The air flow system is the same as the common air-conditioning system except it uses a HEPA filter and more air changes to reduce the contamination level. This type of cleanroom is generally employed to maintain Class 1,000 to 10,000, but when it is supplemented by local laminar flow work stations, it can provide a high degree of contamination control for critical operations. The construction cost is economical.

One conventional cleanroom type is also the wall-to-floor airflow. This design is adaptable to a wide choice of sizes inasmuch as the length is limited only by the space available.

Horizontal Laminar Flow (Crossflow) Cleanroom

HEPA filters are placed on entire wall surfaces and supply the air at constant velocity across the entire room and the air exits through the ceiling or wall at the opposite end of room and is recirculated. A major limitation is that downstream contamination in the direction of air flow will occur, but this clean room has Class 100 cleanliness with a practical design and is used extensively throughout the electronics industry as well as for bio-clean operating rooms or patient isolators.

Since these rooms are normally longer than they are wide and the filter bank occupies only one end of the room, a substantial cost savings can be realized over vertical flow rooms due to the reduction in HEPA filters, supporting structure, and air handling equipment.

Vertical Laminar Flow (Downflow) Cleanroom

Ceiling-to-floor airflow. This vertical downflow design usually has the capability of providing the greatest control for the entire clean working environment, because airborne contamination generated by personnel or specific operations is immediately carried down and out of the room. This design may be varied such that the blowers and HEPA filters are remotely located and the filtered air is ducted to the top of the room and enters the room through a diffusion ceiling arrangement. This variation may reduce cost, the area of filter bank required, noise, and vibration, but it may also require greater motor/blower capacity and greater attention to leakproof duct joints.

This type of room is rectangular in shape, usually 12 to 16 feet wide and 30 feet or more in length. Generally, these are Class 100 or better.

Wall-to-open-end airflow. This design combines features of both the horizontal room and the downflow curtain unit. The filter bank is normally composed of prefabricated modules, each containing a motor/ blower unit, prefilter, and HEPA filters. The rigid or flexible plastic ceiling and side walls are supported by a simple exterior wood, pipe or angle iron framework, while the end opposite the filter bank is open. Plastic material used in this application should be the self- extinguishing type. The tunnel room is the least costly type of room, can be disassembled and moved, and its effectiveness is comparable to the normal horizontal room.