Water Heater - the tank only

[Chorky]

Ok so question for you all. There undoubtedly is a lot of discussion on water heating types. Propane, diesel, solar bags, etc...

Though I am still trying to figure out needed battery bank size for a variety of things, and what this means in terms of battery size, type, recharge rate, etc....


A current plan has me installing a 30 gal water tank, 5-10gal water heater (heat exchange unit) with a diesel heater - in one of the boxes of a flatbed. This way fresh hot (and cold) water is at the ready regardless of a camper being present. Hey, sometimes when you're just cutting trees you still need a quick bath, or to wash off and clean that steelhead you just caught with the first home made fly!

Ok so, the question regards water tanks. There is a lot of discussion here about the diesel heaters, and the electrical side, but I have searched and find very little regarding tanks.

What sort of tank set-ups are out there, pros/cons, all things associated with them? There are different theories I notice. Some plumb into the vehicles coolant system. Some have a dedicated coolant box just for a heat exchanger for the water tank/interior heat, etc... I'm looking for some reading material on this since I really don't understand a good way to do a hot water tank, how it would hook up, what size it should be, or where to even source one quite honestly.

Looking forward to the communities input!

 

[grizzlyj]

Hiya
I have a diesel Espar hydronic heater running in part through a Surejust calorifier of 35 litres which is maybe a bit big, build not yet finished though. We wanted a vertical model because thy're supposed to keep heat in for longer, and it takes up less garage floorspace. It also has 1KW of electric heat if wanted, and two coils to allow engine and diesel heat independantly if wanted, but our diesel heater circuit goes through twice instead which is supposed to heat it more quickly than a single coil. I should have asked if a single coil is half a double, or are they the same area inside just with different connections.. The heat circuit should approach maybe 90 degrees C, the water out of the calorifier gets blended via an adjustable valve and they say if blended to 65 deg C you get 25% more water than the tank volume at that temp. I'll probably set it to more like 45 degrees C to prevent scalds.
You could also think about how much water you have available, so how much you'd use per "shower". How will that hot water get heated? With a powerful heater and a quick reheat after a shower of a calorifier that's been sized to produce just one shower, by the time a second person is ready to use the facilities the tank will be hot again.
If you want to use and store engine heat for hot shower water you'd need a bigger hot water volume, but that is dead weight, so we have 35kg of water we can't get at and maybe you'd need bigger still. We won't use engine heat, but an Espar isn't silent, so a maybe oversized hot water tank for us means the heater won't be burning for longer than one tanks worth of heat if that's all we need, so neighbouring campers hopefully won't mind.
I was also told by Espar to have a slightly bigger flow and return pipe size (22/26mm, we have 22) with smaller (we have 16mm) spurs Tee'd off to each use of that heat, each with an air valve and balancing tap. If you try to get the Espar water pump to push everything directly through the calorifer coil or fan heater matrix it will be too much of a restriction. The heater and header tank have 20mm connections, the fan heater 16mm, pipe diameter was partly decided by what fittings suitable for 120 degrees C were available between those fitting sizes required by circuit design. SoI found 22mm equal tee's and 22/16/22 to a suitable temerature. HEP20 push fit is supposed to be OK with a short length of copper inside, and the heater hose pushed over with double jubilee clips but that adds more length and potential leak points to each joint instead of just a one piece t.
If that kind of thing is what you're asking?!

 

[Chorky]

Woah, well that went right over my head haha. But yes this is what I was looking to hear. Thank you for the reply! I will be looking up Surejet to see what their options are all about. So did you just tell Espar what your desires were and did they make certain recommendations for those pipe sizes and also the calorifier size? Why would you blend hot water back into cold water? I would think this would just be done at the tap like a normal home faucet. Maybe I'm wrong? 35L sounds like a nice large tank! any ideas what your re-heat rate will be? I was considering something more like 20L (5 gal), since this will be for a flatbed dedicated water system that can be hooked up to a camper when loaded. I'm really struggling with the whole system though. How all the pieces work together. I get the diesel heater bit, that's easy. But where can one go to learn and find out how it is best to be hooked up for various situations or options? Or what kind of material to use, or coolant type (if that matters). I had considered plumbing into the vehicle's system, to help heat the engine when in sup zero temps, but that would require nearly 15' of extra coolant hose line under the truck....probably not a good idea.

