The Relation Between Airflow Pattern and Indoor Air Quality in a Hybrid Personalized Ventilation with Under-Floor Air Distribution System

This study aimed to determine the relation between airflow pattern characteristics and indoor air quality of a hybrid personalized ventilation (PV) with under-floor air distribution (UFAD) system in a standard office. Actually, it was tried to introduce a practical design consideration for a suitable airflow division between inlet diffusers based on streamline analysis. In each scenario, the total airflow rate was 47.5 L/s. When each PV unit was set at 1.25 and 2.5 L/s, the cold/dense consequent airstreams of PV and occupants’ exhalations were returned to the inhaled zones after losing the required momentum in penetrating the background airflows to reach the ceiling level. The density differences between airflows formed steady vortexes at the occupants’ micro-environments. These negative interactions acted like obstacles in contaminant transference and could decrease the micro-environment air quality between 21 and 62% compared to the standalone UFAD. At high or dominant PV flow rates (equal to 7 L/s), the air change efficiency reduced to 0.50 which meant the PV flow quickly escaped through the exhaust, and the weak UFAD couldn’t remove the heat and particles at ambient areas as well as the standalone UFAD. When each PV diffuser had the minimum required flow rate which was necessary to prevent any formation of steady vortexes, the micro-environment air quality improved between 19 and 25%. The corresponding ventilation effectiveness and air change efficiency indexes were 1.4 and 0.55, respectively which showed acceptable conditions at ambient areas. The balancing PV flow rate was 5 L/s for each PV diffuser.