The double shoe box rocket is elevated off the floor about 18 inches, and instead of an exhaust on top- in front, it is channeled horizontally under a glass stove top from left to right.
Having the water tank inside the bell was an idea suggested at http://donkey32.proboards.com that led me to my design, which in appearance is like a glass stove top, with an extended simple porcelain covered metal counter top.
This extended bell houses a naked 20 gallon water tank with two fittings, one for cold water at the bottom and one for hot at the top.
The top fitting connects directly into the hot waterfeed for my house system, and while in operation the hot water valve to the shower head in my tub is left open, and the cold water flow to the tank is shut off. This allows excess pressure to escape safely, and notifies me when the water is hot as steam starts to escape. Note that this is primarily proof of concept, and not yet ready for prime time water heating, it could easily have safety features added that would further ensure a more automatic type system.
note the new visions fry pan “door” to the batch box, The lid I was using had broken into two pieces possibly from rough handling, possibly the lids are not as thermally robust as the pans
Last night I was burning the third batch of wood in the firebox,low grade poplar and some mystery wood, likely not completely dry, when I started to hear the steam. That produced a luxurious long (10 min at 4-5 gal/min), very hot shower (mixing lots of cold water). I was concerned about stratification, and the possibility that all the water would not heat evenly, but the length and relatively constant heat of the shower indicated this was not an issue.
The design inside takes the combustion gases exiting under the stove top into a very broad vertical opening that directs the hot gases forward into a circular motion around the whole vertical surface of the tank, with some small horizontal space over and under the tank. These gasses that are further cooled start to sink to the bottom as they circulate. The “stack” entrance is below the bottom of the tank in back of the system, so the exhaust comes in contact with about 270 degrees of the surface of the tank, with some minor contact top and bottom. Note that this stack is actually a powered exhaust by a very cheap, low wattage (about 10)fan. This provides a more or less guaranteed exhaust even at startup, and the exhaust is so cool (around 100F) that more robust (and expensive) equipment is not needed.
The test run last night reached temperatures on top of the port between 900 and 1000 F during the third batch of wood, with a very robust secondary burn at the port. Without testing equipment I have no way of knowing just how clean this is burning, but it appears that the system gets more efficient into the second and third batch of wood by the size of the secondary burn. Perhaps using insulated Fire brick at the port would get the port to temperature more quickly (it is currently standard , full fire brick), and adding ceramic fiber blanket over the stove top might also enhance the temperature build up by reducing convection and radiation losses there.
Location: Central Virginia USA
posted 1 year ago
I thought I would update this post with a month of experience burning the thing and actually using the water feature. The DSR (Double Shoe-box Rocket) is probably not the best iteration, of the glass cook top type stove, since the after burner (heat riser) needs to maintain a very high temperature, but the top starts to dissipate heat immediately. The DSR2 on the other hand exits the batch box in back into an insulated riser(even though it is quite short) and has that extra time at high temperature before contacting the cook top. With simple ir measurements I can see a difference of at least 200 degrees F between the naked top, and when it is covered with ceramic fiber.
The somewhat unique feature of this build, the water heating tank (the boom squish part), has been an interesting experiment, and I am still incubating ideas for automatic thermostatic controls. Taking the pressure off the tank by leaving the shower head valve open still works, but this particular tank has a hot water ftting on the side, slightly lower than the top of the tank meaning more water is lost when there are steam bubbles than my previous tank which had the hot water fitting on top.
I installed the tank before I had a temperature safety valve, and it is a major hassle to try and install it now, so things will likely stay as they are, but the pressure relief valve will be a part of the next build, and automatically dump water or steam into a drain if someone does something stupid (namely me forgetting to open the shower valve)
The actual heat exchange to the water seems about equal, but heating the tank directly has the advantage of not needing a circulating pump to move heat from the copper coil to the tank. I do use the circulating pump when heating the floor, and it can run for longer periods, which I believe is a more efficient transfer of heat to the radiant floor than short intermittent bursts of hot water.
At this point the likely changes I will make have to do with changing the DSR to a DSR2, reducing the size of the cooktop, eliminating the "oven" which never did effectively get much past 200F, and installing the larger water tank (40 gal) which would increase the surface area for heat exchange.
As a side note, I used pex fittings on the tank inside the bell, and they have been functional for some time, but I think the top fittings for the hot water should be cast iron until it exits the bell. It makes more sense for a mechanical robustness when moving the tank in close quarters inside the bell.