Melting and solidification of a phase change material (PCM) held within a vertical cylindrical enclosure that is integrated with a heat pipe (HP) is simulated as a single module. The HP is heated from the bottom to melt (charge) the PCM that is positioned in the middle of the HP length, and is cooled from the top to solidify (discharge) the PCM. Three modes of operation are considered in this study (i) charging-only, (ii) simultaneous charging and discharging, and (iii) discharging-only. All modes of operation are handled with a single HP within a PCM (single HP-PCM) of which the top and bottom sections are inactivated during charging-only and discharging-only modes, respectively. A parametric study of the influence of the PCM enclosure height and input/output heat transfer rates shows that, for the same mass of PCM, a longer enclosure exhibits a lower HP bottom average wall temperature and relatively more PCM melting during simultaneous charging and discharging. Increasing either the input, output, or both heat transfer rates has a significant effect on the temperature of the HP bottom and top sections, but only a minor impact on the temperature of the HP middle section. (C) 2014 Elsevier Ltd. All rights reserved.