planning thread

[yesimag]

Let me start by saying hello. I'm new to the forums, and have already found a ton of info here I didn't know before, and that's after lots of research into rocket stoves already. You are truly a gifted bunch.

So my interest stems from another near future project. I will be building a treehouse completely off-grid. Water is fed from a not-so-nearby spring, electricity will be provided by some combination of renewable (micro-hydro and/or solar) and combustion engine generator.

As the project is still in the planning phase, and me being the model over-planner, I still have a lot of things to work out. Suspending a several hundred square foot dwelling from a few trees is not exactly the least of my concerns.

But back to the topic, I'd like to build a rocket mass heater which does some or all of the following:

-heats the house
-heats water for showers and hydronic floor heating
-bakes food in an oven
-cooks food on a cooktop
-is able to burn both wood and used vege/motor oil
-releases steam into shower room

I will be shying away from the mass of mass strategy. As I'm already stuffing the treehouse with more amenities than is sane or prudent, a few tons of cob won't help my engineering obstacles. I hope to overcome this by burning a bit more wood more often and distributing the heat more evenly and efficiently through the use of floor heating. Since my space will be small, 200 sq feet at the absolute max, I feel these goals aren't too outlandish.

I do not expect this system to provide me with 24/7 hot water. It will only serve to lessen the load on a tank-less hot water heater.

To make matters even more complicated, the whole unit needs to be as compact as possible, as every square foot of the house must be used to its maximum efficiency. For a number of practical reasons, the stove will likely share a wall with the bathroom. With some of the metal exposed this should heat it rather nicely and make for easy steam creation should I desire.

Something that crossed my mind was a system where the oven sat above the heat riser, and was surrounded by a chamber of water for the heat exchange. Also this way by regulating the water flow I could control the temperature of the oven. This process could be automated or manual, budget permitting.

So I'm sure by now you've come up with a few dozen reasons why some or all of this won't work. And that's exactly what I'd like to hear. Hopefully by the time I have a structure suspended and framed up I will have a pretty decent plan together for building this beast. I may not decide to go with all of the features, but that's my wish list at this point.

[swizzlenutz]

So why have you decided on a tree house of all things? Why not an underground house where you can utilize the earth itself as natural air conditioning in the summer and with a southern angle provide heat throughout the winter? A tree house seems rather inefficient right from the start. How high is this tree house going to be from the ground? Maybe an over-sized mass heater could be built with the top of the riser being used to heat the floor. Build a small pocket rocket in the tree house for extra heat and keep your water and weight on the ground. You'd just need to consider pumping the water you need up to the tree house or go down and fill a 5 gallon bucket and use a pulley system to haul hot water up. Maybe get a 7 gallon bucket with a shower head attached to it and fill that with your shower water. Attach your shower up to a storage tank to hold your gray water for your garden or lawn. Just some of my thoughts on the whole thing.Maybe you can change your user name to Tarzan. lol. Swizzle

[Donkey]

Interesting project. You've got some pretty major engineering to do, lots of difficult but fun hurtles to jump.

On to the stove.. I've found that when building a stove that does a lot of things, you tend to get one that doesn't do any of them really well. That is not to say that it can't be done, just that each job adds yet another difficulty level and they tend to compound and multiply.

With hydronic heating, if the stove and water is above the parts that you want to heat, this means pumping, which will add to the energy load on your system. Hydronic floors are nice on the feet but they tend to radiate half of the heat down as well. Insulation can help but it will never completely stop this energy loss. With a floor on the ground, the heat will charge the mass (earth) below and act as storage but with a floor elevated into the air, you loose this advantage. If you hydronically heat an interior wall, it can kill a couple birds with one stone. The wall piping can be above the heat source so it can be a passive convective loop, eliminating the pump AND you can heat both sides of the wall, (two or more rooms) AND all the heat stays in the house. Also, hydronic walls produce radiant heat to your largest (body) surface area, where heated floors actually heat your body (besides the feet) by convection, not radiation.

I'm looking forward to your process and progress on this. It might be most helpful if you do up some drawings even rough pre-lims) and post them. I am in particular far more visual in my comprehension, you can tell me in words a thousand times and I won't get it, but show me a picture and I can grok it in a moment..

