HVAC Control in the New Millennium.pdf - HVAC.Amickracing

Advanced HVAC Control, Information Technology and Open Systemssurrounding corridor to block the leakage of contaminated air. The cleanroom is made up of work areas which are considered as zones. Theremay be several hundred zones in a plant.Zone ControlAir is supplied to the zones through filters located in the ceiling.The flow and temperature of the air are both controlled. The exhaust airis evacuated in the lower area of the zone. In semiconductor manufacturing,each workstation has its own air supply filter and exhaust outlet.In order to contain any toxic fumes, clean air enters the workstationat a velocity of about 75-fpm (0.38 m/s). The air that is not pulledin by the exhaust system is recirculated back into the workstation witha fan. The rest of the air is returned by a return air header. A damper inthis header is modulated to control the air pressure.Pressure ControlThe pressure in the isolating corridor acts as the reference for thearea pressure controller. This controller maintains a few hundredths ofan inch of positive pressure relative to the isolating corridor.The quality of the building construction determines how high thissetpoint will be. Even with lower quality buildings where leakage mayFigure 4-1. Clean room area with workstations and isolating corridor.©2001 by The Fairmont Press, Inc. All rights reserved.