Water jacket around the barrel

I had a theoretical thought and wondered if it would work.

I am planing to build a greenhouse with extra heating from a rocket mass heater in the near future, only problem is the greenhouse will be polycarbinate with a wood frame and i am worried the barrel could melt the polycarbonate or burn the wood if it is too close.

Additionally i will be using water mass to store heat in the greenhouse. This gave me a thought, I could put another barrel around the sides of the existing barrel, seal it, and run a pump through to my water stores to ack as a water jacket, thus cooling the barrel and trapping the excess heat in the water for later. (With something to release pressure should the water start to boil)

Would this work as i intend it too and harness more heat from the system? Or would it do something to effect the draw of the air? Could it even potentially improve the draw?

I think it should not affect the draft too much.
It is effectively equivalent to cobbing the barrel in terms of where in the flow of gasses you have added a heat sink.
You might want to consider cob as an alternative to the water jacket, its much simpler to fabricate!
Actually, flat out insulating the areas facing the plastic is not out of the question.
To do that I would use rockwool, and a thin lay of cob between the wool and the barrel, rockwool does better with a a hot face to protect it from direct flame, plus cob is fire proof glue.

If you were to do a water jacket, I would suggest an open system. In that case, the worst you could expect would be the need to dehumidify. If a sealed system developed an issue with pressure relief or circulation, you could easily expect an explosion.

Otherwise, William has some good points about cob and insulation.

Let us know how you proceed, and good luck.

-CK

Cob has slower heat transfer than air, so a cobbed barrel would not shed heat as fast, potentially reducing the draft boost from barrel cooling.
Water has very fast thermal conductivity, and would cool the barrel considerably faster than air, assuming the water has a flow path to carry the heat to remote storage.

If you are depending on circulating water to warm areas away from the heater core, the water jacket would probably be an effective if complex means of aiding that. If the space is small enough that radiation from the barrel can reach most of the space, I think it would be as effective and much easier to just surround the barrel with cob or other mass, and store heat at the source.

If your space is small enough that you need to be concerned with protecting the sidewalls from heat, I think cobbing or bricking around the barrel would be your best bet. This would also reduce the amount of instant heating and temperature spikes while the fire is burning.

Thanks for all the replies, i am still curious for the water jacket, if nothing else than that i am already going to have external water thermal stores so not really any extra space will be lost. As well as the thermal capacity of the water is going to far exceed any amount of cob.
Probably not a completly open system but If i did this i would definetly have vent points along it to stop explotion chances.

My only worry was that if i took too much heat away from the barrel too fast then i prevent the flue from creating a propper draw. As long as that isn't an issue then it could be a fun project.

The flue will also be burried in a stone mass at ground level to leach more heat before exhausting as well.

Cooling the exhaust too much to have draft is a real concern. It depends on your layout; if you have a chimney inside the space, preferably near the barrel, it can be reheated a bit for good draft. If it is all exterior from the ground up, you have to be concerned about a cold chimney blocking draft.

Another option to jacketing or cobbing the barrel would be to install a heat shield/reflector between the barrel and the vulnerable structure to protect it.
In fact, you could use a heat shield in addition to (whatever you do) and get the "belt and suspenders".

You could also consider siting the barrel to the North or West* and not glazing  those walls, but build with a heat resistant material instead.
(*assuming Northern Hemisphere here)

A passive greenhouse design, such as the U.of Missouri one, are only glazed on the South wall, or very minimally on the East/West walls, allowing for more insulation.

Here is a wierd thought. What would happen if you put the barrel upside down...
so instead of it being connected at the base and standing up into the room, it would be connected at the top and the barrel and placed into the ground with the flue then coming from the bottom of the barrel.

Would it stop functioning if the flame could not rise or would the draw still be potentially great enough to force the flame downward.

Just a wierd thought that if it worked could save a lot of space.

The riser needs to go up in order to get the rockety draft in the core. Going down from the burn tunnel (if that is what you are talking about) would just not work.

Matt Walkers has a riserless rocket,  Peter is hashing out his double shoebox rocket,  and 8" batch box rocket can perform cleanly with 24" risers.
Given that these things violate what has or does pass for "conventional wisdom " in the rocket stove world,  I suspect an inverted riser could work.
Is it your best choice?
Well,  even without trying something that new,  let's talk about some other choices beyond a barrel and J.


Matt's riserless core kinda twists the riser in a knot,  the flame path goes downward and sideways as well.
He has a nice design which pairs it with glass salvaged from an electrical cookbook to make a cabin stove.

