Engine coolant hot water heating tank design idea

[Bogo]

I also posted this over at IH8MUD. It is a rough draft of an idea I had. Text is a bit modified here. There are also a number of other ideas in that thread.

This is for a engine heated hot water, not direct shower water. Mixing the hot water with cool water would be needed for showering as the water temp in this tank design would eventually get close to the engine coolant temperature. The tank idea is modified from the boat hot water heaters like the Isotherm units. I haven't built this yet. I'm not yet to the stage in my vehicle build to be installing stuff like this. It is just a possible design at this point.

I designed it using standard off the shelf parts available here in the US. Only a very little fabrication is needed and that is only to support the ends of the copper tube against road vibrations and for the outer case.

Start with one 2.5, 3, or 5 gallon premix soda keg. Get one that has a pressure relief valve in the lid. Note the type of input and output connectors it has. The parts I show and link are for ball lock kegs. There are pin lock versions of the parts I show. When you pick up the tank and other parts you may wish to pick up some extra o-rings for the lid and quick connects on the keg.

OK, wrap a length of 1/2" copper tube tightly around the keg near the base. See picture below. Orientate the input and output tubes suitably for your installation. Use a tube bender for tight bends, or just use suitable angle fittings. How long should the tube be? I don't know. What spacing to use between wraps? I don't know. Personally I'd just get a 60 foot length and wrap it all and pack the wraps together.

On each end of the copper tube install a hose barb appropriate for your heater hose size. Use a brass barb rather than clamping to the copper tube because clamping to the tube will likely crush it plus it is a smooth tube with no grip. The fitting could either be soldered on or a flair fitting. It don't matter. Some support for the ends is a must. It would be good if they were affixed solidly so the tube does not flex from road vibrations. You will need to fabricate something to do this.

I'm thinking of using liquid nails to glue the tube in place, but I don't know on that. Suggestions? It is important to have a good thermal connection and that it holds up over time. I suppose you could solder the tube on.:sombrero:

I'd plumb the coolant source and return hoses in parallel with the heater core hoses. Just use a couple y fittings plumbed inline before the heater control valve. I'd also insulate the hoses if they have to run any distance.

For extracting hot water out. There are keg faucets that directly connect to the output port of the keg.

I'm not sure how the quick connect and keg faucet will respond to 180F water, but it is worth a try. It can always be replaced by regular pipe fittings. The keg faucet works for extracting the water because there is a small tube going from the bottom of the keg to the output port.

For pressurizing so the water will flow out. Use quick disconnects with hose barbs to connect your pressurizing system up to the tank.

Add to that a hose and bits for whatever pressurizing method you want. It could just be a metal valve stem cut off and clamped into the hose, or and elaborate regulator hooked up to the on board air system.

Around the whole tank I'd insulate it with expanding foam. It would be good to have an exterior case but that can be your choice. I'm thinking a stainless steel tube then filling expanding foam in between it and the keg. Depending on the strength of the expanding foam the keg could either be supported by it or need some extra support structure.

Refilling the keg is via it's lid. Open the lid up and pour in water from your jerry can or use a hose. Leave a couple inches expansion room at the top.

Heating happens while you drive. With enough insulation it should keep the hot water hot for many hours.

With all new parts it should be under $300 without the case. Using a used reconditioned keg will chop $60 to $70 off that. As an aside I will mention that an Isotherm water heater unit is only around $700 to $800 but would require a pressurized cold water system due to how they plumb the exit port.

It would be possible to use a temperature controller and heater valve to control the temperature in the tank, but I was looking for simplicity. The temperature control could be as simple as a bi-metallic switch glued to the side of the tank. I'd make sure the circuit is de-energized when the engine is off.

Alternate types of tanks could be used with this design. I've seen people use old fire extinguisher tanks for pressurized shower systems. They would work too.

I attached the images in case they vanish on the web.

 

[78Bronco]

It's a grand idea but running the coil around the outside of the tank is going to make heat transfer very inefficient. I wouldn't use copper line at all.

Where are you going to mount this tank?

 

[Bogo]

I have three reasons for wrapping the coil. First is simplicity. It involves the least amount of fabrication. No need to add any more ports to the keg than it already comes with. Second is if there is a rupture of the heating coil then there will not be any antifreeze in the hot water. The third is mechanical. Wrapping the coil around the outside of the tank easily fully supports it. In a bouncing environment like an off road vehicle this support is a must, especially when the water level is low and it is sloshing around.

