Mounteer and Scholler (1987) describe a cleanroom design at a pressure-transducer manufacturer that uses an arc-shaped filter, which helps cut operating costs.
Even though the cleanroom facility was originally designed for Class 1000 operation (less than 1,000 particles of 0.5 or larger/ft3 of air), testing by Federal Standard 209b shows the operation approaching the Class 100 standard. Class 10 operation is obtainable by changing the high-efficiency particulate air (HEPA) filter.
The heart of the cleanroom facility is the arc-shaped HEPA filters and the resulting air-flow control. Because the filter sits where the wall and ceiling meet, the air falls diagonally across the room to a low-exhaust, return-air prefilter on the opposite wall at floor level. The exhaust vent draws heavy and light particles alike. Air flow is uni-directional with little turbulence, but it is not perfectly laminar. In any laminar or unidirectional flow, the stream is disrupted by many factors, such as equipment, convected heat, and people. These flow-disrupting factors create turbulence, which causes particulate matter to re-enter the air stream.
Turbulence is also a function of air velocity. In so-called laminar-flow cleanrooms, where the HEPA filter occupies an entire wall or ceiling, air velocity must be high to meet the federal standard for air velocity through the filter (90+20 fpm). ...the arc-shaped HEPA filter occupies only 1/3 the space of a full-wall filter. Hence, the required air-flow volume is cut by a factor of three. The exit air velocity is from 90 to 100 fpm, but the overall air velocity in the room is less, drastically reducing turbulence.
Operating costs are directly related to air flow. Fans and air conditioning equipment in ... [the] cleanroom facility are much smaller, which accounts for the 67% reduction in operating costs.
Design for the future. The cleanrooms are expandable for future growth and are portable in case they need to be moved. The structure is of white, melamine hardboard-and-insulated-core prefabricated panels assembled into extruded, anodized aluminum frames. The entire structure is sealed with silicone-rubber to control air loss and particle intrusion. In fact, these cleanrooms, which have been in operation for 9 years, have required only one filter change. With the filters being near the ceiling instead of occupying an entire wall, ...the whole room [can be used] and is not bound by an "unusable" wall. And the filter's arc shape does not limit location of lights, doors, and windows.
