Research on Balcony-Sliding Door Coupling Ventilation Mechanisms and Energy Efficiency Optimization Based on CFD Simulation—Threshold Effects of Opening Degrees and Multi-Zone Collaborative Design Strategies

In response to the Energy Saving and Carbon Reduction Action Programme 2024-2025, this study constructs eight working conditions including balcony window opening 0%-75%, with or without sliding door for a three-room house model based on CFD, and verifies by k-εmodel that a fully closed balcony makes the living room air-age up to 196s and increases the health risk. Window openings≥ 25% improved ventilation but elevated air age in the master bedroom at >50%. Sliding doors slightly increase balcony air speed, but overall ventilation is uneven. Optimisation strategy: Prioritise the use of fixed windows without sliding doors and in the middle of 25% opening windows on both sides of the balcony; deploy an air-detection linked intelligent ventilation system. The results support residential energy-saving renovation and help achieve energy-saving goals, and will be followed up by deepening the research by integrating climate parameters and user behaviours.