Categories
Electricity Energy

How Burning Works

There’s an interesting group called All Power Labs who research biomass gasifiers: in lay terms they make machines that can convert hay, wood chips, nutshells (a large variety of biomass substances) into clean gas products which can be used to power other things – such as a diesel engine generator (which they do). You can see this system at work here:

They got my attention because if/when we go off-the-grid we will likely need a backup source of energy in winter months – the simplest being a diesel generator. But that requires diesel. So the potential of a generator that can run on biomass of which we have plenty is pretty exciting and fills another gap in the sustainability puzzel.

Their CEO Jim Mason appears in a series of 3 videos (~2.5 hours) which finally provided me with an explanation on how burning works. I admit that parts of it were a bit beyond me but for the most part I was able to follow it and learn what actually happens when I burn wood for heat  (namely 4 processes: drying, pyrolysis, gasification, combustion).

It refined my understanding and appreciation of what goes on inside Rocket Stoves. Most  stoves or fireplaces are only able to burn ~20% of the potential energy in wood, most of the rest is released as gasses which for the most part escapes out the chimney unburned. A lose-lose situation: losing potential energy and releasing pollutans into the atmosphere. A typical rocket stoves will burn most (if not all) of those gasses – already making it 4 to 5 times more efficient then most wood burning stoves. Then, after a clean and efficient burn the heat that is generated is retained in a thermal mass … which easily brings them to 10 times better.

via Matt

Categories
Energy Rocket Stoves

Fixing Our First Rocket Stove

Our first (bedroom) rocket stove worked really well … it literally saved us during our first winter here. We did not have enough wood prepared … and it’s super efficient burn-and-battery kept us warm. However there was one recurring problem. The top surface was made of metal. It was intended to both radiate heat quickly into the room and to provide a potential cooking surface. It was also an easy way to cap the brick tower. This metal surface responded to the intense heat of the rocket by warping which in turn placed pressure on the cob seams that sealed it in place … which in turn leaked poisonous gasses into the room. The temporary solution was to keep fixing it and adding more layers of cob to it (which we did all winter long). The long term solution was to replace the top.

I started by modeling the top and I opted to use rebar to support the bricks that would make up the new top. I didn’t want to mess with or work on the existing brick tower so as not to mess up the room (cutting bricks creates alot of dust). So I added half-height layer of bricks and notched it to accommodate the horizontal rebars.

Opening up the existing top was fairly simple since it was already coming apart. I took this opportunity to replace the insulation around the heat riser. When we built it we used ashes (which is all we had) and they settled quite a bit. I scooped and vacuumed out the ash insulation and replaced it with a perlite & clay slip mix (we managed to find perlite in preparation for the second rocket stove). Then a little bit of refractory (heat resistance) mortar and the rocket was fixed.

Later (this was done back in October, I just now got around to posting about it), when we got to work on the second rocket, Andreea added a layer of finishing.

I still wonder if there was an alternate solution, to somehow prevent the metal from warping …

 

Categories
Energy Rocket Stoves

Our Second Rocket Stove

It is almost the end of December and winter is well upon us. It arrived much earlier then last year (we are now experiencing snow and temperatures that arrived in late January last year). I am relieved that we got the second rocket stove done in time … it means this year we can enjoy life not just in the bedroom but also in the living room. We were able to find a barrel which means it looks (and works) more like a standard rocket stove. Circumstances still did not invite building a proper bench for thermal mass. So we opted to build another “bell” like chamber to retain more of the heat inside the space. We also experimented by building a small metal oven into the bell.

Despite a successful rocket construction during our first build, I was hesitant about this second build. While rocket stoves are a relatively simple, do-it-yourself technology, they do require a certain level of precision and accuracy in design. I am not really worried about efficiency (it’s so much better then standard stove technologies – that you really can’t go wrong with it. I am worried about smoke and poisonous gases leaking into the room. Two things can prevent that (1) a proper design (proportions of different elements) and (2) good finishing. I have proper design pretty much under control. Finishing was, and continues to be somewhat of a mystery. Our experiences with cob and earth finishes have been … well … mysterious. We are still not confident about it.

