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  1. #1
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    Air curtains - do they really work?


    Hi all,

    My situation:
    Outdoor air: 30C, 90%RH
    Indoors: 5-level retail building served by 1000 RT of chilled water air conditioning

    Some areas near entrances are consistently too warm, thought to be due to outdoor air coming in, through the people-sensing-auto-sliding-glass-doors.
    The opening is about 2m wide by 2.4m tall.
    Condensation is also often seen on the cold air outlet grilles.

    I have a suspicion that air-curtains aren't very effective if there is mass air flow due to pressure differences.
    i.e. an air curtain might be effective for a walk-in freezer since it is quite small, and is close ended. But for a multi-level retail building, there are bound to be changing pressure differentials, due to multiple doors at the perimeter of the building opening and closing, and also due to imbalances of the air distribution.

    Are some characteristics of air curtains superior to others?
    Faster is better?
    Downward blowing versus door-mounted vertical-axis side-blowing?
    Should the air-curtain be situated to blow indoor air or outdoor air?



  2. #2
    Join Date
    Mar 2007
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    Re: Air curtains - do they really work?

    That is a much debated issue. The moisture ingress by air flow can be restricted by maintaining positive pressure in the control space. However, when the door opening is large and the openings occur quite frequently, control pressure gets disturbed.

    Theoretically, there shouldn't be any air flow across an opening if the pressure difference is zero. The main culprit for moisture ingress in this case is diffusion. Though you keep higher air pressure in the control space, partial pressure of water vapor is lower than the outer space, as humidity is controlled, and moisture permeates into the space.

    Munters suggest to have a minimum air flow velocity of 150fpm to minimise moisture ingress by diffusion. Air curtains may come handy in this situation. When you install a horizontal air curtain on top of a 2.4m door, the air velocity will be less than 1m/s below 1m from the air curtain exit. That means half of the door opening is vulnerable to moisture ingress. Vertical curtains can overcome this and will be better, IMHO.

  3. #3
    Join Date
    Mar 2007
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    Re: Air curtains - do they really work?

    BTW, condensation at grilles can be minimised by reducing the ADP or using non metallic grilles.

  4. #4
    Join Date
    Oct 2003
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    Belgium
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    Re: Air curtains - do they really work?

    There's a technical article in the last Racca Journal (South Africa)
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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