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The Swimming Pool Pumpthat will turn the pool water around forfiltering purposes, and in the extreme avariable speed pump with digital controlcan be set to run continuously at verylow speed/power, and to only speed upoccasionally for a short period to operatethe automatic cleaner, which needs at least100 Watt to function. See results furtheron, of an experiment to determine howlong such a cleaner needs to run daily.Comparative energy use figuresNote that the key effect here is variablespeed, and not motor efficiency, whichcontributes only a minor share tominimising energy for pumping a fixedvolume of water.Also very significant is the “unintendedenergy demand result” of automatedsanitisers like salt water chlorinators, UVexposure, and oxygenator/ionisers, whichprescribe varying, but long, periods ofwater flow irrespective of the strength andconsequential energy usage of the pump.A minimal energy pump setting seems tobe the answer to this dilemma, and willenable total eco-friendly swimming poolsthat have very small carbon footprint, andchemicals-free water.A long term experiment withfiltering and automatedcleaner time periodsBecause it is difficult to find out whyprivate pool owners are advised to runtheir automatic cleaners and filters for somany hours every day, it could be helpfulto look at an 8 month history (half a winter+ half a summer) of a medium-sized pool(50 000 litres) in a city garden, where afocused effort was made to maintain it to asimilar standard as neighbourhood pools,but using 5 % of the energy, or less.Basically energy is required to sweep orsuck the bottom clean and deposit the wastematerial (dust/sand, leaves, dead algae)into a strainer or filter. It is also necessaryto circulate water through a fine filter36 | wattnow | january 2012Daily operation of filter pump, and monthly energy usage, Kwh/monthNote 1 This is the power consumption of the variable speed Badu Eco Touch on its LOWsetting. The motor efficiency is > 90%Note 2 This is the marked output power of these conventional induction motors, withefficiencies varying from < 70% to around 80%, depending on size.(most commonly sand) to catch suspendedparticles. An automatic pool cleaner wasattached during this experiment, but noother devices. Sanitising and algae controlwas done manually. The same adjustable3-speed pump was used for the experiment,and it was found that the lowest setting(300 Watt) could still drive the pool cleanerwith vigor, with a circulation of 7300 l/hourthrough the system.In summary: a 300 Watt pump is sufficient todrive a pool cleaner system for long periods,but if the pool is in a bad shape, it will needthe medium or high setting and a few backwashingsto clear it up first. The cleanermoves at a speed of 4 meter/min across thebottom, and can theoretically sweep thepool in less than 30 minutes. In practice,with some prodding not to skip some areas,one hour is sufficient. The clarity of the waterwas as good as that of neighbouring poolsthat filtered for extensive periods daily. Itwas thus demonstrated over a prolongedperiod (8 months) that it is possible tomaintain this pool, running the filter pumpfor only one hour per day, on average, andusing less than 10 kWh/month.To appreciate the significance of this, thetable below displays the range of energycost across different sizes and types of pumpmotors, run for different daily periods.The bottom line is therefore that the energycost of a domestic swimming pool can bereduced dramatically without sacrificingwater quality, and for some installationsthe price differential between mature*2and new*1 pump motor technology canbe recouped in less than a year, dependingon requirements. It has been shown thatlong hours of swimming pool filtering andautomatic cleaner operation to maintainclean internal surfaces and clear water isunnecessary and wasteful in energy usage.A low power pump motor (300 Watt) candrive a cleaner as effectively as a strongmotor (1100 Watt), and one hour's operationper day can be sufficient for a medium-sizeddomestic swimming pool (50 000 liters). Ifpool chemicals are manually administered,no extra pump time is required, and themonthly energy requirement to maintainthe swimming pool, can be as low as 10kWh. If in-line sanitising is implemented,additional energy will be consumed, becauselonger water circulation times are required,but in view of the previous analysis there ishope that this unintended energy demandcan also be drastically reduced, to the samelevel as that of the automatic cleaner.In final analysis: the stage is set for thedomestic swimming pool to become morefrugal in energy usage (< 50 Kwh/mo) thanthe family fridge, and simultaneously more