Unimogadventures - Our build and travel thread

[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.

 

[dzzz]

The engine loop may be a bit tricky to do right without a manifold. It's the engine water pump that will do the work of moving the water and I can't quite see that in my head. Usually the calorifier is always in the circuit with the weabsto. That circuit is extended with three-way valve(s), but there is still a single path. A manifold would allow multiple paths, but usually that would be done with a pump for each path. An ideal one pump system will only allow one path for the water. If a "T" connection needs to be used you may want gate valves on the supply side to correct potential flow imbalance. Since a boiler system is a heat transfer device flow control is more precise than a domestic water system.

I did find a minimum coolant volume in the tsl-17 manual (12 liters).

I do think you will benefit from having multiple ways of controlling camper temp until you can decide what works best. Personally I would prefer to design in that control now rather than trying to figure it out while traveling. The logic side of these boilers isn't ideal for central heating and the work-arounds need to be discovered for the system to work as desired. For example, I would like to know the work-around for the two hour on timer limited.

 

[charlieaarons]

Iain, it's just a matter of ordering the RV heater model, which has no 2hr,limit built in.
My input on sizing is that if the unit is going to preheat motor/truck cab and cabin you want 9kw. if just cabin (living space)
5kw. This is how Unicat does it.

Charlie

 

[Iain_U1250]

Just to clear things up - in my shed is a Webasto 90ST, a 20lt hot water tank and two Kalori Silencio 2 heaters.

I now have to figure out the plumbing to do what I need it to do.

TO start from scratch I need the following:

Summer Mode:
Driving
Engine cooling system to provide heat to the hot water tank.
Heater circuit to be isolated

Parked
90ST to provide engine pre-heat (nice to have)

Winter (Australia) mode

Driving
Engine cooling system to provide heat to the hot water tank.
Engine cooling system to provide heat to the camper via the 2 x heaters

Parked
90ST to provide night time heating to cabin
90ST to provide heat to hot water tank
90ST to provide engine preheat.

Nepal/Siberia/Finland/Alaska Mode ( Assume -15 Degrees C)

Driving
Engine cooling system to provide heat to the hot water tank.
Engine cooling system to provide heat to the camper via the 2 x heaters
Extra heating to both camper and truck cab if required

Parked
90ST to provide night time heating to cabin
90ST to provide heat to hot water tank
90ST to provide engine preheat.


To complicate matter, I am also running a water cooled turbo - so the truck cab heater circuit has a small bypass loop through the turbo. Main heater pipe is 19mm hose, the bypass is 12mm hose through the turbo. I do have an auxiliary Davies Craig electric water pump that I can fit to increase flow around any system whilst driving if necessary, but it draws a bit to much power for overnight use.

Thanks again for all the input.

 

[dzzz]

The boat diagram above does all that by replacing the flat plate heat exchanger at the engine with a three way valve.

-The main always open loop is webasto and calorifier.
-One three way valve extends the loop to the heating circuit
-One three way valve (Or a "T" and a valve) extends the loop to the engine

Three pole switch selects either:
1) On/Off Switch to webasto is selected for hot water or engine heat. Webasto keeps water temp at 160F
2) Off camper heat while driving without webasto assist. Webasto never runs
3) Thermostat to webasto is selected when using camper heat. Webasto turns on and and off by cabin thermostat.

Normal cold weather use is simply operating the engine valve when changing from camping to driving and setting the three pole switch in the camper.

A second thermostat can be used to control camper fans. Or a single thermostat could be switchable between webasto and fan.

It gets a little simpler when you realize each circuit needs only one valve to stop flow.

A system where each zone calls for heat is easy to design with the Sure Marine wiring board. Your fan control schema wouldn't work with that approach, however. The fans would need water supply thermostats that start the when hot water appears in that part of the system.

FusoFG build:
http://www.expeditionportal.com/forum/showpost.php?p=142161&postcount=8

 

[dzzz]

I did a bit more research and with webasto the timer is in the switch, not the unit. So that's good. The concern I had about the thermostat "timing out" was unfounded.

I've talked to several marines suppliers who are more expert and accessible than truck installers or webasto/espar tech support (in the U.S.). The Seattle marine suppliers I've talked to have done campers/RV too.

