## 2 Methodology
### Thermophysical Characterization  
The last step of the methodology was the analysis of the thermophysical properties of the best candidates to select the most suitable PCM for each system. The thermophysical characterization included the analysis with a differential scanning calorimeter DSC 3+ (Mettler Toledo, Schwerzenbach, Switzerland). The amount of sample used was around 10 mg and experiments were performed under N\({}_{2}\) flow. The PCM samples were located into 100 \(\upmu\)L cold-welded aluminum crucibles. The methodology followed to obtain the phase change temperature and enthalpy of the PCM is based on dynamic temperature programs from 20 \({}^{\circ}\)C under their theoretical phase change temperatures to 20 \({}^{\circ}\)C above it. The equipment precision is \(\pm\)0.1 \({}^{\circ}\)C for temperature and \(\pm\) 3 \(\mid\)/g for enthalpy results. Thermogravimetric analysis (TGA) was used to characterize the PCM maximum working temperature (defined as the temperature at which the material has lost 1.5 wt % of its mass) and the final degradation temperature. The equipment used was a TGA 2 (Mettler Toledo, Schwerzenbach, Switzerland), which allows measuring samples up to 1000 \({}^{\circ}\)C and has a sensitivity of 0.1 \(\upmu\)g. The analyses were performed under a 50 mL/min N\({}_{2}\) atmosphere. The heating rate used to perform the thermogravimetric analysis was 10 \({}^{\circ}\)C/min from 25 \({}^{\circ}\)C to 100 \({}^{\circ}\)C (low-temperature PCM) and from 25 \({}^{\circ}\)C to 200 \({}^{\circ}\)C (high-temperature PCM). Opened 100 \(\upmu\)L alumina crucibles used were filled with around 1/3 volume of material leading to average sample masses of around 10 mg. The cycling stability of the selected PCMs was characterized using a thermal cycler GeneQ BIOER TC-18/H(b) (BIOER, Hangzhou, Zhejiang, China). Due to the operating temperature range of the thermal cycler, it was only possible to cycle the pre-selected PCM for the CON system. The cycles were carried out from 20 \({}^{\circ}\)C to 80 \({}^{\circ}\)C using a heating rate of 12.5 \({}^{\circ}\)C/min. Samples were taken after 10, 100, 100, and 8000 cycles. The chemical characterization of the PCMs before and after cycling was carried out using a Fourier transform infrared (FT-IR) spectroscopy with attenuated total reflectance (ATR), which analyses the PCM chemical degradation caused by thermal cycling. The advantage of ATR is the possibility of obtaining the spectra directly from the sample, without any specific sample preparation. The partial or total disappearance of the characteristic peaks and/or the appearance of new peaks can indicate \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Weight (\%)**} \\ \cline{2-5}
**Decision Parameter** & \multicolumn{2}{c}{**MED System**} & \multicolumn{2}{c}{**CON System**} \\ \cline{2-5}  & **Scenario 1** & **Scenario 2** & **Scenario 1** & **Scenario 2** \\ \hline Phase change range (C\({}_{p}\)-T curve) & 25 & 25 & 20 & 20 \\ Enthalpy & 30 & 25 & 25 & 20 \\ Availability & 15 & 25 & 10 & 20 \\ Price & 30 & 25 & 25 & 20 \\ Maximum working temperature & - & - & 20 & 20 \\ Total & 100 & 100 & 100 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Reference values of the weights. that the material is being oxidized or degraded. This analysis was carried out with a PIKE MIRacle(tm) ATR (PIKE Technologies, Madison, WI, USA) sampling accessory with a Diamond/ZnSe ATR base, FT-IR 6300 (Hachioji, Tokyo, Japan). It allows analyzing substances in solid and liquid states. It was optimized by a wavelength range between 4000 cm\({}^{-1}\) and 650 cm\({}^{-1}\), and its standard spectral resolution is 4 cm\({}^{-1}\) accounting for 64 infrared scans for each analysis; the data recorded are their means. Its functionality is based on the characteristic wave numbers at which the molecules vibrate in infrared frequencies. Since no thermal cycling tests were performed with the PCM samples for the MED system, the FT-IR analysis was only done for the PCM candidates for the CON system.