Experimental assessment of thermal and acoustics interactions on occupant comfort in mixed-mode buildings

Mixed-mode buildings use natural ventilation (NV) through operable building envelopes (e.g., windows) and mechanical air-conditioning (AC) systems to condition indoor spaces with the goal of energy savings without compromising occupant comfort requirements. As a result, occupants within such buildings experience different thermal and acoustic conditions. In mixed-mode buildings, however, there is no clear guideline on assessing or predicting occupants’ thermal perception (e.g., thermal sensation and acceptability) and the interaction effects between thermal and acoustic comfort. This study investigates thermal and acoustic comfort as well as their interaction effects in mixed-mode buildings under NV and AC modes. A field study was conducted in a mixed-mode office building in Singapore with a tropical climate. The results showed that subjects’ actual thermal sensation and thermal acceptability were affected by the operation modes. Elevated air movement by ceiling fans improved subjects’ thermal acceptability, particularly in the NV mode. The results indicated the need for a different thermal comfort model even when switching between NV and AC modes within the same day. Traffic noise also significantly affected thermal sensation and thermal acceptability at noise level higher than 55 dBA. The findings suggest that mixed-mode buildings are potentially applicable in the tropics and provide valuable information on the practical operation of mixed-mode buildings from thermal and acoustic perspectives. Future research needs to investigate how to integrate thermal and acoustic studies and their results into mixed-mode operations to improve building energy efficiency and occupant comfort.