Research on relationship between the thermo-physical parameters of green facade and leaf area index (LAI)

Green facades have become a common nature-based solution in dense urban areas and are widely used. The purpose of this study is to propose a method of obtaining more precise and optimal thermos-physical parameters of the greenery layer of green facades, and determine the thermos-physical parameters as functions of LAIs. The process of this method can be divided into 3 steps. Firstly, the thermal parameters of the green facade with different LAIs (1.07 similar to 4.54) are measured by experiment. Secondly, the optimal thermophysical properties of the greenery layer are calculated with orthogonal experiment method by COMSOL numerical and measured results. Finally, more optimal thermophysical properties are obtained with GA method by orthogonal analysis and measured results. The results show that the values of heat conductivity coefficient (lambda) and solar transmissivity(tau) will decrease, and density (rho) will increase when LAI becomes larger. However, specific heat (C-p), and solar absorptivity (alpha) are constants, not changing with LAIs. The regression curve equations for parameters lambda, rho and tau are fitted. The fractional function for lambda and polynomial function for rho and tau have high fitting and applicability. Finally, the thermo-physical properties of the greenery layer with two different LAIs are calculated by the fitting equations respectively, and verified by the measured parameters of corresponding LAI. The results show that the simulated results are coincident with experimental data satisfactorily. The results of this study can be used with building energy simulation tools and evaluate the energy saving and thermal performance of the green facades.