Impact of ambient air temperature, orientation, and plant status on the thermal performance of green facades

The growing interest in energy savings and environmental sustainability in buildings has led to green buildings and green facades being considered as innovative solutions. This paper aimed to quantify the impact of ambient air temperature, orientation (west and north) and climbing plant status and type (leaf area index, percent coverage, deciduous and non-deciduous) on the thermal performance of green facades including external wall and gap cooling/warming effects. Temperatures of biological facades (i.e. green facade) and non-biological facades (i.e. shade sail) were monitored over 12 months in Perth, Western Australia, under a Mediterranean climate. Air temperatures within the gaps between the facade and external walls were also monitored. The average monthly daytime gap temperatures behind the green facades were always lower than ambient air and those behind the shade sails (up to 4 degrees C). The orientation of the facade relative to solar angle controlled the duration of solar irradiance; seasonal variations were observed in the relative contribution of evapotranspirative cooling to overall gap cooling, even in non-deciduous green facades. Despite the complex relationships between evapotranspirative cooling and a range of ecophysiological and micro-climate parameters, simple linear correlations were found between ambient air and gap temperatures (R2 > 0.8). This emphasizes the dominance of ambient air temperature in controlling the thermal performance of green facades. This thermal performance assessment and the gap temperature simulation can help urban designers, architects, and environmental engineers improve building and facade design to reduce energy consumption and greenhouse emissions.