Crispin Pemberton-Pigott

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since Mar 28, 2012
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Recent posts by Crispin Pemberton-Pigott

There is a whole book printed privately by TATU, then called the ECATU, now a branch of the Eastern Cape Agriculture Department on building with gabions. It was dated about 1982 and has been used in hundreds of building in the Eastern Cape. There is a manual device from New Dawn Engineering that can make the gabions by hand called a Netwire Board. There is also a heavy duty version for making earth dam walls called TriNet based on the same principles. See for ideas. /products /wire /fencing Something like that.

It is possible to contact Cecil Cook to ask how to get a copy of that Roneo publication. It used both the gabion style wire and soil cement bricks, in-filling between wooden posts. It was very cheap and relatively insulating. The TATU offices in Mthatha were made using that system.

1 year ago
Brick greenhouses in China:

China Agricultural University has an experimental farm in Haidian North (Beijing) with several of the greenhouses described above. I am attaching several photo taken of these from inside and out.

This one is attached to the Biomass Stove Testing Laboratory which is run by the CAU College of Engineering at which I am a supervising 'visitor' (grad students, stove design and testing protocols).

The greenhouse is used as a storage facility though there are some biochar experiments going on in the photos. That is why it is not full of plants.  The fuels and stoves are stored prior to testing. All the stoves in the photos are low pressure boilers (hydronic heaters) made in Hebei Province. Testing is part of a clean air initiative for 18m farmhouses.

As described above the greenhouse top and south are curved, with a descending cover. The ropes and handles hanging from the ceiling are to control vents. There is a fan visible in the west wall. The building to which it is attached is occupied by not heated, it is just convenient to use the back was as part of another structure.

I can confirm that it is warm enough to grow things all year though I didn't pay much attention to what, or for how long. The structure was destroyed by the local government who declared that it had been built on 'farmland' illegally. No comment. The 'destroyed' picture shows the West wall, the fan and a bit of the structure - bricks.

The thermal mass of the walls is very large. I did not calculate the heat storage and return, but it is a substantial structure. There is every reason to think it is capable of keeping temperatures above some given value for a given period based on ordinary calculations. The length to width ratio would be important in that if it is really long, the influence of not having light enter on the east side is less important. I suspect the ratio is about 1:4 East:South. Although the West wall shelters the 'house from late sun, light still hits the inside of the East wall so the loss isn't all that much.

The metalwork is modern with modern conventional vents and levers. Nothing is automated except the fan thermostat.

Crispin in Muizenburg
1 year ago
Yes. Quotations come from Thabsile Shongwe. Sea Freight is possible. Air freight is sometimes cheaper. Other times it is better to make your own.

You can click on any of the email links to send an email to Thabsile (a lady).

There are masses of photos available of these technologies in use - just a taste on the web. Many have been on the market for 20 years. For home construction also see the hand operated rock crusher. There are 90 in Haiti.
2 years ago
The idea of using 'fencing' as a deterrent or structural element is good in that you can make by hand precisely what you need. For example if you are making Square Mesh on site, you can make a single sheet of 'fence' as wide as you want - no joints for example over an entire roof.

You may have seen the Diamond Stucco Mesh on the same website. This was specifically designed to make a wire product that could hold cob or plaster without and backing - sort of like a chicken wire that is sized to hold plaster. It has a thickness of about 5mm meaning if you push it against a mould, the cement still gets behind half the wires and onto the other half.

The purpose is to be able to add a very strong reinforcement to plastered things like hay bales without investing a lot of money.

The Diamond Stucco Mesh machine is also used to make stainless steel mesh for bird cages. Unlike chicken wire (rigid hexagonal holes) it is stretchy so it can form over complex shapes like barrels. The machine is not easy to learn to use it - it takes a few days. Experts make about 25 m^2 per day (14mm holes). There are no machines in North America.

The Square Mesh has been made by hand down to 30x30mm. It is used to make gabions with internal dividers. The usual size is 76mm (3") holes.

The savings over buying fence may not be much where you live - check the cost of plain wire in bulk per kg and fence per kg first. The difference is the available savings. Most places it is 40% but watch out. Same warning for barbed wire.

If there is any interest in making water tanks from cement and mesh I can forward drawings for making a mould based on a galvanised corrugated iron water tank. We made dozens of such moulds for thousands of tanks in Southern Africa. The finished tank is 40mm thick (1-1/2"). Sizes were 1000 and 2000 Imperial gallons (4500/9000 litres)
2 years ago
Gabion making by hand.

There is a set of hand operated equipment (two actually) for producing gabions from plain galv wire.

