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Exploring Water as the Primary Thermal Battery for Rocket Mass Heaters

C.J. Murray


Joined: Dec 02, 2011
Posts: 92
Location: 5,500 ft. desert. 13" annual precip.
It seems to me that utilizing water as the primary thermal battery for a rocket mass heater has its place in the grand scheme of things. This, naturally, leads to hot water for other needs as well. I am here to be put in my place by all of you if I misspeak so please feel free.

I am very desirous to see RMHs accepted by building officials utilizing cob and other natural materials as a thermal battery. From what I’ve read on these forums there are people who have put a lot of time and treasure into working on proper design. I applaud you for your determination and persistence for little reward. You have my admiration.

It seems to me that part of the challenge utilizing cob is that it is hard to get things just right so that the flue gases exit at the velocity they need to for safe, consistent operation regardles of outside condions and yet not so quickly they carry away precious heat. Since the rate at which water contacts the flue to draw away heat is easy to regulate it seems like that method of heat extraction from the flue gas could potentially make it easier to achieve as near to perfect flue gas exit temperature as possible. I’m not saying move away from cob. I’m saying there may be applications in which water serves the need appropriately. Perhaps a very small amount of regulated water flow could be the final arbiter of flue gas temperature after the cob bench. I’m stunned by the beauty and creativity of the cob creations I see.

Ernie has stated that an RMH can be used to heat water or bench but not both. On the surface that seems to say that a water container can be buried in the cob bench instead of flue resulting in the ability to store a greater amount of heat in the same area as cob and that the cob would act to slow down the release of that heat compared to a steel water container alone. I say it can be a win-win. This then leads to a need to figure out how to best implement that. Seems like a passive system is desirable and possible but…..

Thoughts?

A pair a what shift?
John Sizemore


Joined: Mar 27, 2011
Posts: 96
Location: West Virginia/ Dominican Republic
Ok I far from an expert as everything I know am from reading.
Problems with water would be construction cost. The materials would need to be welded in place and of higher strength.
Moisture. Hot water equals vapor and unless your tank was covered your home would become s steam room.
Calcium builds up in the water tank.
Legionnaire’s disease. It is a problem in hot tubs and other water bearing indoor locations. You would have a petri dish in the center of your home.
My thoughts about code would be if one kit was made that could be installed with a uniform construction method it would be easier to sell to the code enforcement group. As it is now, the construction is not uniform without something to take the liability away from the building inspector.

I am the first generation of my family to grow up on the grid eating out of the super market. I hope to be the last.
Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 4053
Location: Victoria British Columbia-Canada
    
  57
I think it would be important to ensure that the water is not allowed to cool the effluent before complete combustion is achieved. Wood stoves with water jackets are prone to creosote buildup if unburned hydrocarbons go up the chimney. The heat riser and several feet of pipe may need to be far hotter than a water jacket would allow.


QUOTES FROM MEMBERS --- In my veterinary opinion, pets should be fed the diet they are biologically designed to eat. Su Ba...The "redistribution" aspect is an "Urban Myth" as far as I know. I have only heard it uttered by those who do not have a food forest, and are unlikely to create one. John Polk ...Even as we sit here, wondering what to do, soil fungi are degrading the chemicals that were applied. John Elliott ... O.K., I originally came to Permies to talk about Rocket Mass Heaters RMHs, and now I have less and less time in my life, and more and more Good People to Help ! Al Lumley...I think with the right use of permie principles, most of Wyoming could be turned into a paradise. Miles Flansburg... Then you must do the pig's work. Sepp Holzer
Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 4053
Location: Victoria British Columbia-Canada
    
  57
This is coppied from a thread I started 6 months ago entitled --- Water vs. cob - Thermal storage --------------------------------------------------------------------------------------- Here are some very useful figures for anyone who is trying to choose whether or not to include a water tank within an RMH. Cob weighs 95 pounds per cubic foot. Water weighs 62 pounds per cubic foot. The heat capacity of cob is .2 which is 1/5 that of water which has a capacity of 1.00 So supposing we want to build a RMH which occupies 100 ft.³ of space.

First the cob - 100x95 equals 9500 pounds. 100 ft.³ of cob will weigh 9500 pounds. 9500x.2 equals 1900. So our cob bench has the same heat capacity as 1900 pounds of water.

Water weighs 62 pounds per cubic foot, therefore the tank containing 100 ft.³ of water weighs 6200 pounds

6200 divided by 1900 equals 3.26

A given volume of water can store 3.26 times as much heat as the same volume of cob.

