A detailed process analyses is required already during the development of the layout. Here, the process flow must be broken down into its single steps and the corresponding flow chart has to be compiled showing the flows of material, personnel, waste etc. as well as the required clean room class. Then follow the linking of the process steps, an analysis of the flows and finally the design of layout concepts and the determination of the area required. Particular attention should be paid to the need to keep rooms with high clean room requirements as small as possible.
Air technical protection concepts make a distinction between the turbulent mixing flow (TMF) for ISO classes 7 and 8 and the low-turbulence displacement flow (LTF) for ISO 5 and better. In the case of the turbulent mixing flow the clean air is introduced into the clean room in a turbulent (swirling) way. It causes a constant dilution and thus "cleaning" of the clean room. If the personnel behave correspondingly the required cleanliness class can be maintained. In the case of the low-turbulence displacement flow the clean air flows low in turbulence ("laminar") in the clean room and ensures that sensible working areas and machinery are contaminated as little as possible.
As concerns the relation between clean room classes or air exchange and size of the HVAC system for each increase of the clean room class from ISO 8 to ISO 6 can be assumed at least a doubling of the amount of air and a doubling of the ventilation system. For the step from ISO 6 to ISO 5 (laminar) it is even the factor 7 that has to be assumed. Clarity or planning security can be reached by means of a corresponding flow simulation of different variants.