Occupant's preferred indoor air speed in hot-humid climate and its influence on thermal comfort

Abstract

As an energy-efficient and high-comfort indoor environment control method, the rational application of airflow in modern buildings has brought renewed attention, especially in hot and humid areas. Chamber experiments were conducted to examine occupants’ preferred air speed and its effects on thermal comfort in hot-humid climate, and the extended thermal comfort zone limit was obtained. Three temperature levels (26 °C, 29 °C, and 32 °C) and two relative humidity levels (40%–60% and 70%–90%) were set, achieving six experimental conditions. During each condition, thirty-six participants were sequentially exposed to two stages with still air and personal controlled stable mechanical airflow produced by electric fans, each lasting 30 min. Their subjective perceptions were collected repeatedly, and skin temperature was measured continuously. For the six conditions, the average preferred air speeds were estimated to be 0.53 m/s, 0.62 m/s, 1.06 m/s, 1.31 m/s, 1.28 m/s, and 1.48 m/s respectively. The preferred air speed at high humidity (70%–90%) was approximately 0.15 m/s-0.3 m/s higher than that at moderate humidity (40%–60%), and such difference increased with air temperature. Elevated air speeds may be used to offset thermal discomfort, as indicated by a 0.2°C–0.5 °C significant decrease in the mean skin temperature and improvements in subjective perceptions. However, for extremely hot and humid conditions including 29 °C/85%, 32 °C/55%, and 32 °C/85%, the discomfort cannot be completely eliminated. When local control of airflow is provided to occupants, the acceptable operative temperature range could be extended by approximately 1 °C regardless of humidity, compared with that under near still air speed below 0.1 m/s.