Monitoring Airflow in Occupied Buildings, the Dynamics of Balloons

Carrying out tests on occupied buildings presents several challenges. Typical instrumentation that can be used in unoccupied test cells cannot be used in occupied spaces. We have videotaped the behavior of helium filled balloons to track the airflow patterns within the building. If the balloons closely follow the local average airflow behavior they will provide substantial insight. For neutrally buoyant balloons, the observed horizontal motions should provide an accurate picture of the corresponding air motions. Although the balloons are adjusted to be neutrally buoyant when they are launched, if they move into a region where the air temperature differs, neutral buoyancy is no longer assured. In this paper the equations of motion in the vertical direction are solved for a balloon to predict its behavior within building interiors with typical vertical temperature patterns. If the balloons, initially balanced to neutral vertical equilibrium move into a region with a different air temperature, the balloon will exhibit vertical motion. The motion will be contrary to intuition Balloons will tend to rise in colder air and fall in warmer air.