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Old 01-07-2010, 12:01 PM   #15
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Mineral oil and etc.

I can't us mineral oil or antifreeze coolant because my intent with the radiant heating system is to use the same water as is used for the shower and sinks. I was intending to install what is called an open loop system which uses water from the same water heater that is used for other things. One of the posts a little earlier in this thread has a pointer to how this type of plumbing is done. Otherwise I would need to have two water heaters which would add to the overall expense of the system.

When I was thinking about running the water heater while driving I was not so much thinking about pumping water around through the floor. Rather I was thinking about keeping the water in the tank hot so that I had a head start on heating the floor when I stopped. My thought is that if the water is already hot that it should not take all that long to heat up the floor.

I am hoping that water heaters with electronic spark ignition would not have as much of a problem blowing out. Is that true? Do they reignite themselves if the flame blows out? I also wonder how long a tank of water will stay hot in a modern tank type water heater.

Sure I will have to drain the water out of my system if I park for a while while it is cold. Since the radiant heating tubes are part of my hot water plumping I should be able to drain them easily enough. I might even be able to use the hot water pump to help with that. I will have to give that some thought.

As far as complexity of installation goes I agree that installing radiant heating in the floor is a bit more work than installing catalytic heaters or some other form of propane heater. I do not think that it will be more expensive however. I need to have a water heater anyway so as long as the one that I pick has enough capacity then that is almost a giveaway cost wise. PEX tubing is not very expensive. I think it runs about $10 per fifty feet at Home Depot and I might need 200 or 300 feet. The hot water pump is probably the most expensive item at about $209. I need a new thermostat regardless of what I do for heat - at least for my AC unit. Sure I need a few other odds and ends but nothing else that is all that expensive. If I do indeed decide to go through with this approach I will have to start a new thread and go into details about the whole job.

Yes I agree that the body ribs are going to leak heat faster than other parts of the wall. I did do something to help minimize that when I installed by reflective foil insulation though. I bought felt at the fabric store and attached strips of it on the ribs before I put the inner skins back on. I do not know how much that will help but it will no doubt help some.

I am still looking for feedback on the heat loss calculations...

Thanks,

Malcolm
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Old 01-07-2010, 12:33 PM   #16
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Unless you run 2 water heaters, one with antifreeze for the floor heat, this sounds like a bad idea to me. If you do not run the system when you are going down the road how will you keep the tubing in the floor from freezing? I wonder how fast the system will make up for running an exhaust fan in the kitchen or bathroom or if the entrance door is opened during a strong wind. Floor heat is very slow in making up for large amounts of fast heat loss. The volume of air in a AS is very small compared to a house. I have floor heat in the mud room and greenhouse of my house that is run off of the domestic hot water heater. Though it works very well I have had many warm, not hot showers if the floor heat is running at the same time that I am showering. Also how will you keep the waste and fresh water tanks from freezing? Not that it can't be done, but I think it's an unproven system with more questions then answers and way too much trouble for what it accomplishes over a conventional forced air system.
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Old 01-07-2010, 01:39 PM   #17
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Unless you run 2 water heaters, one with antifreeze for the floor heat, this sounds like a bad idea to me...
i sure agree.

1 water heater=problems.

sure the modern igniters will RElight (up to 3 tries) and they don't tend to blow out while moving...

also one can typically HEAT the water tank in the am, turn it off and have HOT water ALL DAY, even on the road.

but most of the NEW water heaters don't have ADJUSTABLE TEMP CONTROLS...

which means the water is REALLY HOT without a mixer valve.

using the same water to shower/wash is a clever idea, adds WAY to many issues and complexity.

but then again the entire idea is more complex than needed to heat and predictably a disaster to a huge restoration job.

cats can be 'zoned' and it's common with the furnace or heat pump or cats to CLOSE OFF the rear bedroom.

just heat the front until bed time or 30 minutes prior.

typically there are NOT water pipes or internal plumbing to deal with at the EITHER end of long trailers.

DRAINING?

that's gonna be an issue since leveling/tilting will be needed, OR a blow out valve.

are up planning a compost toilet, wind farm and solar grid too?

i don't think ANY ONE can supply reliable "heat loss" calculations on a vintage unit REBUILT

and without considering the LARGE LOSSES into the metal and out the sides.

one would need to know your EXACT insulation and thermal barrier plan.

cheers
2air'
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Old 01-07-2010, 03:33 PM   #18
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Originally Posted by ventport View Post
Unless you run 2 water heaters, one with antifreeze for the floor heat, this sounds like a bad idea to me. If you do not run the system when you are going down the road how will you keep the tubing in the floor from freezing? I wonder how fast the system will make up for running an exhaust fan in the kitchen or bathroom or if the entrance door is opened during a strong wind. Floor heat is very slow in making up for large amounts of fast heat loss. The volume of air in a AS is very small compared to a house. I have floor heat in the mud room and greenhouse of my house that is run off of the domestic hot water heater. Though it works very well I have had many warm, not hot showers if the floor heat is running at the same time that I am showering. Also how will you keep the waste and fresh water tanks from freezing? Not that it can't be done, but I think it's an unproven system with more questions then answers and way too much trouble for what it accomplishes over a conventional forced air system.
You make some good points. Let me try to address some of the things you mention here...

