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Old 02-28-2013, 01:13 PM   #183
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Quote:
Originally Posted by perryg114 View Post
That thin white foam material that is commonly used for packing stuff would make a good thermal barrier. The problem with aluminum is that it has such high thermal conductivity that even if it touches in a few places it is still going to conduct heat well. I would use twice the number of pop rivets since the rivets will be able to float more with a barrier between. You could use just about any plastic sheet material between the skins and the ribs. You can get rolls of Mylar etc. You could glue it to the ribs. You going to use the old skins or make new ones?

Perry
Thanks Perry and Wabbiteer for you excellent advice, as always. I am going to make new skins. When I got my Airstream, the interior skins had been replaced with cheap bathroom fiberglass paneling. It was sad, because it was fitted with a pretty impressive amount of care, but it was so ugly and totally nonstructural.
Tim
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Old 02-28-2013, 01:31 PM   #184
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There is alot of debate over the structural contribution of the inner skin. I don't think it does much. You could even use thin wood strips as an insulator or make the entire inner skins wood paneling. The major week areas of the shell are places where they have broken the ribs for some sort of protrusion through the skin.

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Old 03-13-2013, 11:02 PM   #185
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Progress!


I installed my Maxxima stop turn tail lights.


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The hardest part was making an 1/8" aluminum backing plate to provide more support. I cut out a circle the size of the OD of the light using a circle cutter on my drill press. Then I cut out the hole in the center. I cut the hole in the skin and then buck riveted the1/8" thick donut on the inside of the skin using flush countersunk rivets. Then with a generous bead of Vulkem and stainless screws I attached the lights.


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I also replaced all of the marker lights with new LED lights. There were a couple,ghastly discoveries when I removed the old lights.


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I patched the hole in that one before installing the lights. I went ahead and drilled a new hole in the skin for the more central wire leads which did not line up with the existing hole. I patched the old hole with a small circle of Al and a rivet. I used new stainless screws to attach and a big gob of Vulkem on the inside for the wire connection. I will finish later with a bead of Parbond on the top edge.


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I also removed the existing waste vent and cleaned up the piles of old goop.


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Wood 1 x 2 s ripped at 60 degrees made the best scraping tools to get rid of old sealant,
Then I positioned my new vent using a 1 1/2" aluminum tubing fitting I purchased at LDS vacuum supply. I attached it with Vulkem and pop rivets and it is very secure. I then used the old vent cover with a new screen and gasket from Andy R. And Olympic rivets. I sliced a gap in the bottom of the gasket for drainage. It won't leak anywhere but into the grey tank.


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Old 03-13-2013, 11:20 PM   #186
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Now thinking about heaters.

I really wanted to do a Newport Dickinson LPG fireplace but I've struggled to find a practical place to put it. I have looked for alternatives that are quiet and use less battery than a standard RV furnace. The two alternatives I like are the Propex LPG forced air furnaces or a hydronic system based on a water heater. The Propex seems efficient small and quiet but at about $900 with all the parts seems a bit expensive. If I was rich, I'd buy a twin temp Jr and be happy but I am not rich. I've read a lot of interesting things about using potable water for hydronic heat and think it could work ost simply with a tank based water heater. Malconium has done an incredible job documenting his experience and research. I would use radiators in strategic places instead of in floor radiant heat due to ease of installation and complexity. I saw that some of the Atwood water heaters have a heat exchanger designed to be able to use the engine coolant of a motorhomes to heat the hot water.
http://www.statetrailer.com/display....ywords=9106800
What about using the water heater with the built in heat exchanger to heat a loop of glycol which could be pumped through radiators or Radex exchangers?. The XT version is even more tempting since it maintains the main tank at above 160 deg. Note, the very respectable Lewster has warned about problems with the mixing valve on the XT models. Anyway, thought would be appreciated.
Tim
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Old 03-14-2013, 10:04 AM   #187
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Looking at the Propex I had a little daydream of using two or three of them in zones...

With the great age possible with things Airstream my vote is stainless steel (SS) tanks! I settled for aluminum tank water heaters only because I got them for 25 on the Dollar (or less!).

