Deck level air extraction and its impact on trichloramine concentrations in an indoor swimming pool: A numerical study

Abstract

Trichloramine (NCl3) is a disinfection by-product (DBP) that forms in swimming pool water due to water chlorination. It easily becomes airborne when water is agitated and can impair lung functions and cause illnesses such as asthma and bronchitis in workers and bathers, when inhaled. In indoor swimming pools, NCl3 must be removed from the breathing zones with mechanical ventilation. Since it tends to accumulate at the water surface, ASHRAE's recommendations are to add lower extraction vents to capture DBP. However, no guideline is found in literature on the number of vents, their position in the enclosure or their minimum airflow rate. This paper presents a numerical investigation of the impacts on NCl3 concentrations when adding extraction vents at deck level in a swimming pool hall in Montreal (Canada). The efficiency of four ventilation scenarios that include low extraction vents was determined numerically and compared to the reference case which does not have lower-level exhaust vents. Results show that the position of these vents affects the air movement above the water surface, causing either unwanted accumulation or reduction of NCl3. The most significant reduction was obtained when placing these vents on the side of the enclosure where low level air supplied grills are located. Finally, the NCl3 that is not extracted is sent upwards and diluted thanks to the nearby air delivery grills. The results demonstrate the importance of a numerical assessment of the airflow patterns in a pool enclosure and especially above the water and deck before planning the position of these deck level extraction vents.