Air Distribution and Its Uniformity

Air distribution system in plant factories with artificial lighting (PFALs) is responsible for the air exchange and replacement to create desired growing conditions for plants. Combined effects of multitiers, heat from supplemental light ing, improper air conditioning, and air distribution system design can lead to environmental nonuniformity in PFALs. The principle for the design of air distribu tion system is to understand the physics of wind and how crops response to wind. This chapter describes how wind affects the photosynthesis and transpiration pro cesses of crops by briefly explaining the theory of leaf boundary layer and boundary layer resistance. Then an example application of improving air movement to prevent plant physiological disorder (e.g., tipburn in lettuces) is introduced. For the design of air distribution system, the overall control with mixing ventilation systems and the localized control with cooling fans and perforated air tubes are described. Finally, several indices for assessment of ventilation performance are defined such as air exchange effectiveness, local mean age of air, efficiency of heat removal, and coefficient of variation.