Post by stoker on Mar 8, 2015 17:44:05 GMT -8
This post is a request for suggestions, or for comments on the thoughts I've written here.
I'd like to make, buy, or buy-and-improve a wood-burning heating-stove for a canvas tent (currently a 5m-diameter bell-tent) for when the outside temperatures are in the range of maybe -10 to +15 degrees C.
Being able to cook on it as well (or even just have hot water) would be a bonus, but not essential.
For transport and storage I don't want it to be much more than, say, 20kg or 70 litres: there's limited space in the car. This means a mass heater is not an option.
Given the shape of the tent (mostly-conical roof on low walls), a stove could go near the central pole with a flue going up through the roof, or near a side of the tent with the flue going through either the roof or the wall. If it's near the side then it can't be too high, since the walls are only two feet high (perhaps a little less).
It needs to be raised off the ground enough not to melt or burn the groundsheet.
If I didn't know or care about issues of efficiency or smoke, I'd probably buy something like a Frontier stove...
www.badgerbushcraft.com/kit-tried-a-tested/the-frontier-stove-by-camping-solutions-review.htm
quite cheap at around £150 (including flue) from many sellers
Or I could get one of the many different cheap simple inefficient-looking things on ebay, e.g.
www.ebay.co.uk/itm/WS1-/271760575276
www.ebay.co.uk/itm/M-/371274292672
along with a flue and something to protect the groundsheet from the hot stove.
A nice point about the Frontier is that the flue can be stowed inside the stove for transport. (That flue is only 6cm diameter though, 2.36"... very narrow.)
I'm sure any of those will work, but I'd much rather have something that burns cleanly, and preferably heats the tent efficiently rather than sending most of the heat up the chimney.
Are things like that the best I can do given the constraints, or is there a better alternative?
Perhaps a rocket, but not necessarily.
I've read a lot, but haven't seen much that's obviously directly appropriate.
There are two parts to the problem: one is burning wood cleanly at an adequate rate in a small stove, and the other is transferring the heat to the surroundings from limited surface area.
Some threads with ideas that could be useful:
A 3.5" system that's almost a conventional J-rocket, except for the capped feed-tube and L-style air-feed:
donkey32.proboards.com/thread/1001/successful-portable-low-mass-rocket
Small and hot, though it runs on pellets and I'd be using sticks or split wood:
donkey32.proboards.com/thread/1591/killer-3-incher
I like the riser made from soft rather than brittle material, given that I'll want to transport the thing by car several times per year.
I imagine something just a little like vortex's stove with its damper open could be made by adding baffles (and some insulating tiles/bricks) inside the Frontier stove or similar:
donkey32.proboards.com/thread/703/vortex-stove
That might be a decent compromise in terms of cost, time, effort and results... depending on how easy it is to get suitable curved bits to go in there... maybe the part that contains the wood could be one of the tougher varieties of riser-sleeve or similar... or is it too fragile? donkey32.proboards.com/thread/1002/heatriser-vacuum-formed-refractory-ceramic
Some secondary air would probably help, and wouldn't be too hard to arrange with some copper plumbing-pipe.
Any thoughts or comments on that?
Maybe I should consider a standard Peterberg-type batch-box-and-riser. What's the smallest this has been tried? I get the impression the batch-box gives more power than a J-tube for a given size of riser and box-or-J (or can be smaller for a given power output). In a comparison experiment, radek was able to burn 8.5kg/hour in 15cm batchbox or 4.5kg/hour in a 20cm J-tube: donkey32.proboards.com/thread/965/approximet-output-20cm-tube-batch
I'm not sure which will be more valuable: radiant heat (heating whatever's in line of sight of the stove) or conduction/convection (heating the air in contact with the stove, which will then mostly go to the top of the tent).
To get a lot of power out of a limited surface area by radiation, it has to be at a very high temperature, perhaps glowing. (This is how gas-fires and electric bar-fires do it, after all.) Insulation of combustion areas helps there. So does preheating of air, which quite easy for secondary air, but not practical for primary unless I were to use a fan or similar (and I'd rather not).
Radiant heat will warm the things and people it hits, but not the other sides of those people, and most will strike the tent walls which are kept cold by the wind outside.
For air-heating, the surface temperature helps, but the other factor is the rate of flow over the surface. A fan could help a lot with that. I'd rather avoid it if possible, but I'm not ruling it out completely.
Some calculations:
For a 3" diameter riser with 1" insulation, its cross-sectional area is such that a 5.83" barrel (or equivalent) around it would give the same area in the 0.42" gap between riser and barrel.