I was able to delay the project itself by two preparations that needed to be made. The first was to build some kind of small platform on wheels that would enable me to get the existing metal stove out of the way. Though this picture comes later in the time-line … this is the platform in action. Due to two wheels with brakes I was able to get the metal stove onto it and out of the way on my own (though the story of getting it out of the house took a funny turn):

The second preparation was to prepare the barrel. First I had to cut it open and then I had to burn the paint off it (so that no poisonous paint fumes would be emitted from it as it got hot on the rocket stove):

Because of my hesitance I started the project slowly, giving myself time to get back into the “rocket vibe” and to explore what I wanted to build. It began with a rough model that was constructed in the garage. I completely took apart and rebuilt the model a few times over many weeks. I spent quite a bit of time staring it, letting questions appear, letting solutions appear, moving parts around … I took my time with it … until I had a reasonable model … and restored confidence to start actual construction. I lit the model once to check for good draft … but given its design (round barrel meets square bell) it was kind of pointless since it was difficult to temporarily seal.

When I took the model apart I took a few images to document the different layers. I used those images to recollect and reconstruct dimensions during the actual construction. The construction began with a “subfloor” upon which I could build the floor of the rocket itself. The subfloor is built with mostly used adobe bricks. There are two ash-pits (the one in front and on the right is just under the feed chamber and the one on the left is under the future chimney exit) which are built with firebrick.

The floor itself is made of half-thickness firebricks.

Then came the first layer of the core. Though at the end of the day I decided that this would create a burn tunnel that was too deep so the next day I ended up taking apart most of what I built the previous day and removing this layer.

So this second layer was actually the first layer of the burn tunnel (though the picture still has the above pictured layer before I took it out)::

… and then on with the core including a (this time) brick riser (the oven is just set in place to measure precise location optimized for brick sizes), not yet built in):

… then a test fitting of the insulation container – rounded sheet metal tied in place with thick wires:

… and then a test fitting of the barrel itself:

with the core complete it was time to start building the heat-storage bell that contains the oven:

I then realized that it would be easier to continue building up the bell with the barrel in place (so that the quirky round-square meeting could be properly built). But to do that I had to first put in the insulation. The insulation is a mix of perlite and clay slip. It went all around the heat riser and almost all the way around the burn tunnel (no insulation was put in on the bell side of the burn tunnel).

All insulation openings were then sealed with a thick clay (cob-ish) mortar to keep the light and airy perlite from flying around.

Then it was time to complete the bell walls.

… and a concrete-slab we had lying around (of which there are more) was placed on as a cover (it was already fitted in place in the model) providing a lot of thermal mass (it was very heavy – a job for two) and an easy solution for bridging the wide opening of the bell:

The last part that was built was the ash collection pit/chimney exit chamber (on the left):

A few more cut firebricks were used to close the gaps between the barrel and the bell … including the installation of another clean-out opening that gives access directly to the passage-way between the two. Then all that was left to do was to seal all the opening with cob:

and install the chimney:

… and we fired it up and it worked like a charm. The immediate heating effect is new to us (in the first rocket we built where we didn’t have a barrel to radiate heat it takes time to heat up on the inside before that heat is radiated into the space. With this one the barrel gets hot within minutes (with still just the initial kindling wood burning) and quickly becomes too hot to touch. The room it was in was very cold since we had not heated it at all this season. We had a little smoke during the first firing (natural since the entire stove core is cold and damp) so a window was open … and the door to the entry hall was open and the hall itself was open to the outside … and still there was a very fast and noticeable heat throughout the entire space.

I never get tired of watching a hissing fire fire get sucked into the burn tunnel:

 

Then came the finishing stage. Despite numerous soil composition tests we seem to have ended up with cox mix that was clay rich. We were starting to run out of time (=running into extra cold) and drying the cob takes a good firing up of the rocket over two or three days … so I decided to risk it and applied the cob to the entire stove. Being clay rich meant that it contracted a lot … leaving a lot of cracks … which we could have dealt with … but is also pulled away from the body of the stove itself … and fell of in large chunks.