 

[Neil]

There are many ways to do this and if it works for you its the right way.

Our system is pretty simple.

We have a 15 lt calorifier that is heated in several ways to about 85 degrees. This gives us about 40 to 45vlitres of useable hot water which is more than enough for two showers and a couple of washing ups each day.

The calorifier has one coil and onec220v 600w element

The 600 watt element takes about 30 mins to heat the tank and is powered via an inverter from our batteries. It takes about 2 to 3 hours forour solar system to replenish this . We use this method 99 % of the time.
( we are full time travelling ))

We like this method its free and clean.

The second method is heating via the coil using the 10kw Eberspacher. This is fastest method and takes about 10 to 12 mins to heat it up.

The last method is using tgecengine heat to heat the cabin wayer circuit via a heat exchanger. If the engine is hot it takes about 15 mins to heat to 80 degrees. We also like this method.

The bigger the tank the more energy or fuel you need. Our tank is small but there is only two of us.

It has worked faultlessly for 5 years and works for us, free most of the time

You can see more detail an our build blog

Neil

 

[luthj]

If you are using a coolant/hydronic heater, there are numerous options in the coolant heated field. Isotemp sells several (a bit pricey). They have a coolant loop and a electric element. They also have an external tempering valve, so you can heat the tank to 180F or so without worrying about scalding (more hot water for the same volume). There are numerous calorifiers in the euro and marine markets. Many propane or propane/electric heaters for the US RV market have a coolant heating loop. Not all are made equally though, as the heater loops size impacts heating rate, and heater cycle rate (on/off).

Another option that you can do instead of, or in addition to a hot water tank. A plate type heat exchanger can be installed after the water heater (but before the tempering valve), or by itself. This will allow of much faster hot water if your tank is cold. The downside if used on its own, is that a plate exchanger requires the coolant heater to be running. Note that you MUST have a tempering valve or anti-scald valve in the system. It is very easy to get the water tank up to 160F or higher, and this can readily scald/burn.

I would suggest considering connecting your vehicles coolant system your water heater. Properly executed, you will have hot water for many hours after a short drive (20-30 minutes). My 4 gal Isotemp with a bit of extra insulation will still provide hot water for about 20 hours after I heat it to 160F (in mild weather).

Heating form batteries is going to need lots of battery power, and a significant charging on the back end to support it. If you have access to 400-700W of power via an alternator, you can go that route. It will take an hour or more to get the tank up to temp that way, likely longer. This can be achieved with a small inverter powered by the vehicles electrical system (when driving). There are 12V/24V elements available that will fit most water heaters with screw in heating coils. Usually these are in the 300-600W range.

 

[Chorky]

There are many ways to do this and if it works for you its the right way.

Our system is pretty simple.....


Neil

Thank's for the input Neil. I will check out your blog. I like your thoughts. It does seem simple compared to other things I have seen - then again, maybe seeing the actual piping would then confuse me haha. I certainly plan to have a electronic side to the heater as well, but that will most likely only be used when I have access to shore power of some sort...whether at a work site, or campground, etc.. I won't have a battery bank large enough for that to use while stationary. Possibly while driving if I'm not needing that extra power to charge the batteries from a few nights of camping though. A good thought to consider.

So, I may be confused, but how is a calorifier different from a heat exchanger? are they not the same?

