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Author Topic: Bus A/C Options  (Read 4277 times)
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« on: March 24, 2011, 02:28:30 PM »

  Now that I have a Bus coming home, among other issues I will have to start considering is air conditioning. As many others here feel, I absolutely can not stand anything up on the roof, it totally detracts from the Buses looks, and looks terribly crude having boxes up in the airstream. I want those two ugly turds off the roof. So im looking for innovative ideas that can be done DIY for reasonable costs.

  Currently the Bus still has the original road air. I know most everyone here rips it out, but I would like to work with it if at all possible, and am interested in any ideas that would make it more efficient and hopefully help others in the process.

  Obviously the heat load on the system will be greatly reduced, and I intend gut the inside, reinsulate, cut out two window units on each side and wall over them so that that area will be insulated equal to the walls, as will the rest, floors etc., reducing the load further

  Starting from that premise, I have been trying to estimate the heat load. Ive tried residential calculators and tried to make assumptions, but obviously these are not accurate, or you wouldnt see RV's with 4 or 5 roof top AC units and 20KW generators. However, I only have a single on the 32' Bounder, and while its uncomfortable above mid 90's, its better than opening the windows. But if two would work, it seems safe to assume 20-25K BTU would be sufficient, so maybe say 30K just to be safe. And considering the furnace in the Bounder is 25K Btu output, and can keep it warm down in the teens, thats probably a reasonable figure.

  My thoughts then, are to replace that giant 600 pound compressor with a small automotive type, cut down the size of the evaporator to match the lower maximum heat load, pull the big DC motor and blowers out of the condensor bay, leave the condensor its full size, and put in a flat radiator fan that draws less energy. I may also consider changing out the heater blower fan for something lower HP.

  Another idea I would like someone to comment on, is teeing in a residential 230 volt 2 - 3 ton compressor with check valves, that could run on shore power, gen power etc., and wonder if its possible to also construct it as a heat pump?

  My desire is to keep as many systems as possible operating on 12/24 volt DC and/or engine powered, but increase their efficiency any reasonable way. I want to stay away from ac powered air conditioners, inverters, at least large ones, as well as stay away from a large battery bank.

  Any ideas, even revolutionary ones would be welcome.

 
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robertglines1
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« Reply #1 on: March 24, 2011, 02:41:14 PM »

? what kind of bus? Using 3 mini split on new project. super efficient only about 1500$ for 30,000 btu heating and air.
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« Reply #2 on: March 24, 2011, 02:44:11 PM »

Thanks for letting us know what you think about roof airs Roll Eyes.

You could has stated that you don't care for the looks, without saying that everyone of us that has roof airs, has a bad looking bus....
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« Reply #3 on: March 24, 2011, 03:02:13 PM »

Thanks for letting us know what you think about roof airs Roll Eyes.

You could has stated that you don't care for the looks, without saying that everyone of us that has roof airs, has a bad looking bus....

  Uhmmmmmm. Hmmmm. Whats that saying about bein careful who's toes you step on?

  Sorry for sharing my hard feelings against them, one mans pleasure is another mans, etc... and all that. No hard feelings?
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« Reply #4 on: March 24, 2011, 03:10:06 PM »

? what kind of bus? Using 3 mini split on new project. super efficient only about 1500$ for 30,000 btu heating and air.

  MCI 5B. Then im back to runnning AC all the time in order to cool.  The engine is running going down the road, why not take advantage of it. When its not running, why not incorporate something into the existing system? Thats what I would really like to look into.
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« Reply #5 on: March 24, 2011, 03:35:32 PM »

My experience in the commercial bus world is the coach AC is always needing fixing. It's a constant, expensive, maintenance item. For the price of one time in the shop you could buy a few roof airs or minisplits. But then you need a generator. But a quality generator will not need alot of fixing.
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« Reply #6 on: March 24, 2011, 03:57:42 PM »

You will lose 1 to 2 mpg running the factory air then you need turn it off every time that DD see a hill lot more guts than I have trying to keep a 50 year ac unit going hope you have deep pockets
good luck
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« Reply #7 on: March 24, 2011, 04:12:51 PM »

  Now that I have a Bus coming home, among other issues I will have to start considering is air conditioning. As many others here feel, I absolutely can not stand anything up on the roof, it totally detracts from the Buses looks, and looks terribly crude having boxes up in the airstream. I want those two ugly turds off the roof.

