Mixed-mode buildings: a double standard in comfort

This paper investigates how mixed-mode (MM) ventilation affects occupant comfort by presenting results from a longitudinal field study within an office building located in subtropical Sydney, Australia. The building automatically switches into air-conditioned (AC) mode whenever indoor temperatures exceed 25°C. Coincident indoor and outdoor climate measurements along with 1359 subjective comfort questionnaires were collected. Thermal sensations during natural ventilation were, on average, 2.1°C warmer than those predicted using Fanger's PMVPPD (Fanger 1970). Differences in thermal perception were also apparent between these two modes. Within AC mode, a +1 PMV environment elicited much 'warmer-than-neutral' thermal sensations than the same environment within naturally-ventilated (NV) mode, suggesting thermal perceptions were affected by the building's mode of operation over and above the indoor climatic conditions. These discrepancies emphasize the complexity of thermal perception and the inadequacy of using PMV models to describe occupant comfort in MM buildings.