Performance Assessment of Living Wall and Secondary Skin Façades as Passive Cooling Strategies in Tropical Buildings

Abstract This study investigates the thermal and energy performance of two passive façade systems—a living wall and an inclined secondary-skin façade—as sustainable strategies to improve indoor comfort and reduce cooling energy demand in tropical educational buildings. The research was conducted experimentally at the Department of Mechanical Engineering, Universitas Andalas, using a quantitative field approach supported by IoT-based environmental monitoring. Two identical lecture rooms were tested under control and treatment conditions. Environmental variables, including air temperature, relative humidity, air velocity, and solar radiation, were recorded at 15-minute intervals between 10:00 and 14:00 local time. Cooling load analysis was performed using the Cooling Load Temperature Difference/Cooling Load Factor (CLTD/CLF) method, while thermal comfort was assessed using the Predicted Mean Vote (PMV) index following ISO 7730 and ASHRAE Standard 55. The results show that the living wall reduced the cooling load by 20.3% (488.10 W) and improved thermal comfort by 14.7%, with a PMV reduction of 0.159884. The inclined secondary skin façade achieved average cooling load reductions of 11.05%, 10.95%, and 10.80% for slope angles of 10°, 20°, and 30°, respectively, with PMV improvements of 5.03–7.20%. Statistical analysis confirmed that these effects were significant (p < 0.05). The findings demonstrate that both façade strategies are effective passive cooling solutions for tropical climates, supporting energy-efficient and climate-responsive building design.