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Post by dustin on Nov 16, 2015 21:41:45 GMT -8
Do you have more detailed instructions on how to build a safe water heater like the one you show in your Facebook page?
Dustin
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Post by Donkey on Nov 17, 2015 1:34:51 GMT -8
I haven't written anything, no. What in particular would you like to know?
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Post by patamos on Nov 17, 2015 13:47:32 GMT -8
I'm curious too.
What if any changes have you made since the earlier experiment in your cabin?
Questions about bell size relative to tank size…
The pics give a pretty good indication, and/but a few comments might add to it...
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Post by dustin on Nov 17, 2015 15:45:16 GMT -8
I am building a Rocket Mass Heater in China. I want to also use it to heat water, as well as my bench inside the house. The heater is outside. I have some questions:
1. Why not just wrap high temp stainless steel tubing inside the heat riser, instead of using your method? 2. I am considering adding a steam engine to the system. Does your system boil the water inside the holding tank? 3. My RMH is below my roof and I don't think my roof is tall enough to compensate for the added height of the water barrel. Are there any options which would not require adding much height, such as putting the water somewhere else lower in the system? (or if I have no choice I would have to mess with my roof to get the thing to fit) 4. Could I use a barrel insulated with cob, instead of using bricks? 5. Will there be enough heat left over which I can use to channel through my cob bench? (It is about 30 feet in length and the temperature here is mild, not too cold)
I can send pictures to explain further...
Dustin
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Post by patamos on Nov 17, 2015 21:22:43 GMT -8
Hi Dustin Most of your questions can be answered over at the RMH forum: Donkey32.proboards.com (i think). In short though: 1. steel doesn't lsat in these combustion environments 2. boiling water is undesirable as one must enter the world of high pressure systems. Coupled with a short intense fire-cycle of many rockets… not a good combo. These water tanks are vented so that pressure has a way out if it gets to 100c 3. lower wider water tank in a lower wider bell. 4. barrel *for the outer casing i presume) yes. but cob is non insulating, so perlite-clay mix or ceramic wool or rock wool or the like instead. 5. depends on a few things: how big your water tank is; how hot you want to get it: heater CSA system size and type of feed chamber (J… L… matchbox... An 8" J-might do it. Maybe a 6" batch. BUt you could be asking for a lot at once. Perhaps setting up a bypass damper so that you can route the gasses towards your preferred application at that time. Lots of info over at the other boards. As in: you could study the threads full time for years and still be learning new things...
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Post by Donkey on Nov 18, 2015 12:18:13 GMT -8
For question # 1: Removing heat directly from the riser breaks the first rule in Rocket Stoves. Intense heat is REQUIRED inside the riser for complete combustion and removing heat there will only reduce efficiency and promote dirty burn. Though water would keep coils in there from being eaten away by the fire, it is a steam explosion risk.
I should get it together and post the newest water heater, both here and at the Rocket Stove forums. I'll do it in the next day or two.
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Post by dustin on Nov 18, 2015 14:56:29 GMT -8
Dear All, I already built a 8 inch J. I built a custom made barrel but I don't think it is wide enough so I want to build another one which gives 4 inches of space between the riser and barrel. 1. Can I put the hot water absorbing tank lower to the ground by building a second "bell"? 2. How effective would it be to use the thermal mass rocks/sand to create a heat battery to keep the water very warm for many hours? (I want to experiment with not only using the hot water for showers, but also to pump through PEX tubing in floor inside house, so I need a continuous heat source but I don't want to keep putting wood in the stove all day. I have an electric water heating wand which can bring my 80 gallon water reserve tank up to 100 degrees in 4 hours. So if I combine that with the heat from the J-tube and thermal mass it might be enough to power the radiant floor heating in my 3.5 diameter room. I live in a mild climate. It doesn't snow or freeze here. ) 3. How big (gallons) should the water holding tank be? In the Sundog Builders example it was 20 gallons. Was that the right size, or could it be bigger? I think I want to build a stone/concrete water tank on the ground with the hot gasses flowing under and around it. I assume this would allow me to take advantage of the thermal battery effect of the stones. Perhaps at the bottom I would put more stones and on the sides use a thinner layer of concrete and stones so that I get both longer heat storage and quicker heat up times. 4. Will there be enough heat (hot gasses) left over to heat a bench?Dustin
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Post by dustin on Nov 19, 2015 4:35:52 GMT -8
Here are some more pictures... Below, I have the 80 gallon water tank above a mass of concrete and stones. Inside are 2 - 8 inch tubes. I am not sure if it is a good idea to use both of them? I assumed if I use 2 I have more area to heat up underneath the water tank.Below, the bottom tube goes into the 3.5 meter diameter room which has a bench and tubing inside. I am not sure if the fact that the hot gasses would have to go downhill will affect performance?I used cardboard tubing as a form and clay/sand mixed with sodium silicate. It seems pretty strong now that it is dry. I don't think there is enough space between the riser and the barrel, less than 2 inches I think. I want to build a new barrel that gives at least 4 inches. Then cover it with perlite/clay. I need to figure out where to build the water heater. The roof is above the barrel and I don't think there is enough space to put the water above the barrel.