This is Ricky (in one of her winter outfits) making good use of the straw-bale we used to create the cob mix:

So we ended up pulling it all off and creating an alternate mix … a formula we learned of when we re-finished the north wall of the house. The base was a different clay earth … very sandy (10-15% clay and the rest a fine silt). At first we added to it gypsum as a binder (instead of aiming for a more precise clay-betonite mix). The resulting mix dried way too fast, so we added to it some hydrated lime to slow the drying. We ended working with a formula of 1 part gypsum, 1 part lime and 4-5 parts sandy clay. It gives a hard finish that had much better adhesion and seems to be heat-resistant. It did crack a bit, but that did not compromise adhesion. We will probably try to add another finish coat and maybe some color to it in the spring (all the soil is frozen now).

Initially we had to keep the rocket going for longer periods to really drive the freezing cold out of the room and the walls. The more regularly we use it the less we need to keep it going to enjoy a warm room. When the room is already warm it takes one feeding of the rocket to drastically boost the temperature in the room. It is crazy efficient.

It works amazingly well (to my surprise) as a cooking surface. The only limitation is that you can only cook on it when there is wood burning inside (and for a short time after the fire dies … while the barrel is still hot enough) which, because it’s really efficient, is not a lot of time. So to use it we need to consciously plan to do our cooking while we light and feed it.

The oven in the bell does not work. The rocket is so efficient in heating up the space that it simply does not run long enough to heat up the bell enough to get the stove warm enough to be useful. That’s the nature of this super-efficient stove!

There is more to be said about its performance, but that will come in a later post and after we’ve had some experience living with it. So far we are very happy 🙂

 

 

Categories
Construction Electricity Energy Water Infrastructure

Water – Electricity

Despite the irony of the title – electricity was an inevitable next step in the water infrastructure. The basic needs was to get an electric outlet for the pump. However I decided to take it one step further and install additional power outlets that would be available in the fields (so that I wouln’t have to stretch out long extension cords). So I set out to put in power adapters in both the flow junction concrete box and in the pump concrete box.  Though it should have been a straightforward task I did run into a few difficulties and learned a few lessons worth mentioning.

Electric Cable

We purchased a 200 meter roll of three wire cable. I don’t remember the exact specification – but I do remember we chose the one with thicker diameter wires (also more expensive) that were rated for a higher current. I would have wanted to put in more then one supply cable – but the cost was prohibitive.

Much later I learned that there is a 5 wire cable which is usually used for three-phase electric installations. However, I believe it can used as if it were three separate electric cables bound into one. The ground and zero wires are shared and then there are three current supply wires.

I don’t have a specific short-term need for this in mind, however it isn’t every day that you dig a 60 meter long, 1 meter deep trench on your property. So there’s that 🙂

Burying Electric Cable

The cable was buried alongside the water pipe. To protect it we purchased a ribbed plastic tube (2×100 meters length) meant to protect it.

The cable was a perfect fit in the protective tube. As a result, getting the cable into the tube was hard work. Rather then going into the details of how we did it (hint: using a pull-wire and cutting the protective tube into manageable segments) I would suggest getting a more spacious tube. I thought about this when we purchased ours but I thought that a tight fit would offer better protection to the cable. I still think that too large a tube, with too much free space, may collapse under the pressure of the earth and may give out sooner.

Modularity

For the better part of a day I struggled in vain to get the electric-accessories (splitter box and sockets) installed. I wired them together indoors and then headed out to fit them into the concrete walls. Remembers this is work done in a confined underground space. I failed … completely. I couldn’t get is assembled in place.

After a long and mostly fruitless day I realized I had been going about this the hard way. It dawned on me that I could do most of the assembly work inside if I were to simply mount the electric-accessories onto a wood panel and then simply mount that panel on the concretewalls. So, the next day I tried this and it worked like a charm. I predrilled the panels in place and then worked comfortably on them indoors. These are the two panels prepared for installation.

The only electric fitting I had to do underground was to connect the ends of the buried cabled to these boxes. In the image below you can see that I left empty sockets on the left hand side – so all I needed was a screwdriver and a few minutes of work.

Since our electricity infrastructure is outdated and partially improvised this entire supply line is simply plugged into an existing power outlet.

 

Categories
Construction Earthship Energy Heating

Building an Earthship in a Cold Climate? STOP

… and read the book Passive Annual Heat Storage – Improving the Design of Earth Shelters by John Hait.

