Evaluation of thermal efficiency of solar-assisted backfill coupled heat exchanger with seasonal heat storage system

Abstract

The swift consumption of non-renewable resources like fossil fuels underscores the importance of renewable energy development for the sake of long-term sustainability. The mining area is rich in solar and geothermal energy resources. This study introduces a solar-assisted backfill coupled heat exchanger system with a seasonal heat storage system (SABCHE-SHS) as a sustainable energy solution, which stores abundant solar energy in the pre-set mine backfill body, aiming to achieve heat storage in the backfill body during the non-heating period and heat extraction during the heating period. This study employed numerical simulation methods to compare the long-term performance of the SABCHE-SHS with that of the backfill coupled heat exchanger system (BCHE) relying solely on geothermal energy over a decade. The results show that the SABCHE-SHS had good heat storage and heat extraction performance, high outlet water temperature, and maintaining stable annual heat transfer efficiency under multi-cycle operation. By year ten, the SABCHE-SHS can provided higher heat storage and extraction rates of 747.34 W and 987.85 W, respectively, which are 286.34 W and 232.87 W higher than those of the BCHE. The initial outlet water temperature and the initial mean temperature of the backfill body of the SABCHE-SHS, which has been in operation for ten years, change by no more than 0.13 °C and 0.68 °C respectively. In addition, the solar energy utilization rate of SABCHE-SHS reached 57.87 % to 65.59 %, which improved the efficiency and reliability of heat management.