Energy analysis and performance assessment of a hybrid deep borehole heat exchanger heating system with direct heating and coupled heat pump approaches

•A transient model for a hybrid DBHE heating system is first developed in TRNSYS.•Direct heating and coupled GSHP approaches are designed in hybrid heating system.•Importance of direct heating approach and dynamic load characteristic is assessed.•Energy shifting behavior of different components is observed over 10-year operation.•Parabolic soil temperature isotherm appears at the end of heating season in reality.