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Old 01-11-2010, 09:59 PM   #71
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Not enough surface area...

It is becoming fairly clear that unless I can keep the heat loss values really low in my Airstream that I will not be able to have enough surface area of floor to sufficiently heat the space with radiant floor heat alone. While I am still not sure exactly what the answer to my original question in this thread is regarding the heat loss of my Airstream it is likely to be a bit too much. I may still decide to go ahead with some heat loss testing using a watt meter but I do not know yet.

Switching to a different type of radiant surface may still be OK but I did not really want to use an approach where the surfaces were small and tightly concentrated. I wanted the effect of very evenly distributed radiant heat. Frankly if I were to go with a tightly concentrated heat source I might like to go with one or the other of these two products:

http://www.boatownersworld.com/dicki...aces_p9000.htm
Newport Solid Fuel Heater. Accessories are ONLY sold with the purchase of a heater..* Manufacturer: Dickinson Marine

Or maybe even one of these:

Traditional Cast Iron Marine Stoves by Navigator Stove Works,Inc.

As far as complexity and cost issues are concerned I think that I could develop a very cost effective implementation for in floor radiant heating as long as I keep things very simple. The design and the principles involved need not be simple for this to be possible though. I happen to very much like simple but profound solutions to problems.

Regarding heating enough hot water for a radiant heating system I believe I mentioned somewhere in this thread that I was willing to consider a tankless water heater mounted outside. I like the following unit:

Eccotemp L10 high capacity battery and propane powered tankless water heater

Notice that it is cheaper than a typical 10 tank type water heater. One problem that I have run into in my research regarding tankless water heaters is that there can be a problem when using them for radiant heating in that the input temperature might not be very much different than the output temperature when you are recirculating water for heating. Eccotemp told me that could be a problem with the unit above because the overtemp circuit might turn the system off if the input water temp gets to around 105 degrees. Most of the information that I have seen about using a tankless water heater for hydronic heating suggests that a holding tank is necessary. This seems to me to somewhat defeat the idea of having a tankless water heater.

Well I have not given up the idea yet but my enthusiasm has gotten a bit damp...

Malcolm
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Old 01-12-2010, 10:06 AM   #72
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Originally Posted by malconium View Post
Well I have not given up the idea yet but my enthusiasm has gotten a bit damp...

Malcolm
I can understand that.

Here's something else to think about—what is the expected life of an RV water heater? If used for heating the trailer, wouldn't that (1) violate the warranty, and (2) shorten the life of the unit, perhaps significantly? Some of the water heaters work well for years, others are always trouble.

One option with water heaters is a dual fuel unit—it can run on electricity or propane. Propane heats water much faster and, therefore, the question arises whether the electric element would provide enough heat for a hydronic system. The advantage for an electric option is you are using a campground's electricity rather than your propane.

My suggestion is to go investigate RV's with hydronic heating so you can see it in operation. That may give you some practical tips.

Gene
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Old 01-12-2010, 10:48 AM   #73
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Malconium
Prehaps your dampened enthusiasum is trying to take too big a step the first time you try. If you stick to a simpler system and it only produces enough BTU's to be comfortable down to say 30 deg , that still may represent 90 percent of your camping needs. by leaving the original furnace in to help when you are below freezing it would only be used 10 percent of the time and eliminate the tank freezing problem , again making the system less complex. 12v tank heaters that run off the TV would solve the intransit freezing of tanks. A closed loop antifreezed radiant would also solve the intransit question.

To address the original question , trying to calculate heat lose in an Airstream by formular would be a daunting task. I feel the only way you can come close is with field testing most likely with electric heat as it is 100 % efficient , which eliminates another unknown. I seriously doubt that any RV hot air furnace is 85% efficient , more like 70% at best.

Good luck with your quest , it's a very interesting topic.
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Old 01-12-2010, 12:11 PM   #74
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I wouldn't worry too much about the emissivity of aluminum. You can always paint it if you care enough but despite all the pr crap most of the heat in a so-called radiant system is a result of convection, not radiation.

