## 3 Results
### HFM Average Method  
Both the experimental mock-up and the detached house were monitored for 168 h, obtaining 337 datasets of readings for each case. The experimental campaign of the building mock-up was conducted with a heater, with an average air temperature difference much higher than 15 \({}^{\circ}\)C [79]. However, the experimental campaign of the detached house was performed under actual environmental conditions, which ensured that the average temperature difference was greater than 10 \({}^{\circ}\)C [20; 21] (Figure 5). Hence, the temperature during process monitoring was not a significant factor that influenced the results of the second case study. Measurement periods, as well as the average temperatures differences, are detailed in Table 4.  
The measured thermal transmittances and their related uncertainty were calculated in 7 consecutive cycles of 24 h (Equations (1) and (2)), using accumulative data. Thus, the first cycle was calculated with data obtained during the first 24 h tested, the second cycle with data from the first 48 h tested, \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Experimental Mock-Up**} & \multicolumn{4}{c}{**Detached House**} \\ \hline \hline  & & \(\begin{array}{c}\mathbf{U_{mHMM}\pm}\\ \mathbf{u_{c}(U)}\end{array}\) & \(\begin{array}{c}\left|\begin{array}{c}\mathbf{U_{m}-u_{m}}\\ \mathbf{u_{c}}\end{array}\right|\\ \mathbf{v_{c}(\%)}\end{array}\) & \(\begin{array}{c}\mathbf{CV}\\ \mathbf{v_{c}(U)}\end{array}\) & \(\begin{array}{c}\mathbf{U_{mHMM}\pm}\\ \mathbf{u_{c}(U)}\end{array}\) & \(\begin{array}{c}\left|\begin{array}{c}\mathbf{U_{t}-u_{m}}\\ \mathbf{u_{c}}\end{array}\right|\\ \mathbf{v_{c}(\%)}\end{array}\) & \(\begin{array}{c}\mathbf{CV}\\ \mathbf{v_{c}(\%)}\end{array}\) & \(\begin{array}{c}\mathbf{CV}\\ \mathbf{v_{c}(\%)}\end{array}\) & \(\begin{array}{c}\mathbf{CV}\\ \mathbf{v_{c}(\%)}\end{array}\) \\ \hline \multirow{4}{*}{**Number of cycles (duration)**} & **1 (24 h)** & \(0.246\pm 0.018\) & 0.33 & – & \(0.212\pm 0.018\) & 8.84 & – \\ \cline{2-6}  & **2 (48 h)** & \(0.244\pm 0.013\) & 0.35 & – & \(0.225\pm 0.014\) & 3.47 & – \\ \cline{2-6}  & **3 (72 h)** & \(0.248\pm 0.011\) & 1.05 & 1.39 & \(0.225\pm 0.012\) & 3.06 & 6.80 \\ \cline{2-6}  & **4 (96 h)** & \(0.246\pm 0.009\) & 0.44 & 1.40 & \(0.227\pm 0.010\) & 2.37 & 1.15 \\ \cline{2-6}  & **5 (120 h)** & \(0.249\pm 0.008\) & 1.59 & 1.13 & \(0.227\pm 0.009\) & 2.33 & 0.84 \\ \cline{2-6}  & **6 (144 h)** & \(0.250\pm 0.008\) & 1.98 & 1.57 & \(0.230\pm 0.008\) & 1.13 & 1.43 \\ \cline{2-6}  & **7 (168 h)** & \(0.251\pm 0.007\) & 2.41 & 0.81 & \(0.225\pm 0.008\) & 3.09 & 2.02 \\ \hline \multicolumn{2}{c}{**Measurement period**} & From 29 December 2016 to 4 January 2017 & From 26 February 2019 to 4 March 2019 \\ \hline \multicolumn{2}{c}{**AT average (\({}^{\circ}\)C)**} & \multicolumn{2}{c}{19.7} & \multicolumn{2}{c}{10.8} \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Measured U-values and their associated combined uncertainties, deviation between theoretical and measured U-value, and coefficient of variation of the measured thermal transmittance in both the experimental mock-up and the detached house, using the _HFM_ average method. Figure 5: Temperature data obtained from the process of monitoring for both (a) the experimental mock-up and (b) the detached house. and successively for each cycle, up to the seventh day. The results obtained are depicted in Figure 6 and detailed in Table 4, where Um-HFM \(\pm\) U(C) is the measured thermal transmittance, using the HFM average method and its associated uncertainty. It is noteworthy that uncertainties of measurement decreased as the tests were extended and when the average air temperature difference increased, which is in line with the results obtained by [PERSON] et al. (2018) and [PERSON] et al. (2018).