Evaluating Facade Retrofitting Strategies for Indoor and Outdoor Thermal Comfort under Extreme Heat Events
A case study in Milan
M. Fardelli (TU Delft - Civil Engineering & Geosciences)
A. Luna Luna-Navarro – Graduation committee member (TU Delft - Building Design & Technology)
HR Schipper – Mentor (TU Delft - Applied Mechanics)
D. Maiullari – Graduation committee member (TU Delft - Environmental Technology and Design)
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Abstract
Due to climate change, heatwaves have increased their frequency, intensity and extent. In particu-
lar, in cities the phenomena is exacerbated due to the urban heat island effect. More than half of
the global population lives in urban areas. As a result, adapting the built environment to these
changing climatic conditions is becoming a priority. To address this need, the present research aims
to evaluate how different retrofit strategies influence outdoor and indoor thermal comfort during
heatwaves, bridging two aspects which are usually studied separated. The Acquabella district in
Milan is used as a case study.
The study includes a review on thermal comfort metrics, followed by an assessment of which metrics
are most suitable for comparing outdoor and indoor thermal comfort. An RC thermal model of a
facade was developed to identify the parameters who were mainly influencing the heat transfer,
which were then used to define the retrofit scenarios to be tested. The scenario considered include
two different aspect ratios, cool facades, external and internal insulation, and their combinations.
The outdoor microclimate was simulated with Envi-met, while indoor thermal conditions with
EnergyPlus. The outputs from Envi-met were used as boundary conditions for EnergyPlus.
The simulations outcomes revealed a strong correlation between the buildings and street geometry
and the varying impact of facade retrofitting on outdoor thermal comfort. Cool facade showed
a marked negative effect on outdoor thermal comfort particularly in courtyards, where inter-
reflection phenomena occurred more intensely. Nevertheless, cool facades also achieved the greatest improvement in SET, with a reduction of about 0.25°C. Across all scenarios, the wider street canyon consistently gave a better performance. While most existing studies focus exclusively on either the indoor or outdoor effects of facade retrofitting, the findings of the present study demonstrate the importance of assessing both, as interventions on the facade affect the two environments simultaneously and, in some cases, in contrasting ways.