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diy exhaust heat to water transfer for rear cab heater

 
 
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(pete)
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PostPosted: Mon Sep 02, 2013 1:40 pm    Post subject: diy exhaust heat to water transfer for rear cab heater Reply with quote

Any arctic guys out there build anything like this for overland type trucks if so any one got any ref websites that they used

Cheers
Pete

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kentm11
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PostPosted: Mon Sep 09, 2013 3:40 pm    Post subject: Reply with quote

Been thinking about this a bit and it should be fairly straightforward to get the heat from the exhaust to the cab area but I considered if you are better running oil rather than water? That way you can use a oil cooler radiator as the heat exchanger. Rigging a ducted fan to blow the air is obviously easy but running a 12v oil pump is expensive to buy.

That being said your going to need to be handy with a tig welder.
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Jim1064
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PostPosted: Mon Sep 09, 2013 6:26 pm    Post subject: Reply with quote

In order to get the most of the heat of the exhaust gases, you'd need to install a heat exchanger as part of the exhaust system (similar to an intercooler on the air intake).

Just welding or brazing a pipe coil around the outside of the exhaust pipe is hopelessly ineffective.

Given the high temperatures and potentially corrosive gases (superheated steam!) I'd say the heat exchanger needs to be made of stainless steel.

I'd recommend against oil - for wo reasons:
(1) ...the obvious: what will happen if there is a leak? Shocked
(2) Water is simply much more effective as it has a much higher heat capacity than oil Idea

Just my 2 pence worth of thoughts...

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spannerman69
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PostPosted: Mon Sep 09, 2013 7:02 pm    Post subject: Reply with quote

or you could do what the army did , just use a arctic heater , plumbs into the water system and has a simple tap to control water flow and a heater blower mounted to it .








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spannerman69
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PostPosted: Mon Sep 09, 2013 7:03 pm    Post subject: Reply with quote

or you could do what the army did , just use a arctic heater , plumbs into the water system and has a simple tap to control water flow and a heater blower mounted to it .








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Jim1064
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PostPosted: Mon Sep 09, 2013 10:48 pm    Post subject: Reply with quote

The nice thing about capturing the heat from the exhaust gases is that you're tapping a heat source that otherwise goes wasted.

As a rule of thumb, the energy from the fuel gets split approximately three-ways:
- one-third is converted into forward motion
- one third goes into the cooling water
- one third goes down the exhaust

Assuming the car already has an optimised heater that runs on the cooling system (i.e. capturing all the heat without the cooling water getting too cold), the exhaust heat exchanger is the way to go...

Or an auxilary diesel heater as found in campervans...(probably easier...)

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(pete)
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PostPosted: Tue Sep 10, 2013 12:33 am    Post subject: Reply with quote

That arctic heater is almost what I had in mind but a separate stand alone system from the engines coolant as I don't want to risk the engine running too cold or water pump problems caused by the extra water needing to circulate

I'm a welder and a dab hand with a tig torch even if I say so myself

So wrapped copper will be ineffective.... Even if it was heat wraped to the pipe with exhaust tape to insulate it to the exhaust....

Keep the ideas poping up though guys

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teamidris
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PostPosted: Tue Sep 10, 2013 7:43 am    Post subject: Reply with quote

I'd weld in a stainless steel tube to the system with a water jacket around it. But fitted after the last silencer, as you'll chill the exhaust gas below boiling point and the acidic water will drop from suspension and eat the system down stream of your 'recuporater'.
If you go thick walled stainless why not try air-over-gas? Same as a beetle.

The proper way to do this sort of heat recovery is to take the heat early on, just after the turbo. Maybe with water cooled manifold and turbo, using standard marine engine kit.
But that pipe under the cab of my S1 is looking spot on for an air heater shroud Smile

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(pete)
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PostPosted: Tue Sep 10, 2013 9:43 am    Post subject: Reply with quote

Its a common misconception that stainless is rust proof.... For stainless to stay shiny and rot free it has to be in contact with the open air. below water away from the air stainless will and does rust,

I'm thinking that I may make a copper coil inside a section of exhaust like a dummy silencer fitted just after the manifold on the down pipe, the more coils I can get in the box the more surface area I will have to transfer the heat to the water via the copper, also inside the box can be insulated to remove the effect of surface cooling on the outside. The copper tube can be extended outside the box and run to a place where I can attach the coolant hose for a rad in side the car. If I was to use a small motorcycle rad and electric fan its a nice slim line fitting in the truck and could be mounted on the rearwards side of the bulkhead behind the seats. Run a small auxiliary 12v water pump and jobs a goodun

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dxmedia
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PostPosted: Tue Sep 10, 2013 11:06 am    Post subject: Reply with quote

In the process of building an overlander, I've just wired and plumbed in an eberspacer 3K diesel heater into the cab with capacity for the air to be re-routed into the living area.

