A damper control system for preventing reverse airflow through the exhaustair damper of variable-air-volume air-handling units

Traditional air-handling unit (AHU) control systems link the position of th e exhaust, recirculation, and outdoor air dampers. Laboratory rests of a va riable-air-volume AHU using the traditional damper control approach reveale d that outdoor air could enter the AHU through the exhaust air damper. This can negatively impact indoor air quality. This paper examines the conditio ns that lead to this phenomenon and presents a new control system that can help alleviate the problem. The new control system links only the position of the exhaust and recirculation air dampers. During occupied rimes, the ou tdoor air damper is fully open. Simulation results are presented that demonstrate that the new damper contr ol system prevents air from entering the AHU through the exhaust air outlet for all but extreme conditions that are described in the paper. Laboratory and field rest results are presented that demonstrate that the new control system prevents air from entering the AHU through the exhaust air outlet f or the same conditions that cause significant reverse airflow for the tradi tional control system. Furthermore, reverse airflow tvas not observed for a ny of the conditions examined in the laboratory! and field tests when the n ew control system was used.