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Old 05-27-2019, 06:37 PM   #1
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One mini split for a whole bus?

My first post on this forum! Sorry of this question has been asked before - the search function did not yield a result.

Building out a 35' international. By my calcs, with the amount of insulation I'm installing, one 12 BTU mini split should be enough to cool the bus. BUT... where to put it? if I put it in the bedroom in the rear, I'm afraid the living room will be warm and vice versa. I'm sure others have confronted this issue... can I somehow divide up the cooling power of a mini split? Thanks in advance.
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Old 05-27-2019, 06:49 PM   #2
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The 12k BTU I just ordered is suppose to efficiently cool and heat a 500-750sf room. Without my garage I'm only cooling around 190sf. I'm hoping if the numbers are right that should be plenty for the whole bus. If not, at $432 I'll add a second one. With your concern I would find somewhere midship to mount it. If comes with 15' of line for the compressor.
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Old 05-27-2019, 06:50 PM   #3
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Dan,

It depends on a number of factors.

Insulation?
Windows?
Climate?
Target temp?

A few years ago I had a 40' bus with spray foam insulation, RV windows and 2 x 12,000 btu air conditioners.


It did a pretty good job in moderate climates but August in the Southwest was another story. I spent too many days when both A/C's running full blast struggling to keep the inside temperature under 90F.

I recently sold a 39' 5th wheel trailer that had a single 12,500 btu A/C. Parked in the woods in the shade it would keep us comfortable until the outside temp got up into the low 90's.
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Old 05-27-2019, 10:04 PM   #4
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Quote:
Originally Posted by DanBarwick View Post
My first post on this forum! Sorry of this question has been asked before - the search function did not yield a result.



Building out a 35' international. By my calcs, with the amount of insulation I'm installing, one 12 BTU mini split should be enough to cool the bus. BUT... where to put it? if I put it in the bedroom in the rear, I'm afraid the living room will be warm and vice versa. I'm sure others have confronted this issue... can I somehow divide up the cooling power of a mini split? Thanks in advance.


Specs for a house are not helpful for a bus. I have a full foam envelope, but the windows are a major loss of efficiency. I have insulation panels that I cover them with in extreme temps.

When it is mid 90s and up my main living space is cool enough to be comfy, but my units run flat out. I think one is enough to make a difference, but will get overcome pretty quick once hot enough.

If you are always in the shade one might be enough, or if you have deleted and insulated a lot of windows. I insulated very thoroughly but still need two. Have even considered adding a third, but decided not really that important.

As far as placement, we have one in the master bedroom in back and one above the windshield.

The rear one can heat or cool the master bedroom in any situation, but is limited it cooling the living space. The front one definitely cools the overall living space of the bus best, but leaves that master bedroom little affected.

At times we have used a fan to circulate air from the master bedroom to the rest of the bus. It does help.

If I could only do one I would probably do the front. Depends on your layout though.
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Old 05-27-2019, 10:28 PM   #5
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Where did you put your front condenser?
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Old 05-28-2019, 01:36 AM   #6
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... can I somehow divide up the cooling power of a mini split?
Google "dual zone mini split" Here's a 24k BTU unit, but I also saw 30k, 18k and I think 12k
https://www.acwholesalers.com/LG-LMU...EaAkBXEALw_wcB
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Old 05-28-2019, 02:01 AM   #7
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Google "dual zone mini split" Here's a 24k BTU unit, but I also saw 30k, 18k and I think 12k
https://www.acwholesalers.com/LG-LMU...EaAkBXEALw_wcB
I think pretty much everything bigger than 12kBTU requires 220v, a whole different neighborhood.
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Old 05-28-2019, 02:41 AM   #8
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I think pretty much everything bigger than 12kBTU requires 220v, a whole different neighborhood.
That makes sense. I've Never stayed at an RV park, so never considered...does this mean that even the 50 amp hook ups are only 110 volt? I KNOW you're not going to run a pair of 13.5 roof AC units on 30A, and was guessing that the 50A hook up was 240V. Not a problem if you're running a generator, but the little Honda 2200 ain't gonna cut it, even a pair of them.
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Old 05-28-2019, 05:13 AM   #9
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Where did you put your front condenser?


My bus is a pusher. Condenser is between frame rails about a foot behind the bumper. Roughly where a pullers motor would be.
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Old 05-28-2019, 05:18 AM   #10
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I think pretty much everything bigger than 12kBTU requires 220v, a whole different neighborhood.


50 amp service is 2 legs of 50 amp, so yes you could run a 220 v appliance off of it. Most of us want to be able to run off of a generator or inverter though.

I can run both my 110 v units from a standard extension cord, my inverter, or my generator.

In extreme situations a little borderline sometimes, but the systems are impressive in efficiency and breaker friendliness.
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Old 05-28-2019, 02:03 PM   #11
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I'm not saying you're wrong - still planning our own bus so maybe I'm wrong (most likely we're both wrong) - but my calculations for cooling capacity differ from yours significantly.

