Thermal investigation of in-series vertical ground heat exchangers for industrial waste heat storage

• A novel ground heat exchanger for seasonal thermal storage is proposed.
• The transient heat transfer model of the multistage-series GHE is developed.
• The steady-flux model is established for the design of thermal storage.
• The thermal effects of some parameters on thermal storage are investigated.

This paper presents a novel ground heat exchanger configuration with vertical boreholes connected in series to be used for the seasonal thermal storage of industrial high-temperature condensation heat. The transient simulation model of multistage-series circuits is developed and the simplex method is employed to solve the outlet/inlet temperatures and the heat transfer rate fraction of each circuit. A simplified steady-flux model is also proposed to design a large-scale seasonal heat storage system. Finally, the effects of some critical parameters on the thermal performance of the GHE with multistage-series circuits are investigated. The results show that both optimum borehole spacing and the higher thermal properties of the ground can improve the thermal efficiency of the storage system and reduce the capital cost accordingly.