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Old 11-23-2020, 10:11 PM   #1
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Anyone use infloor hydronic heating?

LOL, of course they have, thought that title be funny given so many asking the same questions over and over.. I just read through many threads on it, however many seem to have a fairly complex setup. I'm wondering if I can do something very simple, and even try to use thermosiphon and not even have a pump. Given one can't change the floor later, this needs to be decided on early.

My Nautibus is a trailer, not a motorhome, so I have no need to use engine heat or heat it while moving, it is basically a tiny house. It is also pretty small.
And from what I understand, you don't want the heating tubing to run under any cabinets or bed, which leaves very little floor space to heat! Basically my floor plan will have a kitchen floor area to heat, a narrow hallway next to the bed into the bathroom.

So what I'm wondering, instead of snaking tubing around, just put in some parallel tubing and have a heat exhanger under the floor that has one end with the cold return, one end the hot, and perhaps a small tank that is raised up and feeds into the tubing. OK, let me draw this..lol excuse third-grade drawing, i am at shop with basic computer..

The heat exchange could be anything, not critical right now, now I need to determine how to setup the floor. I am thinking maybe I should try it before putting anything real flooring in or cabinets, etc, and see if it works. On the other hand, i've spent too much time on this project already...could just punt and use air heater and call it good, but that isn't my style.
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Old 11-24-2020, 04:17 PM   #2
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Not sure if there is enough thermo siphoning going on with that low of height differential.. also the water temp should be pretty consistent high over the full travel in the floor. A small dc brushless pump as in a Prius works really nice but most water heaters come with a pump integrated.

Our webasto does fine for our whole bus .. three loops parallel.

I choose the tsl17 because of it low power draw... Alpine 44, member here, has a military style heater with peltier or better seeback elements that generate electricity for the unit.

Johan
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Old 11-24-2020, 08:01 PM   #3
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Quote:
Originally Posted by joeblack5 View Post
Not sure if there is enough thermo siphoning going on with that low of height differential.. also the water temp should be pretty consistent high over the full travel in the floor. A small dc brushless pump as in a Prius works really nice but most water heaters come with a pump integrated.

Our webasto does fine for our whole bus .. three loops parallel.

I choose the tsl17 because of it low power draw... Alpine 44, member here, has a military style heater with peltier or better seeback elements that generate electricity for the unit.

Johan



the TSL-17 i have in my red bus modulates whereas the VVKB I have in the DEV bus (45,000 BTU) is on / off at the coolant setpoints.. I like the modulating feature of the TSL, sems to me more efficient to have it run almost continuously vs kick on and off
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Old 11-27-2020, 01:10 PM   #4
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The idea for passive flow is not likely to work well because of how long it will take to xfer the heat. And a small pump is not too big a deal really.

But after looking over many solutions, I think the best approach for a small space is to use electric in-floor heating. It is really simple and heats up evenly, much thinner and lighter weight. Can always run a generator if not enough solar.
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Old 11-27-2020, 07:36 PM   #5
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Maybe nice, since you are into serious experiments, to make hydronic floor heat with a heat pump.. more efficient... Add a supercooler / heat exchanger to your mini split.

I always wanted to use a heat pump for our electric car instead of the resistance heater.

First draw the high temp with a fan coil and then condense further with the floor.

Depending on your square footage you could go freon all the way and run copper tube in the floor.

Johan
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Old 11-28-2020, 04:06 AM   #6
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I did consider a heat pump setup, and putting the condensor coils in the floor, as I have a lot of them and they come free with broken/free fridges... But it seems complicated and the heat varies as it passes through the coils, so makes it difficult to get right, whereas a wire heats up the same everywhere. I am reconsidering it though.

I will have a lot of solar, but in january, maybe not so much. A little 800watt generator should fill batteries in afternoon, so can heat at night via battery and keep it quiet, whereas the compressor and fans will be running for a heat pump.

I was doing some basic figures, the trailer is only what <200sf, seems to me a 1500 watt a/c and heater should do it? A normal fridge compressor is not that big, like 200 watts. I do have a lot of car a/c compressors, those are quite powerful, and can easily be driven with a 12v motor. I did get that free 2hp from the lawn motor (about 1500 watts).
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Old 11-30-2020, 06:22 PM   #7
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Oh man, you got me going on this heat pump condensor coils in floor thing. Given the heat pump can heat at half the electrical draw as resistance wire, seems worth the effort if running on batteries off-grid.

I took the condensor from the big commercial freezer to the recycling place, so I could not measure the lengths of the tubes, but I still have the evaporator, and it looks to have 100ft of 3/8 copper tubing. With that length of tubing I could fill the kitchen floor area, but not the hallway or bathroom. I took apart the rather big compressor that was in this freezer, has a scroll compressor and I'm guessing about a 2 or 3hp 3-phase 220vac motor. So maybe with a 5hp car compressor I could use a bigger condensor.

While this is interesting, seems to me it makes more sense to use a heat pump to either just output hot air like they normally do switching the a/c to heat, or use in floor water and use the condensor coils in a heat exchanger to heat the floor water.

The issue with heat pumps is they don't work when the outside temp gets close to freezing, as the evaporator has no heat to pump anymore. In this case, one needs another method. With water in floor, one could have propane to heat the water.
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Old 12-05-2020, 12:08 AM   #8
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Alright, got another thought here..i was looking at the cost of copper tubing, and for a small space, it really isn't very expensive compared to PEX. Lowes has 10ft 1/2 copper tubing for $10, so 100ft for $100. And so if one uses copper tubing the idea of passive heating might work. And since I have 100ft of 3/8 tube from the freezer evaporator, I can just use that, break it down into individual copper tubes and resolder them into a flat configuration.

Also a heat pump can work in freezing temps if you heat the outdoor evaporator. It is not going to be as efficient, but it would work, probably the same heat electric resistant heating would.

Just wanted to throw out some additional ideas, I might test out the passive heating idea.

I should also mention that the floor in the Nautibus is some 2in polyiso foam panels with metal cladding. The metal is coregated, so it already has some channels in it to tubing, although I think even 3/8 is too tall, and I am wondering how I can flatten it?
Any try to take a round copper tube and make it into an oval? This would be better for floor heating and it increase the surface area contact to the floor above.
and as one might notice, radiators use flat oval tubing.

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Old 12-05-2020, 07:39 AM   #9
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I am sure you can rig up a bank of rollers to push and pull the copper tubing thru....

Another thought would be to make a tube in tube or tube in hose heat exchanger and go to more conventual water / coolant floor heating.

Regarding trailer and no engine heat... I saw once a Volvo military Tp21 duggar that had coolant take off for the hydronic tent heaters. If you would go coolant then there is a backup ..

We use for our home floor heating the sanden CO2 heat pump hot water heater.

The hot water heatpumps that are readily available work sometimes with the condenser right in the tank.. maybe easier to adapt that to you heating quest since it is set up for high temps already...and also in the right power range.

I have not seen them in the scrap but I live in a small town so you might be more fortunate.

Johan
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Old 12-05-2020, 07:51 AM   #10
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I once made a heat exchanger by putting 2 automotive A/C evaporators in a styrofoam cooler and filling with water and a bit of antifreeze.. one evaporator had freon in it and the other had water. (I was playing with a water chiller idea).. and it actually worked pretty well.. im not saying ride around with a styrofoam cooler but the concept was simple junkyard parts and nothing fancy (or expensive)..



I have no idea the longevity of an A/C evaporator submerged in water but they are designed to get wet every day so im thinking it wouldnbt be an issue..
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