This study focused on circuitry arrangement optimization for a multi-tube phase change material heat exchanger. The optimization approach was developed based on a genetic algorithm approach coupled with numerical simulation and was aimed at maximizing the equivalent hot water output during the discharging process. Validated two-dimensional and three-dimensional simulations were used to support the genetic algorithm optimization process and to accurately investigate the thermal performance of the optimal circuitry arrangement. The results showed that adding more connections near the outlet side of the phase change material heat exchanger could lengthen the flow path in the high temperature zone, which was beneficial for a high mass flow rate condition of 1.68 kg min(-1) with a 5% increment. Under medium and low mass flow rates of 1.2 kg min(-1) and 0.5 kg min(-1), a 3% increment and a 6% decrement, respectively, were observed. It was found that different mass flow rates require their own optimal circuitry arrangements, and the arranged rules were not necessarily the same. Therefore, circuitry arrangement optimization should be performed according to the operating flow rate or designed range to maximize the optimization effect. The proposed optimization approach could serve as an effective way to improve the energy efficiency of multi-tube latent thermal energy storage systems.