Understanding Air Curtains

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Home remodeling

Air curtains are a popular solution for buildings with large open doorways that require constant access. They help to conserve energy and reduce costs.
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Revolving doors are one of Theophilus van Kannel’s inventions that he patented in 1888. The idea was to prevent pollution and unpleasant odors from entering a building when a person entered or left. Van Kannel also wanted to eliminate the need for someone to hold open a door, which he was tired of doing for his wife. Another one of his inventions was the air curtain, which he patented in 1904. It was first installed in a building in 1916 [source: Miniveil.com]. An air curtain is essentially a continuous flow of air that is blown from the top to the bottom of an open doorway. Commonly used as a second line of defense inside a closed door or to replace hanging plastic flaps in an open doorway, air curtains form a barrier that people and products can flow across, but air can’t. This means that the climate on one side of the air curtain doesn’t shake hands with the climate on the other.

The air curtain serves two purposes. First, it insulates, and we all know the insulating power of air. For instance, it’s the layer of air trapped between double-pane windows that keeps heat from moving across them. Secondly, an air curtain used as backup inside a door can be angled to blow outside air back out from whence it came.

Although it may seem like an invisible curtain of air from Star Trek, air curtains can increase energy efficiency and keep pollutants and insects out of an open doorway when installed and used correctly.

Air Curtain Mechanics


An air curtain is installed inside the doorway, and air blows down toward the floor, sometimes at a slight angle outward.
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There are two ways to use an air curtain. You can use it in an open doorway, in which case a stream of air runs continuously. You’ve probably felt the puff of air from this type of air curtain when you’ve entered a big-box, warehouse-style store. Or, you can use the air curtain as a second line of defense behind a closed door, in which case the air curtain is activated only when the door opens. It springs into action, blasting air for a couple seconds until the door is again closed.

In both cases, the curtain is mounted on the heated/air-conditioned side of the doorway, extending across the length of the door opening. Its intake sucks in conditioned air and blasts that air either straight down or at a slightly outward-tilted angle (see more on next page) to push away any outside air that otherwise would enter through the doorway.

An air curtain can be enhanced with an electric heater, providing a stream of warm air when entering a building on a cold day. Additionally, the curtain helps to circulate heated air that may pool near the ceiling. It also creates a strong enough current of air to keep out flying insects, dust, pollution, and other unwanted contaminants, making it ideal for use in sterile environments. Some businesses even use air curtains to protect open ovens and freezers.

The effectiveness of an air curtain depends on the force of the air blowing from it and its direction. The force must be strong enough to overpower the force of the outside air, and the direction should be mainly downward towards the floor of the doorway. The air must maintain its velocity as it reaches the bottom of the doorway and be stronger than the velocity of the outside air. To achieve this, the air curtain acts like a wall that outside air comes towards and bounces off of. Adjustments can be made to the air curtain by increasing the volume or speed of the air blown or directing the velocity outward at an angle of 10-20 degrees.

The air curtain was invented by Theophilus van Kannel, who also invented the revolving door and the Witching Waves, an amusement park ride at Coney Island in 1907.

The Economics of Air Curtains

The cost and benefits of air curtains vary depending on several factors. A small 36-inch (91.4-centimeter) unheated air curtain can be as affordable as $200 [source: Amazon]. Conversely, a high-velocity heated air curtain for a 9-foot by 14-foot (2.7-meter by 4.2-meter) door can cost nearly $450 [source: Grainger.com]. Therefore, the first step in air curtain economics is to pay only for what you need. Determine the size of your door, and then decide if you want comfort or efficiency. If you prefer comfort, consider a heated air curtain. If not, an unheated model may be a better option. Additionally, estimate the force required by your air curtain to counteract outside air. For example, if you live in a windy area of Minnesota, you will need more air at a higher speed than in a milder climate with no wind.

Air curtains also have environmental benefits. They can help a building earn Energy and Atmosphere points, Indoor Air Quality points, Innovation in Design points, and Indoor Environmental Quality points, which add up to Leadership in Energy and Environmental Design (LEED) certification [source: Air Conditioning, Heating and Refrigeration News].

