Sizing of Systems
The major difference is in the airflow calculations. A C-17 paint barn will have a cross sectional area of 210 ft x 70 ft (14,700 sf). Even if only part of this area is ventilated the air volume will be around 1.1 million CFM. A paint “booth” will require 200 ft x 25ft (5,000 sf) and require only 500,000 CFM of airflow. This is a significant difference in the amount of utilities required. The horsepower required for the paint barn would be about 1850 HP. The horsepower required for the paint “booth” is only 860 HP.
If humidity and temperature control is required, the refrigeration load of the paint barn is about 4000 TR. The size of the mechanical plant for this tonnage is impressive and of great significance. It requires a couple of very large chilled water systems, pumps and expansion tanks, and large piping systems. In addition, a cooling tower system is required to cool the condenser of the chillers. The cooling tower requires much of the same ancillaries, such as piping, reservoir, water treatment and pumps.
All of this large equipment requires much floorspace and probably a separate building to house and maintain the equipment. The electrical plant is also quite significant, involving a sub-station and high voltage distribution. The engineering of the electrical plant is quite significant of itself. With a paint booth, the refrigeration load falls to about half of that figure, proportional to the airflow.
If recirculation is used in either arrangement, the installed horsepower stays about the same, but the refrigeration load falls to a quarter of the above numbers. In the case of the paint booth, approximately 500 TR is required to cool the booth. This is a much more manageable proposition and may even be accomplished with standard packaged chilled water systems.
Lights are carefully arranged to get maximum intensity in the area where paintable surfaces are located. In addition, the lights are only 7-8 feet above the fuselage at this point and lighting is extremely good. The large number of lights is also arranged to cast light onto the floor in strategic locations to allow for reflectivity to the underside of the fuselage and wings.
Sidewall lighting further augments the reflected lighting to give a highly visible surface at any point on the airplane. This helps the painter to eliminate skippers, runs and dust and dirt inclusions. More importantly, areas where corrosion would originate are found and repaired.