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Old 02-23-2007, 10:19 PM   #43
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I just ran across this thread for the first time. I had wondered what could be done with diesel as a power source and now I guess I know. Your system looks like a great piece of work. The one thing I might change if I were to follow your general approach would be to put the hydronic heating into the floor using PEX tubing rather than using the radiator/heat exchangers. How expensive are the heat exchangers?

Thanks,

Malcolm
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Old 02-23-2007, 11:13 PM   #44
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Malcolm:

You mean using pex tubes under the floor to create radiant heating, right?

Thatís a good idea. Probably not cost effective however.

The heat exchangers cost only $414 Cdn for all three of them. The hose and fittings were about $200.

The total was around $2500, ($2100 your currency).

I got the Webasto, a warranty return, for only $570. The water heater was $632. The balance is for fittings, controls/shut-offs and the thermostat.

The other reason under floor tubing is probably not reasonable in such a small space is the fact that the very quiet fan-coil units are, in effect, a form of radiant heat. They silently waft the heat across the floor and into the space.

Sergei
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Old 02-24-2007, 12:44 PM   #45
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Heating in the floor could be cost effective...

I have been intending to install radiant heating pipes on top of my sub-floor for sometime now. My remodeling is going pretty slowly though so I am not there yet. I just finished installing reflective foil insulation in my walls so I am ready to start re-installing the inner skins next.

I don't expect to be spending more overall for radiant heating in the floor than your approach. Just a rough check of PEX tubing prices shows that it will likely be something less than $1 (US) per foot. I have been thinking of tubing spaced somewhere between 6" to 9" on center. My total floor area (1973 31') is right around 200 square feet. There are some places that I won't put heating tubes (such as where the wheel wells are for example. So if I heat about 180 square feet at 6" on center that means that I would need about 360 feet of PEX tubing. At $1 per foot that would still be less than $400. I still need the pump of course but the PEX tubing itself covers most of the hot water delivery so I would not expect to need much else in the way of tubing.

I think your approach does have the advantage of being a bit faster in response time to putting the tubing in the floor. Both approaches should work fine - I think it boils down more to a question of personal preference. In any case the thing I like about both approaches is that they do not require a seperate forced air furnace.

Regarding your diesel fired heating unit - is there any reason that it wouldn't work for heating potable hot water directly? Is its response time fast enough that it could, in some sense, be considered an on demand hot water heater? I understand the desirability of running coolant in the pipes especially if the heater is outside - I was just curious.

Malcolm
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Old 02-24-2007, 04:21 PM   #46
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Malcolm:

If you go radiant from the floor you will have eliminated the noisy furnace and ducting and gain a better quality of heat.

Soft and gentle instead of TOO HOT followed almost immediately by TOO COLD.

I donít know if a Webasto TSL can be rigged to heat potable water in-line but Iíll ask both of my very useful contacts.

If they say no I will ask them to explain why not for us.



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Old 02-25-2007, 08:27 PM   #47
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Heat exchangers...

Sergei - I found the pics of the exchangers - ignore my other request

I know you don't smell anything, but as a thought, many people in the NW here use Biodiesel. I really find the smell quite easy on the nose. FWIW.

Fasinating stuff!
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Old 02-25-2007, 09:07 PM   #48
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Malcolm,

Have you calculated how much heat you can transfer though the floor, and will it be enough to keep the trailer warm without making the floor overly hot.

I'm not trying to be Mr. Negative, but I would get a heating engineer to run the numbers. Or have a backup method available, like a space heater.
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Old 02-26-2007, 07:12 PM   #49
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Marc:

The manufacturers of the diesel cook tops have told me to be sure not to use bio diesel.

The reason is that the stoves are very precisely engineered.

They said that, unlike regular diesel, there are no standards for bio diesel. Well-intentioned people make some of it in backyards and the varying results wreak havoc with these things.

Sergei
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Old 02-26-2007, 09:04 PM   #50
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Malcolm:

Markdoane makes a good point, one I hadnít thought of.

I have electric radiant heat in a bathroom in my home. It can be set to be too hot for comfort but it is easily controlled with a thermostat.

You would have to do a careful test. There should be ways for you to control the fluid volume, something like a heater control in a car. Iím using control units for a Honda car in my system, to ďbalanceĒ the flow to the water heater.

Another thing you will want to consider is serviceability. Unless you can do the piping in one continuous loop, without connectors, there could be a danger of leaks that you canít get to without tearing up your work.

Sergei
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Old 02-26-2007, 10:26 PM   #51
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I'm no expert, but i did look at a research paper done by Univ of Kansas for ASHRAE to determine heat transfer rates in hydronic systems.

They found heat transfer rates as high as 47 Btu/hr*ft^2 for systems with heat transfer plates laid over the Pex, and 25 Btu/hr*ft^2 in a regular loop configuration.

It's hard to equate to forced air type heating, because the hydronic system is more radiative heat transfer, and may feel warmer even if the air temperature is lower. However, even the higher heat rate only gives you about 8500 Btu/hr.

I think the small footprint available for heating surface might be a problem.
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Old 02-26-2007, 11:41 PM   #52
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Quote:
Originally Posted by SmokelessJoe
Marc:

The manufacturers of the diesel cook tops have told me to be sure not to use bio diesel.

