A numerical assessment of a latent heat storage system for district heating substations

This work deals with the development and sizing of a latent heat storage system for an urban district heating system (UDHS). The investigated system is a cylindrical tank containing spherical phase change material (PCM) capsules. A physical model based on the apparent specific capacity method was adopted and validated to describe the phase transition within the capsules. The effects of various designs and operating factors on storage performance are detailed and addressed, including the thermal energy provided by the system during the discharge period, the melting temperature, tank volume, and water return temperature. The results show that the energy efficiency of such a device can be enhanced only through a judicious choice of the mentioned parameters. For example, it was found that increasing the UDHN thermal power demand influences the system's performance and leads to reduce the discharging duration. Based on the presented analyses, it can be concluded that the proposed numerical tool can be used by thermal designers of urban heating networks to size, optimise, and predict the actual dynamic behaviour of the storage system under real exploitation conditions.