Analysis of hybrid pumped thermal - liquid air energy storage integrated with a district cooling system

Liquid air energy storage is a thermo-mechanical energy storage technology that offers high energy density, geographical flexibility, and scalability. However, its relatively low round-trip efficiency and high capital cost
limit its widespread adoption. Pumped-thermal liquid air energy storage (PT-LAES) is a hybrid system that uses a reversed Brayton cycle (pumped-thermal branch) for air liquefaction during charging. During discharging, the air that evaporates in the liquid air branch acts as a heat sink for the Brayton cycle in the pumped-thermal branch. The PT-LAES configuration can match or exceed the efficiency of traditional liquid air energy storage while increasing the energy density and potentially reducing the cost. Moreover, the hybrid system eliminates the need for high-grade cold storage and allows full liquefaction of air during charging, unlike traditional systems using a Linde liquefaction cycle. While liquid air energy storage can be integrated into multi-energy systems, using cold storage for district cooling reduces the round-trip efficiency due to a strong reliance on recycled cold energy. The objective of this study is to evaluate the impact of cold extraction from pumped-thermal liquid air energy storage on the round-trip efficiency. Furthermore, this paper is aimed at identifying an optimal system design for efficient district cooling supply using the investigated storage system. Design, steady state thermodynamic models were developed, and thermodynamic optimisation was conducted. Multiple system configurations were investigated and optimised, including single-stage and two-stage pumped thermal cycles. This study introduces the novel application of pumped-thermal liquid air energy storage for district cooling, optimising two system configurations to enhance the round-trip efficiency. The results suggest that PT-LAES can more efficiently use the evaporation energy of liquid air for district cooling. When 20 % of the total evaporation energy is applied to district cooling, the round trip efficiency penalty is less than 1 % for the two-stage PT-LAES system and 5 % for the single stage, compared to 25 % for the traditional liquid air energy storage. The findings are relevant for developing a reliable multi-modal liquid air energy storage system capable of efficiently supplying heating, cooling, and electrical power.