## 4 Discussion  
Table 2 summarizes the number of hours when the surface temperature of PCM materials is lower than the phase change temperature for the period from 1 June to 30 September. Two material variants were analyzed--with a plasterboard containing PCM and a Dupont board--and two calculation variants were analyzed--with and without PCM hysteresis. In both material variants, the frequency distribution is similar--the number of h with the surface temperature below the phase change temperature is greater than the calculations without hysteresis, by 10.6% for the variant with plasterboards and by as much as 29.4% for the variant with Dupont boards, respectively. This may lead to an erroneous conclusion regarding the possibility of releasing the energy stored in PCM. According to the calculations without hysteresis, the solidification of liquid PCM may occur more often, which in turn determines the effectiveness of PCM in subsequent cycles. Depending on the algorithm, the difference in the time when the temperature enables the phase change is 212 h for a plasterboard with PCM and 341 h for a Dupont board. Calculations of the average surface temperature of materials are presented in Table 3. The results confirm the lower surface temperature in the calculations without taking hysteresis into account. The average temperature of the plasterboard with PCM is lower by 0.62 \({}^{\circ}\)C for the variant without hysteresis. In the case of the Dupont board, the difference is 0.49 \({}^{\circ}\)C. It should be noted here that the errors mentioned are averages for the entire course of the presented graph-including the periods in which no phase change occurs. The maximum errors mentioned earlier are much larger. The above result shows a tendency to lower the surface temperature when hysteresis is not taken into account, which results in \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Material Variants**} & \multicolumn{3}{c}{**Number of Hours of Surface Temperature below**} \\ \cline{2-4}  & \multicolumn{2}{c}{**The Phase Change Temperature, h**} \\ \cline{2-4}  & \multicolumn{2}{c}{**Variant**} & \multicolumn{2}{c}{**Difference, h**} \\ \cline{2-4}  & **Without Hysteresis** & **With Hysteresis** & \\ \hline \hline \multicolumn{1}{c}{Plasterboard with PCM} & 1993 & 1781 & 212 \\ \multicolumn{1}{c}{Dupont board} & 1161 & 820 & 341 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Frequency of occurrence of the surface temperature of PCM below the phase change temperature in individual material variants and calculation variants. Figure 9: Average hourly values of radiation temperature of partitions inside a building with Dupont boards in the period 17 June–24 June. the generation of erroneous information on the discharge of the material. Increasing the accuracy of the simulation influences the possibility of selecting the material better. Figures 10 and 11 present the values of the operative temperature inside the building analyzed. The results obtained confirm the observations based on the analysis of the average radiation temperature of the partitions. The use of a modified algorithm results in a higher operative temperature inside the building compared to the calculation results according to the standard algorithm, which does not take into account the hysteresis of the materials. The differences between the results of the operative temperature obtained from different algorithms are in the following ranges: from \(-0.92\)\({}^{\circ}\)C to \(2.43\)\({}^{\circ}\)C in the case of plasterboard with PCM, while in the case of Dupont board from \(-0.65\)\({}^{\circ}\)C to \(2.42\)\({}^{\circ}\)C.  
The graphs in Figures 12 and 13 show a comparison of the time of occurrence of individual ranges of operating temperature. Figure 12 is for the Dupont variant and Figure 13 for the PCM plasterboard. The calculation results according to the hysteresis algorithm indicate a higher risk of overheating the building in both material variants.