In a traditional ventilation arrangement, a wall return system containing a ceiling air supply and wall exhaust is used in non-unidirectional airflow type cleanrooms. In industrial cleanrooms, such as semiconductor cleanrooms, however, larger process tools result in smaller passage of airflows towards the wall-exhaust vents due to larger footprints and volumes of process tools. Additionally, only sub-micron particles are a concern for semiconductor cleanrooms (Hu and Wu, 2003) and these particles are with very small magnitudes of terminal velocities when moving in cleanroom air (Hinds. 1999). The conventional wall return system used in existing high cooling load cleanrooms aims to create a uniform air temperature distribution and a diluted particle concentration environment in which the downward cold supply air from ceiling filters encounters upward air currents due to exhaust heat as well as particle sources from process tools. To address the problem, this study proposes a unique local air exhaust system that can significantly improve the air cleanliness level and remove heat loads efficiently. The main component is a Fan Dry Coil Unit (FDCU) installed on the ceiling above the process tool in order to extract heat and particles released from the tool. The new proposed system is therefore referred as the FDCU system. An experimental study was conducted in a fullscale cleanroom with real process tools to compare the performance of both systems. Results show that more than 50% of particles were eliminated by the proposed FDCU system as compared to that of the conventional wall return system. The proposed FDCU system is also useful for solving problems such as a high negative static pressure in the supply chamber and high flow resistance in the flow path of the conventional wall return system. The measured pressure in the supply chamber was 2 Pa (2.9 × 10^{–4 psi}) for the FDCU system, while that of the wall return system was a negative value which varied proportionally to the air change rates of the cleanroom.

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