Experimental evaluation of thermal adaptation and transient thermal comfort in a tropical mixed-mode ventilation context

Abstract

Mixed-mode ventilation offers a promising solution for achieving comfortable indoor environments in an energy-efficient manner. However, in the tropics, characterized by a year-round hot and humid climate, opportunities for natural ventilation (NV) are typically limited to specific hours, necessitating operational mode switches on an intraday basis. Much of the thermal comfort research on mixed-mode ventilation relies either on cross-sectional data collected from different subjects or longitudinal data spanning a few seasons. This raises an open question: Can occupants thermally adapt when switching between NV and air-conditioning (AC) modes within a single day? To address the gap, our experimental study engaged 57 tropically acclimatized subjects, exposing them to combinations of five operational modes and four ceiling fan speeds (0.15-1.15 m/s) over an eight-hour timeframe. The results revealed that the subjects preferred a Standard Effective Temperature (SET*) that was 2-3 °C higher when operating in the NV mode compared to the AC modes, indicating thermal adaptation within the same day and in the same space. Specifically, the adaptation process was observed to stabilize between 35 to 45 mins following a mode switch. These findings contribute to the optimization of thermal comfort in mixed-mode controls, considering the dynamic characteristics of thermal adaptation.