It is true that the cob bench could be heated to temperatures far beyond the boiling point of water. But in order to store the same amount of energy as water at 200°F, a cob bench would have to be heated to more than 650°F. This is not common practice and if it were it would result in lowered efficiency with higher exhaust temperatures and badly burned bums Water stores much more heat at temperatures which are practical and safe. And because heat transfers through a body of water through convection, heat being absorbed by the thermal mass will be available in short order. If some lag time is desired the tank could be cobbed over.

Some may be worried about the danger of steam explosion. A water tank which has an open vent to the exterior is no more dangerous than a rattlesnake on TV . It's easy enough to monitor the temperature and allow the fire to burn out before the boiling point is reached.

It would be a shame to have a giant water tank like this for thermal storage only. Water could be drawn off to heat a hot tub and for regular domestic uses. For those who don't want to do any fiddling a tank could be placed into a cob bench which would be a pre-heater on the way to the hot water tank. During the heating season your hot water tank would receive preheated water. During the summer when the heater is not in use cold well water would absorb heat from the thermal mass. This would have a mild air conditioning effect and the water would enter the hot water tank at a higher temperature.

                


Joined: Jan 20, 2012
Posts: 8
http://www.youtube.com/watch?v=YTnr8ua54Uw

Saw this. Haven't really read the whole thread but seem applicable.
Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 4053
Location: Victoria British Columbia-Canada
    
  57
I'm so glad you posted that. It's nearly identical to how I intend to heat water except that mine will be inside and I won't use a coil.

Mine will be a batch heater with an open vent to a drain so that the tank will not be pressurised. This allows for short pipe runs and customized batches.

During cold weather it could be fired in the evening and work as a mass heater. Whenever it is heated beyond 140F a thermostat will lock it so that nobody gets scalded. A separate tap which is normally padlocked may be used to draw off water at temperatures up to boiling. Really hot water will be used to shock the hot tub and to fill a trough in a sauna/steam room.

There are probably 20 days in the year when excess indoor heat is a problem on my site. Since I'm including lots of thermal mass, it may turn out to be zero. If it ever contributes to excessive indoor heat, I'll wrap it in an insulating quilt for the summer.
C.J. Murray


Joined: Dec 02, 2011
Posts: 92
Location: 5,500 ft. desert. 13" annual precip.
So I finally bought the Rocket Mass Heaters book from http://www.rocketstoves.com/ and read it. Holy smokes people have put a lot of effort and thought into these things.

John Sizemore wrote:Problems with water would be construction cost. The materials would need to be welded in place and of higher strength.
Moisture. Hot water equals vapor and unless your tank was covered your home would become s steam room.
Calcium builds up in the water tank.
Legionnaire’s disease. It is a problem in hot tubs and other water bearing indoor locations. You would have a petri dish in the center of your home.


I can't argue with you there. The costs/difficulty of construction will go up depending on the configuration and one's scrounging ability.

To avoid indoor moisture buildup the water storage will need to be vented to the exterior in some manner. There may be other options. I haven't researched this one yet.

If calcium/mineral precipitation will be a problem I'm assuming distilled water can be used.

Legionnaire’s disease is a valid concern. I'm not sold on the idea of using a large volume of water which eventually ends up at the hot water heater as being wise. If not much hot water is being used and the water is held at the wrong temperature for too long prior to hitting the water heater a lot of bacteria growth can occur.

140º F will kill the Legionnaire’s bacteria. I suppose one needs to be aware and take the temperature of the water thermal mass above that on a regular basis. I have done no research to see what other options there are.

Dale Hodgins wrote:I think it would be important to ensure that the water is not allowed to cool the effluent before complete combustion is achieved. Wood stoves with water jackets are prone to creosote buildup if unburned hydrocarbons go up the chimney. The heat riser and several feet of pipe may need to be far hotter than a water jacket would allow.


Definitely the water will have to rob the heat after the heat riser to avoid the problems you’ve mentioned.

Dale Hodgins wrote:It would be a shame to have a giant water tank like this for thermal storage only. Water could be drawn off to heat a hot tub and for regular domestic uses.


It seems the Legionnaire’s risk will preclude the drawing off of water unless the 140º F can be maintained. If one desires to pre-heat the hot water heater feed I think coils robbing heat from the rocket mass heater water mass will be more prudent. The challenge will be preventing bacterial growth in the rocket mass heater water mass which, theoretically, one will not be contacting on a regular basis anyway.