Assuming an 8-row bus and stock windows all around, I got a hair under 16K. Bare Minimum. That's presuming the south-facing windows are shaded (but not the north), 6 occupants, 600 watts of internal appliances running at any given time, and 40w of lighting. And that's just to account for heat gain. Under these conditions we'd need more to actually do any cooling.

The basis for my calculations was the following website:

Heat load calculations – heat gain for air conditioner sizing

I used the second (more detailed) calculation method. As its designed for houses, I took 30% off of the internal area to account for reduced height as compared to a standard house. For window area I added 1/2 of the front and rear windows to the combined window area for each side (north or south), and added the door (as a window) to the south side.

There's plenty of factors this method doesn't take into account, as well as limitations to the accuracy of my assumed values, so if I'm lucky it will be a ballpark estimate at best.

Perhaps more important than the actual numbers I got was learning just how huge an impact the windows, and their orientation/shading, had on cooling requirements. I mean, I knew it mattered... I just didn't realize how much it mattered. The windows alone were nearly 1/2 of the total heat gain. And the calcs don't appear to even account for climate/solar radiation.

From going through this exercise, I know now that our 'cooling' plan absolutely must focus, first and foremost, on minimizing as much as possible heat gain. And the windows (which are one of the things we love most about school buses)... those are the front lines in the battle.
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Old 05-29-2019, 08:21 AM   #12
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Originally Posted by o1marc View Post
The 12k BTU I just ordered is suppose to efficiently cool and heat a 500-750sf room. Without my garage I'm only cooling around 190sf. I'm hoping if the numbers are right that should be plenty for the whole bus. If not, at $432 I'll add a second one. With your concern I would find somewhere midship to mount it. If comes with 15' of line for the compressor.

Hi Marc, where did you order yours from?
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Old 05-29-2019, 10:13 AM   #13
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Hi Marc, where did you order yours from?
eBay, make offer, I was able to get them down to $432

https://www.ebay.com/itm/12-000-BTU-...72.m2749.l2649
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Old 06-08-2019, 03:11 PM   #14
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Would it help circulation if your walls stopped short of the ceiling?
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Old 06-08-2019, 03:25 PM   #15
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I have a single mini split 9K BTU, Pioneer. External condenser is mounted on the Rear deck of the bus that's been closed off from the rest of the bus.



The inside unit is on the driver's side wall near the front (will be above the sofa)



I've removed and insulated where some of the windows used to be, walls have an extra inch of foam insulation on top of the existing FG between the metal wall panels. Floor is insulated but only with 1/2" of foam.

For circulation, I'm running a duct from the rear bedroom to the front of the bus with a quiet fan that will run when the AC does.
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Old 06-09-2019, 12:12 PM   #16
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Works - However

We have an Alpine 12K Btu minisplit I mounted above the rear door. It works great; however, We place a fan 1/3 of the way down the bus to blow cool air forward. Will soon install two small 12v fans on ceiling to assist. It is supposed to reach 102F today here in Texas. This is the hotest day we’ve had since we installed the ac. We have done no modifications to the ceiling or insulation. The roof has 4 coats of elastomeric paint which makes a HUGE difference. Part of the roof is also partially covered by a deck and solar panels. We’ll let you know how it goes
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Old 06-09-2019, 01:30 PM   #17
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Even coated with hi-gloss white paint, 1/2" insulation board glued to the roof's underside, dead air space then ReflecTix atop 1/8" stained & polyurethaned luaun plywood, it's plenty sweltering here in Grimes County, where ambient/heat index respectively are 92°/105°, ATM.
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We have an Alpine 12K Btu minisplit I mounted above the rear door. It works great; however, We place a fan 1/3 of the way down the bus to blow cool air forward. Will soon install two small 12v fans on ceiling to assist. It is supposed to reach 102F today here in Texas. This is the hotest day we’ve had since we installed the ac. We have done no modifications to the ceiling or insulation. The roof has 4 coats of elastomeric paint which makes a HUGE difference. Part of the roof is also partially covered by a deck and solar panels. We’ll let you know how it goes
BTW, kudos on making your 1st post!
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Old 06-09-2019, 04:33 PM   #18
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I put 2-1/2" or closed cell spray foam in my first bus(40'). I had removed all of the bus windows, resided and installed RV windows. I had two 12k Btu air conditioners.

I remember more than a few times that I had both A/C's running full blast to keep it under 90F inside. To be fair... It was in the high 120's outside and there was no shade.

It all depends on how cool you want the bus and how hot it is outside. The bigger the delta the more A/C capacity you will need.

Tip: Don't visit the Mohave desert in August.......
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Old 06-09-2019, 06:19 PM   #19
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You are so right. UV is the killer. We made it to 96 with a heat index of 111 today. Our bus was cool enough to be comfortable. One thing I failed to put is that we have a short 30’ Blue bird TC2000 so it takes less to cool and heat
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Old 06-09-2019, 07:51 PM   #20
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Has anyone tried solar reflective film on the windows to help???
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