With a tankless you're going to have to modify controls which isn't something that I'd recommend unless you have considerable experience with that sort of thing. For hydronic, a boiler really works best. There are units out there that don't have fans, in the size you need, like these:

Sentry Gas Boiler

But they're not really suitable for an RV, because they're not compact, use a vertical flue, and depend on indoor combustion air. Maybe you could make it work especially if you're contemplating a fixed or semi-fixed install - the boiler could go in a little hut separate from the 'stream.
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Old 01-12-2010, 03:25 PM   #75
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My latetest thinking...

Here is what I am currently thinking of doing:

1.) Install a 10 gallon Suburban water heater that runs off of both Propane and electric. Something like the following model:

Suburban SW10DE Direct Spark and Electric Water Heater 10 Gallon Trailer Camper RV

The LP input is 12,000 BTU and the electric input is 6,000 BTU. I am not at the moment sure if both LP and electric can run at the same time. I am hoping that they can. That would give me a maximum potential of 18,000 BTU of input providing of course that I am plugged into shore power.

2.) I will still install radiant heat PEX tubing in the floor. I will probably use aluminum fins and will likely space the tubing in the range of 6" to 8" on center. I will have only about 140 square feet of exposed floor. Part of the reason for still doing this is that I have already made several provisions for this with the way I have installed my interior walls and roughed in cabinets. It will be easy to do so I am going to do it. I will also consider doing some tests with it both before and after putting the finish floor in place. I have a hand held infrared thermometer that I would like to try taking readings with in various parts of the system.

3.) For additional BTU output capacity I think I will make provision for two of the following single radiator/fan units.

http://www.boatownersworld.com/dicki..._air_heate.htm

Here are the specifications:
http://www.dickinsonmarine.com/Manuals/Radex-2008.pdf

They are rated to be able to output as much as 12,000 BTU each. They have a 12 volt fan that draws less than one amp of current. I might initially just plumb and wire to the install locations until I get a better feel for what the floor heat will do by itself. My thought is to install one of the units in the back bedroom and the other under somewhere in the front. They probably would be capable of heating the entire space by themselves for most conditions.

I think I will set up to have 3 hot water loops driven by the one pump that I have on order. One loop will go to the floor and the other two will each go to one of the Radex units. I will install a valve on each of the 3 loops that I can use to adjust the balance of the flow. I still am intending to do the system as an open loop system with potable water throughout.

I still intend to leave out the foil insulation over my holding tanks with the thought that the bottom level of sub-floor should be able to radiate enough heat downward to keep the tanks from freezing. Each of the waste tanks has about 10 square feet of floor above it and the fresh water tank has about 20 square feet of floor over it. Even if I only get 10 BTU per square foot of heat going downward that seems like it should be enough. What do you all think?

I think that I could plan to run the water heater while I am driving and set the thermostat to maybe 55 degrees to keep some heat flowing in the system if it is really cold outside.

One question I still have is whether or not an expansion tank and air valve are needed. My guess is that will not be but I have wondered where the expansion of the hot water in a 10 gallon water heater goes in a normal potable water plumbing layout. Does a typical water heater somehow take care of that?

Malcolm
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Old 01-12-2010, 05:08 PM   #76
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I had TWO posts to this thread fail from "expired token" syndrome - loosing text, etc. so here's another try...

I plan to have baseboard style heaters as well as a radiant panel in the sleeping area. Three loops/zones sounds about right. Please read this site for a peek at someone else's RV hydronic work.

I really want to discourage you from using a RV tank water heater. Use this to see the BTU input to raise 10.6 gallons of water 90° or 100° (the 'recovery test' specs vary) and you will calculate 65% heat transfer efficiency, and 56 hours minimum run time from a 30lb tank of propane.

Even the $200 75000btu tankless water heater linked in above is calculates to 80% efficient (1.6 gal raised 77F = 1010BTU times 60 minutes divided by input 75000 btu) and something like the Takagi 140,000 BTU T-K Jr that has a proportional modulating flame where endless loop water just gets enough heat applied to maintain the set point would be a huge energy savings.

