Personal thoughts on Air Conditioning

[Scott & Heather]

Not an expert, but my dad was in the business for over 20 years. Just wanted to share my wife and I's personal experience fulltiming 4 years in various climates ranging from 4 feet of snow and -22°F to 107°F and everything in between.

For our first two and a half years, we had one Coleman Mach III 13,500 btu roof unit mounted in the front of the coach. It worked just fine in almost all of our climates. Of course it ran nonstop in anything above 90°F but it kept the bus cool and comfortable. Let me interject that we like it cool. We sleep at night with the bus around 62°F. When we hit Wisconsin for two months in 2012, they broke all their heat records. Temp hovered around a staggering 104°F which is unheard of up there. With the single Coleman humming away, and an occasional dousing of the roof condenser with hose water, we managed to keep the humidity inside the coach down and keep it around 78°F. At the time we didn't have any windows and we kept the front shades on the windshield down. Never ever opened them. Our fluorescent and LED interior lights kept it bright. There were four of us living in the coach that summer. It worked. Fast forward and we installed small dual pane HEHR windows (four of them) and a second Coleman Mach III 13,500 btu roof unit in the bedroom. We never really used it until we came down to Texas and here we are this summer with daily consistent temps of 100°F or more and sunny every day for weeks on end. We are using both during the day, and only one at night (mind you at 11pm last night the outside temp was still over 90°F). Here are my observations:

1. Having your cool air come from the ceiling is key, and having it properly dispersed throughout the coach is also key. Cold air, of course, drops and then finds the lowest place to settle. In the coach, if you have a ton of cold air just dropping to the ground from your ceiling unit and you aren't dispersing it throughout the cooling area, you are basically just supercooling one area while the rest of the coach is warm. Roof units set with their vents dispersing the air so that it settles over a large portion of the cooling area work best and keep the temp more evenly cool. This is also why I ducted one of our non-ducting units using a gutter. (Arcadia rally peeps have seen my ghetto setup)

This allows me to direct the air where I need it and when. Allows me to turn off my loud front unit and just close the bedroom vent and turn on the rear unit which ducts the cool air to the front of the coach quietly. Ghetto, but works. Even thought we want ducted mini splits in our new 102C3 coach, we will be sure the ducting runs to the ceiling to drop the cold air. I can't imagine it would stay very cool in there with floor vents.

2. BTU's matter. Obviously BTU's matter. You can't cool a bus on a hot sunny day with a window unit. Just not gonna happen. 5000 BTU's is 5000 BTU's and you can't change that. We have a combined 27,000 BTU's of cooling between our two units. It seems to be plenty for our fulltime needs. That being said, here's the monkey wrench. When we cook anything on our 4 burner gas stove/oven and it's over 90°F outside, the rooftops can barely keep up. They can hold their own and keep it around 78°F or 79°F and if it's 104°F outside like it is now, you're interior temps climb to 80°F or more when cooking a pizza for 20 minutes in the oven.  So, a third unit would allow us to cook freely and help fight the heat BTU's coming from the oven. But our solution? Cook in the mornings and evenings. Works for us. Next bus, I will have more cooling BTU's on hand though to give us enough to spare. But let me interject one thought here. Some think that the more BTU's the better. This isn't always true. Too many BTU's and your a/c isn't running enough to remove humidity from the air. You want to size your BTU's to your needs so that the unit runs enough to remove humidity but not run non-stop either. Mini split units today have tech that includes variable speed compressors and a "dehumidify" mode so they help mitigate that issue.

3. Insulation is key. We didn't spray foam, we just cut blocks from the pink boards at Home Depot, stuffed them in place, and spray foamed the cracks. But we also layered the entire coach in reflectix before the foam board was in place. I know some people don't believe in this stuff, but it works for us and we are very happy with its performance in our coach.  Next bus, we will spray foam entire coach, likely use reflectix again, and should have an even tighter sealed coach. We raised our roof 9" but didn't square it off and add roof insulation. I think that would have been a great idea and I highly recommend it.

Air conditioning needs are highly personal, I know I'm not saying anything new here and I'm not trying to reinvent the wheel, but I see a lot of a/c discussion threads and I wanted to share our experience as full timers in all sorts of conditions. We know people here in our rv park who have their windows open all night and day. They are parked in the shade (we are not) and they don't use a/c at all. I know we like it cool, and these two work horse units do the trick.

Just a data point for those that like proof. Here's a photo indicating the interior temp of our bus at 2pm on a 102°F day in full sun at both roof units cranking away. Windshield wasn't covered so sun was coming through a sheer white shower curtain we had up. Front cap of bus above doorway and drivers windows are not yet insulated, but have a layer of reflectix up.

Here's the temp of the interior of the bus when both units crank away during the day:



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[luvrbus]

All parts of the country are different when it comes to AC,here humidity is not a problem so over sizing a unit btu's is no big deal.

