# CFD Assessment of Car Park Ventilation System in Case of Fire Event
## 4 Discussion and Conclusions  
The simulations conducted using OpenFOAM provide valuable insights into the behavior of the jet fan system in controlling smoke dispersion caused by car fires within enclosed areas. The analysis involves deriving velocity fields and evaluating visibility conditions to understand the efficiency and effectiveness of the system. The main findings of the study can be summarized as follows:  
* Jet fan positioning and back-layering: The positioning of the jet fan system components significantly impacts its efficiency. Jet fans placed near the ceiling create a jet among themselves, necessitating the use of multiple lines of jet fans to prevent back-layering. Back-layering refers to \"_Movement of smoke and hot gasses counter to the direction of the ventilation airflow_\" according to National Fire Protection Association NFPA, which can reduce the ventilation efficiency. In the proposed design in this study, adding 10 extra jet fans to form additional lines in Zone 1 and Zone 3 enhances the capability of the ventilation system to prevent lateral smoke dispersion. * Jet fan air flow rate: The analysis of air flow rates shows when jet fans direct an excessive airflow towards the exhaust shafts (which have a designated flow rate of  
Figure 10: Visibility distribution for the proposed fan positioning, when two fans adjacent to the fire source in Scenario 2 are non-operational. Figure 9: Illustration of the jet fans’ operational status, with specific emphasis on the scenario where two fans adjacent to the fire source in Scenario 2 are non-operational. 22.5 m\({}^{3}\)/s), recirculating flows occur, leading to the dispersion of smoke throughout the car park. Consequently, the utilization of low-velocity jet fans (11.2 m/s) proves to be more effective in clearing smoke compared to high-velocity jet fans (22.3 m/s). * Optimal positioning of supply and exhaust shafts: Achieving optimal smoke control involves positioning the supply and exhaust shafts on opposite walls or minimizing the number of air flow turns between the supply and exhaust points. Ideally, all outlets should be placed directly opposite the inlets throughout the design, ensuring efficient ventilation and smoke control. In the proposed design, for instance, placing the exhaust shafts closer to the supply shaft in Zone 4 results in reduced back-layering compared to the same zone in the base case. * Fire resistance of jet fans: It is crucial for the jet fans utilized in the system to possess fire resistance capabilities, enabling them to continue operating for a certain duration during fire events. The study underscores the significance of utilizing fire-resistant materials and components in jet fans, as their failure can result in severe conditions. * Future research is recommended in the following directions:
* In order to further validate the findings of this study, it is recommended that future research incorporates experimental studies. By combining computational simulations with real-world experimentation, this approach will provide stronger evidence and enhance the credibility of the study's findings. * To gain a deeper understanding of the effectiveness of jet fan ventilation systems, future research should compare their performance with conventional systems, such as ventilation through ducts. This comparative analysis will offer insights into the advantages and limitations of each approach. * Future research is recommended to conduct sensitivity analysis on key properties of jet fans and supply/exhaust shafts, such as air flow rate, air velocity, thrust, etc. By systematically varying these parameters, researchers can identify their impact on system performance and optimize their values accordingly. * Future research should focus on investigating optimal jet fan positioning, aiming to provide practical guidelines that are solid and robust. This would enable engineers and practitioners to implement jet fan systems with confidence, knowing they are following the most effective and efficient layout.