The impact of thermal mass on envelope heat loss in the caldarium of Yazd's traditional baths

Abstract

Traditional Iranian bathhouses (hammams) represent remarkable examples of vernacular architecture optimized for thermal performance in hot arid climates. This study quantitatively evaluates and compares multiple passive heating strategies employed in hammams to mitigate envelope heat loss through thermal simulations of two exemplar cases - the Khan and Golshan baths in Yazd.A post-positivist research approach combined physical documentation, computational modeling using DesignBuilder V7.0.1.004 software, and quantitative analysis. Heat transfer through the caldarium (hot room) envelope was simulated sequentially, first without any heat retention strategies, then adding thermal mass, unconditioned buffer spaces, earth-coupling, and finally urban morphology factors.Results indicate thermal mass was the most effective approach in the studied Yazdi hammams, yielding 37.5 % and 37.3 % reductions in winter heat loss compared to 8.4 %, 5.3 %, and 1.8 % from unconditioned zones, earth-sheltering, and integrated compact urban fabric, respectively. Overall, leveraging thermal mass outperformed the combined impact of the other three strategies by over five times for these cases.The quantified insights highlight vernacular passive heating principles extracted from this historic architectural typology that can potentially inform sustainable high-performance building practices for hot arid regions.