  • Should Earthships be insulated? Yes (but not in the obvious way it’s being done today).
  • Should Earthship floors be insulated? No.
  • Can an Earthship provide a comfortable (21c) climate using passive means during the winter season in a cold climate? Yes.
  • Can heat be collected and stored during the summer for a winter with very little (mostly cloudy) passive solar gain? Yes.
  • Can an Earthship be properly ventilated without having to sacrifice precious heat? Yes.
  • Are skylights a must? No.
  • Is the corridor wall (introduced systemically in Global Model) Earthships required in cold climate? Not necessarily.
  • Can an Earthsip be built in clay-rich expansive soil? Yes, if the soil kept dry.

When it comes to cold (moist and frozen) climates like ours here in Romania, there are quite a few things that felt, to me, incomplete, missing or even wrong in Earthship design (including the latest and greatest Global Model). To me what was missing most is the lack of explanations of how things work and why they are designed the way they are. I could not find satisfying answers in any of Michael Reynolds’ Earthship books (Earthships have evolved way beyond their description in the original Earthship books) nor online in many of the documented builds and open discussions about Earthships.

Then a few days ago I published this post about ventilation problems in an Earthship and began to compose my thoughts for a follow-up post. The solution seemed to come in the form of earth-tubes. The first resources I came across (pretty much as they were presented in the search results) were:

  •  Wikipedia – which provided basic technical information.
  • The Natural Home – which provided a convincing argument for earth tubes.
  • BuildItSolar – which raised some questions and left me with some doubts.

Luckily I stubbornly pressed through a few more pages of superficial search results and on the 3rd or 4th page found an article by John Hait inaptly titled Umbrella Home. The article blew me away. I ordered the book and couldn’t put it down – I read it word for word in just over a day and will be re-reading many parts of it again.

The book truly lives up to its subtitle “improving the design of earth shelters”. Not only does it open a door to a much deeper understanding of earth-tubes but to do so it introduces a fantastic concept of a large insulating/blanket which surrounds an earth-sheltered house in which earth-tubes can really come to life.

The core idea (backed up by accessible explanations and practical research) is to create an insulated and water-proof blanket that encompasses the house and a large area (~6 meters) around it (which can be achieved with more or less the same amount of insulation materials used for standard wall insulation).

This insulated umbrella creates a large body of earth which is dry and functions as a huge thermal battery attached to the house. The house itself acts as a solar collector to slowly charge the immense thermal battery during summer. Then, during winter that battery slowly discharges heat back into the house.

Earth tubes are used with this umbrella (in a way that could not achieved without the umbrella) to passively generate both ventilation and temperature regulation (cooling & warming) of the house. Because the earth-tubes run through the thermal battery surrounding the house they work as a super-efficient heat exchange system. A passive air-conditioning AND heat-exchange system that is simple and affordable.

 

As a cherry on top  – imagine running an uninsulated water supply pipe under the umbrella and having water preheated to 21 degress (celsius) during winter  (cold water supply has to be insulated under the umbrella). As someone who washes dishes with freezing-cold water (unless I fire up the wood boiler) I am watering at the mouth at the thought of washing dishes with passively heated (no additional energy expense or effort) warm water. Not to mention energy savings in heating bathing water.

This may cause a problem with Earthships that include rain-water harvesting stored in buried cisterns. The cisterns, if buried close to the house, under the umbrella will become a source of warm water. Cold water would have to be cooled somehow and I don’t know what effects this may have on the stored water. Since we’ve decided to forgo rainwater harvesting and put in a green-roof this is not a problem for us.

If you’ve already built an Earthship in a cold climate and it isn’t functioning as well as you thought it would I believe that at least some of the measures described in the book can be added to your Earthship to make it a much better home.

I don’t recommend trying to implement this from the basic information in the article. I STRONGLY recommend reading the book word for word. It is educating and empowering and fun to read.

I am now (again) heading back to the drawing board to revisit and rethink our house design. I feel I know better now and I am grateful to John Hait for his work and for making it available to others.

Categories
Energy Energy Links Rocket Stoves

Solunit Rocket Stove

http://organicart.com/mud/solunit-rocket-stove/

Categories
Energy Hot Water Rocket Stoves

Rocket Stove Water Heater

I’ve been looking at lots of applications for Rocket Stoves. It is a beautiful and simple DIY technology I want to use as much as possible in our new house. This includes heating water. We currently have a simple (purchased) wood-based boiler that does an OK job and I suspect even has an inherent “rocket” effect … and mostly prooves that it can be done. So I’ve been looking around for hot water solutions based on Rocket Stoves.