Our city tap water is 460ppm carbonates & salts and a pH of 8.4 and does tricks on metals - render inoperable tankless exchangers in a year or less which I took as example that places I travel to might have less than friendly water - and ultimately will look for SS tanks for the final form of my trailers heat/water setup.

There are Isotemp double-exchanger SS water heater tanks that I've been unsuccessfully searching on eBay for a couple of years but are way rare and are typically $750 to $1000 new. The dual-exchangers offer some more flexibility on designs, perhaps heating the tanked fluid and having multiple 'instant' hot water taps?

Smokeless Joe chose Isotemp when he did his hydronic set up. Quick is another stainless tank with single exchanger.

I'd like to explore using passive baseboard heaters instead of listening to forced air blowers. Many fanned radiator units are designed for commercial vehicles that noise is not a factor in - choose carefully!

I have not found the tank($) I wanted so I've gotten two 6-gal heaters to use as storage and plan on using the $30 a gallon dow-frost non-lethal anti-freeze 50/50 mix in one tank and use the second tank as potable hot water. Also, one tank is 240 and one tank is 120VAC heater element for when I'm tethered. The heater I've chosen boosts output at start up and throttles back to an idle output - so the heated fluid can see radiators and HW tank and 'maintain' them once the bulk of recovery has happened.

A calculation for energy - to heat 6 gallons of water from 35F to 160F takes 6120 Btus. A camping water heater measures energy input not resulting output. At 80% efficiency thats 7350 Btu input and I'd be surprised if common RV water heaters are 80%. But again - the water heater itself is a radiator of sorts that might be appreciated in cold weather.

Notes: the 'curve' of heat transfer at less than a 40F differential between metal radiator and air falls off sharply... so once you've heated the interior to 70F there is just 2460 Btus (160-(70+40)=50F) usable heat energy stored at a target 160F tank temperature which equals the energy produced by a 120V heater on low for an hour (720 watt-hours).

Use the calculator link and explore your usages, Propane 21622 Btu per pound and 20 pound bottle nets 432440 Btu. So 60~ hours run time off one 20-pound tank for a conventional 6-gallon water heater. I know you're not choosing to go camping where the heater has to run 24/7 but there may be occasion
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Old 03-14-2013, 12:57 PM   #188
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Atwood XT with heat exchanger

Quote:
Originally Posted by Wabbiteer View Post
Looking at the Propex I had a little daydream of using two or three of them in zones...

With the great age possible with things Airstream my vote is stainless steel (SS) tanks! I settled for aluminum tank water heaters only because I got them for 25 on the Dollar (or less!).

Our city tap water is 460ppm carbonates & salts and a pH of 8.4 and does tricks on metals - render inoperable tankless exchangers in a year or less which I took as example that places I travel to might have less than friendly water - and ultimately will look for SS tanks for the final form of my trailers heat/water setup.

There are Isotemp double-exchanger SS water heater tanks that I've been unsuccessfully searching on eBay for a couple of years but are way rare and are typically $750 to $1000 new. The dual-exchangers offer some more flexibility on designs, perhaps heating the tanked fluid and having multiple 'instant' hot water taps?

Smokeless Joe chose Isotemp when he did his hydronic set up. Quick is another stainless tank with single exchanger.

I'd like to explore using passive baseboard heaters instead of listening to forced air blowers. Many fanned radiator units are designed for commercial vehicles that noise is not a factor in - choose carefully!

I have not found the tank($) I wanted so I've gotten two 6-gal heaters to use as storage and plan on using the $30 a gallon dow-frost non-lethal anti-freeze 50/50 mix in one tank and use the second tank as potable hot water. Also, one tank is 240 and one tank is 120VAC heater element for when I'm tethered. The heater I've chosen boosts output at start up and throttles back to an idle output - so the heated fluid can see radiators and HW tank and 'maintain' them once the bulk of recovery has happened.

A calculation for energy - to heat 6 gallons of water from 35F to 160F takes 6120 Btus. A camping water heater measures energy input not resulting output. At 80% efficiency thats 7350 Btu input and I'd be surprised if common RV water heaters are 80%. But again - the water heater itself is a radiator of sorts that might be appreciated in cold weather.

