Questions about heat in floor

[justduck]

The basic plan of the floor is a 2x3 steel frame. The area of the floor that is walkable, plus the head, will be framed with a 2" height leaving a void of 1". That 1" will have 1/4" plywood on top of the floor framing with hot water tubing on top of the plywood. (the walking area will have 2" of rigid urethane under the 1/4" ply, the rest will be 3") The whole base of the cabin will then be decked with plywood.

It seems that the heat would be more even if there was some kind of heat sink in the void with the tubing. The thing that immediately comes to mind is sand, but that would be approximately 160 pounds of unwanted weight. Any ideas? I am open to advice about floor heat and the whole plumbing scheme in general. I plan to use a water heater/heat exchanger augmented with an Espar. I'll post my plumbing diagram later. I think I have come up with a workable plan, but I'm no expert. This is all one big experiment.

Earl

 

[lblampman]

Earl - Had a more extensive reply, posted & got the dreaded "data base problem" so lost it....
The short version - tubes are cheap - if they are close together wouldn't that make the heat pretty even?

I'm trying to figure out how to take the 170ish degree water from the Espar coolant heater, run it through my water heater, mix it with cold water down to 110? 120? then run that through my radiant circuit back to the water heater maintaining that 110/120 degrees in the radiant circuit water with small heat inputs from the Espar. I'd like to see your plumbing diagram very much. Peter

Mr. Ranger,

I enjoyed following your build thread very much, thanks for posting. When I type out much on these forums I always hit CTL-A and CTL-C to select all then copy all so if the forum software has a hiccup I can just paste (CTL-V) in all my typing again when I get a new reply form back up (guess that would be a bit differnet keys if you're using a Mac).

Also, I know you could use a thermostatically controlled valve for what you're trying to accomplish. They're often used in really nice showers and are made by Moen, Kohler, Delta, etc. Once you set the temp (usually no higher than 110* F) they'll keep it there. Might be a bit pricey but there may be other thermostatically controlled valves out there too that are more mundane (and don't have to have the brand name paid for). Like this one perhaps: http://www.samsclub.com/shopping/na...65&pid=_Froogle&ci_src=14110944&ci_sku=748280

Justduck...sorry for the threadjacking!

Les
Whidbey Island, WA

 

[lblampman]

The basic plan of the floor is a 2x3 steel frame. The area of the floor that is walkable, plus the head, will be framed with a 2" height leaving a void of 1". That 1" will have 1/4" plywood on top of the floor framing with hot water tubing on top of the plywood. (the walking area will have 2" of rigid urethane under the 1/4" ply, the rest will be 3") The whole base of the cabin will then be decked with plywood.

It seems that the heat would be more even if there was some kind of heat sink in the void with the tubing. The thing that immediately comes to mind is sand, but that would be approximately 160 pounds of unwanted weight. Any ideas? I am open to advice about floor heat and the whole plumbing scheme in general. I plan to use a water heater/heat exchanger augmented with an Espar. I'll post my plumbing diagram later. I think I have come up with a workable plan, but I'm no expert. This is all one big experiment.

Earl

Hi Earl,

Have a look at the Unimog camper that Stephen Stewart did in England. A page describing his in-floor heat is here: http://www.xor.org.uk/unimog/mymog/heating.htm.

I would say based on the research I've done for in-floor heating that you do not want a void. Rather most tubing (like PEX) is laid into subflooring that has channels routed out for it (and it sort of snakes back and forth). In fact, in one installation I read about the folks doing it had installed a layer of aluminum over the subfloor and PEX tubing to enhance the heat distribution. Not sure how this plays out with your flooring plan but hope the ideas help.

There was a website that I wanted to share and just couldn't remember...but I finally did and located it again. It's quite in depth, the guy is converting a Greyhound style bus but it's all the same needs. It's at this horribly long URL:
http://www.gumpydog.com/Bus/MC9_WIP...ic_Heating_System/hydronic_heating_system.htm.