Before I go into the details of the one I found I would like to point out one piece of advice about Rocket Stoves that I came across, stuck with me and is exemplified by it. Rockets work best when they are designed with one primary purpose in mind. This means that a rocket designated for hot water will probably be more feasible and work better then a rocket that is used to heat a space AND heat water. I can testify that it can be very tempting to build a supreme-do-it-all rocket … but it just doesn’ work.

With that in mind I came across the following Rocket-based hot water system. The project is documented with a set of images and a blog post.

Rocket Stove Hot Water Schematic

It is a rocket-stove dedicated to heating water and does nothing else. Because it is a single task rocket it is actually simpler then the basic rocket-stove since there is no heat exchange barrel and the water tank itself is the thermal mass. The key element is a heat-exchanger that sits on top of the heat-riser. It is a metal box within a box – where the heat from the rocket is transferred into the water. Depending on the position of the water tank flow is either achieved either passively via thermo-siphoning or with a pump.

The heart of this solution is the heat exchanger and at the heart of the heat-exchanger are small plates of metal welded into it, which increase the contact surface between the hot exhaust and the metal itself. With these plates a 1 meter tall heat exchanger can be designed to have 6+ meters of contact surface (as if the exchanger itself was 6 meters tall!). The trick is to size the internals in such a way that the surface area of air-flow will not become smaller then that of the heat-riser so that the exhaust can flow smoothly out. If designed optimally then, as with most good Rocket Stoves, there should be very little exhaust heat left in the chimney pipe.

We don’t have (yet) the skills to make this kind of heat exchanger but I am confident we can find a metal-worker who can create one for us. My thoughts are to connect a 6 inch rocket to a 300 liter tank of water and that should provide a simple and efficient and backup for days where the sun does not provide enough heat for the solar hot water panels to kick in.

Categories
Cooking Energy Heating Uncategorized

Our First Rocket Stove

If you are reading this and interested in the technical aspect of Rocket stoves you may want to scroll down to the last part of the post where there is a description of what we actually built. But first, I do will indulge in some personal reflection about rocket stoves.

What is a Rocket Stove?

If you’ve never heard about rocket stoves, though I’ve mentioned them before, this short video is the place to start. This video drew me out of the theoretical reading and into action – anyone can experience the wonder of rocket stoves by recreating what is demonstrated in it:

A rocket stove mass heater is a more elaborate stove built around this concept … it is simple to build, efficiently burns wood – the rocket part  (more then most existing stoves) and equally effectively stores and radiates the generated heat – the mass part.

To learn more you may want to:

However if you want to build one I strongly suggest you get the book – there are a few core details that you have to get right – once you get those down you can play around with it a lot. Though there is plenty of freely available information you will be hard-pressed to find all these core details without the book – at least that’s been my experience.

On to our personal rocket story

A Screeching Halt

Last year, as we were in the process of purchasing the land we currently live on, we were also working closely with our friend and architect on designing our hemp-built house (much more on that in coming posts). He designed a beautiful (and functional!) house, but the more beautiful it got to be the more I began to question its economic feasibility = I didn’t think we would be able to afford to build it. We were really committed to the process and invested much effort and resources in pursuing it (including a visit I have yet to write about to the UK to consult with an architect experienced in hemp construction).

As we were working on our rocket stove it was Andreea who insightfully recognized the point at which our beautiful house came to a screeching halt. We were doing some financial planning and were inquiring with our architect for some input on the house systems. We were sitting in his office discussing options for a house heating system – seeking a rough budget to plug into our calculations (which were already looking grim). He picked up his phone and called a fellow engineer. The conversation resulted in a mind-blowing figure ouf 15,000 euro (half of our target construction budget). We realized that something was not right – we felt that the architect and the engineer lost touch with us and our wishes. Further inquiry into the subject brought the figures down to 7,000 euro – still a lot of money and out of our budget.

