Energy saving potential and life cycle environmental impacts of a vertical greenery system in Hong Kong: A case study

• VGS on the exterior wall could reduce electricity consumption for cooling in a flat.
• LCA was conducted to analyze the environmental impacts of VGS.
• Environmental burdens of VGSs could be paid back in 20 years.
• VGS on building envelope is environmentally sustainable regarding energy saving.

Although there is increasing demand for vertical greening in urban areas, few studies have examined its environmental impacts. The aim of this study was to quantify the environmental benefits and burdens of a commercially available vertical greenery system (VGS). The electricity consumption for cooling in flats with and without a VGS (8.22 m2) in a public housing estate in Hong Kong was compared. A life cycle assessment (LCA) was conducted to analyze the environmental burdens of the VGS in its material, transportation, use and end-of-life stages. The daily electricity saving by the VGS in sunny, cloudy and rainy day in summer were 1.30, 0.84 and 0.71 kW h, respectively. The VGS saved as much as 16% of the electricity consumed for air-conditioning in August and September which are typical hot and wet summer months. The material stage contributed to 43–97% of all the environmental impact categories. A comparison of the environmental burdens and benefits gained from cooling showed that the environmental burden of the VGS in regard to abiotic depletion of fossil fuels could be paid back in 20 years. Overall, vertical greeneries installed on building walls can conserve energy for cooling in summer and are an environmentally sustainable option in cities where there is little land available for urban landscaping and gardening.

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