Occupant behavior-driven optimization of PCM parameters for enhancing energy performance in lightweight buildings across different climates

Lightweight buildings have low thermal inertia and are therefore highly sensitive to climate disturbances and internal heat gains caused by occupant behavior. Phase change materials (PCM) can enhance thermal inertia, but their activation and effectiveness strongly depend on occupant behavior (how buildings are operated), which is often neglected in existing studies. Therefore, a behavior-driven adaptability assessment framework for PCM applications (energy-saving) in lightweight buildings was constructed in this study using EnergyPlus. Four representative climates, four envelope materials, and three occupancy variables are coupled with PCM parameters, including phase transition temperature (PTT), transition width (ΔT), and layer number, to evaluate energy-saving contributions and parameter matching. Results show that occupant behavior fundamentally reshapes PCM effectiveness by driving systematic shifts in optimal parameters of PCM. Under optimal conditions, PCM reduces annual total load by 6.75%–10.40%, and heating/cooling loads by up to 24.9%/40.5%. Both PTT and ΔT present optimal ranges rather than monotonic trends. Expanding ΔT from 1 ℃ to 3–5 ℃ yields an additional 7%–12% reduction in annual load, after which the benefit approaches saturation. Raising the air-conditioning (AC) set temperature by 2–4 ℃ shifts the optimal PTT (PTT_op) upward by about 1–2 ℃ in summer and 1–5 ℃ in winter. Continuous AC running (all day) achieves 12.1%–26.4% savings, whereas intermittent use may weaken or even reverse the benefit. Increasing indoor occupancy density (IOD) from 0.1 to 0.5 persons/m² further moves the PTT_op higher by 1–3 ℃ and reduces annual load by 2%–6%. PCM performs better in low thermal resistance envelopes (9%–12%) than in high resistance ones (4.6%–7.2%). The energy-saving contribution and behavior-sensitive parameter ranges of PCM proposed in this study can provide theoretical support for PCM configuration and deployment in lightweight buildings.