Diesel heating for Merc Vario Pros/Cons

[MARIŌVERLAND]

Has anyone had any experience of fitting a diesel fired wet heating system in a Mercedes Vario?

After quite a bit of looking around at different systems I'm edging towards this option for hot water and blown air heating in the back of the Vario. I'm aiming at installing a Webasto Thermo Top inline to feed engine coolant to a calorifier and a matrix heater with blower for hot air. Has anyone done this? Is it a good way to go for primary heating?

The bonus of this system, as far as I can see, is that the heat from the engine will be utilised by the calorifier and matrix heater when the truck is moving/engine is warm. When stationary the Webasto takes over and does the job of heating the coolant. It also comes out at a reasonable price for the system compared to separate diesel air and water heaters.

If anyone has any knowledge, I'm trying to figure out the best way of routing the pipes from the engine bay to a Webasto Thermo top, pos still under the bonnet, then on to the living area. Also trying to figure out what is required pump wise to move the water round on the two circuits (coolant/fresh water).

Any advice would be greatly appreciated.

 

[mhatakka]

I like the idea. In addition to the blower heater, I'd consider under floor tubing for even warmth distribution. Also, a simple liquid-to-liquid heat exchanger between engine coolant and living area heater liquid might be something to think about. It would keep the engine coolant circuit separate, less prone to problems. Some calorifiers has a separate connection for engine coolant, that might be the solution?

Markus

 

[Joe917]

The system you describe is similar to ours. It works very well. We have hot water radiators instead of a matrix heater. Underfloor heat is great if you can fit it into your build.
There is no need to separate the engine and camper coolant loops, you should have shut off valves in case of a hose failure and to allow easier servicing. Closing one valve will stop coolant circulating through the engine when the webasto is run to heat the camper. Close only one valve in this case to allow coolant to expand into the engines overflow pressure tank and at the same time stop engine loop circulation.
There is no need for extra pumps. The engine coolant pump serves when the engine is running and the Thermotop comes with a pump.

 

[MARIŌVERLAND]

Thanks for the comments. My Vario is limited in terms of height inside, it's a high roof van but there's not a huge amount of room to play with. What pipework is usually used for the underfloor system? Presumably the floor underneath would also need thick insulation to prevent heat loss through the floor? this would probably add too much height for mine..

I would want the engine and camper coolant loops integrated so I can utilise the heat produced by the engine with the calorifier and rads.

Joe how do you find the radiators? Presumably these are just household flat panel type? What size/output rads do you have in your 917?

So I have it clear in my head, you are using the engines overflow pressure tank to deal with the coolant expansion from the Thermo top/Engine circuit and a separate header tank in the living area to deal with the expansion of the hot water circuit? Presumably you just T off from the engine coolant circuit to add the Thermo top and Calorifier part of the circuit into the loop? Where did you locate the shut off valves to allow the use of the engine overflow pressure tank?

Thanks

 

[grizzlyj]

Thanks for the comments. My Vario is limited in terms of height inside, it's a high roof van but there's not a huge amount of room to play with. What pipework is usually used for the underfloor system? Presumably the floor underneath would also need thick insulation to prevent heat loss through the floor? this would probably add too much height for mine..

I would want the engine and camper coolant loops integrated so I can utilise the heat produced by the engine with the calorifier and rads.

Joe how do you find the radiators? Presumably these are just household flat panel type? What size/output rads do you have in your 917?

So I have it clear in my head, you are using the engines overflow pressure tank to deal with the coolant expansion from the Thermo top/Engine circuit and a separate header tank in the living area to deal with the expansion of the hot water circuit? Presumably you just T off from the engine coolant circuit to add the Thermo top and Calorifier part of the circuit into the loop? Where did you locate the shut off valves to allow the use of the engine overflow pressure tank?

Thanks

Hi

You might want to broaden your query to other vehicles and campers.

