Air Make-Up Ventilation Unit
Direct Gas-Fired Make-up Air Units supply tempered and filtered air to the indoor environment. In summer, a direct-fired unit may be used as an air handler, with the heater disabled. By adding a DX or evaporative cooling section to the unit, it may be used to supply conditioned air year round.
While there are no facts and figures to show how many buildings in the United States provide the correct amount of makeup air, it can be surmised that there are probably a great many that do not have sufficient makeup air. And there's no one solution that is available for every building. Each building must be analyzed with a careful air balance calculation and evaluated based on the diversity of sources of exhaust air and infiltration.
Make-Up Air Volume Requirements:
The recommended method for calculating Make-up Air Volume is to determine the total CFM capacity of exhaust fans, blowers, stacks, etc. in the building and add 10%. This will create a positive pressure in the building.
When information is not available, the following estimates may be used to determine approximate requirements:
- Paint / Spray Booth: 100 to 200 CFM per sq. ft. of face opening.
- Oven Exhaust: One air change per minute.
- Fume Exhaust: Area of Pipe (in square feet) x velocity (3,000 feet/min average) = CFM.
- Roof Ventilator: same as Fume Exhaust.
- Canopy Hoods: 100 to 300 CFM per square foot of hood open area.
- Pickling or Cleaning Tanks: 150 CFM per square foot of door opening or 200 CFM per square foot of hood face opening.
Additional information can be found at the Fan and Blower company web site http://www.fanblower.com
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ABOUT THE AUTHOR
Air Handling Units (AHU) Engineer
Fan and Blower Co.