Thermal mitigation strategies based on the study of facades and roofs at an urban scale

Global warming and rapid urbanization have exacerbated the urban heat island (UHI) effect, resulting in higher temperatures in metropolitan areas compared to rural regions. This phenomenon is primarily caused by the concentration of impervious surfaces, the scarcity of vegetation, and the heat produced by human activities. Numerous studies have investigated UHI mitigation strategies, including the use of vegetation, shading, enhanced materials, and urban geometry analysis. However, in existing neighborhoods, residents often have limited options for implementing these strategies to the building envelope.

This research evaluates various thermal mitigation strategies applied to the building envelope in the “El Carmen” neighborhood of Seville, utilizing the ENVI-met simulation tool. The objective is to enhance outdoor thermal comfort, as measured by the Universal Thermal Climate Index (UTCI). The study includes a validation and calibration phase of the simulations, followed by a parametric analysis of different envelope-based strategies. These strategies include the integration of vegetation, external thermal insulation systems with varying albedo, and the use of photovoltaic panels.

The analysis reveals that while roofs with insulation and photovoltaic panels do not improve outdoor thermal comfort at pedestrian height, green roofs and photovoltaic panels offer benefits at higher elevations for residents of adjacent buildings. Facades with external thermal insulation systems significantly worsen outdoor thermal comfort in the afternoon, raising the UTCI index by up to +6.8°C, with higher albedo contributing to greater discomfort. The most effective strategy combines green facades and green roofs, which markedly improve outdoor thermal comfort in the morning (up to -1.8°C) and in the afternoon (up to -5.1°C). The study concludes with an optimal proposal for neighborhood improvement.