A comparative assessment of the external and internal insulation for an intermittent air-conditioned building was numerically performed. The energy consumed for cooling was used to evaluate the insulation configurations of exterior walls. There was concern about the effect of the periods that the building was occupied, the air conditioner (AC) operation modes and the power of the heat source in this study. The results show that the external insulation configuration have a better thermal performance compared to the internal insulation configuration, when the building was occupied at daytime. When the building was occupied at night, the internal insulation configuration have a better thermal performance if the AC runs continuously. If the cold storage of the building was applied for energy conservation, the power of the heat source should be considered to determine the insulation configuration. The determination of the insulation configuration of the exterior walls should take those three factors into consideration, including the occupancy time of the building, the AC operation modes, and the power of the heat source.