Mitigating the Urban Heat Island Effect by Enhancing Green Structures and Implementing Double Skin Facades in Urban Areas.

Urban heat island (UHI) which is the effect of having higher air temperature in urban areas, is the result of urbanization and changing the surface properties, as during the daytime, buildings and structures would absorb more solar radiation and reflect less. Conversely, during nighttime they emit more longwave radiation, and these phenomena exacerbate the effects of climate change, leading to higher energy consumption and reduced outdoor thermal comfort in urban areas. This research investigates the potential of green facades (GFs)—specifically Green Walls (GWs)—to mitigate the UHI effect and enhance urban thermal comfort under both current and future climate projections (2050). The primary research questions addressed in this study are: How do GWs affect thermal comfort in urban environments, particularly in terms of air temperature, mean radiant temperature (Tmrt), Universal Thermal Climate Index (UTCI) and their effect in reducing carbon emissions by decreasing buildings energy demand. Using remote sensing techniques to detect existing surface UHI along with employing numerical simulation methods, this study models the effects of GWs on urban microclimates. A case study was conducted in the urban area of Via della Consolata, Turin, Italy, where simulations, validated with onsite measurements, were run for typical weeks across different seasons and future climate projections (RCP8.5 - 2050). Simulation results show that the evaporative cooling effect of GWs does not significantly reduce air temperatures and in some hours during the day we would experience even higher air temperatures, with a maximum reduction of 1.6 °C during winter in the 2050 compared to baseline conditions. Additionally, we would face reduction in average mean radiant temperatures and outdoor comfort in both current and future climate projections in all the simulation periods. For instance, on 29th July, the mean radiant temperature (Tmrt) decreased by 1.92 (°C) at noon, when the solar radiation is at its maximum under current climate conditions, and by 2.27 (°C) in 2050. Additionally, improvement in UTCI by 0.51 (°C) under current climate conditions and by 0.55 (°C) in the 2050, indicating a notable improvement in outdoor thermal comfort during summer. Carbon emission intensity analysis reveals that GWs reduce cooling demand in summer, resulting in a decrease in overall carbon emission intensity from 0.100 [kg CO2/m²] to 0.069 [kg CO2/m²]. However, a slight increase in heating demand during the cold months led to an increase in carbon emission intensity from 0.527 [kg CO2/m²] to 0.549 [kg CO2/m²] in 12th January and 0.022 [kg CO2/m²] to 0.032 [kg CO2/m²] in 15th October. Despite this, the overall impact of GWs remains positive, contributing to more sustainable urban environments. These findings demonstrate that GWs offer an effective strategy for urban heat mitigation, improving both thermal comfort and energy efficiency and emphasizes the importance of integrating green infrastructure into urban planning to address the challenges posed by climate change. This study contributes to the growing body of knowledge on sustainable urban solutions and provides a framework for incorporating GFs into future urban development strategies.