Air Curtains for Large Buildings Doors

The idea of having an invisible barrier across the doorway to enable unimpeded access yet effectively prevent temperature flow, dust, odours and insects to cross, is appealing in itself but add to this the cost-saving in reducing energy use and the idea becomes more compelling, especially as air curtains are relatively inexpensive items. 
   
  Appropriate for industrial applications 
  Keeping warm air out of insulated cold stores or refrigerated facilities is the Number 1 objective yet a mockery is made of this premise when freezer of chiller doors are left wide open and, in some cases, chocked open to facilitate the movement or storage of perishables.

Self-generated pressure evolves from a non-circulatory type of air curtain as the jet induces ambient air into the stream. When the air curtain is installed on the outside of a cold room, the air spills back into the room and continues to do so until the pressure builds up to such a point that the air stream deflects to the outside.

The pressure-form-stack effect evolves when the cold air in the room is denser than the warmer outside air. The higher the ceiling, the higher the pressure becomes inside the cold room. The velocity of the air curtain should therefore be high enough to compensate for the outward pressure at the lower part of the cold room.

Wind pressures occur because of the conversion of the velocity pressure in the wind into static pressure. Of particular significance is the stability of the air curtain, which is directed by its outlet momentum. The curtain of air must be able    to withstand pressure variations between the inside and the outside of the cold room. The outlet momentum should be sufficiently sustained and strong enough to stabilise the air at the floor. It is therefore essential to incorporate controls in the design of the air curtain to increase the strength of the velocity and ensure a stiff curtain of air and to decrease the velocity to prevent unnecessary heat and moisture transfer at the door.

In refrigeration applications, a high volume of turbulent air hitting the floor tens to form ice on the floor of freezers - this is not desirable or necessary so air flow needs to be adjusted so that it barely hits the floor. This can be accomplished by adjusting air louvers or fan speed to obtain the desired velocity. Drafts are eliminated by ensuring that air flow is vertical. The air curtain may be mounted on either the warm or cold side of the cooler with equal effectiveness. 

The volume of air flow varies according to temperature difference between internal and external air and air exchange is therefore caused by thermal temperature differences. Using known values for the indoor and outdoor temperature difference, the densities, pressure differences and ultimately the air flow through the opening can be calculated. 

Properly installed air curtains cut cold air loss and reduce humidity, thus reducing the load on refrigeration or air-conditioning plant and thereby saving energy by reducing compressor running time, maintenance, gas and recharging intervals. These units are an alternative to fast-acting roller doors    and PVC slat curtains, and can be situated above or to the side of industrial doorways to create a powerful seal across the opening, keeping cold air in while providing complete visibility and access. This means that forklift drivers don't have to get out of their cabs to open and close doors so that moving from one area to another is a lot easier and productive. Unlike plastic slat curtains, which quickly become opaque with use, an air curtain provides 100% visibility at all times. Units have been installed in loading bays, factories, hangars and production facilities, such as food processing and pharmaceuticals, where differential temperatures are encountered overseas. 

Canadian Air Systems Co. is a well known designer and manufacturer of industrial and commercial air curatain systems and environmental air barriers.

For special applications Canadian Air Systems offer tangential air curtains to achieve high volume alminar air flow - to create permanent environmental air barriers.

For additional information please refer to http://nis-co.com/Index.html.

Oleg Tchetchel
Ventilation Engineer
Canadian Air Systems
http://www.nis-co.com
http://nis-co.com/aircurtain/Index.html