In general building ventilation terms, what is the primary reason for introducing outdoor air into a space?

• A. To replace air and dilute contaminants
• B. To increase indoor humidity
• C. To heat the space
• D. To filter moisture from outdoor air

Answer: (A)

Introducing outdoor air into a space serves to maintain indoor air quality by replacing some of the indoor air with fresh air and diluting contaminants that accumulate from occupants, activities, and building materials. This dilution lowers concentrations of CO2, odors, moisture, VOCs, and other pollutants, helping the space meet ventilation requirements and keep occupants comfortable and healthy. The outdoor air is then conditioned—heated, cooled, humidified, or dehumidified—as needed to achieve a comfortable environment, but the primary purpose of bringing outdoor air in is to dilute and refresh the indoor air. The other options describe side effects or separate functions (warming the space, increasing humidity, or moisture filtering) that are not the main reason for introducing outdoor air.