Post by hollandlef on May 12, 2016 14:23:59 GMT -8
Hi All,
We've just bought a rural property in the mountains and after many years of theorising about permaculturey-type things, we're finally getting round to putting some of them into practice. One of the important considerations is space and water heating. At the moment we have LPG-powered water heating and some simple wood stoves for space heating. I'd like to replace both of these with a combination solar and rocket-powered heating system. I'd like to build a Peter Berg batchbox rocket that we can light 1-2 times a day during the winter and capture all the heat for use during the remainder of the day.
We've just bought a rural property in the mountains and after many years of theorising about permaculturey-type things, we're finally getting round to putting some of them into practice. One of the important considerations is space and water heating. At the moment we have LPG-powered water heating and some simple wood stoves for space heating. I'd like to replace both of these with a combination solar and rocket-powered heating system. I'd like to build a Peter Berg batchbox rocket that we can light 1-2 times a day during the winter and capture all the heat for use during the remainder of the day.
My thought at the moment is to have a batchbox rocket that dumps some heat into a bell, but also to place a heat exchanger of some sort into the top of the bell. This would feed a coil in a DHW cylinder, and possibly also a thermal accumulator that could be used for space heating via underfloor heating. Both the cylinder and the accumulator could potentially also have secondary coils fed from solar to supplement/provide an alternative for water heating in warmer months.
My primary question concerns the design and placement of the heat exchanger. Does anyone have any experience with this? I'm not enormously keen on the approach taken by Geoff Lawton in his video, because it doesn't really address the requirement for storing the energy efficiently from a batch burn. The only thing that seems very clear from all that I've read is that whatever mechanism is used should be placed after the main heat riser rather than e.g. coiled around it. The obvious choice would be something immediately above the main heat riser, but I worry that this would be far *too* fierce, and it would also make a thermosiphon much harder to achieve. Instead, my thought was to place a tall copper coil inside a bell immediately after the heat riser, but I have no idea of e.g. I would be better off with a plate exchanger, or if I should be thinking of putting it earlier/later in the system.
The second question I had arises from the fact that I don't really want to have any immediate radiant output from the system - everything should either end up in the water or in the mass. Does this have implications for the flow through the system? Most of the designs I've seen have a highly conductive radiant surface immediately above the primary heat riser, which I guess cools the exhaust gases quite dramatically and encourages them to fall down and through the rest of the system. If this first part of the system were instead quite well insulated in order to move more of the heat extraction later (and lower) in the system, is that likely to compromise the efficiency of the burn?
Cheers,
Lucian
My primary question concerns the design and placement of the heat exchanger. Does anyone have any experience with this? I'm not enormously keen on the approach taken by Geoff Lawton in his video, because it doesn't really address the requirement for storing the energy efficiently from a batch burn. The only thing that seems very clear from all that I've read is that whatever mechanism is used should be placed after the main heat riser rather than e.g. coiled around it. The obvious choice would be something immediately above the main heat riser, but I worry that this would be far *too* fierce, and it would also make a thermosiphon much harder to achieve. Instead, my thought was to place a tall copper coil inside a bell immediately after the heat riser, but I have no idea of e.g. I would be better off with a plate exchanger, or if I should be thinking of putting it earlier/later in the system.
The second question I had arises from the fact that I don't really want to have any immediate radiant output from the system - everything should either end up in the water or in the mass. Does this have implications for the flow through the system? Most of the designs I've seen have a highly conductive radiant surface immediately above the primary heat riser, which I guess cools the exhaust gases quite dramatically and encourages them to fall down and through the rest of the system. If this first part of the system were instead quite well insulated in order to move more of the heat extraction later (and lower) in the system, is that likely to compromise the efficiency of the burn?
Cheers,
Lucian