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Author Topic: Bus heating system  (Read 3147 times)
Lee Bradley
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« on: November 06, 2007, 09:17:02 AM »

One more piece bought for the bus. The heart of the heating system a Webasto DBW 2020 24 volt 80,000 b.t.u. diesel fired heater. My question is can/should I add a 50 gallon reservoir tank to reduce the cycles with longer burn times. Photos at ebay http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120177078252
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DrivingMissLazy
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« Reply #1 on: November 06, 2007, 09:49:28 AM »

Lee, sounds great. I had a 40,000 btu unit and it kept the coach comfy down to 0 with no problem.

With that big a unit I would think an auxiliary tank would be a great idea, otherwise it will be cycling quite often I believe.

Might want to consider a loop into the engine also for cold starts.
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« Reply #2 on: November 06, 2007, 10:03:54 AM »

Thanks. I am planning on a loop to the engine both for heating the engine and using engine heat in the system.
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Chaz
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« Reply #3 on: November 06, 2007, 10:52:27 AM »

Great buy Lee!!! I need to keep my eyes peeled for one.
  I think an auxilary tank would be the hot ticket also. Maybe even a loop to somewhat heat the fresh water in your bus in the winter.
    Justa thought,
       Chaz
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Lee Bradley
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« Reply #4 on: November 06, 2007, 11:56:41 AM »

I did not plan on that brand or size but the price was right.
Do you mean a loop as freeze protection or to heat the potable water? I plan on installing this system in the rear bay; it should keep the rest of the bays above freezing even skiing Jackson Hole. Now I'm looking for a deal like you got on your invertor.
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Chaz
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« Reply #5 on: November 06, 2007, 02:09:43 PM »

Quote
I did not plan on that brand or size but the price was right.
That is ALWAYS a good deciding factor for me also!  Wink The invertor was a good deal. I'm very happy I got it then as I would not be able to afford it now.

As far as a loop thru the potable water, yeah, some sort of line thru there to keep it from freezing, but i was also thinking in the winter when you need to use the Webasto, heating the potable up to say 70* or maybe even a bit more would be nice. Cold water -to me- sucks most any time, but especially in the winter!! Grin
 How to go about it........well....... I'd have to do a bit of thinking, but I'm sure it could be done.

  Good luck!!!
      Chaz
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« Reply #6 on: November 06, 2007, 02:17:16 PM »

Hello Lee.

Do you expect the Webasto to keep the other bays warm by convection or by routing pipes?

My DBW300 is in the centre bay and will NOT keep the other bays from freezing by simple convection.

Too much surface area to the outside, doors, and floors, and the Webasto Bay is vented.

Now, if you are insulating and boxing in....

happy coaching!
buswarrior
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Lee Bradley
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« Reply #7 on: November 06, 2007, 02:21:56 PM »

Thanks! That is good first hand information I can use. So maybe a small heater/fan with a thermostat to keep them at 40 or 50 degrees.
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DrivingMissLazy
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« Reply #8 on: November 06, 2007, 03:31:59 PM »

I had a heater in the bay for the water system. It was a piece of copper line with fins about two inches square and about one half an inch apart. All the hot water from the Webasto ran thru this and it provided enough heat to keep the fresh, grey and black tanks, as well as the pump and filter, in temperatures down to zero. I really do not know how much lower I could have gone, but it the compartment doors are sealed fairly good, I suspect you could go even lower. No thermostat or fan required.

My cold water heater was built to accept a heat exchanger which was about three inches in diameter and about six inches long. Seldom, if ever did I have to run the electric heater in the cold water tank. Engine coolant also circulated thru this system.

The genset was also kept warm by the Webasto and/or the engine, so it was always easy to start.

The complete heating system used engine coolant and circulated it as required. It was really a very  nice system.

Richard
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« Reply #9 on: November 06, 2007, 03:42:36 PM »

Many report good results with lining the floor with the syrofoam of your choice, topped with plywood, acts both as a temperature and a sound insulator for road noise.

The water tanks need to be insulated/closed in somewhat. The bay doors offer nothing but a giant heatsink by themselves.

Popularly, I've seen folks rig it up that the insulating panel is removeable, all plumbing is behind/inside and the "wall" is mounted just inside the bay door. It will pull out to access for maintenance, or for warm weather running.

