A Full Factorial Analysis of Albedo, Window-to-Wall Ratio, and Ventilation on Energy Use and CO2 Concentration in a Mediterranean Apartment

This study investigates the combined impact of wall albedo, window-to-wall ratio, and natural ventilation duration on heating and cooling energy demand and indoor CO2 concentration in a naturally ventilated, well-insulated apartment in Izmir, Türkiye. A validated building energy model was developed using DesignBuilder and calibrated with real indoor and outdoor measurements collected over a three-month period. A full factorial 33 design was applied to evaluate 27 combinations of the three variables. Statistical analyses, including ANOVA and regression, were conducted to determine the significance and direction of each factor’s effects. Results revealed that natural ventilation duration was the most influential parameter, explaining over 94% of the variance in CO2 concentration and having the largest effect on energy demand. Window-to-wall ratio showed significant but seasonally opposing impacts on heating and cooling loads, while wall albedo affected energy demand but had no statistical effect on indoor CO2. The findings highlight the importance of considering design-operational interactions in passive residential strategies. The study offers practical recommendations for energy-efficient and health-conscious retrofits in Mediterranean housing, particularly where mechanical ventilation is absent, and supports the use of factorial simulations for informed decision-making in climate-sensitive design contexts.