## 3 Studies of PCMs Incorporated in Passive Systems
### Experimental Studies
#### 3.1.1 At the Composite Scale
[PERSON] and [PERSON] [62] found that the thermal conductivities of fatty acid/expanded vermiculite composite PCMs were increased by 104-150% by the addition of 10 wt% expanded graphite. [PERSON] et al. [63] have suggested that dopamine modification can solve the problem related to the measurement of the latent heat of expanded vermiculite (EVM)-based composite PCMs. Indeed, the measured latent heat were significantly lower than the calculated values during the phase change process. This mismatch is reduced by increasing the concentration of dopamine. The effect of the dopamine is the modification of the surface of EVM leading to an increase of the latent heat and the encapsulation capacity. [PERSON] and [PERSON] [64] investigated the combined effect of loading expanded graphite (EG) and expanded vermiculite (EV for \"expanded vermiculite\") on the thermo-physical and thermal regulator properties of commercially available low-cost PCM (OM37). Four samples with different compositions of EG, PCM and EV were prepared with 0, 3, 5, and 7% expanded graphite, respectively. The heat of fusion of the composite was reduced from 50% to 57% compared to pure PCM due to the increase in the mass percentage of expanded vermiculite and expanded graphite in the composite, which do not contribute to latent energy storage. Increases of 33.1%, 79.3%, and 114.4% in the thermal conductivity were observed for the composites containing 3%, 5%, and 7% EG compared to pure PCM. The prepared composites exhibited the same thermal characteristics after 1000 heating and cooling cycles. In addition, when incorporated into the wall panel, the composite containing 7% EG showed excellent ability to regulate the interior temperature. Biochar has been used to fabricate stabilized shapes due to its interesting porous structure [65; 66; 67]. [PERSON] et al. [68] prepared a shape-stabilized composite material by impregnating a eutectic mixture of lauric-stearic acid (LA-SA) into carbonized corn cobs (CNCC). The latter, thanks to its porous structure, constitutes an excellent support material allowing the LA-SA eutectic mixture to be suitably encapsulated with a maximum impregnation rate of 77.9 wt%. DSC analysis showed that the LA-SA/CNCC composite melts at 35.1 \({}^{\circ}\)C with a heat of fusion of 148.3 J/g and solidifies at 29.7 \({}^{\circ}\)C with a heat of solidification of 144.2 J g\({}^{-1}\). Moreover, its stability after 200 cycles makes it a good candidate for an application in energy storage in buildings. To minimize the degradation of the thermal regulation performance of PCMs composites, [PERSON] et al. [69] proposed the multi-layer sandwich structure of Na\({}_{2}\)SO\({}_{4}\).10H\({}_{2}\)O, expanded vermiculite and magnesium oxychloride cement (MOC) with a melting temperature in the range of 20-40 \({}^{\circ}\)C. Compared with the MOC house-like model and ambient condition, the multi-layer sandwich PCM composite exhibited better results with time shift of 93 min and 84 min for heating and cooling, respectively. Different techniques are available to integrate PCMs into building envelopes. However, between the high cost of micro-encapsulation and the leakage problems of impregnation and direct incorporation techniques, shape-stabilized PCMs are a good compromise. Moreover, the availability and the wide range of support materials considerably increase the field of application of shape-stabilized PCMs. Numerous experimental studies have shown that it is possible to increase the thermal conductivity of PCMs by shape stabilization with suitable support materials [70]. Table 4 summarizes some studies using materials of natural origin to shape-stabilize PCMs. It appears that bio-sourced materials, in particular, insulating materials, are promising for the future.