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Old 02-22-2005, 11:51 AM   #15
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Flueless heaters...

It seems to me that supply air is already needed for our propane refrigerators. My AS has a permanently open vent through the floor behind the refrigerator. It would be interesting to know just how much combustion air an Olympian Wave heater needs. It does not seem like it would be that big of a deal to add some additional permanent venting to make sure there was enough air flow.

It would be interesting to know just how safe these various types of non-flue heaters and fireplaces are. I am seeing all sorts of heaters, water heaters and even fireplaces advertised these days that do not require a vent. In case anyone is interested here is the web site where you can see information about the Olypian Wave line of heaters:

http://www.uscatalytic.com/heater_index.html

Here are a couple of sites where you can buy them:

https://www.rvpartsoutlet.com/newstore/nojava/index.cfm (look under heaters in the general index)
http://www.rvstuffusa.com/heatingac.html

Here is a site that has information about a ventless continuous flow water heater. Note that this company also makes one that is power vented.

http://www.excelamerica.com/calentadores_eng.htm

I guess my basic point is that these type of heaters are for sale all over the place these days. Surely this at least suggest that the safety issues have been worked out? If this is really true then these types of heaters (and even water heater) could be a great addition to an AS.

Does anyone reading this have more information about these flueless appliances and their safety ratings?

Malcolm
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Old 02-22-2005, 11:54 AM   #16
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Quote:
Originally Posted by mandolindave
Excuse my half witted post...But I did remember the "guy" saying
that he only needed a low volume water pump for his heating system.
A higher efficientcy fan and the low volume pump used a lot less
electricity than the furnace blower did.
The problem I see with a hot water heating system is the water.
I don't want water in my trailer in the winter. But a heater is fun
to have in the winter. Couldn't you just fill the system with antifreeze?
Ideally what we need is some sort of anti-freeze that could be added to the water system (including the radiant heating) during the winter to keep it from freezing while it was parked that would not contaminate the system and could be safely flushed out in the spring. This would keep the system from freezing and would allow us to run the heater anytime that we wanted to.

Does anyone know of such an anti-freeze?

Malcolm
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Old 02-22-2005, 01:41 PM   #17
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The ventless devices, such as the Excel inline water heater, depend upon small size, large room, and high efficiency. i.e. minimize pollutant density and depend upon normal traffic in and out to disperse over time. In an RV you have to take additional precautions such as keeping a vent or window open while using a catalytic heater. This is also why the RV fridge has its own vent system to outside air - both in and out, even if it is barely more than a pilot light.

The site referenced by Malcom (thanks, good info!) says that anti-freeze is going to reduce heat transfer efficiency by nearly a factor of 2. A similar problem exists with automotive cooling systems, I think. Unless you use ethanol as an antifreeze, it won't be potable (and even that way there are some other problems ;-)

The radiant company site also illustrated how to plumb the fresh water feed for the water heater through the radiant system to help prevent stagnant water in the system. They also got into some of the problems with matching heat flow in passive radiant systems depending upon pipe size, length, and so on.

The floor radiators are the interesting challenge, I think. Malcom's other thread idea with 3/4 insulation and another 3/4 or so for radiators is one possibility but would cause a 6'er in a trailer some headroom problems. Maybe someone will invent a radiant cooling mat somewhat like those work area rubber mats that has internal heat management and fluid flow built in. The other option would be to use a radiator run along the cabinets - hang 100' of pex tubing around the ceiling throughout the trailer for a new decor style, maybe even color coordinated?

One thing about the floor mat idea. They could be easily removed and hung out to dry for protection against freezing when not in use.

Oh well, Malcom probably has the most feasible idea if you don't mind the thick floor. But I'd run all the tubing to a manifold on each end (rather than looping the tubing) to facilitate draining. maybe.

Still some thinking to do.
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Old 02-23-2005, 03:21 PM   #18
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Bryan,

I am not intending to add 3/4" of insulation. Rather I am intending to use reflective foil insulation on top of my 3/4" thick Polyboard floor (instead of the plywood). The foil insulation is thin and along with the tubing and aluminum fins would fit into 3/4" of space above the sub-floor. Actually I could also save 1/4" if I went with 3/8" ID tubing instead of the 1/2" ID I have been contemplating. I am 6'2" tall and I think I can stand losing the 3/4". I measure right at about 80" from the top of the subfloor to the ceiling in the middle which would still give me enough head room.

I did think about installing the radiant tubing inside the ceiling by the way. I thought it would be nice to figure out a way to lay in the tubing so that it would contact the inner skin surface. This would make the inner aluminum skin become a radiator. I still think that could be a good idea but decided it would be harder to work out the details than doing it on the floor - mostly because of all the obstructions in the wall.

