## 3 Results
### Mode 3: Simultaneous Charging and Discharging  
According to the set of experiments shown earlier in the methodology section, the experiments in Mode 1 and Mode 2 showed total feasibility, while for Mode 3a and 3b could only be performed partially because the condensing unit stopped in less than three minutes therefore not providing enough data to analyse. A summary of the feasibility of the experiments in Mode 3a and 3b is available in Tables 8 and 9, respectively. Figure 16: Influence of the HTF flow rate on the average PCM discharge rate and time of discharging at constant HTF inlet temperature of 12 \({}^{\circ}\)C. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{4}{c}{**Mode 3a: Initial Temperature at 12 \({}^{\circ}\)C**} \\ \hline \multirow{2}{*}{**Compressor Power [\%]**} & \multicolumn{3}{c}{**Flow Rate [L-h\({}^{-1}\)]**} \\ \cline{2-3}  & **50** & **100** & **150** \\ \hline
15 & **✓** & **✓** & **✓** \\
30 & **✓** & **✓** & **✓** \\
45 & X & **✓** & **✓** \\
60 & X & **✓** & **✓** \\
75 & X & X & X \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Feasibility of the set of experiments in Mode 3a. Figure 15: Influence of the HTF flow rate on the cold energy stored in the PCM during discharging at constant HTF inlet temperature of 12 \({}^{\circ}\)C.  
3.1. Mode 3a: Simultaneous Charging and Discharging of the RPW-HEX with the PCM Initially Completely Discharged  
Temperature Profiles during the Simultaneous Charging and Discharging of the PCM  
In Mode 3a, both the refrigerant circuit and HTF circuit were simultaneously switched on, with the PCM initially at 12 \({}^{\circ}\)C. Figure 17 shows the temperature profile in Mode 3a for the experiments performed at an HTF flow rate of 100 L-h\({}^{-1}\) and inlet temperature of 12 \({}^{\circ}\)C, and for compressor powers at 30%, 45%, and 60%. In all the cases it was observed that, after a certain period of time, the RPW-HEX attained stable conditions, meaning that the cooling capacity of the refrigerant was entirely used to cool down the HTF, while the PCM remained at a constant temperature. Therefore, in steady state conditions the RPW-HEX does not act as an active energy storage component, but only as a heat exchanger. Furthermore, in steady state, the phase change was not fully achieved in all the PCM, especially at the top and near the HTF inlet (TP1 and TP4), meaning that the RPW-HEX was only partially charged. There is a strong temperature gradient inside the PCM in the vertical direction even at lower compressor powers, being the PCM temperature difference between the top and the bottom levels as high as 20 \({}^{\circ}\)C, at compressor power of 60%. This means that the region where most of the heat transfer takes place is towards the bottom part of the RPW-HEX probably because of a higher concentration of the liquid phase of refrigerant in that part due to its higher density, while the vapour phase of the refrigerant flows mainly on the top part without producing relevant cooling effect. Figure 17: PCM temperature profile in Mode 3a with HTF inlet temperature at 12 \({}^{\circ}\)C and at a flow rate of 100 L-h\({}^{-1}\), for compressor power of (**a**) 30%, (**b**) 45%, (**c**) 60% and (**d**) position of the sensors. Dotted lines denote PCM temperature at top level, dashed lines at middle level, and solid lines at the bottom. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Mode 3b: Initial Temperature at \(-4\)\({}^{\circ}\)C**} \\ \hline \multirow{2}{*}{**Compressor Power [\%]**} & \multicolumn{3}{c}{**Flow Rate [L-h\({}^{-1}\)]**} \\ \cline{2-4}  & **50** & **100** & **150** \\ \hline
15 & ✔ & ✔ & ✔ \\
30 & X & X & X \\
45 & X & X & X \\
60 & X & X & X \\
75 & X & X & X \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Feasibility of the set of experiments in Mode 3b. Instantaneous Cold Energy in PCM, Total Cold Energy Storage and Time to Reach Equilibrium  
Figure 18 shows the influence of compressor power on the PCM instantaneous cold energy.