Les
Whidbey Island, WA

 

[justduck]

Thanks for the replies.

The major problems that I see in using a tempering valve is that in a closed system there is no way to add cold water without opening a valve to drain off some of the hot water which is obviously not a solution.

A tempering valve will work fine on faucets, so I'm focusing on making the 180* water work in the floor. That pretty much excludes PEX as it will only tolerate that temp for a very short time. I found a 12V magnetic pump rated for 212* that only uses 5W-it's sold as a circulation pump for solar water systems. As I remember, aluminum and copper have an electrolysis problem so I guess it's copper and plywood.

In the past I've built a lot of equipment, trailers etc, for the local river outfitters that have held up well to really hard use, but I built them out of heavy enough material that I knew that they couldn't break them. I've designed the cabin to be much lighter but to be sure it's not under built I'm having a local fab shop put my drafting into Solidworks and do a stress analysis on it. Actual construction awaits their suggestions.

Earl

 

[lblampman]

Thanks for the replies.

The major problems that I see in using a tempering valve is that in a closed system there is no way to add cold water without opening a valve to drain off some of the hot water which is obviously not a solution.

A tempering valve will work fine on faucets, so I'm focusing on making the 180* water work in the floor. That pretty much excludes PEX as it will only tolerate that temp for a very short time. I found a 12V magnetic pump rated for 212* that only uses 5W-it's sold as a circulation pump for solar water systems. As I remember, aluminum and copper have an electrolysis problem so I guess it's copper and plywood.

In the past I've built a lot of equipment, trailers etc, for the local river outfitters that have held up well to really hard use, but I built them out of heavy enough material that I knew that they couldn't break them. I've designed the cabin to be much lighter but to be sure it's not under built I'm having a local fab shop put my drafting into Solidworks and do a stress analysis on it. Actual construction awaits their suggestions.

Earl

Ah, I know better than to post to two folks in the same thread! :wings:

The tempering valve was for Basinranger but you're absolutely correct about not being able to get rid of add-in water from his closed loop...my bad!

Yes, if you're going to run 180* water and use copper then laying a sheet of aluminum over it wouldn't be a good idea. I've acutally only seen that done once so it's hard to tell if it was really effective. With your hotter water and small space I don't think it's going to be an issue anyway.

Looking forward to following your build.

Les

 

[ntsqd]

Heating water (coolant?) from the Espar heater is 180*F? Is the Espar's output temp not adjustable, or is that temperature desirable for some other need that is more important?

Assuming that it is not adjustable, is the water used to heat the floor totally a closed loop with no accumulator tank? If there was such a tank, would the tank's contents be of a low enough temperature to enable using it to temper the Espar's output down to a more reasonable level? Still closed loop, just partially by-passes the Espar.

In place of sand could those hollow glass beads used as filler in some composite construction be used? Assuming that is, that it isn't prohibitively expensive....

Perhaps one of the 'plastic' clad aluminum sheets would disable the electrolysis and also not be too insulative?

I don't know much about this, I've never worked with such a system so I'm tossing out ideas that seem plausible in the hope that one works or spawns an idea that does work.

 

[dzzz]

If you can do only in-floor heat ( I don't think you can), the camper will warm up very slowly. I'm using a very large heat exchanger with a variable speed fan. On high it does 44000 btu, but will normally be run on low speed.

This gives the option of fast warm up with normally quiet operation.

 

[justduck]

The only experience I've had with floor heat is my son's house. The heated water (from a wood fired boiler) is tempered to about 135* where it enters the PEX that is embedded in the concrete floor. The temp of the slab is very comfortable in stocking feet.

I'm thinking the heated water from the engine will heat the water in the exchanger to 180. I suppose I could place a thermostat controlled solenoid in the line from the engine to exchanger, but that would be limiting BTU storage. One possibility would be to use a water to air exchanger (radiator with fan) between the exchanger and floor. With the right formula you could size the radiator/air volume to bring the water entering the floor to about any temp desired - and help bring the cabin temp up quicker. It's really great to be able to bounce these ideas around. Thanks, guys.

