Rocket Mass Incorporating Water Heating?

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Rocket Mass Incorporating Water Heating?

Postby mannytheseacow » Thu Feb 28, 2013 5:34 pm

Anyone ever try incorporating water heating into the design? My current potbelly has a 1/2" copper coil around the exhaust cased in steel mesh and mortar. It's worked okay for a few years but the mortar is falling apart. All the reading on these rocket stoves is teaching me how I could have done it much better... but anyway... I'm thinking when I cast my core for a RMH I can incorporate the copper coil into the core cast, right along with the temperature sensor which turns the circulation pump on and off.

I'm thinking maybe recessing a small piece of conductive tubing like copper or something that I can place the temp. sensor in and remove it should it need replacing.

Through experimentation I arrived at 1/2" copper coil for the potbelly, but I'm wondering if anyone has experience with my idea for RMH and if so what size heat exchanger they used? Also, how the exchange affected the ability to heat the thermal bench? I'm currently circulating water into a 250 gallon tank with another pump that circulates through 148 sq.ft. of solar collectors. Theres a 250 roll of 1" pex that sits in the tank and acts as a heat exchanger bringing my well water up to temp before hitting the hot water faucet. I only use the water in the tank for thermal heat storage for heat exchange and radiant in-floor heat.

I was trying to add an image of the current coil system but can't figure out how~ wah wah wah....
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Re: Rocket Mass Incorporating Water Heating?

Postby matt walker » Thu Feb 28, 2013 6:16 pm

Manny, to post a pic you should put it up on a hosting site like Flickr or photobucket, then link to it here using the IMG tags in the posting window.

As for water, I haven't done it, but here's the thing; the advantages of the rocket stove come from the relatively new concept of keeping all the heat on the burning fuel, then harvesting it after the burn is complete. So, don't try to take the heat from anywhere in the burn works. Instead, incorporate your coils into the mass, around the flue, after the main barrel. In that way you can still get a complete, efficient burn. My bench is still well over 100*F 12 hours after a burn, so there should be plenty of heat available there. It won't heat as quickly as it might in the burn zone, but with a properly designed system I would think it would be far easier to have available hot water at all times. Be safe, as I'm sure you are aware there are extremely dangerous pitfalls in water heating systems.
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Re: Rocket Mass Incorporating Water Heating?

Postby pa_friendly_guy » Thu Feb 28, 2013 8:26 pm

I am not an expert, and I do not have a RMH, so what I am saying is gained from what I have read, and what I can figure out from what you have said about your use of the hot water. I agree that putting the water lines inside the burn chamber or around the upright burn chimney inside the barrel are OUT. The heat is too high and the chance for a steam explosion are way too high. Even with circulating the water as you burn the chance of a steam explosion would still be very high in my opinion. I have heard of people wrapping flexible copper lines around the outside of the burn barrel and they felt it worked ok, but they did not have enough hot water in the lines to take a bath with out adding more hot water from a stove. Matts idea of running the lines through the cobb makes good sense. You will still need a fairly long water line run either back and forth through the cobb or around the exhaust pipe. I would have a concern about having the copper line directly around the exhaust pipe. I think running it through the cobb would have the advantage of staying warm for a much longer time. Since you are using the storage tank as a heat exchanger and not using the water directly you have the advantage of being able to use water of a much lower temperature to your advantage. Heating the floor can be done with water at 90 degrees or so, taking a shower can't use water of the lower temps. Matt is correct that it would take longer to heat up at 1st, but you get the fly wheel effect at the back end as it stays warm for an extended period. You should still have a pop off safety valve on the system and maybe a one way check valve to insure the warm water always flows the right way into your tank.
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Re: Rocket Mass Incorporating Water Heating?

Postby mannytheseacow » Fri Mar 01, 2013 7:10 pm

Oops, I should have included that my system is vented, not sealed. Yup, those sealed systems can be dangerous. I get what you're saying about incorporating it into the core mass, perhaps I'll try putting lines in the mass itself. The downside is that I'm running on solar electricity, too so I don't want the circulation pump running too long. Quick heating is most efficient. I'm currently keeping my water right at 110* F. Any cooler is too cold for showers and stuff, and any warmer is just wasting energy.

I'm reminded by a quote by Luna Leopold: "The answers ain't in the book. The answers are in the river." I'll do some experimenting and tweaking as the build evolves, and let you know how it works!
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Re: Rocket Mass Incorporating Water Heating?

Postby matt walker » Fri Mar 01, 2013 7:36 pm

Right on man. Just FYI, my mass, under a cushion, 12' downstream from the stove, idles at around 250° when the stove has been running for a few hours.
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Re: Rocket Mass Incorporating Water Heating?

