Description:
Negative Air Pressure in industrial manufacturing facilities can create problems such as:
- Exhaust fans losing performance, as the building pressure becomes negative.
- Pilot light outages and exhaust system failure on natural draft gas equipment.
- Cold air drafts and infiltration of dirt and contamination from outside.
- Difficulty opening or closing exterior doors.
Headaches and nausea among personnel due to inadequate ventilation. In temperate climates or during mild weather, moderate amounts of make-up air can be supplied by simply opening windows or overhead doors. However, this is usually not the case in industrial and commercial facilities. Forced ventilation Make-up air is required.
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.
Make-Up Air Applications:
There are three general applications for Make-Up Air Units:
- Direct Compensating Ventilation
- General Area Ventilation
- Door Heating
Direct Compensating Ventilation.
Conditioned Air is Delivered to the Immediate Vicinity of Exhaust. This is the case for welding fume extractors, stovetop exhaust hoods, paint booths, or similar applications.
General Area Ventilation.
Conditioned Air Blankets Entire Area of Building to Compensate for Many Exhausts. Introduced in Cleanest Part of Building - Flows to Negative Pressure Areas - Picks up Dust, Vapors, and Odors en route.
Door Heaters
Heated Air is introduced at open doors to warm incoming air or compensate for loss. Heater may also be used as part of an “air door” system.
Typical Industrial Uses:
* Plating Tanks
* Paint Spray Booths
* Welding Operations
* Chemical Exhaust
* Degreasing
* Factory Ventilation
* Plastic Molding
* Foundry Works
* Grinding & Buffing Operations
Typical Commercial Uses:
* Warehouses
* Kitchens
* Entryways
* Gymnasiums
* Pools
* Exposition Buildings
* Garages
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.
- Furnace Combustion Air: Minimum CFM = BTU/hr rating / 6,000.
- Drying, Baking, Curing Ovens: 100 CFM per square foot of booth cross section.
- 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 Buffalo Fan company web site http://www.buffalofan.com/news.html.
Susana Terlitsky
Canadian Ventilation HVAC Engineer
Buffalo Fan Co.
http://www.buffalofan.com/hvac.html
http://www.buffalofan.com/contact.html
http://buffalofan.com
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