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Old 04-28-2005, 09:42 AM   #1
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AC Sizing

I've been working on figuring the size for a new AC. I did some online research and found that too big is indeed too big and less comfortable with alot of cycling on and off.

Each time a calculate the size I come up with 10000BTU for the extreme assumptions. 105 deg outside and 75 inside, no insulation, average infiltration, ect.

Has anyone else done this? It's looking like I could use that 9000 BTU Coleman.
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Old 04-28-2005, 10:00 AM   #2
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I never went into detail on working the formulas. I felt that the 15k BTUh was too big.
I went with a Carrier AirV 13.5k BTUh and I am totaly pleased with the operation and performance of the unit.
One person had suggested that we go with the biggest possible unit. I felt that overkill was a bad thing so I went with the smallest that Carrier had to offer.
There is some turth in the fact that the bigger unit will not run as much as the smaller unit.
What I would consider is the volume of air that the unit can move. If you have 60 degree air and you are only moving it half as fast as another unit then it stands to reason that it will work harder and longer to cool the same amount of space at the same climate conditions.
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Old 04-28-2005, 10:11 AM   #3
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One thing you need to remember is that the Airstream aluminum finish will not reflect the sun as well as a white painted trailer. I had a 13.5K unit on my 27' Safari which in my opnion was undersized as you approached temperatures of 90+ degrees in full sun.
At one trip where we were approaching 100 degrees in full sun, my unit barely kept the interior at 85 degrees. My neighbor in a similar sized SOB with the same sized unit was in the upper 70's. My dealer, Airstream at Jackson Center, and the manufacturer told me that the unit was operating within specs. From my own testing I agreed with them. I believe the unit was just undersized and unable to deal with the heat gain occuring in a full sun extremely hot midwest summer.

When I ordered my Classic, I upgraded to the 15K unit. I'm glad I did.

My feeling is a 13.5K unit is probably the best size for your 26' unit. Obviously if you are going to be in areas of extremely high heat or full sun camping, you might consider the 15K.

Jack
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Old 04-28-2005, 10:16 AM   #4
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This topic has come up before. Usually people wish they had put in larger units.

You're right an undersized unit is more efficient and controls humidity better.

Kudos for undertaking the calculations. I think we need to consider actual field data, that seems to favor 13,500 btu (or bigger) units.

http://www.airforums.com/forum...ead.php?t=3500
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Old 04-28-2005, 05:28 PM   #5
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Quote:
Originally Posted by markdoane
This topic has come up before. Usually people wish they had put in larger units.

You're right an undersized unit is more efficient and controls humidity better.

Kudos for undertaking the calculations. I think we need to consider actual field data, that seems to favor 13,500 btu (or bigger) units.

http://www.airforums.com/forum...ead.php?t=3500
Don, thanks for resurrecting this thread. I went back and reread it and found some good conversation.

Regards,

Jack
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Old 04-28-2005, 05:41 PM   #6
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My 1977 25 footer does well in 97 degree sun, Coleman 13.500
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