Welcome to the boards.

[yesimag]

Thanks for your replies. I figured you two would both be the first to respond, and I wasn't disappointed.

swizzle, to answer your question the height hasn't been decided yet. Nor has the location or the design. Its still completely in my head. However I've found a few 3 and 4 tree stands which might work out well. Ideally I'd like to have the first floor about 20 ft off the ground, although there are very few flat areas so it might be 10 on one side and 25 on the other. The hauling water thing simply won't work though, I'm willing to give up a lot of creature comforts, but hot water on demand isn't one of them. As I said I will likely use this in conjunction with a tank-less hot water heater as I don't want to have to fire the stove in the summer just for hot water. However if it works out well it would be nice if the tank-less didn't have to run much in the winter.

I had thought of a house half sunken into the ground, and the idea isn't dead yet either. There is a chance the treehouse could end up being only a bedroom, or just a bedroom and half bath. I will likely have some sort of structure nearby on the ground regardless to house various other things. It may be a steel building, stickframe, or even a shipping container. If the treehouse does end up just being a bedroom, the ground building would contain the other living facilities. And should winter get really rough (I'm thinking lightning and wind more than cold) it might be nice to have a retreat on the ground. This could certainly contain a rocketmass furnace with water lines being the only thing delivering heat to the treehouse. They would have to be well insulated of course, as this is in northern california where freezing is an issue.

I am no stranger to the fact that the treehouse will be less efficient from an energy standpoint. However that isn't my primary motivation. I'm stuck on the idea of a treehouse, its challenges, and unique attributes. However I think by living itty bitty and planning some passive solar elements into the design the efficiency loss will be rather unnoticable. Either way I will be burning far less btu's than your average home in suburbia and I have a virtually inexhaustible supply of fallen trees and scrap lumber for firewood.

One idea I had thrown around is having a small utility room one story below the treehouse. It would have a smaller footprint, 4-6' square and house a variety of things I didn't want taking up floor space. The mass heater could be built here and use a convective loop to heat the floor. Also if the utility room was well insulated (I'm thinking 2x6 stick framing of the walls, 2x8 floor joists with blown-in recycled newspaper insulation for 100% coverage) most of this heat would travel up into the house. The utility room would not need to be full height, probably just high enough to stand (6'.)

However the water system works, it would be greatly beneficial if it was passive. I will have the ability to create plenty of passive water pressure, it just means putting a spring fed holding tank up the hill. While I'm not against the idea of running a pump, and I plan to have a inverter + battery array, I'd like if the basic function of heating the treehouse did not rely on electricity. To the contrary it would be nice to be able to produce a small amount of electricity with the stove instead. The sun doesn't always shine and generators do fail (unless they say honda of course.)

I'm just starting to get the hang of sketchup, so I'll try to get some drawings together soon. Drawings always seem to help me understand much better as well.

[Donkey]

I've been thinking about your dilemma all day..
It kinda ties into a line of reading (and ruminating) I've been doing lately on bell stoves (thanks much peterberg).
I might need to eat my previous words a little, I quote "I've found that when building a stove that does a lot of things, you tend to get one that doesn't do any of them really well."


With bell stoves, you can get a fine degree of control of temperature usage. You can actually create separate temperature zones in multiple bells and use each temperature zone for it's best application. The ability to separate heat zones gives us the opportunity to drive more than one function at it's optimum temperature.
The Russian stove builder Kuznetsov is doing extensive research and provides a lot of great information on his website. I think his ideas can pretty easily be adapted for rocket stoves.

[Donkey]

There is a letter from (microsoft .doc format) Kuznetsov on the MHA website. Here's the link to download.
I think it lays out the bell principle pretty well. It also (at the bottom) is an invitation to the global stoving community to help figure out the grey areas.

[yesimag]

Thanks, I'll have to check out those links.

I've been thinking about it too... While having a wood-fired oven would be nice, its not crucial.

To simplify the design a bit, what if I were to coil copper piping inside the upside down burn barrel? Water could be thermosiphoned to a recycled hot water heater tank in the attic just above the stove for gravity fed hot water. Once the tank was full, excess water would flow down into the hydronic floor system from an overflow line at the tank.

