Evaluation of outdoor thermal comfort in sunlight, building shade, and pergola shade during summer in a humid subtropical region

Abstract

This study evaluated outdoor thermal comfort during summer in a humid subtropical region. Meteorological inspections were conducted in sunlight, building shade, and pergola shade. The participants included 42 collegiate male subjects who completed questionnaires on thermal sensation and thermal comfort. To evaluate the thermal environments, we used three thermal indices: the universal effective temperature (ETU), the universal thermal climate index (UTCI), and the outdoor standard effective temperature (OUT_SET*). We confirmed that the ETU model is a suitable index for evaluating outdoor thermal comfort in the range of this study. Thermal neutral temperatures, as measured by ETU, UTCI, and OUT_SET*, were 33.1 °C, 34.0 °C, and 28.9 °C, respectively. Under sunlight, intense solar radiation raised the ETU value considerably; however, humidity and air velocity lowered it due to increased skin wettedness from the hot environment. The ETU model can provide a more detailed understanding of the various parameters affecting thermal comfort in the outdoor environment. At 800 W/m2 of total solar radiation in sunlight, the building shade and pergola shade with plants provided cooler thermal environments with ETU reductions of 18.4 °C and 16.2 °C, respectively, compared with sunlight. In cloudy conditions with total solar radiation of 300 W/m2, the building and pergola shades had ETU reductions of 9.3 °C and 6.8 °C, respectively.