Zones indicating the air draft created under the flow fans, which offers relatively better air velocities and lower air dispersion after the air draft leaves the plenum.
Air draft created by the dispersion of centrifugal flow fans air flow when it enters the plenum. This zone of air barrier will offer lower air speeds, resulting into weak zones within the air curtain created by such units which are prone to rupturing. Such air curtains usually fail to meet stringent performance norms set by ISO/ANSI for measuring air curtain’s air draft efficiencies as dust/fumes/odor/humidity/insect barrier.
Zones indicating the air draft created under the flow fans, which offers relatively much superior air draft specs [air velocities + cfm] with low to negligible % variation in air draft’s velocity across the width of the opening. This leaves little scope of air dispersion and resultant slowing of air draft speeds, reasons of better efficiency of the air barrier to repel contaminants.
Source: https://www.acmeaircurtain.com/why-choose-cross-flow-suction-air-curtains-over-centrifugal-suction-air-curtains/