Peter's shoebox takes a standard batch box heater, chops the riser to match the height of the burn chamer,  and exhausts it into a horizontal box setting atop the burn chamber.
He is still experimenting with it,  last I checked, so details will change.

Peters original calculations for an 8" batch box called for a riser 58" tall.
This thread: http://donkey32.proboards.com/thread/1845/scandal?page=1
revealed to us that a roughly 24" riser would do just fine.

Check out Donkey's Forums for more discussion on things that seem unlikely, but work none the less.
http://donkey32.proboards.com

Given a good final chimney that provides all the draft you need, it is possible to do without some or all of the vertical riser, though a riser going just down would be working completely against the draft.
I'm going to be building one of Matt's cook stoves, with a good chimney.

Good stuff! That Matt’s stove with good chimney sounds great. Hope to hear more about your build. A draft inducer on a side vented chimney is what I’m considering as I don’t want a tall chimney.
I like cob. I like water. Water can be pumped places or thermosyphon places.  And soaking in hot baths with the plants in a rocket stove greenhouse is on my bucket list of projects. Dang would that be awesome!

Just learning on this RMH stuff so this is just an idea.
And my terminology is going to be off.
 What if you had your rizer pushing heat up,.. next to a water heater, propane style,
that the gasses could cool as they dropped through.
The heat would enter the top of the water heater and exit the bottom.

would the cooling of the exhaust help it thermosyphen?

The water heater might not have a large enough center tube.

I think you're right on both counts: The water jacket effect of using the water heater tube as a downdraft path would help the pump effect, but the flue diameter would be too small for adequate airflow.

If you are not using the barrel for heating directly and only intend to store the heat in water, the shell and tube heat exchange is the most efficient option. Can save you more than 50% labor for chopping wood. The flue gas shall pass inside the tubes and water outside the tube/ inside the shell. Cold air enters the top exit to the bottom. Fire enters the bottom exit the top. Will prevent thermal shock. If you can weld you can fabricate one.

Neat picture. I’ve wondered about using a liquid to liquid heat exchanger as a air to liquid heat exchanger. I haven’t tried it yet but I have a couple similar heat exchangers I got from a scrap pile. They might not be big enough, 2” ports.  The heat exchange surface area is important especially for air as it’s lower thermal conductivity than water. Having a counter current might help, the mediums, air and water, going in opposite directions.
 It might be good to have clean-out access for cleaning the heat exchanger tubes with a rifle barrel cleaner brush. Because I’m not sure how much flue gas condensation might occur on the heat exchanger. Fuel quality, temperature, moisture content, stove design..... all play into it. Liquid to liquid heat exchangers can get scale build up that impedes heat transfer. I poured phosphoric acid through a copper coil heat exchanger and lots of crud came out.
 My understanding is cooling on the downdraft helps the “pump” effect of the flue. But as Glenn mentioned it might not be good to cool the exhaust tooo much.
I’m sure looking forward to building a stove and not depend on propane.

shell and tube HE normally have clean outs. Water to air HE normally use fin tubes. Air velocity can be compensated with higher riser and air spinner in the riser.

Here is what I did.. I am measuring about 70-90k BTU/hr
https://www.youtube.com/playlist?list=PLgT0Z9NIZwSnhAy9_byeeTI0FRtdRbuBh
Maybe this can give you some ideas. I will post a "what I would do differently" soon.

If you did use water heaters;
Getting the exhaust flow rate up might require more than one.
Hard to imagine what the input manifold or plumbing would look like with three 40 gallon water heaters
but that would allow enough exhaust flow.
Maybe even let some heat run down between 3 of them tied together,... without insulation.

I'm using a conventional 'wrap around' wood stove boiler as a heat exchanger on top of a 5" BB rocket riser to help heat my hot water and provide central heating. The boiler is rated at 45,000 btu/hr and this output, it appears, can be achieved if you keep the firebox well stoked with decent dry hardwood mixed with a little softwood.

The BB also heats a single skin brick bell.

When I get the chance, I'll post details of my build and how the system performs.

To build a water jacketed barrel without welding,  I would use the tank from an electric water heater,stripped of insulation and cut down to size, maybe 30" tall.
Standard barrels are 35" tall,  so open one on both ends,  and slip it over the tank.
At the bottom of the space between the outer barrel and inner tank, pour hydraulic cement a few inches deep.
Seal with regular silicon caulk, the temperatures involved will not exceed 212 degrees.
I would pump water in and out of this waterjacket over the lip of the barrel to avoid poking holes in it.

I think this will work,  it's a scaling up of a small one I built to cool the feed tube on a J rocket, that worked, but needed a way to circulate a large volume of water.