Mixed-mode ventilation for indoor health and energy efficiency in subtropical climates

The widening wealth gap has made it increasingly difficult for many households to prioritize indoor environmental health, thereby elevating the risk of physical illness. To address this challenge, maintaining adequate air quality and thermal comfort is essential. This study proposes a mixed-mode ventilation strategy by combining a single-mode single-split air conditioner (set to 25°C) with scheduled window openings, aiming to evaluate its energy-saving potential and health benefits under hot and humid subtropical climate conditions. Results show that, when integrated with thermal comfort indices, the proposed strategy can achieve energy savings ranging from 14.2 % to 37.8 % during the summer. Furthermore, without increasing electricity consumption, it enables two air changes per hour (2 h −1 ), fulfilling the fresh air requirement of 30 m 3 /h per person. A comparison of electricity pricing schemes reveals that a two-tier tariff allows for approximately two additional hours of system operation compared to a three-tier tariff. With the growing adoption of AI-powered smart appliances, this strategy offers promising potential to further reduce energy costs while enhancing indoor environmental quality and health protection. • Saves up to 37.8 % energy under subtropical climate using mixed-mode ventilation. • Achieves 2 h −1 without increasing energy consumption. • Two-tier tariff extends system operation by around 2 h vs. three-tier. • Improves thermal comfort and air quality for vulnerable households. • AI appliances help further cut energy costs and reduce financial burdens.