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RV water heater idea

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hot_rod
hot_rod Member Posts: 22,271
The most common DHW homebuilt around here is a 4" piece of ABS lay it in the sun for the day, a bicycle pump to pressurize it. I was looking for something a bit more reliable.

This 20 gallon well tank will push out about 4.8 gallons of water. A spring loaded heat aluminum transfer plate wraps around the exhaust pipe, and pushed against the tank.

I may need to put a thermostatic "motor" in the transfer component if it over-heats. I know the tailpipe gets hot as you can see from the melted mudflap.

Headed out for a test run.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
WMno57

Comments

  • psb75
    psb75 Member Posts: 845
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    This was just printed in an article on electric vehicles in the Wash. Post this morning
    "In a gas car, only 16 to 25 percent of the fuel energy actually goes into the wheels — the rest is lost mostly in the form of heat and friction". Nice idea hot_rod!
  • WMno57
    WMno57 Member Posts: 1,349
    edited April 14
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    psb75 said:

    This was just printed in an article on electric vehicles in the Wash. Post this morning
    "In a gas car, only 16 to 25 percent of the fuel energy actually goes into the wheels — the rest is lost mostly in the form of heat and friction". Nice idea hot_rod!

    16 percent might be about right for a 57 chevy that needs a tune up and has a slush box powerglide transmission. For a 2024 Camry non-hybrid I'd guess mid 30s. Camry Hybrid (not plug-in) I'd guess low 40s. I'll try to find exact numbers.
    Electric cars have friction and aerodynamic losses too.
    I DIY.
    bburd
  • Jamie Hall
    Jamie Hall Member Posts: 23,455
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    You might be a redneck... Is there any way you can get some insulation -- or at the very least a wind tight shield around the whole thing? But it mustn't hold water...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EdTheHeaterMan
  • JUGHNE
    JUGHNE Member Posts: 11,077
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    I was subscribed to the "Mother Earth News" since their inception in about 1980.
    There were a lot of innovative ideas shown in the magazine back then.

    One was someone who installed a large water storage tank in his vehicle. He bypassed the radiator and used the tank to cool the engine. He had a fairly long commute to work so could heat up the entire tank.

    When he got home he then had hose connections to circulate the water thru some form of heat exchanger in his house.

    I never saw any follow up on this concoction so don't know how well it turned out.

    I must have 3-4 years of this unique publication. Very original ideas that were thinking outside of the box.

    There also was an article on "Sky Lids", they were roof shutters that would open and close by R-12 refrigerant phase change thru heat gain. 2 canisters on a "teeter totter" type mechanism that would control solar heat gain.
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 9,754
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    I was going to say, hx off of the coolant for the engine would be more effective.
    ZmanPeteA
  • Sylvain
    Sylvain Member Posts: 147
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    One should look at co-generation to see what has been developped for heat recovery:
    engine coolant + exhaust gases
    I read about 40% of engine fuel is lost in exhaust gases
    mattmia2 said:

    I was going to say, hx off of the coolant for the engine would be more effective.

    Yes... as long as it does not void the engine waranty.
    hot_rod said:

    The most common DHW homebuilt around here is a 4" piece of ABS lay it in the sun for the day, a bicycle pump to pressurize it. I was looking for something a bit more reliable.

    You will still need this if you don't move.

    mattmia2
  • Sylvain
    Sylvain Member Posts: 147
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    mattmia2 said:

    I was going to say, hx off of the coolant for the engine would be more effective.

    The advantage of this solution, if one keeps the original engine radiator and temperature control, is that there is (practically) no risk of water turning into steam.
    I don't see any control on the OP system.


  • hot_rod
    hot_rod Member Posts: 22,271
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    My water tank is at the rear of the truck right over the exhaust, so I was looking for a KISS solution that worked with or without sun.

    So far a swing and a miss, after an hour of 70 mph driving it was still ambient temperature.

    I think Jamie has it right i need to insulate and maybe a wind shield. Stop and go driving may get the tailpipe hotter also.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mattmia2
    mattmia2 Member Posts: 9,754
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    Your transfer area is essentially that 1in^2 cross section of metal. that is more how you make a handle that stays cool than how you transfer energy. Even if you found a small gas water heater and routed the exhaust through the flue I don't think you'd transfer a lot of heat.
    PRR
  • Derheatmeister
    Derheatmeister Member Posts: 1,550
    edited April 12
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    I understand that you are trying to keep things simple without many moving parts..
    Maybe you could just hook it up to the defrosting circuit... 5/8" radiator hose a ballvalve,some tees with a HX and some extra PE glycol will do.
    Edit: Do not forget the Reliefvalve and thermostatic valve(Overtrop with capillary) that will prevent overheating of tank.
    Or...Just get a 5 gallon Sunshower.. :)
  • hot_rod
    hot_rod Member Posts: 22,271
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    I understand that you are trying to keep things simple without many moving parts..
    Maybe you could just hook it up to the defrosting circuit... 5/8" radiator hose a ballvalve,some tees with a HX and some extra PE glycol will do.
    Edit: Do not forget the Reliefvalve and thermostatic valve(Overtrop with capillary) that will prevent overheating of tank.
    Or...Just get a 5 gallon Sunshower.. :)

    I've seen all sorts of those portable. Yakima has a 10 gallon pressurized tube type that fits on their roof racks.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,338
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    Hi, I've used a shell and tube heat exchanger with the exhaust of my back-up generator, but pump water through it. I just get condensation dripping out the exhaust, so it seems work. Don't know if the exhaust side might foul after time... Also @JUGHNE , Sky Lid was invented by Steve Bear of Zomeworks in New Mexico. He created a lot of interesting things. Elegant simplicity being a design factor in his work, his stuff just kept on working while the motorized solar trackers and other things on the market would fail. I got to work with him for years, so I try to follow with simple and durable design.