Malcolm
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Old 02-23-2005, 07:02 PM   #19
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using the existing floor as the base with 3/4 on top for radiator makes sense.

half inch pex is good for 25 BTU/hr/foot. That would be 400' to get 10k BTU/hr which will keep an Airstream warm, kinda', down to near zero F temps (78 Sovereign 31' experiment this winter). 10k BTU is also what you can expect to get out of a typical RV water heater, I think.

If you had 7' x 7' for the living area, 15' x 2' for kitchen and bedroom, and 3 x3 for bath and closet, you would need to space piping on 5 or 6 inch centers to lay out 400' -

400' of half inch OD, 3/8 ID is about 2 gallons of water. (I get confused by whether the standard spec is ID or OD for copper tubing size but it seems to be OD, maybe).

Since you are dealing with fairly low water pressures in an accessible fixture, using 1' vinyl squeezed to be oval might be a possibility. Another idea would be to incorporate a couple of feet of heat exchangers in convenient places to augment the floor radiant system.

The excel water heater, in an outside vented compartment, would be interesting for this use. It has 2 or 3 times the heat output of a typical tank type RV water heater, is half the price of the RV-500, and a regulated water output temp in this sort of application isn't very important.

This could get interesting. Do the numbers I cite fall in line with your calculations?
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Old 02-23-2005, 07:23 PM   #20
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This would seem to need alot of careful designing.
Design assumptions? Small heater that runs continuously at the outside design temperature and maintains the ?? inside temperature or ?? keeps up with the BTU's leaving the trailer?? or some other standard??
Then there is the question of how fast (gallons per hour) the water should circulate at what temperature. Logic (not that it always gets you where you want to be) suggests that any given heater running full time with any given pump running full time and size pipe and floor material ect. will reach an equilibrum of water temperature reentering the heater. Do you design these systems to get a return temperature? Of course this doesn't translate into an air temperature since we aren't going to heat the air but it may indicate people heating potential. I think the furnance size would be in the same BTU range as a gas air heater or less? If I remember a BTU is a pound of water one degree. So 12000 would replace 50 degrees of heat in 30 gallons of water an hour.? That assumes it isn't losing any which it will be to heat people. Less water is good. For 3 gallons it only takes 6 minutes. So the pump needs to move at least 1/2 gallon a minute.

Prehaps this calls for an experimental approach like the roof paint.
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Old 02-23-2005, 08:59 PM   #21
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Bryan,

I think your calcs generally fall in line with what I am expecting. They actually go into more detail than I have so far - and thanks for that. I ran the whole idea by someone locally who does radiant heating and they felt what I was proposing was feasible. I also spoke with someone at the website I posted earlier about the approach. On the PEX tubing they are sized by ID by the way.

What I was thinking of doing was putting the heating tubes at 6" on center and putting them under the entire floor not just the living areas themselves. It occurred to me that this would help keep everything in the AS warm including the things in my storage spaces. I generally thought that these extra areas would not draw as much heat as the open areas so this would not really hurt anything and might actually help. I calculate that my total floor area is about 200 square feet. Tubing everywhere at 6" o.c. should give me right around 400 square feet if I calculated correctly.

I do like the looks of the Excel heater especially for its price point. If it were in a comparment that was isolated from the interior air I suppose that it could still be insulated so that it would not actually be entirely outside.

Over59,

One of the interesting problems with using a continuous flow water heater has to do with the regulation issue. The RV500 for example turns on when it senses enough difference in temperature between the input and output sides of its plumbing. If there is not enough difference it might not turn on. It could be that the Excel would actually have an advantage here.

I am counting on a few assumptions for this to work. For one thing I am installing reflective foil insulation with the expectation that I will have better insulation - especially relative to radiant heat loss. I am also counting on the 6" on center tubing placement to be a bit of an overkill compared to what I have been reading about for typical installations.

I am basically just going to follow my assumptions and see what happens - just like with the roof paint.
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Old 02-23-2005, 09:01 PM   #22
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> This would seem to need alot of careful designing.

that would be one way. trial and error would also not be out of order as both the risk and costs can be rather low.

> Design assumptions?

generally you would be talking about a thermostat regulated mechanism (circulating pump powered via thermostat) that could provide acceptable heating at some given worst conditions. A starting point would be the existing nominal heating systems which deliver about 20k to 25k BTU/hour from a forced air furnace for the larger Airstreams. One potential limitation would be an existing RV water heater capable of maybe 10k BTU output.

> there is the question of how fast the water should circulate at what temperature.

