McIlvaine (1992) describes a horizontal laminar flow cleanroom distribution system in a particular 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.
McIlvaine (1992), explains the details of a tunnel cleanroom with wall-to-open-end air flow.
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. This design combines features of both the horizontal room and the down flow 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.
Patel et al. (1991) describe the design of a high-performance tunnel cleanroom for a semiconductor manufacturer.
The key to reducing the overall system pressure drops was in opening up the air returns. ...the service bays and interstitial spaces...are one continuous open area. The side wall returns...were continuous openings, twenty to thirty inches high. Proper airflow direction and pressurization were controlled by utilizing portable panels of two types, solid and louvered. Return air required by the makeup air handler for temperature and humidity control...was returned directly though a grill in the roof to the mixing chamber. Return air for the local tunnel modules...was returned directly through the service bays. The tunnel modules were designed to use low-pressure drop, single row, sensible heating cooling coils,...energy efficient motors,...and low pressure drop HEPA filters...Makeup air was supplied to the local tunnels...through solid ducts...(versus flex ducts). They were not connected to the units but were terminated in close proximity to the prefilters. It should be noted that in the Class 1000 areas, the air was also delivered in the same manner to self-powered 2' x 4' drop-in ceiling units. No solid connection was used between the makeup air handler and final units at any point. This was planned to reduce the pressure drop in the delivery duct system, but, even more importantly, to allow the delivery system to remain balanced when small changes are made throughout the fab area. Temperature and humidity were controlled by the makeup air handler.
