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