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Efficient swimming pool filtration

02/02/2015

Water filtration is, along with the chemical treatment, the most important part of the swimming pools maintenance in order to always have crystal clean water. The filtration process combines two primary elements: the filter and the recirculation pump.

Pool water is sucked up by the pump, taken out from the swimming pool through the skimmer and later on, going through the same pump and the other hydraulic parts enters the filter. The filter is in charge of retaining the water impurities, which get stuck in the filter, and then the clean water goes back to the swimming pool. The filtration process duration depends on the area of the filter, the power of the pump and the quantity and quality of the water that is going to be filtered. Taking all these factors in to consideration when it comes to private swimming pools, professionals normally recommend to recirculate the water between two and four times every day in order to have completely purified swimming pool water.

Besides the filtration process, the pump also needs to have the proper speed in order to do the cleaning and backwashing, a process which is done periodically depending on the dirtiness of the filter. This cleaning process has to go on between three and ten minutes to do a suitable maintenance of the filter. A clean filter is more efficient than a filter that is overfilled with particles. The most used filters are made of graded sand but there are also other materials such as small crystals, cartridge filters, etc. There is no difference between the quality of the filtration depending on the material inside the filter.

European Union countries must comply with the requirement to reduce the energy consumption by 20% in 2020. Due to the fact that households are responsible for the 30% of the energy consumption in Spain, the technological options which have energy savings are always very welcomed. The Physics Department of the University of Girona together with ESPA pumps has conducted a study about filtration efficiency and it has found out very compelling results about the filtration efficiency and energy savings.

The lab experiments done by the Physics Department were conducted under very controlled circumstances following the norm and protocols used in the industry with standard particles called “Arizona dust” according to the ISO 12103-1 for the study so it can be calculated  the filtration efficiency in comparable and repeatable conditions.

The swimming pool water cleaning capacity has been analyzed at several filtration frequencies from 20 to 60 Hz according to the different filtration speeds between 16 and 50 m3/h/m2. In this study it has been introduced a concentration known as ‘Arizona particles’ in the swimming pool water in order to emulate dirty particles and it has been observed how this concentration was reduced with time as filtration went on.

The analyses have been performed with a laser system that measured the particles that were suspended in the water. The results show that in all of the scenarios there is a reduction of the particle concentration suspended in the water as the filtration goes on.

However, the filtration at a low frequency rate cleans the water more effectively, achieving lower levels of particle concentration suspended in the water for a lower number of recirculations compared to the one that is obtained in higher speed filtrations (and frequency).

The cleaning level of the swimming pool water at a filtration frequency of 20 Hz is equivalent to the cleaning level achieved in three recirculation programs at a frequency of 50 Hz, which is the speed and frequency that is normally used in the filtration process. Therefore the conventional filtration at 50 Hz achieves a lower level of cleaning of the swimming pool water.

These three recirculations obtained in the study for the conventional filtration frequency coincide with the recirculations established by the standard procedures in order to obtain pure water. However, it has been proven that a filtrating at a lower speed is more efficient due to the fact that the capacity of retaining more efficiently the water particles of the swimming pool is higher and as a result the water is even cleaner.

With this system, the results not only show an improvement in efficiency regarding the quality of the water, but they also provide significant savings in the energy used in the process. In this study, conducted by the Physics Department of the Unviersity of Girona, it has also been measured the energy consumption for the water recirculation.

In the graphic “Gasto Energético” it is shown the energy consumption depending on the speed filtration for a single speed pump and as the results show when the filtration is at a lower speed, the energy savings are quite significant, reaching up to a 70% saving for the lowest speed taken into consideration which is 20 Hz.

All in all, the best filtration system would be the one that would allow working at a low frequency, supplying a cleaner water in a short period of time resulting in a significant energy saving. Nevertheless, the filtration system would have to be able to do the backwash periodically to ensure the filtration is done properly. This last process requires a high speed in order to achieve a complete washing of the filtration element and ensure the cleaning of the filter. The results of the study conclude that an initial investment in a pumping system and filtration that can filter at a low speed but at the same time can clean the filter at a high speed, provide a cleaning guarantee in the short term and significant energy savings that would be quickly recovered. 

Article published in the maganize Actualidad Piscinas n.165 in December 2014.

Dres. Teresa Serra and Jordi Colomer

Physics Department - Universitat de Girona

 
 

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