About now we should hear about RV qualified tankless heater versus residential style but our Airstreams with good axles are the Cadillacs of the fleet and ride smooth enough so its almost a moot point if intelligently installed and maintained, the liability and insurability of the Suburban tank style heater as discussed is an issue when one changes it into a constant-duty device versus intermittent.

Expansion tank and air valve? It could be as simple as a blind vertical pipe "T'd" onto the main line that holds an air cushion and collect bubbles as the fluid passes through with provision to manually renew or discharge the air pocket, or a 2-gallon Hydronic expansion tank off ebayfor $20 or $30...
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Old 01-12-2010, 07:12 PM   #77
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Quote:
Originally Posted by malconium View Post
Here is what I am currently thinking of doing:

1.) Install a 10 gallon Suburban water heater that runs off of both Propane and electric. Something like the following...
i mentioned this EARLY in the thread but will repeat it here...

there is NO ADJUSTABLE THERMOSTAT on the direct spark dual mode suburban water heaters...

they come PRESET to 130 F and cannot be adjusted.
_________

yes one can use the gas AND electric element together, this helps with recovery as hot water is used...

but don't combine to make HOTTER water.

the temp/pressure release valve will DRIP if the water remains at full HOT...

it may be possible to REMOVE the oem SEALED thermostat, but this would obviously void the warranty.

pilot light models are still available with an adjustable temp control, typically these are NOT dual mode units.

Quote:
Originally Posted by malconium View Post
I have wondered where the expansion of the hot water in a 10 gallon water heater goes in a normal potable water plumbing layout. Does a typical water heater somehow take care of that?

Malcolm
the "expanded" pressurized hot water LEAKS out of the pressure/temp release valve and drips down the outside housing.

this is the NORMAL operation but as the springs ages, collects crud and so on the dripping may vary.


cheers
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Old 01-12-2010, 08:09 PM   #78
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Quote:
Originally Posted by Wabbiteer View Post
I had TWO posts to this thread fail from "expired token" syndrome - loosing text, etc. so here's another try...

I plan to have baseboard style heaters as well as a radiant panel in the sleeping area. Three loops/zones sounds about right. Please read this site for a peek at someone else's RV hydronic work.

I really want to discourage you from using a RV tank water heater. Use this to see the BTU input to raise 10.6 gallons of water 90° or 100° (the 'recovery test' specs vary) and you will calculate 65% heat transfer efficiency, and 56 hours minimum run time from a 30lb tank of propane.

Even the $200 75000btu tankless water heater linked in above is calculates to 80% efficient (1.6 gal raised 77F = 1010BTU times 60 minutes divided by input 75000 btu) and something like the Takagi 140,000 BTU T-K Jr that has a proportional modulating flame where endless loop water just gets enough heat applied to maintain the set point would be a huge energy savings.

About now we should hear about RV qualified tankless heater versus residential style but our Airstreams with good axles are the Cadillacs of the fleet and ride smooth enough so its almost a moot point if intelligently installed and maintained, the liability and insurability of the Suburban tank style heater as discussed is an issue when one changes it into a constant-duty device versus intermittent.

Expansion tank and air valve? It could be as simple as a blind vertical pipe "T'd" onto the main line that holds an air cushion and collect bubbles as the fluid passes through with provision to manually renew or discharge the air pocket, or a 2-gallon Hydronic expansion tank off ebayfor $20 or $30...
The Espar units do seem interesting. I could find websites that described them but I was having trouble finding one that actually listed prices for them. Do you have a pointer that I can check out? Were you referring to these units when you said they were around $200?

In considering the tank tank RV heater I was thinking in terms of the BTU input relative to the BTU capacity needed to heat my trailer. I figured that for the heating loops the return water would only be 10 or 15 degrees colder than the tank temperature. The heater would have to work hard to keep up with the need but it would not have to raise the water temperature 90 to 100 degrees.

Thanks,

Malcolm
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Old 01-12-2010, 11:57 PM   #79
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Malconium,

There are lots of alternatives in fan-forced units if that's what you want.

Rear Air Conditioners RV Van SUV Specialty Vehicles

The amp draw and quiet operation benefits are lost however so scorched air starts to look good again.

If you anticipate having shore power available then there are many choices for boilers. The yacht guys all use electric for hot water. They're small and cheap, install as many as you need and have electricity for.