1.) The tubing will not be under the floor - rather it will be between the sub-floor and the finish floor. The sub-floor will have a layer of reflective foil insulation on top of it and the PEX tubing will be above that. My guess is that this will be enough insulation to keep the pipes from freezing for the amount of time that it takes to get from place to place. The pipes should not be at more risk of freezing than any other pipes in the trailer. Also if I am traveling where it is exceptionally cold all I would have to do is to run the heating pump for a few minutes at each rest stop to warm them up. I could also leave the heating system on with a lower thermostat setting that would turn on the pump from time to time to keep the interior at a reasonable but low temperature. For example I could set the thermostat to something like 55 degrees. This would help keep other things in the trailer from freezing too by the way.

2.) It is my understanding that a radiant system could very well be comfortable again after loosing warm air faster than a forced air system simply because of the radiant effect. How quickly does your mud room feel comfortable again after you close the door to the outside?

3.) I think it would be pretty easy to turn off the floor heat for the short amount of time that it takes to take a shower. I will want to make a point of having an easily accessible on/off switch for this anyway. Probably if I pick the right thermostat I can just turn the heat off there.

4.) My fresh water and waste tanks are all directly under parts of my floor. My intent is to leave out the reflective foil insulation over these areas and put it instead under the holding tanks. I am anticipating that there should be just enough heat leaking downward in these areas to keep them from freezing.

5.) This is not really an unproven system. It is my understanding that most high end motor homes use hot water heating systems of one kind or another. Perhaps most of them use the little radiators and fans but I do know that some of them have tubing in the floor. I was told that by a VP of Precision Temp. Of course radiant heating in the floor has been around for a very long time. My first exposure to it was in the late 70's when I built it into a house that I designed and built for my family. At that time we used copper tubing because PEX was not available.

Malcolm
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Old 01-07-2010, 03:56 PM   #19
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Originally Posted by 2airishuman View Post
i sure agree.

1 water heater=problems.

sure the modern igniters will RElight (up to 3 tries) and they don't tend to blow out while moving...

also one can typically HEAT the water tank in the am, turn it off and have HOT water ALL DAY, even on the road.

but most of the NEW water heaters don't have ADJUSTABLE TEMP CONTROLS...

which means the water is REALLY HOT without a mixer valve.

using the same water to shower/wash is a clever idea, adds WAY to many issues and complexity.

but then again the entire idea is more complex than needed to heat and predictably a disaster to a huge restoration job.

cats can be 'zoned' and it's common with the furnace or heat pump or cats to CLOSE OFF the rear bedroom.

just heat the front until bed time or 30 minutes prior.

typically there are NOT water pipes or internal plumbing to deal with at the EITHER end of long trailers.

DRAINING?

that's gonna be an issue since leveling/tilting will be needed, OR a blow out valve.

are up planning a compost toilet, wind farm and solar grid too?

i don't think ANY ONE can supply reliable "heat loss" calculations on a vintage unit REBUILT

and without considering the LARGE LOSSES into the metal and out the sides.

one would need to know your EXACT insulation and thermal barrier plan.

cheers
2air'
Let me see if I can address some of the valid concerns you raise here...

1.) I fully intend to have a mixing valve on the output of the water heater where it connects to the domestic hot water part of the plumbing. That way I can set the temperature of the water heater higher if I find that it helps with the heating part of the system.

2.) I am not sure I understand your comment about using the same water to shower/wash. Was that what you mean or did you mean shower and heat? I hope that I did not convey the idea that I intended to reuse gray water.

3.) Actually it would be very easy to create zones with my radiant heating system. All I would have to do is have two separate branches of the heating loops running from the same pump. If I just have a simple manifold with two valves on it I can adjust the flow so I have whatever balance I want between the two zones including turning one off. I might do that for the adjust-ability part. Because radiant heating is a little slower to respond to changes I think it might be better to run the whole system all of the time - just with the right balance between zones.

4.) The original plumbing in my 31' unit started at the street-side rear corner with the water inlet. The water heater was under the head of the bed in the rear bedroom. It is true there was no plumbing forward of the kitchen but the plumbing was definitely strung out over about 2/3rds of the length of the trailer. If I recall correctly my service manual says something about tilting the trailer as part of the draining process. In my new arrangement the inlet will still be in the rear corner but the water heater will likely be under the kitchen sink. The regular part of the plumbing should not be any harder to drain out than the original was. I do agree that effectively draining the whole system does have some challenges but I think I am up to that. I do have an air compressor if it turns out that this would help and it seems like adding a blowout valve somewhere in the system might be a good idea. I will also give some thought to placing my hot water pump to see if there is a way as to be able to drain the heating pipes with it.