Though the project continued to move forward and is still alive though dormant today, from that point on it was winding down. Our wish to have a comfortable and warm home, it seemed, could not be fulfilled within the budget we had.

Preparing for Winter

By the time we moved out it became painfully (at the time) clear that we would not be building a new house this year and that we would probably be spending a few years in the existing traditional Romanian village (cob) house. So, we began a long and ongoing (though definitely coming to a first end) effort to fix it up.

The house has a small hall, a small pantry (we converted into a bathroom) and two rooms. One room has a traditional Romanian wood-stove (the other had nothing). We had lots of plans to do lots of things. Though we did lots of the things, many were not in the plans and most of the plans did not reach execution. Our plans did not include building a rocket stove this year. They did include buying a second stove and a third wood-burning boiler.

Then, we discovered the (above mentioned) 16 brick video, we purchased some firebricks and tried it out … and it worked fantastically. We used it quite a lot for cooking outside.

At one point, just for the fun of it, I even built up around it and simulated a rough rocket stove . I used the parts of an old wood-boiler for the heat riser:

Seeing the horizontal burn for the first time was a magical experience:

And then when I placed a barrel on top, it got really warm really fast:

Then came the two+ weeks of non-stop cooking during which we made loads of winter preservations. We were practically living next to the small rocket stove outside. Then when we moved indoors in the evenings to escape the cold and complete the jar preservations we would light the wood stove. It was painful to see how much wood this stove consumed (and continues to consume) compared to the 16 brick rocket stove outside. Everyday I would have words of awe about the outside rocket stove and complain about the wood-greedy stove inside.

Slowly I gathered the courage to suggest we  try building a rocket stove instead of buying another wood-guzzling metal stove. And so it began … from here on it’s going to get a bit technical.

Constraints

There were a few constraints shaping this project for us:

  1. Timing – we had already finished putting in wooden floors including a corner of ceramic tiles in each room to house a stove. We did not feel inclined into removing parts of the floor to install a cob-bench (the mass part of the rocket where heat is stored) and we were not keen into working with cob as it takes time and experimentation … and we already had quite a bit on our plate. So we were going to build a stove without thermal mass … making it’s heating efficiency questionable.
  2. Barrel – This is going to be a recurring theme here at Bhudeva – but finding used/2nd hand anything is much more difficult here in Romania then in the USA, UK or other western countries. This is especially true in villages where everything is used, reused and used again, often beyond the point of efficiency or even safety. A key element in the rocket stove is a metal barrel – and for many weeks (which delayed the project) we couldn’t find one. We finally decided to build a rocket stove with “firebrick chamber with a top metal plate” instead of a barrel (we have since found and purchased one used barrel and have a few more lined up … we will keep them stored for future needs).
  3. Insulation We also could not locate (at reasonable prices) any of the suggested insulation materials for the internal combustion chamber – we ended up using wood-ashes – they may not offer the same level of insulation and they may settle over time but this is what we had available to us.
  4. Size – the actual stove – where all the burning takes place is a systemically and purposefully twisted path which, from a certain point early in the path (the horizontal burn chamber) must not become narrower. This is to prevent smoke and dangerous gases from returning into the room – the stove generates a powerful draft and nothing must impeded that flow. The traditional Romanian stove configuration is for a 12cm chimney flue – which is also the size of the chimneys usually built into the walls. Since we did not want to make a new opening in the wall for a chimney we had to adapt to that limitation. This is when rocket stoves designs are suggested for either 15 cm (6 inch) or 20 cm (8 inch). This meant a smaller scale and tighter design and indeed everything was scaled down accordingly. However, in retrospect, given that we built a spacious “brick barrel” as thermal mass – which slows the flow of gases before they exit, I believe we could have gone with a larger dimension in the stove with the limited 12 cm exit flue.

Model First

Like most of the good recommendations in the book, building a model of the stove is an important stage of work – and, as recommended, it should be done on a level surface (I tried to cut this corner and it was a waste of time). To that I would add that it should be built somewhere where you can (a) work on it over a period of time; (b) light it; (c) keep it out of the rain or other wet elements. I built our model in a corner of our barn which answered to all of these criteria – and luckily so because we went through quite a few iterations.

