Air Curtains
Air curtains for air conditioned areas
Air conditioned areas are normally well balanced and don't normally have negative
pressure. A slight over-pressure is common where air conditioning systems are
bringing in fresh air. air curtains for interior doors need only be sized for
the draft due to the temperature differences between the two sides. On interior
openings between the air conditioned areas and non air conditioned areas, the
air curtain should be mounted on the non air conditioned side, angled away from
the air conditioned areas, and the air should be dampered back until there is
a minimum amount of air splitting at the floor and going in toward the air conditioned
side.
Doors between an air conditioned area and the outside are exposed to winds which
must be considered in the selection of the air curtain. For application on such
doors the air curtain should be installed on the inside for the best possible
efficiency, and the nozzle angle should be adjusted so that a minimum of air conditioning
is discharged from the inside. This inside mounting allows the air curtain to
be used in the winter to prevent cold outside air from entering.
Air curtains for industrial climate control
The primary purpose of the Climate Control air curtain is to prevent the influx
of outside air through an opening in to heated or cooled area. Opening where an
air curtain would typically be used are exterior shipping and receiving doors
to plants and warehouses and interior doors between plant areas of different temperatures.
(these applications are discussed in further detail below). In addition there
are special applications such as the control of oven temperature, humidity and
dust or the control of the fresh air. Other applications not discussed here are
preventing the drifting of over spray from spray paint booths; blowing water off
of hot steel after it has been dipped; and blowing scrap paper from a paper cutter
into a collecting intake.
 In
order to control the temperature, an air curtain pumps out an air stream with
enough velocity at the nozzle and the width of the nozzle. For different entrance
sizes and different wind conditions, different air velocities at the nozzle are
required. To prevent the entry of outside air the nozzle is angled towards the
outside so that the air leaving it meets the air trying to enter. The wind will
meet or strike the air curtain stream in the doorway.
In many buildings with high ceilings the air tends to stratify into a warmer
layer at the ceiling and a considerably cooler one at the floor. For such buildings
it is recommended that the air curtain be mounted across the top of the doorway
opening and that it be provided with a top intake connected to a duct extending
up to the ceiling. The warm air will then be drawn down into the air curtain and
blown to the floor putting otherwise wasted heat to use. This warmer air also
helps to reduce the wind chill of the moving air.
 Air
curtains for dust and humidity control
air curtains should be installed on the clean or humidity controlled side of
the opening, blowing toward the dirty or uncontrolled side. This will prevent
the influx of the dust particles or atmospheric vapour. air curtain units for
dust and humidity control are approximately 70% efficient. The 30% inefficiency
is caused by particles are air becoming entrained in the air curtain stream and
working their way through.
Air curtains for commercial building entrances
Commercial entrance air curtains are becoming widely used in building entrances
to reduce energy consumption and provide comfort. In winter they retain warm inside
air and prevent the influx of cold air. They can also supply additional heat in
the door area using optional electrical, steam or hot water heaters. In the summer
air curtains keep hot humid air out and prevent the escape of air conditioning.
The working principle of Commercial Entrance air curtains is to provide the most
effective air screen possible without blowing so hard that it is objectionable
to people passing through. air curtains are ideal for application on high traffic
doorways in commercial establishments such as stores, restaurants and banks. They
are also ideal for public buildings such as hospitals, terminals and schools.
In many cases where a vestibule was installed, or planned, to reduce the inflow,
an air curtain is a better approach. This is particularly true for high traffic
entrances where both doors are frequently open at the same time, defeating the
purpose of the vestibule. A continuously operating air curtain allows the vestibule
to be dispensed with resulting in large savings -- both in initial and operating
costs -- and increasing the usable floor space.
Commercial Entrance air curtains are normally mounted horizontally above the
door which keeps the unit out of the way and practically eliminates any chance
of damage and/or accidents. During the heating season, the air stream should be
directed slightly toward the outside and should never be obstructed by door operators
or the door header. It is recommended that the air curtain fan motor be run continuously,
since the power needed to operate it is minimal. It is preferable to control the
heater in heated units with a built-in, or wall mounted, thermostat, in order
to maintain a constant, comfortable temperature in the entrance area. In addition
to providing comfort through the elimination of cold drafts and the addition of
heat to door areas. Commercial Entrance air curtains have many other benefits.