Or if the riser were 4" with 1" insulation, then a barrel of 7.21" internal diameter barrel would match its CSA in the 0.61" gap.
Those don't seem excessively bulky, but might be too small to give off enough heat, and might need to be a little fatter to reduce flow-resistance.
I wonder if a batchbox (or the core of a J system) could be packed for transport inside its own barrel-radiator-equivalent, perhaps wrapped in the ceramic blanket that acts as heat-riser when assembled.
On these forums I've seen some examples of people using glass for doors, sides or tops of batchboxes and burn-tunnels. That could help with radiant heat. It means the fire isn't as hot, but so long as it burns cleanly I suppose that's fine.
How about glass (the kind used on halogen hobs?) over the top of the heat riser, with a shiny aluminium or stainless-steel mirror at an angle above it to reflect the light and infra-red in a useful direction? I don't know if anyone's tried glass over a heat riser; the closest thing I've seen is this man using a glass disc cooking-plate, but not over a heat-riser:
www.youtube.com/watch?v=GuNS0q457wE
www.youtube.com/watch?v=jxcP7IR2Qo4
In general it's quite impressive how cleanly most of his contraptions seem to burn, given the lack of insulation: it looks as if you can get away with a lot if you have sideways flames and a decent-height chimney with reasonably hot gases entering it.
As for warmth through the night and at getting-up time, I think that's probably not going to be practical. A mass heater is not an option (I think the possibilities for stored heat are limited to hot water bottles or those sodium-acetate-solution clicky things). For a stove to keep burning for several hours it would need a lot of wood stored up somehow.
This is about the best I've seen for self-feeding, but he ended up using a forced-air arrangement:
bundles of wood, sliding down a long capped feed tube, with air entering the burn chamber horizontally in the first version.
greenenergyexperimenter.com/wp/?p=123
It was a bit problematic, and worked better with air pushed down the feed tube by a fan.
More detail on that in Geo Schoonmaker's comments on this thread:
www.permies.com/t/10419/rocket-stoves/Rocket-stove-slide-burning-foot
I'd like to make, buy, or buy-and-improve a wood-burning heating-stove for a canvas tent (currently a 5m-diameter bell-tent) for when the outside temperatures are in the range of maybe -10 to +15 degrees C.
Being able to cook on it as well (or even just have hot water) would be a bonus, but not essential.
For transport and storage I don't want it to be much more than, say, 20kg or 70 litres: there's limited space in the car. This means a mass heater is not an option.
Given the shape of the tent (mostly-conical roof on low walls), a stove could go near the central pole with a flue going up through the roof, or near a side of the tent with the flue going through either the roof or the wall. If it's near the side then it can't be too high, since the walls are only two feet high (perhaps a little less).
It needs to be raised off the ground enough not to melt or burn the groundsheet.
If I didn't know or care about issues of efficiency or smoke, I'd probably buy something like a Frontier stove...
www.badgerbushcraft.com/kit-tried-a-tested/the-frontier-stove-by-camping-solutions-review.htm
quite cheap at around £150 (including flue) from many sellers
Or I could get one of the many different cheap simple inefficient-looking things on ebay, e.g.
www.ebay.co.uk/itm/WS1-/271760575276
www.ebay.co.uk/itm/M-/371274292672
along with a flue and something to protect the groundsheet from the hot stove.
A nice point about the Frontier is that the flue can be stowed inside the stove for transport. (That flue is only 6cm diameter though, 2.36"... very narrow.)
I'm sure any of those will work, but I'd much rather have something that burns cleanly, and preferably heats the tent efficiently rather than sending most of the heat up the chimney.
Are things like that the best I can do given the constraints, or is there a better alternative?
Perhaps a rocket, but not necessarily.
I've read a lot, but haven't seen much that's obviously directly appropriate.
There are two parts to the problem: one is burning wood cleanly at an adequate rate in a small stove, and the other is transferring the heat to the surroundings from limited surface area.
Some threads with ideas that could be useful:
A 3.5" system that's almost a conventional J-rocket, except for the capped feed-tube and L-style air-feed:
donkey32.proboards.com/thread/1001/successful-portable-low-mass-rocket
Small and hot, though it runs on pellets and I'd be using sticks or split wood:
donkey32.proboards.com/thread/1591/killer-3-incher
I like the riser made from soft rather than brittle material, given that I'll want to transport the thing by car several times per year.