That said 140º F may not be that hard to maintain for an extended period depending on how large an area one is trying to heat.

In this thread, http://www.permies.com/t/12344/stoves/Rocket-Powered-Sterling-Engine-water Dale has proposed the coupling of a Stirling engine powered generator with the RMH to produce electricity (along with other mechanical needs such as water pumping and clothes washing) while using water thermal mass as the coolant for the Stirling engine. After much consideration it seems to me that in order to most effectively use water as the thermal battery for a RMH the water needs to be located at floor level. In other words, if I understand how a thermo siphon works, if one if going to use a passive means to heat the water thermal mass the thermo siphon is doable but only if the tank is located higher than the heat source. Am I understanding this correctly? This would not allow the water thermal mass to be located in a cob bench unless the RMH was sunk below floor level significantly. Dropping the RMH below floor level may have it’s usefulness as can be seen in this thread: http://www.permies.com/t/5937/stoves/rocket-mass-floor-heater-finally. But can one really heat below the floor and a water thermal mass located in a bench on the floor? I suppose it’s a function of how long the burn is.

It seems to me that in order to realistically use water as the primary thermal mass one needs the ability to move water around on an active basis utilizing steam, a steam powered engine/pump or a Stirling engine powered pump. In other words to really utilize water’s heat storing/transferring ability well the ability to circulate the water though various connected by piping water storage vessels and through the heat exchanger piping either next to or inside of the RMH barrel becomes necessary. I am continuing to research what is the quietest and most simple method to actively circulate the water without steam.

Questions:
1) Is anyone familiar with a passive design for circulating water which works with the water tank and heat exchanger being at the same level? For all I know there is a simple method of passively circulating the water and I’m not bright enough to see it.
2) What is a simple, quiet pump design which can utilize Stirling engine principles to actively circulate the water?
3) Is there another mechanical, quiet, simple design which can utilize the heat generated by the RMH to pump the water?

Thanks for your input.
Matthias Rascop


Joined: Jan 21, 2012
Posts: 9
1) For passive convection of water you need 2 things: a) Vertical difference in height of of some meters. b) Some serious cross sections (at least 3 inches width) of the piping, two have the water moved by the minimal differences in pressure. You don't need that much flow, because the heat up of 1 liter per minute from 140F to 200F means ca 2,5kW of power. The colder the water gets at the low end, the better for the convection. Generally its possible, but I'm not sure if it can be done with tinkering means...

2) You can basically take every pump you find, because you dont need much power. If you use a sterling engine and a car alternator, possible pumps would be out of the computer-watercooling or aquarium area. Most of them run on 12V, are quiet, efficient, have sufficient flow, and some are capable of continuous duty. I'm not sure, if they are available in the States, but one really good thing for that would be the "Laing vario D5" Its not really cheap, but it'll run, and run, and run...

Dave Bennett


Joined: Jun 25, 2011
Posts: 641
C.J. Murray wrote:It seems to me that utilizing water as the primary thermal battery for a rocket mass heater has its place in the grand scheme of things. This, naturally, leads to hot water for other needs as well. I am here to be put in my place by all of you if I misspeak so please feel free.

I am very desirous to see RMHs accepted by building officials utilizing cob and other natural materials as a thermal battery. From what I’ve read on these forums there are people who have put a lot of time and treasure into working on proper design. I applaud you for your determination and persistence for little reward. You have my admiration.

It seems to me that part of the challenge utilizing cob is that it is hard to get things just right so that the flue gases exit at the velocity they need to for safe, consistent operation regardles of outside condions and yet not so quickly they carry away precious heat. Since the rate at which water contacts the flue to draw away heat is easy to regulate it seems like that method of heat extraction from the flue gas could potentially make it easier to achieve as near to perfect flue gas exit temperature as possible. I’m not saying move away from cob. I’m saying there may be applications in which water serves the need appropriately. Perhaps a very small amount of regulated water flow could be the final arbiter of flue gas temperature after the cob bench. I’m stunned by the beauty and creativity of the cob creations I see.

Ernie has stated that an RMH can be used to heat water or bench but not both. On the surface that seems to say that a water container can be buried in the cob bench instead of flue resulting in the ability to store a greater amount of heat in the same area as cob and that the cob would act to slow down the release of that heat compared to a steel water container alone. I say it can be a win-win. This then leads to a need to figure out how to best implement that. Seems like a passive system is desirable and possible but…..