For example, they can decrease door maintenance costs since doors need to be opened
and closed left often. In restaurants they stop uncomfortable cold drafts at customer's
feet. Many schools purchase air curtains to save energy and find that, as an additional
benefit, they keep floors dry and safe and hallways warm during the winter months.
In buildings with high ceilings the air curtain re-circulates the warm stratified
air that rises to the ceiling. Commercial Entrance air curtains are quiet and
compact and pay for themselves in a very short time. Most units may be used all
year round and are adjustable for seasonal conditions using either a damper or
a duel speed motor.
 Air
curtains for cold storage
When opened a door separating a cold storage area from a warm room permits
a substantial loss of refrigerated air. Warm air flows into the cold room through
the lower part. This results in energy losses, safety hazards in the form of condensation
and icing on the floor and fog in the doorway; and possibly food spoilage. Strip
doors used on coolers and freezers to reduce these effects impair visibility and
are unpleasant to pass through due to condensation and frosting and accumulate
dirt and possible bacterial growth.
Studies have proven that air curtains, when properly sized and adjusted, are
up to 85% efficient in controlling the flow of air through cooler and freezer
doorways. If the cold storage door is open over one hour per day the air curtain
is a cost effective way to save refrigeration costs.
Installed on the warm side of the doorway the air curtain emits an air stream
which reaches the floor at an angle and splits into two separate air streams.
By properly adjusting the volume of the air and the angle of the nozzle, one air
stream is made to balance against the other which is trying to leave the cooled
room, while the other counteracts the warm air trying to enter. The correct air curtain sizing and adjustments must be made for each specific application so that
a narrow, high velocity, low volume stream of air is projected over the entire
opening creating a sufficiently stiff curtain of air. Built-in adjustments in
the air curtain must include fully adjustable mounting brackets, variable volume
controls and individually adjustable louvers in the nozzle. The narrow nozzle
limits the amount of air in the doorway area and hence the turbulence, thus increasing
the efficiency of the unit.
In addition to providing a substantial energy savings and increased safety,
Cold Storage air curtains can increase the time between defrosting almost four
fold, depending on the particular freezer or cooler. Also, their ability to maintain
the cold room temperature right up to the doorway improves product quality and
increases the useful floor space.
 Air
curtains for insect control
Insect control air curtains, sometimes called "Fly Fans," are used
in food processing plants, dairies, bakeries, bottling plants, restaurants, supermarkets,
hospitals, school cafeterias and other areas where the control of flying insects
is required. The powerful stream of air that is produced by an Insect Control
air curtain is an excellent deterrent to insects which will usually avoid the
air stream simply because of it's unnaturally high velocity.
The most effective air curtain design for insect control has a nozzle that
can angle the air stream away from the area to be protected. An angle of about
20° from the vertical is usually optimal. The unit should meet or exceed Department
of Agriculture and Federal Drug Administration standards, which call for an air
stream 2-5 inches wide at the nozzle capable of producing a minimum velocity of
1600 fpm of air 3 feet above the floor and across the entire door opening. It
is very important that the entire doorway be covered so that there are no gaps
for the insects to enter.
The Insect Control air curtains can be mounted on the inside or outside of
the doorway. When mounted on the inside the unit can help control the building's
climate in the winter by stopping the influx of cold outside air. (For more info
on this effect see the Industrial Climate Control or Commercial Entrance Sections).
When the building contains odours which are attractive to flying insects it is
recommended that the air curtain be mounted on the outside.
When a negative pressure exists inside the building one of two approaches must
be taken to make the air curtain fully effective in keeping the flying insects
out. One alternative is to slightly alter the mounting of the unit, moving it
out form the wall to relieve pressure on the air curtain and to allow the outside
air to enter the building. The outside air will be drawn to the intake of the
curtain through the gap between the wall and the unit. This gap must be covered
by a screen and the gaps along the door jamb, caused by moving the unit back from
the wall, should be closed by side panels. The air curtain is equally effective
mounted horizontally or vertically. However, measures should be taken to prevent
damage to the air curtain caused by traffic when mounted vertically.
Summary
Over the long life of an air curtain system, tremendous benefits can be realised
which pay for the system many times over. Some of these include:
- Increased employee comfort.
- Energy savings through control of air transfer.
- Faster and safer traffic flow and increased production due to clear and open
doorways.
- Door maintenance cost savings due to decreased breakdowns.
- Increased usable space near door areas.
- Elimination of ice and fog in cold storage areas.
- Increased safety in door areas due to better visibility.
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