## 2 Materials and Methods
### In Situ Measurement of Facades' Thermal Transmittance
#### 2.3.1 Instrumentation  
Proper instrumentation was carefully selected for the in situ measurement of the actual thermal transmittance of the walls. The apparatus consisted of an internal acquisition system, to which two heat flow plates and an internal environmental temperature sensor  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Case Study**} & \multirow{2}{*}{**No. Layer**} & \multirow{2}{*}{ \begin{tabular}{c} **Material Layer** \\ **(Inside-Outside)** \\ \end{tabular}  } & \multirow{2}{*}{**Thickness (m)**} & \multicolumn{2}{c}{**Thermal**} & \multicolumn{2}{c}{**Thermal**} & \multicolumn{2}{c}{**Total**} & \multicolumn{2}{c}{**Theoretical**} \\  & & & **Conductivity** & **Resistance** & **Thickness** & **U-Value** \\  & & & & **(W/m\(\cdot\)K)** & **(m\({}^{2}\cdot\)K/W)** & **(m)** & **(W/m\({}^{2}\cdot\)K)** \\ \hline \multirow{4}{*}{Case study 1} & \multirow{4}{*}{ \begin{tabular}{c} 1 \\ 2 \\ 3 \\ \end{tabular}  } & \multirow{4}{*}{ \begin{tabular}{c} 1 \\ 2 \\ 3 \\ \end{tabular}  } & \multirow{4}{*}{ \begin{tabular}{c} 0.13 \\ 2 \\ 3 \\ \end{tabular}  } & \multirow{4}{*}{\ \begin{tabular}{c} 0.12 \\ 2.20 \\ 3 \\ \end{tabular}  } & \multirow{4}{*}{ \begin{tabular}{c} 2.20 \\ 2.00 \\ 3 \\ \end{tabular}  } \\  & & & & & &  
were connected, and an external environmental temperature sensor with its acquisition system. Table 3 summarises the main specifications and a priori accuracy of the calibrated instrumentation. The monitoring process was designed following ISO guidelines [31]. Taking into account the considerations of [PERSON] et al. [14], [PERSON] et al. [16], [PERSON] et al. [41], [PERSON] et al. [49; 50], [PERSON] et al. [51] and [PERSON] et al. [52], the placement of equipment was examined with an infrared thermographic camera (FLIR E60 bx Infrared Camera). Proximity to defects, joints and borders of the wall, direct solar radiation and direct impact of heating or cooling devices were avoided, as recommended by [PERSON] et al. [42] and [PERSON] et al. [53]. The two heat flow meter plates were placed on the inner side of the wall due to it is the location where the temperature was most stable. Proper thermal contact was ensured between the entire area of one heat flow meter plate and the wall surface by carefully applying a layer of thermal interface material. The other heat flow meter plate was meticulously installed by applying a film between the layer of thermal interface material and the wall (Figure 2), which is usual procedure to protect the wall surface, as described in Section 1. During the experimental campaign, climatic conditions were observed. The monitoring process took into consideration that the internal environmental temperature always exceeded the external environmental temperature, ensuring a stable heat flow direction. Alternating this flow direction could lead to inaccurate measurements, as described by [PERSON] et al. [43], and could greatly influence the minimum test duration and the variability of the results [39]. Data were sampled every 1 s and recorded every 30-min averaged data in both dataloggers. Figure 2: View of two heat flow meter plates, without and with a film between the layer of thermal interface material and the wall surface. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type of Equipment** & **Model and Manufacturer** & **Range** & **A Priori Accuracy** \\ \hline Heat flow meter plates & HFP01, Hukseflux & \(\pm\)2000 W/m\({}^{2}\) & \(\pm\)5\% \\ \hline Inside environmental temperature sensor & T107, Campbell Scientific, Inc. & \(-\)35\({}^{\circ}\) to +50 \({}^{\circ}\)C & \(\pm\)0.5 \({}^{\circ}\)C \\ \hline Inside acquisition system & CR850, Campbell Scientific, Inc. & Input \(\pm\)5 Vdc & \(\pm\)0.06\% of reading \\ \hline Outside environmental temperature sensor and its acquisition system & 1751, Instrumentos Testo, SA & \(-\)35\({}^{\circ}\) to +50 \({}^{\circ}\)C & \(\pm\)0.5 \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Main specifications of the instrumentation.