To determine your energy savings beyond the initial outlays, you will need to consider factors such as wind speed and energy costs. Suppliers of air curtains, such as Berner International and Mars Air Systems, provide calculators on their websites to help estimate the costs and savings of air curtains over time. For example, an air door that costs $3,000 and is installed on an 8-foot by 6-foot (2.4-meter by 1.8-meter) doorway with an average outside temperature of 50 degrees Fahrenheit (10 degrees Celsius) and wind speed of 8 miles per hour (12.8 kilometers per hour) will pay for itself in approximately one year.

Author’s Thoughts

Before writing this article, I had no idea what an air curtain was. However, now that I am aware of them, I notice them everywhere. I wonder, “Is that blast of hot air every time I enter the local supermarket an air curtain?” I also see them at the dentist’s office. It turns out that there has been a silent revolution in entrance gasket technology going on around us every day, unnoticed. Join the revolution or be left out in the cold, inefficient dust.

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Sources

  • Air Conditioning, Heating and Refrigeration News. “Air Curtains Save More Energy.” October 6, 2008. (April 13, 2012) http://www.achrnews.com/articles/air-curtains-save-more-energy
  • Air Distributors. “W25 Series.” (April 17, 2012) http://www.airdoordistributors.com/category/11/Air_Curtains_W25_Series_Mars_Air_Curtains.htm
  • Bondor Manufacturing Company. “Air Curtains.” (April 13, 2012) http://www.bondorseals.com/more_info/air_curtain/air_curtain.htm
  • Hickman, Leo. “Why is the Ritz Getting Rid of Its Revolving Door?” The Guardian. July 11, 2011. (April 17, 2012) http://www.guardian.co.uk/travel/2011/jul/11/leo-hickman-revolving-doors
  • Johnson, David. “Specifying Air Curtains for Savings and Performance.” AMCA International InMotion. Spring 2009. (April 13, 2012) http://www.amca.org/UserFiles/file/inMotion/inmotionspring09.pdf
  • Manufacturing.net. “Green Code Now Allows Air Curtains.” March 8, 2012. (April, 13, 2012) http://www.manufacturing.net/articles/2012/03/green-code-now-allows-air-curtains
  • Miniveil. “A Brief History of the Air Curtain.” (April 13, 2012) http://www.miniveil.com/history.html
  • Powered Aire. “Aire Curtain Fundamentals.” (April 13, 2012) http://www.poweredaire.com/food_service_air_curtains/fund.htm

FAQ

1. What is an air curtain and how does it work?

An air curtain is a device used to separate two different environments, such as the inside and outside of a building, while still allowing for easy access. It works by creating a barrier of high-velocity air that blows downward across an opening. This air barrier helps to block out insects, dust, and other contaminants from entering the interior space. It also helps to maintain a consistent temperature, reducing the workload on heating and cooling systems.

2. What are the benefits of using an air curtain?

There are several benefits to using an air curtain. Firstly, it helps to improve indoor air quality by keeping out dust, pollen, and other pollutants. This can be especially important in commercial kitchens or other environments where air quality is crucial. Secondly, it can help to reduce energy costs by reducing the workload on heating and cooling systems. Finally, it can help to improve the comfort of people inside the building by maintaining a consistent temperature and reducing drafts.

3. What types of air curtains are available?

There are several different types of air curtains available, including electric, hot water, and ambient air curtains. Electric air curtains use a heating element to warm the air, while hot water air curtains circulate hot water through a heat exchanger to warm the air. Ambient air curtains use the temperature difference between the inside and outside of the building to create an air barrier.

4. What factors should be considered when choosing an air curtain?

When choosing an air curtain, several factors should be considered, including the size of the opening, the location of the opening, and the intended use of the building. The size of the opening will determine the size of the air curtain needed, while the location of the opening will determine the type of air curtain needed to provide adequate protection. The intended use of the building will also determine the type of air curtain needed, as different environments may require different levels of protection.

5. How can air curtains be installed and maintained?

Air curtains can be installed either horizontally or vertically, depending on the location of the opening. They should be mounted as close to the opening as possible to provide maximum protection. To ensure proper operation, air curtains should be regularly inspected and maintained. This may include cleaning the air filter, checking the electrical connections, and ensuring that the air flow is properly adjusted. Regular maintenance can help to ensure that the air curtain continues to provide effective protection and reduce energy costs over time.

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