Thoughts?

My first thought is that it cannot be a closed system. When water flashes to steam the expansion is extremely difficult to control in such an environment. I used to be a certified boiler operator and have given much thought to using a RMH for heating water. I decided that the safest method would be to have a system that is open to the atmosphere to prevent explosion. In my opinion using a water reservoir as the mass heat sink would only be efficient if the water was circulated through the heat source and not attempt to use the flue to heat the water.


"When there is no life in the soil it is just dirt."
"MagicDave"
Erica Wisner
volunteer

Joined: Feb 10, 2009
Posts: 747
Location: Okanogan Highlands, Washington
    
  89
Matthias Rascop wrote:1) For passive convection of water you need 2 things: a) Vertical difference in height of of some meters. b) Some serious cross sections (at least 3 inches width) of the piping, two have the water moved by the minimal differences in pressure. You don't need that much flow, because the heat up of 1 liter per minute from 140F to 200F means ca 2,5kW of power. The colder the water gets at the low end, the better for the convection. Generally its possible, but I'm not sure if it can be done with tinkering means...

2) You can basically take every pump you find, because you dont need much power. If you use a sterling engine and a car alternator, possible pumps would be out of the computer-watercooling or aquarium area. Most of them run on 12V, are quiet, efficient, have sufficient flow, and some are capable of continuous duty. I'm not sure, if they are available in the States, but one really good thing for that would be the "Laing vario D5" Its not really cheap, but it'll run, and run, and run...



I may be misquoting Ernie here, but I believe he's mentioned around 18" as a minimal workable height for a thermosiphon. That's e.g. a coil that runs through a heat source, with each end connected to the top and bottom of a nearby tank. Gives passive circulation as long as there's a temperature differential, useful in applications where a pump may not be reliable or necessary. Seems like you will get more convective circulation in a water tank even if short, than you would get in a cob mass. Especially with the heat source (ducts) on the bottom of the tank, where I imagine it would be easiest to locate them coming as they should from the bottom of the bell (barrel). But maybe shallow water just settles out into thermal layers and doesn't circulate. If you need active circulation.... how about extremely hardy tropical fish? From an island volcano lagoon maybe?

We've done so much work in off-the-grid situations that we tend to try to make things solid-state, that is, no pumps to fail, no valves to be turned the wrong way, nothing that can allow people or circumstance to * things up. If you can assume reliable electricity for the entire time you would be using the wood-fired heater, you have a much easier design problem because you can add pumps or fans to make things go where you want them. We tend to be working on emergency and off-the-grid scenarios where people depend on it to work when the electricity goes out, or tend to get scrappy pumps that aren't that reliable. If the pump goes out, but the fire doesn't, the design needs to default to a safe state.

This thread talking about a large tank with relief valves located in the downstream area of the heater sounds like a solution that handles this issue. No coils that absolutely have to be kept moving to avoid boil-off, and no poaching on the fire's clean burn temperatures - it's a win-win.
It would be relatively simple to run a coil through this tank to separate potable water from the pond-scum-factory that is an intermittently warmed stagnant tank.

I like the idea of nearly-passive 'air conditioning' from running well water through thermal mass. This effect would also operate in winter, meaning you'd use more firewood as you were heating water as well as home. Earthen materials (containing clay) are also good at the actual air conditioning, that is the humidity adjustment, so they might be useful to help mitigate condensation. On the other hand, sufficient condensation might push the limits of the earthen materials' moisture tolerance (about 13% for a stable load-bearing wall; low benches can remain relatively sound at slightly higher percentages, if the don't depend on straw for tensile strength).

The higher heat capacity of water also means this could be an option when people want to fit a very small system into an existing room. We have a stove in a 9x4x4' footprint here, with a bench so it's actually about 3/4 of that size, and that's about the smallest footprint I can see for a serious masonry heater. We have a lot of fieldstone in it which I think (hope) is denser than the dry cob, and concrete rubble which I know is, too.

