Pool turnover period and filtration rate

What is turnover period?

Turnover period is the planning time required to circulate a volume equal to the pool water volume through the circulation system. It does not mean every water molecule passes through the filter exactly once.

For the same pool volume, a shorter turnover period produces a higher required flow. Application, bathing load, treatment method and local rules influence the selected period.

What is filtration rate?

For a media filter, filtration rate is the flow passing through each square metre of effective filter area. It is commonly expressed in metres per hour.

A lower filtration rate requires more filter area for the same circulation flow. The correct rate depends on the pool application, media, water-quality objective and product data.

Why the pool application matters

A private pool and a public or children’s pool can have very different operating conditions. The Bilanda calculator supplies application-based starting points so a customer is not left to invent a value. They remain editable because local codes or project requirements may call for something different.

• Private pools commonly allow a longer turnover period and higher preliminary filtration rate.
• Hotel and club pools generally require a more conservative starting point.
• Public, competition and children’s pools may require shorter turnover or lower filtration rates.
• Spa pools have small volume but can require rapid turnover because of concentrated bathing load.

A worked relationship

If a 375 m³ pool uses a 6-hour turnover period, the required circulation flow is 62.5 m³/h. At a preliminary filtration rate of 25 m/h, the required effective filter area is 2.50 m².

Do not select the pump from flow alone

The calculated flow is a duty point, not a complete pump selection. Pipe length, fittings, elevation, equipment pressure loss, dirty-filter condition and the pump curve determine the required head and actual operating point.