# Numerical Design and Laboratory Testing of Encapsulated PCM Panels for PCM-Air Heat Exchangers
## 3 Results and Analysis
### Laboratory Test
#### 3.2.3 Charging and Discharging Time  
Figure 19 presents the results for one and two TBs; more time is needed to charge and discharge the new TB. This is due to the capability of the new TB to hold 17.5 kg (total latent heat of 3202.5 kJ) against 13.5 kg (total latent heat of 2470.5 kJ) of the existing TB. This 30% extra PCM made the surface temperature of the new TB solidify and melt gradually while the phase change in the existing TB (which has a thinner panel) is more pronounced. Due to that, Figure 19 clearly shows the onset and endset for both melting and solidifying (20-18 \({}^{\circ}\)C and 24-26 \({}^{\circ}\)C, respectively) for the existing TB. When two thermal batteries are used a similar behavior is observed.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Airflow (L/s)** & **Shape 11** & **NP 3 TB** & **\% (Experiment/Design)** & **Difference (Pa)** \\ \hline
100 & 34.31 & 41.9 & 22.1\% & 7.6 \\ \hline
140 & 61.28 & 56.7 & \(-\)7.5\% & \(-\)4.6 \\ \hline
180 & 112.27 & 111.0 & \(-\)1.1\% & \(-\)1.3 \\ \hline
220 & 132.60 & 162.5 & 22.6\% & 29.9 \\ \hline
260 & 176.80 & 207.0 & 17.1\% & 30.2 \\ \hline
300 & 228.24 & 250.4 & 9.7\% & 22.2 \\ \hline  & Average & & 10.5\% & 14.00 \\ \hline  & Standard Deviation (\(\sigma\)) & & \(\pm\)11.4\% & \(\pm\)14.15 \\ \hline \hline \end{tabular}
\end{table}
Table 10: Pressure drop increase between existing and new batteries.  
Figure 18: Head curve of the panels simulated and tested.  
In terms of time required to melt and solidify, the TB is considered fully charged or discharged when the surface temperature achieves stable conditions. Figure 20 shows that the new TB needs more time to complete the cycle and this is explained by the capacity that the new TB can hold. However, the time required to solidify is lower than the time to melt the PCM properties. This is an interesting result as the mechanical ventilation system needs less time to charge the TB. For one TB, 4 h is necessary to solidify the existing TB while 5 h 30 min is needed for the new TB, an increase of 38%. For two TB, 8 h 30 min is needed to charge the new TB and while 5 h is needed for the existing TB, representing 66% more time.  
Figure 19: Solidifying temperature for the existing and new panel with one and two thermal batteries.  
Figure 20: Melting temperature for existing and new panel with one and two thermal batteries.  
When the discharging period is analyzed, the new TB is capable to provide cooling for a longer period of time. This is explained by the additional PCM it can hold. As it can be seen in Figure 20, the outlet temperature gradually increases to reach the inlet temperature. For 1 TB with the existing panel, the TB is completely discharged after 3 h 30 min while the new TB need approximately 6 h 30 min to completely discharge, an increase of 86%. When a mechanical ventilation system with 2 TB is analyzed, the existing TB is fully discharged after 4 h 30 min while the new TB lasts double the time.  
The first laboratory test proved that the new panel is more efficient in terms of heat transfer than the existing panel, an important feature when a faster thermal response is needed. However, Figure 20 (left) shows that the temperature for the existing and new TB increase at the same rate until the PCM starts to melt. This could be explained by the number of panels the existing TB have. With two panels more when compared to the new TB, it has 28% more surface area and reflects in an outlet temperature similar to the new TB. For the same reason, the outlet temperature during the solidifying period in Figure 20 (right) shows a similar pattern.