## 2 Materials and Methods
### Laboratory Analysis
#### 2.1.1 Materials and Instrument  
The PCM panels selected for the laboratory testing are commercially available products named \"Infinite RTM\", which are produced by \"Insolcorp, LLC\" [29]. The encapsulation envelope is based on polymeric films shaped into small bags (50 \(\times\) 100 mm\({}^{2}\)) filled with inorganic PCM (Figure 1a). The panels have an area that is easily adjustable by just cutting between the PCM bags. Three different samples, characterized by the same envelope but with different nominal phase change temperature PCMs, were tested (Table 1):  
* Infinite RTM 21 (sample X), characterized by a phase change temperature of \(\sim\)21 \({}^{\circ}\)C
* Infinite RTM 23 (sample Y), characterized by a phase change temperature of \(\sim\)23 \({}^{\circ}\)C
* Infinite RTM 25 (sample Z), characterized by a phase change temperature of \(\sim\)25 \({}^{\circ}\)C  
The laboratory tests were carried out by adopting a Dynamic Heat Flux Meter (DHFM) FOX 600, (Figure 1c). The instrument can perform both steady state and dynamic thermal tests that allow different thermal properties to be measured to fully characterize the different samples in terms of:  
* Equivalent thermal conductivity (solid and liquid phase)
* Heat capacity
* Enthalpy variation as a function of temperature
* Latent heat capacity \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Value** & **Unit** \\ \hline Size & \(555\times 546\) & [mm\({}^{2}\)] \\ Thickness (s) & \(\sim\)6.9 & [mm] \\ Weight (M) & \(\sim\)1.45 & [kg] \\ Surface Mass (SM) & \(\sim\)4.8 & [kg/m\({}^{2}\)] \\ Volume (V) & \(\sim\)2091 & [cm\({}^{3}\)] \\ Nominal melting temperature & 21 (X), 23 (Y), 25 (Z) & [\({}^{\circ}\)C] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main characteristics of the Infinite RTM samples. 2.1.2. Measured Thermal Properties  
The equivalent thermal conductivity (\(\lambda_{\alpha q}\)) was measured according to the EN 12664:2001 standard [30]. The final value was calculated according to Equation (1). \[\lambda_{\alpha q}=\frac{q\cdot s}{\Delta T}\left[\frac{W}{mK}\right] \tag{1}\]  
where: \(s\) [m] is the sample thickness, \(\Delta T\) [K] is the temperature difference between plates, \(q\) [W/m\({}^{2}\)] is the specific measured heat flux. The tests were performed using different set-point temperatures to determine the equivalent thermal conductivity of the samples with PCM in both a solid and liquid state. Moreover, tests were carried out with downward and upward heat fluxes to assess the influence of the heat flux direction. A summary of the different set-points adopted during the tests is shown in Table 2.  
A key-property that should be considered to assess the energy storage feature of a PCM is the enthalpy variation as a function of temperature over its phase change range. A series of measurements was conducted by repeatedly increasing the temperature (in 1 K steps) to perform this test through a dynamic heat flow meter device (ASTM C1784:2020 [28]). The setpoint temperatures for each test performed are shown in Table 3. The cumulative amount of energy that entered the specimen was recorded, starting from the time of the temperature change until a steady state was achieved.