A new type thermal energy storage system consisting of a triple concentric-tube arrangement is proposed in this study for the storage performance enhancement. The motivation for the present proposal is that an annulus shaped PCM layer, that is in contact with the heat transfer fluid from both inner and outer surfaces provides a larger heat transfer area. For the present purpose, a numerical investigation is conducted by using enthalpy method. Based on the numerical calculations, the effects of system parameters such as mass flow rate and the inlet temperature of the heat transfer fluid and the variation of the tube radii on the system performance are investigated parametrically. The results indicate that, a significant enhancement in the system performance can be achieved by replacing a classical hollow cylinder type storage with the presently proposed triple concentric-tube storage system. Another outcome of the present study is that the most important design parameters for a triple concentric-tube storage system are the radial location and the thickness of the PCM filled annulus. (C) 2013 Elsevier Ltd. All rights reserved.