Impacts of airflow interactions with thermal boundary layer on performance of personalized ventilation

Abstract

The flow interactions between the personalized air and the thermal boundary layer (TBL) may play an important role to the inhaled air quality and energy efficiency performance of a personalized ventilation (PV) system. This paper aims to investigate these interactions and their impacts on the performance of a PV system. Schlieren imaging technique, Laser Doppler Anemometry (LDA) and tracer gas measurements are employed to identify the airflow patterns in the breathing zone (BZ) and the effect of the interactions on ventilation effectiveness. Although it has always been considered that it is difficult for a PV jet of low flow rate to penetrate the TBL, it is found in this study that the TBL is penetrable even at invading velocities lower than the normally recognized value of 0.3 m/s. The advantage of the reduced blockage effect allows for a more effective delivery of fresh air to the BZ. It is also shown that the airflow interactions alter the airflow distributions in the BZ and affect the inhaled air quality. This interaction depends on the positioning and direction of the non-uniform invading flow from the nozzle, which should be carefully considered for optimal ventilation design to enhance the effectiveness of ventilation at relatively low energy consumptions.