There seem to be two key differences between these marine systems and the truck kits that are advertised. First, marine installers order the pump, boiler and fuel pump as separate components. Primarily to use specific pump sizes, but also to space the components from the hot boiler portion. Secondly installers use custom electronic boards, primarily for multiple thermostat and pump control. (I intend to avoid the board)

Boat Electric makes a board for Espar, I've mentioned the frequently used Surewire board from Sure Marine.

The most common units for RV hydronic would be the Webasto TSL-17, and the Espar D 4/5. Both makers sell both kits or separates. It seems very unlikely the boiler unit or electronics vary by market. The pricing varies 3-4X by market (in the U.S.).

I expect what happens when using the more common truck kits of both brands for camper heat is that the pump is too small for the burner to run on high for extended periods. So the full capacity of the boiler may be unusable. But I also expect the camper heats fine and the high/low cycling of the system is unnoticed or assumed to be a normal.

The downsides beside lack of max heat is that component life is probably reduced and possibly a dirtier burner.

Brand comparison:
The upside of the webasto tsl-17 truck kit is that the water pump is easily replaced. Buying the truck kit and replacing the stock pump with a 6 gallon Johnson pump gives a price of 50% or better of a marine supplier. A muffler needs to be added. Sure Marine sells a large muffler that's 1/2 the cost of the webasto unit. Due to size it may be more effective than the standard webasto unit.

The upside of the Espar D4/5 is that there is a high altitude kit that can be added to the unit. Webasto does excellent high altitude in their air heaters, but not the hydronic units.

Anyway, much of this isn't specific to Iain's build but I thought this was a good place to put what I've found so far. I need to decide if I should buy another webasto or the D5. I don't have a clear choice due to altitude considerations.

 

[dwh]

I expect what happens when using the more common truck kits of both brands for camper heat is that the pump is too small for the burner to run on high for extended periods. So the full capacity of the boiler may be unusable. But I also expect the camper heats fine and the high/low cycling of the system is unnoticed or assumed to be a normal.

The downsides beside lack of max heat is that component life is probably reduced and possibly a dirtier burner.

It seems to me, that what you just described is more or less the behavior of a unit that is setup for high altitude. Some installations have two pumps, with one being a lower capacity for higher altitude. Erik Badger modded his stove by making the pump strokes per minute adjustable, so he can slow down the pump at higher altitudes.

On a unit with a factory switch for high altitude operation, what does that switch do? Slow down the pump, no?


On the subject, I recalled that Stephen Stewart had mentioned somewhere on his site that he'd had some problems with his Hydronic. I can't find exactly what the problem was, but this page mentions replacing the ignitor plug every six months and carrying a spare:

http://www.xor.org.uk/unimog/mymog/heating.htm

 

[mog]

On a unit with a factory switch for high altitude operation, what does that switch do? Slow down the pump, no?

It is basically a barometric controlled potentiometer.

From the Espar HIGH ALTITUDE COMPENSATOR 20 2900 70 00 06 manual

The Altitude Compensator is an electronic altitude sensing
device intended for fuel-rate altitude compensation of vehicle
cabin heater units. It is designed to be powered from a vehicle’s
12VDC or 24VDC electrical system, installed in-line
between the heater controller’s fuel-pump drive output and the
fuel pump. Ambient atmospheric pressure and the heater
controller’s fuel pump drive output are continuously monitored,
and the vehicle’s approximate altitude above sealevel
is calculated and updated every 5 seconds based on a linear
pressure-versus-altitude algorithm.
The module’s fuel pump drive output is then adjusted to provide
a corresponding fuel rate that optimizes fuel combustion
efficiency and minimizes exhaust emissions.

If you would like a copy of the manual (10 pages), PM or email me.

 

[dzzz]

Webasto air heaters do it the right way by increasing combustion air fan speed at altitude (stock feature in newest design)

Espar hydronic decreases fuel pump pulses with the optional kit mentioned. Before that option was created it was the two pump system controlled by a switch. Significant loss of BTU.

Webasto hydronic doesn't have an option, AFAIK. Someone mentioned partially blocking the exhaust (?) pipe at altitude. Increased back pressure?

It seems to me, that what you just described is more or less the behavior of a unit that is setup for high altitude. ....

The result may be the same, but the reason is very different. I was just talking about water flow being inadequate to remove the heat of normal full combustion.

The problem at altitude is too rich a mixture. All the units can be set up for high altitude, but then they are too lean near sea level.

............

If you would like a copy of the manual (10 pages), PM or email me.

Thanks, I was able to read the manual online. I was disappointed at the complicated wiring.