## 3 Results  
The data acquisition process was conducted following the indications in Section 2, with a sampling duration of 168 h in Case study 1 (337 readings) and of 144 h in Case study 2 (289 readings). Two measured thermal transmittances and its confidence interval were calculated, for 24-h test cycles using the dynamic method in the two case studies [54]. One value was calculated using data from the heat flow meter plate installed with a layer of thermal interface material directly on the wall surface and the other value was calculated using data from the heat flow meter installed with a PVC film between the layer of thermal interface material and the wall. The minimum test duration was checked considering the ISO standard [31]. The first requirement is that the sampling duration must be an integer of 24 h and at least 72 h (Equation (3)). Consequently, the second and third requirements were verified from the third day onwards. The second requirement for test completion is that the value of thermal transmittance obtained at the end of the sampling duration shall not deviate more than 5% from the value obtained 24 h before (Equation (4)). In accordance with this condition, in Case studies 1 and 2 the test could be ended after 72 h, as the requirement was met for all cycles with both HFM installation methods. The last requirement for ending the test is that the U-value obtained by analysing data from the first 2/3 of the sampling duration shall not deviate more than 5% from the value obtained from the data for the last period of the same length (Equation (5)). According to this condition, in Case study 1 the monitoring process could be ended in 96 h using an HFM installed directly on the wall surface and in 120 h when an HFM was used with a PVC film between the layer of thermal interface material and the wall surface. In Case study 2, the test could be stopped at 72 h when the heat flow meter was installed directly on the wall surface and in 120 h when the heat flow meter was installed with a PVC film between the layer of thermal interface material and the wall surface. The minimum test duration when using an HFM installed directly on the wall surface was found to be shorter than when using an HFM installed with a PVC film between the layer of thermal interface material and the wall surface. The results of the measured thermal transmittance for the two case studies are shown in Table 5 and depicted in Figure 4, where \(U_{m\text{-}Dyn\pm 195\%}\) is the measured U-value using the dynamic method, \(HFM_{NF}\) indicates the use of a heat flow meter plate installed with a layer of thermal interface material directly on the wall surface and \(HFM_{F}\) indicates the use of a heat flow meter installed with a PVC film between the layer of thermal interface material and the wall. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Duration of the Test (h)**} & \multicolumn{2}{c}{**Case Study 1**} & \multicolumn{2}{c}{**Case Study 2**} \\ \cline{2-5}  & \multicolumn{2}{c}{\(\mathbf{U_{m\text{-}Dyn}\pm I_{95\%}\) (W/m\({}^{2}\cdot\mathbf{K}\))}} & \multicolumn{2}{c}{\(\mathbf{U_{m\text{-}Dyn}\pm I_{95\%}\) (W/m\({}^{2}\cdot\mathbf{K}\))}} \\ \cline{2-5}  & \multicolumn{2}{c}{\(\mathbf{HFM_{NF}}\)} & \(\mathbf{HFM_{F}}\) & \(\mathbf{HFM_{NF}}\) & \(\mathbf{HFM_{F}}\) \\ \hline
24 h & 2.19 \(\pm\) 0.12 & 2.03 \(\pm\) 0.10 & 0.34 \(\pm\) 0.02 & 0.27 \(\pm\) 0.02 \\
48 h & 2.21 \(\pm\) 0.10 & 1.62 \(\pm\) 0.05 & 0.35 \(\pm\) 0.01 & 0.28 \(\pm\) 0.01 \\
72 h & 2.25 \(\pm\) 0.09 & 1.64 \(\pm\) 0.05 & 0.35 \(\pm\) 0.01 & 0.27 \(\pm\) 0.01 \\
96 h & 2.24 \(\pm\) 0.06 & 1.69 \(\pm\) 0.03 & 0.34 \(\pm\) 0.01 & 0.27 \(\pm\) 0.01 \\
120 h & 2.24 \(\pm\) 0.05 & 1.70 \(\pm\) 0.03 & 0.35 \(\pm\) 0.01 & 0.28 \(\pm\) 0.01 \\
144 h & 2.23 \(\pm\) 0.04 & 1.70 \(\pm\) 0.02 & 0.35 \(\pm\) 0.01 & 0.28 \(\pm\) 0.01 \\
168 h & 2.24 \(\pm\) 0.04 & 1.70 \(\pm\) 0.02 & - & - \\ \hline \end{tabular}
\end{table}