For a super-simple just-heating setup, in summer the tank could simply be drained and refilled with cool water when you want to 'boost' the coolness of the house. You might be surprised how seldom this is necessary: even a shaded thermal mass a huge effect on cooling. We used 2-3 fans in the Annex our first summer there, and none for the following 3 years after we installed our RMH, and our cob bench does not absorb heat as fast as water would.
You might find if you were using a lot of domestic hot water that the mass got too cold, as well water typically can be around 55 degrees - not that anybody would mind. Lighting the fire to warm it up might be trickier in summer, though - you'd have to balance the draft so there's excess in winter, if you want to be able to control the temperature with both inputs (wood and water) in hot summer weather. The tank might sweat if very cool, too.
I think a tank system would be less comfortable for curling up and you'd lose the added efficiency of contact with heat or cool that you get with a larger mass. But someone who wants this system so the stove doesn't clutter up their small space typically doesn't care as much about efficiency, or adapting their behavior choices to take advantage of a more frugal comfort; they tend to be the ones who don't have room for the rocket-stove bench because they already have a couch they like.
It's a slippery slope because next you are talking about whether, if it's not part of the conversation grouping in the living room, it might be better tucked away out of sight, or outside with some pipes coming in, and that leads to people not tending the fire as they should. Outdoor wood 'boilers' are notoriously smoky (and take away their other design flaws, there's still heat lost to distance), and a non-tended rocket heater won't perform the way a pampered living-room companion does.
One of the nice things about the Victorian and even many modern woodstoves, is the elegant detailing that makes them part of the decoration of the room, not a cheap appliance that lives in a closet. I am still looking for nice ways to gussy up the barrel or bell; we just had a brainstorm about casings here, and I think I'll start another thread about it.

Just some random thoughts on the concepts above. Nice thread.

Thanks,
Erica


Play with nature, make nifty stuff:
www.ErnieAndErica.info
Mark Rose


Joined: Jul 19, 2009
Posts: 36
    
    1
I've been thinking an interesting way to make an outdoor hot tub would be to use an open pool of water as the thermal mass. If the exhaust pipe is short enough, this ought to work, right? Obviously there would be other design issues with making everything water tight.
Rufus Laggren


Joined: Feb 23, 2012
Posts: 338
Location: Chicago/San Francisco
    
    4
Handling water with materials that last more than 15 years requires a little thought. Depending on water composition, galvanized steel can last 50+ years; I'm living in an old house which was last plumbed in the 40's with galvanized pipe. However. Some water will rot the pipes in 20 years or less; heat will speed up any chemical process and some hot water piping needs replacement "regularly" at 15 years. That's for "Schedule 40" steel pipe.

Tanks are much lighter steel. Again, some hot water heaters from the (very) late 80's are still working; but _most_ conventional water heaters are leaking in less than 10 years and many in less than 5. Heat again plays a part because the spot heating experienced at the bottom of the tank in gas fired WH's seriously shortens their life; electric WH's which have heating elements _in_ the water leaving the tank itself at a more or less uniform temperature usually last 10 years or more but often leak at the connections (though no more than other WH's).

Now this doesn't matter if you figure you're "Out o' Here!" in 5 to 10 years. But if you're looking at long term and dependable use you would like your living space to fail gracefully at intervals of 30+ years - or more. Gracefully means no catastrophic disasters, failure is telegraphed far enough ahead that major repairs can be scheduled for the best season and that major repairs should be accomplished w/out moving out of the home for a month and at a cost of less than 5% of the value of the property.

When you try for that ideal with plumbing, materials become important as well as installation. Traditionally copper has been the most reliable for pressure systems. For drains heavy "service weight" cast iron has lasted 50+ years. Plastic is barely into the adolescence of it's track record and has seen some serious embarrassments. Plumbing is also attached from "outside". Salt air rots any pipe fast; some soils eat cast iron, some eat copper. Everything eats steel! Galvanized pipe will usually last 10 years before showing rust spots on the outside except that... It last less than 5 years at any threaded joints where the threads are exposed with no galvanizing and where pipe wrenches of scratched the surface.

IOW, once you've got something the functions, you may want to figure how to set it up so it lives a while.


Rufus
Jim Cleary


Joined: Nov 01, 2012
Posts: 3
i'm very interested in water thermal storage and I think I have a cheap easy solution. What about directing the exhaust through the open holes of a foundation of cinder blocks (two passes for a total of 10 feet). The cinder blocks would be sealed together using high temperature silicone caulking, and would be lifted off of the cement floor by rows of bricks for an air gap. Once this cinderblock heated slab (I'm thinking about 3'X5') is built, I will make a plywood box around it and use plastic sheet, like pond liner, to hold a mass of water about 2 feet deep.

