Numerical modelling validation of a living wall in a facade fire test

Vertical Greenery Systems (VGS) are a modern biodiversity improvement in the built environment. Previous research on the fire safety of living walls has focused on the fire spreading potential through vegetation in different moisture contents.

The main objective of this work is to decouple fire hazards from vegetation and groundcover systems related to the modular living wall (LW) in building exterior applications. For this purpose, we implemented experimentally determined fire spread data to model the fire behaviour of the LW including organic materials and polymeric pots. The results obtained numerically were compared with full-scale experiments at various moisture content of vegetation. Fire Dynamics Simulator (FDS) was used for the numerical study. This CFD code solves numerically a form of the Navier-Stokes equations appropriate for low Mach number, thermally-driven flow with emphasis on smoke and heat transport from fires. In the present study, a one-dimensional pyrolysis model was used to model a groundcover system filled with soil as a multi-layer solid body in Cartesian coordinates combined with a discrete Lagrangian particle vegetation model with thermal degradation. Reaction kinetics of pyrolysis and combustion process was incorporated based on vegetation fires state-of-art parameters.

Reaction to fire of soil supports elements (groundcover systems) is an important element in a comprehensive fire safety assessment of living walls. Hydrated plants do not affect the flame spread and are charred by heat radiation, while dried plants have increased ignition sensitivity and are involved in combustion. The separation of the fire hazard generated by vegetation and groundcover systems, makes it possible to predict the development of a living wall fire at arbitrary configuration. The fire validated living wall model with adjustable moisture content can be used in further studies to evaluate the fire behavior of living wall in an actual building application.