Multidimensional analysis of temporal and layered microclimatic behavior of subtropical climber green walls in summer

Existing studies emphasizing the magnitude of green-wall thermal benefits paid little attention to temporal microclimatic behavior. To bridge the knowledge gap, we employed high-precision sensors to monitor the microclimate of two wirerope-type climber green walls and adjacent control bare walls in humid-subtropical Hong Kong. Sample days were systematically selected to represent the results on sunny, cloudy and rainy weather in summer. This study aimed at: (1) evaluating the magnitude and daily temporal occurrence of maximum temperature, cooling and insolation at different positions of the layered green walls, and (2) analyzing temporal occurrence patterns of maximum values of microclimatic variables. The results demonstrated the paramount importance of insolation on green-wall microclimate. Varied solar inputs under different weather brought a sequence in maximum insolation, temperature and cooling: sunny > cloudy > rainy. Achieving an average cooling of 8.5 °C against bare wall surface exterior on sunny days, climber foliage acted as a heat sink for the street canyon and the building shell. The posterior air gap (PAG) generated an effective insulation layer with average cooling of 2.5 °C against ambient air in sunny conditions. However, ambient air anterior to the green wall experienced minor warming up to 0.05 °C. Cooling was stronger on more solar-exposed aspect and under stronger insolation. Green walls steered humidification effect by 0.17 kPa on average on sunny days. Daily temperature oscillation was moderated most obviously at the building exterior with average 4.3 °C reduction in sunny conditions. Implications were drawn on climber-species selection and PAG provision to enhance the multi-dimensional thermal benefits of climber green wall.