The idea is to make one of three types of mesh, then fasten it to a wire frame that is held on a large spindly jig. Then fold it up.

The three types of mesh are Diamond mesh (chain link) and Trinet which has triangular holes and Square Mesh which looks like diamond mesh turned 45 degrees. All three can be hand made under a tree.

The website is under fence products.

The Trinet jig product was designed for Dam construction and bad be made with quite thick wire. The others are normally 11 gauge or thinner, 12 gauge being most common (2.5mm).
2 years ago
On the thermodynamic side I can make two small contributions.

The angled riser AKA chimney: a chimney's draft is related to its average temperature (of that section) and its vertical height, even if it is on an angle. Your system consists of several sections with different drafts, at least one of which is negative (being a Rocket Mass Heater). There is a draft calculator in the library at (search for draft calculator nigel). You can use it to determine the sum of five or eight sections, can't recall which. At least five.

Second, the 'corrugated' flexible pipe sections which you can use for elbows: the flow 'restrictions' which these represent is not really because of the bumpiness. It is that they have a more effective heat transfer rate (higher surface area) than a straight smooth surface. In short, they drop the temperature more, reducing the heat available at the exit thus reducing the net draft on the system because it will be cooler at the end.

You have two main sources of draft: the initial internal chimney (use bricks) and the final exhaust. The sum of these is your total draft, pretty much. You should measure the temperatures involved at the end to prove you have 'some draft' at the late fire stage when things are the most dangerous. The heat stored in the bricks of the internal riser help greatly at that time.

Generally speaking feeding into the leg of a Tee is a bad idea, rather use a branch Y + 45 degree elbow on one side then a 90 degree elbow for the other direction, which doesn't have to go directly opposite because you can rotate it on its axis. The combination has less flow resistance that a tee heading off in two directions.

In that same draft calculator there is a section on the left which you can use to 'burn' your fuel and it will tell you the gas flow rate if you know the excess air level (separate discussion). The flow rate can be used to calculate the total flow resistance of the proposed pipe network using conventional HVAC methods. The bottom line is that below about 10 feet per second 'resistance' to flow is not significant, and is far outweighed by changes in total draft caused by small changes in temperature (as can quickly be seen using the draft calculator) and chimney height.  

There are municipal rules for the exit height of the pipe above the roofline for very good safety reasons (to do with wind).

It is common here in Central Asia to wrap the outside portion of the chimney in insulation to improve/conserve the draft at the end.

Good luck
Crispin in Bishkek
2 years ago
Congratulations Andy

Great achievement.

>Based on the available stove pipe having a 15 cm diameter (5.9 inches) it is essentially a 6" system.

Do you think this is adequate? People think pipes are expensive so cost matters a lot. There is a pipe making machine at GIZ in the West end (they have a rented workshop). There is a bending break with a cutter attached, a roller and a seaming machine, all hand op. The chimney pipes are made locally so you can get any size you need by asking them for it. The common sizes at the market are 95, 108 and then the big one. Elbows can be sourced locally. The Korean TLUD briquette stoves with a heat exchanger beside them have a 90 elbow at the bottom of the stack.

>The Mongolian ladies from the community laughed with delight when they sat on the bench today and felt the warmth on their butts.

That is very comfirming. The lower portion of the ger is space that is lived in!

>...I had the idea to place one of their round bottomed cooking pots in the feed tube ring.

Were you burning wood or coal?

I have a list of retailers/importers selling firebricks, both of Chinese and Russian origin, stuffed away somewhere. Let me know if you need it. Some keep a little stock. Some don't. Expect them to be in the Tg1400-1600 range each.

A stove development and training cnetre is about to get started and it would be good if you could give either a class or field demonstration (or both) to the staff of that centre-to-be. The idea is to work with people who are doing-the-doing on the ground to offer them theoretical and practical back-up, product testing and social science impact assessments. The latter as we all know is often missing from 'technical development'. User acceptance, opinions on the fueling, functions, cost, flexibility and durability must be part of the hardward development. That means bringing the formal sector producers into more contact with the users. A very helpful study was done by Cecil Cook the American about a year ago that raised some eyebrows and legitimate issues. It seems old hippies can still make a contribution and get attention.

Would the RMH benefit from a cast iron top where the pot sits? CI is quite cheap. It would be easy to produce at the artisanal level by one of the township foundries. Ditto for the grate.

I wish you success in the coming season.
6 years ago
Dear Andrew'n'All

YOu are really hitting the nails on the heads with that post. Congrats.

>Focusing on the original question about burning coal in an RMH, if one retained the J-tube Rocket configuration, what adaptations must be made to deal with burning coal?

