Need A/C ducting help


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Old 07-15-09, 12:42 PM
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Need A/C ducting help

My business is in a 'T' hangar at an airport. I also have an additional amount of space adjoining it. I just purchased as used mobile home a/c from a mechanic. Fairly old, 36K btu. It has 10in output, 12in return. I want to cool (as much as possible) the portion of the hangar in the shape of a 'T'.
The output will go to 3 or 4 registers. Is it better to continue with 10in ducts or reduce from 10in to 8in? Can I go down as low as 6in or not?
The return is 12in. The cooling ducts will hang about 9 feet off of the floor. What is the best set up for the return? Stay low, or put up high with the cooling? Should I split out the return into multiple returns using 'Ys' and if so, how small should I go.
The entire area is open, the 'T' consisting of 4 blocks of 225 sq st each for a total of 900 sq ft., the roof is metal and uninsulated, and the area cannot be totally sealed off. Right now it runs about 115 degrees when it is 100 here in Texas...I am just hoping to get it down below 90. Thanks for any input.
 
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Old 07-15-09, 03:04 PM
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With a totally open area you are just wasting your time (and money!) trying to air condition that space, especially with only a 3 ton unit. You might be able to get some specific "spot" cooling by running a single duct to the specific location but it will still be expensive to operate.

I think you would be better served insulating the underside of the roof and using some big fans to ventilate the entire hanger.
 
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Old 07-15-09, 03:09 PM
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Ideally I agree. I only rent this hangar and run a business out of it. Any cooling will help, as we have to work from 4am to 12pm before it gets suffocating in there.

With what I have, I am trying to make the best of it. If I can seal it up a bit and drop the temp a bit, it will help just getting through the day. Thanks for the note.
 
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Old 07-15-09, 05:09 PM
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In that case you might want to make a portable wheeled stand for the unit and connect a long power cable of sufficient current-carrying capacity and then wheel it to wherever it is needed and try blowing the cooler air towards the area needing cooling. If you could enclose the area somewhat using something like welding screens it would help. Of course it will be necessary to use a flexible duct if you use an enclosure and keep the machine outside the cooled space. Do not reduce the size of the ducts.

There will also be the matter of any condensed water that would normally just drip onto the ground. You would probably need to fabricate a collection pan and container for this and empty as needed.
 
 

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