## 5 Results and Discussion
### Stage 2--TES Properties in the Fireplace Operational Conditions  
Results from the second stage of the experiment, in which samples were heated up to 400 \({}^{\circ}\)C, are shown in Figure 5.  
The highest temperature reached was in the CGA-PC specimen (393 \({}^{\circ}\)C), while the lowest--similar to the first stage-- was the AC sample (297 \({}^{\circ}\)C). As the heating temperature increases, the differences in the final temperature of the materials also increases. In this case, the temperature of steel (303 \({}^{\circ}\)C), immediately after heating, was only higher from the AC. This shows that the thermal properties of the materials, besides the material's structure and type of bonding between molecules, also depend on the temperature at which the materials operate. The temperature drops during cooling showing that aerated concrete cooled down in the shortest time, but a different cooling pattern was observed for the steel sample (in comparison to the first stage). The S sample was characterized by the lowest rate of the temperature drop in a function of the cooling time. After 9 min of cooling the S sample had a higher temperature than all concretes tested and, after 12 min, the S specimen had the highest temperature of all the materials. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline
**Material Type** & **S** & **AC** & **SLB** & **CB** & **FB** & **CGA-PC** & **CGA-AC** & **CCA-PC** & **CCA-AC** & **G** \\ \hline \(m\) (kg) & 2.078 & 0.252 & 0.465 & 0.536 & 0.439 & 0.574 & 0.575 & 0.520 & 0.560 & 0.666 \\ \(c\) (J/(kg-K)) & 449 & 1130 & 800 & 850 & 850 & 1130 & 1130 & 1130 & 1130 & 670 \\ \(\Delta T\) (K) & 85.6 & 51.2 & 94.1 & 73.5 & 58.1 & 91.7 & 74.0 & 84.5 & 83.4 & 77.9 \\ \(\Delta\)Q (k) & 79.87 & 14.55 & 35.01 & 33.49 & 21.68 & 59.48 & 48.04 & 49.65 & 52.77 & 34.73 \\ \(t\) (s) & 9000 & 9000 & 9000 & 9000 & 9000 & 9000 & 9000 & 9000 & 9000 & 9000 \\ \(p\) (W) & 8.874 & 1.616 & 3.889 & 3.720 & 2.408 & 6.608 & 5.337 & 5.516 & 5.863 & 3.89 \\ \hline \end{tabular} where: \(m\): sample weight; \(c\): specific heat; \(\Delta\)T: temperature difference; AQ: amount of emitted energy; \(t\): emission time; \(P\): thermal power; S: steel; AC: aerated concrete; SLB: sand-limic brick; CB: ceramic brick; FB: fierclay brick; G: granite.  
\end{table} 
Table 7: The thermal power of the materials tested—the first stage of the experiment. The initial temperature after heating of the concretes made with ceramic aggregate was higher than almost all materials, i.e., CCA-PC and CCA-AC, at 354 \({}^{\circ}\)C and 349 \({}^{\circ}\)C, respectively. Only the CGA-PC sample obtained higher initial temperature, at 393 \({}^{\circ}\)C. During the first stage, more materials (S, SLB, and CGA-PC) obtained higher initial temperatures in comparison to the ceramic concretes. The test at 400 \({}^{\circ}\)C shows that the TES properties of concretes based on ceramic aggregate are better when the operational temperature increases, compared to other materials. In the case of the temperature measurement using an infrared camera, when a high-temperature object (interior of the furnace) is reflected, an adulteration of the measurement results may appear unless the ambient temperature is considered. During measurements, the angle of the observation did not exceed 30\({}^{\circ}\), and the emissivity coefficients of the materials' surface were taken into account. The analysis of thermal images was carried out using the comparative method. The samples' temperatures were compared, which were obtained from the thermograms made at one time for the materials. The brightest color on the thermal image during the entire cooling period was observed for the steel sample, which was in agreement with the temperature reading from the thermocouple. The darkest color was recorded for the aerated concrete sample. This fact was consistent with the temperature readings--the AC sample reached the lowest temperature during the heating process, and the temperatures recorded for it in subsequent points in time were also the lowest.