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Author Topic: Solar hot water with LPG boost  (Read 1076 times)
404wanderer
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« on: August 28, 2013, 01:27:25 AM »

Hi all,

I'm in Australia here and am currently undertaking a Mercedes O305 to motorhome (rv) conversion.

I'm looking for a solar hot water system with on demand LPG boost. I have one on my house but I can't seem to find any RV specific ones. Can anybody point me to any suppliers?

Thanks.
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TomC
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« Reply #1 on: August 29, 2013, 09:27:46 AM »

Put in an 10gal electric water heater and be done with it. I have 2-10gal electric water heaters that have givin me zero problems since I installed them in 1994-can hardly beat that. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Ralph7
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« Reply #2 on: August 29, 2013, 10:27:54 AM »

            Friends tried solar hot water, they were not happy. As for the on demand units, not cost efficient, use extra large burners, waste propane.
           Many like me use the electronic 6 gallon, has a switch inside bus/motorhome, turn it on 5 min. before shower and no need for blended water.
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luvrbus
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« Reply #3 on: August 29, 2013, 11:05:56 AM »

Precision Temp make a demand hot water heater for RV's draw back is the price almost a 1000 bucks nice hot water heaters you see the unit in higher end RV's not bad on propane they say.

I had a Seaward electric heater with a heat exchanger it wasn't ideal for camping like we did it made hot water driving ,when the heat was on,plugged in or generator time

 It all depends on how you plan on using your bus if going from pole to pole electric heaters are fine camping with no electricity pretty worthless IMO
« Last Edit: August 29, 2013, 11:19:52 AM by luvrbus » Logged

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Iceni John
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« Reply #4 on: August 29, 2013, 12:17:56 PM »

I plan on making some simple solar water panels that will preheat the water for my Suburban SW6PE 6-gal propane and electric water heater.   I'll have a small hot-water circulation pump slowly move the water through the panels and back to the water heater, then repeat this throughout the day for as long as there's enough sun.   During the summer I probably won't need to turn on the water heater at all, and during the winter if I preheat the water even slightly then that's less propane to burn.

How much PV power will you also have?   (A lot of Australian RVs and conversions have a sizeable amount of PV  -  will you?)   The reason I'm asking is that I just bought 2,040 watts of solar panels yesterday, and with that much power I could conceivably power my water heater's 1500 W electric heater through an inverter if I have power to spare after charging all my batteries.   I reackon that I'll have finished recharging my batteries by midday or so, at least during the summer, so the afternoon sun can be used for heating water, maybe?   Just an idea.   Once everything's up and running I'll have a better idea if this is doable.   If not, the solar water panels will always work.

One way or another, if I can have a free hot shower every night for most of the year I'll be happy.   (See, it doesn't take much to make a busnut happy!)

John
« Last Edit: August 29, 2013, 12:29:24 PM by Iceni John » Logged

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Ed Hackenbruch
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« Reply #5 on: August 29, 2013, 01:33:52 PM »

John, hope you plan on putting in a blow off valve in your system. When we lived on Maui we had a solar panel hot water system put in. Worked really well, in fact in the summer time i would come home from work and find hot water coming off off my roof because it had reached maximum temperature and pressure and the relief valve had opened. We had 2 6x3' panels and either a 50 or 80 gallon tank and the panels were mounted on the west side of the roof so did not get a lot of morning sun. We had electric backup on a timer that was set for an hour before we got up but the only time it went on was if we had a storm for a day or two and had no sun. Drawback for a bus is that you could end up wasting a lot of water if the relief valve opens. You could plumb it so it goes back to your holding tank but then you would not have cold/cool water on hot days.  We  have a 6 gallon propane water heater on our bus and it has been fine for us for almost 10 years of fulltiming. Between the water heater and the stove top we use about 20 gallons of propane every 6 months or so.
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Don4107
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« Reply #6 on: August 29, 2013, 01:36:45 PM »

Unless your solar is on demand it probably has/needs some sort of storage tank.  If that tank was the typical RV propane heater with some added insulation it would function as both storage and back up heat.  I flip on the heater when I roll out.  Plenty of hot water in 10-15 minutes for two showers and stays hot for most of the day.

 
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sledhead
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« Reply #7 on: August 29, 2013, 02:37:14 PM »

I have 3 units on my house for hot water use , 4 units on my bus barn for in floor heat in the winter they work great .   http://www.wsetech.com/WSE58ST.php     for hot water you use a pre heat water tank with the panels witch feeds your hot water tank .


dave
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Iceni John
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« Reply #8 on: August 29, 2013, 04:00:21 PM »

John, hope you plan on putting in a blow off valve in your system. 
Yes, either a T/P valve, or a thermostat to shut off the circulation pump when the water is hot enough.   I would also have to deal with the residual water in the solar heater, otherwise it could flash into steam or back-pressure the whole system.   Just another little challenge to solve!   I know that water can get surprisingly hot, even in simple solar heaters  -  when camping in the Anza-Borrego desert in spring time my little solar shower (a black plastic bag of water you lay out in the sun) gets too hot to use after about mid-afternoon on a typical late-April day.   And that's just a plastic bag of water!   I saw a home-made outdoor swimming pool water heater in England that heated the water sufficiently to allow almost year-round pool use, and it was only black pipes in glass-fronted panels, definitely nothing too high-tech.   I've also thought of buying a small 10-gal electric water heater to use as a hot water storage tank, but then there's the temptation to take crazy-long showers and use up all my water in a week or two!   A 6-gal RV water heater of very hot water should give eight to ten gallons of shower-temperature water, and that's more than enough.

John 
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Ed Hackenbruch
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« Reply #9 on: August 30, 2013, 06:55:11 AM »

Just a garden hose laying in the sun can get remarkably hot in a short period of time. A few years ago MythBusters did a segment or two on what happens to a hot water heater when it over heats and the relief valve fails. Amazing how much force can build up in a tank.
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lvmci
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« Reply #10 on: August 30, 2013, 08:12:21 AM »

Wanderer, an electric hot water tank, could be a great thermos to keep your hot water stored, you can look for the highest degree of insulation, here in the southwest US, we have tank wraps to add external insulation to the tank. Swimming pools here in LV, were heated by black hose wrapped in coils on house roofs, when I was a kid, also circulated by a small pump. I have both a tankless propane and 10 gallon 120ac, use one or the other, it gets to hot, when in a park I take a long hot shower with the tankless, lvmci...
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404wanderer
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« Reply #11 on: August 30, 2013, 08:18:41 AM »

Hi all,

I'm in South Australia. Summer temperatures range from 30C to 45C so solar hot water is a great option down here. On my house I have three water panels which heat a 120 litre tank and has an LPG instant boost to follow. In the summer the tank is often venting because it constantly at max temperature meaning the gas is never used.

I'm surprised I can't find any similar systems for motorhomes here. I'll look at the domestic ones to see if any are suitable.

I'm going to be running solar pv on the van as well. I've not specced the system yet so not sure how much power I will have to spare. I have 5kW of PV on my house.
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TomC
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« Reply #12 on: August 31, 2013, 08:53:35 AM »

The problem with solar panels for a motorhome, is they aren't nearly as big as the ones in a house. Granted you'd get some warm water out of it, but not nearly enough for a shower. Plus you're adding weight to the roof. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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