Unimog Camper under construction

[bajajoaquin]

Iain, this is a great build. Thank you for all the time spent documenting it!

I just skimmed through, and I didn't see any dimensions on the box and living space. Did I miss it, or do could you post some up?

[Iain_U1250]

The box is a funny shape, but in summary, on the inside, taking into account the thickness of the lining, floor etc, it is 2.1m wide, 3.5m long at it's 1.95m high in the middle

[Iain_U1250]

I have finally made the decision on our heating / hot water system.

After discussion with Charlie (from Alaska) I've gone with a Webasto 9kw T90 diesel furnace and two 4kw Kalori Silencio II heaters elements. I have had a lot of discussions with the Webasto technical people about block heater and the hot water system as well. That should be able to keep us warm in the colder climates. We have also gone for a 20lt hot water tank - more than enough for a hot shower.

Here is a basic schematic of the system.

Water system.pdf

I will either use the electric solenoid valves as shown, or ball valves. I will also add some more solenoids or ball valves to the inlets of the cab heater system to stop the flow through the them when in hot climates.

I've also bought our diesel cook top - the Webasto X100.

WEBASTO-COM-AU_Caravan_CookTop_16x9_445x250__rdax_445x250.jpg

[dzzz]

-You probably want 8-9 gallons of water capacity with that heater to keep the unit from short cycling. 7 gallons is the magic number for the smaller webasto tsl-17

- the hot water tank probably has smaller pipes in the heat exchanger than your heater hose. A gate valve across the front allows some water to bypass, eliminating back pressure.

- a three way valve allows taking the heaters out of the circuit in the summer.

- the pump should be about 6 gal/minute. The kits designed for engine pre-heat will have too small of a pump. A marine supplier will likely have a kit with a bigger water pump.

- the way FusoFG set up his system is a thermostat for winter, and an on/off for summer. With on/off the unit will run for up to 120 minutes (user setable) or until water reaches 160-170F. Much simpler flipping a switch once or twice a week rather than a water thermostat/solenoid valve setup.

I think the 5kw unit may be fine for your needs, unless you plan to do a lot of winter engine pre-heat from a cold camper system. But I assume most of us building these trucks are not designing for sub 0F temps.

Too big of a boiler is not desirable, but I'm no expert of sizing. I have the 9kw unit on my truck engine, but will definitely put nothing larger than the 5kw in the camper.

There's really no need for two units on a camper. I just don't want to mess with my factory engine unit to heat the camper. In the U.S. the tsl-17 kit can be purchased for about $850.

Sure Marine Services in Seattle are excellent sources of information and parts for hydronic heat.

[Iain_U1250]

Hi Don, thanks of the info. The 20lt hot water tank is more than sufficient for our needs. I'm not sure what you mean about short cycling - it that is the diesel furnace will be stopping and starting then having a larger hot water tank will make little difference since it is pretty well insulated and I doubt we will even use the furnace in summer, relying on the insulation to keep it warm enough over night. In winter, especially on our round the world trip, the heater will be going, so not much chance of a short cycle.

I will be plumbing the system so that whilst driving, the engine will provide the heat for the hot water tank and if necessary, the rear camper heaters. When parked up, the diesel furnace will provide the heat for both hot water tank and the heaters. To stop the engine freezing up, and to provide a warm start up, I will open up the valves and allow the water to flow through the block - this might just be on a timer or thermostat. The engine cooling system also acts as the buffer tank, allowing for expansion and bleeding etc.

Regarding the amount of heat needed in the camper, I did all the calculations for heat loss based on my insulation, the large amount of windows I have compared to most campers and taking a -15 degree outside temp found I needed around 5Kw of heat to keep the inside at 22 degrees. A single 4kw heater will mean I have to run the fans flat out, whilst having two rigged to a thermostat means I can have them on half speed most of the time which is virtually silent, and then once up to temperature, the fans will switch off and allow the natural convection to keep the place warm. I think It's better to have a bit more heat so that the furnace is cycling in and out, rather than going flat out all the time. The extra 4kw from the 90ST means it is be able to keep the block warm as well, allowing for better cold starts. I can also heat up the auxiliary tank for the furnace /cooktop fuel as well.