    Yours, Larry
  • jumper
    jumper Member Posts: 2,289
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    For summer homes use solar to achieve over 80° and then convert an old refrigerator to a heat pump to boost that to useable DHW. Fridgidaires worked particularly well.
    Derheatmeister
  • PRR
    PRR Member Posts: 156
    edited April 22
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    JUGHNE said:

    I was subscribed to the "Mother Earth News" since their inception in about 1980.

    1970. And IMHO, the '70s had a LOT of thought-provoking ideas. (Not all good, but worthy of thought.) Although some of them were welders' wet-dreams. (Yes, you can re-sprocket a VW Bug as an effective farm tractor, plus DIY implements... but the welding-rod alone may be more $$ than a old FarmAll.)
    Much of their stuff is on-line, but the Search function is slow. It says "0 found" for many seconds and then jumps to 7466 found.
    https://www.motherearthnews.com/search/heat
    Would You Heat a Room With a Heat Grabber?
    Heating a Pool to Heat a House
    Living the Simple Life For a Dollar a Day - By Victor A. Croley • Published on Jan 1, 1970
  • jumper
    jumper Member Posts: 2,289
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    Did MotherEarth advocate cheating electric provider via "guerrilla market"?
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,338
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    Hi @jumper , I don't remember ever seeing anything suggesting stealing power. The most "anti-establishment" I remember was installing PVs without permits in your apartment to offset some power usage. o:)

    Yours, Larry
  • JUGHNE
    JUGHNE Member Posts: 11,077
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    I agree with Larry, no "free" power methods were recalled by me.

    Some mentioned it went from "Hippe" mode to "Yuppie" mode and interest was lost by many.

    Larry Weingarten
  • jumper
    jumper Member Posts: 2,289
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    What I remember is advocating using home generated power to reverse electric meter.Was it even possible in nineties?

    Of course electric provider loses compensation for distribution costs. It also destabilizes their facility. Nowadays many jurisdictions insist that power company pays for home power regardless.

    My own opinion about home power is that it can pay off if you can divorce the grid. Otherwise somebody pays. I enjoyed the magazine but many ideas there were simply hobby rather than practical solutions to anything.

  • PRR
    PRR Member Posts: 156
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    reverse electric meter.Was it even possible in nineties?

    Yes (I have the book). Most/all AC spinning-disk wattmeters will go backward.

    BUT synchronizing a stand-alone single-phase alternator to the line is tricky and dangerous. Requires exact sync or machines and wires go BOOM. (Is much easier with 3-phase machines.)

    This got "trivial" with smart semiconductor phasing. But 1990s is a bit too early (you'd pay more for electronics than domestic electric is worth/credited).

    https://en.wikipedia.org/wiki/Synchronization_%28alternating_current%29#Conditions

  • hot_rod
    hot_rod Member Posts: 22,271
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    I remember that magazine as a farmstead or homestead aimed at DIYers and hobbiest

    The ASHRAE Journal was more for the intellects and engineering nerds😯

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Sylvain
    Sylvain Member Posts: 147
    edited April 23
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    reverse electric meter

    Now with the smart watt hour meters a different price can be applied for what is taken from and what is injected in the grid. One has to pay for the connection though as you might need it when your solar panels are not enough (night).

    https://en.wikipedia.org/wiki/Smart_meter

    Too much private injection in a street will rise the voltage. Then the private inverters disconnect. This destabilise the grid. One solution is (private) batteries to bufffer the local production excess.

  • jumper
    jumper Member Posts: 2,289
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    How much battery does one need for conditioned power?

  • Sylvain
    Sylvain Member Posts: 147
    edited April 24
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    No idea, mys step son (4 people house) has spent 7000 EUR on one and has a very low electicity bill. It is quite an investment though.

    One has to program the use of the wash machines (laundry, dryer & dish) and use the locally produced electricity to store DHW while the sun is shining.

    I wander what Hot_rod will finally do for his RV?

  • Dave Carpentier
    Dave Carpentier Member Posts: 596
    edited April 25
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    I'm too generic, I can only see heating a mass of water up by using the waste engine heat during the drive to site. If more hot water is needed, then resistance/gas heater or idle the truck for a while.

    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • jumper
    jumper Member Posts: 2,289
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    hundred gallons weighs a lot.

    WMno57
  • JR3_Home_Performance
    JR3_Home_Performance Member Posts: 23
    edited April 26
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    Assuming full recharge and discharge then the minimum would be (Solar panel installed wattage- minimum constant load) x 6. Better to have way more capacity though. Lifepo4 batteries are getting cheap. 10kwh storage is getting around $3k right now.

  • jumper
    jumper Member Posts: 2,289
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    I believe lead-acid can be less expensive than 10kwh storage is getting around $3k right now.