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Old 11-13-2015, 07:13 PM   #1
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Alternative Hot Water Heater

I was planning on installing a compact 110V water heater in my bus over the winter so as a temporary stop gap for the last couple months I just bought one of those 5 gallon solar shower bags and installed it in one of my skylights. Wow, not much water, but it warmed up fast and stayed warm for a while after sunset. (I'm not full-time boondocking, just weekends with generator)

Today, my inventor's imagination got fired up after seeing this on facebook:



I decided why not try the solar bag permanently as my daytime hot water supply. So I start planning the water lines and connections, took some time walking around the bus and it hit me.

Has anyone ever considered using the heated coils on the back of an RV fridge to heat fresh water? As with the above idea, why not repurpose the existing energy(heat) coming off the back of the fridge? I know this method will not be very efficient, but since the fridge will be running full-time (gotta keep the beer cold) and mine gets extremely cold, why can't I siphon off some of that energy thru a simple heat exchanger and heat the water to my sink ala point-of-use instant-on water heater?
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Old 11-13-2015, 08:41 PM   #2
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Interesting idea. With an electric fridge you could make some sort of heat exchanger to attach to the cooling coils. If you have a propane fridge you could do the same but the heating unit wouldn't be running full time and when it's off the outside air vent would probably cool the water instead of heat it.

If you could link the solar water heater to the fridge you'd have two heat sources.

Washing your face in the toilet top sink may be a bit weird.
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Old 11-13-2015, 08:43 PM   #3
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You could, but, If you didn't use the hot water it could reach a point where you couldn't get there thermal transfer from the inside to the water and your fridge would stop working. To solve that you would need at least 20gal of water. Secondly it isn't that much energy being used therefore you wouldn't get that much heat. Thirdly, if anything happens to either part of your system the other part goes down too.
So while it could be done I wouldn't do it unless you just stored beers and pint glasses in that fridge. Spoiled food = Short trip.

The toilet thing you could also just run the line to a small tank above the sink and run a line from the sink back to the top of the toilet tank. Man that thing would slosh going down the road.
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Old 11-13-2015, 09:02 PM   #4
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Good point about potentially heating the fridge coils. That's probably the fatal flaw in the plan.
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Old 11-13-2015, 10:26 PM   #5
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So while it could be done I wouldn't do it unless you just stored beers and pint glasses in that fridge. Spoiled food = Short trip.
Is there anything else needed after a day of racing???
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Old 11-13-2015, 10:38 PM   #6
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Good point about potentially heating the fridge coils. That's probably the fatal flaw in the plan.
But I thought the thermostat was on the inside of the fridge, i.e., temperature inside the fridge, not the temp of the boiler.

By your example, the bag would cool, but the fridge would be colder than the thermostat setting until the bag cools below the boiling point of the ammonia.

If I can find that sweet spot just below the above the fridge would come on as soon as the water fell below and it would maintain both the fridge and the hot water at an equilibrium point.

Said another way, if the solar water got too hot, it would be the catalyst to keep the fridge cold instead of the electric boiler on the fridge. So I would have to turn down the fridge thermostat and even on its lowest setting the electric boiler wouldn't turn on till the solar water cooled below the boiling point of the ammonia in the fridge boiler. At some point during the night, the solar water temp would fall below the ammonia boiling point and the fridge thermostat would turn the boiler on and off to maintain the fridge temp overnight while also heating the water above room temperature.
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Old 11-14-2015, 09:29 AM   #7
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There is no ammonia in a fridge.

I don't think you fully understand the way fridges work.

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Old 11-14-2015, 09:35 AM   #8
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So you want to turn your toilet into a water heater?
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Old 11-14-2015, 09:41 AM   #9
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May as well collect the heat from poop and pee too. Lol

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Old 11-14-2015, 10:25 AM   #10
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There is no ammonia in a fridge.

I don't think you fully understand the way fridges work.

Nat
RV fridges have ammonia, large commercial do too.


Ammonia Refrigeration | Ammonia RV Fridge | Ammonia Fire | RV Fridge Refrigerant
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Old 11-14-2015, 09:55 PM   #11
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Damn Nat, and I thought you were one of the forum gurus. I guess Don's my new hero. ;)

http://www.ehow.com/how-does_4572467...ator-work.html
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Old 11-15-2015, 12:56 AM   #12
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I learn something everyday.

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Old 11-15-2015, 02:09 AM   #13
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Damn Nat, and I thought you were one of the forum gurus. I guess Don's my new hero. ;)

How Does a RV Refrigerator Work? | eHow
It is a simplified version of what is going on. My concern is if the water gets above about 120 deg F surrounding those coils the ammonia won't condense very well most of it will stay gaseous. Eventually you will boil the water in the fridge system until it blows out causing it to rapidly vent thru the hole it creates (almost always by the propane burner) causing the ammonia and hydrogen to catch on fire. If it were a good idea believe me this hot water/ fridge monster would already be on the market. RVers and especially boaters would love such a space saving fuel efficient system.

Not to mention the higher the temp surrounding the coils the more level you need everything or you won't get the condensation either.

Nats from the great white north, they use fridges to keep things warm in the winter.
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Old 05-26-2016, 10:52 AM   #14
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alternative water heating solar, wood, lp

here is what im trying to do with solar and wood. i'm trying to figure out my water system specifically the hot water because I want to have alternative heating methods. in the diagram below the very simple drawing on top is a tried and true water heater that I grew up with. hot water tank elevated above heating coils, 4 outlets to the tank hot and cold intake and out put then tank water to and from heating coil. the heating coils was 3/8" copper tubing coiled around the 6" chimney pipe. 6" pipe x pie 18+" time 10 coils a little better than 15' of coil creating thermal up lift and cycling the water WITH OUT any pumps or moving parts. only 2 cons to this. 1 too hot a fire and the water would boil in the coil... not bad just make funny sounds and then the pressure valve would vent. 2. we had hard water so every few years the coil would lime up and we would have to replace it. my dads advice was to use coolant/ oil in the coil.

this is where i need you guys the bottom part of the diagram is my skoolie blue is cold water, red is hot water, green is coolant. i'm going to have a disconnect panel going to the solar for movement and possibly for cold months, wood for winter, and LP heater if I end up some where with no room for panels and to hot for wood. now the question is where do i place the heat exchanger and the oil reservoir where i can still capitalize on the thermal moment and reduce the need for 3 pumps for the system.


the feed in to the bus is looped so when i take it to cold climates there will be more circulation to keep the pipes and tanks from freezing. i also wanted to have the heat exchanger in the under storage with the tanks but i'm not sure if that will be conducive to thermal flow.

also i thought i had an exchanger lined up that would be conducive to thermal flow but this is all i can find now.
50 Plate Wood Boiler Heat Exchanger 1" Ports Outdoor Wood Boiler Radiant Heat | eBay

let me know your thoughts
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