How to design a salt chlorination system for a public pool

Designing the salt chlorination system for a public pool isn’t simply a matter of knowing how many cubic meters of water the pool holds and choosing equipment to cover that volume.

In a collectively used installation, many more factors come into play: number of bathers, operating hours, filtration time, water temperature, sun exposure, installation characteristics, intensity of use, and the treatment control system.

That’s why two pools with the same volume can need completely different chlorine production equipment.

In a private pool, volume can serve as a first approximation. In a public pool, on the other hand, sizing must be based on the installation’s actual operating conditions. Innowater’s own technical documentation recommends considering, in addition to volume, parameters such as the number of daily bathers and filtration hours.

Before talking about models or production capacities, it’s worth gathering all the available information about the installation.

At a minimum, the project should take into account:

• Actual water volume.
• Filtration flow rate.
• Filtration operating hours.
• Approximate number of daily bathers.
• Usual water temperature.
• Outdoor or indoor pool.
• Intensity of use.
• Time of year the installation operates.
• Characteristics of the hydraulic system.
• Space available for installing the equipment.
• Need to automate pH and ORP control.
• Possibility of integrating the system with a monitoring or management platform.

This information makes it possible to move from a selection based solely on cubic meters to sizing adapted to the actual situation.

Water volume matters, but it’s not enough

Volume is the starting point because it determines the amount of water that needs to be treated. However, it doesn’t on its own indicate how much disinfectant a pool needs.

An outdoor pool of 500 m³ with high bather traffic can have very different requirements from another 500 m³ pool used moderately.

The scenario also changes considerably depending on whether the installation runs 12 hours a day or the filtration works 24 hours a day.

The chlorine production system itself is constrained by the hours available to produce it. If the operating time is short, a higher production capacity will be needed to generate the required amount of chlorine in that period.

That’s why the calculation must take volume, use, and operating time into account together.

The number of bathers completely changes the sizing

In a public pool, this is one of the factors that most sets the calculation apart from that of a residential pool.

Each bather introduces organic matter into the water. Sweat, cosmetics, and other contaminants increase disinfectant demand and force the treatment system to respond to load variations that can be significant throughout the day.

A municipal pool with hundreds of daily users doesn’t need the same production capacity as a pool at a small tourist accommodation.

What’s more, occupancy is usually not constant. There can be a significant difference between a weekday and a weekend, or between normal operation and a period of peak occupancy.

That’s why, when designing the system, it’s best to work with the most demanding conditions of use that are likely to occur regularly, not just with the average situation.

Filtration hours matter too

Chlorine production is linked to the operation of the electrolytic cell and, therefore, to the circulation of water through the system.

An installation with many operating hours can spread production throughout the day. In a pool where the filtration system runs for less time, the production capacity needed during those hours will be higher.

This is one of the reasons why it doesn’t make sense to select a chlorinator based solely on a fixed ratio between cubic meters of water and grams of chlorine per hour.

Innowater’s recommendation documentation for public pools specifically distinguishes between configurations based on filtration hours, in addition to taking into account volume and the number of daily bathers.

The pool’s location is also an important aspect to consider.

• In an outdoor installation, sunlight affects how the disinfectant behaves, and environmental conditions are far more variable. Temperature, UV radiation, rain, wind, and pollution can all change treatment requirements.
• In an indoor pool, conditions tend to be more stable, although high water temperature and intensive use can also create considerable demand.

That’s why applying the same sizing criteria directly to both an outdoor and an indoor pool can lead to an incorrect selection.

Water temperature is another decisive factor

As water temperature rises, treatment requirements can increase as well.

In heated installations, spas, indoor pools, or certain intensively used pools, this aspect becomes even more important. Temperature must be analyzed together with the other variables. It doesn’t make sense to consider volume alone and then apply a separate correction for temperature.

The goal is to know as much as possible about the actual conditions the system will have to operate under during periods of highest demand.

How many grams of chlorine per hour does a public pool need?

This is probably the question that interests professionals most when they start sizing an installation. The answer can’t be a fixed number.

The chlorinator’s capacity must be set based on the pool’s specific characteristics and how it operates. In fact, Innowater has a specific table for public pools that relates volume, number of bathers, and filtration hours to guide equipment selection.

Not only that, we also offer an exclusive online calculator that lets you assess the best option for your pool.

In larger installations, the required capacity can reach several hundred grams of Cl₂ per hour.

The SMC-M range, for example, currently offers models of 75, 100, 150, and 180 g Cl₂/h, designed for medium-sized public pools with intensive use.

For higher-capacity installations, the SMC-H range offers models of 250, 300, 500, 750, and 1,000 g Cl₂/h.

This makes it possible to match production to installations with very different needs without having to rely on a single large-capacity model.

Let’s imagine an outdoor pool of 500 m³ that receives approximately 200 bathers a day.

At first glance, it might seem enough to look for a chlorinator rated for 500 m³. However, that information alone isn’t enough to make a correct selection.

You also need to know how many hours the filtration runs and how intensively the pool is used.

Innowater’s recommendation table addresses exactly this kind of situation. For an outdoor pool of 500 m³ with 200 daily bathers, different configurations appear depending on whether the installation runs with 12 or 24 hours of filtration.

This difference matters because it shows something that’s often overlooked in projects: the same pool may need a different configuration depending on how the installation is operated.

That’s why, before selecting the equipment, it’s best to define the operating conditions rather than simply looking for a model based on volume.

Is it better to oversize the salt chlorinator?

In professional installations, it’s usually worthwhile to have some capacity margin. The reason is simple: actual conditions don’t always match the average conditions used during design.

Situations such as an increase in bathers, a heatwave, a rise in water temperature, or more intensive use may occur during certain periods.

Equipment with sufficient capacity, with some margin, lets us handle these situations without the equipment having to run at the limit of its output all the time.

This doesn’t mean we have to install the largest equipment available. Excessive oversizing doesn’t necessarily offer an advantage either. In fact, it can unnecessarily increase the initial investment.

The key is to size the system by finding a balance between expected demand, the most demanding operating conditions, and the system’s regulation capacity.