Latent heat thermal energy storage (LHTES) systems are becoming increasingly useful due to their high energy storage density and nearly isothermal operation; however, thermal conductivity of phase change materials remains low. Passive heat transfer enhancement techniques have been heavily studied, but the effect of heat transfer fluid (HTF) parameters on the thermal performance of a LHTES unit has not. In the current study, the effect of variable flow rates and inlet temperatures of the HTF during the charging and discharging processes of a LHTES unit enhanced with annular fins have been evaluated experimentally. The experimental data shows that as flow rate is increased, charging and discharging times decrease. In addition, higher HTF temperatures for charging and lower temperatures for discharging have a greater impact on decreasing overall charging and discharging time.