The reason is that the stoves are very precisely engineered.

They said that, unlike regular diesel, there are no standards for bio diesel. Well-intentioned people make some of it in backyards and the varying results wreak havoc with these things.

Sergei
This sounds like a bit of a boilerplate warning to me and a cop-out from the manufacturers. Surely commercialy sources of bio would suffice.
Doesn't the EarthRoamer use both a diesel cook and bio?
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Old 02-27-2007, 03:21 PM   #53
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Quote:
Originally Posted by markdoane
I'm no expert, but i did look at a research paper done by Univ of Kansas for ASHRAE to determine heat transfer rates in hydronic systems.

They found heat transfer rates as high as 47 Btu/hr*ft^2 for systems with heat transfer plates laid over the Pex, and 25 Btu/hr*ft^2 in a regular loop configuration.

It's hard to equate to forced air type heating, because the hydronic system is more radiative heat transfer, and may feel warmer even if the air temperature is lower. However, even the higher heat rate only gives you about 8500 Btu/hr.

I think the small footprint available for heating surface might be a problem.
I will certainly want to make sure the numbers work out OK. I admit that I have been just using rule of thumb guestimates so far. I have, though, had quotes for radiant systems in a residential setting that typically run heat pipes at 8 to 12' on center. I was thinking of the 6" on center as one way to help compensate for the poorer quality of insulation in an Airstream. I have also been focussing entirely on reflective foil insulation since it is very good at blocking heat loss by radiation.

One other somewhat wild thing that I have been giving some thought to as well was the notion of putting the heat tubing on my ceiling instead of in the floor. There are a lot of things on the floor that potentially get in the way of radiant heat from the floor. On the other hand there is a band of ceiling down the middle perhaps 5' wide that is largely un-obstructed. There also happens to be an aluminum skin there that might make an interesting heat transfer plate if I can get it heated up. If I didn't want to connect to the inner skin I could also put another layer of reflective foil behind the heat tubing. I had given some thought to either covering up the tubing with another aluminum inner skin or maybe even levaing the tubing exposed for a rather novel visual effect. I was giving some thought to running the tubing at 3" or 4" on center too. The more challenging part of the idea if I want to heat up the inner skin is how exactly to connect PEX tubing to the inner skin in such a way as to maximize heat transfer.

As far as controlling the heat levels go I can install a thermostat and I can also install a temperature sensor in the floor itself somewhere if there seems to be a danger of getting the floor too warm. It is my understanding, though, that the floor does not really need to be heated to more than perhaps 80 degrees to do the job effectively enough.

I wonder what the typical rate of heat loss through the floor, walls and roof are likely to be with the reflective foil insualtion? As a note in passing I am not particulary interested in going to places with my Airstream that are experiencing extremes of tempurature so my needs relative to the heating system might not be as great as some other peoples could be.

Malcolm
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Old 02-27-2007, 03:35 PM   #54
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How does household heating oil compare to diesel fuel? Isn't it pretty much the same?

Malcolm
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Old 02-27-2007, 06:42 PM   #55
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Quote:
Originally Posted by markdoane
Malcolm,

Have you calculated how much heat you can transfer though the floor, and will it be enough to keep the trailer warm without making the floor overly hot.

I'm not trying to be Mr. Negative, but I would get a heating engineer to run the numbers. Or have a backup method available, like a space heater.
You could be right. I will want to take a closer look at the numbers before I finally commit. I admit that I have been using rule of thumb thinking so far about my system. I have had quotes, though, for residential systems that typically suggest anywhere from 8' to 16" on center. I was thinking of 6" o.c. as one way to help compensate for the poorer quality insulation in an Airstream.

Another somewhat wild idea I have given some thought to was putting the heat tubing on my ceiling instead of on the floor. There are a lot of things on the floor that get in the way of radiant heating. On the other hand there is a largely un-obstructed strip of perhaps 5' wide down the middle of my ceiling. There also happens to be an aluminum inner skin that might make a nice heat transfer plate should I chose to heat it up. I could also opt to add another layer of reflective foil between the skin and the tubing if I thought that would be better. One challenge is how exactly to connect PEX tubing to the inner skin in a way that would maximize heat transfer. I have toyed with the idea of either covering the tubing with an aluminum skin or maybe even leaving it exposed for a rather interesting visual effect. I have also thought about using 3" to 4" on center spacing. Maybe copper tubing would be an intersting effect...

As far as temperature control goes I will want to install a thermostat and possibly a sensor in the floor itself to moderate total floor temperature. From what I gather it is not really necessary to heat the floor to more than about 80 degrees for a system to feel comfortable.

I wonder what kind of thermal loss I can expect through the skin of my Airstream with reflective foil insulation? As a note in passing I am not particularly interested in taking my Airstream to places when they are experiencing extremes of temperature. It could be that my heating needs will, therefore, be relatively modest.

Malcolm
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Old 02-27-2007, 06:54 PM   #56
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Malcolm,

I love the idea of running tubing exposed. Kind of retro/industrial look.

The plastic mounting clips could make a really attractive installation. Mounting on the walls or ceiling would also be a better method for heating the sleeping quarters, where the beds would provide too much blocking of radiant heat coming from the floor.

PS: In the Kansas study the pex was run 8" on center.
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