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Post by raymilosh on Feb 22, 2019 9:53:01 GMT -8
I built a standard 8" j tube rocketstove with a standard 55 gallon drum in a 1500 ft2 shop in NC. I built it to be low mass because I only use the shop periodically, so I want it heated quickly and I don't need it to stay warm after I leave. I set a small electric water heater tank atop the 55 gallon drum and plumbed it to the hydronic floor heating system in the shop. I wrapped the supply line (50 ft of 5/8 copper) around the chimney to preheat it and also wrapped the return line (5/8" copper) around the chimney to additionally boost the temp.
I encased the 8" chimney with the copper tubes wrapped around it inside a 10" diameter galv pipe to act as a radiant insulator. I also covered the water heater in a galvanized tin cover to trap the heat/act as a radiant insulator. I then covered the tin cover with a piece of a 55 gallon drum for aesthetics.
The sensor to turn on the pump to circulate the water is on the chimney pipe. As soon as the chimney gets warm, the pump turns on. I'd rather have it turn on too soon than risk overheating water in the tank.
So the heater quicky warms the garage. the water in the tank takes a long time to get warm. The tin cover over the water heater tank works remarkably well. the 55 gallon drum cover gets slightly warm on the outside and that's it. All the remainder of the heat coming off the top of the heater presumably winds up in the water.
Wrapping the supply and return around the chimney was a lot of work and cost a fair amount of money, but it does do its job of scavenging additional heat from the chimney, so I kind of guess maybe it was probably not worth it.
I had to throttle the circulator pump way back to prevent it from circulating the water so fast that it didn't have much time to get warm.
The way I burn this heater for occasional evening heating makes the whole rocketstove hydronic heating idea not exactly worth the effort. I think the low mass aspect just wastes some to the heat. I don't run it enough to get the floor warmed up much. If the shop gets used more frequently in the future, I'd install a mass bench and I'd imagine that the floor would warm up more. I may have done as well to have a large, low mass super efficient radiant woodstove (if such a thing exists...I have never looked for one).
All that being said, it is a great conversation piece and it is introducing many people to rocketstoves and I love it anyway.
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Post by gadget on Feb 22, 2019 18:44:39 GMT -8
The way I burn this heater for occasional evening heating makes the whole rocketstove hydronic heating idea not exactly worth the effort. Thanks for sharing your experience. I'm was running into similar results when I first started heating water with my mini tester rocket. I'm now getting some decent water heat after some upgrades and more testing. I'm heating a total of 385 gallons and circulation in grow beds. Check it out; Mini Rocket with forced induction
I think the reason you didn't get much increase in your water temps is because of where you where collecting. Its all about the temperature gradient. You need to get the heat exchangers exposed to higher temps. I first started with a 5 foot long 3/8 copper coil INSIDE the drum above the riser. It worked ok. Problem was I was getting water condensing on the coil and dripping inside the drum area. This heater has a draft inducer. I upgraded the blower and started getting much more heat out of the heater, way more. I now have 25 feet of 3/8 copper in the drum and 20 feet of 1/2 copper in the second bell. I have a 55 gallon central water barrel that sees about a 1 degree rise in temp every 10 minutes or so. I am upgrading the coil in my drum to a 50 foot 1/2 coil. It is about 2.5 times more surface area for the heat exchanger. I still have to much heat leaving the barrel and hopefully this will add more heat to the water. I went from not having enough heat to having to much. Heating water quickly with a rocket looks feasible from what I have experienced. It just takes a ton of heat. That brings up the other problem. Good water heat exchangers tend to kill the draft. It may be that for good/quick water heating a blower is needed. Any final build I have will be open loop on both ends and gravity drain back.
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Post by Orange on Feb 24, 2019 0:53:19 GMT -8
I have a central heating system without the water tank. If a fire in a bach box last for an hour radiators will cool down shortly after fure runs out.
Any idea of putting steel/copper exchange pipes into clay mass, how that works compared to water tank as heat storage?
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Post by gadget on Feb 24, 2019 12:04:44 GMT -8
I have a central heating system without the water tank. If a fire in a bach box last for an hour radiators will cool down shortly after fure runs out. Any idea of putting steel/copper exchange pipes into clay mass, how that works compared to water tank as heat storage? I had the same question and tried some copper in a very hot part of some clay mass. It does not work very well. Problem is the slow heat transfer through the mass. You will get some heat but I don't think its practical. If a very large amount was buried through out the entire mass it might do ok. It would take hundreds of feet of tubing. Even then, it would not be as good as a few feet of copper inside the gases path. The other problem is the temperature difference is not enough. In my experience a large temperature gradient is much more affective. This is universally true for heat exchangers, the higher the gradient the better the transfer. It would be safer but you pay a huge price on performance = basically no performance at all. I'm currently experimenting with water tank storage with very good results. I have one tank that is the main centrally located heat storage. After I heat it up, I run a pump from it to heat my grow beds. It stays warm all night. Water is the best storage for heat in the sub 180F
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Post by Orange on Feb 25, 2019 11:05:27 GMT -8
thanks for the info. There's also a possibility of directly heating the water tank, without heat exchanger.
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