Ventilation performance and pollutant distribution in a traditional ceiling-type ventilation system, a top-return (TR)-type and a floor-return (FR)-type underfloor ventilation systems were performed in a controlled experimental room. Tracer gas method was utilized to determine the age of air and the contaminant removal effectiveness. Tobacco smoke was also introduced to study the particle-phase pollutant distribution. The TR system delivered conditioned air more efficiently in the occupied zone and exhibited higher gaseous contaminant removal effectiveness. It also showed the lowest smoke particle concentration compared with the other two systems. The FR system showed better ventilation performance over the mixing system at the space that was close to the floor supply outlet and at the lower height level. The FR system was less effective than the TR system in removing buoyant tobacco smoke particles at the upper part of the room indicating its highly localized characteristics. Differences in experimental conditions between the present and the previous studies and their effects on the experimental results are discussed. In general, the experimental data suggested that both types of the underfloor ventilation systems have the potential of improving air quality at the breathing zone over the ceiling-based mixing system with suitable designs.
Practical implications: This study shows the possibility of improving indoor air quality using underfloor ventilation systems compared with the traditional ceiling-based ventilation system. However, different configurations of the underfloor ventilation system show various ventilation characteristics. The engineers should consider these features when implementing an underfloor ventilation design. The top-return (TR) configuration improves indoor air quality by creating a displacement-like flow pattern while the floor-return (FR) configuration shows highly localized ventilation characteristics. The FR configuration improved the indoor air quality at spaces near the floor diffusers and up to certain heights.