From fixed comfort boundaries to adaptive psychrometric regions: An exploratory comparison with seasonal field comfort data

Introduction: Thermal comfort standards often represent acceptable conditions as fixed temperature and humidity boundaries. While useful for design guidance, these zones may underrepresent seasonal adaptation, air movement, and local climatic expectations, especially in naturally ventilated or mixed-mode buildings. Psychrometric charts can visualise these variations by locating comfort within combined temperature and humidity space. This study examines whether literature-derived adaptive psychrometric regions provide a more flexible reference for interpreting seasonal field comfort data than a fixed comfort zone.

Methods: Adaptive and strategy-modified psychrometric polygons were reconstructed from studies proposing comfort or comfort-related regions under different air-speed, ventilation, or passive-strategy assumptions. These included ASHRAE 55 still-air and elevated-air-speed reference zones, plus locally derived polygons from warm, composite, and hot-humid climates. Polygon boundaries were digitised and intersected with fixed humidity-ratio levels to compare lower and upper operative-temperature bounds. The adaptive regions were overlaid with independent seasonal field comfort observations from Japan’s Kanto region. Comfortable responses were defined as SHASE thermal sensation votes of 3–5 and compared against ASHRAE reference zones and expanded seasonal regions.

Results: Increasing air speed from 0.1 to 0.5 m/s shifted the ASHRAE-based comfort zone warmer by approximately 2.4°C on the lower bound and 1.6°C on the upper bound. Locally derived adaptive and strategy-modified polygons extended further, with upper-bound increases commonly exceeding 3–8°C relative to the still-air reference. In summer, only 892 of 11,428 comfortable votes, or 7.8%, fell within the ASHRAE 0.65 clo zone, compared with 10,657 votes, or 93.3%, within the expanded zone. In winter, 2,186 of 4,611 comfortable votes, or 47.4%, fell within the ASHRAE 1.0 clo zone, compared with 2,554 votes, or 55.4%, within the expanded zone.

Conclusions: Adaptive psychrometric regions can function as exploratory seasonal reference spaces rather than fixed universal comfort boxes, with particular value for warm-period comfort assessment.