Characterizing the performance of green walls in building envelopes through simulation and prototyping

In modern life, people spend the majority of their day in office spaces. Therefore, maintaining elevated levels of indoor air quality is especially important. Natural ventilation to reduce CO2 levels can only be valuable if ambient air pollution levels do not exceed recommended margins (Cecchi 2014). However, urban air pollution is becoming even more concerning recently. Consequently, poor ambient air quality affects building occupants’ comfort (Moghbel and Erfanian Salim 2017). The use of green roofs and green walls as natural-based solutions in cities is considered in multiple studies to be feasible due to the presence of buildings with large areas available to accommodate them (Mohajeri, Gudmundsson, and Scartezzini 2015).

Findings indicate that green walls have a direct effect on indoor comfort throughout the entire building, whereas the effect of using green roofs is limited only to the upper floor. While lawns only provide an indirect effect (Malys, Musy, and Inard 2016). However, to further establish effective results, studies of vertical greenery systems should move on to design methodologies on actual building facades (Lundholm et al. 2010). Identifying the appropriate species of vegetation for each environment is challenging, considering the typical characteristics of varied species and the climatic conditions required for their development (Dunnett et al. 2008). The differences between the poorest and best-performing species, lifeforms, and mixtures are significant enough to suggest that informed plant selection should provide considerable improvement in the overall system performance. Numerous articles have focused on indoor phytoremediation, due to the ease of working in closed environments, and less variables, pollutant concentrations, environment, and lower plant diversity. (Prigioniero et al. 2021).

Nevertheless, the potential of enhancing indoor air quality through green walls within building envelopes is still unstudied. Although exposure chambers do have certain limitations (Rao et al. 2014), they allow measurements of plants' gaseous uptake in a highly controlled manner. Studies using exposure chambers have typically observed an effective reduction of the initial pollutant concentrations by plants (Prigioniero et al. 2021). Parhizkar and Elzeyadi (2020) demonstrated that plants show higher removal efficiencies when placed in enclosed spaces with a higher ratio of leave areas to chamber volumes, which also helps in increasing air filtration. Modelling approaches have been proposed to study plants’ ability to act as natural-based solutions in air phytoremediation. But they have not always been parameterized by experimental data obtained through targeted and precise laboratory practices (Prigioniero et al. 2021).

To compensate for the lack of information and the link between lab testing and real-life measurements it would be necessary to establish a methodology that allows full control of the experimental environment with the possibility to replicate the ambient environment. The idea of parametric performative design is highly growing and can integrate into advanced Building Performance Simulation which provides answers to the diverse needs such as thermal, lighting, acoustic, and ventilation performance. This study focuses specifically on the performative design of building modular green wall systems within the building facade. The methodology used in this study includes the creation of Python-based simulation components in the design software (Rhino), validation, optimization of the system, building digitally fabricated mock-ups, evaluating the performance of the module physically, and finally conducting digital experiments on the building scale digital