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Old 08-22-2006, 08:53 PM   #1
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Air Conditioning Questions?

We are converting a school bus into a limousine style bus. The bus is 25ft. and was a 45 passenger. We will be running lights, stereo, tvs, etc. We need a plug outside and a few inside. How many AC units should we have? How would we set this whole thing up? Generator size? I am pretty much clueless about buses. The mechanic says the bus is great condition. Just trying to figure out some things... any help would be great.

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Old 09-27-2006, 10:44 PM   #2
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It depends on use (passengers, windows, how often doors open, insulation etc). For RV use you would usually want 30,000BTUs of cooling. Transit buses and highway coaches usually have 90,000BTUs of cooling. I know that sounds like a lot but you have to take into consideration all hte heat gain.

A big steel tube crusing down the highway at 65 in 100f heat will get hot. All that hot air being forced in through all those little cracks will add to the heat gain. All the glass in a bus will act as a greenhouse and the steel structure will radiate lots of heat in.

Peoples bodies also generate heat. Differetnt electrical appliances generate heat. Then you also have to figure how often the doors will be opening and closing.

Depending on where the engine is you also have to figure out how much heat is going to radiate in. From what I have seen rear engine buses stay cooler than dog nose buses. Front engine transit skoolies are in the middle. Again insulation makes a lot of difference.
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Old 09-27-2006, 11:19 PM   #3
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Funny you should mention body heat. I'm from Minnesota and one of the big things they advertised when the Mall of America opened was how energy efficient it was (in the winter anyway) because it doesn't have any source of central heating. All the heat is generated by the electronic equipment in it and more than anything, the people moving around.

With what you're talking about running in that bus, you're going to need one HECKUVA generator. A big battery bank and a good inverter or two will help, but running an AC off the inverter is tough, as discussed before. My recommendation might be to consider getting an engine driven AC compressor along with a gennerator head or a second alternator. Having it all driven off the engine might sound like you're wasting a lot of fuel (the engine has to be running all the time then obviously), but it would be a lot easier than hauling out a big gennie all the time and a lot more cost effective than getting a built gennie ($$$). You may want to look into reducing the power consumption somehow. Flourescent lights are GREAT. They draw less energy, kick out less heat, and are more resistant to the bouncing a bus does. The only downside might be cost, but they last so much longer so it kind of offsets....

Another option would be to run a swamp coolre if the environment isn't too humid. Even in my humid environment I plan to try and build one. Even on the humid days when Ican't use the evaporative cooling, I will have a central air exchanger. Just keeping the air moving can make a big difference.
Skooling state at a time...
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Old 09-29-2006, 10:40 PM   #4
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You can always look at a commercial bus A/C system. Some skoolies in the southern states have A/C systems built in. Some are driven off a seconary engine and others off the bus engine. Usually both systems use two Saden compressors. Transit and coach buses use one really big compressor. These are probably going to be too big for your needs. They also are said to use around 30 or 40 HP. They also use R22 and they tend to leak over time.

If in your application the bus engine will be running most of the time I would use two Saden compressors and have an evaporator in the front and rear. You would also want big condenser coils to dump all that heat. You will also want to look at pully size for the compressors. You want them to run at higher RPMs to work better.
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Old 09-30-2006, 10:38 AM   #5
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I would think that starting with two rooftop 13500 btu RV units run off a geni, preferably somthing quite like a honda or yamaha, would be a good start. You can always add more later.

We use one 13500 btu duotherm to heat our 600sq ft home during the hot summer months and it does a great job.

If you decide to get more ac units, just get a second honda eu or somthing similar to run it at that time. The nice thing about this system is you don't need to run all ac units if it isn't too hot out, so only one geni. And if one craps out you always have a backup.

This is my 2 cents.

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