Postby pa_friendly_guy » Fri Mar 01, 2013 10:04 pm

Do you think that it could be possible to have the water syphon through the system by putting check valves at each end, and perhaps even along the main run through the mass. Hot water rises, so it would naturally flow up toward the top of your storage tank from the cobb mass which would be lower. That would create a void and suck in cooler water from the bottom of your storage tank into the system. I know that kind of heat syphon has been tried before, I do not know how well it works. If your system is open and there is space at the top of your storage tank you should be able to hear the water pouring into the tank. I have thought about trying to make a hot water system like that to naturally circulate hot water through a floor for heating. Making the hot water flow down to the floor level seemed to be problematic in my mind. But with one way check valves along the water lines to keep the expanded hotter water moving along and an expansion tank to create a small amount of pressure through the system I think it should work. I would put the expansion tank on the cold water side to keep the water moving through the system. At least it works in my mind, :lol: It may not work in practice with out a pump to help it along, but I can not see any reason why it would not work. Remember, I am NOT an engineer, so hopefully someone smarter than I am can think about the idea and pick it apart. My neighbor tried to heat his hot water to heat his house on his metal wood stove, He had a boiler, but he put a large metal tank on top of the wood stove to heat the water before it went into the boiler system. He still had a pump on the system when it called for heat in the house. His system did not work well, his tank was not insulated and only the bottom of the tank touched the top of the stove. He had trouble getting the water in the tank much above 90*. The stack temps from the stove were around 200* so he was burning the stove slowly for a long burn time. With the high temps in the rocket stove you should have a lot better system to heat your water.
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Re: Rocket Mass Incorporating Water Heating?

Postby mannytheseacow » Mon Mar 04, 2013 5:01 pm

pa_friendly_guy: I've given a lot of thought to this syphon idea in the past but I don't think it would work in my system. My storage tank and heat source are both at the same level (on a concrete slab) and the water lines are running above through the ceiling. It would be great if it could work. I've read some info on Gary's Builditsolar site but I haven't convinced myself that it could work in my situation. Also, if there was a way that I could get it to work, I wouldn't want a negative syphon working when the water in my tank is warmer than the heat source and thereby cooling my water off. Rereading your post, I see that you mentioned one-way check valves, which would address that. I'm more of a "stumbling by dumb luck" kind of guy and by no means an engineer, but I think that I could never get a syphon to work anyway since my system is vented and not sealed. We need some engineers to figure this out and then give us the plans! It's really an interesting concept, though. Thanks for getting my wheels spinning. Like many ideas, I think that if one were building a new site from the ground up, maybe this idea could be incorporated to make something really great!

Matt: Your comment really got me thinking, too..... 250*??? Wow! So should I be concerned with what this mass is in contact with as far as building materials go? I'm even a little surprised that your cushion stands up to that. Maybe I'm over worried.... but better safe than sorry. I was thinking of putting my mass along a wooden wall (finished in rough sawn oak). I guess 250 isn't enough to start a fire, but I'm just wondering about the long-term effects... or would there be any? I see in your videos that you have your bench shaped up with wood in some places and can't tell what the walls are made of around it. Anyway, just wondering....
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Re: Rocket Mass Incorporating Water Heating?

Postby pa_friendly_guy » Mon Mar 04, 2013 5:57 pm

I looked on Wikipedia to see what they had to say about Thermal siphons. here is the link.

http://en.wikipedia.org/wiki/Thermosiphon

From their design it looks like it would work if you elevated your storage tanks higher than the stove. I think the check valves on each side of the heater would still make sense to guarantee that there was no back flow to steal the heat from the tanks. From their design it looks a lot simpler than what I had in mind. I was trying to work against gravity and make the hot water go down. What was I THINKING,,,,lol. Would it be possible to raise your storage tanks just slightly higher than the coils in the stove? If so I would say, Hold your Cards Everyone, We have a BINGO here. Hold your cards we have a BINGO. ;)
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Re: Rocket Mass Incorporating Water Heating?

Postby mannytheseacow » Mon Mar 04, 2013 10:59 pm

Hmmm.... I like that! As of now, it wouldn't be possible to raise the tank, but once I get this RMH built if I bury the lines in the mass then it would be lower than my supply and returns from the tank... This just might work! I'll have to add some check-valves to my materials list! :lol:

Digging around I found this link to Ernie and Erica's efforts to getting RMHs permitted through the city of Portland, Oregon: http://www.portlandonline.com/bds/index ... 16&c=48661

I'm such a newbie at this, so forgive me if I'm posting something everyone has seen already. I found it really helpful though to see the codes, specs, etc.

I know there's a book out there too, and I haven't read it yet. Waiting for my local library to track it down for me.
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Re: Rocket Mass Incorporating Water Heating?

Postby pa_friendly_guy » Mon Mar 04, 2013 11:51 pm

You will have to take a long hard look at your instillation and the elevations of both the storage tank and the RMH . Since your use of electric is some what limited by being off grid the natural heat syphon idea can definitely solve one of your problems. Why can't you raise the level of the tank a bit to help the syphon work better? It would not have to be raised that high off the floor, but any increased height of even 6" to 12 " looks like it would help the unit work better naturally. Any time we can get nature working with us instead of against us its a win win in my mind. :D
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