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Old 11-13-2015, 08:13 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, 09:41 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, 09:43 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, 10:02 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, 11:26 PM   #5
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Originally Posted by CaptainInsaneo View Post
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, 11:38 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, 10:29 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, 10:35 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, 10:41 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, 11:25 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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