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

Traditional air-handling unit (AHU) control systems link the position of the exhaust, recirculation, and outdoor air dampers. Laboratory tests of a variable-air-volume AHU using the traditional damper control approach revealed that outdoor air could enter the AHU through the exhaust air damper. This can negatively impact indoor air quality. This paper examines the conditions 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 times, the outdoor air damper is fully open. Simulation results are presented that demonstrate that the new damper control 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 test results are presented that demonstrate that the new control system prevents air from entering the AHU through the exhaust air outlet for the same conditions that cause significant reverse airflow for the traditional control system. Furthermore, reverse airflow was not observed for any of the conditions examined in the laboratory and field tests when the new control system was used.