# Facades-as-a-Service: The Role of Technology in the Circular Servitisation of the Building Envelope
## 3 Materials and Methods
### Case-Study Implementation through Full-Scale Field Prototypes  
The case-study phase consisted of two field pilot prototypes [48] using fully operational TU Delft buildings as case studies during the facade leasing research project (2015-2020).  
The project focused on (1) developing working, full-scale facade-as-a-service (FaaS) built prototypes, through which to identify technical drivers and barriers to implementation, and (2) finding organisational, managerial, and regulatory solutions to address these drivers and barriers, by exploring the legal, financial, and corporate implications of a PSS model for the contracting of facades-as-a-service (FaaS).  
The two full-scale pilot prototypes built were:  
_The EWI faculty building Facade Leasing technical mock-up (2017)_, in which was explored the technological readiness of modular facade-integrated technologies to deliver energy savings and indoor-comfort improvements in a generic meeting and lecture room at the target building [49].  
_The CiTG faculty building large-scale demonstrator prototype (2019)_, in which were explored the broader systemic drivers and barriers to the implementation of facade-integrated technologies through a PSS contract, beyond the purely technical. The project resulted in the deep energy retrofit of over 2.600 m\({}^{2}\) of the target building's facade [50; 51]. Figure 1 shows the new CiTG facade system, which includes centrally monitored and controlled operable windows, an upper ventilation window to enable night-cooling during warm summer nights, and vastly improved thermal performance of both framing and panelling.  
In the process of engineering and developing the FaaS pilot projects we listened to the requests of diverse stakeholders for new and existing functional requirements which need to be physically or digitally in place in order to enable the construction, financing, operation, management and/or monitoring of a FaaS contract, as well as the high-value maintenance and recovery of components and materials. This research-through-design approach was based on an ongoing feedback loop between researchers and stakeholders during a design, engineering, and planning phase spanning almost a year--in the case of the small-scale EWI pilot project--and nearly two years in the case of the CiTG large-scale pilot project. The research-through-design feedback loop is illustrated in Figure 2.  
The study was carried out in an iterative feedback process bridging supply and demand, academy and industry. Due to the innovative and explorative nature of the Facades-as-a-Service model few references could be found beforehand to determine the exact technical and organisational challenges that would be faced in practice, or the entire range of technical solutions which would be needed to address these challenges. The research consortia, therefore, approached the problem as a practical engineering and business modelling process, testing the system through real-life case-study projects and implementing diverse facade-related technologies as specific and unexpected challenges  
Figure 1: Interior photograph of the FaaS facade renovation at the CiTG faculty building large-scale demonstrator prototype, at TU Delft, in the Netherlands. Credits: [PERSON], 2019.  
Figure 2: Research-through-design feedback loop in the multi-staleholder co-creation process of the two facade leasing (FaaS) prototypes.  
related to the FaaS model implementation and operation emerged. These iterative technical development steps, and their relevance to a circular facade economy, are reviewed and structured in a FaaS development matrix.