Water Heater - the tank only

[Chorky]

Thank you all for so much great information! For some reason this portion really has been confusing me more than other options as I continue my build. For reference, I am putting all this together on a '97 F350 diesel. The plan (as loosely described in post #1) is to have a water system integrated with a custom bed so fresh (including hot), purified and filtered water is always at the ready on the truck with a draw feature from various water sources (or a fill from a standard garden hose, or city water hook-up) to be used with either a camper or in work situations.

So to summarize the discussion so far:
There are really two ways to go about (diesel) hot water systems.
1) A isolated system where the diesel heater would run hot coolant thus heating cold water plumbed from the tank. This would also require a second tank specifically for the cooling system (even if its only a small amount) to allow for coolant expansion when hot.
2) instead of a isolated heat system, plumb the system in with the engines coolant. This would allow for engine pre-heat, water heat from engine heat, would remove the need for a water heat system specific coolant tank at the cost of a more complex system that is tied to the engine.
3)Regardless, for either system, a heat exchanger of some sort, such as a calorifier, is required. So the system is in fact more complex than a normal RV style water heater because coolant is necessary for prolonged life of the diesel heater as two fluids (water and coolant) are needed.

The benefits of:
1)the system is isolated and does not require messing with the engines coolant system, which could cause a headache, would allow for easier bed transfer to a different vehicle if necessary, allows for future changes to hook up to the engine if desired, does not put extra strain on the engine coolant pump as coolant runs would be long to the bed
2) engine pre-heat would be very nice in very cold northern climates, allows for hot water when engine is running and reduces amount of run time for water heater unit, thus lowering total fuel consumption

Some notes regarding:
1) Seems to be the simplest system, but does not take advantage of all possibilities
2) I suppose this would warrant some isolation (shutoff) valves at the engine heater core and at the diesel heater, or where ever the 'tie-in' portions are so that if damage to the lines under the truck occurs, the engine at least will be operational at the expense of no hot water. This certainly seems to me to complicate things when a simple system is desired, and is the purpose of desiring a diesel system in the first place, especially since I can't seem to find any info discussing the direction of coolant flow of my engine. A standard propane system would be more simple it seems, at the cost of a secondary system that is not as fuel efficient and is highly volatile. In super cold temps, having extending engine coolant hoses below the vehicle may further reduce the engine's ability to operate at a proper temperature even if insulated?? Maybe instead of flexible and vulnerable coolant hoses, one could source out aluminum tubes, and fabricate a skid plate?

To pull over some conversations that have occurred in the following thread (which was supposed to be about electrical requirements, but turned into diesel coolant discussions:
https://www.expeditionportal.com/fo...g-battery-needs-for-uses.202021/#post-2580488
1) plumbing the water heater system into the engine would also reduce total ah required of batteries (in theory) as water would be hot by the time a campsite was reached. However, in reality, the diesel water heater could be ran while in motion, thus the real savings is in diesel fuel, not electrical power.

So some more questions for you all:
1) anyone willing to show just a couple of pictures of your heat exchangers and diesel systems please?
2) if I did decide to plumb into the engine system, what would be the best way to run coolant under the cab (it's a crew cab), across the frame to the passenger side, and back up into the bed - this seems like a long run to me. I suppose I could put the heater on the passenger side; however, that is where the electrical dist. box and batteries are planned to be and I didn't like the idea of having water and electrical in the same area. If I put the electrical on the drivers side then I would have a long wire run from the alternator. So I'm not sure which compromise is the better one.... THis is of course assuming the tank and diesel heater 'system' would take up an entire side box which is the purpose for #1 above, as I dont' know the dimensions of what a 'system' would be.
3) do you not think that having this much extra of a coolant system run would cause extra strain on the vehicle's coolant pump?? What about trying to pump coolant through the entire engine with the diesel heater's pump. I guess I'm unsure of how much 'strain' they stand up to and where the failure point is of this topic. Also, having the water heater hooked up to the engine coolant as well would make for a longer water heater warm-up time as the entire engine coolant would have to be heated instead of a significantly smaller amount that is also not loosing heat from a huge iron diesel block. - thoughts on this?
4) how much space is actually needed for a diesel heater with a heat exchanger? I'm hoping all this could in fact fit in a standard side box of a flatbed.
5) If the diesel heater was inside one of these boxes, fully enclosed, of course with an exhaust and fresh air inlet port for combustion, how much residual heat is given off from the heater itself? In other words, if I had in this same compartment, the actual water pump, water draw pump and various filters, would the residual heat from the operation of the heater keep temps above freezing to protect other water components, or will I be looking at needing to use a 12v heat pad or something
6) I think I would probably not use a mixing valve. For one it's just another connection point that could leak or get damaged, and second, I think proper mixing could happen at the faucet just fine. I would hope appliances could handle 180 degree water anyway... I probably should check on that. It would also be nice to have the option for super hot water if I needed it for washing something that is not my skin. Thoughts on this?