If you are using a coolant/hydronic heater, there are numerous options in the coolant heated field. Isotemp sells several (a bit pricey). They have a coolant loop and a electric element. They also have an external tempering valve, so you can heat the tank to 180F or so without worrying about scalding (more hot water for the same volume). There are numerous calorifiers in the euro and marine markets. Many propane or propane/electric heaters for the US RV market have a coolant heating loop. Not all are made equally though, as the heater loops size impacts heating rate, and heater cycle rate (on/off).

Another option that you can do instead of, or in addition to a hot water tank. A plate type heat exchanger can be installed after the water heater (but before the tempering valve), or by itself. This will allow of much faster hot water if your tank is cold. The downside if used on its own, is that a plate exchanger requires the coolant heater to be running. Note that you MUST have a tempering valve or anti-scald valve in the system. It is very easy to get the water tank up to 160F or higher, and this can readily scald/burn.

I would suggest considering connecting your vehicles coolant system your water heater. Properly executed, you will have hot water for many hours after a short drive (20-30 minutes). My 4 gal Isotemp with a bit of extra insulation will still provide hot water for about 20 hours after I heat it to 160F (in mild weather).

Heating form batteries is going to need lots of battery power, and a significant charging on the back end to support it. If you have access to 400-700W of power via an alternator, you can go that route. It will take an hour or more to get the tank up to temp that way, likely longer. This can be achieved with a small inverter powered by the vehicles electrical system (when driving). There are 12V/24V elements available that will fit most water heaters with screw in heating coils. Usually these are in the 300-600W range.

What do you mean by a heating loop (for the US RV market)? My trailer's tank is super simple (and most are). Cold water in the tank, hot water out of the tank, with an electrical element physically in the tank, and a heat plate for the propane burner outside and under the tank. That honestly seems like the simplest system.... I would think a diesel system could be just as simple - through some coils of a heat exchanger. 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?

Plumbing into the vehicle coolant was another option I initially thought of a while ago (as being currently discussed on another thread) but the issue with this is the physical length of coolant hose necessary to run under the vehicle, and for places I travel there is a good chance of damage to rubber hoses occurring - which of course would be bad.

 

[dwh]

A calorifier is one of many different types of heat exchanger.

The term calorifier is normally applied to a system where a fluid in some sort of storage tank is being heated by a coil in the tank through which another hot fluid is moving - such as steam in a big commercial building or engine coolant in a vehicular application.

There are several reasons why most vehicular diesel fired liquid heating units (called "hydronic" units, as opposed to diesel fired "air heaters") use calorifiers and do not heat the water directly...

One is corrosion and/or impurities. Pumping raw water through the heating coil of a hydronic won't be good for the hydronic over the long term as it will cause corrosion, and it would be difficult to clean out scale buildup inside the coil.

Another is that the hydronic is often plumbed into the engine cooling system, which enables things like engine/cab preheating.

Even when not plumbed into the engine cooling system, hydronics are commonly used not only to provide hot water, but also to provide cabin heat through liquid-air heat exchangers (a.k.a. "heater core" in a vehicle).

Thus the use of a hydronic to make hot water almost always includes a calorifier, though some use a liquid-liquid heat exchanger, called a "plate heat exchanger".

https://en.m.wikipedia.org/wiki/Plate_heat_exchanger

The disadvantages of a plate heat exchanger are normally the requirement for an additional pump as well as a hot water storage tank. There are already two pumps, one to circulate the hydronic fluid and one to pump water from the cold water tank.

IF you can get enough heat from a plate heat exchanger to heat water in "real time" on an "as needed" basis, then you can do away with the hot water storage tank and only need the two pumps. But if you can't get enough heat then you'll still need a hot water tank (and probably a calorifier unless you have the plate exchanger attached to the bottom of the tank) and now you'll have three circuits and three pumps.

(There are times when you would want to do it that way, such as combining the hydronic and engine cooling system but without actually plumbing them together. The engine already has the third pump on it anyway.)

