## 3 Studies of PCMs Incorporated in Passive Systems
### Experimental Studies
#### 3.1.3 Dynamic Numerical Simulations of Buildings Incorporating PCMs
The thermal performance and energy consumption of a prefabricated building with PCM was investigated using EnergyPlus software in five different climate regions in China: severe cold area, cold area, mild area, hot summer and warm winter area, hot summer and cold winter area [118]. The study focused on the optimization of the thermal properties of the PCM, its position in the building structure, and the orientation of the PCM added to the building envelope using the direct incorporation technique. The results showed that adding the PCM to the building envelope on the East or West side is more energy efficient compared to the other orientations. For different regions, based on a comprehensive evaluation of the relationship between energy savings rate and cost, increasing the thickness of PCM has a limited effect on improving the energy savings rate of buildings. The authors suggested to place the PCM on the interior side of the building regardless of the area, as the energy saving rate is 77.11% and 32.53% when PCM is located on the interior and exterior sides of the wall, respectively. [PERSON] [119] reviewed the related literature that examines the application of PCMs in different positions inside the walls of buildings to determine their optimal position and influential parameters. It was found that the optimal positions of PCMs are highly dependent on parameters, such as climatic and weather conditions, and the purpose of the application, melting temperature and melting enthalpy of PCMs, amount of PCMs, thermal properties of wall materials, and wall orientation. In order to improve the thermal inertia effect in buildings using shape-stabilized PCM wall panels, [PERSON], [PERSON] et al. [120] analyzed the enthalpy-temperature function based on the thermal properties of 22 types of shape-stabilized PCMs and applied it to a dynamic energy simulation program. The modeled building has a wooden structure and is south-facing. Then, the PCMs were integrated into the internal and external face of a 20 mm thick wall. A preliminary study was carried out to determine where the PCM should be integrated. During cooling periods, the PCM should be placed on the outer layer of the wall and on the inner layer during heating periods because it is effective in storing and releasing the heat generated in the room during this period. On average, total energy consumption was reduced by 5% per year. Recently, [PERSON] et al. [36] conducted an optimization process with COMSOL Multiphysics to find the best value for critical parameters such as: the location of the PCM layer, its thickness, the melting temperature of the PCM, and different loading conditions (monthand city). The authors used two performance indicators to evaluate the performance of the wall: the instantaneous fluctuation of the indoor temperature and the intensity of thermal discomfort, which is defined as the period during which the temperature is outside the chosen thermal comfort range between 22 and 28 \({}^{\circ}\)C. The optimal position is obtained for PCMs placed close to the inner layer of the wall. The analysis of several thicknesses ranging from 2.5 to 15 mm showed better results obtained for thicker layers due to the comparatively larger amount of PCMs. It was also found that the selection of the melting temperature of PCMs is highly dependent on the loading condition. Indeed, the authors recommend PCMs with a melting temperature between 26-30 \({}^{\circ}\)C for cooling and 20-24 \({}^{\circ}\)C for heating.