Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 218 of 331

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 effi- ciently, resulting in a build-up of cont- aminated 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 out- side air entering the building through them. 5. It is difficult to maintain an even tem- perature throughout the interior space. OSHA requires the work compartment of a spray booth to be maintained at a min- 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 ef- ficiency 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 travelling to different areas of the building. The air make-up unit reduces fuel bills by eliminating drafts. Fig. 22. Vertical air replacement. Sizing 217

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