A review of outdoor thermal comfort indices and neutral ranges for hot-humid regions

This paper reviews frequently used outdoor thermal comfort indices in hot-humid regions and neutral thermal ranges to offer guidelines for selecting an appropriate index for hot-humid regions. An overview of the development of outdoor thermal comfort (OTC) indices based on type of approach, from linear equation approach – to adaptive thermal comfort model – is provided and the advantages and limitations of each index are presented. Subjective neutral ranges from 31 studies conducted in hot-humid regions were assessed on the basis of geographical location, Köppen-Geiger’s climate classification, parameters, a survey method, instrumentation set-up, respondent profile, method of analysis, neutral range, and coefficient of determinations in order to gain an understanding of their deviations. The review of 31 calibration studies of (m)PET’s, (OUT_)SET*’s and UTCI’s neutral ranges indicated that the lower threshold of (m)PET’s neutral range needs to be lowered, while the lower threshold of (OUT_)SET*’s and UTCI’s ranges should be raised. The appropriateness of (OUT_)SET*’s thermal range for hot climates was proven by its full-coverage neutral range in the evaluation. However, the accurate response to ambient thermal conditions was determined by the advancement of a human thermoregulatory model.