Thermal comfort in mixed-mode buildings: A field study in Tianjin, China

Abstract

Mixed-mode (MM) buildings, integrating a naturally ventilated (NV) mode and an air-conditioned (AC) mode, have gained popularity in recent years. However, there is no consensus among previous studies on how to evaluate the thermal comfort of occupants of MM buildings. This study aims to compare the applicability of the PMV-PPD model and the adaptive model in MM buildings and to verify whether the occupants' thermal perception varies with different operating modes. A field study was conducted in an MM office building in Tianjin, China from March 2019 to January 2020, covering four seasons. Through a statistical analysis of environmental parameters and occupants’ thermal responses, the difference in the thermal perception of occupants was observed between the two modes. The actual neutral Top (24.5 °C) was higher than the prediction calculated by PMV (23.0 °C). When the indoor Top was within the 80% acceptability limit of the adaptive model in ASHRAE Standard 55, over 80% of the occupants found the thermal environment acceptable in both AC-cooling mode and NV mode. The results revealed that the PMV-PPD model was not suitable for MM buildings, and the adaptive model showed better applicability in both AC-cooling mode and NV mode. Compared with the Beijing case in ASHRAE Global Thermal Comfort Database Ⅱ, the occupants in the current study had a higher neutral SET (24.3 °C) and better adaptability to the thermal environment. This study also showed that well-designed MM buildings were potentially applicable in mid-latitude temperate regions with four distinct seasons.