The thermal performance of cylindrical latent heat storage units (C-LHSUs) in hot water tanks can be improved by using a hollow geometry structure, which effectively reduces the average distance between the heated/cooled wall and the solid-liquid interface during the charging and discharging process. To comprehensively evaluate this improvement, an unconstrained melting model for phase change materials (PCMs) was developed, enabling detailed investigation of the thermal behavior of hollow geometry LHSUs (H-LHSUs). Moreover, the impact of the ratio between the inner hollow tube radius (r) and outer tube radius (R) on the charging/discharging performance of H-LHSUs was analyzed. The results demonstrated substantial enhancements in heat transfer performance for H-LHSUs compared to conventional C-LHSUs. Specifically, the average heat transfer coefficient increased by 82.9 % during charging and 176.47 % during discharging. This improvement translated to a charging rate that was 2.46 times and a discharging rate that was 3.9 times higher than those of the C-LHSU. Furthermore, the study revealed that as the r/R ratio increased, both charging and discharging rates improved significantly, with the rate of heat transfer enhancement becoming more pronounced at higher r/R values. This research provides actionable insights for optimizing the design of LHSUs in practical applications. It underscores the importance of balancing thermal performance gains with the associated capital costs when selecting the optimal r/R ratio. The findings contribute to the advancement of energy storage technologies, offering a robust framework for improving the efficiency of thermal energy systems in hot water tanks.