5.) Regarding the heat loss calculations I am not asking someone to try to second guess what it might be for my unit. I am just asking if anyone besides me has attempted to calculate heat loss for their trailer and has data to share.

Thanks,

Malcolm
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Old 01-07-2010, 04:36 PM   #20
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Malcom: I do radiant floor design and heat loss calculations for a living.
Post the number of windows and sizes and i can run the software program. How much insulation are you putting under the floor? I expect you will need hotter water in the floor tubing system than you will want in your domestic system. Generaly we see 130-140 degree temps in this type of install. Check out UPONOR'S quick trak radiant system. You may also think about using a small plate type heat exchanger for the radiant heat. It would eliminate the need for bronze pumps and you would not be running high pressure in your radiant lines. Add glycol to the radiant and not worry about freezing. I have not replaced the belly pan on my camper because i want to do radiant also.(someday)
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Old 01-07-2010, 05:08 PM   #21
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Malcom: I do radiant floor design and heat loss calculations for a living.
Post the number of windows and sizes and i can run the software program. How much insulation are you putting under the floor? I expect you will need hotter water in the floor tubing system than you will want in your domestic system. Generaly we see 130-140 degree temps in this type of install. Check out UPONOR'S quick trak radiant system. You may also think about using a small plate type heat exchanger for the radiant heat. It would eliminate the need for bronze pumps and you would not be running high pressure in your radiant lines. Add glycol to the radiant and not worry about freezing. I have not replaced the belly pan on my camper because i want to do radiant also.(someday)
Thank you for stepping up to the challenge...

The windows are the following sizes (includes vista windows):


Size Quantity Living Room 16x24 2
44x24 1
32x9 6
32x22 3 Kitchen 30x22 1 Bathroom 18x20 1 Bedroom 30x20x 2
30x9 2
42x22 1
I do also have 3 Fantastic roof fans that are perhaps as large as 13"x13".

I have 3/4" Polyboard for my subfloor instead of 3/4" plywood. I am intending to put reflective foil insulation on top of that under the PEX tubing. There will be 1/4" plywood above the PEX with a layer of seamless vinyl flooring. The walls and roof are also insulated with foil with strips of felt on the ribs under the skin to provide some thermal break.

Do you have what you need for the rest of the dimensions?

I had considered using a heat exchanger but thought that would add more extra cost than I wanted. I would also need a second pump. I was having trouble finding a suitable pump that would work with 12 volts by the way. The one I found is from a solar energy systems supplier. I am open to suggestions as to sources for heat exchangers and pumps. I will also check out the system you mentioned.

I was thinking of setting the water heater temp to something in the 140 degree range and using a mixing valve to lower the temperature of the domestic hot water part to prevent scalding.

Thanks,

Malcolm
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Old 01-07-2010, 06:41 PM   #22
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How much weight will this system add to your airstream?
Andy will warn you your rear bumper will be dragging on the road after the rear separates!
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Old 01-07-2010, 06:47 PM   #23
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Ouch, this is gonna hurt.

How about measuring the thermal loss?

If you are lucky enough to have a time period where the outside temp is fairly cold and constant you can use small electric heaters to measure the thermal input to keep the trailer at a consistant temp. Use a Kill-a-Watt meter to totalize the watt/hrs over the time period and record the temperature difference between the inside and outside. You then have KWH/Delta degree constant for your trailer. KWH's convert to BTU's and you have a handy way of calculating how many BTU's it takes for a given temp difference. It's not perfect but it will give you something to go with...

If you use 1200W over 6 hours = 200WH = .2 KWH =700 BTU
for a 40 degree differental (20 outside, 60 inside)
700/40 = 17.5 BTU per delta degree F

If you have a 15,000 btu water heater and have 30 degrees of temp gain needed (40 outside and you want 70 inside) you need 525 btu (17.5 X 30)and have 15,000 available so it would run 525/15,000 =3.5% of the time

I have no idea where all of that came from...
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Old 01-07-2010, 07:49 PM   #24
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A common misconception is that most heat is lost when you open a door (the mudroom example). Actually some cold air comes in and mixes with the warm air and you feel the difference right away on your skin. But the mass of the room, ceiling, floor and furniture hardly change at all (unless you leave the door open for a very long time). Air is a poor conductor of heat (or lack of heat, something we call "cold"); water is a fairly good one (1,000 times better than air I seem to recall), oil is better I think.

