Multi-mode operation of a PVT heat pump soil cross-seasonal energy storage system with fuzzy logic control

To enhance the energy efficiency and reduce the CO2 emissions of integrated building energy systems, this study addresses the limitations of conventional ON/OFF control by developing an advanced fuzzy logic control strategy for a PVT heat pump soil cross-seasonal energy storage system. Operational analysis of a system in a Dalian commercial building across eight modes revealed suboptimal pump operation, with loop temperature differences frequently below the 5 °C design threshold, indicating significant pump energy wastage. The fuzzy control strategy dynamically regulates the flow rates of both the source and PVT pumps. A dynamic simulation model was developed in TRNSYS, uniquely integrating the coupled effects of variable flow on temperature difference and hydraulic resistance to accurately assess system annual performance. The results demonstrate, compared to the conventional ON/OFF control (heating COPs is 4.2, cooling COPs is 4.4), the fuzzy control applied to the PVT pump, source pump, and PVT + source pump increased the heating COPs by 1.5%, 4.1%, and 5.7%, enhanced the cooling COPs by 7.1%, 18.3%, and 25.7% and reduced CO2 emissions by 1.4, 3.7, and 4.7 t, respectively. The fuzzy control of PVT + source pump achieved the lowest emissions, with control of the source pump identified as the dominant factor for CO2 emissions reduction. This study demonstrates that a novel fuzzy logic control strategy, which optimizes pump flow by considering hydraulic-thermal coupling, is highly effective in unlocking the system's operational efficiency and environmental performance potential.