After much discussion with Webasto, it was a choice between the 5kw and 9kw units - I went with what I have, time will tell whether I am right, but when we get to Siberia, Finland or Alaska, I think I will be happy to have a bit of extra heat. I got the whole system and the stove for a reasonable price direct from Webasto as we are classified as "Manufacturers"

[dzzz]

I forgot your engine connection, but there is still a minimum amount of coolant that needs to circulate in the boiler circuit when the valve to the truck radiator is closed. This is largely independent of calcifier capacity. Coolant heaters are designed for very low back pressure and circulating a lot of fluid surrounded by cold steel. That environment needs to be recreated for a camper system to work well over time , which I'm sure Charlies systems does.

With a small amount of coolant the temp rises too fast and the webasto shuts down (short cycles). You only have a liter or so circulating when the valve to the truck engine is closed.

I'm also concerned about the check valve you show in the return line to the engine. Fluid will need to move in both directions (towards the camper heater when the webasto cools, towards the engine as the webasto heats). Flow in both directions eliminates the need for an expansion tank.

Your heat exhangers will put out the same heat on low with either the 5kw or the 9kw webastos. The 9kw unit will cycle the burner more often. Probably not a big problem, but not ideal. You will, of course, be able to warm up a very cold camper faster with the bigger unit.

Your system does temp. control by fans, which seems to mimic the unicat system of radiator valves. But that has potential to overheat your camper in typical travel-type heating situations. Your system, as I understand it, has a minimum continuous heat output of a couple thousand BTUs . You may notl find that acceptable. You may find yourself having to turn the system on and off manually due to being too warm. The more engineered unicat system have temp control by mechanical valves that cut of fluid. Your heat exhanger will remain in the circuit even with the fans off. Which is meaningfully different than the unicat design.

Do you intend to run the webasto pump continuously when heating is switched on and the truck off? Do you know how to wire this sysem to overcome the 120 minute max timer in the webasto controller? (If you do, I would like to know this) Do you have battery capacity to run the pump and the fans? The elegant unicat system doesn't have to run fans.

The more common solution is to have the thermostat cycle the webasto directly instead of the fans. The fans turn on when water temp reaches 100F (integrated temp sensor on heat exhanger). The fans still have high/low or high/low/off switches.

I'm certain unicat addresses everything I've mentioned, plus adds a lot on implementation experience and possibly some custom electronics. Personally I wouldn't try to partially implement that system without radiator thermostats and experimentation in different thermal conditions. A simple system with only three mechanical valves eliminates the overheating problem and does not require detailed engineering calculations or experience. Many thousands of heating systems have been based on Sure Marine's designs. (However their wiring box provides little benefit to a single zone system using a webasto truck kit, IMO).

Here's an Sure Marine diagram (no copywrite). With a direct engine connection no expansion tank is necessary. Coolant first flows through the heat exchangers, then the water heater. Fans turn on when they sense warm water. Webast turns on/off by thermostat.

[Iain_U1250]

Thanks Don - so if I understand correctly, I should add an additional thermostat to control the Webasto, to switch that on and off with cabin internal temperature, or alternatively, put in a couple of solenoids to take the heater out of circuit on the thermostat.

I agree that with the cabin heater out of the circuit, there is only a small volume for the furnace to heat up. Looking at the manual, it seems that the furnace operates in a variable mode - so that it puts out between 1.7kW - 7.6Kw normally, and only goes to 9.1Kw in "Booster mode"- I'll check up with the Webasto technical guys and ask about the one way valve as well. A simple solution is to put a "t" into one of the lines that connects up to the engine expansion tank or get rid of the one way valve.


The heaters draw 10w on full power, and around 4w on half power - so all up both heaters on will draw around 8w when controlled by the thermostat or 20w on full manual. The furnace draws 40-80W. I will have 200+A hour of house battery - I have added the furnace and fans into the calculations for current requirements for my solar power, so I should have enough provided I don't stop for more than a few days in overcast conditions.

[dwh]

http://www.ki7xh.com/campheat.htm

[Iain_U1250]

Thanks - that's quite a useful site

[MrBeast]

Ian, you can call me jealous! (I have always wanted a mog)

I am liking your build, you are doing some good work. I will be interested to see how it winds up.