Natural ventilation for thermal comfort: a simulation-based comparison of manual and automated window control strategies in temperate climate housing

• Co-simulation models natural ventilation with detailed inter-zonal airflow. • Passive cooling can increase heating demand; holistic energy balance is essential. • Automatic windows nearly matches mechanical systems with lower energy use. • Occupant behaviour and weather significantly affect passive cooling results. The assessment of heating, ventilation and air conditioning (HVAC) systems in terms of energy and environmental performance is crucial in the context of sustainable buildings. This study investigates the environmental and energy efficiency of using natural ventilation as a passive cooling strategy in a residential building located in the temperate climate of Central Europe. Both manual and automated window operation scenarios are analysed using a co-simulation approach (EnergyPlus and CONTAM) that accurately models inter-zonal airflow, including through open windows and stack chimneys, often neglected in previous studies. The numerical thermal model was validated on the basis of the results of field measurements in the building. Thermal conditions, air exchange, and energy use were assessed both in terms of instantaneous variability and annual performance. The study demonstrated that passive cooling through automatic window opening can ensure human thermal comfort for at least 94% of the time, achieving a performance nearly the equivalent to mechanical cooling while reducing total energy use by about 13% in case of heat pump. In contrast, manual window operation led to significantly worse conditions, with discomfort hours increasing by up to 59% and heating energy use rising by 40% under partial compliance. Moreover, excessive air exchange occurred for up to 19% of occupancy time during high wind periods. These findings highlight the need for integrated control strategies and demonstrate that a low-cost automatic window system, even without direct airflow control, can offer a feasible, energy-efficient alternative to mechanical systems in residential buildings, provided heating demand is also considered.