Thermal Comfort in Vernacular Shavadans vs. Contemporary Above-Ground Rooms: A Two-Season Field Study in Dezful, Iran

Background and Objectives: Shavadans—traditional underground spaces in Dezful, Iran—have long served as passive thermal spaces in a hot semi-humid climate. Despite their historical significance and recognised potential for moderating extreme temperatures, comprehensive two-season field studies comparing their thermal comfort performance with co-located above-ground mixed-mode rooms remain scarce.This study aims to provide empirical evidence on how Shavadans perform in both summer and winter, determine seasonal neutral temperatures, and assess  their potential contribution to contemporary climate-responsive design. Method: A two-season field campaign was conducted in ten Shavadans during winter (December ۲۰۲۲) and summer (July ۲۰۲۳). Air temperature, relative humidity, and air velocity were measured every three hours from ۰۶:۰۰ to ۱۸:۰۰ at multiple depths. Simultaneously, Level-۳ adaptive comfort questionnaires were administered to residents, yielding in ۴۲۲ valid responses (۱۰۲ winter and ۱۰۹ summer datasets for both underground and above-ground spaces). Linear regression of TSV–temperature relationships and the Bin Method were used to derive neutral temperatures and acceptable comfort ranges for each season and space type. Findings and Conclusion: Summer results showed that Shavadans maintained significantly cooler indoor conditionsthan above-ground rooms. The neutral temperature decreased from ۲۶.۶ °C (above-ground) to ۲۴.۵ °C (Shavadan), and only depths greater than ۵ m remained fully within the comfort range. The deepest zones (>۷ m) were up to ۱۶.۱ °C cooler than the courtyard at peak heat, demonstrating the strong thermal buffering capacity of underground construction. In winter, both environments exhibited neutral or near-neutral conditions; however, the Shavadan maintained more stable temperatures and slightly warmer sensations due to its high thermal mass, with a neutral temperature of ۲۳.۱ °C compared with ۲۲.۵ °C above-ground.Overall, Shavadans mitigate heat stress effectively in summer and provide stable thermal conditions in winter, while above-ground rooms offer slightly better comfort during the cold season. These findings deliver the first dual-season empirical benchmark in Iran and highlight the potential of hybrid underground–surface strategies for low-energy, climate-responsive architectural design.

کلیدواژه ها:

Shavadan ، Thermal comfort ، Underground spaces ، Adaptive comfort ، Mixed-mode ventilation