Passive ventilation for sustainable underground environments from traditional underground buildings and modern multiscale spaces

Ventilation is the primary means to control the health risks from ‘high heat, humidity and pollution’ in urban underground spaces. Natural ventilation helps reduce the energy and carbon of mechanical ventilation but remains a challenge, especially in high-density cities and global warming. This study aims to explore the potential of passive underground ventilation in high-density modern cities, which contributes to alleviating potential conflicts between health and energy. As a historic and widespread method, passive ventilation improves the climate adaptation and energy efficiency of building forms while introducing natural elements to improve physical and psychological health. This paper reviews the representative cases and studies on passive ventilation in traditional underground buildings and analyses their principles and problems using computational fluid dynamics (CFD) simulations. Further, this paper proposes design highlights and space prototypes for ‘space–airflow’ coupling from multiscale spaces. The design highlights include the following: 1) urban scale: urban wind corridors and downdraught from the ground/overhead; 2) site scale: microclimate and coupling layout between the pressure difference and the air inlet/outlet; 3) building scale: integrated layout of ventilation and functional spaces; and 4) room scale: ventilation mode and efficiency. The CFD results indicate that optimising the layout and form of spaces effectively enhances the natural ventilation. These findings were previously obscured and overlooked in urban design and architectural design. This study helps urban designers, architects, engineers and researchers achieve comfortable and adequate natural ventilation when exploring sustainable underground spaces.