Which brings up another reason raw water isn't just pumped through the hydronic coil on the way to the faucett...moving too fast, it probably won't get very hot.

The hydronic + calorifier/hot water tank + heater core setup is the normal way it's done a vehicular situation. This gives you hot water and cabin heat from the hydronic, and if desired, a way to use excess engine heat and/or provide engine/cab preheat.

And of course, an electric heating element can easily be added to the water tank if desired.

 

[grizzlyj]

Using water pipe that will stand the temperature created either by the engine or by a hydronic heater Espar type thing isn't the usual type of food grade water pipe used for tap connections in UK campers at least. More like vehicle engine coolant heater hose. The food grade stuff here may go pop at 80 deg C, so maybe that's also a reason to have a blender valve? Coolant hose at 85 degrees C, water hose at 60 or less.
Once you have a water tank at say 80 degrees and start using it (which is by the cold supply pushing in) that temperature will start to drop as it's blended in the tank anyway. If you blend it immediately as it comes out of the hot water tank down to a more usable tap temperature then maybe you get a more consistent hotness without tap adjustment?
You can get vehicle based units that give hot water directly, but the biggest current consumption on a diesel heater is the glow plug on start up. The more on and offs you have the higher the drain. These are usually for end of job hand washing for instance on a work van, I have seen one in a VW T5 sized campervan but it had a really low flow rate. Calorifiers seem to be what most do, I've used one for several years previously so didn't go looking for alternatives.
The attached sketch was supplied by an Espar dealer as an example that I could follow. No-one was interested in designing something like that for me and I wasn't asking, but they will if you pay them I'm sure! So how the header tank is plumbed in was particularly something I should follow but I don't know the reason it's like that.
You can also get a mains powered block coolant heater which could be about 1KW with a water pump included, I might put one in the camper heating circuit for when we're hooked up or the sun is shining.
Further reading could be ISBN 9781785210761 and/or ISBN 9783981855319 which both cover vehicles builds including sections on heating. You can download the second directly from Ulrich Dolde's website.

 

[Neil]

We used Hep20 pipe for everything. The tube with the membrane inside. We only used 15 and 22 mm teplicating a home circuit. The fittings have teeth and to date (5 years) i have bever had a leak. I contacted Hep20 who agreed its suitability for the project. They also confirmed that it was good for antifreeze.

We dont have a blending tank. Didnt even consider it. The kitchen basin has a manual monoblock domestic tap. The shower has a standard shower thermostatic domestic mixer that is good for low pressure. ( the system is max 3 bar ) . The washing machine has a simple thermostatic mixer.

I doubt we ever get above 85 degrees and its been fine.

I can recommend Hep20 as a useable brand as I said I have had no issues and its took some severe vibration on South American Ripio roads

The diagram that Grizzly shows is exactly how i installed ours.

However , ifci was doing it again i would not install the radiators as they are pointless and uneccesary in our truck.

I would simplify things even more with just a heater matrix in the livingcarea and one on the bathroom. These are the only things we use and have never hadcto have them on for more than 30 mins at a time. 2 kw matrix is all you need in a well insulated cabin. I now know you could heat it on less than 500w output.

Neil

 

[grizzlyj]

We have two fan matrices, one at each end, but mainly two so that we won't have to run either on high hopefully just from a noise point of view.
One will be turned on by the Eberspacher so can be timed, the other will just have a direct power feed so can be on when the Eberspacher is off which may be handy for just a cool breeze??
Neil, isn't the red twiddly knob at the bottom of your calorifier a blending valve to adjust the hot temperature you get out of the tap, so never the 80ish degrees the heater circuit produces in the tap run?
Eberspacher also told me HEP20 would be fine in the heater circuit, rather than John Guest at least although they are all supposed to be the same. As I said above, I think a HEP20 T takes up more room than just a simple push fit tee, and the car heater hose tees I ended up with were quite a bit cheaper too. Pic hopefully shows the HEP20 22mm equal t, 100mm of 22mm copper each side pushed fully home, an olive that I've nestled inside the heater hose when I can get it in, and then it would have a jubilee clip each side of the olive as the tap in the pic has. The much smaller black plastic t is also a 22mm equal t, so if you need a lot of connections in a small space HEP20 would need some creativity perhaps So the plastic t used with rubber hose adds about an inch to the pipe length, the HEP20 t adds maybe three using their own pipe or the rubber. I like the easy bendability of the rubber but the HEP t adds a fair length of unbending length with the copper inserts into a rubber pipe run.

