This study is focused on investigation of the natural convection and the parametric (flow and design) effects on charging and discharging periods of water in a shell-and-tube type latent heat thermal energy storage unit. An electronic ice thickness measurement method is used to monitor the solid liquid interface variations during phase change and this method is validated by the comparisons of visual and temperature data. Experiments are carried out for different values of heat transfer fluid (HTF) flow rates and inlet temperatures. Three different tube materials and two different shell diameters are also tested. A control volume approach is utilized on the experimental data for the determination of the total stored/rejected energies. Experimental results indicate that, for both solidification and melting processes, natural convection becomes the dominant heat transfer mechanism after a short heat conduction dominated period. In addition, inlet temperature of HTF, thermal conductivity of the tube material and the diameter of shell have considerable effects on the storage capability of the system, for charging period. For discharging period, the inlet temperature of HTF is more effective on rejected energy in comparison with the flow rate, for selected parameters. (C) 2011 Elsevier Masson SAS. All rights reserved.