Air curtains, also called air doors, tend to be part of a building's HVAC package. Building operators integrate these systems with the facility's existing HVAC equipment in addition to the structural, architectural and electrical designs.
As part of a foodservice operation, air curtains provide environmental separation, temperature and insect control, and these units can minimize the infiltration of other windborne contaminants, including dust and fumes. The U.S. Food and Drug Administration (FDA) recommends air door use to repel insects at loading docks and delivery doors. A number of states require air curtains at specific openings in food production facilities.
An air curtain works by producing an invisible shield of air that separates the climate-controlled indoor air from the non-conditioned outdoor air. The unit accomplishes this with a powerful fan that creates an air barrier, separating one environment from another. Typically mounted over doorways, air curtains and doors pull in conditioned air, accelerate it and force it through an air curtain. Discharged air hits the floor and is directed outward and inward.
Air curtains come in a variety of configurations and types. A non-recirculating air curtain, the most common version on the market, draws air into the unit directly from the surrounding environment. A recirculating unit draws air from ductwork.
When specifying air curtains, architects and engineers must consider numerous factors, including the opening's dimensions and orientation and the air curtain's specific application. Factors, such as wind loads and the building's pressure represent additional key considerations.
In terms of installing an air curtain, operators should take into consideration its location in relation to staff and, especially, the front of the house. This is because different units have distinctive noise outputs and air velocities, which can impact an operation's atmosphere and customers' dining experiences. It's also important to look at clearance around the air curtain to make sure it is not projecting too far out into the room or obscuring an opening.
For this reason, the size of the door opening represents the primary consideration when choosing an air curtain. These units come in various sizes and types to accommodate doors of all types, including those in coolers, loading docks and drive-thru windows. Air curtains for doors typically run between 36 and 144 inches wide, but operators can purchase custom sizes for doors as wide as 16 feet and as high as 20 feet.
Air velocity is another key attribute to consider when specifying an air curtain. For example, an air curtain providing environmental separation indoors should be less powerful than a unit used on an exterior door. Also, a system geared for insect control will need to have a higher airstream velocity to be effective.
As the units progress in size related to the height of the door, the air velocity becomes more powerful. The unit directs a stream of air all the way to the floor, which protects the entire opening from the encroachment of flying insects and other debris as well as ensures that the expensive heated or air conditioned air does not escape through the open door way.
When specifying air curtains, operators need to determine whether the system is best mounted horizontally above doors, which blows air down, or vertically on the door's side, which blows air across.
In-ceiling-mount, or recessed, models also are available and popular for front-of-the-house applications. Because these units house all of the internal components above the ceiling, this type is a popular choice for operations that pay particular attention to their interior design. For these models, manufacturers offer special bracket systems for installation.
Also, air curtains are available with all components contained within the housing so there are no visible outside controls, unless the unit is remote mounted.
It is important to decide whether the unit is best mounted on the inside or outside of the door frame. For insect control, mount the air curtain on the outside of the frame, while an inside mount is better for environmental separation. One common mistake is not mounting or adjusting the air curtain correctly during installation. When this occurs, the unit will not operate properly or fulfill the operator's needs.
Operations where doors remain open for extended periods may benefit from a recirculating air door, which redistributes air from an establishment's interior. This not only prevents the loss of heated and cooled air, but also helps maintain an operation's interior temperature. Because air is reused, these models utilize less energy.
If the system will be used at the entrance of a walk-in cooler or freezer, operators may want to include plastic strip doors or swinging plastic doors when specifying the air curtain.
Operators also can utilize air curtains on front-of-the-house reach-in coolers, which help keep food in the coolers at safe temperatures while maintaining the temperature of the surrounding area. These units are typically mounted horizontally on the exterior of the equipment's opening. To work effectively, these types may need to be vertically mounted.
Operators can also use air curtains alongside ovens to minimize the loss of heat. By mounting these units horizontally, operators can angle them to block air from escaping.
Units used at drive-thru windows not only keep temperatures consistent in the area, but also can help exhaust car fumes.
Operators can also use air curtains in conjunction with makeup air fans to balance the atmosphere in operations where negative air pressure is strong. It is important to note that the same amount of air an operation exhausts has to be brought back in to the atmosphere to build balance. In addition, a certain amount of air exchanges are required per hour. Contractors or HVAC professionals can assist with this.
Although most air curtains operate on volts of between 115 and 480, operators can choose from gas, electric or steam heating, which is available on most models. The rule of thumb is to choose an air curtain with the same type of heating device that is used to heat the facility whenever possible and ensure the electrical information is accurate as it relates to the building.
Air curtains offer a choice of motor speeds, depending on the application. These range from 1/5 up to 20 horsepower.
Depending on use, air velocity can range from 1,800 feet per minute up to 5,100 feet per minute. Single- and dual-speed models, with either remote or automatic switches, are available.
Because air curtains come in various sizes, shapes and colors, factor the restaurant's design and color scheme into the decision making. Operators can choose from a variety of finishes, including satin anodized aluminum, bronze anodized aluminum, stainless steel, white aluminum, powder-coated and custom-painted types. Some finishes are more high end and suitable for front-of-house use.
Operators often don't consider aesthetics when choosing an air curtain for the front of house. It's key to consider the unit's placement and goal when specifying. Not only will a more visible system need to be more visually appealing, but it also may benefit from a variable speed option as well as supplemental heat.
For facilities prone to vandalism, such as schools and prisons, operators should consider specifying air curtains with tamper-resistant features.
Energy-saving options for these units include a time-day control for air curtains used in high-traffic areas. One manufacturer offers a controller that can be built in or serve as a remote control to operate the air curtain. It offers start/stop capabilities, a thermostat and time delay feature. Units with motion detectors and upgrades in control panels also are available.
For an air curtain installed over a sliding door, such as a drive-thru window, operators can choose to add an automatic roller-door switch that turns the unit on when someone opens the window, and off when the window closes. Similar door switches are available for hinged doors, as well. Experts do not recommend combining such features on air doors equipped with heating systems. The amount of time such systems would be active is limited, thus rendering the heating process ineffective.
Air curtains that will experience heavy use may benefit from automatic thermal overload that can protect the motor from burnout, washable air filters and High Efficiency Particulate Air filters to remove airborne contaminants.
One mistake operators commonly make is installing a unit that draws air from inside a building and expels some air outside. This can create negative pressure, which can make opening doors difficult. Also, customer entrances should not be equipped with high-velocity air-door systems, as they can create an unpleasant environment. Systems installed at customer entrances should include a heating function that can be turned on during colder weather.
An air curtain as it stands has been an energy-saving device and a green innovation since its inception. The stream of air directed over any opening protects the inside environment from outside air and contaminants. The control packages available, including various speed and time options that allow the installation point to select the unit's run and heating time, also helps save energy.
For years, architects and engineers have specified air curtains for vestibules in larger buildings to save energy and cut costs, but this usage was blocked by International Energy Construction Codes (IECC).
Last year, proposals to the International Green Construction Code (IgCC) by the Air Movement and Control Association International were made to help establish air curtains as a vestibule alternative under the stipulation that these systems are tested in accordance with ANSI/AMCA standards.
This proposal was buoyed by a research study by AutoDesk, which showed that air curtains are 10 percent more energy-efficient than vestibules.