The original downdraft stove was a J stove. With a flat J Iguesss you could say. So far there is not an available downdraft stove though I taught several artisans to make them. One surprised me by calling it a Russian name and he knew how to light it, andreally loved the performance. He got a 13 hours burn from a single load by putting a choke ring in the chimney. So they are known in Mongolia.

The huge advantage of a downdraft is that when burning high volatiles coal like Nalaikh (which is about 2/3 of domestic consumption in UB) it deals really well with the volatiles and the refuelling emissions which are horrificon a traditional stove. Remember the trad stove is a wood stove with bricks in it.

>Would one keep the downdraft configuration, or would a crossdraft or a dasifier/pasifier work better?

I have seen some pretty wild things tried in UB so I remain open to anything that will burn. I put a video on YouTube about the stove with the rotating grate - that was off-the-wall crazy and partly worked. Would have been better if it was made to tighter tolerances. Thermal eff was 35% tho.

>Is there still a risk of runaway burning?

I really think not. The coal burns pretty much like wood - you have to restrict the primary air to slow it down which is a problem with the trad stoves because of the poor fit of the ash drawrs, as I said.

>Would one need to inject secondary air at some point, heated or otherwise?

That is really likely. As the primary air is necessarly restricted because of the high volatiles, secondary air is needed. With hte GTZ 7 series stoves this was provided by running it through the grate at the low-level end where the coke is. It is an odd way to do it but it sure worked well. Very little additional secondary air is needed on top of that. As others have suggested above, restricting hte primary air at the entrance of the RMH will provide negative pressure in the firebox limiting the chance that anything will leak out.

>I would guess that a refractory combustion chamber would be a requirement. Would cast refractory be sufficient, or would kiln fired material be necessary?

To avoid a general discussion, yes and in the case of Ulaanbaatar, I suggest using the widely available (meaning three outlets or more) of the Chinese boiler liners. They are about $1.25 each and are really well made, can take tremendous thermal shock and are cheaper than the Russian ones. Mentioned above was the need to deal with higher temperatures. Quite right. Metal does not last when exposed to the coal fires at high revs, so to speak.

>Is the startup time for coal significantly longer than wood?

Definitely, especially as the fuel is 25% moisture. It is often frozen like a popsicle when it put in.

>If so, would some sort of draft inducer be necessary to maintain draft until the system is heated up?

In short yes, but what kind? The nest answer seen so far is the heat exchanger bypass which is a hole approx 40 x 50mm leading directly to the chimney bypassing the heating box. The box is made slightly larger to compensate for the heat bleed. It brings the stoves up to temp quickly and has been adopted by several manunfacturers. This is of course not necessary on the RMH.

>Addressing the issue of condensation, would a feasible solution be to make sure the flue in the bench, or whatever the mass is shaped like, is sloped to drain with a trap placed inside the heated structure at the bottom of the chimney, or before the exhaust vent perforates the exterior wall?

I was hoping Ianto or someone with experience would comment on this aspect. How is the condensation dealth with? Is it drained outside or pooled and evaporated later?

>Addressing cooking, I get the feeling that making a single combo stove for the cold extremes of Mongolia may become a case of "Jack of all Trades, Master of Nothing."

Yeah, a serious possiblity. The thing is, the population is in a state of flux and there are definite market segments for specialised products which the RMH might be one. In its favour is that they are used to mass walls which they call heating walls. I have heard one report of a fixed heating wall in a portable ger.

>While the barrel over the internal chimney of a heating stove may be used to make or warm tea, or slow cook, I don't know that it will be able to cook a meal in a 20 liter wok without some major alterations.

The cooking height is a non-negotiable so this has to be considered. Possible cooking locations are the horizontal portion between the firebox and the vertical hot chimney, or on top of the chimney which is too high for short women to put 10 litres of soup. Woks slosh easily.

>Could a cooking top be fabricated to fit the barrel, something that would lift the wok above the chimney to maximize heat at the top of the barrel, and make a good airtight seal at both the barrel and the wok?

The problem is still going to be the height. Making tea might fly.

>Would it be safer to put the cooking unit ahead of the internal chimney?

Exactly. Possible, as they say.

>Would it be simpler to just buy one stove to cook with and another to heat with?

We have available at least some social anthropoligical survey material (American, Cecil Cook) indicating that above a certain income level there is a strong preference for electric hotplate cooking, like a rice cooker and so forth. People also cook with bottled gas if they can afford it. This is also the group that a) has more money and b) probably lives in a house that the RHM could heat.

