Phase change materials embedded with tuned porous media to alleviate overcharging problem of cascaded latent heat storage system for building heating

Cascaded latent heat storage (CLHS) has been used for building heating to balance renewable energy supply–demand mismatch and improve thermodynamic performance. In a cascaded latent heat storage system, the asynchronous phase transformation process of phase change materials (PCMs) at each stage leads to an overcharging problem, which reduces the heat storage rate and increases the heat loss. This study proposes a new solution to overcome this problem by embedding porous media with tuned porosity arrangement in cascaded PCMs. A 3-D transient numerical model is established to investigate the effects of tuned porosity arrangement on the charging and discharging performance of a CLHS system. The results show that this solution improves the synchronization of the phase transformation process of the PCMs to increase the latent heat storage rate and eventually the total heat storage rate of the system. Compared with a uniform porosity arrangement, the overcharging time and the overcharging time ratio of the system with tuned porosity arrangement decrease up to 89.66% and 91.93%, while the mean total heat storage rate increases by 73.21% during the melting process. In addition, the tuned porosity arrangement is beneficial to prolong heat supply time and increase the accumulated discharged heat. In all cases, the optimal tuned porosity arrangement is 0.90–0.95–0.97. The CLHS system with tuned porosity arrangement has the general good performance under different charging and discharging conditions. The proposed solution provides guidance for performance enhancement and optimization of CLHS systems for building heating.