I actually used such images to document my progress of the layers (both as I built them up and took them apart) in building the actual stove in place. There were many small details and the images unburdened my memory and were very useful in actual construction. I spread construction sand on the floor to level it. This is  the first floor level model (it changed later in the process) … it is designed to raise the rocket off the floor and create ash collection both under the feed chamber (right) and at the exit flue (left).

On top of that came the “floor” of the rocket itself – intentionally adding more depth to the ash collection chambers.

Then of course the burn tunnel

… and off we go  – and you can already see the fire climbing up the feed chamber (the feed tunnel is not yet built up):

The model worked OK. The biggest problem, and one that carried over to the actual stove was the fire crawling up the sticks and out of the feed chamber. I now believe that the cause of this was that the feed-chamber and ash-clean-out beneath it  were not sealed properly. So the stove instead of sucking air down from the top of the feed chamber was now also sucking air up from below which both lowered the intensity of  the down-draft AND provided an alternate up-draft.

Also, if you decide to build something not quite by the book be prepared to take risks – as not everything can be tested (simply) in the model:

  1.  When I built the model I realized that I could not seal the brick chamber nor the top metal plate to the bricks. This meant that we could not assess how effective the generated heat would be contained and radiated from the stove.
  2. Though the top metal plate (can be used for cooking) heated up rapidly it had a surprise for us in the actual stove. The heat generated by the rocket is so high that the metal (5mm thick) warps … the corners fold out creating stress on the cob that seals the plate to the brick structure beneath it. The cob has cracked numerous times (and let out poisonous gases) and we have had to reseal it (simply applying another coat of clay-slip)… it looks like we have reached the point where it is properly sealed – though only time will tell – we check it regularly.

Our Stove

The following images depict the actual stove in construction. First a simulation of the base layer to get its position in the corner. Next time I would try to leave more space between the rocket and the walls to make it easier to access and install the chimney parts – it was a struggle.

Then a little messier with the clay-sand mortar to keep things in place:

In the middle layer (top image) I installed a metal grail to support the feed chamber and let the ashes fall – I notched (with a grinder masonry disc) three parts of brick to support the grail itself:

Then a metal heat riser (used pipe cut to size at a metals shop in Cluj) went on:

and over that  went a piece of sheet-metal tied into a roll and then filled with wood ash

Starting to look like a rocket stove

Here the heat riser is sealed with the clay-sand mortar mix

Here you can see that the heat riser is positioned away from the center of the brick box. One reason is that I assumed that the brick-barrel would behave like a steel barrel does and that the wider space would heat up more/faster then the narrow space – so in this case the wide space facing into the room. The space from the other (left hand side) wall is determined by the location of the ash-pit and exit flue (in the dark area at bottom left of the image). Though I don’t know if this actual works – I preferred to have the gases “linger” in the box rather then get pushed out by making the space near the exit flue narrow.

The almost finished stove with a completed brick chamber (I decided to use refractory cement which has adhesive function for the brick chamber instead of the sand-clay mortar which has no adhesive function it simply keeps the bricks from moving and when fired solidifies into a brick-like material) and metal top still undecided feed chamber, a temporary chimney leading out the door and to the hall, a small pot of water heating up and Andreea checking something out (and providing you with some sense of scale).

We still had smoke-back and fire climbing up the feed chamber … which frustrated me greatly … until Andreea intervened with a bit of feminine surrender and wisdom and suggested we let go of the vertical feed and go with a front feed … which not only worked but demonstrated that the stove had excellent draft with absolutely no smoke-back. Here you can see a fully loaded feed with fire swirling into the stove and absolutely no smoke coming out:

Then Andreea took over the clay plastering. It failed miserable the first few times – the plaster cracked and fell of in chunks.

The third time she (1) added hemp fibers and some acrylic construction glue; (2) wet the bricks thoroughly before applying the plaster; (3) applied it in thin layers and worked it in thoroughly with a wet sponge; (4) continued to moisten and add clay slip as the stove was heated up gradually over the next two days.

The chimney winds through 3 corner bends (poor planning?) so it was a bitch to install … but we now have a great looking and working kind-of-rocket-stove in the bedroom.

Performance

Before I talk about the stoves heating performance I’d like to talk about it’s other values – at least those that are important to us.

