Ventilation effectiveness measures which of the following?

• A. The total airflow rate supplied by the ventilation system
• B. The fraction of outdoor air actually reaching occupied spaces
• C. The energy use of ventilation equipment
• D. The noise level of the ventilation system

Answer: (B)

Ventilation effectiveness is about how well the outdoor air actually gets to the spaces where people are. It measures the fraction of outdoor air that ends up in the occupied areas, taking into account how air flows and distributes within the building. A system can move a lot of air overall, but if that air doesn’t reach the occupied spaces efficiently, the effectiveness is low. The other aspects—total airflow, energy use, or noise—describe magnitude, efficiency, or acoustic performance, not how effectively outdoor air reaches occupants. So the best choice is the one that captures the actual delivery of outdoor air to the occupied spaces.