As for inefficiency, that is why the long length of the coil. The hot water heaters for boats only use a few feet of tubing for heat transfer to the water. Granted their coil is fully submerged in the water. Also they use acid proof steel for the tank and coil.

Flexible stainless steel tubing can be substituted for the copper tubing and from what I understand for some diesel vehicles it may be a requirement. Unfortunately stainless steel tubing is expensive.

 

[cruiseroutfit]

I'm interested to see how it works out for you. Honestly I can't see it working all that well, your trying to transfer heat from a fluid (coolant) to copper to stainless and back to water, each time losing efficiancy. You have an extremely finite (for giggle lets say 10%) contact area between the copper tubing and the 'shell' in your case the soda jug. The rest of that heat transfer is lost into the air. Given the vase size and logistics in mounting I'm interested to see how implement it. Kudos for trying something new... but at the end of the day there is a reason there are a half dozen commercially made tube-in-shell vehicle shower heat exchangers... they are simple, they are proven and they are easy to mount and plumb. Keep us posted!

 

[78Bronco]

Would an electric coil work?

$70 ebay
http://cgi.ebay.com/12-volt-600-Wat...EEZE-SEN._W0QQitemZ300299348921QQcmdZViewItem

You could have a thermostat and two coils (hi/low) switched with the ignition. Take the tank, cut two holes then have threaded bungs TIG welded to it. Much easier, less risk and cheaper IMO. Now you can mount it anywhere.

 

[Bogo]

The whole idea is it uses waste heat from the engine to heat the water. Using an electric coil will end up using more fuel to generate the electricity to heat the coil. Also because it is heating while you drive, when you pull into camp you have shower water available immediately without having to heat it. All you need to do is draw some hot water out of the tank and mix with cool water to suit for showering.

The other thing is I commented it would be insulated with foam so minimal loss to air. Also this allows for still having hot water hours later. With enough insulation hot water can still be available the next morning.

As for heat transfer. It doesn't need to be perfect. It just needs to transfer enough heat while driving to raise the temperature of the water above shower water temperature. I'm fairly confident with only an hours driving time this design could produce 5 gallons of over 120F water. Isotherm's 24 liter unit has at most 6 feet of heat transfer tubing. That's it, and it will raise the temperature of 20C water to 55.8C with 70C engine coolant water. I can buy a 60 foot coil of 1/2"ID tubing and wrap the whole thing around the tank. Sure, per foot it isn't as efficient, but it is made up for by being much longer.

Here is a PDF of a test of a number of water heaters made for boats. You can see how they are made and how little amount of heat transfer tubing some good ones use. They have the figures for how much heat is transfered to the water in an hour and you can see the internals of the units because they cut them open. Nice for learning.
http://www.indelmarineusa.com/pdf/Depliant_GB.pdf

 

[dieselcruiserhead]

Helton makes a great one (that Kurt sells). Also the wast e vegetable oil guys use something called a Hot Plate that also works very well, neither of which are two expensive. These would be the route I'd take.

 

[Desert Dan]

You would be better off using a real heat exchanger in your design.

There are pre made kits you put in-line on your radiator hose witha 12 volt water pump and temperature valves hose etc.

 

[Desert Dan]

No affiliation but this set up looks pretty good:

R&M VEHICLE MOUNTED HOT WATER SHOWERS

http://www.hotcampshowers.com/vehicle_mounted_shower

 

[cruiseroutfit]

Cool, sounds like you've done your research and have a sound game plan in mind. I'm well aware of the heat transfer abilities of a tube in shell heaters such as the Indel Marine units, I've been running a tube in shell heat exchanger on my Land Cruiser for 4 years now and recently installed one on my Tacoma too (plus spent a year in Thermodynamics studying these type of transfer properties ). However to compare their heat transfer specifications with yours is literally apples and oranges. Much like those that have tried various lengths of copper tubing, tightly wound around there exhaust manifolds or header pipes... to realize a 5-10 temp increase. Would a foam shell have increased the heat transfer in their cases, sure... but the logistics, cost and serviceability often lead them to other means.

Plate heat exchangers are another very efficient means of transfer too, like the tube/shell the mounting is simle (~3" diameter and 10" long in the case of a tube/shell exchanger) and can produce 5 gallons of 100*+ water in the time it takes to pump that water, say 5 minutes. If you have an instant need for hot water when you arrive to camp, a storage tank like your plans would satisfy the need. I'm truly interested to see yours come to fruition. Keep us posted and I'd love to see more pics as you get to the build.