We had a D5WS plumbed into a Unimog cooling system, all done by the previous owners. A lot of the coolant circuit was normally un-accesable. If we opened the taps to share engine heat with the camper a load of air entered the camper circuit which took so long to work its way out again we never did it again.

We've also since learned that the pressure the engine may want it's coolant circuit to run at will be unreachable when you have a much bigger volume and pipe length, so you should have a heat exchanger between camper and engine plumbing so they can run different pressures.

It's certainly doable, and how ours was set up, despite the correct connections in the correct place may still have had other issues I wasn't aware of.

For the amount of fuel such a heater uses, and considering how quickly they heat up enough for a shower, the free heat from the engine is nice but not worth the headaches a self install "may" cause.

Cold starts when you are at the limit of what the vehicle can do may well require a pre-heater which is a whole bigger level of justification, but I'm sure Merc have a fitting kit to do that and work perfectly.

 

[MARIŌVERLAND]

Thanks for the heads up on some of potential problems, good to know. I was originally looking at this option because it utilises the waste engine heat but if it is going to open a can of worms I might keep it separate. The longer runs of pipe to the engine bay would also add to inefficiency if connected presumably.. Also no need for a calorifier if it is separate system, can just get away with a flat plate heat exchanger. Simple might be the best way to go..

 

[grizzlyj]

Hi

I didn't mean you can't do an install that is trouble free, but I suppose I've become more cautious about fiddling with the manufacturer set up.

I'm fairly sure Webasto does a diesel fired water heater with no tank giving you instant hot water at a slow rate, maybe not enough for a shower. Something like a 5KW water heater will have a minimum water capacity for it's system (so needing a calorifier, it's own circuit with anti-freeze in and then the hot fresh water circuit) or it will cycle on and off too quickly and inefficiently, the noise annoying your neighbours. Aiming for a 5KW water heater and a big enough calorifier to usually give enough water for the evening means you can run the heater while driving giving the batteries the best chance of being charged when you do stop. Any heat "lost" in the plumbing will be heating your cabin, just depends how hot or not ambient is as to wether you want that or not!

 

[jostein]

Simple or not, I have already jumped into it in my 815da. I am finished installing the hydronic underfloor heating pipes.
I Will also install hydronic loops in the fresh and grey water tanks.

My setup will have a twin coil calorifier with an electric heater.
One coil will be connected to the 9 kW diesel heater in the engine bay. I think I will install a 3-way valve for changing between engine heating and camperbox heating. The other coil will be used for the floor/ tank heating. The calorifier also serves warm water for shower and taps.

This setup isolates the hydronic heating from the engine coolant loop, which I think is wise to avoid problems with air or leaks potentially compromising the engine cooling. The hydronic floor heating loop will of course need its own circulation pump and expansion tank.

 

[Anton2k3]

Hey jostein,

Curious about your under floor heating. How are you going to control the floor temperature? Anything above 35-40 degrees would burn the feet. The diesel water heaters are set temperature, ~80 degrees I think. I'm just looking at how to control it myself. We're also running grey and fresh tank loops, as well as garage and bathroom towel rail. Eberspacher air heating as backup.

 

[jostein]

Hello,

I think you are right, they are set at around 80.
I also think it should be relatively easy to reduce the floor loop temperature with a bypass.

On the other hand I do not expect anything close to 80 degree floor temperature, at 80 degree diesel heater outlet temperature.
The following will reduce the Temperature before comming in contact with your feet:

-Temperature loss from diesel heater to calorifier coil nr 1.(not much if properly isolated)
-The water in the calorifier will be colder than water in coil 1
- Coil nr 2 will again be colder than the water in the calorifer.
- The water in the floor loop will gradually become colder under its way trough the loop, making the average temp significantly lower than coil nr2 temp.
- Finally the floor surface temp will be noticeably lower than the loops average water temp, this is mainly because you spread the heat from a small diameter pipe out on a larger surface. Pipe diameter and pipe c/c are central here.

