An air curtain is a device that creates a barrier of air across the entire opening of a door that separates two environments.
Most commonly, the air curtain separates conditioned inside air from outside air, preventing the infiltration of cold or hot air, bugs, fumes, humidity, dust and debris. Depending on the industry or even the geographic region, air curtains can be called Fly Fans, Air Barriers, Air Doors or Air Shields.
How Does an Air Curtain Work?
Typically, the air curtain is mounted over a doorway on the inside and the air is pulled into the intake of the unit. There it takes form to match the conditioned environment.
This air is accelerated and forced through a narrow discharge along the length of the air curtain creating a laminar airflow. The discharge angle can be adjusted using the provided turning vanes to achieve optimum performance.
As the discharge angle increases, the air has to travel further until it hits the floor.
Since the velocity of the air decreases as it gets further away from the air curtain, if the discharge angle is too large the air curtain won't be able to stop much wind from entering near the floor. If the discharge angle is too small, the air leaving the unit will not have enough horizontal force to stop a significant gust of wind from entering.
Ideal velocity at the proper mounting height prevents infiltration of outside elements while preventing conditioned inside air from escaping, which boosts energy savings.
Underpowered air curtain with too little velocity to reach the floor allowing outside air to enter near the bottom of the opening.
Overpowered / Too Much Velocity
Overpowered air curtain with too much velocity causing excessive turbulence at the floor and causing inside air to be blown outside.
Usually the ideal discharge angle for maximum wind-stopping capability is around fifteen degrees. When the discharged air reaches the floor it splits, forcing some air outward and some inward. Therefore, when a unit is used for climate control, it should be placed on the opposite side of the doorway from that of the air that is to be kept out.
For example, if it is winter and you are trying to keep cold outside air from entering a building, the air curtain would be placed on the inside so that it is blowing warm air. When the warm air hits the floor, some is leaked to the outside and some is blown back inside.
If the unit is on the other side of the opening, some of the cold air that needs to be kept out would be blown inside, defeating the purpose. If the unit is to be used for insect control, the air curtain can be mounted on the outside of the doorway as long as the discharge is adjusted so the air is blowing back toward the outside.
In this situation, it doesn't matter if some of the outside air is blown inside after it splits at the floor. This air should already be free of insects because they will not fit through the intake screen.
The Physics Behind Air Curtains Effectiveness
Computational Fluid Dynamics (CFD) is one of the branches of fluid mechanics that uses numerical methods and algorithms, rather than model experiments, to solve and analyze problems that involve fluid flows. Computers are used to perform the millions of calculations required to simulate the interaction of liquids and gases with surfaces defined by boundary conditions.
These CFD images illustrate how air at different temperatures mixes when a door is open.
Temperature + Environmental Separation
A core function of an air curtain is its ability to separate temperatures/separate environments. Whether you're blocking frigid winter winds from entering through a customer entrance door or separating two interior rooms, air curtains create an invisible barrier to prevent the mixing of one environment with another. In Cold Storage applications, the mixing of refrigerated air with ambient air can create safety hazards such as ice, fog and moisture buildup. Air curtains help prevent this while lessening the strain on the unit's cooling refrigeration.
From Alaska to Florida, air curtains effectively separate environments and complement your building's primary HVAC system, helping drive down costs by lessening the need for the system to constantly be running. While an open door may signal a booming business, it also lets the inside/conditioned air leak out and the outside air seep in. Air curtains prevent the inside air from escaping and the outside air from entering. In turn, the HVAC system will not have to work as hard. Ultimately, this can lead to considerable cost savings.
Increased Comfort for Customers and Employees
Whether a large dock door or a customer front door, the infiltration of unconditioned outside air can make life miserable for those close to the door. That can easily and negatively affect productivity, well-being, performance and sales.
Perhaps one of the most important and overlooked benefits of an air curtain is its ability to improve the level of safety on doors where it operates. The downward stream of air helps keep the floor free of slipping hazards like water and ice buildup. In busy warehouses, air curtains are an ideal replacement for grimy, dirty strip curtains that impair visibility, which can be particularly dangerous in forklift zones. UVC-based air curtains use UVC light to kill airborne viruses before recirculating clean air back into an area.
Air curtains deter flying pests from entering workplaces. For restaurants and food service industries, this is imperative as insect problems can impact the bottom line. Air curtains create a barrier that significantly reduces flying insects from entering without impacting workflow. As curbside and touchless delivery grows in popularity, air curtains complement these doors by creating a barrier that keeps bugs out but allows for unfettered ingress and egress.
As construction ramps up in the post-pandemic boom, project managers are looking for ways to save time, money and resources. Per the ANSI/AMCA 220 standard, air curtains are now permitted to be used as an alternative to vestibules in select climate zones. Along with the standard, Vestibule Exception air curtains offer considerable cost savings, including less resources since there is no need to build the vestibule (less wood, steel, glass, etc.). This also saves time, money and manpower. In many applications, vestibules are not properly installed, which negates their intended purpose. Along with being more economical, vestibule exception air curtains can also be more effective.
The coronavirus pandemic highlighted the dangers of airborne germ contamination. Extraordinary measures were taken to reduce the transmission of airborne pathogens and Powered Aire's air purifying air curtains are excellent tools to enhance these measures.
Powered Aire's UVC-Aire air curtains incorporate UVC light into an air curtain to create a machine that actively kills airborne viruses before recirculating clean, sanitized air back into an environment. As the germs are pulled into the air curtain, they are exposed to the UVC light, rendering them inactive. The air curtain then expels a barrier of sanitized air. The continual recirculation of air is able to eliminate 99% of airborne viruses without the need to recirculate the air.
UVC-based air curtains can be used above a door for germ control and environmental separation or mounted in common areas such as conference rooms, gyms, lobbies, classrooms or other areas with an influx of people. In these rooms, air purification/germ control is the main function.
Fumes, Dust, Exhaust + Debris Control
In areas with heavy amounts of dust, fumes and debris, air curtains are able to create a barrier that prevents the infiltration of these unwanted byproducts. Of specific benefit, these elements are prevented from entering areas where people work/congregate, which increases overall safety. From drive-thru windows to busy warehouses, being able to block these harmful elements is critical.