Post by nick on Jan 30, 2009 3:55:52 GMT -8
Hi all,
Been gleaning information from here for a while so I thought I'd let you guy know about our new rocket powered water heater.
It's based on a six inch rocket.
The burn chamber made out of low density fire brick (seconds i got for 50c each) covered in cob.
The heat riser is a chunk of scrap stainless flue pipe (single wall but over 1mm thick) insulated in a 60 litre drum full of vermiculite.
The bit I'm most proud of is the heat exchanger. I made it from a salvaged old school Australian wood fired water heater. A very low tech device known locally as a ... wait for it... a donkey :)
A donkey (at least the local version) is made by welding sheet steel into a simple water jacket, a cube in a cube, double skin on the sides, open bottom and flue collar and feed door on the top. The water being able to flow around the sides, entering through a pipe near the bottom and exiting near the top. A fire is built in the guts of the donkey and after a while it produces hot water for a bath or shower.
A donkey has the advantage of being easy to make by anyone who can weld and because a large volume of water is being heated at any one time there is virtually no risk of steam locks occurring. (unlike with coils of pipe). Of course it has a major disadvantage of producing a very cool burn.
So i took the donkey, cut off the useless bits, welded a series of baffle plates inside the inner cube and a new flue collar on a new bottom plate and mounted it above the heat riser of my six inch rocket. I was very careful to ensure the baffles reduced the cross sectional area of the gas path to just a little wider than the six inch flue.
www.flickr.com/photos/cicada/sets/72157613058564419/
It works great, because of the very low mass of the stove it heats up very quickly and draws, well, like a rocket ... and within ten minutes i have enough hot water to have a five minute long hot shower. A one hour burn gives about 40 minutes of hot water.
The heat exhanger is much easier to make than the complex heat exhangers in the big wood fired furnaces because of the gas -> steel baffle -> water pathway of the energy. No complex welds like in a manifold based design, no large complex joins of a back and forth flue through a water tank. The only welds that need to be waterproof are the ones around the simple water jacket.
Not sure exactly how many BTU's it's harnessing and it is the middle of summer here, but it works soooo much better than the donkey did.
I'm chuffed :)
Sorry i have no detailed photos of the heat exchanger, but i did shoot video of the welding process, so we should have it up on our blog in the next few weeks www.milkwood.net
Been gleaning information from here for a while so I thought I'd let you guy know about our new rocket powered water heater.
It's based on a six inch rocket.
The burn chamber made out of low density fire brick (seconds i got for 50c each) covered in cob.
The heat riser is a chunk of scrap stainless flue pipe (single wall but over 1mm thick) insulated in a 60 litre drum full of vermiculite.
The bit I'm most proud of is the heat exchanger. I made it from a salvaged old school Australian wood fired water heater. A very low tech device known locally as a ... wait for it... a donkey :)
A donkey (at least the local version) is made by welding sheet steel into a simple water jacket, a cube in a cube, double skin on the sides, open bottom and flue collar and feed door on the top. The water being able to flow around the sides, entering through a pipe near the bottom and exiting near the top. A fire is built in the guts of the donkey and after a while it produces hot water for a bath or shower.
A donkey has the advantage of being easy to make by anyone who can weld and because a large volume of water is being heated at any one time there is virtually no risk of steam locks occurring. (unlike with coils of pipe). Of course it has a major disadvantage of producing a very cool burn.
So i took the donkey, cut off the useless bits, welded a series of baffle plates inside the inner cube and a new flue collar on a new bottom plate and mounted it above the heat riser of my six inch rocket. I was very careful to ensure the baffles reduced the cross sectional area of the gas path to just a little wider than the six inch flue.
www.flickr.com/photos/cicada/sets/72157613058564419/
It works great, because of the very low mass of the stove it heats up very quickly and draws, well, like a rocket ... and within ten minutes i have enough hot water to have a five minute long hot shower. A one hour burn gives about 40 minutes of hot water.
The heat exhanger is much easier to make than the complex heat exhangers in the big wood fired furnaces because of the gas -> steel baffle -> water pathway of the energy. No complex welds like in a manifold based design, no large complex joins of a back and forth flue through a water tank. The only welds that need to be waterproof are the ones around the simple water jacket.
Not sure exactly how many BTU's it's harnessing and it is the middle of summer here, but it works soooo much better than the donkey did.
I'm chuffed :)
Sorry i have no detailed photos of the heat exchanger, but i did shoot video of the welding process, so we should have it up on our blog in the next few weeks www.milkwood.net
