## 3 Results
### Phase 2--Sensor Sensitivity Adjustment
In this case, it is obvious that the initialization, which was done between Day 1 and 14, is out-of-date and not effective anymore. The entire process of re-initialization can be easily done by utilizing the principles of the proposed method. The discrepancy detected in this particular case could be attributed to the overall change in environmental conditions (represented by temperature in the first place). However, occupants' behavior associated with an excessive increase of convection or radiation may be a causation as well. On the other hand, the heat flux data from the FHF01 surface probe (green line) obtained by using default factory calibration proved to be insufficient for a building performance analysis as the probe undervalued the heat flux to a significant extent. This fact, indicating the low sensitivity of the sensor, may bring major uncertainties to any analysis built on those outputs. Therefore, a custom calibration was essential to improve the sensor accuracy and to keep the sensor involved as an integrated part of the experimental arrangement. The sensor sensitivity adjustment (see Figure 10) was done by means of seeking for such a combination of \(A\) and \(B\) coefficients that will produce the least \(RMSE\) between average value of \(q_{\rm IN}\) and \(q_{\rm OUT}\), i.e., \(q_{\rm REF}\) (see Section 2.2, step 4), and the heat flux \(q_{\rm EXP,\,adj}\) calculated from the raw data as  
\[q_{\rm EXP,adj}(t)=A\cdot U(t)+B, \tag{8}\]  
where \(U(t)\) is the thermoelectric voltage recorded on the thermopile (heat flux probe) in particular time \(t\). Following Equation (2), when the condition \(T_{\rm i}=T_{\rm s}\) is met, a zero-heat flux should occur on the interior surface of the wall. However, the quick inspection of experimental data revealed that when \(T_{\rm i}=T_{\rm s}\), a non-zero-heat flux is detected by the surface probe indicating that some kind of systematic error is present in the measurement. Regardless the source of that error, searching for the adjusting function \(S\) in the linear form should compensate this type of error. Such an approach to the sensor adjustment makes the entire process slightly different from that performed by the manufacturers, which usually tend to determine the sensitivity as a single value  
It should be noted that the data presented in Figure 10 are supposed to be carefully analyzed to provide relevant information on the applicability of the designed calibration procedure or to suggest modifications that might improve the approach with respect to the particular areas of its application. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Period** & \(A\) **(W**\(\cdot\)**V\({}^{-1}\)**\(\cdot\)**m\({}^{-2}\))** & \(B\) **(W**\(\cdot\)**m\({}^{-2}\))** & _RMSE_ \\ \hline
28 September 2020–4 October 2020 & 0.4880 & 0.8915 & 1.078 \\
30 November 2020–6 December 2020 & 0.3412 & 0.2712 & 0.888 \\
1 February 2021–7 February 2021 & 0.4570 & 0.3482 & 0.889 \\
29 March 2021–4 April 2021 & 0.6468 & \(-\)0.0156 & 1.270 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of sensor adjustment and optimized parameters. Figure 9: Comparison of surface heat fluxes before calibration (Phase 2).