## 3 Studies of PCMs Incorporated in Passive Systems
### Experimental Studies
#### 3.1.2 At the System Scale (Envelopes and Buildings)  
PCMs can also be integrated into existing building envelopes through the insulation layers. [PERSON] et al. [105] integrated paraffin with a melting temperature of 28-30 \({}^{\circ}\)C into cellulose wall insulation. Two experimental cells of quasi-cubic shape (5.09 m\({}^{3}\)) with a window size of 0.32 m\({}^{2}\) were constructed to evaluate the energy performance of insulation with PCMs. Molten PCM is sprayed on the cellulose insulation and the mixture is blown into the wall cavities. Only summer data was studied, as the objective was to reduce space cooling and shift the thermal load over time by measuring the indoor air temperatures on the inside and outside of each wall. The incorporation of paraffin in the insulation reduced the heat flux from 16.1% to 38.5%. The maximum heat flow is delayed from 1.5 to 3 h, which reduces the electricity bill. Analysis of the results for each wall individually showed that only the west-facing wall exhibited a significant reduction in maximum heat flow. [PERSON] et al. [106] studied different forms of hydrated salt-based PCM macro-encapsulated in aluminum foil to test the influence on the convective heat transfer during phase change. The PCM used is a mixture of 50 wt% MgCl\({}_{2}\)-6H\({}_{2}\)O and 50 wt% CaCl\({}_{2}\)-6H\({}_{2}\)O with a melting temperature of about 21 \({}^{\circ}\)C. Several brick block samples containing four different shapes of PCM macro-capsules were fabricated: cubic, cylindrical, spherical and plate shapes, and then compared to reference brick blocks. The results showed that changing the design of a set of PCMs can adjust the thermal behavior without changing the mass of the PCM. The best results were obtained for the plate and cylindrical shape but the complex production process required outweighs the positive thermal effects obtained. [PERSON] et [PERSON] [107] conducted a study on three types of wall: a horizontally hollowed-out clay wall taken as reference, a wall with macro-capsules of PCM and a wall with macro-capsules of PCM plus an insulation layer (XPS) named M1, M2, and M3, respectively. The walls are made of horizontally hollowed-out clay bricks (0.009 cm\({}^{3}\)) with insertion of parallelepiped steel macro-capsules of two different thicknesses (2.8 cm and 0.75 mm) filled with RT18, an organic PCM with a melting temperature of 18 \({}^{\circ}\)C. The tests were \begin{table}
\begin{tabular}{c c} \hline \hline
**PCM** & **Temperature of Fusion (\({}^{\circ}\)C)** \\ \hline CA & 29.87 \\ CA (72\%)-LA (28\%) & 21.14 \\ CA (84\%)-MA (16\%) & 24.24 \\ CA (87\%)-PA (13\%) & 27.95 \\ CA (93\%)-SA (28\%) & 26.91 \\ LA (71\%)-MA (29\%) & 33.07 \\ LA (79\%)-PA (21\%) & 35.46 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Fatty acids of interest for the targeted application, CA: capric acid, LA: lauric acid, MA: myristic acid, PA: palmitic acid, SA: stearic acid [103; 104]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Insulator** & \begin{tabular}{c} **Density** \\ **(kg m\({}^{-3}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Thermal** \\ **Conductivity** \\ **(W m\({}^{-1}\) K\({}^{-1}\))** \\ \end{tabular} &
\begin{tabular}{c} **Cost** \\ **(6/kg)** \\ \end{tabular} & **References** \\ \hline Bamboo fibers & 431–538 & 77–88 & – & [21] \\ \hline Hemp fibers & 25–100 & 40–49 & 2–5 & [97] \\ \hline Flax fibers & 20–100 & 35–45 & 5–25 & [97] \\ \hline Cotton stalk fibers & 150–450 & 58–82 & – & [98] \\ \hline Chénevotte & 100–140 & 80–122 & 0.8–1 & [99] \\ \hline Kapok & 17.24 & 30–48.6 & – & [96; 100; 101] \\ \hline Fibres de coco & 40–90 & 501.09–57.58 & 63 & [102] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Bio-sourced insulators considered in a future study as support materials for the fabrication of shape-stabilized PCMs. conducted in a climate chamber simulating the equivalent temperature profile for different cities in Portugal.