Marine Water Heaters on Sale

You asked about expansion tanks. Hydronic systems have more water in them than a water heater alone and so the amount of expansion is proportionally greater. Expansion tanks are cheap and easy to install. You want one.
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Old 01-13-2010, 12:06 AM   #80
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No to the $200; that times five is a valid starting point..

Quote:
I figured that for the heating loops the return water would only be 10 or 15 degrees colder than the tank temperature. The heater would have to work hard to keep up with the need but it would not have to raise the water temperature 90 to 100 degrees.
There is no modulation to the flame, either on of off. If thermostat is not satisfied unit will be running full out. At three gallons per minute the tank contents will be exchanged 17 times per hour, heating 180 gallons of water 10°F requires 14760BTU, 15°F requires 22140 BTU!!!

To stay within the 12k BTU heaters range: 12000 * 0.65 efficiency = 7800 BTU / 60 minutes = 130 BTU per minute, which heats 1.6 gallon of water 10°F or 1.0 gallon of water 15°F; Those numbers with a residential recommended 30 BTU/hr/sq ft means 250+ sq ft BUT double that to 60BTU/hr/sq ft for our aluminum cold-sink and single pane windows trailers means 125 sq ft of carpeted flooring... AND the burner running 100% of the time.

Anyhow - I've had a spare new RV water heater replacement tank for a while, I squirreled it away for it directing generator (or the diesel hydronic burner exhaust?) through it to scavenge otherwise wasted heat...

Some more RV Hydronic livability reading: HydronicRVHeating : Hydronic-RV-Heating
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Old 01-13-2010, 01:32 PM   #81
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Quote:
Originally Posted by Jammer View Post
Malconium,

There are lots of alternatives in fan-forced units if that's what you want.

Rear Air Conditioners RV Van SUV Specialty Vehicles

The amp draw and quiet operation benefits are lost however so scorched air starts to look good again.

If you anticipate having shore power available then there are many choices for boilers. The yacht guys all use electric for hot water. They're small and cheap, install as many as you need and have electricity for.

Marine Water Heaters on Sale

You asked about expansion tanks. Hydronic systems have more water in them than a water heater alone and so the amount of expansion is proportionally greater. Expansion tanks are cheap and easy to install. You want one.
Is it your thought that radiators that do not have fans in them would be a better way to go? I was looking at the fan base units as extra heat capacity when it was cold. I do not mind going with some back up radiators but I need to find (or build?) some economical and lightweight units of some sort. The fan driven heaters at about $170 each are pretty reasonable for the extra capacity when it is needed.

I see that the electric marine water heaters for the most part are only 1500 watt appliances. I believe that translates to just over 5,000 BTU. That being the case it would take several units and probably more shore power than my 30 amp system would handle to do the heating. I was interested to see though that a large number of these units had built in heat exchangers through which hot water could be pumped when available. This might be an interesting type of unit to go with if I had a tankless LP water heater. I could have both a heat exchanger and a holding tank without the need for an extra pump or a siphon action. The electric element could be backup for the potable hot water heating only. I could run coolant in the rest of the heating system too if I wanted too. More food for thought...

Malcolm
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Old 01-13-2010, 02:30 PM   #82
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A new-in-box heater core for a 5 or 7 year old car can be had for $25 shipped off ebay - add a one or two low RPM Panaflow 12VDC Fans (also off eBay) and borrow the neighbors rural route mailbox or kids' Transformers metal lunch box and you have a $40 heat exchanger...

Only hitch to using automotive is they are designed for 200°F water and may not be too efficient at 140°F - but its better than being bled $170 for something you could do yourself...



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Old 01-13-2010, 08:45 PM   #83
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How about copper radiators?

I remember that some years back you could buy copper solar collector panels that were made out of copper sheets that were stamped with a pattern of channels and then were soldered and/or crimped together. I have done some surfing but I can not find any source for this type of copper panel. Has anyone seen this type of panel anywhere?

I thought this might be an interesting way to get some extra radiant heat surface above the floor depending on size and price of course. They should be relatively thin so they would not intrude into the living space too much. I might even be able to flex them a bit to get them to conform to the curve of the outer wall or ceiling depending on where I wanted to put one.

