Indoor air quality and thermal comfort studies in the tropics: a comparison between under-floor supply and ceiling-based mixing ventilation systems using female subjects

An experimental study was conducted in a field environmental chamber with the aim of comparingceiling-based mixing ventilation (MV) system and under-floor supply system (UF) from the perspectives of indoor air quality and thermal comfort. Six tropically acclimatized female subjects participated in the experiments and they were required to complete a set of questionnaire pertaining to IAQ and thermal sensation every 20 minutes during each exposure of 2 hours. The UF system showed higher ventilation effectiveness as concentrations at occupant breathing zone of CO2, CO, formaldehyde, TVOC and particulate matters were significantly lower than those under MV system. The subjects perceived less odour intensity and better air quality when they were exposed to UF system but no statistically significant difference existed. It was also found that UF systems created a bigger temperature gradient and higher air velocity in occupied zone (0-1.2m above floor) than MV system, resulting in colder thermal sensations and more frequent feelings of air movement atdifferent body parts. However, such feelings of air movement were perceived by the subjects to be acceptable and may be an important and positive factor in promoting thermal comfort for the tropics.