The thermal performance of a latent heat energy storage unit was studied experimentally at the periodic steady state generated by cyclic energy storage and recovery. The periodic steady state was obtained by alternating identical freezing periods with identical melting periods. The storage unit was a cylindrical container of commercial paraffin wax. Energy was transferred to (and from) the wax by temperature controlled water flowing through a submerged helical coil. Measurements were made of the amount of energy stored and recovered as functions of the freezing and melting times, the temperature of water and the geometry of the coil. A simple model was proposed to calculate the energy stored or recovered in the periodic steady state.