I would really like to incorporate the oil burner into the design somehow though. My neighbors use a lot of motor oil in their gene's which has to be hauled out. Even if I had to prime the stove with a wood fire first, being able to slow drip waste oil would make for unattended heat.

[Donkey]

IMHO, hydronic walls are better than floors.
Thermosyphoning up to a tank works fine. Trying to passively move hot water down again to an in floor heating coil doesn't really work, unless it's just run through and out the bottom..

The dual use waste oil/wood burner really interests me. Seems like it shouldn't be TOO awful hard.

[swizzlenutz]

On the whole waste oil thing, how does this idea sound? Take a 5 gallon bucket and fill it almost full of wood and then dump your waste oil into the bucket. At night put the oil soaked wood into the stove and add new pieces to the bucket. I'm thinking that adding oil soaked wood to a hot fire just might make the wood burn a little longer. Its gotta be worth a test just to try it. Swizzle

[Donkey]

It might be worth trying, though I doubt it will be a very efficient use of the oil. It will likely be a pretty dirty burn.
I could be wrong..

[swizzlenutz]

If the stove is already hot and its burning like a rocket should then it should burn all of the "dirty" that you would normally see. The oil will give a nice dense, black smoke which should ignite and maybe burn hotter. Personally I would start with soaking a half stick and adding some longer, unsoaked pieces with that. The longer pieces should help to keep the stove hot where a stove full of oil soaked wood may just cool it down. I think the real trick would be to keep the stove hot until the oil soaked wood really takes off. Maybe even put the soaked piece in the burn tunnel and not just in the down draft. With regular oil burners you have spritzing fuel and flame. With the rockets you have 2 separate flames, the fuel and the smoke. As long as you can turn the oil into smoke it should ignite. I would never try this with a cold stove, if that smoke doesn't burn then it would be a very dirty system. I've been looking at paper logs and even leaf logs. Maybe oil could be used as a binding agent. In a pellet mill the oil would most likely ignite so I'd stick with real wood or paper logs. Swizzle

[yesimag]

swizzle, seeing as I don't have a rocket stove at all yet, perhaps you could try it out and let me know the results. If that works I'm all for it, the more simple the better. If not I was thinking about somehow incorporating an oil burner into the burn tunnel some how. Once I get the stove nice and hot with wood I can start juicing the fire with some oil. Even if I never burn exclusively with it, putting it to a good use would be nice. Its starting to look like I'll be building 2 rocket stoves. I'll build my mockup outdoors as suggested, build one in the treehouse to match, and then use the outdoor one for further tests and possibly some outdoor cooking in the summer.

I think I've figured out the water heating system. I'll have a small reservoir out of which the system is fed. This tank can sit on the ground (or in the ground) below the treehouse. Water will get pumped up and into the stove. Hot water will thermosiphon up into a holding tank where the overflow will flow into the floors and/or walls. If such a thing exists, a thermo cooling valve could release water below a certain temperature to be dropped back into the holding tank.

And just because I wanted donkey to get a little tingle, I drew up a very rough diagram. Please pardon my lack of artistic ability. And those are maple leaves, at least that's what the developers of gimp claim.

[yesimag]

I was also thinking about using any steam that's created to drive a diy steam turbine. Probably wouldn't make a ton of electricity, but enough to trickle charge my batteries some.

A system something like this:

www.stginternational.org/how-it-works.html

[canyon]

Are you planning on a closed loop hydronic heating system or open to the atmosphere? If you are going to heat this small elevated space with water why do you want the rocket up in the tree? Utility space with insulated thermal storage (hot water) in the ground could keep all the weight down there and properly designed, the system could work by thermosiphon without a pump.

[yesimag]

ya canyon, thats something I'd considered from the start. However I'm going to be overbuilding the main runners and floor joists considerably anyway so an extra 1000 lbs won't be that huge. I'm interested in being able to stoke the fire and cook on the stove without venturing outside. I will be having a female companion joining me full time so I must make a few concessions. also I must admit I'm always a sucker for the cool factor. A tree-dwelling rocket definitely scores high.

as I mentioned before though, the treehouse may not be a full time haunt. So in the case that its simply a bedroom, I will probably opt for keeping the rocket on the earth and only heating by water line.