Measuring Indoor Airflow Patterns by Using a Sonic Vector Anemometer

Air-velocity diagrams are used frequently to describe flow patterns into exhaust hoods, but they are applied rarely to problems involving room-scale airflow. This report describes the use of a novel instrument to evaluate airflow patterns associated with dilution ventilation in a test room. Air velocity was measured with a three-dimensional sonic anemometer, which determines velocity by sensing the time of flight of ultrasonic sound pulses. This sonic anemometer can resolve both the magnitude and direction of the vector at low air velocities, making it well suited for large-scale room measurements. Air-velocity measurements were made inside a controlled ventilation test chamber with the anemometer. The time-averaged directional velocity measurements were incorporated into a vector-mapping computer program that provided a visual presentation of the airflow patterns in the chamber. Tests repeated on several different days revealed a reproducible and stable flow pattern. The test results indicate that vector anemometry may be a useful technique for identifying and quantifying room airflow patterns.