Seasonal and Botanical Influences on External Thermal Performance near Green Façades: CFD Simulations on a Reference Building Envelope in a Humid Temperate Climate

Green façades are acknowledged as passive strategies that reduce heat accumulation, enhance biodiversity, improve particulate matter absorption and provide psycho-physiological benefits for users. However, evaluations of their thermal performance—accounting for seasonality, vegetation density, and leaf characteristics—remain incomplete. This study addresses this gap by assessing two green façade typologies on a sample building located in Northern Italy (Cfa climate). ENVI-met microclimate simulations compared a bare wall with vegetated façades featuring Hedera helix (evergreen) and Parthenocissus tricuspidata (deciduous) across four orientations and seasonal conditions, considering the sample building and the immediate surrounding outdoor space. Both species reduced wall-surface temperatures (T0) and improved outdoor thermal comfort perception (PET), influenced by LAI dynamics, foliage persistence, and façade orientation. Results indicate that Parthenocissus tricuspidata achieved the greatest cooling effect during hot periods due to higher LAI, with absolute T0 reductions of up to 22.1°C on southern façades and 30.0°C on western façades. In these orientations, PET improvements reached up to 3.0°C (south) and 8.0° C (west). Conversely, Hedera helix ensured stable year-round performance and performed better on northern façades during colder periods. The results stress the need for integrated design that aligns plant choice with orientation and seasonal growth to optimize thermal performance, cut cooling demands, and improve outdoor comfort.