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Old 02-11-2010, 10:39 AM   #1
Skoolie
 
Join Date: Apr 2009
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Air Conditioning

I need opinions on A/C sizing.

Here are the variables.

240 sq ft (1440 cu ft)
Roof has stock yellow fiberglass insulation(a Texas bus)
Roof will be 90% shaded 100% of the time
Walls will have one inch insulation on top of what is already in walls
bus windows removed and replaced with actual rv widows(no leaks)
Floor no insulation other than laminate underlay
50 amp service but only a 5.5kw genny

The original plan was two 13500btu units, which I already have one 13500. The generator will run two 13500's and nothing else. Or two modified 13500's(better start capacitors) with power to spare.

I am wondering if one 15000btu centered will be enough for Texas summers.

Anyone have any experience here?
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Old 02-11-2010, 03:42 PM   #2
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Re: Air Conditioning

I have posted this link before, but here it is again...

http://www.modmyrv.com/2009/05/27/rv...tart-capacitor
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Old 02-11-2010, 03:52 PM   #3
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Re: Air Conditioning

Ahhh, dehumidification. I understand. I would have to buy another unit regardless. Either replace the 135000 with a 15000 or an additional 13500. I was trying to reduce watt requirements of the generator I bought. It is a Onan Marquis 5.5kw with only three hours on it for $1200. I couldn't help myself. Its practically new.

I also trying to get out oF cutting two 14" squares. Which brings me to another question:

I have two fantastic fans. The plan is to mount both in the escape hatches and cut new holes for the a/c units. I m wondering if I should mount one fantastic fan centrally(the one with a thermostat) and use the other one to move air throughout the bus.

Any thoughts
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Old 02-11-2010, 03:54 PM   #4
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Re: Air Conditioning

sojakai

i have that bookmarked....prolly from the last time you posted it. It's a great idea.
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Old 02-11-2010, 05:55 PM   #5
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Re: Air Conditioning

This is a great thread! Smitty, I like your floor vent idea for better air circulation. How does that impact your insulation scheme though? Even if the vent has an open/close feature, still it will be a "hole" in your insulation blanket, right?
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Old 02-11-2010, 06:29 PM   #6
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Re: Air Conditioning

Ventilation:
Two exhaust fans at opposing ends. An intake vent(mobile home register?) centrally located.
Or, One exhaust vent centrally located and two intakes floor level front and rear. I am not sure the cfm of this particular fan but fantastic fans in general have some of the highest outputs. I fairly sure the better of the two I have is the 5000 series and moves the following:
Performance: SCFM AMPS Decibels
High 920 3.00 40
Medium 653 2.29 39
Low 478 1.86 39
With correct airflow, that is a complete air exchange on medium every two minutes if I understand it correctly.


A/C

Two A/C units front and rear.

I am doing bunks like "good news bus" which each will have its own 12v fan. I suppose I could configure those to aid in interior circulation while using only one A/C but that exposes them to an already narrow walkway.

I think in most cases I might be able to get away with one A/C as long as there is alot of circulation.
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Old 02-11-2010, 10:00 PM   #7
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Re: Air Conditioning

Smitty,
Most surfaces that will receive direct sunlight will have insulation added.

The pros of two smaller A/C's outweight the negatives, specifically ".....if one fails."

My concern now is maximizing airflow with one A/C running and more importantly with no A/C at all.

Do you think with properly located inlets that one exhaust fan pulling 600+ cfm is adequate?
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Old 02-12-2010, 10:50 AM   #8
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Re: Air Conditioning

Thanks Smitty

Do you have any ideas on air movement inside the bus while running a single A/C unit?

I thought maybe a couple of ducted bilge blowers but I am afraid it will be alot of labor for little return, ie. not much air movement for the time to fabricate it. I prefer not to rely on a box fan on the counter top.

S
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Old 02-23-2010, 10:05 PM   #9
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Re: Air Conditioning

Not a poorly insulated bus but a poorly insulated RV.

We have 1 13,500 Coleman TSR rooftop RV air conditioner unit. It is in a 22 ft Class C. When we need to run it, we usually turn it on in the late afternoon on high for a little while (hour or less) to get the temps down then switch the fan over to low and the thermo is usually set fairly warm. We are not into AC. We do not set it so cold that we feel like curling up and dying every time we step outside. We have spent the summer in SW GA (near Albany), and NM (near Albuquerque). I coated the aluminum roof with Elasto Seal/Snow Roof http://www.snowroof.com/catalog.asp. The temp drops are fantastic and it was fairly cheap and easy to put the stuff on the roof. Only downside to it was I wore long pants and rolled it out on overcast mornings... I still got a sunburn on top of my feet and almost up to my knees from the reflection once I put the first white coat on (I put 2 coats on).

Hope that helped at least a little.
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