Radiant heat warms objects and is much more efficient than forced air. When you turn on forced air, you feel the warm breeze right away, but the objects in the room take a long time to heat up and the furnace has to run a long time. With radiant heat, the objects get warm and stay warm; the heat is even. With forced air, temp ranges are pretty wide.

The more and thicker objects in a room, the more heat will be even and stay fairly constant. Same in reverse for a refrigerator—a full one will stay cold even if you open the door a lot and stare at the food trying to find something to eat.

The only time is appears to take longer to warm a room with radiant hot water is when you start from cold. An advantage of hot water heat is you can run the tubing through the areas where the pipes are rather than have to open the cabinets as is often done with forced air.

One thing for sure, is to make sure you don't use up all the water. And you need a valve that will purge air from the water or the gurgling will become annoying. And an expansion tank. But more power to you Malcolm—trying difficult things is a great thing to do.

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Old 01-07-2010, 07:57 PM   #25
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More food for thought...

What you suggest sounds like a reasonable idea. Does a Kill-a-Watt meter log the total power consumption for a given period of time? I would guess it would have to if it was going to take into account on and off periods for something like a heater.

I think I can manage the cold part but there are a couple of variables involved right now that will go away in time. For one thing I have not yet installed new rubber seals around the windows and doors. I know that some of them will be quite leaky. I guess I could tape them up for now though. The other variable is that the center panel of my inside skin is still off. I have to finish connecting my DC wiring to the new power panel before I put that panel in place. Maybe I could just tape a piece of foil insulation over that place for now. I don't have the foil on my floor yet either.

I will see what I can do. Any thoughts on the best place to buy a Kill-a-Watt meter?

Thanks,

Malcolm
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Old 01-07-2010, 11:01 PM   #26
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Malcolm, I really like the idea of radiant heat. I designed and installed a system in my house which happens to be a log house. I spent way too many hours under the house running tuning, both pex and copper. My heat source is a wood boiler outside by the wood shed.

I agree with kittrick, use a water to water plate heat exchanger and run antifreeze in a closed loop system. This will solve a bunch of issues with both freezing and keeping water in your tanks and domestic system and air in your radiant system. Even with the open system you are thinking about you will need a separate circulating pump as your domestic pump won't run unless a tap is open. With proper placement of your heat exchanger you might be able to take advantage of thermo-siphon and just use a single circulating pump.

An interesting set up would be to plumb the floor heat water directly to your water heater. Install a 5 or 6 gallon well insulated tank for domestic water and heat it with the plate heat exchanger. You now have two separate systems with your existing water pump providing domestic water and a circulating pump for floor heat with the only link being the heat exchanger. You can run the water temp hotter with a mixing valve on the domestic tank that will effectively give you more gallons from a smaller tank. During the summer you just valve off the tubing in the floor and the domestic water is heated through the heat exchanger rather than directly. There will be a small efficiency loss through the exchanger but I think it would be minor in the grand scheme of things. When plugged into 110 an electric element in the water heater could take care of both systems. I don't know what the electric capacity vs propane is on the new water heaters. By the way I heat my domestic water at home with a heat exchanger and thermo-siphon.

Like Gene said radiant heats objects not air. The aluminum inner skin will heat and cool rapidly, the cabinetry and upholstery not so fast. The logs in my house for example take a long time to heat soak from cold.

The BTU output of the forced air heater would be a good starting point for the heat loss of the trailer. After all heat is heat whether air or water, comfort is the big difference. I don't think you will see any big efficiency gains or losses. A few degrees up or down outside will have a greater effect. If you want a faster warm up then run more tubing. The greater the volume of water running through the floor, the more BTUs of heat will be transfered and the faster the warm up. The more important issue will be the recovery time of the water heater. Will it keep up with the heat being removed in the floor? I run my boiler water through a mixing valve so the floor supply is 130 and the return is about 100 to 110. It's not exactly like heating water from your tank at 50 or 60 to 110 for your shower.

As far as holding tanks go I don't know if running water over the top will bleed enough heat down to do any good. I would suggest running a tubing loop under the tank and cover the bottom with an insulation blanket. Any excess heat will wind up going up into the trailer where you want it.

Just a few things to think about but I think it is doable.
Good luck, Dan
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Old 01-08-2010, 12:35 PM   #27
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One thing for sure, is to make sure you don't use up all the water. And you need a valve that will purge air from the water or the gurgling will become annoying. And an expansion tank. But more power to you Malcolm—trying difficult things is a great thing to do.

Gene
I can see that an expansion tank and air purge valve would make sense for a closed heating loop. Are they really necessary for an open loop systems such as what I am proposing here?
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Old 01-08-2010, 12:51 PM   #28
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A closed loop system can be open to the atmosphere requiring no purge valve or expansion tank. The water merely circulates with no pressure other than from it's own weight. The open system you are proposing requires pressure and expansion relief as the water heats assuming there is a check valve to prevent hot water from flowing back into your water tank.
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