## 2 Materials and Methods
### Measuring Equipment  
The technical specifications of the measuring equipment used for NDT tests are presented in Table 1. For the _HFM_ tests, the inner equipment layout included three heat flux meter plates (HFP01, Hukseflux) with a thickness of 5.0 mm, a diameter of 80.0 mm, and a guard made of a ceramic-plastic composite, with an inside air temperature sensor (107, Campbell Scientific Inc., Barcelona, Spain) consisting of a thermistor encapsulated in epoxy-filled aluminum housing, both connected to an acquisition system (CR850, Campbell Scientific Inc., Barcelona, Spain) consisting of measurement electronics encased in a plastic shell with an integrated wiring panel with external power supply. The outer equipment consisted of an air temperature sensor and its acquisition system (175T1, Instrumentos Testo, SA, Barcelona, Spain). The optimal location of sensors was investigated with qualitative _IRT_, according to the procedures reported in ISO 6781:2015 [42] and UNE EN 13187:1998 [43]. In this way, it was possible to avoid unknown heterogeneities or disturbances (i.e., corners, the vicinity of junctions, direct solar radiation, and the direct influence of a heating unit) [22; 34; 61; 76]. The transducers were installed on the internal side of the prefabricated panels, to achieve the most stable operating conditions before and during the tests. Data loggers were configured to store the 30-minute averaged data in their memories, considering a sampling frequency of 1 s and a total test duration of 7 days. Quantitative infrared data (instantaneous wall surface temperature-\(T_{Wall}\)- and reflected ambient temperature-\(T_{REF}\)-) were recorded by using an IR camera (FLIR E60 bx) and FLIR TOOLS+ Software [83]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Equipment** & **Output** & **Measuring Range** & **Resolution** & **Accuracy** \\ \hline \multirow{3}{*}{\begin{tabular}{c} Heat flux meter \\ plate \\ \end{tabular} } & \multirow{3}{*}{\(q\) [W/m\({}^{2}\)]} & \(\pm\)2000 W/m\({}^{2}\) & & \\  & & Sensitivity of HFM 61.68 \(\upmu\)V/(W/m\({}^{2}\)) & & \\  & & Sensitivity of HFM 62.129 \(\upmu\)V/(W/m\({}^{2}\)) & & \\  & & Sensitivity of HFM 63.07 \(\upmu\)V/(W/m\({}^{2}\)) & & \\ \hline \multirow{3}{*}{\begin{tabular}{c} Inner air \\ temperature sensor \\ \end{tabular} } & \multirow{3}{*}{\(T_{IN}\) (\(K\))} & \(-\)35 to +50 \({}^{\circ}\)C & 0.1 \({}^{\circ}\)C & \(\pm\)0.5 \({}^{\circ}\)C \\ \cline{1-1} \cline{2-5}  & & & Input \(\pm\)5 Vdc at 0 to 40 \({}^{\circ}\)C & \(-\) & \(\pm\)0.06\% of reading \\ \hline \multirow{3}{*}{\begin{tabular}{c} Infrared camera \\ \end{tabular} } & \multirow{3}{*}{\
\begin{tabular}{c} \(T_{Wall}\) (\(K\)) \\ \end{tabular} } & Temperature: \(-\)20 to +120 \({}^{\circ}\)C & & \\  & & CFOV: 25\({}^{\circ}\)\(\times\) 19\({}^{\circ}\); IFOV: 136 mrad & & \\  & & Spectral Range: 7.5-15 \(\upmu\)m & 320 \(\times\) 240 pixels & \(\pm\)2 \({}^{\circ}\)C or \\  & & Thermal sensitivity: \(<\)0.045 \({}^{\circ}\)C, at 30 \({}^{\circ}\)C & & \\  & & Sensor: FPA, uncooled microbolometer & & \\ \hline \multirow{3}{*}{
\begin{tabular}{c} Outer air \\ temperature sensor \\ \end{tabular} } & \multirow{3}{*}{\(T_{OUT}\) (\(K\))} & \(-\)35 to +55 \({}^{\circ}\)C & 0.1 \({}^{\circ}\)C & \(\pm\)0.5 \({}^{\circ}\)C \\ \cline{1-1} \cline{2-5}  & & & \\ \hline \end{tabular}
\end{table} 
Table 1: Main technical specifications of the equipment. Hence, each _IRT_ test involved the post-processing of a sequential video with 120 or 180 thermograms. The wall surface emissivity (\(\varepsilon_{WALL}\)) was estimated at 0.88, for all walls, by means of aluminum crinkled foil (0.20 m \(\times\) 0.15 m). The IRT measurements were performed over a period of 2-3 h, with a data acquisition interval of 1 min. For both NDTs, the inner and outer ambient air temperatures were monitored by using the same integrated sensors (107, Campbell Scientific, Inc.; 175T1, Instrumentos Testo SA).