The phase change material (PCM) used in the building envelope can decrease the building energy consumption and improve the thermal comfort by enhancing the thermal energy storage capacity of the wall and the roof. In this research, two new PCM systems, i.e., PCMOW (capric acid contained in the panels installed on the outside surface of building) and PCMIW (capric acid and 1-dodecanol contained in the panels installed on the inside surface of building), have been developed numerically. The main study constitutes four parts: (1) the model and its validation; (2) the analysis on temperature variations of the wall and the roof; (3) the analysis on the internal temperature developments of the wall and the roof; (4) the study of thermal energy saving. A mathematical model and its corresponding numerical solution were presented. Relative error analysis inclusive of maximum and average errors and Bland-Altman analysis were employed for validation. It is found that the numerical simulation achieved good validity. The theoretical analysis of temperature variations of the walls and the roofs for the PCMOW, PCMIW and reference rooms has been conducted. Then, the internal temperature developments of PCMOM and PCMIW systems were analyzed to reveal the operation of the PCM panel in the wall and the roof. This study also explored the analysis method of thermal energy savings for the two PCM systems to maintain the indoor temperature within thermal comfort zone. (C) 2014 Elsevier B.V. All rights reserved.