• Air Curtain Technologies & generalities

  • It is known that on open doorways with two adjacent areas in different conditions the air is interchanged between them because the laws of physics tend to equalise the temperature and pressure difference between both sides.
    Basically air transfer on doorways happens due to these 3 factors:
    • Temperature difference: is the natural convection effect that creates an air transfer between two areas with temperature difference. Warm air will escape through the top of the doorway and being replaced by cold air coming in at the bottom. As bigger temperature difference bigger air infiltrations and energy losses.
    • Pressure difference: it is recommended to equilibrate the pressure difference as much as possible because it affects the air curtain performance. But in some installations like clean zones a little pressure difference helps to prevent the particles entering from outside.
    • Wind, stack effect and draughts: by modifying the air jet strength and the outlet discharge angle, the air curtain can work against forced air movements like wind or draughts. But if the velocity of the incoming air is excessive the air curtain will become less efficient.
    The efficiency of an air curtain depends on the optimization of performance factors.
    Air Curtains Performance Parameters h = effective width of the jet
    α = discharge angle
    U0 = discharge velocity
    θ = negative impact angle
    H = opening height
    P1 = outside pressure
    P2 = inside pressure
    The most important ones are:
    • Turbulence of the jet: low turbulence jet will be much more efficient and save energy
    • Air speed: air velocity should be enough across the doorway
    • Air volume: a wider jet makes the air curtain stronger against air transfer on doorways
    • Angle discharge: according to a situation if jets are well oriented it will increase the energy saving
    • Fan type: axial, tangential wheel, centrifugal, etc… Higher pressure fans create a higher pressure jet that reaches farther. For instance, if we compare an air curtain with tangential fan against an air curtain with centrifugal fan (with same air volume), the jet made of centrifugal fans will be stronger and larger.
    UPC University air curtain studies have proven that air turbulences are one of the most important parameters that will affect the distance of the air jet.
    air curtain turbulences
    UPC University schema shows the air turbulences behaviour.
    Optimized shape of the outlet plenum, the position and fans type, the shape of lamellas, etc… substantially affects the air jet performance.
    Air Curtains Angle Discharge:
    Tests and University studies have proven that the angle discharge helps substantially helps the air curtain to be more efficient.
    When factors like wind, temperature or pressure difference causes air transfer from outside to inside, we can aim the jet towards outside some degree. Then the jet direction against the air entrance will help to keep the air outside. The trajectory of the jet will be parabolic but at the end will reach the floor approximate by the doorway. If we can’t adjust the angle discharge, the jet will be pushed in by the external air forces.
    The forces parallelogram theory explains how the forces behave on a doorway. The following diagrams show the difference between air curtains with fixed lamellas against adjustable ones.
    Air curtain with fixed lamellas Air curtain with oriented lamellas
    less efficient (1) more efficient (2)
    air curtain with fixed vanes Air curtain with adjustable vanes
    (1) The first one, fixed vanes, where the entrance air velocity pushes the jet of the air curtain, the resultant of the parallelogram of forces is diverted inwards. This allows outside air to enter inside.
    (2) The second one, adjustable lamellas, when the air jet is oriented against the entrance, the resultant of the parallelogram forces is directed perpendicularly to the floor. This means that outside air does not enter and inside air does not escape. Besides internal temperature level is maintained.
    Airtecnics has a long term agreement with the UPC University of Catalunya in order to use the latest technologies and knowledge to achieve the optimum performance characteristics of our air curtains.

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Air Curtains

Airtècnics - Motors i ventiladors S.L.
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