This study analyzed the building energy performance of apartment buildings using retrofit systems with phase change materials (PCMs). The apartment type, building orientation, and height are considered to evaluate the implementation of an innovative PCM system. The building models selected were a flat-type apartment and tower-type apartment. According to the results, building orientation, height floor, and climate factors have a complex correlation with each other. Depending on the solar characteristics, solar altitude, solar time, wind direction, and wind speed, the suitable Building orientation and height for energy reduction of buildings vary. Such parameters also affect to the suitable PCM application for energy savings. As a result, PCMs of 20 °C and 26 °C showed to be suitable for the flat-type apartments with a southward orientation a westward orientation, respectively. Tower-type apartment with eastward and southward orientation showed the highest energy saving with PCM of 24 °C; the units with westward and northward orientation showed the highest energy reduction at 23 °C. Since the PCM efficiency for the energy savings are different depending on building orientations, heights, and climate factors, such variables are necessary to consider for the PCM application to the apartment building. •Retrofit of apartment buildings is required for energy savings in building sector.•Building orientation, height, and climatic factors influenced the PCM efficiency.•PCMs melting at 23 and 24 °C were suitable for energy saving in tower-type apartments.•PCMs melting at 20 and 26 °C were suitable for energy saving in flat-type apartments.•Different approaches with multiple variables needed for optimizing PCM efficiency.