I think I might be able to get away with the plastic sheet directly on the cinder blocks, since the water should strip the heat away very quickly, but if that doesn't work, I could build up a thickness of cob or sand and try the liner again. My basement has a floor drain, so I'm not too worried if there is a leak during R&D.


[Rocket Mass Heater.jpeg]

Adam Stickler


Joined: Oct 14, 2012
Posts: 9
I'm really interested in your design concept. personally I would use sand on the bottom for sure. At least a thin layer. When you put in an above ground pool you put down sand to keep any rocks or sharp objects from ripping the liner. This would be the same I would think. Pressure from the water pushing down the plastic against the blocks might give you some pin holes. I would love to see some pics if you build it.
David Graber


Joined: Sep 03, 2011
Posts: 16
I'm in process of building my third RMH doing both water heating and floor thermal mass. My first one, now into our 4th Eastern Montana winter, uses a single loop, stainless 3/4 pipe, in the firebox (overbuilt). It is thermally syphoned via copper to a 300 gal. elevated vertical steel storage tank (junk propane tank roasted to red hot over a bonfire. fun event.). Inside this tank is a 1/2" copper coil under domestic water pressure (no pressure in the tank itself), the cold water supply to the 30Amp 240V inline water heater made for tropical wells where the incoming water is not below 70F. The gravity flow no-pressure tank water connects to a pex header for four floor zones to store heat in our 14" of sand/gravel over 2" of EPS insulation, topped by our wood floor. I have a 1/25 HP conventional pex pump to loop the warm water down into the floor zones. With this system, in Montana cold cloudy windy winter nights, I never get up to fire up the stove. In 12 hours we lose less than 5 degrees F. I think there is a signficant heat loss in the fire box itself with this system, one of several areas where I lack the wisdom/research of most writers in this forum. I think it's compensated a bit with my 8" dia chimney of sched. 40 steel 42' long helping my bottle neck rocket effect in the firebox. I'm also helped with a whole-house fan (mostly for allergies) that accesses outside air increasing rather than cutting inside ambient pressure. I almost always turn it on (1 hr timer) when I start the stove, to run until the core is hot enough to rocket.

Our tank gets heat in summer, spring, and fall, rarely in winter, from a solar collector loop driven by a 120V aquarium pump through 80' black rubber hose coiled under a double glass window and over an insulated aluminum surface spray-painted with highly selective chrome-based solar collector black paint made specifically for aluminum surfaces. Both systems regulate themselves fairly well. The rubber hose in the collector is freeze-immune. A cheap 110v. AC thermostat strategically placed inside a window in an insulated pocket switches the pump on or off easily with maximize temperature swings from insolation and out radiation at this sensor pocket.

My latest RMH will have 1/2" copper coiled flat on top of the RMH barrell where the highest temperature is exposed, and from there thermally syphoned in a loop via 3/4 pex to a poly tank. I value passive systems, and if active, internally powered--and if externally powered, not overpowered or overbuilt technically. Stainless steel pipe inside the firebox is a case of overbuilding, and would make sense only if the loop were check-valved or closeable or under pressure. It's entirely 100% open. Copper coiled in the open on top of the barrell leaves room in the center for a teapot, and still gets adequate heat on stormy cold cloudy days to raise the temp on the tank. Those are some of the improvements over RMH 1 at greenwoodfarmmt.org. Others were gleaned, with lots of gratefulness on our part, from real permies writing in this forum.
allen lumley
pollinator

Joined: Mar 16, 2012
Posts: 2785
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
    
  40
Jim Cleary : Regular "cinder'' block is insulating, there are higher grades of Building block that might serve you better. Stealing an idea from Paul Wheaton you could consider layering high clay content magazine pages-down on top of your cinder blocks. I'm talking about those slick shiny mouthly subsription magazines, they have a very high clay content to allow for the hi-definition type pictures they favor. These magazines are
Not Re-Cycleable
due to the clay. A little research/questioning family, friends will get you enough mags - once you remove the staples in the 'models' belly button to do the little job that you have , asking at a news stand will probably get you a 1/2 ton or more, as they have to pay to get rid of the hi clay mags . this would give you a 'layer' of additional protection, and might even allow you to use lighter plastic. Please keep on sharing your ideas/projects here, as I'm sure there are many people here why would love to follow your progress ! g'LUCK , Allen L.