I know, lots of questions..... But I really want to do this right the first time.

Thank's again for all the great info. I think this is turning into some excellent discussion

 

[grizzlyj]

Maybe more relevant stuff here https://www.expeditionportal.com/forum/threads/mb-1120-coming-to-america.190398/
So if you isolated the camper and engine coolant circuit with a heat plate exchanger between then the pumps aren't doing much more than they're supposed to, and isolating them for disconnecting might be easier? There probably isn't a max pipe run that any pump will be ok at, because fittings curves pipe material and size etc etc will all add up to how the fluid behaves. That's also partly why I went with rubbery coolant hose to get smooth curves everywhere with less fittings, and where I have used rigid pipe it will end up looking messy because I'd rather radius a pipe than put a 90 degree bend in. One spur zigzags under the bed in 16mm but might end up being about 10m long, fingers crossed I will get heat down it but maybe I'll have to squeeze down the flow from the other spurs to force it there. We'll see.

The loom on my heater came at about 5.5m long between it and the power source. The fuel pump has to be quite close to the tank but then you can again have maybe 5m of fuel line. Pick a heater and look up the installation guide for the limits on runs for it's feeds. Fuel pump to heater should be one pipe no breaks. Marine kits can come with copper fuel pipe which perhaps lend itself to 12v electrical heat to prevent waxing in the 1mm diameter pipe depending on how much cold you're expecting. I don't know how "winter" diesel behaves differently in such a small pipe?

Also, how long will you be stopped for? Residual engine heat works for 24 hours maybe for water in the insulated calorifier, and maybe an hour in the heater mounting box after switching it off, maybe less. The Surecal website has dimensions on all the models they do. Having water without antifreeze in outside is surely asking for it to freeze if that's what you're suggesting by everything in one box?
Fuel consumption of a diesel heater is I think so small you might as well ignore it, unless you give it it's own tank in the camper. But then you could in the UK at least run it on agricultural type diesel with minimal tax, although then you'd need to keep filling it of course.
Bugs in water get killed at something like 62 degrees C so above that is waste for that purpose. If we didn't have a little one on board then perhaps I wouldn't have chosen a blending type valve, but I didn't choose it as it came on top of the calorifier anyway. I can imagine that if the water in the hot pipe is blended at source to say 45deg then there's less heat to lose on the way to the tap compared to unblended max hot all the way to the tap. You wouldn't notice if you didn't trial before and after though.

Having a header tank in your camper might be needed anyway (with just one circuit for heating) if the high point in the camper is above the filling point under the hood? Unless you park on a slope to fill But it will need a way to get and then keep air out at all high points too.
Lots of variables, YMMV etc

 

[dwh]

Factory rear air/heat in vans is usually just a bundle of added coolant and freon hoses run to the rear to a box with a second heater core, second evaporator, and second blower fan.

No, it doesn't overstress the engine water pump or the a/c compressor.

The normal failure mode for those things is freon loss because the extra lines are usually connected with hose clamps instead of the threaded fittings used on the freon lines under the hood.

 

[Neil]

You wouldnt want to put the header tank on the cabin . They are noisy and smell as they are vented

The Eberspacher M10 uses over 1 litre pf fuel per hour on full power. Thats about £1.29 in the UK.

Much more at altitude.

This is an expensive way of heating water. You might want to bear this in mind when calculating the size of the hot water tank.

Heating extra un needed litres will cost extra money .

My tank is only 15 litres and its on full power for about 10 mins then drops to a lower power for the next 10.

So it would stand to reason that a 45 litre tank would probably be on full power for 30 mins. And then drop down for another 30 to get the water to full temp.

I gues this would use maybe 2/3 to 3 quarters of a litre for every tank of hot water.

This cost will soon add up.