I will be adding a loop from the Webasto with some pieces of finned rads inside the tank box.

It has also been frequently suggested that a water bed mattress heater placed under the tanks gives you some electric back-up.

happy coaching!
buswarrior
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Lee Bradley
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« Reply #10 on: November 06, 2007, 03:44:46 PM »

Richard,
Sounds like a good system. Do you remember how much diesel you used in zero weather?

Thanks,
Lee
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Chaz
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« Reply #11 on: November 06, 2007, 04:03:11 PM »

Lee,
  I don't recall what kind of luxury liner you run, but speaking of insulating............ I was thinking about doing something, well, maybe stupid. (WHO? ME???!!!)
  My 4108 has, for lack of a better word, a corrugated type floor. I was thinking about filling the voids with foam expanding insulation. Now, that would only do basically half the floor, but I was also thinking about filling the outside (or bottom) corrugations with foam also. (wax paper over plywood, etc.) I "think" that would do a decent job of insulating and when the bottom is coated would "slick off" the bottom for possibly less "drag".
  My demented mind is always "on".  Grin
     Chaz
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Jerry Liebler
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« Reply #12 on: November 06, 2007, 05:14:08 PM »

Chaz,
    Your plan for the bay floors will have truly negligible insulating effect.  The floors and ribs are aluminum which is such a good conductor of heat that the insulation will be completely bypassed by conduction through the aluminum.  A much better idea is simply lay a sheet of good insulating foam over the floor and top that with a sheet of say 3/8 plywood.  The floor probably isn't the most significant heat loss site though, the bay doors are likely going to conduct more heat out of a bay.  My answer is no fresh water tanks or plumbing below the floor, all above the floor in the insulated & heated passenger area, coupled with lots of water softener salt in the waste tank, which is in the rear bay, for the winter.
Regards
Jerry 4107 1120
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captain ron
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« Reply #13 on: November 06, 2007, 09:19:41 PM »

I was told I didn't need a tank as I am running mine through my whole system. Engine heat etc.
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DrivingMissLazy
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« Reply #14 on: November 07, 2007, 04:31:30 AM »

I was told I didn't need a tank as I am running mine through my whole system. Engine heat etc.

What is the btu of your furnace? With 80,000 btu I would suspect very short cycles as it is hard to get that much heat out of the unit quickly.
Richard
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« Reply #15 on: November 07, 2007, 05:58:23 AM »

Jerry,
  I kinda thought that may be the case. Dang. But I don't want to put anything on the floor. I do have insulation under my tanks tho.
  Chaz
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« Reply #16 on: November 07, 2007, 07:19:25 AM »

Just for some comparison on my 40 x 102 transit with big windows, my propane furnace is a 35,000btu that works well down to 25 degrees (the coldest I've been in).  I have two elec water heaters that have 5300btu heating coils each.  So both furnace and water heater is 46,600btu.  Kick in a block and oil pan heater of around 8000btu and your at 54,000btu.  So your 80,000btu burner is huge for what is needed-not a bad thing, just it will be cycling shorter, possibly more though.  Sounds like it will be a nice system.   Good Luck, TomC
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Lee Bradley
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« Reply #17 on: November 07, 2007, 08:37:10 AM »

I have a Neoplan Cityliner. It has a LOT of glass and I plan on keeping most of it. 80K should be enough to heat it but cooling it down south should be interesting.
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« Reply #18 on: November 07, 2007, 10:54:47 AM »

Lee,

My plan is to use the hot water from my hot water(hw) heater to freeze proof my fresh water(fw) holding tank.  I will plumb the hw directly to the fw tank through a freeze control relay.  As the temp drops I would meter enough water through the fw tank from the hw heater to maintain a predetermined temp. in the fw.  I will do this whether I have a hydronic system or not.  This keeps me from adding coils to both the hw heater AND the fw tank letting my hw do double duty.

I plan to design my tank arrangement to have the grey and black above my fw so the freeze proof of the fw will serve protect the other two.

The exhaust of the hydronic, and propane heater for that matter, is forced air driven.  That ex pipe can ex straight down.  It can also be plumbed through the other compartments to capture that wasted heat.  The other compartments would only be heated when central heating was called for so they wouldn't overheat.  Have to have an alternate source for hw in the summer though or the compartments would get just to darn snuggly.  That ex should have a slope like a drain and be made of stainless tubing as if you deplete the ex heat you get a LOT of condensation in the pipe.

