## 3 Studies of PCMs Incorporated in Passive Systems
### Experimental Studies
#### 3.1.2 At the System Scale (Envelopes and Buildings)
The results showed a strong reduction of the temperature peak for M2 and M3 compared to the reference (M1), up to 50% and 80%, respectively. In addition to the reduction of the temperature maximum, the peak is delayed in time by 3 h for M3. These results provide clear evidence of the thermal regulation effect of macro-encapsulated PCM and the value of combining PCM with well-managed insulation layers to achieve energy savings. [PERSON] and [PERSON] [108] conducted an experimental study to determine the optimal thickness of a roof incorporating PCM macro-capsules containing paraffin wax of melting temperature 44 \({}^{\circ}\)C under the hot climate of Iraq. Three different thicknesses of 10, 15, and 20 mm were studied based on energy indicators, such as ambient temperature, interior surface temperature, and average exterior surface temperature. The values obtained were compared to a reference roof without PCM. The roofs with PCM showed a reduction in maximum room temperature between 7.25 and 9 \({}^{\circ}\)C compared to the reference roof. Increasing the thickness from 10 to 15 mm reduced the room temperature by 2.3% compared to only 0.4% when the thickness was increased from 15 to 20 mm. The average decrease in room temperature fluctuation during the day and night is defined as the sum of the average decrease in room temperature during the day and the average increase in room temperature during the night. This parameter allows comparison of different storage devices. The best value is obtained for 15 mm of macro-encapsulated PCM. The reason is that the 20 mm is too thick to solidify passively during the night, which reduces its performance. To solve the moisture transfer problem caused by macro-encapsulation, [PERSON] et al. [109] proposed a method for encapsulating PCMs in pipes. The tests were conducted in a cubic dynamic wall simulator. n-Octadecane with a melting temperature between 27.5 and 38 \({}^{\circ}\)C is used as the PCM. The PCM is melted and then poured into a copper pipe and placed inside the wall cavity by using a wooden frame. Two pipes of different diameters, 1.9 cm and 1.27 cm, are used and placed at two different locations: medium depth and next to the wall. The maximum reduction in peak heat flux was 36.5% for a mass fraction of PCM of about 25% when the maximum wall surface temperature was 55 \({}^{\circ}\)C. When the PCM is encapsulated in the 1.27 cm pipes and placed next to the wallboard, the maximum reduction in peak heat flux was 22.45%. Based on these results, the authors conclude that the optimal position should be between the middle depth and the wallboard to complete the daily melting/solidification, and that the PCM should be encapsulated in smaller tubes with a larger surface/volume ratio so that the phase transition process can proceed easily. In order to increase the apparent thermal capacity of buildings, it is possible to incorporate PCMs not only in the building envelope but also in the partition walls and windows. [PERSON] et al. [110] conducted an experimental study in two small rooms separated by a hollow glass brick wall and filled with three different PCMs: fatty acid, paraffin, and salt hydrates with melting temperatures of 21.4 \({}^{\circ}\)C, 25 \({}^{\circ}\)C, and 27.5 \({}^{\circ}\)C, respectively, and compared with an identical cell without PCM. The maximum temperature of the test cell with PCM is lower than that without PCM. The temperature decrease varies between 3.5 and 4 \({}^{\circ}\)C for fatty acid, 2 and 3 \({}^{\circ}\)C for paraffin, and between 3.5 and 5 \({}^{\circ}\)C for salt hydrate. These results are difficult to compare because of the varying boundary conditions. For this reason, a 1D model based on the Kondo method [111] was developed with TRNSYS. The simulated PCM temperature follows the same dynamics as the experimental temperature. In fact, the result of the simulation compared with the experiences showed that the assumption of a plane liquid-solid interface of the model is not valid because the PCM melts mainly at the center. [PERSON] et al.