I rarely use the eberspacher to heat water, prefering electricity ( solar ) or engine heat

Neil

 

[Chorky]

on my heater came at about 5.5m long between it and the power source. The fuel pump has to be quite close to the tank but then you can again have maybe 5m of fuel line. Pick a heater and look up the installation guide for the limits on runs for it's feeds. Fuel pump to heater should be one pipe no breaks. Marine kits can come with copper fuel pipe which perhaps lend itself to 12v electrical heat to prevent waxing in the 1mm diameter pipe depending on how much cold you're expecting. I don't know how "winter" diesel behaves differently in such a

This is a good point and something worth considering. I think the planned location would put a fuel line run about 10' to account for a few turns and bends. Winter temps can usually hover in the teens I think, but can easily dip below -30F. Winter blend I'm sure (moving, and haven't spent a winter there yet) is a normal occurrence, but how it would work in such a small pipe would be interesting. Maybe some testing with a 'cheap' diesel heater is in order before doing a fully functioning system.

You wouldnt want to put the header tank on the cabin . They are noisy and smell as they are vented

The Eberspacher M10 uses over 1 litre pf fuel per hour on full power. Thats about £1.29 in the UK.

Much more at altitude.

This is an expensive way of heating water. You might want to bear this in mind when calculating the size of the hot water tank.

Heating extra un needed litres will cost extra money .

My tank is only 15 litres and its on full power for about 10 mins then drops to a lower power for the next 10.

So it would stand to reason that a 45 litre tank would probably be on full power for 30 mins. And then drop down for another 30 to get the water to full temp.

I gues this would use maybe 2/3 to 3 quarters of a litre for every tank of hot water.

This cost will soon add up.

I rarely use the eberspacher to heat water, prefering electricity ( solar ) or engine heat

Neil

1 L/hour seems more than I remember reading, but I don't think I looked up the specs for the M10. That's about $0.825 for me. As I am now, in a normal travel trailer, in winter, I usually go through 20-30 gallons of propane a month which averages to about $65 depending on the price of propane at the time. But consider that this is for use when I am home, as I currently live in a temperate climate that rarely goes below freezing and can turn appliances off during the day when gone. Also considering this includes use of electric elements for hot water tank and an electric space heater. If I had a full winter below freezing (which will be the case next year) I'm sure propane use would more than triple to as appliances would be left on to prevent things from freezing, and shore power may not be available. I would probably figure that a 5 gallon hot water tank would certainly be sufficient, to account for the shock of near freezing water hitting the system. So that would be a 18 liter tank or so. It would be nice if I had recorded (and I should do this next month) the actual usage rate per hour of propane for my trailer's water heater and furnace. From previous research I have done, diesel systems are more than double as efficient as propane systems. So considering diesel now is about 3.30/gal, and propane is, well an average of 2.30/gal, and all the other factors of possibly no electrical availability, full time running during winter, and significantly colder overall temps, I think a diesel system next year in colder climates would have a potential cost similar to that of what I currently use in propane of a temperate above freezing climate. But some better calculations would be necessary to be sure. Also considering too though that this would be fore a well insulated truck camper type deal rather than a travel trailer.


So in terms of the debate between hooking the system to the vehicle or not, possibly a simple way to deal with this is to add some t-fittings with valves on the engine's heater core side as well as the diesel water tank side. This way lines would be relatively easily plumbed and/or just turned off if not desired. This seems to be the better way to go about it as I am interested in the engine pre-heat possibility but just unsure if desiring to have such long coolant hose runs. This would provide the flexibility to do either, and also provide for a way to close the circuit off if a leak did occur.

Is there any reason why the diesel heater cannot be physically lower than the rest of the engine's cooling system? I'm assuming the physical elevation of the heater in relation to other components does not really matter (except for the fuel tank)

 

[Neil]

My heater is well below the engine under my chassis. No problems. Obviously the header tank needs to be higher than the highest radiator.

However, my engine coolant and heater coolant are not directly connected. I use a small plate heat exchanger .

Neil

 

[grizzlyj]

Previously we had a D5WS 5KW Eber which was quite noisy, it had either half or full power, it decides which to use, and when to shut down, based on the water temperature. It did only have a basic silencer though.
Neil suggested during his build to use a bigger heater because, as you can see in the attached, they can cycle down to a 1.5KW setting, if they can stay at that then you remove the on off cycling we had, and hopefully less noise.
I'm told that the only difference between an M8, 10 and 12 is the ecu, so all parts are interchangable. Put an M8 ecu on an M10 and it behaves like an M8.
Our first camper didn't have a header tank or any way of extracting air other than when it was connected to the engine circuit. So filling it and bleeding had to be done by cracking joints and chasing the bubbles. This was a pain but not impossible, but I'm hoping this time a header tank plus a few bleed points will just make it work better.