My thoughts,

John
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captain ron
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« Reply #19 on: November 07, 2007, 11:35:14 AM »

I was told I didn't need a tank as I am running mine through my whole system. Engine heat etc.

What is the btu of your furnace? With 80,000 btu I would suspect very short cycles as it is hard to get that much heat out of the unit quickly.
Richard

I have a 45000 btu pro heat
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Lee Bradley
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« Reply #20 on: November 07, 2007, 12:42:59 PM »

John,
I am not clear how you plan on heating your FW with the water from the boiler. Can you explain that one more time? Are you talking about mixing boiler HW into the FW?

Thanks,
Lee
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« Reply #21 on: November 07, 2007, 05:08:50 PM »

Lee here is a picture ( I hope) of how I heat my fresh water with my webasto or with the engine while driving down the highway.  If I'm running the Webasto  only I have a loop that will circulate thru the engine and this heat exchanger on the side of my water heater.  It will heat the water in the electric water heater when the electricity is not on.
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« Reply #22 on: November 07, 2007, 10:31:25 PM »

Lee,

I'm sure I am niot clear on that.  No, the coolant and fw are not mixed....what a cocktail. 

Generally speaking you have 2 basic methods to heat your fw tank "from the inside".  You can run a coil of copper in the tank and circulate heated coolant OR you can circulate the fw thru your hw heater.  You already have a hw heater so I think it makes sense to use it for as many applications as possible.  I don't want to waste fw running the hw at the faucet till it gets hot.  To avoid that I have a line coming fron the hw line at the faucet thru a push button valve and then returning to the fw tank from whence it came originally.  When I want hw to wash or cook or shower I press the button for a few seconds and the water is hot at the tap and I haven't wasted any.  Simple, huh?

To heat my fw tank I simply ADD a valve to the system that is thermo controled from the fw tank.  When the thermo senses 40 degrees it turns on for 1 minute and purges the hw tank back into the fw tank.  My hw tank is set for 140 degrees and that will burn you if you are careless.  It warms up my fw nicely. It is a highschool physics problem to figure out what the resulting temp of the fw tank will be if you mix 6 gal of 140 degree stuff with 44 gallons of 40 degree stuff.  I don't have the metering system.  I just read the tank temp and purge the hw tank a couple of times in the evening and my tank temp stays up around 50 degrees.

My hw is heated with propane but yours wil be heated with hydonics powered with diesel.  You also can get by without a seperate fw heating system as I have.  My system is in a S&S and my tank is mounted inside but in an unheated space and if it gets down to 20 degrees my tank heads towards 32 and misery.

In a bus I think I would have a propane fired hw heater "and" the one that heats using the engine coolant in conjunction with the hydronic.  I think there is room in a 40 footer.

Hope this helps.

John
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Lee Bradley
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« Reply #23 on: November 08, 2007, 08:12:21 AM »

Much clearer. Thank you.
I am planning on a very similar system to purge the cold FW. I am also planning on a propane tankless water while the boiler/engine can provide heat for that system I don't want to run them while running A/C just to have a hot shower.
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TomCat
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« Reply #24 on: November 08, 2007, 07:03:38 PM »

Lee, if you want to stay with all propane fuel for your water/heating needs, this unit might do the trick for you...
http://www.precisiontemp.com/pt_rvmd_twintemp2.html

Jay
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Chaz
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« Reply #25 on: November 09, 2007, 10:52:21 AM »

Jay,
  looks like a neat little unit, but "proud", aren't they. They are even close to me.
      Chaz
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« Reply #26 on: November 09, 2007, 01:24:01 PM »

Yeah Chaz, it's sorta pricey, but PrecisionTemp makes awesome products with a great reputation.
 
Also if you consider how much a Webasto costs vs the Twin Temp, and then factor in the price of diesel vs propane as fuel, if you used it much, within a year or two you'll probably be about even.

The ideal situation would be to find one on a wrecked S+S for cents on the dollar.

Jay
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Chaz
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« Reply #27 on: November 09, 2007, 01:39:25 PM »

Quote
The ideal situation would be to find one on a wrecked S+S for cents on the dollar.

  I'm backin on that one!!!!!!!!!!!!!! Grin  But glad to hear they are a good product!
   Chaz
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