In an indoor swimming pool, moisture is constantly released into the air. The main cause is evaporation from the water’s surface. Swimmers and water attractions such as current channels, bubble jets, or slides further increase evaporation. That is why every indoor swimming pool needs a properly designed ventilation system that also handles dehumidification.
Evaporation depends primarily on the size and use of the pool, as well as on the conditions of the water and the ambient air.
The VDI 2089 standard uses what are known as water transfer coefficients for this purpose. Simply put: The more a pool is used and agitated, the higher the evaporation rate.
A typical indoor swimming pool, for example, is assumed to have the following values:
| Condition | Water Transfer Coefficient |
|---|---|
| Pool covered | 0.7 m/h |
| Pool not in use | 7 m/h |
| In use, water depth < 1.35 m | 28 m/h |
| In use, water depth > 1.35 m | 40 m/h |
| Wave pool in wave mode | 50 m/h |
Take water attractions into account
For recreational and water parks, it is not sufficient to consider only the normal water surface area. Current channels, water mushrooms, counter-current systems, neck showers, floor jets, and similar attractions increase water movement and, consequently, evaporation.
VDI 2089 therefore requires that the operating modes of these attractions be taken into account during the design phase. To this end, it should be determined in consultation with the operator which attractions will be operated simultaneously and for how long.
The maximum expected evaporation rate determines the required outdoor air flow rate for dehumidification.
VDI 2089 specifies a dehumidification range of 5.3 g/kg for this purpose. This value must be adhered to when calculating the design mass flow rate of outdoor air.
Air changes are also important: In the indoor swimming pool, at least four air changes per hour must be ensured year-round. Supply and exhaust air must be coordinated accordingly.
Don't regulate outdoor air based solely on humidity
A distinctive feature of VDI 2089 is its greater emphasis on air quality. The ventilation system is designed not only to remove moisture but also to eliminate airborne disinfection byproducts from the swimming pool facility. This hygienic consideration takes precedence over purely energy-related considerations.
Therefore, minimum values apply to the outdoor air fraction:
- Swimming and cleaning operations: at least 15% of the design mass flow rate
- in the event of deviations in water quality regarding volatile disinfection byproducts: at least 30%
- Standby mode: at least 10%
If necessary, the outdoor air percentage can be increased to 100%.
It’s not just the volume of air that matters. The air must also be directed through the swimming pool facility in an effective manner.
To prevent condensation in particular, supply air should preferably be introduced along the windows. This requirement may be waived if the windows are adequately insulated.
Exhaust air should be extracted at several points above the water surface. According to VDI 2089, a single, localized extraction point is not sufficient.
The humid, chloride-laden air in swimming pools places high demands on the HVAC unit. Materials must therefore be corrosion-resistant to this type of air.
In addition, VDI 2089 requires, among other things, Class TB2 housing insulation in accordance with DIN EN 1886 and the safe drainage of condensate. For units installed outdoors, the condensate drain must be equipped with trace heating.
Air quality is also a top priority in heat recovery. Heat may be recovered, but the exhaust air must not be recirculated into the swimming pool area if this could lead to a concentration of disinfection byproducts.
VDI 2089 also provides simple guidelines for some typical ancillary rooms:
| Room | Airflow rate |
|---|---|
| Control room | 25 m³/h per m² |
| Shower | 220 m³/h per shower |
| Toilet/urinal | 100 m³/h per unit |
| Communal changing room | 20 m³/h per m² |
| Changing room with individual/shared stalls | 15 m³/h per m² |
- When designing a ventilation system for an indoor swimming pool in accordance with VDI 2089, the key factors to consider are water evaporation, pool usage, water attractions, dehumidification requirements, an adequate supply of outdoor air, and effective airflow.
- The following principle applies: It is important to consume as little energy as possible—but this must not compromise moisture protection or hygienic air quality.
Please contact us early in the planning phase so that we can work together to configure the right Pool Line unit for your needs.