Large-scale living laboratory of seasonal borehole thermal energy storage system for urban district heating

To obtain a better understanding of the characteristics of large-scale seasonal borehole thermal energy storage (BTES), a living laboratory was developed in Chifeng, China. In the living laboratory, combined heat sources of industrial waste heat and solar energy were adopted for 500000 m(3) borehole thermal energy storage. The concept and design of the system, as well as the first operation results of the system, are presented herein. First, critical considerations for developing a large-scale borehole thermal energy storage system were briefly reviewed. The living laboratory was developed to be an experimental platform to conduct long-term field tests of major system operation options while working as an actual running application simultaneously. The flexibility of the system was enhanced using changeable system integration modes and a modular design for each subsystem. According to the monitoring results of the first heat injection period, a total of 33458.6 GJ of thermal energy was injected into the storage. The average soil temperature increased from 10.0 to 35.6 degrees C, and the core temperature increased to approximately 40.2 degrees C. The increase in soil temperature 5 m outside the storage was approximately 2 degrees C. No obvious temperature increase was observed 10 m outside the storage. The results indicate the potential of large-scale borehole thermal energy storage to be integrated into the district heating network to improve the flexibility, robustness, and energy efficiency of the overall energy system.