# CFD Assessment of Car Park Ventilation System in Case of Fire Event
###### Abstract
CFD simulations provide a sophisticated and comprehensive tool for analyzing systems involving heat and mass transfer through computer models [13], offering insights into flow fields that would otherwise be challenging to visualize [14]. The numerical approach of CFD enables the prediction of fluid flow characteristics, including velocity, temperature, and pressure. Moreover, it allows for the extension of these predictions to forecast other factors, such as visibility, which can be compromised by smoke generated during a fire incident. In recent years, CFD modeling has become indispensable for studying large-scale underground car parks, facilitating assessments of air quality and the prediction of smoke and heat propagation in the event of a fire. Some studies have been conducted to analyze the performance of jet fan ventilation systems using numerical approaches. [PERSON] and [PERSON] [15] examined the effectiveness of jet fan ventilation systems in controlling smoke and temperature in an underground car park located in Isparta, Turkey. Utilizing Ansys 18.2 software, their analysis revealed that the smoke dissipated in under five minutes from the majority of areas, with temperatures consistently below 60 \({}^{\circ}\)C, ensuring visibility of over five meters throughout the car park. [PERSON] et al. [16] investigated the effectiveness of single and twin jet fan installations in removing CO gas in Bangkok, Thailand. They discovered that jet fans were successful in reducing harmful CO gas levels, with the most optimal setups consisting of 43 straight twin jet fans with a 1.5 m gap distance and 23 inclined single jet fans. The efficiency of CO removal was affected by energy loss in the air stream and the gap distance between the fans. Taking into account both ventilation efficiency and energy utilization, the inclined single jet fan emerged as a promising choice. [PERSON] and [PERSON] [17] numerically analyzed ventilation and smoke control of jet fan system in a garage with a capacity of 38 cars. Through CFD analyses, it was determined that the concentration of CO and air velocity profiles were influenced by the car occupancy rate and the hanging heights of the jet fans. Optimization of the jet fan hanging heights was found to be crucial in achieving effective CO exhaust and ventilation. In the context of the SARS-CoV-2 epidemic, [PERSON] et al. [18] conducted a study using the OpenFOAM C++ libraries to examine the influence of jet fans on the spread of the virus in an underground car park in Tabriz, Iran. To mitigate viral transmission, the authors recommend the establishment of safe pathways near fresh air ducts, considering the flow patterns generated by the jet fans. Additionally, the study suggests equipping jet fans with ultraviolet light emitters and high-efficiencyparticulate air (HEPA) filters as effective strategies for eliminating viruses. In addition to the abovementioned studies, some similar studies exist [19; 20; 21; 22; 23] that are summarized in Table 1.  
Despite existing numerical studies on jet fan ventilation systems in car parks, there is a need for additional research to enhance and supplement previous findings. Previous studies often focused on small-scale car parks or considered a limited number of fire scenarios to minimize computational costs. Additionally, limited attention has been given to analyzing visibility conditions following smoke propagation in car parks after fire incidents. To address these knowledge gaps, this paper aims to provide practical insights into jet fan ventilation design, with a focus on safeguarding human health during unforeseen fire events in underground car parks. The research questions to be addressed are as follows:  
* What is the impact of adding an appropriate number of jet fan lines on the ventilation system's capability to prevent back-layering and lateral smoke dispersion? * How does the comparison of jet fan airflow rates between the high and low velocity jet fans affect the dispersion of smoke in underground car parks?