Experimental study into turbulent characteristics of airflows under stratum ventilation with pulsating air supply: Comparison to steady air supply

Abstract

Stratum ventilation is more energy-efficient than conventional ventilation strategies, whereas its thermal comfort can be further improved. Compared with steady airflows, dynamic airflows are capable of improving thermal comfort. Turbulent characteristics of airflows can affect human thermal comfort. This study aims to investigate the turbulent characteristics of airflows in the occupied zone under stratum ventilation with pulsating air supply, which can produce dynamic airflows. The turbulent characteristics were compared with that under conventional steady air supply. Experiments were conducted in a classroom mock-up using stratum ventilation. Five cases, namely, one with steady air supply and four with pulsating air supply were designed. The turbulent intensity (Tu) and power spectrum of air velocity signals were analysed. The results showed that the Tu of the airflows in the occupied zone under pulsating air supply was greater than that under steady air supply by 10-15%. Power spectrum density exponents (β) of airflows under the two air supplies fluctuated within the same range of 0.5 to 1.2. However, the power spectrum density function showed different distributions on low frequency area. The turbulent characteristics of airflows created by pulsating airflows may provide better thermal comfort.