Malcolm
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Old 01-15-2010, 03:57 PM   #84
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I have been looking at various combinations using some of the componets that various ones have mentioned. First of all it seems like I need a water heater of some sort that puts out more heat than does a typical 10 gallon tank type water heater. I thought for a bit that using a marine electric water heater with a heat exchange coil built into it would be a good way to isolate potable water from heating fluid. I say fluid because the heating part of the system could be some form of coolant if it was isolated from the drinking water. I thought about using just one heating pump with two solenoid valves that would select what part of the system got water flow when the pump and tankless water heater were running. One valve would let the heating fluid flow through the heating loops and the other would let the heating fluid flow through the heat exchanger in the electric water heater. I thought that I could tap into the heat sensor of the electric water heater for a signal to tell the system when to pump water to that part of the system. In investigating the various configurations I found out some interesting things.

From what I can tell solenoid valves that can handle hot water run close to $200 each. See the following:

Asco-Valve | 2 Way Valve | 8221 Series Slow Closing Solenoid Valves

Adding two such valves is way more expensive than just adding a second hot water pump to pump fluid to the hot water tank.

While the marine electric hot water heaters do not cost much more than a flat plate heat exchanger would there still is the space and weight issue of having a tank full of hot water - as well as the expense. Also it seems to me that having to maintain a tank full of hot water somehow defeats the intent of having a tank-less on-demand water heater to begin with.

I don't really like the idea of having fans involved in my heating system both for noise and electrical consumption reasons. I would rather supplement the heating loops in the floor with radiant panels mounted somewhere on the walls or ceiling. I am leaning in the direction of figuring out how to make something that fits the need my self rather than buying something. I might use some sort of radiant heating fins attached to PEX tubing for this. Perhaps this type of fin could be made to look attractive enough in an exposed location.

Ultra-Fin Radiant Floor Heating System

Maybe there is some type of radiator that I can scavenge from some other type of system. I also happen to have some flexible copper tubing left over from an old project that I might be able to use. Any thoughts on how to build an inexpensive radiant surface for mounting on the the wall or ceiling would be appreciated.

I seem to be gravitating back toward my original idea of having an open loop system where the domestic hot water is taped off of the same plumbing that is used for heating. The system is very simple and the number of components is reduced. If I use an outdoor tank-less water heater that has freeze protection and consider letting my heating system run at least some while on the road when it is cold I should be able to avoid needing coolant in my system. The unanswered questions at this point are:

1.) Which tankless LP water heater to use? This issue also involves figuring out a way to get around the potential problem of having the water heater shut down if the input water temperature is too high. The front runner right now is the following unit:

Eccotemp L10 high capacity battery and propane powered tankless water heater

I have been told though that it might shut off if the input water temp reaches about 105 degrees.

2.) Where to find a suitable mixing valve to temper the heat of the output for the domestic hot water part. That is an item that I have not yet found and priced.

3.) Identify an appropriate type of thermostat and pump controller for running the system. I might need to have some sort of temperature sensors on the radiant surfaces - at least the floor. That is unless the wall mounted radiant surfaces can run at the same temp as the floor. What I am concerned about is keeping the floor from getting too hot.

4.) Determining what type of pressure and temperature gauges to use in the system. I would love to find some sort of monitoring panel to which I could attach electronic sensors such that I could centralize control and monitoring of the system. I need to find something that is cost effective though.

5.) Find a specific expansion tank to put in the system.

Any further input would be appreciated. Once I get all the details sorted out I want to start another thread to detail the progress of the installation and testing.

By the way the hot water pump that I ordered just arrived today and it is a nice little unit. One very interesting feature is that it can run on voltages from 8 to 24 I think. Also it has a flow rate adjuster. The brush less motor has an estimated lifespan in excess of 50,000 hours at 12 volts. The company that I bought it from was very helpful on the phone and shipping was very quick too. Take a look:

East Coast Solar :: Laing D5 VARIO Bronze PV-Direct Circulating Pump $169.90

Malcolm
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