## 1 Introduction  
A great recent challenge has been to reach world climate-neutrality by 2050, and at this moment, with the buildings sector still being responsible for 40% of greenhouse gas emissions and 36% of final global energy consumption, it is clear that perspectives must change [1]. For the construction of skyscrapers during the 20 th century, architects and building designers focused on high-rise buildings made of concrete and metal structures wrapped in glass facades. These shiny and high-energy-consumption buildings are no longer in accordance with the standards and needs of our times. Thus, strict energy requirements are emerging around the world, making buildings and energy systems more efficient and sustainable. The Renovation Wave and Nearly Zero-Energy Buildings (NZEB) regulations in Europe [2] are part of the objectives of this global movement for highly efficient new buildings and highly efficient deep renovated buildings to prepare the European Union for a decarbonised and clean-energy future. To work towards a successful energy transition, a new energy system must be proposed, and the architecture of buildings must be thought of in a more sustainable way. The energy-efficient solutions can be embedded in the building structure, and from these, our attention is focused on the building envelope/facade. Building facades can facilitate the access to a huge source of energy, which, for a long time, has been ignored in the building conception phase. The building envelope has the capacity to capture large amounts of free energy from the sun [3]. Active ventilated facades, such as Transpired Solar Collectors (TSC), have the advantage of insulating the building envelope and providing heated air for the building'sthermal needs [4]. Thus, the TSC can reduce the building's energy use and provide a clean, renewable energy source for air heating. In this wide domain of Building-Integrated Solar Thermal Systems, we find the Transpired Solar Collectors (TSC) as being among the most efficient ones. TSCs can be glazed (GTSC) or unglazed (UTSC), usually being implemented on large-scale facades, such as those used for industrial buildings, office or multi-family residential buildings, as well as for ventilation and space-heating during cold periods. This kind of solar air collector has the advantage of being affordable and easy to integrate for a building retrofit. [PERSON] et al. found [5] that the use of modular UTSC could cover ventilation heating needs for an apartment for about 74.6% of the days examined during their study. Furthermore, in addition to air heating purposes, UTSCs have the potential to be used for nocturnal passive cooling, and this increases the annual yield of such a system [6]. During the last three decades, transpired solar collectors have been intensely analyzed through numerical and experimental approaches. Computational Fluid Dynamics (CFD) have initially been applied to TSCs via 2D numerical models [7] highlighting heat transfers occurring on the perforated absorber plate. The same team conducted by [PERSON] et al. [8] revealed the importance of the suction velocity to mitigate the negative impact of the wind on thermal behaviours of TSCs. They found an optimal range of suction velocity from 0.0125 to 0.039 m/s. In the early 2000s, [PERSON] et al. [9] highlighted several specificities concerning TSC, such as the non-uniform distribution of the heat transfer through the collector. They assessed that heat transfer occurred for about 62% on the front, 28% in the hole and 10% on the back of the plate. In 2002, a group of researchers led by [PERSON] and [PERSON] [10] profoundly contributed to the understanding of the thermal behaviour of TSC, focusing on the absorber plate characteristics, the suction velocity, and the wind speed [11]. One of the main advances in their work was observing the low influence of the conductivity of materials on the thermal behaviour of the TSCs, which only a few works in the literature have demonstrated.