Like you I do not buy into a 6000 btu unit replacing a 13,500 btu unit not going to happen in the real world. Now Scott when you convert the new bus install windows and the challenge begins   no matter what AC you have  

I will tell you something strange my AC comes on 3 or 4 times a day during 108+ degrees then at night when cools downs a little it seems to run all the time even while we are sleeping.I don't know if the humidity goes up or what the deal is but I have noticed the same happens in the bus.I read enough to know humidity is good for the heat cycle but not good for the cooling cycle    

[Seangie]

Scott,

You forgot to mention that after the reflectix and 1.5" of insulation you have 1" knotty pine covering your entire bus floor to ceiling.  Plus as Clifford mentioned your lack of windows. 

Our windows are what really bring the heat in.  The metal frame around the windows (original Eagle bus windows) gets hot in direct sun.  That transfers to the frame inside the bus and heats up pretty quick.

Also - putting refectix over the metal frame before you screw anything into it will stop the heat transfer from the frame to the wood of the walls. If you check the shell section of our website I have a few pics as examples.

RV roof airs are very inefficient.  But often times are cheaper and easier to install, repair and replace.  Mini Splits are excellent but not really designed for RVs.  So there are challenges with those for sure. But if you can make the mini split work its awesome.

Cliff -  maybe you just wake up everytime the AC comes on so it seems like its always on

-Sean

[belfert]

62 degrees would be like a meat locker to me.  I like it cool, but 62 is way too low.  I keep my house at 75 degrees in the summer.  One of our computer rooms at work is running at 62 degrees and I have asked to have it turned up to maybe 68 degrees to save on energy.  If you have to put a jacket on it is too cold. 

I have tons of glass in my bus and I have two rooftops up front to keep it cool.  On a warm day I doubt I could get it down to 62 degrees in my bus.

[Scott & Heather]

Cliff, I wonder why your ac is coming on at night more. What ac do you have? Roof units?? What btu? Concerning how cold we keep it, during the day we keep it at 75, but at night we like it cold. So 62-65 is where we keep it. Sean is right, we have installation and reflectix and knotty pine walls (3/4"). So that all plays in. But we do have four windows now. They are on the small side but I'm seeing some of the new trailers and fifth wheels now coming out with smaller windows lately here at the RV park and they don't have a giant windshield so I'm thinking our bus has a similar amount of glass as some of these late model fifth wheels. Here's our bus now with 4 small windows:



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[TomC]

I have big windows-we like to see out. They are single pane Penn windows, but are tight. I had three Coleman 13,500btu roof tops. A bit noisy, but still work 20 years later. I usually use the front two going down the road, with the third kicked on when the temp gets above 100. With 2.25" of sprayed foam, the inside stays at a comfortable 70 degrees in even 108 weather (hottest we're been in). The front A/C is aimed at the driver's seat and I have a dash mounted fan blowing on me-works well. 
The nice thing about three roof tops is that it will bring the inside temp down very quickly (in about 30 minutes). I suggest you install a third. Good Luck, TomC

[John Z]

Have you tried exhausting the heat from cooking that pizza, rather than battling it with ac? Up north here, we rarely use the ac. When we cook we run a powered vent to exhaust. Works fine for us.

[oltrunt]

In our little bus we turn on the exterior exhausting fan whenever we use the propane stove.  If we don't turn it on in the summer the bus turns into a sauna and if we don't turn it on in the winter the stove sets off the CO alarm.  Jack

[Scott & Heather]

I need to put one of our Sean shanks donated fantastic fans to use in this capacity. I have a microwave above the stove. Can I mount the fan on the wall?


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[sledhead]

We have a fantastic fan above our cook top and always have it open when using the cook top and as the heat from the cook top will turn on the fan by it self when needed .

we have a large toaster oven in stead of a built in oven we had in the old s/s rv and use it outside under the awning when needed

as for a/c I have a split unit 9 k above the drivers window ( 5 years old with 0 problems ) and a 13500 btu roof shaker ( I hate due to the noise ) in the bed room

my next set up will be a 18 k above drivers window with a 9 k cassette over the bed on 1 split unit in my 1st bay

dave   

[chessie4905]

   I don't know if a fantastic fan is designed to be mounted vertically. I'd contact them before you do it.
   I would think the heat soak from the sun all day is trying to work into the interior at night, as the cooler temps drive it in.

[Scott & Heather]

I have been researching but haven't seen a vertical application yet. In a related note, guys, when you use a vent fan to exhaust air, moisture, whatever out of your coach, how effective is it really? I mean I know it works, but aren't you in theory creating a slight vacuum inside which draws in an equal amount of outside air through cracks and crevices in your coach to replace the interior air you're sucking out? So if it's 104 outside, and I'm cooking and exhausting 200 CFM of  hot stovetop air outside, aren't I sucking in 200 CFM of 104 degree air from outside into the bus to replace exhausted air? Same goes for winter time, when I open a vent to exhaust hot moist shower vapor in the bathroom, I'm in theory drawing in a similar amount of cold air from outside. This then, has to be heated. Seems so inefficient.


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[lvmci]

hi Scott, if you install a fantastic fan on the wall, I would put hinges forward, tom...

[Scott & Heather]

Not down? I was thinking of installing it like this:




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[niles500]

Scott - google "air to air" heat exchangers - HTH