METHOD 1 – AIR CHANGE RATE
Quantity of fresh air required (CFM) = Air change rate (changes per hr) x Room volume (FT³) ÷ (60 MINUTE)
👉Air changes per hour (ACPH or ACH, or air change rate) is a measure of the air volume added to or removed from a space in one hour, divided by the volume of the space.
QUESTION – Calculate the fresh air requirements for the BEDROOM, if the air change rate was specified to be 4 changes per hour.
Room Dimension is 15’x15’ & 12’ height.
Quantity of fresh air required (CFM) = Air change rate (changes per hr) x Room volume (FT³) ÷ (60 MINUTE)
Volume of the Room = Lenth x Width x Height
= 5’ x 15’ x 12
= 2700 cuft
Quantity of fresh air required (CFM) = 180 CFM (Put the value in the formula, Consider 4 ACPH for the Bedroom From the above Chart)
METHOD 2– UNKNOWN OCCUPANCY
👉 If the occupancy of the building is unknown but if it has a particular application, such as an office computer room, then the fresh air requirements can still be calculated
👉 For the example above the fresh air requirement would be
Occupancy rate = Total Floor area (ft²)/ Floor area per person (ft²)
Occupancy rate = Total Floor area (ft²)/ Floor area per person (ft²)
Occupancy rate = 1200 (ft²)/ 200 (ft²)
Occupancy rate = 6 People
Note –
For Office Space – Person per 1000 sqft is 5 = 200 sqft/person
Quantity of fresh air required (CFM) = Occupancy rate * Rate/person (CFM per person)
= 6 * 5 (CFM per person)
= 30 CFM
