Clean room system

Claim 1

A clean room system for constructing a clean room having clean zones of different degrees of cleanliness ranging from Class 100 to Class 100,000 according to the U.S. Federal Standard 209b, by forming a ceiling in an exsiting building to form an enclosed space insulated from the ambient atmosphere by said ceiling and suitable floor and walls and installing an air treating equipment for supplying clean air into said enclosed space and withdrawing an air amount therefrom substantially corresponding to the amount of the clean air supplied thereinto, characterized in that: said ceiling is formed by horizontally suspending ceiling bars provided with a plurality of rectangular openings having substantially same predetermined configuration and dimension and supporting removably to the openings of the ceiling bars prefabricated ceiling elements each having a base area adapted to close each of said openings so as to close each opening by each ceiling element, said ceiling element being selected from the group consiting of a blind panel, a return air inlet port unit and a fan filter unit having a built-in fan and HEPA filter; an air conditioner is installed outside the enclosed space, supply air duct means for introducing air conditioned by the air conditioner into each fan filter unit and return air duct means with a connecting duct which can introduce air taken in at least one of the air inlet port units into each fan filter unit without passing the air through the air conditioner are installed outside the enclosed space; and the positions and numbers of said ceiling elements removably supported to the openings are selected according to the positions and the degrees of cleanliness of the desired clean zones to form clean zones having different degrees of cleanliness in the enclosed space by ceiling surface exhaling and inhaling air flows.