Evolution and performance analysis of thermal comfort indices for tropical and subtropical region: a comprehensive literature review

Thermal comfort is a significant aspect of human well-being and productivity, particularly in tropical and subtropical regions where high temperatures and humidity prevail yearly. However, research on indoor and outdoor thermal comfort in those regions is lacking when compared to other areas, and a significant gap exists in the comprehension related to the suitability and application of existing thermal comfort indices. This study intends to provide insights into existing human thermal comfort indices based on their applications in tropical and subtropical regions of Koppen climates for indoor and outdoor. PRISMA guidelines are used for conducting a systematic literature review using 86 articles. Of these, 38 were original thermal comfort indices articles and 48 were case studies (indoor and outdoor). This research discussed the most and least preferred indices as well as the approaches and parameters considered by the thermal comfort indices. The result shows that most efforts were made in temperate and continental climates to derive thermal comfort indices. For outdoor thermal comfort assessment, 72% of studies used Physiological Equivalent Temperature; 21% used Discomfort Index and Universal Thermal Climate Index. Whereas for indoors, > 90% of studies used the Predicted Mean Vote index and Operative Temperature. Overall, the used thermal comfort indices in reviewed studies underestimate the comfortable ranges observed in tropical and subtropical regions. The findings of this study can be utilized by researchers, urban designers, and planners to increase understanding related to human thermal comfort in tropical and subtropical climates.