Earl

 

[etbadger]

Although a heated floor would be way cool, don't underestimate the simplicity and comfortableness of a well-insulated floor and some 20$ down booties. For us that was plenty in sub-0's outside with an air furnace keeping our van interior at about 65-70deg.

If you do go with a plumbed floor, consider how to detect and repair leaks that may develop on the go.

-e

 

[dzzz]

An expansion tank can be avoided if the radiator is in the loop with the return line always open. In addition the entire system needs to be below the radiator cap.

I'm considering using Espar's thermostat to call for heat, with a temp sensor on the heat exchanger turning the fan on and off. This would behave similar for a forced air heating system.

But with that system I need to figure out how to do hot water only in the summer. I expect needing to run the Espar this way infrequently, as the water heater also has an engine loop.

I don't like the power drain of adding a second pump.

Unicat uses two radiators and under bed heating on their 16' camper. The heated towel bar in the bath is a good idea. They have a mechanical thermostat on each radiator. No central thermostat, I believe.

With Espar don't forget the high altitude sensor. With Webasto they lean out the burner (less btu's always) to keep the unit from running rich at altitude. Crude compared to Espar, but less to break.

 

[justduck]

I don't like the power drain of adding a second pump.

This pump only uses 5w of power.http://www.discountpv.com/solar_water_heating/sid5pv.htm

 

[whatcharterboat]

Justduck, If I can jump in here as well,

I'm not sure about how you get the heat to transfer from the pipes ? or lines? through a timber floor without loosing a fair bit . Won't the wood insulate to a certain degree. I've never done one in a camper before but have done heated slabs when I worked for an electrician in Tasmania. Same principle I imagine.

Also I've done some heated molds before rather than use an autoclave. The problem trying to heat a mold is the same as you are probably facing. We used strands of carbon fibre to conduct electricity the same way an electric blanket would however others were doing a similar thing with heated oil lines. The tricky thing we came up with was to use a blend of epoxy resin and aluminum powder on the outer skin. Then a layer of resin and aluminum granules. If you were to lay up a panel (on a smooth table as a mold) this way then drop the coolant pipe into the granules and back it with a couple of layers of glass matt to keep it all together , then you would end up with a type of formed aluminum heated floor cover panel . Really even heat with maximum efficiency and heat transfer.

Maybe this is overkill or maybe I've just had too much caffeine today.

BTW if you are trying to control heat through 2 separate coolant circuits in parallel you can do this by slowing the flow right down through a valve. Even a simple gate valve will work there. Well it works OK on warmed/heated main water tanks and battery warming pads, etc. anyway. Or did someone already say this???

Now where's that coffee grinder??????
Regards John

 

[TimS]

Sounds like a cool plan. One thing to remember about heat. It will always go to cold. On radiant systems you really need to insulate under the floor or the cold will suck the heat out of the floor quick. I would use 2" foam board. Also, it may end up like others have said that a normal heater with good insulation will suffice.
A product I use:http://www.viega.net/productcatalog.html#modeldetail-group2772655483218
It comes preassembled and folds out like an accordian or seperate.
It folds out and screws to the sub floor. It works good.
With a 3 or 4 way mixing valve, dc pump and some sensors, you could have some nice heat.
80 to 85 degrees is the most you want for water temp. I installed 8000 sgft of this stuff 2 winters ago and the temps of the water is no higher than 80 degrees on the coldest day of the year. Its a 3 story refurbished barn.
Good luck.

 

[dzzz]

Heating water (coolant?) from the Espar heater is 180*F? Is the Espar's output temp not adjustable, or is that temperature desirable for some other need that is more important?

Warming engine coolant is how the temp is selected.

Always having the water heater in the circuit should help reduce stop/starts of the heater. But that won't lower the temp.
The only way I can think of lowering the temp is to run it through a heat exchanger before it enters the floor.