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  1. #1
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    help on a question



    help on a question . im learning

    have a question which im not sure how to answer:-

    Name a specialist application that does not use a recirculated air system when supplying airconditioning through a air handling unit AHU.

    would this be evaporative system ?
    regards



  2. #2
    Join Date
    Feb 2007
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    Re: help on a question

    Evaporative or not is about how you cool the air.
    As I understand this question it is about how the air is re-circulated or not.

    Normally an AHU (Air Handling Unit) is used to supply air in to a building, the AHU is most likely also filtering/heating/cooling/humidifying/dehumidifying the air as it passes through. When it is used to control the indoor climate as well as supplying fresh air you will need vast amounts of air to enter the building (compared to the fresh air needs) but to condition all that air takes a lot of energy so to save energy there are a couple of options;
    -Traditionally you mixed recirculated air (close to the condition/temp you want to achieve) with the fresh air. The ratios for this could be as high as 90% recirculated to 10% fresh air.
    -You could have a coil in extracted air and another coil in the fresh air and connect the two by pipes and pump water (with antifreeze if needed) between the two coils to transfer heat from one to the other.
    -You could have a big "honeycomb" wheel made of thin metal that slowly rotates between extract and fresh air streams to transfer heat.
    -You could also have the two air streams going through multiple small ducts "wall to wall" with each other and the walls of the small ducts transferring energy between the two.

    Have a look at THIS PICTURE and THIS ONE to get a better idea of what I'm "talking" about.


  3. #3
    Join Date
    Feb 2007
    Location
    UK
    Posts
    2,479
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    Re: help on a question

    Evaporative or not is about how you cool the air.
    As I understand this question it is about how the air is re-circulated or not.

    Normally an AHU (Air Handling Unit) is used to supply air in to a building, the AHU is most likely also filtering/heating/cooling/humidifying/dehumidifying the air as it passes through. When it is used to control the indoor climate as well as supplying fresh air you will need vast amounts of air to enter the building (compared to the fresh air needs) but to condition all that air takes a lot of energy so to save energy there are a couple of options;
    -Traditionally you mixed recirculated air (close to the condition/temp you want to achieve) with the fresh air. The ratios for this could be as high as 90% recirculated to 10% fresh air.
    -You could have a coil in extracted air and another coil in the fresh air and connect the two by pipes and pump water (with antifreeze if needed) between the two coils to transfer heat from one to the other.
    -You could have a big "honeycomb" wheel made of thin metal that slowly rotates between extract and fresh air streams to transfer heat.
    -You could also have the two air streams going through multiple small ducts "wall to wall" with each other and the walls of the small ducts transferring energy between the two.

    Have a look at THIS PICTURE and THIS ONE to get a better idea of what I'm "talking" about.


  4. #4
    Join Date
    Sep 2010
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    Re: help on a question

    I would suggest either a positive pressure clean room or perhaps an operating theatre.
    Brian, retired in Devon.

  5. #5
    Join Date
    Mar 2005
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    u.a.e
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    Re: help on a question

    Air conditioning units for specialized chemical storage area used 100% out side Fresh Air and there is no air recirculated due to toxic gas hazard.

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