AC on the road

[SSPAdventures]

So as we plan our build, we are sorta stumped. Our bus is not equipped with any ac system. We are considering a rooftop unit. But, seeing as we have no engine driven ac, how stout would a circuit need to be in order to run a rooftop unit while driving? Id love to hear what you guys have done regarding this. Im looking at a 13.5k btu unit.

[Ninjakitty]

Do you plan on running it from a generator or from your alternator?

[JDOnTheGo]

The roof mount RV style A/C and heat pump units in the 13.5k-15k btu range generally draw around 1500-1600 watts running and have a rather high "Locked Rotor Amps" rating (of 60-40 amps). As far as I am aware, they are all 120VAC. So, that means the pull about 15 amps @ 120VAC when running (1600 watts / 120VAC). The larger problem is the startup power - that is the locked rotor amps thing. It is only momentary but if trying to run from an inverter or noise maker (generator), it has to be sized to handle the load.

Might be useful to fill in your profile so we know what kind/size of bus you have. There are many posts here about roof mounted A/C being insufficient for busses while driving. I have done it very successfully with a 40' motorhome (two 13.5k but A/C running from generator) - as has the entire motorhome industry. But, of course, a motorhome and a bus are two different things so I can imagine different results.

[SSPAdventures]

Ok thanks for the info. I'll fill in the info so later posts can be more specific. Its a 32 plus passenger handicap international 3800. 7.5x23 behind the driver. Down the road, i plan on charging the bank off the alternator and running the inverter from the bank. I do have a generator, but probably wont be carrying it unless the park has no hookups. We really dont plan to boondock often, we plan to roadtrip and camp. We'll be hitting lots of offroad parks too. We are doing some insulation, but not goin crazy since its not our full time home.

[cadillackid]

motorhomes and coaches are in different league than school busses when it comes to stock-insulation..



and also conversion type has a lot to do with how much A/C you'll need.



a stock 11 window school bus will be running 100,000 - 120,000 BTU of A/C if its factory equipped.. more on the flat nose 14 window units..


achool busses have terrible factory insulation.. plus aluminum-frame (uncoated) single pane windows.. if lucky they are tinted.. otherwise not..



factory built motorhomes and large coach busses are typically much better insulated.. and therefore can get away with a couple rooftop A/C's.. although I venture to say most all of the better motorhomes also include a dashboard Air-conditioner (those are good for about 12,000 - 15,0000 BTU) to help cool the driver and front passenger.. even dating back to the days of 1970s van cutaways many had Dash A/C..



if you are planning to completely gut your bus down to the studs, spray foam. and build back up.. perhaps with a few less windows than it has now.. along with dynamat and insulate the front driver compartment, floor, doghouse, firewall, etc... then a couple camper A/C's plus a Dashboard (under-dash or custom system) would keep you cool.. but you'll need to run your generator.. its possible to run a minisplit or rooftop off an alternator but it will require an additional large alternator or two and a couple big inverters.. much better would be to permanently set-up your generator to run on the road or install a proper road A/C.. (probably cheaper to sell the bus and buy one with A/C unless you can find one where someone wants to remove it and is giving it away)..


school busses with their original interior walls and ceiling require lots of energy to heat and cool.. (heat is easy on the road.. bus heaters are very powerful)..



when you are saying you'll do some insulation.. are you planning to pull the factory interior panels and spray foaming? or something else?

[SSPAdventures]

We are gutting it and doing subfloor and wall insulation, we are removing 7 windows iirc, and definitely insulating the firewall and step area. I know any insulation makes a big difference.

[kazetsukai]

My understanding is that in-transit, BTU requirements jump quite considerably... like, triple in some cases. 12k BTU parked may be fine, but at 50mph?

I haven't tested mine at speed yet, or cooling for that matter (just heating) but I did build anticipating needing more than a single split (9k front + 12k back) for use while in transit. My energy usage: My single 9k keeps my cabin temps at 70F, tested down to 10F ambient. Amp draw is between 1.5A and 5A (220V) with an average ~700W power draw over a 24 hour period at 20F ambient. I also have far-better-than-stock insulation.

I guess it depends on the speed, ambient temp and desired cabin temp what your power usage is.