Lots feel that way though dew share it with your eloquence. Huh Roll Eyes Grin Grin

 So im looking for innovative ideas that can be done DIY for reasonable costs.

The absolute cheapest and easiest way to install AC is with the roof units.  They are also the easiest to replace and cheapest to do so.  They are noisy and intrusive but if you duct them they are OK.  Duct them and they become less efficient...trade-off.

Go with the Mini Split.  Look it up c ause you don't sound like you know what that is.   You can install three zones and the only unit that comes on is the ones that need cooling.  Three separate thermostats.  Much higher efficiency than can be had with roofs.  USE A HEAT PUMP whichever way you go.  36KBtu plus.  Augment the Heat pump with a propane furnace in the 30KBtu range.

  Currently the Bus still has the original road air. I know most everyone here rips it out, but I would like to work with it if at all possible, and am interested in any ideas that would make it more efficient and hopefully help others in the process.

The OE bus air is extremely over sized for our application.  The enormity of the unit makes it a serious power drain and consumer of fuel.  It is also prohibitively expensive to repair....like in the thousands every time.  Use the front evap unit for the driver and front and just replace the huge compressor with a LARGE automotive unit.  Install a separate evap in the bedroom and maybe one amidships.  I think the stock condenser is a great idea but our resident AC guru, and I say that with sincerity, is Nick Badame and he says that the system needs "sized and matched" so a new condenser is needed.  Uhhh, I dunno but I can't contradict Yoda.




  Obviously the heat load on the system will be greatly reduced, and I intend gut the inside, reinsulate, cut out two window units on each side and wall over them so that that area will be insulated equal to the walls, as will the rest, floors etc., reducing the load further

Use spray in foam insulation for the best performing insulation and to add an enormous amt of sound deadening.  No other way.


  Starting from that premise, I have been trying to estimate the heat load. Ive tried residential calculators and tried to make assumptions, but obviously these are not accurate, or you wouldnt see RV's with 4 or 5 roof top AC units and 20KW generators. However, I only have a single on the 32' Bounder, and while its uncomfortable above mid 90's, its better than opening the windows. But if two would work, it seems safe to assume 20-25K BTU would be sufficient, so maybe say 30K just to be safe. And considering the furnace in the Bounder is 25K Btu output, and can keep it warm down in the teens, thats probably a reasonable figure.

Double paign all glass.  The roof used to have R5 or so and the bus stayed cool but then it was fed by a 50KBtu AC unit.  So you weill push the R to at least 22 and it should be about R30.  The walls will be at R 15 and the floor should be 20 with the foam spray under the floor and on the ceiling of the bays.  All of this is just blah blah blah.....45K Btu of roof air works for everybody.....do what works.  The Btu for roof airs is less than a house would be specified at so instead of 3 ton of Mini Split you might get by with 2.5 ton.  But why scrimp?  Ask the board which Mini's they used and how big.  With the condenser in the bay you will be giving up a bay and that is why I will have warts on my roof and for that reason alone.

  My thoughts then, are to replace that giant 600 pound compressor with a small automotive type, cut down the size of the evaporator to match the lower maximum heat load, pull the big DC motor and blowers out of the condenser bay, leave the condenser its full size, and put in a flat radiator fan that draws less energy. I may also consider changing out the heater blower fan for something lower HP.

Great thoughts except the heat blower in the front.....leave entire system.  Maybe add a evap unit with the blower shooting the cold air back into the living room.  The condenser will get by with auto rad fans if they can move enuf air.


  Another idea I would like someone to comment on, is teeing in a residential 230 volt 2 - 3 ton compressor with check valves, that could run on shore power, gen power etc., and wonder if its possible to also construct it as a heat pump?

If this is the deal where the OR AC has a ac powered compressor for use with shore power and you only have one system with two compressors.....my local ac dude says he can do that without problems but Yoda was not very encouraging.  I think that would be optimum and worth the engineering.  On the other had with the engine and AC powered unit you will always have a spare installed and waiting no matter what.  Parked you can run the engine or while driving you could run the genny and the AC powered units.  Decisions?Huh
?

