Adaptive Tropical Summer Index: adaptive thermal comfort for naturally ventilated and mixed-mode residential dwellings in Indian composite climate

This study is conducted to update Tropical Summer Index (TSI), the first thermal comfort model of the Indian subcontinent, which was developed in 1983 by studying 18 male subjects in a static environment. Researchers carried out a year-round study in 22 residential buildings in five different cities within the Indian composite climate during the monsoon, winter, and summer seasons. To update TSI and propose a-TSI, 2274 observations were collated in the morning, evening, midday, and night, where subjects had access to various adaptive actions. The CEN EN 15251 approach is applied to evaluate comfortable temperatures, and the ASHRAE 55 methodology is used to determine neutral and preferred temperatures. Correlation and multiple regression analysis, as per TSI, are used to propose a-TSI. Eighty-four percent of participants reported feeling comfortable at a preferred and comfortable temperature of 24.3 °C and 26.2 °C, respectively, and a widely adaptive comfort range of 18.2 °C − 34.7 °C. A steeper adaptive slope of 69.94% indicates that the subjects’ contextual adaptation to environmental influences is high. The proposed a-TSI is verified by comparing it with other Indian residential sector thermal comfort studies as well as the TSI, IMAC, IMAC-R, ASHRAE, and CEN adaptive thermal comfort models. a-TSI is an essential adaptive model that helps understand the prevalent thermal comfort requirements of Indian subjects.