Heating using the hot water tank.

[Shadow Catcher]

In our case the mattress is 5" foam so not much help under bed. We also have a fairly high interior volume, for a teardrop, 400cubic feet.
Our Atwood is a 6 gal direct spark ignition.
I ordered the pump today and I am looking at tubing, it has to be food grade, handle pressure and temperature. Tygon seems to have tubing that fits those requirements.
I figure I can regulate the temperature by using a couple of PWM modules, one for the pump and one for the fan.
I am debating whether to use quick disconnects on the hoses and yes there will be a couple of ball valves.
I will document what I find and where.

[lrrowe]

In my conceptual plan, I was going to regulate the on/off of the pump and fan(s) using a thermostat and some sort of relay.
I do not know much about thermostats, so there is more for me to research on them. And the tricky part, if possible, is to keep the fan(s) running for a short while to take advantage of all the heat left in the raditor after the pump stops. But then again, that might be too much work for the small amount of heat left. The rules of dimenishing returns applies here.

[Shadow Catcher]

My thinking is regulate the speed of the pump and keep a constant but adjusted fan speed, the reason for the PWM modules. I am seeing 120MM case fans that list PWM control but I am wondering how that works if the computer is controlling it. OK a bit of research and it is a separate controller. I have a couple of $10 digital PWM controllers that seem to work well.

[Socal Tom]

It's not intuitive, but pumps draw less amperage if you reduce the flow, so having a way to slow it down to give your heat exchanger a little more time to pull the heat out of it would probably save some power and maybe even improve the heating. It also takes some time for the water heater to do its job, to too short a dwell time could cause problems.
Tom

[bdosborn]

I ordered the pump today and I am looking at tubing, it has to be food grade, handle pressure and temperature. Tygon seems to have tubing that fits those requirements.

Why not use PEX?

Bruce

[MtnDon]

PEX is what my plan uses. It's readily available, approved for potable water and can take the heat. It's only downside is that it is fairly stiff , but can be formed to a 5" radius in 1/2" sizes.

[lrrowe]

My radiant heat home system uses 1/2" Pex. I have plenty left over from that job. Guess I better make sure that particular brand is potable water rated.

[backstrap bandit]

Actually pec can conform to a fairly tight radius if you carefully use a heat gun and heat it up a bit

[Shadow Catcher]

The water tank pump and external inlet for CR are in what looks like the head board at the rear.

The water heater is on the right side behind the bulkhead. The plan is to have the heater core stored above the water pump and on hoses that I can pull out and place some place (undecided where).

[lrrowe]

With all the interest, knowledge and experience shown/mentioned by posters, it is surprising no one has made the first working system. I would try right now, but I have not actually decided which water heater to buy. MtnDon, I am cheering for you and your project.

[Shadow Catcher]

Bob we have had no real problems with out Atwood DSI and the only problem was it acquired a spider one year, once it was blown out no problem. I did encounter one being TIG welded after the owner let it freeze when full. Aluminum tanks can be repaired.

[MtnDon]

For me the deciding point was the physical dimensions. The Suburban and the Atwood are laid out differently. The Suburban tank has the long dimension perpendicular to the wall of the trailer. The Atwood has the long dimension of the tank parallel to the wall of the trailer. The Suburban fits between the usual 16" wall rib spacing of a CT. Note I said "usual"; that can vary from CT to CT manufacturer. The Atwood won't fit between 16" OC (on center) wall ribs. If you can cut and weld steel ribs that is not an issue. Otherwise.....

Of course with a CarMate trailer and the wood wall studs you don't need to weld.That does make configuring the cutout for an Atwood slightly less of a problem than if the trailer had steel wall ribs/studs.

[len19070]

Atwood makes a Water Heater that has a Heat exchanger built in to it. Nobody uses it anymore but they still make it.

Model GCH6A-10E

http://www.americanrvcompany.com/Atwood ... Trailer-RV

It was originally designed to heat water in a water heaters tank from a Motor homes Engine coolant system. As I said, nobody uses this system anymore (That I know of)

In the mid to late 80's a few Manufactures used this product in a different way. Allegro was one.

They would take the "In and Out" on the water heaters exchanger, create a sealed system , filled it with Anti Freeze and connect it to the "IN and out" in a heater core. Some of these Heater cores had Fans, and some were Gravity systems. (simple explanation)

As long as the Water heater was on, you got heat to the Heater Core and it was simply shut off in warmer months.

Now, This was definitely a "Lowering the River instead of raising the Bridge" approach.

But!

They worked! Despite there Logistical Problems

How ever over time were no longer used.

Happy Trails

Len

[lrrowe]

Hi Len,
I originally thought about them and even mentioned that in one of my much earlier posts. I believe Bruce also mentioned it.

And I really believe it would work very well. But my wish list of stuff for my project has gotten to be very high $$$$$ wise.
The regular Attwood/pilot/6 gal/gas only can bought now for $303 and the one with the heat exchanger costs about $543. I could use that $143 elsewhere. Yes, I am starting to get frugal now ( not cheap). MtnDon, just for the heck of it, I am going to look at the Suburban's demensions. I could afford to give up vertical space to gain more horizontal space in the cabinets.

At least for me, i am several weeks away from the point of working on this phase of the project, so I still have time to digest all the comments here and make my final decision.

[MtnDon]

Stage One Test:

This is a very basic hookup for the first performance test.... The general layout...



I'm running the tests off my 12 VDC power supply with a watt meter. The two white PEX pipes in the upper right come from connections near the water heater hot and cold connections. Blue tape = cold(er) pipe.

A closer up view of the heater and pump...



The hot pipe connects to the inlet side of the pump. The pump is rated at a flow rate of approximately 3 gal/minute. The finned radiator is a transmission cooler, approximately 6 x 12 inches. The fans are secured with wire ties; quick and easy for testing. They are oriented to blow air through the fins. At present the pump and fans are wired up to run continuously. At present I do not have a temperature controller or thermostat. That will come if this first stage is deemed a success.

Close up shot of the watt meter reading. This was taken moments after turning the power on. Taking a photo of the display is a tad difficult and needed some manipulation...



With pump and fans running the amp draw is at 0.67 with the watts at 8.7 (at 13.3 volts).

The plan is to run all night and see how many watt-hours are used and what the temperature inside the trailer is in the morning. The water heater thermostat is set at medium. The test started late this afternoon (4:30 PM MST) with the exterior temperature at 58 F and dropping. The trailer interior was at 70 F. The overnight low is forecast to be 37 F.