Configuration optimization of a novel multi-energy coupled low temperature district heating system based on distributed absorption and compression heat pumps

Utilizing low-temperature hydro-geothermal heat for district heating contributes to reducing carbon emission, but low efficiency of geothermal utilization and location mismatch between hydro-geothermal field and load center are two keys to development of the medium-deep hydro-geothermal fields. To solve the above two problems, a novel multi-energy coupled low-temperature district heating system based on distributed half-effect absorption and compression heat pumps is proposed. In the heating substations, the half-effect absorption and electric compression heat pumps integrated with heat exchangers are used to lower return temperature of the primary heating network, improving utilization of low-temperature geothermal heat and heat transmission distance. The proposed systems are analyzed from perspective of thermodynamics and economics, and evaluated using a comprehensive evaluation. Results indicate the proposed system demonstrates superior performance in annual system coefficient of performance (15.92), annual system production exergy efficiency (53.90 %), and annual low-temperature geothermal heat utilization efficiency (90.37 %). This proposed system exhibits the lowest heating cost (53.8 ¥/GJ) and the shortest dynamic payback period (5.6 years). Compared with the conventional heating system, the proposed system reduces carbon emission by 89.14 %. Thus, the proposed system is an optimal solution for long-distance heat transmission, providing development of the medium-deep hydro-geothermal fields far from urban districts.