K.I.S.S - don't tap into your vehicle systems. What happens when there's an undiscovered leak, rubber hose perish etc.. The same way that keep living batteries away from vehicle batteries (although have a facility for jumping in case of low vehicle batteries).

Heat exchangers are also pretty *****. Remember that luke warm air around your feet on the school bus in winter? They are heat exchanger radiators along the sides of the bottom of the bus. I've thrown more of those aware than I'd care to remember in vehicle conversions in the past.

I paid £100 for my eberspacer on gumtree. It cost £34 for the rebuild kit (all second hand eberspacers will need this) and it works perfectly. It also acts as a cold air fan if needed. I can also defrost the cab in the morning without leaving a cold engine on tickover.

Just $0.03's worth.
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(pete)
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PostPosted: Tue Sep 10, 2013 12:36 pm    Post subject: Reply with quote

Thanks dx

I have looked long and hard at buying a solution but I want to build it if I can, its also more of a secondary heater for the car as the heater in the front is not that bad for the cab area but the rear stays coldish....

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dxmedia
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PostPosted: Tue Sep 10, 2013 1:16 pm    Post subject: Reply with quote

Really look into the ebserpacgers / webasto's or other truck night heater brands.

I can buy a 7 day 24 hour times for mine for about £30. Just imagine waking up in the morning, having breakfast and getting into a toasty hot de-misted de-iced truck in the middle of winter Smile Blown air too, length of 4" diameter flexible pipe and you get put that air anywhere you want. Working in the garage on a winters day, just funnel the air in and you've a heated workshop (I did that when I was bench running my heater).

Going laning and sleeping in the back of your truck, well, switch on the heater (they are thermostatically controlled).

They run on drip feed too, so the amount of fuel being used is minimal. Power consumption on startup is quite high on the older larger units, but when running it drops right off.

I've plenty of bad things to say about heat exchanger type air heating systems, but I've nothing really bad to say about the diesel heaters. If you want to look into alternatives too, the rover 75's have a 3kw eberspacer water heater for the engine as an auxilary heater (very common on ebay, very cheap), it wouldn't be difficult to use one of them and create an internal wet system (that's my plan for the camper body with underfloor - using blown air as a backup)

There's only 2 things I'd point out about the eberspachers. 1/ They are noisy on startup.

2/ On a cold day, when starting up they produce a bit of a cloud of smoke till the combustion chamber gets up to temperature. I've a D3LC which isn't the newest of models though, I'm sure that the later ones are quieter / cleaner.
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kentm11
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PostPosted: Thu Sep 12, 2013 5:45 am    Post subject: Reply with quote

It would be expensive but could you use a4 stainless which is marine grade? I agree certainly I would make an internal coil to maximise the heat being transferred to the liquid content. Water does have a greater heat capacity so it would be warmer but it also expands more than oil so your going to need to think about thermal expansion of the water and therefore you should add an expansion tank. Would it be worth making a small expansion chamber to slow the gasses and yet allow them to pass through with a less of an impedance to the gas flow.

How difficult would it be to tap off the hot water from the heater and run two insulated pipes to the rear?

Actually more obvious than that is tge question why do you want to have a scond heater anyhow?
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(pete)
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PostPosted: Thu Sep 12, 2013 6:00 pm    Post subject: Reply with quote

Ya know tapping off the existing coolant pipes seems the way to go its a kiss thing running secondary pumps header tanks etc etc its starting to get over engineered for what is effectively a winter heater only.... The derv heaters are just to costly for the use they will get, I know that they have the advantage of warmming the car before its driven but I cant justify the cost to myself,

So new plan is.... Small motorcycle rad mounted in the rear with a small electric fan to blow the air through in to the load space, run it for a while and if my engine suffers from below normal temps fit a higher rated stat. i I could even run it through the heat exchanger to boost the water temp again before it gets to the rad. the pipework can run allong the underside of the car and up through the seat box area to get to the rad and I will put a bypass valve in the engine bay for the summer,

What do you lot think lol

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cynic-al
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PostPosted: Fri Sep 13, 2013 11:50 am    Post subject: Reply with quote

Didn't they used to do this on the old air cooled beetles? I remember when the exhausts used to fail the occupants got gassed Laughing

I'm sure the cummins truck engines used to circulate the diesel around the engine then back to the tank to warm it up for very cold climates too.

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dxmedia
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PostPosted: Wed Sep 25, 2013 1:30 pm    Post subject: Reply with quote

http://www.mod-sales.com/auction/vehicle/relate..._Night_Heater.htm

?
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(pete)
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PostPosted: Wed Sep 25, 2013 5:55 pm    Post subject: Reply with quote

That is properly cheap but I'm totally broke at the moment
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