The efficient use of our existing energy resources is as important as finding new energy sources, since the demand for energy is increasing day by day. Heating and cooling loads in buildings constitute a large part of energy consumption. Therefore, it is very important to improve the energy performance of buildings. The utilization of phase change materials to increase the energy efficiency of buildings is one of the recent research topics. In this study, the effect of phase change materials on room temperature for winter and summer months was investigated numerically by defining real environmental conditions in the virtual environment. Phase change material with thermophysical properties suitable for Mediterranean climate conditions was selected for summer and winter. It can keep the room temperature at a slightly lower level during the daytime in summer and the room temperature higher in winter than in the insulated state case. As a result, phase change materials can be used as a natural air conditioner in the summer, as well as a natural heater at night in the winter. On the other hand, smart bricks can be produced that can absorb the heat transmitted from the inside to the outside by using different phase-change materials.