This study presents a comprehensive numerical study on a triplex tube latent thermal energy storage (LTES) system under three modes of operation to maximize the utilization of available thermal energy for applications in built environments

including charging-only

simultaneous charge/discharge (SCD)

and discharge-only processes. Charging-only process ensures the onset of SCD with a fully liquified phase change material (PCM) for better thermal performance of LTES in steady-state SCD. Eventually

the discharge-only process is examined during periods of unavailability of a thermal energy source. PCM solidification/melting is modelled using the Boussinesq approximation while various configurations are explored by altering the orientation (horizontal and vertical)

the placement of heat transfer fluid (HTF) tubes (inner or outer)

the HTF flow direction (counter-current and co-current)

and the HTF flow rate. Initially

a constant HTF mass flow rate of 0.062 kg/s is used to identify an optimum configuration. Based on the heat transfer rates between PCM and HTFs

along with steady-state SCD liquid fraction

the horizontal LTES configuration with outer tube charge/inner tube discharge is concluded to be the most effective. Further

variations in charge and discharge HTF mass flow rates reveal that a higher charge fluid mass flow rate offers better performance. Computational results demonstrate that this optimal configuration reduces charging time by 41 % compared to the configuration with the longest charging period. In addition

at steady-state SCD

the optimal case exhibits a heat transfer rate of 84.19 W and a PCM liquid fraction of 0.88. These findings contribute to the optimal design and more efficient operation of thermal storage systems in built environments

thus improving overall system performance.