Notes: the 'curve' of heat transfer at less than a 40F differential between metal radiator and air falls off sharply... so once you've heated the interior to 70F there is just 2460 Btus (160-(70+40)=50F) usable heat energy stored at a target 160F tank temperature which equals the energy produced by a 120V heater on low for an hour (720 watt-hours).

Use the calculator link and explore your usages, Propane 21622 Btu per pound and 20 pound bottle nets 432440 Btu. So 60~ hours run time off one 20-pound tank for a conventional 6-gallon water heater. I know you're not choosing to go camping where the heater has to run 24/7 but there may be occasion
The interesting thing about the Atwood with the heat exchanger is that the hydronic loop would be totally isolated from the potable system so all of my hydronic system would be a closed loop with distilled water and glycol. I wouldn't have to drain it to winterize although I could purge it out occasionally. I don't know anything about the size or efficiency of the built in heat exchanger but if it was enough to heat the 6 gallon tank from the engine coolant of a motorhome, it should be enough to take energy from the 6 gallon tank to pump around my 20' RV. The XT's run at high temps and then go through a mixing valve to generate more moderate hot water at the tap. I've read that the mixing valves are problematic and require maintenance which is a bummer, but I could build my cabinets to provide easy access to the heater to make that better. I totally agree with your idea of a fan free system based only on radiators. I think that with the right radiators and a quiet liquid pump, you could build a system in which the only noticeable sound was the firing of the water heater. Depending on the insulation, I think I could make this work and provide enough heat down to freezing temps.
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Old 03-14-2013, 03:12 PM   #189
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www.atwoodmobile.com/images/waterheaterxt.pdf

The higher temperature was presupposed in the energy calculation.

I'm in agreement that having the hot water tank pull double-duty is a good idea. To meet code the exchanger coil should be double jacket construction to prevent possibility of introducing a long term small seep. The non-toxic anti-freeze amd intermittent use should cover that risk for a long time.

With a closed loop fluid you will need an expansion tank and an air trap and an efficient pump. Oversize coolant lines would help with flow rate restriction as would eliminating any 90 bends, replacing them with two 45's as well as chamfering the connections inside edges and using non-restrictive ball (gas style) valves wherever you need valving...

Making a waste-heat collector to scavenge heat from propane exhaust is a daydream of mine, back in 2007 I got a $40 replacement (bare) RV heater 6-gallon tank to port either water heater or generator exhaust through the internal combustion chamber as a pre-heater for the water tank.

Maybe test the mettle of your metal skills with fabricating a couple of flat-plate radiators? An aluminum plate on a bulkhead with a serpentine coil behind it would give a nice radiant heat effect - screened to prevent accidental burns. If want to be a little sneaky there could be a cold season plate to tuck under carpet in a sleeping area. The possibilities are nearly endless.

We (I!) look forward to hearing more of your plans!!
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Old 03-14-2013, 05:18 PM   #190
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Now you've got me thinking. My floor is made up of 1/8" aluminum plate. How about that for a flat plate aluminum radiator? How can I get the heat to the floor? Maybe a rectangular aluminum tube in direct contact with the floor all around the baseboards? This could have very little resistance to flow with large surface area? We are always fighting the heat conduction of aluminum, but this could be really good. I have 3" of foam beneath the floor,
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Old 03-14-2013, 06:43 PM   #191
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Awww, bummer dude, you rushed the insulation didn't ya? Just kidding, don't throw anything at me! Now the world knows why I'm still lingering at basic stages... Did you isolate the floor from the C-channel & ribs?

Can you pack along a few 2x8 or 4x8 flat panel solar hot-water heaters, a solar panel for a pump and set up randomly to pump free hot water into the trailer?

Coming back from that nice winters mid-day hike to a toasty warm trailer would be very very nice when it was done for free. There is slight danger involved: 'stagnation' is when the coolant water can over-pressure (hot spot boil for a split second to begin with) if the heat has no path out of the insulated box so a safe place for venting or emergency drain-back and/or passive cooling loop should be built in.

