Swimming pool temperature and other factors to determine operating conditions (2023)

Uncontrolled humidity is a dangerous presence in an indoor swimming pool environment. Excessive moisture in the air can destroy the pool and its surrounding structures over time, from developing potentially harmful mould and mildew to causing rot and corrosion across the site’s materials.

In order to manage the humidity load within your indoor pool, it is vital that you are able to determine the operating conditions on-site. Within these operating conditions, there are five major factors to keep in mind:

• Room temperature

• Water temperature

• Relative humidity

• Water content in the outdoor air

• The outdoor air in general

Here we will discuss each of these factors in further detail, and how they should be approached to create the most manageable and pleasant environment around your indoor swimming pool.

1. Room temperature

In order to provide both the most comfortable environment for swimming pool users and reduce energy costs, it is recommended that the air temperature should be a few degrees higher than the swimming pool temperature. Ideally, the water temperature should be 2°C lower than the room temperature itself.

This is because it minimises the amount of evaporation that occurs, although it will naturally make an impact on the heating bill.

2. Water temperature

What temperature is ideal for a swimming pool? That will often vary based on its application and the environment surrounding it. Public and competition pools should typically use lower temperatures, due in part to their scale and the number of people utilising them at peak times, while spas and therapy pools for their purposes will have the water at higher temperatures.

The following benchmarks are a good reference point:

• Competitive swimming pools: 24°C-27°C

• Public swimming pools: 26°C-28°C

• Private swimming pools: 26°C-30°C

• Therapy pools: 30°C-36°C

• Spas: 36°C-40°C

3. Relative humidity

In terms of how you should calibrate your dehumidification system to establish the optimal environment for protecting both the building structure and the people within it, the setpoint for relative humidity (RH) should be between 50% and 60%.

This means that the amount of water vapour in the air is between 50% and 60% of its maximum capacity. These values represent the sweet spot between limiting the amount of moisture in the air so it doesn’t create an uncomfortable environment or causes damage to building materials, but also does not make the air too dry, leading to excessive evaporation.

Going above 60% RH will both impact the comfort of users and increase the likelihood of condensation and fungal growths. Conversely, dipping below 50% RH will increase evaporation, meaning that your dehumidifier will have to work harder to absorb this moisture and thus increasing operating costs. Plus, dry air will cause water droplets to evaporate on swimmers’ bodies faster when they leave the pool, and this creates a chilling effect, which may lead to complaints.

A final point to consider here is that it is often wise to adjust the setpoint at different times of the year. For instance, in the winter, dropping the setpoint to around 50% RH will help avoid condensation problems on the much colder surfaces. In the summer, going closer to 60% RH will keep operating costs as low as possible without impacting people’s wellbeing.

4. Water content in the outdoor air

Throughout the year, the water content in the air outdoors fluctuates significantly. You’ve probably noticed this yourself – in the summer, days are often muggy and humid, indicating more moisture in the air, while winter days are typically drier.

In fact, there can often be as much as 12g of water for every 1kg of air in the summer, compared to just 2g of water in the winter. This is important to account for, as it will influence the overall humidity load within the indoor swimming pool, even though it is not something that we can play a role in changing.

All SET products follow the guideline VDI 2089 from The Association of German Engineers (VDI), which outlines that the standard water content for the air in Northern Europe is 9g water/kg air, as this value is only exceeded 20% of the year.

This value is important in calculating the requirements of the appropriate dehumidifier, to ensure that the moisture absorbed from both inside the pool room and the outside air is not excessive, as this would require the system to work harder and exert more energy to operate.

During the summer, a higher water content in the indoor air can be permitted though. This is because the temperature in the air that enters from outside is high and thus does not contribute to condensation.

5. The outdoor air

As noted, the outdoor air temperature and the water content in the outdoor air affect what dehumidifier should be selected.

For example, for environments with below-average outdoor temperatures, an air handling system with a heat pump is favourable. Conversely, if the water content in the outdoor air is higher than the water content in the air of the pool room, the condense dehumidifier will require a larger capacity.

In typical situations, a dehumidifier should be installed in consideration of the outdoor air temperature and humidity contents on a summer day:

• It should be related to what happens during the day because that is when pools are most actively used, and therefore produce the most evaporation.

• The water content of the outdoor air is highest during summer, so the dehumidifier should be large enough to deal with that.

Identifying the right dehumidification solution for your indoor pool

Now you have gained a stronger understanding of the key factors influencing the operating conditions of your pool, this information can and should be applied to ensure that your dehumidification system handles the humidity load and keeps conditions at a suitable level long term.

Our SET product specialists can help assess your pool environment, and use these findings to determine the most appropriate dehumidification solution for your indoor pool from across our quiet, high-performance range. From small, private pools to large commercial and competition pools, our versatile selection covers all scenarios, and some can be customised to meet your exact needs.

Get in touch with our team today to explore your options.