Thermal performance of two-independent-circuit borehole heat exchanger in solar-assisted ground source heat pump system

Abstract

The Two-Independent-Circuit Borehole Heat Exchanger (TICBHE) has become the focus of attention, partly due to the potential to reduce system complexity of circulating fluid loops and increase the system performance of the traditional Solar-assisted Ground Source Heat Pump (SGSHP) system. However, the ground was usually regarded as homogeneous media, limited research has been conducted on the effect of the geological stratification on the SGSHP system with TICBHE. Therefore, a numerical model of TICBHE is firstly established and validated by relevant experiments, and its thermal performance is analyzed and investigated. Additionally, the thermal performance of the TICBHE is compared and analyzed with different independent systems including the Photovoltaic-Thermal (PVT) Coupled with Single U-pipe Borehole (SUBPVT) system and Heat Pump Coupled with Single U-pipe Borehole (SUBHP) system. The results show that the difference between the inlet and outlet water temperatures of the Heat Source (HS) and the Heat Pump (HP) circuit in the SGSHP system is respectively increased by 0.6 °C and 0.1 °C. The total heat injection of the SGSHP system is 417.2 kWh, 19.7% higher than that of the SUBPVT system. The total heat extraction of the SGSHP system is 457.8 kWh, a 2% increase compared with the SUBHP system in the 12-day operation. Moreover, the whole power generation of the SGSHP system is 4.4% higher than that of the uncooled PVT collectors. The average Coefficient of Performance (COP) of the heat pump in the SGSHP system is 7.7% higher than that of the SUBHP system in the 12-day operation.