Solar electric is 12-18% efficient at capturing solar power, hot water collectors 40% to 55% efficiency. So... anywhere from 750 to 2000 heat Btus per day per square foot of collector even with cloudy skies!

I could see laminating plate together; top/bottom covers and a divider center section to meter fluid pathways, spring loaded clamps to the floor - how about following the contours of the walls and built-ins with a 1/2-inch thick heat plate that is 4, 6, 12 inches deep away from the walls?

Hehehe.... Anyway - how about simpler panels for under the bed mattresses, or a wrap around the dinette area, or the entire bathroom floor from serpentine coil router-inset into a sheet of plywood?

Edit: Note the Atwood literature linked above (board glitch, good link address) states input to the 6-gallon heater is 8800 Btu, and 10000 for the 10-gallon, the fuel to hot water calculations with draw-off can be calculated...
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Old 03-14-2013, 11:04 PM   #192
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Have a hard time getting my head around solar heat in an RV just due to the size of collector and the amount of thermal mass required to store it. Thermal mass = weight so I want to focus on minimizing losses and simplifying and quieting operation. I did realize one cool thing. The rearmost 7' of the floor is not insulated directly beneath it since that is where the grey tank and plumbing go. It would be possible to attach heat track panels http://www.pexsupply.com/Wirsbo-Upon...anel-2111000-p to the underside of the floor to heat the bathroom floor and part of the hallway. It would also warm up the area around the tanks. There's 1 1/2" to 3" of insulation surrounding the bottom and sides of the tanks so the heat would be trapped in there. If it didn't heat the bathroom enough, maybe a toe kick heater with a switch that turned on the fan could provide on demand heat as needed there.
Here is a pic of the floor facing the rear pre shell.
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Old 03-16-2013, 02:13 PM   #193
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I'm not being a crank trolling for unwarranted effort on your part - I think the youngin's & friends would be impressed by a 'green' trailer that wasn't rotting flooring... I know I would be

Sounds like providence & perfect place for reflective insulation to get extra heat bounce up (only thing reflective insulation excels at) leaving some air space around the hoses. Don't need 70F tank water ... Also a good time to located a temperature sensor/aquastat where you foresee the hotspot. EDIT: something will have to safely modulate floor temps to keep the kiddos hopping like barefoot-on-asphalt in the summertime!

On the thermal mass - free is free, if the extra warmth has dissipated in twenty minutes then it must be an Airstre... umnn, then it must have saved some coin by not running the furnace.

Remember to add-in the hassle factor and TV mileage when getting tanks filled. If you can harvest 33% of 750 watts sun energy on an overcast day even a quickee 18-inch by eight-foot collector can harvest 3000 watts of heat. Think the awning reel mechanism can pull double duty by nesting a collector there for travel?

I mentioned having them separate from the trailer to keep them from shading trailer and gaining the ability to relocate to suit the site. Or conversely (equal opportunity tinkering) shade the whole blinkin roof and radiate summer sun away into blue-sky. Just doodling here, apologies.

Or one could also make a Porsche-style whale-tail spoiler wing for the back of the AS that cleverly doubles as a parabolic solar concentrator.
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Old 03-19-2013, 08:58 AM   #194
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Atwood water heater heat exchanger?

I am still struggling to figure out the efficiency of the heat exchanger in the so equipped Atwood water heaters. I found something that said that when it is hooked up to an engine coolant system (in a motorhome) it will be able to get the water in the tank up to about 130 degrees after several hours of driving. This makes me think that it is a pretty small heat exchanger and may not be as useful as I would hope in the opposite direction. The pictures look like it is just a short pipe. http://www.atwoodmobile.com/manuals/...2011.19.07.pdf

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I would like to use that loop as a hydronic heater but it would be important to know how much heat could be exchanged. For example, what would be the temperature increase of water flowing through it at a given rate and a given temp of water in the tank?
Tim
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Old 03-19-2013, 09:04 AM   #195
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heat exchange loop

Here is location of the information about the engine coolant heat rate.
Atwood Water Heater Troubleshooting - Pilot
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Old 03-20-2013, 05:32 PM   #196
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Baseboard radiators seem like the way to go for radiant heat. 500 BTU per linear foot and no fans.
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