Thermo-economic analysis of composite district heating substation with absorption heat pump

A novel composite district heating substation (CDHS) with absorption heat pump was proposed and analyzed in this paper. The CDHS was composed of a water-LiBr absorption heat pump and two plate heat exchanges, which could improve the utilization efficiency of geothermal water and the primary supply water of the primary district heating network. The effect of geothermal water temperature and mass flow rate, and primary supply water mass flow rate variation on system performance were investigated and analyzed by case study. The objective was to maximize net profit and minimize payback period by the cascade utilization of the geothermal water and primary supply water. In addition, economic analysis and multi-objective optimization were conducted to find the optimal mass flow rate of the primary supply water based on the TOPSIS decision making method. Exergy loss analysis was applied under the optimal condition to discover which components had the largest exergy loss. Results indicated that, the proposed system had a net profit of 16.22 M$ in the life time and the minimum payback period was 2.2 years at the optimal primary supply water mass flow rate of 46.16 kg/s where the COP and exergy efficiency of the system were 1.85 and 59.81%, respectively.