  My desire is to keep as many systems as possible operating on 12/24 volt DC and/or engine powered, but increase their efficiency any reasonable way. I want to stay away from ac powered air conditioners, inverters, at least large ones, as well as stay away from a large battery bank.

You can't get there from here.

  Any ideas, even revolutionary ones would be welcome.

 
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« Reply #8 on: March 24, 2011, 05:24:49 PM »

Well, I know I'm the exception, since my bus was an original 1982 factory conversion, thus, not a bunch of miles, but I'll share my experience just in case there is any value for you. When I bought it three years ago, the over-the-road air didn't cool. After much consideration, I took it to a local commercial refrigeration outfit, and asked their opinion. They pulled a vacuum on the system, deemed it worthy, and charged it with "Freeze 12". It has been working like a champ ever since. I wouldn't say it's grossly oversized, but it is highly effective. Driving into the sun doesn't overpower it. My take on it would be, as long as it can be kept without a budget breaking expenditure, it is good to have. Works for me.
Dennis 
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« Reply #9 on: March 24, 2011, 07:32:07 PM »

After much consideration, I took it to a local commercial refrigeration outfit, and asked their opinion. They pulled a vacuum on the system, deemed it worthy, and charged it with "Freeze 12". It has been working like a champ ever since. Dennis 

   Not long ago a search for alternate refrigerants would bring up all kinds of horrific discussions, your going to blow up, kill people, burn, some claimed a building in Texas took out at an entire block when a car with a can of propane refrigerant blew, killing dozens, etc., but of course, if you dug into the story you found nothing to support it. Now with real testing being done in Europe and Australia, and with the Dupont genie out in the spot light, people are returning to natural refrigerants once again, Ammonia, CO2, Propane, etc.. They are now selling refrigerators with Propane, just about everywhere except the USA. Cars in Australia now run Propane refrigerant, and testing has shown its no more dangerous than R-134a in an accident. But im not so sure I would want Propane in the Bus system, as it has a much greater capacity.

  However, R-12/Freeze 12 may be less efficient as IIRC, Bus systems use R-22. Im no refrigeration geek, but the R-12/Freeze 12, may not be cooling as well as the proper refrigerant. I read a site on conversion to propane, and this guy said the expansion valve is the main culprit, that the capillary has to have the same gas as what you run in the system. Then he went on to explain how to convert one.

  I dont know if a automotive compressor is large enough, but definetly the original is much to large for cooling a well insulated Bus with only a handful of people. What I havnt found yet, is how you size the evaporator. Someone, I believe it was Tom C., claimed that if you used too large an evaporator it would ice up. Perhaps pinching off a circuit or so would be enough to do the trick.

  Maybe its not so much it wont work, or cant work, so much as no one really wants to take the time to try. Screwing around with R-22 at $20 pound would get real expensive real fast. And if it leaks out every year and you have to pay someone to service it, your talking $100's of dollars, and I can see that being a real obstacle people would want to avoid. I have a reciept for AC service on the Bus thats over $700, so its nothing to sneeze at. However, if a cheap or free gas can be used, it would offer the ability to experiment a little and see what might work. At least until throwing your hands up in futility.
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« Reply #10 on: March 24, 2011, 08:12:11 PM »

I asked a similar question about "dual powered" air conditioners a few months ago.  I was told that if you want to run an A/C system off a 120V compressor part of the time and an engine-driven compressor part of the time, then the best way is to have two separate systems.  You stack the two evaporator coils one in front of the other so that your air-handling system (blower fans, ducts, etc.) are the same no matter which you're running.  Of course, it increases your cost but you're already doubling the system anyway.  (You'll need to double the condensers, pressure valves, tubing etc. as well as buying two compressors.)  But it sounds to me like a good way to make a versatile system.

Also, on the subject of a freezing up evaporator, you can run a thermostat to the evaporator.  Anytime the temperature at the coils drops to about 36 degrees, you use the thermostat to drop out the clutch on the compressor.  The air blowing over the coils stays pretty much the same temperature but it will warm the coils up pretty quickly.  Once it does that, the thermostat kicks the compressor back in and cools the coils up again.  This process gives you a fairly steady stream of cool air but stops the evaporator from freezing.  It has the advantage, too, if you have a lot of really hot air, as the air-handling system draws that air in, then it is longer before the coils cool down enough to be in danger of freezing.