One must be careful when interviewing because if you ask about stoves, they tell you things that relate to the importance of 'storing heat' (which most stoves do poorly) and portability, even if it is in a fixed installation. It is a hangover from being nomads. We found the same in South Africa. What people think about stoves (which drives their purchases) is different from their use of them and the cost of using them.

People mistake a small smouldering fire as the stove 'storing heat'. The thermal mass of the stove is not large at all but this capacity rates highly on surveys.The reason is they have such a flash-in-the-pan massive fire followed by some smouldering coals. They mostly have never seen a stove that has continuous heat for a long time like Roger Lehet's vertical masterpiece. Have you seen it BTW? Mother Earth has picked it up as a promo technology through their fairs, somehow. He deserves the victory.

Incidentally I met with Adam Perry of Cob House fame together with Cecil Cook at the East London airport on Wednesday. We didn't talk RMH - no time - but got to see each other. He is examining the spread of soil-cement building technology in the old Transkei where is has displaced cinder blocks in low income housing in some towns. Cecil is an adjunct prof at the Univ of Fort Hare and Adam is studying there. There is a strong AT connection in there too I expect.

Stay well
6 years ago
Hi Ernie

Pleased to meet you.

>A few points i would like cleared up and then i need to bow out due to being a moderator and the water already passed.

I am not following the 'water already passed'. Is the thread so old no one is interested any more? That happens....

>1. direct heated chimney? Are you referring to the heat riser?

Is that a reference to another post? I am not sure what a direct heated chimney is - I was trying to describe the traditional stoves as presently used. They have a steel pipe which is often fairly loose on a very short (way too short) stub on the back right (usually) corner of the heat exchanger. The heat exchanger on the traditional stove is a rectangular box behind the combustion chamber.

As for the RMH the central riser is what I presume you meant by the heat riser, yes?

>2. damper? a bit of steel is better than a brick in some way?

I was describing what they use. The common practise is to make a cut with a hacksaw in the chimney and insert a piece of approx 0.6mm flat galv sheet. In virtually all cases I have seen the damper is not capable of closing off the chimney completely. Many stoves have no control on the chimney but do use the ash drawer as a controller epecially during ignition. In general the ash drawers are too loose and do not seal well enough to limit the excess air entering the stove. This leads to two common problems: runaway burning in the first 45 minutes and a negative thermal efficiency in the last 90 minutes. A typical burn is 4-5 hours.

>3. internal pressure? where do you see this as a problem?

If the fire is running well and the damper on the chimnmey is closed enough, the stove is under a positive pressure as gases build up in it and leak into the room. This is so common a phenomenon that people are careful to avoid the condition because when it happens it kills everyone in the house, or makes them very sick. It is not just the CO, there are a lot of poorly burned volatiles in a stove that is choked on the chimney side unless the coal is completely coked by then.

>4. you subsidizing the RMH?

Not me that's for sure. I have no money. But I can train people. In order to have any stove subsidised it has to be tested for emissions and thermal efficiency. I believe the RMH will easily pass the % efficiency rating. To my knowledge there is no unit available in UB for testing for emissions. Was the one mentioned above completed?

Very briefly, the emissions test is the measurement of the CO and PM2.5 emitted during an ignition, a burn until 90% of the burnable mass has gone, then a refuelling and a similar burn. The result is expressed in PM mass per megajoule delivered into the home. That takes care of the thermal efficiency number in the same calculation. Basically it is a measure of how much pollution per unit of heat gained by the house. The current target is an 80% reduction in PM 2.5 relative to the baseline (which is 788 mg/Net MJ). The best stoves are in the 3 nines range (99.9% better than the baseline). The 72,000 MCC sponsored TLUD's are in that range.

>Who has asked you to do this thing?

No one. Just looked like a really good idea. I don't want to estimate the uptake, but a demo is probably warranted. Roger pointed me to the USA work and it seemed to have (parts of it at least) a good fit in some circumstances. I will raise it as a possible design if and when I can, to local producers to see what the uptake is. They are a very easy people to introduce new technologies to. Adoption can be quite rapid. So is rejection. Cooking capability is a big issue and if the women don't like it they won't use something even if it is free. There are strong relationships between the families and their stoves. Second hand stoves are rarely sold outside the extended family.

I believe the RNH will be more applicapable to the many thousands of people who are building fixed housing than gers (because it is a nomadic, temporary house). The use of thermal mass walls is widespread in fixd housing though they obviosuly suffer from not having a proper method for dealing with the condensation. The combination of fuel moisture and combustion moisture is on the order of 450 litres per month condensing inside the wall. Lots of issues. The RMH will have to deal with that too if it is a condensing unit (which I believe from what I read, the best ones are). Handing condensate when it is -40 outside is an issue.

6 years ago