When designing equipment operated by hydrogen as an energy source, safety issues should be considered due to the following physical and chemical properties of hydrogen: hydrogen embrittleness, wide range of flammability limit (4 ~ 75 vol%) and low minimum ignition energy (0.02 mJ). Therefore, it is important to predict the behavior of hydrogen when it is released in an enclosed system. Much research has been conducted to identify hydrogen behaviors and to develop standards and regulations for hydrogen facilities. However, due to the lack of standards and regulations in Korea with respect to hydrogen facilities safety, alternative regulations have been commonly applied: Urban Gas Service Law. Therefore further verification of the effect of hydrogen ventilation is necessary to develop Korean safety regulations around the ventilation systems. In this work, to determine the ventilation requirement in an enclosure system, computational fluid dynamics (CFD) model was developed. To assess the effect of ventilation, further simulations based on the experimental data of HYPER project (installation permitting guidance for hydrogen and duel cells stationary applications) were conducted with a broad range of operating conditions. As a result, the case with crossed ventilation location was the most effective configuration to reduce hydrogen concentration in the system. For other conditions, most of the cases exceeded 1% of hydrogen concentration in an enclosure. In conclusion, the bulk of cases required further reduction of hydrogen concentration and additional measures such as forced ventilation. These results will be a good reference for establishing a standard with regards to safety issues of hydrogen industries and facilities.