Development of a doubly-fed compound control for hybrid ground source heat pump systems in hot summer and cold winter areas

In hot summer and cold winter areas, the impact of soil thermal accumulation is significant even for hybrid ground source heat pump systems (HGSHPs), especially after a long-term operation. To alleviate the energy performance degradation caused by soil temperature rise, a detailed temperature field heat transfer model of ground heat exchangers (GHXs) has been established and a doubly-fed compound control for HGSHPs is developed and integrated into a central controller module. The central controller can automatically control the loop flow distribution of units and achieve group activation of GHXs based on the load sequences forecasting feedforward and system variables feedback processes. Five control modes are included in the central controller, and the energy performances and soil temperature rise distribution of the HGSHPs with different control modes for fifteen years are compared. The results indicated that the HGSHPs performs best in terms of energy performance and soil thermal alleviation with Control Unit 13. Compared to the Normal control mode, the mean water temperature of GHXs, energy consumption of the chiller and heat pump decreased by 1.6 °C, 5.9 %, and 15.5 %, respectively, and the units COP increased by 11.3 %.