The method of claim 33, 34 or 35 including operating the pump in accordance with a repeating schedule, at least a portion of the period during which the pump is inactive being a lockout period defined in the repeating schedule.

37. The method of any one of claims 33 to 36 wherein the period, during which the 10 pump is operated to deliver the treatment output, has a fixed duration.

38. The method of any one of claims 33 to 36 wherein the period, during which the pump is operated to deliver the treatment output, ends in response to the sensor.

39. The method of any one of claims 33 to 38 wherein the sensor is an ORP sensor.

40. A method of any one of claims 33 to 39 including 15 after the period in which the pump is operated at the treatment output reducing the output of the pump to a reduced output having a non-zero time averaged value, and in response to the sensor increasing the output of the pump.

41. The method of claim 40 further including after so increasing the output of the 20 pump, in response to the sensor reducing the output of the pump.

42. The method of claim 40 or 41 wherein the reduced output is substantially continuous.

43. The method of claim 40 or 41 wherein the reduced output is substantially constant.

44. A method of treating water of a swimming pool, 25 the swimming pool including P1148AUAU 22 a pump for pumping water; and an electrolytic chlorinator through which the pumped water flows; the method including operating the pump at an output having a non-zero time averaged value whilst the 5 electrodes of the electrolytic chlorinator are not energised; and in response to a sensor increasing the output of the pump, and energising the electrodes; wherein the output having a non-zero time averaged value is low enough that gases 10 would accumulate if the electrodes were energised whilst the pump is operated at this output.

45. The method of claim 44 including operating the pump for a period at a treatment output to treat the swimming pool water then reducing the output of the pump to so operate the pump at the output having a non-zero time averaged value. 15

46. The method of claim 44 or 45 further including, after so increasing and energising, in response to the sensor reducing the output of the pump; and de-energising the electrodes.

47. The method of any one of claims 44 to 46 wherein the output having a non-zero 20 time averaged value is substantially continuous.

48. The method of any one of claims 44 to 46 wherein the output having a non-zero time averaged value is substantially constant.

49. The method of any one of claims 44 to 48 wherein the sensor is an ORP sensor.