For an 80' x 40' x 20' room, how much air must be moved to achieve 4 ACH?

To achieve a specific Air Change per Hour (ACH) in a room, it is essential to first determine the volume of the room. The volume can be calculated by multiplying the length, width, and height. In this case, for a room measuring 80 feet long, 40 feet wide, and 20 feet high, the volume would be:

Volume = Length x Width x Height

Volume = 80 ft x 40 ft x 20 ft = 64,000 cubic feet

Given the requirement of 4 ACH, this means that the total volume of air in the room needs to be replaced four times in one hour. To find out how much air needs to be moved per minute, use the following formula:

Airflow required (in cubic feet per minute, cfm) = (Volume x ACH) / 60

Substituting the known values:

Airflow required = (64,000 cubic feet x 4 ACH) / 60 = 4,266.67 cfm

This calculation shows that in order to achieve 4 air changes per hour in the specified room size, an airflow of approximately 4,266.67 cubic feet per minute is necessary. Therefore, the first choice is the correct