Climate-resilient operation of hybrid GSHP–ASHP systems: 50-year energy-saving performance under climate change in Tokyo, Japan

• 50-year hybrid GSHP–ASHP simulation under CMIP6 climate scenarios. • Modelica-based model of a practical hybrid GSHP–ASHP system. • Simulation tracks load evolution and long-term subsurface thermal drift. • Cooling-to-heating load (C/H) ratio is a key factor in sustaining GSHP performance. • Designing C/H ratio ≈ 0.4–0.6 in the 2020s sustains long-term energy savings. Ground-source heat pumps (GSHPs) offer high efficiency and strong potential for decarbonizing building operations. However, their long-term performance under climate change and practical integration with air-source heat pumps (ASHPs) remains insufficiently understood. This study addresses this gap by developing a physics-based simulation framework to evaluate the energy-saving performance of a hybrid GSHP–ASHP system over 50 years for an office building in Tokyo, Japan. Future climate conditions were modeled using Shared Socioeconomic Pathway scenarios, and system performance was benchmarked against an ASHP-only configuration. Results indicate that when the GSHP-handled annual cooling-to-heating load (C/H) ratio is designed at ∼0.4–0.6 in the 2020s, the annual energy-saving rate (ESR) remains stable at ∼17–20% across five decades, despite climate-driven shifts in cooling and heating demand. In contrast, designs with C/H ratio ≥1 experience ESR deterioration due to subsurface thermal build-up and reduced heating loads. Sensitivity analysis shows that higher apparent ground thermal conductivity mitigates long-term ground temperature rise, expanding the acceptable cooling share (C/H ratio increases from 0.6 to 1.0 as conductivity rises from 1.5 to 2.0 W/(m·K)). These findings demonstrate that GSHPs can sustain energy-saving performance under climate change when C/H ratio is properly designed. Future work should focus on strategies to manage ground thermal imbalance while optimizing both cost and efficiency.