A few have asked and maybe I missed your answer. Where do you plan to mount this?

 

[78Bronco]

You would be better off using a real heat exchanger in your design.

There are pre made kits you put in-line on your radiator hose witha 12 volt water pump and temperature valves hose etc.

Dan has made a good point here. Move the water you wish to heat, to an exchanger closer to your engine rather than sending all your coolant down a potentially risky journey away from the engine compartment. I love the concept of recouping wasted energy from the engine. I was suggesting the electric cause of how simple it is.

My engine shakes the chasis like mad so in my application I wouldn't want to rely on any soldered connection to retain my coolant in an exchanger system.

Where is the tank being mounted? Low/High? In the back?

 

[ntsqd]

Since the plan is to wrap the coil around the outside of the tank there will be the discussed lower efficiency of thermal transfer and the potential for damage to the coil. A possible solution that addresses both issues would be to silver solder the coil to the tank wall. That would increase the contact surface area from a coiled line to a coil with some indeterminate width and would bond the coil to the tank for far better fatigue life. I doubt that this will be an easy chore to do manually, but it could easily be furnace brazed.

Alternately, you could employ one of the SS stacked plate HE's (sold by McMaster et. al.) and a circulation pump for the shower water. Pump the shower water out of the tank, through the HE and back into the tank. This may be the more cost effective method, dunno.

I'm not trying dissuade you from your original idea, just throwing up modifications to the original plan and alternate ideas for consideration.

 

[Bogo]

Right now the system is nearly passive. Only compressed air is needed for pumping water out of the tank, and everybody needs an air pump for the tires.

As for pumping water to a heat exchanger. First there is the threat of freezing the fresh water in the lines when the water is not flowing. Second, where can I find a drinking water safe pump that will pump 180F water? Most are rated up around 130F or lower. Third the pump is needed for the system to work. With my design if there is a threat of freezing the tank only needs to be emptied. The hoses can be protected with skid plates or they can be routed through the interior. Also modern auto heater hose materials are very sturdy.

Now for where to place it. It is unfortunately TALL. Even using a 2.5 gallon keg it is tall. That is my main problem with the design, but then I'm working with an existing tank. With insulation it will likely be 11 inches in diameter, and around 3 feet tall. Right now the only place for a 5 gallon one in my Micro RV design is between the bunks at the front end of the cabin. A 2.5 or 3 gallon one likely could be placed under the end of a bunk.

As for the design. I had been looking at the Isotherm units and thinking how could I make a unit like that, but for a non pressurized water system. Many ideas went through my head, but they all required allot of fabrication. Then by chance I thought of the pre mix soda kegs that home brewers like. I knew they were pressurized in use. I found out they can easily take 100 PSI and are designed for something higher than that. After that it didn't take long to rough out the design. I deliberately looked for parts that could be used with little to no fabrication.

Alternate tubing possibility. For aircraft they have soft aluminum tubing. It is rated for 305PSI so it will handle engine pressures easily. Also a 50 foot coil is only $40US for 5/8" ID. That is less than 1/2 the cost of copper tubing of the same size. Radiators and engine block heads are often made of aluminum so it isn't a new material in the engine coolant system. The corrosion fighters in modern anti-freeze will help protect it. A copper or stainless steel tube would likely be better in third world countries if going without proper antifreeze is expected. Again, pick the tube type based on what is compatible with your engine cooling system.

 

[UK4X4]

Ian who just left Oman for Southafrica and heading north following about 6-8 weeks behind our present site poster did something similar with his old LC

he added two valves to the standard water circulation route and plumbed
a coil of copper tubing inside his rear mounted water tank.

when hot water was required turn the valves and the larger circuit was complete.

he wanted to fit a solenoid operated valve so he could switch it on from the cab but I don't think he ever got that far.

Tubing from front to rear was just rubber- I did'nt recomend it but thats what was easily available.

water was not presurised just gravity, but Ian's a bucket type of guy rather than a powered faucet with adjustable shower flow:costumed-smiley-007

 

[048642]

All this high technology...:jumping:I just leave the water bottle between the seats in my 404 Mog and after 20minutes of driving I can burn my lips when I drink it it if I'm not careful!