Reverse Relief Airflow Prevention and Building Pressurization with a Decoupled Relief Air Damper in Air-Handling Units (OR-16-028)

Outdoor airflow rate, building static pressure, supply air duct static pressure and relief air plenum static pressure, as controlled variables, are maintained by modulating the speed of the supply and return fans and the position of the outdoor, recirculating, and relief air dampers in an air handling unit (AHU). In practice, the three dampers are interlinked completely or partially to match independent control inputs with the controlled variables. The traditional damper control has all the three dampers interlinked with no control over the relief air plenum static pressure. The reverse relief airflow might occur as the outdoor air damper approaches the closed position. To prevent the reverse airflow, one of solutions is to decouple the relief air damper and maintain positive static pressure at the relief air plenum. Two control methods are available based on the control loop design.