Energy-economic-environmental analysis and multi-objective optimization of district heating and cooling system with long-term and short-term thermal storage

District heating and cooling (DHC) systems are widely applied because of remarkable economic efficiency and significant energy-saving potential. To address the issues of low utilization of seasonal pit thermal energy storage, a novel DHC system integrating long-term and short-term thermal storage is proposed. The NSGA-II algorithm and TOPSIS method are employed for equipment capacity optimization and sensitivity analysis, aiming to reduce both life-cycle costs (LCC) and annual CO2 emissions. In addition, a comprehensive evaluation of system performance and applicability is performed from energy, economic, and environmental perspectives across four building types and ten typical cities. The results indicate that, compared with the baseline system, COP of the proposed system increases by 63.89 %, while its LCC, levelized cost of energy, and annual CO2 emissions decrease by 49.91 %, 51.56 %, and 68.71 % respectively, with an investment payback period of only 2.73 years. The systems are most suitable for hospitals, followed by hotels, markets, and offices. The systems in cold and severe cold regions with abundant solar radiation achieve better performance than those in hot summer-cold winter regions with limited solar resources. The novel DHC systems enhance the comprehensive performance, providing a technical pathway for the low-carbon transition of regional energy systems.