The use of phase change materials (PCMs) in building envelopes is a promising energy efficiency technology. Nevertheless, it is difficult to design a PCM wall for annual thermal regulation since the outdoor environment varies significantly in different seasons. To figure out a design strategy for the PCM walls, three wall specimens with different assemblies were designed and developed to test the thermal performance in summer and winter. A mathematical model was established and validated using experimental data. The thermal performance of the proposed walls was tested, simulated and evaluated using internal surface temperature, thermal inertia and daily heat fluxes compared with a reference wall. The internal surface temperature amplitude was reduced by maximum of 0.73 degrees C by 21.4% during summer and 0.88 degrees C by 23.9% during winter. The thermal inertial which represents the ability of the wall to resist the change in temperature was enhanced from 1.24 to 2.0 by 60.3%. The annual average energy savings by using PCMs were 17.7%, 20.2% and 23.1% when the PCM spheres were placed at the first, second, and third layer, respectively. The optimal position of PCM spheres was the third layer for summer, fourth layer for winter, and third layer for annual application. (C) 2019 Elsevier Ltd. All rights reserved.