# Exploiting the Value of Active and Multifunctional Facade Technology through the IoT and AI
## 3 The Multifunctional Facade Concept  
There is no unambiguous definition of the MF. Despite years of investigation, the \"multifunctional\" term refers to a wide range of functionality and, consequently, technologies that are difficult to fit into closed classifications. For this study, the term MF refers to a fully prefabricated modular building envelope that includes passive and active components to provide a set of non-traditional and customizable functions (Figure 1) [13]. Passive components are generally no-energy-using technologies to assure basic functions, and active components represent additional sub-systems powered by energy for improving or expanding facade functionality. On the one hand, passive components refer to insulation panels, internal or external solar shadings, and other technologies needed to ensure the main envelope functionality, such as mechanical behavior, thermal resistance, air and water tightness, and noise reduction. On the other hand, a wide range of technologies can be considered active components, able to improve facade performances or provide new customized services such as mechanical ventilation or renewable energy systems (RES) [16; 27]. In this context, several EU-funded projects have been developed in the last fifteen years to test and validate the technical feasibility of MF systems [5; 11], as they are considered impactful technologies for starting deep renovation schemes of the existing building stock [28]. Indeed, most of the EU-funded projects presented in Table 1 aim to develop a fully prefabricated facade for building retrofits. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**EU Project** & **Project Year** & **MF Technology Description** & **TLR** & **Website Ref.** \\ \hline Meefs & 2012–2016 & Meefs develops two new energy-efficient modules for retrofitting including PV panels, solar thermal units, and a green facade module. & TLR 9 & [29] \\ \hline Adaptiwall & 2013–2017 & Adaptive wall is a novel panel consisting of 3 elements: lightweight concrete with nano additives; adaptable polymer for switchable thermal resistance; and a total heat exchanger with nanostructured membrane. & TLR 9 & [30] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: EU-funded projects on multifunctional facades. Figure 1: MEZeroE multifunctional facade theoretical scheme (credit [PERSON]). From a qualitative assessment of these projects, some considerations can be made. According to the type of technology to be integrated, different types of Technology Readiness Levels (TRLs) have been reached, and different market adoptions have occurred. Firstly, as demonstrated by Meefs and Energy Matching projects, the integration of RES, including solar and PV modules, has been viable for the construction market for several years [5]. Concerning RES technologies, obstacles to the widespread adoption of MF systems still relate to architectural, aesthetic, and energy efficiency issues. In this context, an intriguing perspective, as explored in the Plug-N-Harvest case, involves incorporating batteries for energy harvesting to transform the facade into active nodes of smart microgrids [36]. Although this perspective is very attractive, the lack of a multi-scalar infrastructure (from the building to the city) limits its application. In addition to this, the integration of advanced materials has gained much interest among researchers. In the AdaptiWall project, phase-change nanomaterials were integrated to enhance energy performance and control temperature, moisture, and indoor health. The integration of such advanced materials is still hampered by higher costs with respect to traditional materials and a lack of knowledge by designers, as well as a lack of communication across the entire supply chain [37]. Again, several EU projects are exploring the benefits of \"plug & play\" facades capable of integrating HVAC systems. Such an approach holds significant promise for technologically upgrading the existing building stock, which must meet escalating comfort and efficiency demands [38].