Non-Recirculating vs Recirculating Air Curtains

Air curtains are used for a variety of purposes including thermal isolation and contaminant control between two open areas. They create an invisible barrier that allows vehicle and pedestrian traffic to move easily between two areas.

There are two main types of air curtain design; recirculating and non-recirculating. They operate differently, but are designed to achieve the same goal. Both designs propel air downward toward the floor at an optimal angle that will accomplish the desired objective of separating two areas of differing temperatures and controlling the direction of air flow.

Non-recirculating air curtains are the most commonly used systems. This air curtain design consists of a single unit, normally mounted horizontally above a doorway. It discharges air downward toward the floor, slightly outside the door opening. Since it is a single unit mounted above a doorway, it is less expensive to install, more economical to maintain, and it lends itself better to retrofit situations.

A recirculating air curtain differs from a non-recirculating air curtain in that, in addition to the overhead unit, it also incorporates side and bottom components that surround the entire doorway. These components collect air that will be returned back to the top unit, to be discharged again. This re-use of air is what makes the unit more efficient than the non-recirculating design. Recirculating air curtains are generally reserved for new construction since labor costs for installation in an existing building are usually prohibitive. Recirculating air curtains are ideal for doorways that see a high volume of foot traffic, such as airport entrances or large retail store doorways.

Air Door Distributors carries both recirculating and non-recirculating designs. All it takes is a phone call to get expert help selecting the perfect unit for your requirements.

Design and Operational Differences

The Non-Recirculating Air Curtain

A non-recirculating air curtain generates and discharges an air stream that is not returned back to the intake. To prevent the entry of outside winds, the discharge nozzle in the air curtain is angled outward at roughly 15 degrees so that the air leaving the unit meets the wind trying to enter the building.  Non-recirculating air curtains draw indoor air through an air inlet screen and into fans that push air downward. As the air travels toward the floor, outdoor air, and indoor air are routed onto each side of the unit’s air stream. This combined air stream strikes the door’s threshold, and splits into two separate air streams.  One flows to the outside of the doorway, and the other air stream flows back into the building. This separation of air streams forces conditioned air back indoors, and keeps outdoor air outside. While very effective, the drawback to this design is that there is always a need to draw in new air from inside the doorway.

The Recirculating Air Curtain

A recirculating air curtain achieves the intended goal in a slightly different manner than the non-recirculating air curtain. It generates and discharges a lower velocity air stream, but with more volume of air. The discharged air is captured by the return grill at the floor, returned to the intake area via the side panels of the unit, and recirculated back to the supply fan.

As the air stream is discharged from over the door, it splits into three separate streams: center, interior and exterior.  The center air stream contains enough air capacity to satisfy the demand of the air handler.  The exterior air stream consists of outside air which flows back outside the doorway. The interior air stream consists of the indoor, conditioned air which flows back into the building. To prevent the entry of outside winds, the discharge nozzle is fixed straight toward the center of the return grill at the bottom of the door. The air stream draws back toward the building, while still being pulled into the return grill.

In order to operate properly, the air stream has to be strong enough to reach the return grill but not so strong that it splits airflow the same way as a non-recirculating air curtain. The discharged air must meet the return grill at the floor in order to ensure a stable air stream throughout the entire process.

The recirculating air curtain is more efficient than the non-recirculating curtain, but requires a greater up-front cost. Installing one of these units in a high traffic doorway at the time a building is constructed makes perfect sense. Installation into an existing building may be cost-prohibitive, but could make sense if a building has been repurposed, and an air curtain is required for the new use of the building.

As you can see, there are some commonalities these two air curtain designs share, but some stark differences in their execution. With all the designs and models available, there are a variety of options to suit your specific air curtain needs. Air Door Distributors has over 20 years of experience helping our customers find the best air curtain for their business. You can consult our professionals at 866-402-1642 or by filling out our online contact form now to determine the type and model of air curtain that is best for you.

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