 

[Joe917]

All our coolant lines and water lines in the cabin are PEX with compression ring fittings. Orange PEX with oxygen barrier for the coolant, working temp 180 f. You cant get a more low profile fitting than crimped PEX.
25 years on the road, no issues. The compact ring tool is light enough to have in the tool kit with some spare rings and fittings but has never been needed for a failure.

 

[Neil]

Jason. The red knob at the bottom of the calorifier is a 3 bar pressure release cap./ valve .

I never heard of a blending tank so i dont know anything about them. I dont see thatcthey are necessary as the modern thermostatic valves are so good it blends in the tap.

We dont use blending tanks in our homes so i am not sure where or why they would be neccesary on a camper.

As i say i dont know much about them but if it works for your set up then its right for you.

I would be interested to know the advatages over thermostatic valves

Neil

 

[Joe917]

An anti-scalding (blending) valve is mandatory on hot water tanks installed in homes in Ontario (and I suspect many other places). Our Isotherm Spa(Webasto) water heater in the camper came with one.
Neil, its not a blending tank, but a therrmostatic valve right on the tank. It uses the cold tank supply with the hot water from the tank.

Isotemp SPA Marine Water Heater Features:

• Exterior casing / jacket made of high quality polypropylene insulation
• Inner tank made of AISI 316 stainless steel
• Includes safety relief valve, themostatic mixing valve
• Robust design and manufactured to highest-quality marine standards for long service life
• Immersion heating element specially designed to heat water at bottom of tank
• Aluminum mounting brackets adjustable for deck or bulkhead installations
• Extra-thick insulation for low loss, keeps water at a useable temperature for up to 24 Hours
• Extra-long corrugated coils for high heat exchange efficiency - see below
• All Isotemp water heaters use two thermostats: a temperature thermostat and a safety thermostat designed to trip in
• the event the tank is run dry
• All Isotemp water heaters come standard with a mixing valve
  • The mixing valve regulates the temperature of the water coming out of the tank to prevent scalding
  • Extends the amount of usable hot water available
• Standard heating elements are 750 watts which won’t overload generators or trip dock breakers
• All Isotemp products are CE certified and manufactured in ISO certified facilities
• All Isotemp tanks are covered by a 5-year limited warranty against leakage due to manufacturing defect or corrosion
  and a 2-year warranty on all other parts
  

 

[Neil]

Thanks Joe. This makes sense now.

I have seen similar loops on european tanks but its more likely an option. Its definately not mandatory.

I am still struggling to see the advantage over having thermostatic mixer valves on the outlets. I guess its just an additional safety feature.

Thanks for the info, the light just went on

Neil

 

[luthj]

The reason for the mixing valve at the tank is because the coolant loop has no thermostat, and can easily heat the water to 190F during extended drives. 190F can cause instant scaling, much faster than you can react to turn it down. In homes most water heaters are set to a lower temp usually 140F (60C) or lower. This allows you several seconds to turn the temp down without burn/scald.

In addition the mixing valve provides consistent temps, even as the tank cools during usage. This reduces the need to constantly adjust a shower mixer during the shower. During a shower our tank will often drop from 180F down to 110F. Having the mixing valve set to 120F means that I only have to adjust the shower control for the last 15% of the shower. Of course this is less of an issue if you are running the diesel heater or electric element.