Success has a Thousand Fathers , Failure is an Orphan

LOOK AT THE " SIMILAR THREADS " BELOW !
Josh Patterson


Joined: Nov 17, 2012
Posts: 1
Jim Cleary : Plastic sheeting will likely not hold up under these conditions due to its poor high-temperature tolerance. For example, HDPE plastic has a working temp rating of only 160F and Polypropylene is 200F. While your water tank may not attain 200F temps, the cinder blocks will be over 1000F so the plastic will break down on the hot side. Additionally, cinder blocks are very susceptible to thermal cracking, so when the plastic springs a leak, the cinder blocks will crack due to the rapid temperature change and lose their structural integrity, which may result in a catastrophic tidal wave in your basement.

As an alternative, can you use the same storage tank, but cycle water into it away from the heat source? Is it possible to extract enough heat energy from the flue by coiling 3/8" copper tubing around it in conjunction with a very small 1/12 HP pump (approx 7gpm)? This would be an open system (both ends of the copper tubing terminate in the holding tank) so there is no issue with pressure. Calcium deposits in the copper would be minimal since the same water is continuously cycled. Evaporated water could be replaced with rainwater.

Water is hard to beat as a thermal battery, so I would like to see a working solution.
allen lumley
pollinator

Joined: Mar 16, 2012
Posts: 2785
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
    
  40
- so I just spent an hour brushing up on Stirling Engines, which means i only need 60-70 more hours to be able to talk intelligently with someone. Taking the position that there is a design out there 1)affordable and 2) build-able that could be 3) in contact with the top of the 55 gal drum where cooling is acceptable 4) speed is not important, a large flywheel can be geared to spin a generator at any desired speed 5) low volt D.C. is the preferred power source for running control devices and lighting -
- Now i need a Heating Ventilation and Air Conditioning Engineer to talk about heat pumps - Long before a closed hot water circulating system could over heat - the Sterling system would come up to temp,do a self check and if needed turn on a circuit to run a heat pump pump and carry the extra heat load away to back-up storage so it would not be lost, or to heat room air through a heat exchanger / radiator , My question to the H.V.A.C. Engineer Regards how to build in the pump cheaply and still carry of enough heat to be a useful Safety
- Again outside my area of expertise, but water heated to 140 F needs very little timed exposure to UV rays to kill virtually all microbes !
- Please feel free to jump in anywhere on this one, the more we share the more we learn ! Pyro - Maticly Yours, Allen L.
John Master


Joined: Dec 04, 2012
Posts: 114
Location: Wisconsin
    
    1
New to the forums, New to rmh heaters as of today and glad to be here. I am a tinkerer dying to tinker with something and this is right up my alley. I will have to get the book and start really digging into the research but already have 4 hours of reading in and can see now a basic idea of what makes them so great. I have a 1300 sf home and 1200 sf outbuilding and dreamed one day of heating both of them with some kind of free central non-petroleum heat (hot water would be a cool bonus too). My idea is to heat a water mass in a shed in the yard and have coils in the home furnace and water heater as well as a radiator in the garage blowing off all of this heat. It would be an open air system. I am going to keep following this forum and keep studying and maybe someday start building some of these interesting rocket heaters.
Frank Rasmussen


Joined: May 02, 2013
Posts: 21
I'm also new to the forums, but I just discovered rocket mass heaters yesterday, after searching for several years to figure out how one might efficiently combust regular garden material. I was considering making some sort of insulated composting device. I had no idea that either RMH or masonry heaters existed, so I spent yesterday researching them like crazy. I have to say that we here in the Anglosphere are retarded in the way we choose to make heat from wood. Why are we lagging behind Europe when they have had the solution for hundreds of years?

Several things occurred to me soon after:
-using either water or paraffin as the thermal battery;
-using water in a reservoir, connected to something like a car radiator that could be operated on a thermostat;
-mounting the water tank above the burn or secondary burn chamber so as to reduce footprint in the room;
-dealing with the problem of having to feed the fire for 2 hours at intervals of every 45 minutes or so (would be more convenient to kindle and then feed everything at once, which I guess is the idea of a masonry heater);

So then I thought to myself, the key feature of RMH and some masonry heaters is the use of an insulated fire box and part of flue above that, which acts to increase the temperature of the combustion to the point where everything is burned, and after that you are only dealing with a nice hot exhaust stream free of creosote. I then thought to myself - why not take something like the existing metal box woodheaters, size them to fit a day's worth of wood that could fuel an RMH, and insulate both the fire box and the secondary burn chamber, using the exhaust stream to heat water using a water jacket?

