Abstract

Thermal comfort in transient indoor spaces, such as transportation terminals, waiting areas, and building lobbies, presents a growing challenge in the built environment. Characterized by fluctuating thermal conditions, short dwell times, and limited occupants' access to environmental control, these spaces cannot be adequately served by conventional steady-state comfort models. Existing literature is fragmented across disciplines, methodologies, and definitions, limiting transferability of findings and operational strategies. This paper addresses that gap through a ten-question synthesis, identifying challenges, opportunities, and future research directions. It proposes a working definition of indoor transient spaces as spatial zones characterized by reduced or absent occupants' access to environmental control, combined with: (a) designed for short dwell time — configured for limited-duration occupancy as part of a single visit rather than sustained use, and/or (b) transitional spatial function — serving principally to connect or mediate between thermally or functionally distinct zones. It further identifies that these characteristics afford designers more flexibility than non-transient environments permit: occupants tolerate broader thermal ranges, and phenomena such as alliesthesia can transform thermal transitions into positive sensory experiences. With existing comfort models proving inadequate for transient conditions, the paper highlights more suitable approaches from passive architectural interventions and function-specific comfort criteria to dynamic, data-driven control systems supported by AI and Digital Twin technologies. Finally, it maps the interdisciplinary scope this research demands, calling for a Transient Comfort Index integrating physiological, behavioural, and environmental variables. Realizing this potential will require the technical advances and definitional clarity this paper works to establish.