The guide here is standard practice for floor radiant heating. This is a low flow rate with a 10 - 15 degree loss in the loop. This usually translates to about 300' of half inch tubing with the usual pumps.

> Less water is good. For 3 gallons it only takes 6 minutes. So the pump
> needs to move at least 1/2 gallon a minute.

http://www.heatinghelp.com/newsletter.cfm?Id=161
indicates that a half inch pipe is good for a gallon and a half per minute in a secondary circulation system. a 400' loop would need a pump good for a 24' head.
- this is close to your calc, which is comforting.

interesting stuff, there is a lot of design information, from the high end HVAC engineer stuff to the backyard mechanic stuff, out there. The pump is really the only critical component and availability is likely to be more important that close specification.
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Old 02-23-2005, 10:43 PM   #23
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Bryan,

I have been thinking that I would find a pump at a marine supply place. I took a look at the various pumps at the following website and it seems like there are quite a few water pumps that can handle from 2 plus gpm.

http://www.defender.com/category.jsp...1|51&id=299222

One of the pumps that looks promising is on the following page:

http://www.defender.com/product.jsp?...6443&id=151097

This pump puts out 3.3 gpm, is rated for continuos duty and is supposedly quiet. Do you think that 3.3 gpm would be too much flow for the application?

I wish there was more information posted about noise levels.

Malcolm
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Old 02-23-2005, 11:20 PM   #24
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Cool, learned stuff again. Why do they call it head? Is this the resistance equivalent of pushing water out of a boat from X feet below the surface. I see pumps with amp draws dependent of the head (lift?).

These pumps tend to draw alot of juice. More than some hot air fans.
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Old 02-24-2005, 01:06 PM   #25
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Oh boy, another history of words lookup! ;-)

If I get it right, head refers to the pressure the pump can create. If so, then 33' of head means about 15 psi of pressure is available from the pump (1 atmosphere). A typical RV water supply pump can get up to 45 psi or so which would be nearly 100' head. I think the pump current draw is going to be pretty much proportional to water volume times pressure. A circulating pump only needs to generate enough pressure to get flow through the pipes and only enough volume to get a flow that provides for effective heat transfer.

The heat flow is a matter of temperature difference and that is fairly low in hydronic systems. Loop input at, say 130F with 70F floor temp means maybe a 60F dif while output temp of 115F means a 45F dif. This is why a lot of surface area is needed to get much heat to the room. The transfer efficiency is probably not a problem because it shows mainly in the circulating pump - all other losses generally trend towards heat into the room.

The other side of head would be the draw or lift of a self priming pump. This isn't a concern with a circulating pump but it is for the RV water supply pump. It takes some pump to be able to lift water more than 5-10 feet to its input. This side of things depends upon atmospheric pressure pushing the water up to the pump.

as for the 3.3. gpm pump, I wonder what kind of pressure that is against? at 7amp my guess would be a rather high pressure as it sounds about like what a typical RV supply pump provides and consumes. Another potential problem appears to be heat and a good hydronic heat circulating pump needs to be designed to operate with hot water.

For efficiency I think you need a pump that is designed for low head (less than 15 psi or 33 feet) and high temperature water. Half inch pipe in a typical 300' run seems to require a 24' head and under 2 gpm for optimum heating. It should probably not draw more than a couple of amps at most, if that.
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Old 02-25-2005, 07:58 PM   #26
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If anyone is interested in using hotwater heat but wants to have a radiator/fan installation somewhat like what was mentioned earlier in a referenced post take a look at the following web page (near the bottom). This marine supply company has two different sizes of hot water forced air heaters that look like they could very well work just fine for an AS. They are capable of outputs from 12,000 to 24,000 btu, have a built in fan that runs on 12v with a small power draw and are pretty compact. It seems like they would be able to run from hot water from a water heater.

http://www.dickinsonmarine.com/shop5...s/SPECSRAD.doc

Malcolm
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Old 02-25-2005, 08:03 PM   #27
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Thanks to Bryan here is a pointer to a source of a couple of pumps that sound like they would work just great for hot water radiant heating. They are a little spendy but their specs sound like they would be perfect for the application. They are designed to handle hot water, run very quietly and have brushless DC moters for very long life. Check them out.

http://shop.altenergystore.com/items...~0~Tp~~Bc~.htm

Malcolm
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Old 02-26-2005, 10:18 AM   #28
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Now if you used a pulsating dimmer switch and a brushless pump could you adjust the flow and amps? If you adjust the voltage on those pumps you are adjusting the flow rate? It is also a way to fine turn the system.

Still, there is no way I am letting water have that kind of access to my new floor. I'll stick with the hot air for off grid and the AC heat pump online. You have an interesting design project.
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