I imagine something just a little like vortex's stove with its damper open could be made by adding baffles (and some insulating tiles/bricks) inside the Frontier stove or similar:
donkey32.proboards.com/thread/703/vortex-stove
| |
| |
| |___________________________________________,
| Modified Frontier stove |
|########################################## |
|## |
|# #######insulating#baffle###################
|# :
|## wood is here : door
|### :
|############insulation##########################
or
| |___________________________________________,
| |
| |
|##########insulating#baffle################# |
|# |
|# :
|## wood is here : door
|### :
|##########insulation############################
That might be a decent compromise in terms of cost, time, effort and results... depending on how easy it is to get suitable curved bits to go in there... maybe the part that contains the wood could be one of the tougher varieties of riser-sleeve or similar... or is it too fragile? donkey32.proboards.com/thread/1002/heatriser-vacuum-formed-refractory-ceramic
Some secondary air would probably help, and wouldn't be too hard to arrange with some copper plumbing-pipe.
Any thoughts or comments on that?
Maybe I should consider a standard Peterberg-type batch-box-and-riser. What's the smallest this has been tried? I get the impression the batch-box gives more power than a J-tube for a given size of riser and box-or-J (or can be smaller for a given power output). In a comparison experiment, radek was able to burn 8.5kg/hour in 15cm batchbox or 4.5kg/hour in a 20cm J-tube: donkey32.proboards.com/thread/965/approximet-output-20cm-tube-batch
I'm not sure which will be more valuable: radiant heat (heating whatever's in line of sight of the stove) or conduction/convection (heating the air in contact with the stove, which will then mostly go to the top of the tent).
To get a lot of power out of a limited surface area by radiation, it has to be at a very high temperature, perhaps glowing. (This is how gas-fires and electric bar-fires do it, after all.) Insulation of combustion areas helps there. So does preheating of air, which quite easy for secondary air, but not practical for primary unless I were to use a fan or similar (and I'd rather not).
Radiant heat will warm the things and people it hits, but not the other sides of those people, and most will strike the tent walls which are kept cold by the wind outside.
For air-heating, the surface temperature helps, but the other factor is the rate of flow over the surface. A fan could help a lot with that. I'd rather avoid it if possible, but I'm not ruling it out completely.
Some calculations:
For a 3" diameter riser with 1" insulation, its cross-sectional area is such that a 5.83" barrel (or equivalent) around it would give the same area in the 0.42" gap between riser and barrel.
Or if the riser were 4" with 1" insulation, then a barrel of 7.21" internal diameter barrel would match its CSA in the 0.61" gap.
Those don't seem excessively bulky, but might be too small to give off enough heat, and might need to be a little fatter to reduce flow-resistance.
I wonder if a batchbox (or the core of a J system) could be packed for transport inside its own barrel-radiator-equivalent, perhaps wrapped in the ceramic blanket that acts as heat-riser when assembled.
On these forums I've seen some examples of people using glass for doors, sides or tops of batchboxes and burn-tunnels. That could help with radiant heat. It means the fire isn't as hot, but so long as it burns cleanly I suppose that's fine.
How about glass (the kind used on halogen hobs?) over the top of the heat riser, with a shiny aluminium or stainless-steel mirror at an angle above it to reflect the light and infra-red in a useful direction? I don't know if anyone's tried glass over a heat riser; the closest thing I've seen is this man using a glass disc cooking-plate, but not over a heat-riser:
www.youtube.com/watch?v=GuNS0q457wE
www.youtube.com/watch?v=jxcP7IR2Qo4
In general it's quite impressive how cleanly most of his contraptions seem to burn, given the lack of insulation: it looks as if you can get away with a lot if you have sideways flames and a decent-height chimney with reasonably hot gases entering it.
As for warmth through the night and at getting-up time, I think that's probably not going to be practical. A mass heater is not an option (I think the possibilities for stored heat are limited to hot water bottles or those sodium-acetate-solution clicky things). For a stove to keep burning for several hours it would need a lot of wood stored up somehow.
This is about the best I've seen for self-feeding, but he ended up using a forced-air arrangement:
bundles of wood, sliding down a long capped feed tube, with air entering the burn chamber horizontally in the first version.
greenenergyexperimenter.com/wp/?p=123
It was a bit problematic, and worked better with air pushed down the feed tube by a fan.
More detail on that in Geo Schoonmaker's comments on this thread:
www.permies.com/t/10419/rocket-stoves/Rocket-stove-slide-burning-foot