General Information

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General Information on Air Curtains

What is an Air Curtain?
Different types of Air Curtains
Principles of A Non-Recirculating Air Curtain
Conclusions

What is an Air Curtain?

An Air Curtain is a device specifically designed to provide a resistance to air flow through an opening, without having any physical barrier there. Simply put, an Air Curtain is a fan that is designed with an air outlet that has a low turbulent air stream (high laminarity) that can be angled towards the incoming air stream in such a manner that the inflow of air can be prevented, and thereby creates a seal.

Different types of Air Curtains up.gif (487 bytes)

Air curtains can either be re-circulating types, or non re-circulating types.

Re-circulating Air Curtains emit air from a discharge grill on one side of the door opening and collect the air on the opposite side. It is then filtered, sometimes heated, and then is returned to the discharge grille. These units are essentially a modified heating system and uses large amounts of air. They are usually associated with high initial costs and high operating costs. Also, because the air has to be filtered, the maintenance costs are also quite high. The feature is that they use low velocity air streams, which is desirable in some commercial entrances. They are usually used in supermarkets and store entrances.

Non re-circulating Air Curtains are much more widely used. They are characterized by much lower initial and operating costs. As they are not re-using the air, it does not normally have to be filtered and thereby they can be made essentially maintenance free. They are also more effective, as the air streams are narrower and of higher velocities. These are the types that we manufacture.

Principles of A Non-Recirculating Air Curtain up.gif (487 bytes)

The non-recirculating Air Curtain operates in a manner that the air is discharged at a high velocity through a narrow discharge nozzle. The discharged air stream must have the proper angle, usually 20 degrees towards the pressure side, and the air stream must be laminar for highest efficiency.

The Air Curtain operates on a very simple law of physics. One force will change direction if it is subjected to another force. The force is air mass and the velocity at which it travels. The outside wind has a certain mass and a certain velocity, so does the air curtain stream. If the Air Curtain force is equal and opposed to the force form the draft through the door then the draft is prevented from entering. If the draft is much stronger than the Air Curtain it will break through and some will enter. However, even in this circumstance, the Air Curtain will prevent some of the outside wind from entering at all times. If the Air Curtain is much stronger than the draft some of the air will go outside. The strength of the Air Curtain follows the formula: mass times the velocity squared. Therefore an Air Curtain that blows at twice the speed has four times the wind stopping power at the same air volume.

Air Curtain can be mounted above, on one side, or on both sides of a door. The most common way is to mount the Air Curtain above the door. The feature with this is that the unit is out of the way and is not likely to be damaged by, for example, forklifts. It is also the most economical way of installing an Air Curtain. The drawback is that a small amount of air at the extreme bottom of the doorway may enter due to the height of Air Curtain.

The Air Curtain can also be mounted vertically on one side of the door. There are some disadvantages to this however. If, for example, a truck is parked in the door way then the entire doorway is unprotected because the truck will break the air stream. With the unit mounted on one side of the door it is more likely to be damaged. Also, if there is no equal force on the other side of the door to stop the stream then the flow will follow the wall for some distance and may disturb people who are standing in the air stream.

The final way of mounting an Air Curtain is on both side of the door with the air stream flowing towards each other. This is the most comfortable way of installing an Air Curtain as it eliminates the above drawbacks, except the damage.

Both of the previous mounting techniques are illustrated below:

All EWD Air Curtains are belt driven. This is the reason for the high efficiency it obtains, as no dampers are employed in order to bring the air velocity down if required. There are some features with this type of system. If for some reason the unit need to be upgraded to a larger unit all that needs to be changed is the motor. If negative pressure increases, as it would if another exhaust fan were added, the unit can be modified with little problems. Since these situations arise in a growing industry this type of system is ideal. Also by not having direct driven fans we are able to have larger diameter fan wheels operating a lower speed, reducing the noise level to an absolute minimum.

Conclusions up.gif (487 bytes)

In order to be able to select a proper Air Curtain there are a few things that have to be considered:

The physical dimensions of the opening and the space available for installation.
Prevailing winds and temperatures for the opening.
If there is any negative pressure in the building (this is usually caused by exhaust fans or stack effect.)
The need for additional heat to be introduced in the Air Curtain.
The need for additional heat in the areas when the door is closed and/or the need for make up air in the building.
 

Miniveil Air Systems
340 Ward St. Port Hope, ON
CANADA   L1A 4A6
Telephone: 1-905-885-4015
Fax: 1-905-885-6478
Email: info@miniveil.com