 

[Neil]

Once it settles down ( M10) its pretty quiet.

I addedd all the eberspacher elbows with built in bleeds and I need to use them during filling. Not all the air gets pushed out into the header immediately but i thing after a bit of use it would eventually work its way out.

One bit of advice given to me by a senior Eberspacher engineer advised me on the install and came to see my truck during the fitting was under no circumstances feel tempted to test the system with clean water. You must always add a diluted solution of antifreeze even when testing . Even if you end up draining it out and losing it.

The reason being was that the antifreeze also acts a a lubricant for the pump.

Just a few minutes of running with just clean water can damage the points on the needle spindle of the pump and can result in a noisy even screaming pump for ever.

Neil

 

[TDIVan]

Hey folks,
My first post. I've been reading for the past year, thought I'd weigh in, and get feedback as I am currently in a new heater/pre-heater/hot water build. I'll attach my schematic for opinions/discussion. The center of the build is an Eberspacher D5WS heater with a 15l Nautic Boiler. Whether on-grid or off, whether hanging, or running, I want hot water and heat at any altitude. I also want to be able to fill up the little-kids pool with near-unlimited warm water from the lake/river. I was also planning on trying the PEX piping, and placing the Eber as far from sleeping location as possible and sound insulated to I'm also planning to use the 15l of water as thermal mass to hopefully minimize cycling. thoughts?
Oh, and Neil, I've followed your builds and discussions (Cloud9), great seeing you here.


thanks,
Delane

 

[offroadkiwi]

You? Wrote
["Which raises to question, why a diesel heater cannot just heat the water directly. Everything I have seen shows diesel heaters being used in conjunction with coolant of some sort specifically, and not just water directly].

[I'm not sure what a plate exchanger is, so I'll have to google that one. Is it no different than a heat exchanger, but just in a different way"]



I'm not sure if this thread is still going, I'm a first-time poster on here, and in editing out the bits I didn't want to respond to, I accidentally edited out your name, sorry...
I am currently ALSO considering heating the water directly with a 5 kw diesel hydronic heater, and will comment on what appear to be the limitations, but first your second statement... a plate exchanger.... has usually 4 connections and allows a primary circuit (usually with food-grade glycol added, a low-pressure circuit; ordinary anti-freeze used in cars is VERY toxic, do not use in case you get contamination). The heat transfers across (usually copper plates) to a second loop which has your shower water in it and ne'r the twain shall meet. It's only doing what a wet-back loop does (but much more efficiently)

That leads me to your first comment...There are some obstacles to heating the actual shower water directly through your diesel hydronic heater, and understanding these, means that it COULD be feasible...(I like the KISS principle (keep it simple stupid). The following appear to be the limitations, or problems to overcome...
The first is the maximum pressure. capability of the heater..
Most hydronic heaters are limited to a pressure under about 39 psi. Water expands as it heats so if heating the actual shower water directly, that means the tank pressure needs to stay lower than that.
Therefore, if a pressurised system, the pressure relief needs to be reliable and accurate (like a higher pressure radiator cap or a precise adjustable pressure hot water relief valve?).
It also means that if your cold delivery is a pressure pump (ie not gravity) that cold water delivery pressure needs to be about 10 psi lower than that, or it will blow the water out the relief valve till your cold tank is empty.
These things are able to be worked around IMO.

The second problem is more difficult, electrolysis.
Being a boaty, and having had a diesel motor get electrolysis, I've had a bit to do with electrolysis, and there are several ways to minimise or prevent it.

1) Inhibitor in the water. Obviously not an option if heating the actual shower water.

2) Keeping the metals used in the tank, the same as the metal in the heater. ie both aluminum? (should be fine)
(That's because the further apart in nobility, the greater the potential to become a battery, where the least noble of the two will get eaten). (You can google nobility charts of metals)

3) Using sacrificial annodes that are less noble (such is anodes on a boat or boat motor) These will get eaten instead of your tank and heater. Zinc or magnesium are both less noble than aluminum.
Options 2 & 3 could be used together. Or you could use a high temp plastic water vessel with an anode
There is concern that drinking water kept in aluminum may cause Alzheimer's, so that is an issue. Obviously, you would drink only water from the cold tap, but no-one knows what exposure one would have from shower water absorption of aluminum?

There are cheaper Hydronic units from Russia and China appearing on the market so if you got 10 years out of it, it could be viable!
I would love to hear from anybody that has direct heated the primary water like this with a hydronic heater?