Air Curtain work as a hidden barrier of high-velocity airflow to separate different environments. Airflow through a door depends on wind forces, temperature differences, and pressure variations. It decreases penetration of dust, insects, and unconditioned air into conditioned space by violating an airstream above the entire entrance. The air stream layer flows with a velocity and angle such that any air that seeks to penetrate the air curtain is entrained. Air curtain effectiveness in blocking infiltration through an entrance generally ranges from 60 to 80%. The fans of the air curtain can be direct or belt-driven. The most frequently used types are centrifugal, axial, and cross-flow.