Emergy based evaluation of environmental performances of Living Wall and Grass Wall systems

Vertical Greenery Systems (VGS) are relatively new structures for architectural green cladding that embed a curtain of plants (Living Wall - hereafter LW) or grass (Grass Wall - hereafter GW) fixed on building facades and nurtured by an automated watering system. An eMergy evaluation (EE) of both LW and GW was performed aimed at assessing potential 'environmental costs' relative to their manufacturing chain, from plants-grass nursery to the assembling of structural elements, until
their sustenance in time. Contextually, benefits were estimated as the energy saving for cooling due to their shading and evaporative effect. A 98m2 south-oriented façade of a hypothetical 1000m3 building
has been investigated. EE is an environmental accounting method that accounts for direct and indirect environmental resource use by systems-processes in terms of solar energy equivalents (i.e. solar emergy joule - sej). The Cost to Benefit Ratio has been introduced, as the emergy investment per saved emergy (CBR: sej sej-1), in order to compare the environmental cost of structure functioning to the overall energy saving, in emergy terms. Results highlighted that, in certain conditions (i.e. Mediterranean climate,
massive envelope, integrated rainwater harvesting system) both LW and GW can provide net environmental benefits and be valuable options for building retrofitting.