Investigation on control strategy for operating mode switching of a PVT heat pump soil cross-seasonal energy storage system

Photovoltaic-thermal (PVT) heat pump soil cross-seasonal energy storage systems face operational control challenges due to complex coupling mechanisms and time-varying meteorological conditions. However, existing studies lack a control approach that responds dynamically to key parameters, including ambient temperature, solar radiation, and soil temperature. This study addresses this gap by proposing an eight-mode operation control strategy based on temperature- and radiation-based switching (TR-8). The proposed TR-8 strategy was implemented and evaluated using a TRNSYS dynamic simulation model. System performance was compared under three control strategies for a building in Dalian (IIB climate zone): the conventional time-based five-mode (TI-5) strategy, the time-based eight-mode (TI-8) strategy, and the proposed TR-8 strategy. Results show that compared to the TI-5 strategy (heating COPs = 4.18, cooling COPs = 2.80), TI-8 increases heating COPs by 1.0% and cooling COPs by 9.6%, while TR-8 achieves larger improvements of 6.1% and 17.5%, respectively. The TR-8 strategy was further extended to three additional zones: IA (Hohhot), IB (Wuwei), and IIA (Shenyang). In solar-rich regions (Hohhot and Wuwei), TR-8 increases heating COPs by 12.7% and 8.3%, respectively, compared to TI-5. In regions with lower soil temperatures (Shenyang and Hohhot), cooling COPs increase by 117.0% and 111.1%, respectively. CO2 emissions are reduced by 10.7 t (Hohhot), 10.7 t (Wuwei), 8.9 t (Shenyang), and 5.3 t (Dalian). These results demonstrate that the proposed TR-8 operation control strategy delivers superior performance in regions with abundant solar radiation and low soil temperatures, offering an effective approach for decarbonizing building energy systems.