Most residential and commercial multi-story buildings feature basement car parks for ease of access and optimization of space. Since these car parks are located underground, designing an appropriate ventilation system is vital for ensuring continued air supply in these areas.

When the car park or service area is in general use, it is vital that the exhaust produced by vehicles are effectively removed and that there are no pockets of stagnant air. Mechartés uses CFD to analyze the effectiveness of ventilation systems in underground car parks as their adequate functionality is necessary to guarantee the fire safety compliance of the facility.

Our engineers perform CFD analysis for daily ventilation of pollutants like carbon monoxide (CO), carbon dioxide (CO2), nitrogen dioxide (NO2), and particulate dust that are emitted from parked vehicles. The ventilation of these underground spaces is essential to ensure the health and safety of the on-site staff and reduce their exposure to pollutants which can lead to respiratory ailments.

Harmful Effects of Carbon Monoxide (CO)

The levels of CO gas are commonly used to indicate the indoor air quality of enclosed spaces like underground car parks. Employees working in such areas are exposed to high CO levels daily, making them susceptible to several respiratory tract ailments. The above claims are confirmed by studies undertaken on breath samples acquired from the employees working in and around underground parking spaces.

Common symptoms of prolonged exposure to CO fumes include breathlessness, headaches, and late afternoon sleepiness. Carbon monoxide is classified as an asphyxiant chemical gas whose toxic action directly results from the anoxia produced by a given exposure. The gas rapidly diffuses across the alveolar membrane and is quickly absorbed through the lungs. A fully functional and equipped ventilation system for basement car parking is essential to ensure the health and safety of the visitors and the employees working at such facilities.

Effect of CFD Analysis on Car Park Ventilation

Until recently, the underground car park ventilation system was based on a ductwork system that prevents the formation of stagnation zones. The appropriate distribution of inlet and outlet openings forms the backbone of the functioning of this expensive and bulky setup. The recent introduction of jet fans generates internal ventilation flow by concentrating the inlets and outlets in some areas of the underground facility. The induction jet fan eliminates the duct system and takes care of the supply and exhaust in the area. The jet fans in the ventilation system helps expel the smoke from the site facilitating ease of evacuation in case of an emergency. The positioning, velocity, and direction of the jet fans inside the facility are important to ensure effective smoke expulsion in case of fires.

A computational fluid dynamics (CFD) analysis of the facility can help visualize the area in 3D space and detect the best possible solutions for positioning jet fans and designing effective ventilation systems in basement car parks. The use of jet fans also promotes the admission of fresh air into the system. CFD is used to provide design recommendations and suggest improvements to the positioning and other characteristic features of jet fans used in the ventilation system. It helps visualize the placement of the fans with respect to the layout in three-dimensional space to understand how multiple fans will interact in a covered basement car park scenario.

CFD models have the ability to account for columns, beams, internal walls, and other construction elements which could form an obstruction to the airflow. Due to these features that allow the analysis and study of smoke movement inside complex spaces, CFD analysis is gaining popularity in recent times to improve the fire safety compliance of these underground spaces. Application of commercial CFD programs like ANSYS Fluent and ANSYS CFX for ventilation simulation in basement car parks reduces experimental human error.

Enhancing Carbon Monoxide Removal Using CFD

Mechartes uses CFD to investigate the performance of existing or conventional ventilation systems in enclosed complex underground car park areas by enhancing the removal of CO gas and improving air circulation. We develop appropriate and functional CFD models using single and twin-jet fan installation setups, like the turbulence model. The tilt angle and gap distance and their effect on ventilation performance are explored. In addition, energy consumption is considered to find the best potential jet fan installation configuration by defining the distance between the fans. Jet fans have a pumping effect entraining the surrounding contaminated air into the jet. They can restrict the dispersion of contaminants provided that the exhaust flow rate from the car park is not lower than the jet flow rate. Jet fans are mainly used to generate a flow so that the pollution is driven to the exhaust outlets.

CFD simulations, when performed correctly, are reliable and complementary to experiments in the sense that one gains additional insight from the analysis. Creating a 3D model of the underground area with the location of fresh supply and exhaust is of paramount importance. The number of jet fans is decided based on the concentration of CO gas that needs to be expelled to meet the desired CO levels and velocity profile inside the car park levels.

After optimization, the system is tested for the transient behavior of smoke and other contaminants like CO gas. The final leg of the process involves testing the time taken by the emergency system to expel the contaminants from the basement area. The knowledge obtained from our simulations helps our researchers and engineers improve the existing ventilation system or to increase its performance. We have undertaken several projects to enhance the circulation of existing facilities while also designing the ventilation systems for newly constructed basement car parks.

The Takeaway

The results from our simulation are used to identify recirculation areas and provide a detailed 3D analysis of the movement and build-up of pollutants like carbon monoxide inside basement car parks. In addition, the simulations provide the performance analysis of ventilation systems while highlighting areas for installing jet fans inside such facilities. Our models can evaluate the airflow rates and thermal loads to optimize energy consumption.

Mechartés undertakes projects which involve reconfiguring existing facilities and designing new ones. So, feel free to contact our service advisor for more details.