Oh, also, be sure that you have a good catchpan and drain system -- anywhere but the bone-dry deserts, you'll be pulling lots of moisture out of the air.

There are a lot of factors here, but these items may help you with some of the details.
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« Reply #11 on: March 24, 2011, 11:30:06 PM »


There are a lot of factors here, but these items may help you with some of the details.

  You know, that is actually a fascinating idea I had never thought of. The original road air looks to be about 8 tons capacity, or about 3 times larger than needed in a typical RV application. That makes the condensor and evap about 3 times larger than needed. Cutting them down would easily leave enough room to slip in second core units to share the same space, and I would still have a redundant system and without roof airs. And if I get that big electric motor and blowers out of the condensor bay I just might have room to stuff the genny in there too.

  Any ideas for building a heat pump out of it?

   

   
 
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« Reply #12 on: March 25, 2011, 12:10:04 AM »

Ahoy, Art,
My Eagle has two automotive compressors, the old GM A-6 items from the 70s or so.  I asked a few years ago, and our A/C Guru noted that the A-6 is likely to be around for a good while.  Big and heavy, but they even have a built in lube pump.  Plenty of capacity, and I seldom need to run both.  My system is hydronic, heating or cooling secondary coolant.  Powerful and effective, but It cannot be considered acceptable because of condensation on the cold hoses which make a mess in the bays.  Id planned to insulate them, but it became too hard to do.
I run four 120vac compressors. There are two separate independent systems.  That is, one A-6 and two 120vac units for each, plus condensers and evaps.  Check valves for each 120vac unit, none for the A-6s, because the valve scheme is a check valve.  Ive never tried (or have needed to) run the engine A-6 units and the 120vacitems at the same time.  Id expect it to be too much.
I cant see how using the original large condenser would present problems.  All the condenser does is condense the gas to a liquid, and bigger would only seem to further cool the liquid.  A shortcoming would be that you would only have one system if you use the existing condenser.
Good luck  /s/   Bob

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« Reply #13 on: March 25, 2011, 05:27:49 AM »

I had a random thought about this - MC-5B only has two bays.  All your wet tanks and such will probably fill one bay (does on mine) so you only  have one bay for carrying stuff.  If you fill it with air conditioners,  you won;t have room to carry stuff.

You have a decent generator on the engine.  if you build in a suitable inverter you can run sufficient AC from the bus engine converting to 120 or 240 VAC to cool the bus on the road.  And plug in to pedestal when parked, or have a generator.

Bus OTR AC typically needs about $1500 annual maintenance.  That solves a lot of roof wart issues for me but maybe you have deeper pockets or are smarter than me.  It draws a lot of power - maybe your engine is more powerful than mine, but my 8V71N was fairly marginal.  It's really heavy, probably adds 400 lbs.  It occupies a bay that is  very useful for a generator or house batteries.  It only works when the bus is running.  Even on a trip, my bus is running only maybe 15%  to 30% of the time.  I do tend to stop and stay a while when I get to where I am going.  My analysis said that the bus OTR was a non-starter.  It came nowhere close to solving my problems, regardless of cost. 

I like redundancy.  While I only have one roof-top now, plan is to add a second small unit of some sort for the bedroom/bath area, and have zone cooling capability.  I like the idea of being able to stop at a camping world or other RV store with a dead unit and a couple of hours later be rolling with a replacement installed and working.  Aside from the weight, they are plug and play.  I can install one by myself with what I carry on the bus in around an hour.

I completely agree the way they look sucks. 

Just some thoughts.

Brian
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« Reply #14 on: March 25, 2011, 06:24:00 AM »

I would think long and hard before pulling OTR system out. Nothing will cool as well as it does down the road.
I have had to replace a hose or two and top off the system once or twice in the last 10 years. Hoses were around $100 Ea. Not that big of a deal to me. Sure wouldn't want to have to do without it.

Learn to repair it yourself. You can save a lot of money that way.
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