Experimental investigation on thermal performance and dynamic thermal property indices of green facades in hot and humid climates

• Published in: Journal of Building Engineering Vol. 108; p. 112840
• Main Authors: Li, Cuimin, Xu, Laiyong, Xie, Jixing, Li, Chunying
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.08.2025
• Subjects: External wall surface temperatures; Green façades; Heat flux reduction; Thermal diffusivity; Thermal storage coefficient; External wall surface temperatures; Thermal diffusivity; Green façades; Thermal storage coefficient; Heat flux reduction
• ISSN: 2352-7102; 2352-7102
• DOI: 10.1016/j.jobe.2025.112840

To further investigate the impact of green facades (GFs) on building cooling loads under varying environmental conditions, this study conducted field experiments using GFs on a school building located in a humid subtropical climate. The effectiveness of GFs was evaluated by quantifying their ability to reduce external wall surface temperatures and mitigate heat flux through the building envelope. To enhance the accuracy of characterizing GF performance under non-steady-state conditions, a novel method was proposed to calculate thermal diffusivity and thermal storage coefficients under periodic boundary conditions. These thermal properties of GFs were then derived from experimental data collected during the study. Field measurements were conducted over a one-week summer period on a school building, with sensors installed on three configurations: a bare wall (P1), a small-leaf plant GF (P2), and a large-leaf plant GF (P3). Results demonstrated that GFs significantly lowered both external wall surface temperatures, with maximum reductions of 7.76 °C (P2) and 9.73 °C (P3) observed. Notably, GFs introduced a phase lag in temperature fluctuations and heat flux propagation, delaying peak loads and reducing internal wall heat flux density. Attenuation ranges of heat flux density were 2.06 ∼ 5.2 W/m2 (P2) and 2.53 ∼ 9.16 W/m2 (P3). Under experimental conditions, GFs exhibited average thermal diffusivity values of 3.92 × 10−7 m2/s (P2) and 1.6 × 10−6 m2/s (P3), with thermal storage coefficients of 0.22 J/(m2 s K) (P2) and 0.32 J/(m2 s K) (P3), with thermal conductivities of 0.0246 W/(m·K) (P2) and 0.0338 W/(m·K) (P3), respectively. The substantial reduction in exterior surface temperatures and heat flux into the building envelope underscores GFs’ potential to lower cooling demands. The proposed method for calculating thermal performance can assist in calculating the long-term performance and energy-saving effect of GF under real transient conditions. These thermal property indices—thermal diffusivity, storage coefficient, and conductivity—can serve as GF-specific design parameters for building energy models, facilitating direct comparisons with conventional materials. •Green facades delayed and attenuated external wall surface peak temperature effectively.•Green facades reduced the heat flux density through the building envelope significantly.•A novel thermal assessment framework was developed for cyclical transient-state conditions.•Dynamic thermal diffusivity, thermal storage coefficient, and conductivity were calculated.