[SSPAdventures]

Thanks for that info! I was looking at maybe running 2 units if necessary as well. My insulation will be way more than stock, plus we're deleting windows.

[PNW_Steve]

My experience with roof airs has been pretty good while parked but on the road in warm weather they were horribly inadequate.

I had a 40' bus insulated with spray foam, RV windows installed and two 12.5k btu roof airs.

Running I-40 through AZ in August....

Both roof air's running full blast and I was wearing nothing but a pair of shorts.

It was miserable.

Some kind of engine driven air is necessary if you plan on driving in warm weather.

[rustymetalgirl]

Apologies if this posts twice...had WiFi issues while trying to send first post.

I have same questions/issues. Do not yet have bus, but looking at international 466 engine 71 passenger dog nose with two factory units (front and rear). Supposedly they work as they should. Does anyone know how effective they would be at cooling the bus while driving in Texas summer? Or the impact on fuel efficiency?

[jctrembly]

Factory air will keep a bus cool. Without knowing which 466 you have it's hard to tell how much power loss you will have as they range from 150hp'ish to 250hp. Yes expect to loose a mpg or so...

If your really wanting a cooler bus you need to consider a RE. That way your not fighting the engine heat. All FE busses and exp Dog Nose busses are going to deal with alot of heat soak.

[Ranchorossa]

Before we bought a bus, I wrote down what missions our bus would make and what our bus requirements were. It is easier to buy a bus with the options you need than to install them later. In AZ, our bus has two engine driven A/C units. They work good in the summer. Not 70° but probably 77° and we have no added insulation.

[rustymetalgirl]

Will it help the dog nose heat soak issue to line the firewall with heat resistant sound and thermal insulating material and maybe double up on insulation on the inside of the firewall? And maybe even add some to the inside of the hood?
Also thinking about engine and road noise as well as heat.

Where I live and where I’m likely to go, there will be much more need to cool the bus than to heat it. Planning on rooftop ac units for when parked.

Thanks!

[SSPAdventures]

Firewall and doghouse insulation plus radiant barrier will make the biggest difference. I also have a dog nose, and im planning on doing a full wrap on the box and firewall too. Our bus dosent have any AC currently, i plan on a rooftop unit for being parked, but im also looking onto retrofitting a mechanical system. I can use any lines or evaporator, but i need a compressor and mounting for our DT466E.

[rustymetalgirl]

SSPAdventures, do you (or anyone else) have any specific products to recommend for insulating the engine compartment and firewall against heat and sound?

Thanks!

[SSPAdventures]

DEI and Thermotech both make top quality products. There's a few other off brand items that amazon carries. Always choose a material that has a good aluminum radiant heat barrier and a high temp adhesive

[kidharris]

Originally Posted by cadillackid

"a stock 11 window school bus will be running 100,000 - 120,000 BTU of A/C if its factory equipped.. more on the flat nose 14 window units"..

How many horsepower is that consuming? 40-50?

[numinousbus]

Originally Posted by PNW_Steve

My experience with roof airs has been pretty good while parked but on the road in warm weather they were horribly inadequate.

I had a 40' bus insulated with spray foam, RV windows installed and two 12.5k btu roof airs.

Running I-40 through AZ in August....

Both roof air's running full blast and I was wearing nothing but a pair of shorts.

It was miserable.

Some kind of engine driven air is necessary if you plan on driving in warm weather.

Never drive through the desert in july and august. Even a car gets kind of toasty. If your going to attempt it, do it at night!

[Mudhutwarrior]

Originally Posted by numinousbus

Never drive through the desert in july and august. Even a car gets kind of toasty. If your going to attempt it, do it at night!

We have a winner!






Next to impossible to add enough BTU's in a bus for transit if not already equipped.
I looked into it and closest I could come to something with enough capacity would be from Thermoking and diesel powered.
I guess you could bolt a trailer unit to the back of the bus but then you would have draft issues underway with the condenser. Would look pretty radical though.

[kidharris]

Originally Posted by numinousbus

Never drive through the desert in july and august. Even a car gets kind of toasty. If your going to attempt it, do it at night!

Wimp....LOL... That's what the window is for