The term "clean room" is a term used to refer to an enclosed room in which air is delivered in highly filtered form to produce a substantially dirt and dust free environment. These types of rooms are used for sensitive manufacturing processes, for example, in the electronics and microcircuitry industry.
Typically, filter modules, for example 2.times.4 feet, are mounted in open gridwork patterns in the ceiling and are thus ganged together to produce a relatively uniform flow of air between the ceiling and floor of the room. The air is removed from the bottom of the room and recycled. Each filter module is independent of the other and has a quantity of air supplied to it. Air is diffused and passed through the filter module into the room through the air plenum assemblies. The diffusion of the air is important for uniform flow of air through the filter and into the room. Typically, air enters the plenum assembly at a central portion of the unit and is deflected laterally with an adjustable horizontal plate before passing through the filter medium. Typically, the plate is perforated so that some of the air passes through a central portion of the filter. One prior art filter plenum has a horizontal top wall along which the air flows. In this type of system, the air flow is not well distributed over the length or width of the filter medium.
Another prior art system is disclosed in the Knab U.S. Pat. No. 3,323,437 (issued June 6, 1967). Knab discloses a filter module with a frusto-converging hood. Radial creases are formed between the open bottom and the apex at the center of the hood to form triangular surfaces which deflect the air downwardly through the filter medium.