  1. Independence – with no past experience in stoves or any of the specific disciplines involved in creating this stove and with no access to people with past experience we managed to build this by ourselves. It can be built fairly quickly (it takes more time to gather materials then to actually build it).
  2. Efficient and Ecological – when the stove is first fired up some smoke comes out the chimney … but once the heat riser gets hot (very hot) there is no smoke – the stove performs a full and clean burn of the wood. Not only does it fully utilize the energy embodied in the wood (every time you see smoke coming from a chimney imagine waster dollars – all of that is wasted energy) – but it is also ecological since it releases very little pollution (compared to most regular wood stoves). If you were to buy an industrially made central wood heating stove you would pay a heavy premium for “re-gasification” – which is essentially the burning of the gases release when the wood initially burns. With the rocket stove this is an inherent and simply to achieve function (the insulated heat riser gets too temperatures high enough to burn the gases).
  3. Beautiful – you can shape and mold it and make it your own … which ends up uniquely individual and special.
  4. Sustained warmth – the thermal mass (in our case the “brick barrel”) contains all of that efficiently generated heat and slowly releases it into the space instead of letting it escape out the chimney.

It works great. Though we purchased a lot of wood we did not have time or do enough to dry it properly. Fortunately we also have a huge pile of junk wood that we collected from all over the place – that wood, after we cut it to size, is very dry and perfect for the stove. In a regular stove it may be desirable for wood to burn “not too fast” because heat is present only when there are flames (once the flames go out the stove and usually the space, unless it is superbly insulated begin to cool). In a rocket stove it is best to have a fast and efficient burn – the heat is stored in the mass and then released. We are currently lighting it with a few batches of dry wood and then some of the partly dry wood in usually larger chunks of wood. If we were to use only dry wood the stove would probably get really hot (too hot to touch) in 2 or 3 hours.  As we are currently running it it takes 4 or 5 hours.

It uses much less wood then the regular wood stove (I can’t say how much as we are not yet setup for measuring and comparing. But more importantly it’s effect on the room is very different. Since we don’t have a radiant barrel (only the small top surface radiates heat immediately into the space) it takes time to warm the space – the other wood stove warms the space rather quickly. But once its warm the space will say warm much longer (again I don’t have measurements for comparison) … but we usually feed the stove one last time at around 10pm and at 7am the room is not cold (though not warm).  With the regular stove the room cools drastically in an hour or two – once the fire is out the room begins to cool!

The heat has a different quality in the rocket stove room – it’s hard to put in words. It is a softer, deeper and rounder warmth then the regular wood stove.

It can be used for cooking – doing so requires using either very dry wood (which burns fast and releases a lot of heat) or patience (it is generally slower heating then the wood stove where fire almost directly heats the pots.

Until recently we have had to deal with the metal warping problem. It strains the corners of the cob that join the metal plate to the brick box to the point that cracks appeared and smoke/gas escaped into the room. It has been easy to fix – adding a clay slip – but has required constant attention. Time will tell if this is going to be an ongoing issue or one that we have resolved.

I would have been happy to make it bigger (see above mentioned constraint 4) and to get the vertical feed working properly. But we didn’t have time … it as getting too cold in the room and we still had plenty of work to do to prepare for the winter. The result is a stove that needs to be fed every 20 or so minutes … but that is a small inconvenience we are happy to accommodate.

We are very happy with the stove. It came to life just as the room was becoming unbearably cold. Creating it was a hugely empowering experience. We are very much looking forward to experimenting with it more and eventually incorporating simple rocket stoves we can build and maintain with our hand instead of complicated systems that cost many thousands of euros and place us at the mercy of technicians and engineers and companies.

We had plans to build a second rocket with an integrated baking stove and a thermal mass bench (wood framed!) stove to replace the existing wood-stove, but time did not allow for it. Next year 🙂

It’s been a frozen two days, it’s dark outside and cold is beginning to set – a good time to go and light the rocket so the bedroom will be nice and warm 🙂

 

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Cooking Energy Resources Videos

Top Lit Updraft Stove

Here is an even simpler cooking version of the rocket stove. I am wondering how to make it a steadier cooking platform – but other then that it’s so simple and looks very efficient.

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Energy Energy Links Energy Links Heat

Radiant Design Institute

http://www.radiantdesigninstitute.com/page2.html