Abstract
It is important to prevent contamination risk in a clean room even if the door is opened or closed. To control pressure difference between rooms is usually applied for a clean room and it goes well when the door is closed. But if the door is opened, pressure difference could not be kept at the setting level, so air currents go back and forth and are mixed in the doorway. And another problem is occurred. After door is closed again, variation of room pressure is too high or too low, so the pressure difference would be sometimes reversed and an air current with dust is inhaled from an unexpected gap to the clean room. We suggest a new technique which switches control methods in response to door opening/closing, which is called hybrid pressure control. If the door is closed, presser control is applied. If the door is opened, air volume control is applied to form an air flow in the doorway from high pressure room to low pressure room. And if the door is opened widely, sufficient air flow in the doorway is formed to prevent dust from coming in the high pressure room. If the door is opened narrowly, the air flow in the doorway is kept slightly and the air volume is balanced in each room to make pressure variation smooth. We verified pressure and airborne particle concentration variation with opening-and-closing operation of the door. And also we verified the flow direction visualized by smoke and measured velocity in the doorway and germ variation near the door. Then we obtained good results that agree with our intention and could verify the validity of our hybrid pressure control.