Then some more googling and I realized that these things already exist (after finding this interesting page - there is a diagram lifted from John Ackerley's presentation showing the Euro progression of Masonry -> Pellet -> Wood boiler with thermal storage). Apparently (Austrian) Froling and other companies make these things, though I doubt they come cheap. I have to wonder how hot the exhaust is in these systems and whether it is smokeless, as if it's near room temperature and smokeless the rest of the system should be very efficient.

I also came across this design, from Australia. It heats water using a water jacket. Well, there's my research to date. Bravo to everyone who has pioneered this stuff here and shared their thoughts.
Robert Hinrich


Joined: Oct 01, 2013
Posts: 1
Jim Cleary. Your Picture and plan seem very close to my Idea for a greenhouse heater. I plan on using a 3x2x10 (400 gallon) galvanized stock tank. Still haven't worked out what to use between the flue and tank thou. Sand would work the easiest but would dry out and may not transfer heat as well a piece of hard dense rock. I might check with the local granite supplier and see about scrap counter top pieces and embed them in sand. Also insulating heavily beneath and on the sides of the flue would help direct the heat to go up. There is the matter of what to cover the tank with also. I plan on using the top of the tank as a heated seed starting bench. Don't want to fill the greenhouse with steam but I don't want to seal the tank and cause a pressure build up so I think I will vent it to the outside.
My heat riser is three pieces of well casing, ( I am in North Dakota as I write). Inner is 9 inches middle is 16 inches and the outer is 24, all are 3/8 inches thick. That ought to last. Is there a maximum height for the riser? All three liners are just over 4 feet long. I will report back with pictures in the spring when I fire it up.
allen lumley
pollinator

Joined: Mar 16, 2012
Posts: 2785
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
    
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Robert Hinrich : I am going to suggest that this thread get added in to 'Rocket Stoves in Greenhouses a topic of our own', it is already a long thread, but there have been lots of
worthwhile comments ! You should have a look !

Have you been to rocketstoves.com for your PDF Copy $15.oo of Ianto Evans' Great Book' Rocket Mass Heaters', with over 100,000 R.M.H.s build world wide,
most of them, and over 95% of the 1st time builds that worked, were built from 'The Book', there is STILL No other book in any language that has as must Rocket Mass
Heater R.M.H. family information ! (and I Don't make a dime !) For the Good of the Craft.

Think like Fire, Flow like a Gas, Don't be the Marshmallow! As always, comments and questions are solicited and welcome . PYRO - Logically Big Al
William Bronson


Joined: Nov 27, 2012
Posts: 420
Location: Cincinnati, Ohio,Price Hill 45205
    
    2
It Is a great book ,available for free, seeming by design of the authors.


I had dropped the idea of water as storage medium until reading this thread. Now I am reinspired.

Taking an idea I had for a small foot print bell and adding water, we would have one 55gal drum with the bottom half of a water heater tank in side, perlite insulation sandwiched between them and sealed off with hydrolic cement. Fill the water tank halfwa with water. Now take a second 55gal drum and cut the bottom off. Invert the drum over the top portion of the water tank and use the clamping band that came with the drums to seal them together.
Now fill the drum with wet sand. Put the lid on it(are both ends the same? ) and seal it.
You will have punched holes in the water tank and lid, for the intake and exhaust. One pipe will end inches from the water, the other just inside the bell.

The two barrel wet bell.

What do you think, feasible?







William Bronson


Joined: Nov 27, 2012
Posts: 420
Location: Cincinnati, Ohio,Price Hill 45205
    
    2
Here is the link to the Ianto Evans/Leslie Jackson book: http://library.uniteddiversity.coop/Energy/Biofuels/Stoves/Rocket_Mass_Heaters-Superefficient_Woodstoves_YOU_Can_Build.pdf

From the book:
All illustrations are copyright Ianto Evans or Leslie Jackson, unless otherwise
noted. The text is non-copyright. You are welcome to use it in any way you want,
but please acknowledge your source. We just want people to get stoveing and stop
supporting the utility corporations. It does help our work if you buy books directly
from Cob Cottage Co. or Leslie Jackson. Buy a dozen or a whole case, give them
as presents or sell them at gatherings, classes, conferences, etc. It will pay for your
firewood. –February, 2006
 
 
subject: Exploring Water as the Primary Thermal Battery for Rocket Mass Heaters
 
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