Optimizing Exhaust & Fresh-Air Duct Ventilation in Underground Parking Facilities Using CFD

Background

       Because underground parking lots are enclosed spaces, exhaust gases emitted by vehicles during operation (such as carbon monoxide CO and nitrogen oxides NOx) tend to accumulate easily. In the event of a fire, smoke must be exhausted within a specified time. To ensure sufficient air circulation, it is critical to install an effective fresh air duct system. For public buildings, the government also sets ventilation standards for exhaust gas concentrations.
       By using CFD (Computational Fluid Dynamics) analysis, the distribution of exhaust gas concentration and the flow of fresh air can be simulated to evaluate the performance of the ventilation system, and to analyze how the fresh air duct layout affects air exchange, ensuring that highly polluted areas can be purged quickly.
       In this project commissioned by a construction company, CFD technology was applied during the design stage to optimize the ventilation layout, adjusting the positions of supply and exhaust openings to enhance air exchange efficiency and reduce the risk of exhaust gas stagnation. Different operating conditions (such as varying traffic flows) were also simulated to predict air quality under extreme scenarios, and to ultimately provide improvement plans so that the fresh air duct system can perform at its best.

 

Illustration of jet fans in an underground parking lot

Results

       In this project, Altair SimLab was used as the pre-processor for model building, and AcuSolve served as the flow solver to conduct ventilation analysis for the underground parking lot. The study provided the distributions of fresh air and exhaust gas concentration as well as airflow velocity and patterns, under different fresh air duct designs, different fan flow rates, and different jet fan configurations.
       With these results, the owner can determine whether the current design meets the customer’s requirements and add jet fans in local areas where performance is insufficient.

Technical Highlights

• AcuSolve can simulate very light suspended pollutant particles, and can also be coupled with the EDEM particle solver to analyze the motion behavior of heavier pollutants such as dust.

• It can estimate whether, over a long period of time, the exhaust removal rate of the ventilation system is higher than the generation rate of exhaust, and can also predict the exhaust removal rate within a specific time interval.

Animation of fresh air and exhaust dispersion over time

Streamlines of fresh air and exhaust distribution

Airflow velocity distribution and vector plot

Extended Applications

       CFD analysis can also be applied to other scenarios, such as smoke control and smoke extraction system optimization during fires. By simulating fire source locations, smoke spread paths, and temperature variations, the layout of smoke exhaust ducts can be improved to ensure clear evacuation routes.
       From an energy-saving perspective, CFD can help optimize fan operating strategies (when full speed is required, when partial speed is sufficient, or when they can be shut down), reducing energy consumption while maintaining good ventilation. For multi-level underground parking facilities, CFD can also analyze airflow distribution across multiple floors to ensure that all areas maintain acceptable air quality.