Impact of modified ventilation strategies on water evaporation rate and thermal comfort in an indoor swimming pool by numerical study

The evaporation rate from a pool surface and the thermal comfort of bathers were evaluated numerically in a swimming pool enclosure in Canada while modifying the ventilation strategies, aiming to reduce trichloramine (NCl3) concentrations in the breathing zone. Air movement is required near the pool surface to remove NCl3 emanating from the water, but this airflow may cause unwanted thermal discomfort and water evaporation increase. A reference case based on the existing conditions and four simulated cases with varied ventilation strategies were evaluated to assess the impact on the water evaporation rate and thermal comfort. We implemented a water evaporation model in the Fire Dynamics Simulator (FDS) code to study how the modified airflow patterns may impact the evaporation rate. We also determined with a PMV modified index how thermal comfort of bathers with wet and dry skin is affected by the modified airflow of each case. Our findings show that adding deck level air extraction vents allow 41% NCl3 reduction without negatively impacting thermal comfort and with only a 4% water evaporation increase. Conversely, with commonly used dilution ventilation strategy and remaining within ASHRAE's recommendations for the airflow rate, we obtain only a 3% NCl3 reduction but up to 51% of dissatisfied bathers (with a local peak of 99%) for a "cool" environment. Water evaporation rate is also increased by 16%. Numerical airflow simulation is recommended as a tool to plan an optimal ventilation strategy balancing air quality, energy expenditure and thermal comfort in indoor aquatic environments.