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Post by dustin on Nov 19, 2015 14:30:10 GMT -8
Dear All,
What if sand and stones was added into the water tank along with the stainless steel water tubing? Would this still considered to be in water and thus the temperature would not exceed 100 degrees celsius? I was thinking that adding sand, stones and rocks into the water could increase the thermal battery properties.
Dustin
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Post by patamos on Nov 20, 2015 10:54:08 GMT -8
I'm flat out busy lately so cannot give much analysis to your overall plan. ALso missed the obvious point that Donkey brought up about keeping the heat riser hot…
All in all though, i think it depends on how much you want to heat the water. I've seen numerous masonry/rocket builds in Europe where they place water lines 4" or so away from the inside bell/flue walls. This probably only pre-heats the water somewhat. This can work, but you still have to be careful about worst case scenarios. e.g., someone firing the unit for hours at a time in summer. It has to be fool proof. To that end, i would always advise for a vented tank. Then you don't have to worry about bombs exploding.
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Post by Donkey on Nov 20, 2015 17:17:26 GMT -8
Dustin, you REALLY should post all of this over at the Rocket Stove forum. There are a LOT of really smart people over there that are very much into this technology and they will be glad to analyse and help work the bugs out of your design. More heads are better than just one or two... donkey32.proboards.comHaving said that: My first thought is that a stove designed to heat water for a floor/hydronic system is going to need to be much larger than what you have there. Rocket Stoves don't actually pump out a lot of BTUs (at least, the J-tube stoves don't), what they are good at is efficiently storing and slowly releasing the heat that they do produce. This makes it so that they don't NEED to produce nearly as much heat as other stoves to get similar benefit. I think that you will be greatly disappointed in a hydronic system with a Rocket Stove as it's primary heat source. You will also need to feed the thing constantly for a long time to get your desired effect. You can place a bell with the water tank in beside your stove and feed heat (down) into it. Remember that the entrance to the bell and especially the exit from the bell (to the chimney) must be at the bottom for it to work properly. 15-20 gallons is about right for showers. My theory (and it seems to work well so far) is that heating LESS water for that system is better. I can get that water hot very quickly for a couple of showers, with very little wood. If I want to give more showers, it can be fired continuously with very little wait time between showers to re-heat. It takes about 30-45 minuets to heat 20 gallons up to shower with, you can imagine how long it will take with a larger tank.
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Post by dustin on Nov 23, 2015 15:22:51 GMT -8
Donkey Do you have any diagrams on the bell portion? I am not clear how big of an opening I should make and how low below the exit needs to be. See my current state of building in the picture below....
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Post by Donkey on Nov 24, 2015 10:47:06 GMT -8
To work at all, bells must have a cross sectional area that is at a MINIMUM, 4 times that of the "system size". Bigger is better. The exhaust from the bell (to the chimney) should be as low on the bell as possible. You want only the coldest gassed to enter the chimney, which can be found at the bottom. Openings further up will interrupt the natural "free gas movement" inside of the bell, effectively draining heat away before it has had a chance to do it's work.
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Post by dustin on Nov 24, 2015 15:01:04 GMT -8
Donkey, thanks for your response! How do I calculate the "system size"? Will this bell setup also work for venting gasses through a bench to heat it up?
Dustin
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Post by patamos on Nov 24, 2015 17:51:07 GMT -8
Hi Dustin,
As Donkey mentioned, all the information and assistance you are seeking is over at the rocket forum. He an many of the others who got that forum up and running years ago have answered questions like 'calculating system size' and 'bench bells' countless times. It really is worth investing some time to read back through many of those threads - particularly the reference library, to gain answers to such questions.
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