Jostein

 

[Anton2k3]

when you say the other coil will be used for under floor heating, you mean you are going to install another pump and turn that coil into a circuit? That means the under floor heating will only work if the calorifier is up to temperature?

 

[grizzlyj]

Hello,

I think you are right, they are set at around 80.
I also think it should be relatively easy to reduce the floor loop temperature with a bypass.

On the other hand I do not expect anything close to 80 degree floor temperature, at 80 degree diesel heater outlet temperature.
The following will reduce the Temperature before comming in contact with your feet:

-Temperature loss from diesel heater to calorifier coil nr 1.(not much if properly isolated)
-The water in the calorifier will be colder than water in coil 1
- Coil nr 2 will again be colder than the water in the calorifer.
- The water in the floor loop will gradually become colder under its way trough the loop, making the average temp significantly lower than coil nr2 temp.
- Finally the floor surface temp will be noticeably lower than the loops average water temp, this is mainly because you spread the heat from a small diameter pipe out on a larger surface. Pipe diameter and pipe c/c are central here.

Jostein

Hiya

FYI the underfloor heating in our house is set to be about 37 deg C when it enters the floor system. The floor is about 100mm concrete screed with 15mm oak on top in most areas, tiles in the kitchen. The tiles let much more heat through and feel nice and warm, but for both areas that construction build up spreads the heat nicely. The floor water pipe c/c was specified for a specific screed and wood finish thickness. Upstairs with carpet has different centres, and ally trays designed to hold the pipes, reflect upwards and spread heat.

You can get a domestic thermostatic radiator valve with the thermostat on the end of an approx 500mm long wire. Supposed to be for house radiators built behind decorative covers, but you still want them to be working on room temps. Maybe you could use those under the floor to control your underfloor water circuit?

I thought of doing the same as you in our new camper, but currently I think having a separate system with a mains powered engine block heater with pipes under the beds and the seating only. So occasional use but if it ends up running too hot they can just be turned on when those areas are not in use, or to regularly air them out. Part of that is I don't want to raise the floor and reduce head room though. Blown air and a few passive radiators from the diesel heater will be the main sources of heat.

Where the heater pipes in our last camper ran from the heater at the front to the calorifier at the back, the pipes ran in a false floor void about 75mm deep at the minimum so plenty of air around those pipes but still really warm on bare feet. Once the calorifier is up to temp then everything gets and stays quite hot. So in summer you need to isolate the floor, and in winter if you want camper heating you may want to isolate the calorifier?

 

[jostein]

No, the underfloor heating will not work if the calorifer is under about 40 degrees. I have a 9kW diesel heater, so with a large enough coil this should not take long to get a 20-40 liter calorifier up to temp, that is at least my thought.. Since ths loop has its own pump, floor heating can be switched of separately.

I do also have hydronic heating {in concrete) in my house, running temperatures between 33 and 38 degrees.
As mentioned there are products and concepts that can be used as they are, or used as inspiration from domestic heating systems.

Keeping height down was a priority for me as well, the solution I ended up with uses 10,5mm pipes layed directly in the sandwich core material, so in height it does not built more than the pipe diameter.

 

[Anton2k3]

Yea we are using 10mm copper piping too. I think I'm going to run direct from the hydronic, but run everything in parallel. I'll have a valve to 'balance' the under floor heating part to get it to roughly the right temp. There will be a 12v bypass linked to a temperature switch (installed in the floor) to maintain the correct temperature. The balancing will just mean the bypass valve doesn't work as hard.

 

[grizzlyj]

Snipped

Keeping height down was a priority for me as well, the solution I ended up with uses 10,5mm pipes layed directly in the sandwich core material, so in height it does not built more than the pipe diameter.

That is a nice idea Will you incorporate any sort of metal plate in contact with the warm pipes to spread the warmth over the whole floor? Have you decided what material to use as the final floor covering?