Displacement ventilation in conjunction with breathing zone air supply: Experimental study on distributions of droplet nuclei and gaseous contaminant concentrations

¹ Toyo University, Department of Architecture, Faculty of Science and Engineering, 2100 Kujirai, Kawagoe city, Saitama, Japan
² Osaka University, Division of Global Architecture, Graduate School of Engineering, 2-1 Yamadaoka, Suita city, Osaka, Japan
³ Nikken Sekkei Ltd., 2-18-3 Iidabashi, Chiyoda-ku, Tokyo, Japan

^* Corresponding author: choi056@toyo.jp

Abstract

This study proposes utilizing the breathing zone air supply (BAS) in conjunction with displacement ventilation (DV) to intensively enhance air quality at breathing level. To explore the distribution of both particle and gaseous contaminant concentrations within this system, full-scale measurements were carried out in an environmental chamber arranged as an office with four desks and corresponding person simulators. Two DV supply inlets were installed near the floor, and four BAS inlets were placed at the breathing height of a seated person. One of the four person simulators was designated as an infected person, generating CO2 and droplet nuclei at breathing height to simulate contaminants released during speaking and exhaling. Temperature and concentration of gaseous contaminant and droplet nuclei were measured under four different BAS temperature conditions and five varying ratio conditions of DV and BAS supply airflow rates. The results suggested that, in the conditions of this experiment, traditional DV offered superior air quality compared to this system. Nevertheless, the system showed potential for enhancement and exhibited strength when there was a downward airflow in a room. To optimize the performance of this system, further research should be conducted with different BAS conditions.