How to calculate
dehumidification needs
in indoor swimming pools?

Friday, April 28, 2017


Swimming pool with Dantherm dehumidification

There are three factors that must be taken into consideration when calculating the humidity load from a swimming pool.

  • The evaporation from the pool - contributes positively to the humidity load
  • Bystanders and users - contribute positively to the humidity load
  • Outdoor air – normally contributes negatively to the humidity load

The calculation of the evaporation from the pool can be carried out in accordance with different formulas. At Dantherm, we use the German guideline VDI 2089, which is the normal standard in Europe.

However, we have chosen to adjust the constants for the level of activity that VDI 2089 has set for private pools and hotel pools, as the VDI 2089 values, in our experience, are too high for the level of activity in these two areas.

In addition, in small private pools the need for dehumidification is often defined by air circulation, more so than by the level of activity in the pool.

The following factors are used in calculating evaporation from the pool:

  • Water temperature
  • Air temperature
  • Air humidity
  • Pool area
  • Level of activity in the pool

To see the exact formula used for calculating evaporation, please sign up here to download our “Selection Guide - Dehumidification of Swimming Pools”.

How users and bystanders affect dehumidification needs

When a public swimming pool is used for competitive swimming, the temperature of both the air and water is usually reduced. This means that the humidity load from evaporation decreases, and that the contribution of humidity from users and bystanders is counteracted.

In this case it is not necessary to take separate humidity contributions from users and bystanders into account.

Users and bystanders affect dehumidification needs in indoor pools

Outdoor air contributes to dehumidification

The air quality in a pool room is crucial for comfort, and poor air quality is often associated with a high RH value and high levels of chlorine or CO₂.

In other words, adding outdoor air is a crucial factor in ensuring a comfortable environment. At the same time, the outdoor air is a key part of the grounds for the choice of the type and size of the dehumidifier. The outdoor often contributes to the dehumidification of the room, as the water content in the outdoor air is normally lower than the water content in the air inside the room.

During summer, the outdoor air in some areas of the world, primarily the Middle East and Asia, can be so humid for long stretches of time that dehumidifying the outdoor air before adding it to the room becomes necessary. This can for instance be done using a cooling coil.

If the pool is used for competition swimming with a greater number of users and bystanders, a separate calculation for the necessary volume of outdoor air must be made. This calculation must be made according to local regulations.

Outdoor air contributes to dehumidification - especially in large pools with a great number of users and bystanders

Room size and insulation matters

The size of the room itself is important to consider, as the air circulation is crucial to the dehumidification process. If insufficient air moves around the room, there will be areas where dry air does not pass through, leading to these areas not being dehumidified. The capacity of the dehumidifier when it comes to air volume must be able to match the size of the room.

Insulation is an important factor as well. If the insulation is not sufficient, the RH value set-point has to be lowered. In some cases, 50% RH may be required to avoid condensation problems.

For a deeper dive into the specifics on choosing and dimensioning the right dehumidifier for your indoor swimming pool, please sign up for our “Selection Guide – Swimming Pool Dehumidification”.

Selection Guide frontpage
Dantherm is a market leading supplier of energy efficient climate control solutions for customers across the globe. Ask your pool supplier for a Dantherm product.

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