Vertical vegetation design decisions and their impact on energy consumption in subtropical cities

Abstract

Vertical vegetation is vegetation growing on, or adjacent to, the unused sunlit exterior surfaces of buildings in cities. Vertical vegetation can improve the energy efficiency of the building on which it is installed mainly by insulating, shading and transpiring moisture from foliage and substrate. Several design parameters may affect the extent of the vertical vegetation's improvement of energy performance. Examples are choice of vegetation, growing medium geometry, north/south aspect and others. The purpose of this study is to quantitatively map out the contribution of several parameters to energy savings in a subtropical setting. The method is thermal simulation based on EnergyPlus configured to reflect the special characteristics of vertical vegetation. Thermal simulation results show that yearly cooling energy savings can reach 25% with realistic design choices in subtropical environments. The most important parameter is the aspect of walls covered by vegetation. Vertical vegetation covering walls facing north (south for the northern hemisphere) will result in the highest energy savings. In making plant selections, the most significant parameter is Leaf Area Index (LAI). Plants with larger LAI, preferably LAI>4, contribute to greater savings whereas LAI<2 can actually consume energy. Change of growing medium thickness from 6cm to 8cm causes a dramatic increase in energy savings from 2% to 18%. It is best to use a growing material with high water retention, due to the importance of evapotranspiration for cooling. Similarly, for increased savings in cooling energy, sufficient irrigation is required. To conclude, the choice of design parameters for vertical vegetation is crucial in making sure that it contributes to energy savings rather than energy The Sustainable City VII, Vol. 1 489 consumption. Optimal design decisions can create a dramatic sustainability enhancement for the built environment in subtropical climates.

Green Facades and Living Walls—A Review Establishing the Classification of Construction Types and Mapping the Benefits

“…Some of the results of thermal simulation by Stav and Lawson [66] show that yearly cooling energy savings can reach 25% with realistic design choices in subtropical environments. "Vertical garden had an efficiency much lower than that of commercial swamp coolers (11% vs. up to 90%).…”

Living walls in indoor environments

“…This is influenced by the evidence discussed earlier in relation to optimal surface cooling benefits being evident during this period. There is preference for this hypothesis to be investigated using simulation studies, with simulations by Stav & Lawson [40] and Kontoleon & Eumorfopoulou [32] for example having estimated reduced indoor temperatures, better thermal comfort, and reduced cooling loads. The dominant preference however is for using experimental design, with many examples presented for the different categories and their variants identifying cooling energy savings.…”

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

“…Based on micro-scale modeling, Hong Kong could experience a 66% decrease in cooling load due to green walls [17]. A study using the EnergyPlus software with various vegetation parameters and scenarios (vegetation height, saturation volumetric soil moisture content and irrigation rate) estimated energy savings ranging from À12% to 20% [20]. In another study, the saving of annual energy loads for cooling by south and west facing vegetated walls in lightweight and heavyweight model formulated using the ECOTECT environmental simulation software were 23% and 11%, respectively [21].…”