With rapid change of production line in Taiwan IT Industries; increased productivity/flexibility in the same cleanroom space is required urgently. We have systematically compared two cleanroom ventilation systems i.e. conventional and ceiling return system. The wall return system has fixed location of Fan filter unit (FFU), return air shaft/wall and dry coiling coil. The ceiling return system with a specially designed Fan Filter Dry Coil Unit (FFDCU) installed just above a production tool with high heat/particle sources. For a wall return system, reduced flexibility and cleanroom spaces, and inefficiently treating the high heat load cases is addressed. The ceiling return type with FFDCU can treat sensible heat of process tools efficiently while maintaining a more uniform temperature distribution. The ceiling return system combined with FFDCU exhibits a less negative pressure profile in the supply air chamber than that of a wall returns system is especially noted. This is both beneficial to energy-saving and AMC control.