What is the first step when applying ACH to IAQ improvement?

What is the first step when applying ACH to IAQ improvement?

• A. Determine the desired ACH
• B. Replace all equipment
• C. Increase lighting
• D. Shut down the system

Answer: (A)

Setting the target air changes per hour establishes the ventilation goal for the space. ACH is a rate that tells you how often the entire indoor air volume should be replaced each hour, so you need to decide that target before you can design the system. Once you know the desired ACH, you can calculate the required outdoor airflow from the room volume (CFM = ACH × room volume in cubic feet ÷ 60) and choose the appropriate equipment and controls to meet that rate. Occupancy, activities, and pollutant sources guide what ACH level is appropriate, balancing IAQ with energy use. The other options don’t provide the design basis you need: replacing equipment, increasing lighting, or shutting down the system doesn’t specify or achieve the target ventilation rate needed to improve IAQ.

Setting the target air changes per hour establishes the ventilation goal for the space. ACH is a rate that tells you how often the entire indoor air volume should be replaced each hour, so you need to decide that target before you can design the system. Once you know the desired ACH, you can calculate the required outdoor airflow from the room volume (CFM = ACH × room volume in cubic feet ÷ 60) and choose the appropriate equipment and controls to meet that rate. Occupancy, activities, and pollutant sources guide what ACH level is appropriate, balancing IAQ with energy use.

The other options don’t provide the design basis you need: replacing equipment, increasing lighting, or shutting down the system doesn’t specify or achieve the target ventilation rate needed to improve IAQ.