## 4 Technical Evaluation of Measurements and Discussion  
_Comparison of Storage Capacities of Selected PCMs_  
To establish the comparison, the results were processed based on the following conditions: a 1000 L storage tank with water as the heat transfer medium was chosen as the reference storage vessel. The accumulated energy in the storage tank for the selected thermal gradient (\(\Delta\)t = 20 \({}^{\circ}\)C) Qat = Qv = 83.7 MJ. Storage tank with 200 litres integrated cylindrical PCM tank and 800 litres of water. For the selected paraffin the weight is about 150 kg (Table 5). Based on the described methodology, the theoretical energy storage potential for organic PCM A43 (from the manufacturer PCMproducts Ltd., Peterborough, UK) [46] was determined, which has a latent heat value of 230 kJ/kg and a phase change at 43 \({}^{\circ}\)C. In terms of comparing the latent heat value against the reference PCM, it can accumulate 50 kJ/kg more energy in the phase change. This means that when keeping the same ratio of 800 L water to 200 L PCM, there is an increase of 25.2 MJ in the amount of energy stored relative to the reference water storage tank (Table 6). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Medium** & **Amount** & **Sensible Heat** & **Latent Heat** & **Total** \\ \hline Water & 800 L & 66.96 MJ & - & 66.96 MJ \\ PCM & 200 L & 7.09 MJ & 34.56 MJ & 41.65 MJ \\  & 1000 L & 73.44 MJ & 34.56 MJ & 108.9 MJ \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Parameters of hybrid tank of water–PCM (A43). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Medium** & **Amount** & **Sensible Heat** & **Latent Heat** & **Total** \\ \hline Water & 800 L & 66.96 MJ & - & 66.96 MJ \\ PCM & 200 L & 6.48 MJ & 27.00 MJ & 33.48 MJ \\  & 1000 L & 73.44 MJ & 27.00 MJ & 100.44 MJ \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Parameters of hybrid tank of water–PCM (selected). Figure 29: Discharging rate of the hybrid tank of water–PCM with copper matrix. The theoretical increase in stored energy when using organic PCM A43 is approximately 30.11%. The third model case represents the use of salt hydrate as a PCM. The chosen material is a salt hydrate (TEAP PCM) [47], and due to the \"know-how\" of the manufacturer, only the parameter for the latent heat value of 260 kJ/kg and the phase change at 36 \({}^{\circ}\)C is given in this work. The ratio of water to PCM volume was kept as in previous cases (800 L water and 200 L PCM), (Table 7). The results of the comparison of the individual PCMs are shown in Figure 30. They indicate that using the more efficient PCM based on salt hydrate allows up to 34.6% more energy to be stored while maintaining the volume of the tank. As a result, even when using a PCM with a lower latent heat capacity, the efficiency is higher than when using a storage tank without a PCM. In the cases of using a PCM with a higher latent heat capacity, an increase of up to 30.11% or up to 34.6% was achieved. The results obtained in this paper confirm and extend the published results of [27], and are in line with studies where the authors achieved a 50% reduction in the storage tank while maintaining the thermal capacity of the storage tank [28], where the authors achieved more than a twofold reduction in the size of the storage tank, where the authors [48] achieved a 14% increase in the thermal capacity of the storage tank with a small increase in the volume of the storage tank and found that the discharge efficiency of the PCM was increased by 83.9%. In the case of this paper, the technically available methods and materials were used to achieve the desired degree. The methods of thermal conductivity and heat flow enhancement described by the authors of [18; 19; 20; 21; 28] have been experimentally verified and underestimate analytical and numerical predictions. The copper matrix shows the best results. These results suggest that the use of PCMs as additive materials to increase the heat capacity of heat transfer media are effective and have benefits for science and practice.