Selection and Design of Air Curtains

Selection and Design of Air Curtains
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What is an Air Curtain?

Air curtains are fans that create a wind barrier between the outside and inside of a room. When well designed and properly installed, these windy barriers can cut down on heating and cooling costs significantly when compared with an unblocked entryway. In any structure- a house, a warehouse, or an office- a very large amount of the heating or cooling costs involve replacing the air that leaks out. In some temperature regulated buildings, the entrance and exit are constantly being used, essentially creating a large permanent leak of hot or cold air. Air curtains shoot a stream of air down along the opening, essentially isolating inside air from outside air. Air curtains can be good for saving money on utilities, and have the added bonus that they keep insects out.

Air Curtains

Air Changes per Hour

A normal home will have one to three air changes per hour. This means the entire volume of the air in the house is completely replaced in that amount of time. In winter this is a significant statistic, since each air change involves heating a houseful of outdoor winter air to room temperature. This usually accounts for over 50% of the heating costs for a house, with radiant heat loss through windows and walls accounting for the rest. Air leaving through an open door or crack under the window is money lost on a heating or electricity bills. A warehouse that has constant traffic through a door can expect to lose significantly more air, up to five or six air changes per hour.

How effective are Air Curtains?

A door is always more effective than an air curtain. Air curtains should only be installed on entryways when traffic is high enough that doors are not an option. The best air curtains will approach the effectiveness of a door by minimizing the amount of air lost. Air curtains can cut down on heat exchange through a door significantly, although varied factors can effect specific installments.

The most effective air curtains are those which have very high air velocities. These installations are generally not retrofitted on existing structures, since they require not only the fan, but also a collecting duct at the floor. These high air velocities are very effective at creating a layer of air separating inside and outside air, although this type of air curtain system cannot be installed where customers or pedestrians are entering or exiting. The high air velocity curtains are reserved for entryways that pass packages and various other objects.

The effectiveness of air curtains is also highly dependent on the local environment. For example, high winds will cut down the effectiveness of any air curtain by disrupting the insulating air layer.

Locations Suitable for Air Curtains

As an application for air curtains, warehouses seem ideal. Many warehouses are kept at a constant temperature, either due to temperature requirements for items held within the warehouse or in the interest to maintain a productive climate for workers. The heating and cooling costs on these warehouses are large considerations for the owners. Warehouses are especially well suited, as some of their entrances and exits do not move people, just boxes or items that can be blown with high velocity air. Savings can be greater for warehouses that act as cold storage. See the picture below for a large and powerful air curtain deployed at a cold storage warehouse.

Large office buildings are also a suitable for air curtains. If the traffic through sliding doors is significant enough throughout the day, sliding doors might spend significant time open, making an air curtain a tempting option to save on heating costs. Cruise ships sometimes also deploy air curtains, which allow for its passengers easy movement around the boat while maintaining temperature and humidity. Retail locations sometimes use air curtains. In certain instances a store chooses an air curtain to attract customers, as having an open entrance is more enticing than a door. Air curtains are also deployed between two indoor areas, a specific example being a colder area of a supermarket.

Air Curtain in an Industrial Setting

Photo from JSaircurtains with permission

Air Curtain Selection - Summary

In deciding whether or not an air curtain makes sense for a particular installation, it is worth repeating that air curtains will always be less efficient than a closed door. That being said, there are instances where traffic dictates a door cannot be maintained closed, then an air curtain should be considered. Air curtains can have high wind speeds, so keep in mind that customers and employees tend to not like getting blasted by air.