Porous plant form-induced amplification of evapotranspiration for enhanced cooling in vertical greenery systems

Vertical Greenery Systems (VGS) installed on building façades have recently gained significant attention for its urban cooling potentials. While current research primarily leans on the Leaf Area Index to estimate the VGS cooling potentials, the evaporative cooling effects of VGS growing media, has largely been overlooked. In particular, the effect of plant growth form on air movement within the VGS, which could notably augment the rate of evapotranspiration, has commonly been ignored. To address this gap, our study undertakes a comprehensive thermal analysis of two distinct plant growth forms (porous and dense), combining systematic Computational Fluid Dynamics simulations with field experiments over a six-month period. Our results, for the first time, demonstrate that the provision of a porous VGS significantly enhances its cooling effects, which could even lead to a negative façade heat flux. Our findings offer a novel perspective for plant and growing media selection in VGS design.