Exploration of applicability of UTCI and thermally comfortable sun and wind conditions outdoors in a subtropical city of Hong Kong

• Published in: Sustainable cities and society 2020-01, Vol.52, p.101793, Article 101793
• Main Authors: Li, Jianong, Niu, Jianlei, Mak, Cheuk Ming, Huang, Taiyang, Xie, Yongxin
• Format: Article
• Language: English
• Subjects: Combined sun and wind conditions index (SWI); Mean radiant temperature; Outdoor thermal comfort; Thermal sensation votes; Universal thermal climate index (UTCI); Wind speed
• ISSN: 2210-6707; 2210-6715
• DOI: 10.1016/j.scs.2019.101793

[Display omitted] Thermally comfortable combinations of sun and wind conditions at Ta ranging from 12.0 ℃ to 36.0 ℃: a) coordinate graph of v and Tmrt; b) v-Tmrt diagram and comfort zone. •Limitations of UTCI in predicting TSV of people in Hong Kong were explored.•Tmrt, DS/W (sun and wind desirability), and v were the top three factors influencing the surveyed TSV.•A combined sun and wind condition Index (SWI) was proposed.•Comfortable SWI ranges were explored and defined respectively.•A v-Tmrt diagram was constructed to indicate thermal comfort zones of combined v and Tmrt. This study conducted simultaneous physical measurements and questionnaire surveys to study the outdoor thermal comfort in the subtropical, high-density Hong Kong. With an innovative analysis method, the study reveals that mean radiant temperature (Tmrt), sun and wind desirability, and wind speed (v) were the top three factors influencing the surveyed thermal sensation vote (TSV), which was not well estimated by the Universal Thermal Climate Index (UTCI); and that UTCI underestimated the effects of v and Tmrt at higher air temperatures (Ta) but overestimated the impacts of Ta and relative humidity on TSV of subjects in Hong Kong. Accordingly, a combined sun and wind condition index (SWI) was defined to explore the combined effects of Tmrt and v on thermal comfort. Within the meteorological parameter ranges of 12.0 ≤ Tmrt ≤ 64.0 ℃, 0  26.0 ℃ and Ta ≤ 26.0 ℃, respectively. A v-Tmrt diagram was thus constructed to indicate the comfort zones of sun and wind combinations, which can be used to estimate the comfort levels of outdoor space in the design stage.