This invention pertains to a ceiling construction for a laminar flow clean room and more particularly to a membrane diffusion panel for uniformly distributing air flow through the clean room without turbulence.
The clean room industry was spawned in the early 1960's. The uniform mass air flow of HEPA (High Efficiency Particulate Absolute) filtered air was dubbed "laminar flow" because of the uniform velocity or non-turbulent (laminar) flow of air either vertically or horizontally across the work space. A typical clean room includes walls, floor, and ceiling, an air supply feeding a duct or plenum, a fan, a planar section of ceiling panels hung below the ceiling comprising HEPA filters, for filtering the air.
The advent of high tech developments in electronics, optics, telecommunications, robotics, medicine, and genetic engineering, to name a few, give rise to an ever growing need for "clean space" in manufacturing and research and development. The cleanest class of room according to federal standards is the class 100 clean room. The contamination level of clean air is generally proportional to the number of air changes per hour that is caused to move through the space. The higher the air exchange rate the cleaner the room, and the larger quantity of air filters required.
Over the last ten years inflation has given rise to the cost of Class 100 clean rooms to the point that they now install for an excess of $200.00 per square foot of work area. Thus efficient use of HEPA filters is necessary for cost efficient use of clean space. Turbulent distribution of air requires a greater number of air changes to achieve a given level of efficiency, wasting valuable filter use. Another reason that the systems are so costly is that the HEPA filters are suspended in the ceiling in an air tight framework. Along with this expensive framework must come a structural system to support the weight of the filters and a provision for the lighting system for the work space. A further disadvantage of the HEPA filtered air distribution system is that the induction of air at the ceiling causes aspiration at the filter face and turbulent air patterns develop adjacent to the HEPA filter and around that part of the ceiling that is occupied by lights and ceiling panels.
In U.S. Pat. No. 3,975,995 (Shuler) a ventilated ceiling construction is shown comprising a first planar surface spaced from the room ceiling, and having a mixed array of filter panels and blank panels, and a second planar section of perforated air diffusing panels spaced from and disposed below the first planar panel defining a clean air plenum therebetween. It has been found that a perforated sheet air diffuser is limited in its capacity to distribute air uniformly. In addition the Shuler system does not account for total elimination of turbulence. The membrane diffusion panel of the present invention is a substantial improvement over the perforated air diffusing panel of Shuler. Air is diffused evenly over the face of the membrane diffusion panel.
An additional patent of general relevance to the present invention is U.S. Pat. No. 4,461,205 (Shuler) which discloses a lighting and filtering unit for a clean room.
As can be seen from the above, in view of the expanding needs of the developing "clean space" industry an increasing need for cost effective quality air filtering exists.