Air doors and air curtains are the fan powered devices that create an unseen air barrier over the doorway while creating two separates environments in the entryway. It keeps the atmosphere clean from pest, insects, dust, pollution, cold or hot air entrance and smells without limiting the access of people. The function of these curtains is based on a high velocity jet of air that covers passageway openings and creates an impediment of continuous air flow.
How do they work?
It’s all about a continuous broad stream of air circulated across an entrance of a conditioned space. It reduces penetration of unwanted air into the building space of a cafeteria by forcing an air stream over the entire entrance. The air stream layer moves with a velocity and angle, such that any type of air that tries to penetrate the curtain is blocked.
Airflow through a door depends on wind force, temperature differences (convection), and pressure differences. Air doors work best when the pressure differential is in-between the inside and outside building’s atmosphere. Negative pressures, extreme temperature differences, elevators in close proximity, or extreme humidity can reduce the effectiveness. These are specially used in those restaurants where doors are required to stay open for operational reasons during customer’s entry, loading vegetables along with other items.
Why the air curtains are ideal for cafeterias?
-They keep flying insects out by creating forceful turbulence.
-Cold drafts can be avoided by mixing in warm air heated by the air door. The most effective air door to maintain the conditioned air inside a restaurant, have a high velocity at the opening. This is generated by top-to-down flow and air recovery by a recirculating air plenum and duct return to the source fans. This configuration is feasible for new construction, but difficult to implement in existing places.
For industrial conditions, high face velocities are acceptable. But for commercial applications like cafeteria entrances, user comfort dictates low face velocities, which reduce effectiveness of separation of exterior air from interior air.