Effects of elevated air speed on thermal comfort in hot-humid climate and the extended summer comfort zone

Abstract

Indoor air movement is beneficial for building energy conservation and human thermal comfort. Chamber experiments were conducted to evaluate the cooling effect of elevated air speeds on thermal comfort. Three temperature (26, 29, and 32 °C) and two relative humidity (40%–60% and 70%–90%) levels were selected for a total of six experimental conditions. Thirty-six subjects in summer clothes (0.5 clo) were exposed to mechanical airflow produced by electric fans and experienced four 30-min exposures at various air speeds (0.01–2.0 m/s), and subjective perceptions and skin temperature were collected. Results showed that mean skin temperatures decreased by 0.2 °C–0.6 °C for every 1 m/s increase in air speed. Airflow may alleviate thermal dissatisfaction, but air speeds up to 2.0 m/s cannot eliminate discomfort in extremely hot-humid environments (29 °C/85%, 32 °C/55%, and 32 °C/85%). In the experimental conditions of 26 °C/45%, 26 °C/75%, 29 °C/55%, 32 °C/55%, and 32 °C/85%, the upper air speed limits were 1.2, 1.2, 1.6, 2.0, and 2.0 m/s, respectively. Based on experimental data, comfort zones with elevated air speed for both moderate (40%–60%) and high humidity (70%–90%) were obtained. The maximum acceptable operative temperatures in two humidity conditions were 31.3 and 28.6 °C, extending the ASHRAE 55 values by 1.3 and 0.1 °C, respectively.