Two-zone models are especially useful for stratification and zoning strategies because of the typical vertical accumulation of heat, contaminants, or water vapor within these strategies. The level of the boundary between the lower and the upper zone is usually determined on the level of the highest temperature or/and concentration gradient.
In the stratification strategy with a replacing air distribution in the lower zone, the height of the boundary layer between the lower and upper zones can be determined with the criteria of the contaminant interfacial level.4 This level, where the air mass flow in the plumes is equal to the air mass flow of the supply air, is presented in Fig. 8.4. In this ideal case the wall and air temperatures are equal on the interfacial level. In practical cases they are not usually equal and the buoyancy flows on the walls will raise the level and decrease the gradient.
In the zoning strategy the height of the boundary between lower and upper zones should be determined with the criteria of the air distribution method and devices. The lower zone should be defined high enough to get nearly all the induction air of the supply air devices from the controlled zone, as shown in Fig. 8.5.
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