Estimating heat flux transmission of vertical greenery ecosystem

Nurturing vegetation on building envelopes provides an innovative and eco-friendly alternative to urban greening especially in compact cities. Whereas the thermal and other benefits of green roofs have been studied intensively, green walls have received scanty attention. This study evaluates the thermodynamic transmission process of the vertical greenery ecosystem. We designed a field experiment to monitor solar radiation and weather conditions, and developed a thermodynamics transmission model to simulate heat flux and temperature variations. The model was calibrated, tested, and proved to be highly efficient. The results show that seasonal global and direct solar radiation drops to minimum in winter in January and February, and reaches maximum in summer in July and August (1168 W m−2 for global solar radiation and 889 W m−2 for direct solar radiation). Diffuse solar radiation attains maximum in summer (586 W m−2) with moderate rainfall in July and August, and minimum in winter with no rainfall in January and February. Radiation transmission of the green wall strongly correlates with canopy transmittance and reflectance (R2 = 0.83). Thermal shielding effectiveness varies with orientation, with the south wall achieving a higher coefficient (0.31) than the north wall. The south wall has lower heat flux absorbance and heat flux loss than the north wall. The south wall can transfer much more heat flux through the vertical greenery ecosystem due to more intensive canopy evapotranspiration effect. The model matches the transmission properties of green wall radiation, and the model simulation fits empirical transmission results.