Heating using the hot water tank.

[Shadow Catcher]

If plagiarism is indeed the sincerest form of flattery consider your self complimented. I just ordered a 12V version of the temperature controller you used on your Crock Pot hack. It is rated for 10A so should be more than enough.
http://www.ebay.com/itm/231387183857

[lrrowe]

MtnDon, as Bruce said....way to go.
My gut tells me it will work.
I say this because I just went out to turn the 72W work light bulb off in my trailer. It has been 32 degrees for an hour or so outside. It is 27 now. The inside of the CT was 42 degrees and I have no ceiling insulation, just 1 1/2" of foam in the walls and floor. I think I will go back and turn it on to see what the temps are in the AM after being on all night.

This morning the inside trailer temp was 24.6 and outside was 21.5. Now with this data I do not kown what I have. The test was sort of a waste of time. First I need all the insulation to be completed and then I need to cacluclate the amount of heat energy that was used. Then it could be compared to other tests.

[Socal Tom]

MtnDon, as Bruce said....way to go.
My gut tells me it will work.
I say this because I just went out to turn the 72W work light bulb off in my trailer. It has been 32 degrees for an hour or so outside. It is 27 now. The inside of the CT was 42 degrees and I have no ceiling insulation, just 1 1/2" of foam in the walls and floor. I think I will go back and turn it on to see what the temps are in the AM after being on all night.

This morning the inside trailer temp was 24.6 and outside was 21.5. Now with this data I do not kown what I have. The test was sort of a waste of time. First I need all the insulation to be completed and then I need to cacluclate the amount of heat energy that was used. Then it could be compared to other tests.

Assuming 100% of the 72 watts went to heat, then the 72 watts is equal to 245 BTU per http://www.rapidtables.com/convert/power/Watt_to_BTU.htm

I did some calculations for my 5x8 teardrop ( insulated ceiling, Plywood walls), and the calculations estimated about 1800btu/hr would be required to maintain a 30 degree difference. A person gives off about 350 BTUs/hr. I don't think 72 watts is adequate to make a big difference.
Tom

[lrrowe]

And it wasn't. See my post two above.

[MtnDon]

One thing to note: While we have some good wall, roof and floor insulation we also have a huge (48" x 29") heat hole in the form of the single pane side window. But we also very much like the daylight and being able to see outside. A lesser heat loss would be the RV door with a small single pane window. Another heat loser would be the roof vent with its single thickness plastic cover. Might buy/make a plug for that.

[lrrowe]

Does the fact that my large window is an insulated model help? I would think it would.
Regarding the vent, that may always be a weak link for me as I think I would always crack it open at a minimum each night.

[MtnDon]

I ordered another IR thermometer from an ebay seller as HF wanted more than double. I should have it next week (US shipper of Chinese goods)

I can tell the return line from the radiator is cooler than the incoming line, but can't tell by how much. That raises the questions of how much cooler should we expect it to be? How much heat transfer out of the radiator would be most efficient? The shipping schedule looks like the IR therm and the temperature controller should both arrive on Thursday next. In the meantime I'll go through the plumbing adds 'n' ends and find a valve suitable for testing restricting the flow. With the IR in hand maybe I can make some sense out of it all.

[Socal Tom]

I ordered another IR thermometer from an ebay seller as HF wanted more than double. I should have it next week (US shipper of Chinese goods)

I can tell the return line from the radiator is cooler than the incoming line, but can't tell by how much. That raises the questions of how much cooler should we expect it to be? How much heat transfer out of the radiator would be most efficient? The shipping schedule looks like the IR therm and the temperature controller should both arrive on Thursday next. In the meantime I'll go through the plumbing adds 'n' ends and find a valve suitable for testing restricting the flow. With the IR in hand maybe I can make some sense out of it all.

