Minimum Outdoor Air Control and Building Pressurization with Lack of Airflow and Pressure Sensors in Air-Handling Units

Abstract

Ideally, minimum outdoor air and building static pressures are controlled through feedback controllers with the use of airflow and pressure sensors in air-handling units (AHUs). Unfortunately, because these sensors are not always installed in AHUs, it is common to maintain the minimum outdoor airflow by fixing the AHU control dampers at minimum positions and maintain the building static pressure by tracking the return fan speed with the supply fan speed. The purpose of this paper is to evaluate the system performance of these alternative controls. The outdoor airflow and building static pressure of an AHU is simulated using a nonlinear network solution. The simulation results show that the fixed damper position method can approximately maintain a constant outdoor airflow ratio with an appropriate damper connection if the building static pressure is perfectly controlled. The return fan speed linear tracking method along with the fixed damper position method shows performance in maintaining the minimum outdoor airflow ratio and positive building static pressure that is better than that with the return fan speed proportional or offset tracking method.