Metal Finishing Guide Book

2012-2013

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hausting contaminants from the space. Exhaust fans are rated for a certain air delivery measured in cubic feet per minute (cfm). This rating is based on a specific static pressure. Static pressure is the friction the fan must overcome to exhaust air. The more cracks and openings in the building (and the larger they are), the easier it is for air to move into the building. As the static pressure rises, the exhaust air decreases. When to Install an Air Make-Up Unit Use the following checklist to determine if a building needs an air make-up unit. 1. Gravity systems, such as vent stacks from a gas-fired furnace or water heater that normally draw air out of the building, are pulling outside air in. 2. Exhaust systems are not operating efficiently, resulting in a build-up of contaminated air within the facility. 3. The inside perimeter of the building is cold because the outside air is being pulled into the building. 4. Exterior doors are hard to open or close because of the pressure exerted by outside air entering the building through them. 5. It is difficult to maintain an even temperature throughout the interior space. OSHA requires the work compartment of a spray booth to be maintained at a minFig. 22. Vertical air replacement. imum temperature of 65��F. To meet this regulation, it is mandatory that heated air make-up be used during the winter months. Installing an air make-up unit sized to the building will improve exhaust system efficiency and provide greater control over the interior temperature. With the correct balance of air, it is easier to control air pressures to alleviate problems in opening or closing doors. Balance also prevents contaminants or odors from 837

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