## 3 Materials and Methods
### Description of the Lightweight Test Cells  
Two test cells with the same constructive characteristics were used, as presented in Figure 1. These cells are used for research purposes concerning different energy solutions for buildings and are characterized by lightweight construction with low thermal inertia and high thermal insulation values. The constructive features of the cells' envelopes are the following:  
* Facades: sandwich panel with 8 cm of thermal insulation (polyurethane foam) with U-value = 0.287 W/(m\({}^{2}\cdot\)K);
* Roof: metallic roof with 16 cm of thermal insulation (mineral wool) in the internal surface presenting a U-value = 0.242 W/(m\({}^{2}\cdot\)K);* Floor: vinyl-based without thermal insulation and ventilated underneath. * Openings: both test-cells have a sliding double-glazed window (U-value = 3.137 W/(m2\({}^{2}\cdot\)K) and Solar Heat Gain Coefficient (SHCG) = 0.762) and an opaque door (U-value = 0.747 W/(m2\({}^{2}\cdot\)K)), both facing South. In addition to the base envelope layers listed above, one of the cells was used as reference (DEMO1) and incorporated commercial insulation panels (WEDI(r) panels) mounted on the internal face of the facade walls. The specific location of the panels placed on 2 of the vertical walls is shown in Figure 2a. The same distribution was applied to the remaining vertical internal surfaces (without covering the window opening area). The insulation panels were fixed to the base layer using adhesive magnetic stripes. The second cell (DEMO2) was used to test the effects of the PCM-containing mortars applied as indoor wall coating and incorporated test boards composed of the same type of WEDI(r) panels with an additional 4 mm-layer of the corresponding mortar. The specific location of these boards is shown in Figure 2b. In this case, they were mounted on the walls reinforcing the adhesive magnetic fixing with additional stripes of Velcro tape. A detailed schematic diagram of the 2 indoor coating solutions (with and without the 4 mm PCM-based mortar layer) is shown in Figure 3 and was presented and explained in further detail in [19]. Figure 1: Test cells used for the demonstration of the PCM solutions: (**a**) South-West view; (**b**) North-East view. Figure 2: Indoor view of the test cells with the thermal insulation panels (WEDI®): (**a**) DEMO1: without PCM; (**b**) DEMO2: with PCM. Test boards with the 2 aforementioned PCM solutions (i.e., CrodaThermTM ME29P and MicronalDS 5001X) were prepared. The characterization of the thermophysical and mechanical properties of the PCM-containing mortars in terms of latent heat capacity and phase change behavior, as well as the thermal conductivity of the external envelope walls (composed by sandwich panels with the different mortars), were also reported in detail in [PERSON] et al. [19]. The main results from [19] regarding hardened density value for the mortar containing the Micronal PCM resulted in a reduction of 36.4% in comparison with the reference mortar, and for the mortar incorporating CrodaTherm PCM, a density reduction of 18.7% was observed. The results obtained for the mechanical strength regarding the PCM-containing mortar with Micronal revealed a decrease of 68% and 76%, and for the CrodaTherm PCM incorporation, a reduction of 57% and 72% in flexural and compressive strengths was attained, respectively. The selected microencapsulated PCM materials were incorporated into the mortar, which has a density of 1600 kg/m\({}^{3}\). The mixture in a 20 wt% into the solid material modifies the density as well as melting and crystallization temperatures in comparison with the pure mortar and PCM characteristics.