So I did some math....
Assuming you want 1000 BTU per hour.( probably a little high)
1 BTU is the amount of energy to heat ( or cool) 1 lb of water 1 degree F ( its always nice when the english units work for something I'm trying to work out)
1 gallon of water = 8lbs
So assuming that the energy removed from the hot water equals the energy put into the air, then for 1000 BTU
At a flow rate of 1 gallon per minute ( 60 gallons per hour), at temp drop of 2 degrees should give you 1000 BTU per hour
at a flow rate of 2 gallons per minute you would need just a 1 degree drop
at 3 gallons per hour it would be about 0.8 degrees

From what I read online, the attwood gas water heaters are about 10K BTU, so I would adjust the flow rate to try and keep the BTUs at a rate lower than 10K.
Tom

[lrrowe]

On my home radiant infloor systems, I used a heat exchanger from my boiler/hot water tank to my radiant closed system. Typically the water temperature going into the exchanger is about 120 degrees F and the outgoing water to the radiant tubes is about 105 to 110 degrees F. I don't know if this is an apples to peaches comparison or not.
I have never measured the temp coming out of the exchanger from the heat source side nor the return from the radiant tubing.

[Socal Tom]

Honestly after I did the math, it's probably not worth the effort to optimize the heat transfer, you should have lots of excess heat.

[bdosborn]

From a quick Google search on heat exchangers and flow rates:

The higher the velocity inside the tubes the better the overall heat transfer will be due to the breaking-down of the inside film coefficient caused by both the turbulence and the sweeping action. The sweeping action will also retard the deposition of contaminants on the inside walls, usually referred to as fouling.

I'd say you have the cart before the horse on trying to slow down the flow rate. Wait and see if the trailer gets too hot with the heat exchanger running to decide if you want to throttle the pump. My hunch is your going to want every bit of heat you can get out the exchanger, meaning higher flow rates. Besides, the higher flow rate helps with fouling...

Bruce

[lrrowe]

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.

MtnDon,
How did the overnight tests work out?

[MtnDon]

My bad.... That night the outside temperature dropped to 41, the interior was at 72. That was with the water heater set at medium, and the pump and fans running continuously. A difference of 31 degrees.


Last night I set the water heater to the lowest setting and let it run all night. The outside low was 36. The interior temperature was 64 degrees, a difference of 28 degrees. Again, the pump and fans ran continuously.


From that I see that...
... This is probably a viable heater. It won't be able to produce the rapid temperature rise available from a Wabasco, a Propex, a Standard RV furnace or a 120 VAC electric space heater. But it also does not take up as much space as the other fuel burning heaters, and is cheaper. It operates quietly. (I would like a Propex but balk at the $700 price tag)
... A temperature control /thermostat is definitely needed as the 72 F was too warm to sleep comfortably.
... Changing the water temperature has an effect on the maximum temperature rise.
... My window probably does lose a fair amount of heat.

... I need to dig out another fan set. These are 45 CFM; I have one that moves 90 CFM, with a little more noise, but still quieter than the pump. I ordered a second unit so I will change them out and run a test with them mounted in a pair in place of the first set. It is scheduled to arrive next Thursday as are the temperature controller and my new IR thermometer. A higher rate of air flow through the radiator should put more heat into the trailer interior.



Today I weighed the propane cylinder and will see what weight of propane is consumed in 24 hours. My problem with this is my scale. My very accurate (to the gram) scale has a upper limit of 12 pounds, more than the weight of the cylinder (18 lbs tare plus propane). The bigger scale will get to to about a half pound accuracy, maybe. Anyhow I'll let this run 24 hours and weigh that just for the heck of it. Water heater set on low still.

Depending on that result tomorrow I might try running a 1 lb cylinder to be able to more accurately measure use. That is if I can find my 1 lb adapter fitting.

Then I expectantly wait for Thursday.

My approach to this is start with simple basic equipment and then make changes driven by what is observed.
Thoughts? Comments?

[lrrowe]

A great report and I believe is enough evidence that says the concept is a good one. I have more thoughts which I will write down tomorrow. I am going to bed now.

[MtnDon]

Further note: It may be that a larger radiator would work better, dissipate more heat. However, (1) that is the one I had on hand. (2) it's size, or at least the 6" dimension is ideal for placing it in front of the shower lip as earlier described.