Hi Crispin, Truly appreciate the info and advice.
I am looking to improve on the stove suggested and develop a range of appropriate stoves for the SSA areas, targeting Zambia. Please advise of other low cost examples you see as appropriate. My method, however, is not completely towards stove design to alleviate IAP, more a community approach to IAP alleviation as opposed to a 'top down' technologies approach. I am modelling this on the Community Led Total Sanitation scheme that has found enormous, very low budget success. Find it here; http://www.communityledtotalsanitation.org/page/clts-approach I believe that solutions found from within the community, once it is recognised locally that there is a need to change, are the most likely to be universally adopted. I believe in a bottom up approach that studies and values local knowledge and behaviours before attempting to inflict change. Local manufacture and development over expensive or complicated alternatives makes the most sense to me. I would rather dedicate time to a range of stoves that can be locally made, than instigate centralised stove manufacturing and make cash from the sales (although of course this is rightly appropriate for some.) Heath effects can be so greatly improved by simple behavioural modification eg. removing children from the cooking room/smoke, pre-drying biomass, do not sit in the smoke), and room/roof/eaves design and other extracting ventilation. I wish stoves to be only a part of the focus, and technological change to be metered out sensitively. Cost and complexity cannot leap, of course, or the long term adoption will diminish. Anyone else working with a participatory focused approach? Are you winning? All the best Dave --- On Thu, 4/11/10, Crispin Pemberton-Pigott <[email protected]> wrote: From: Crispin Pemberton-Pigott <[email protected]> Subject: Re: [Stoves] Chimneys To: "'Discussion of biomass cooking stoves'" <[email protected]> Date: Thursday, 4 November, 2010, 19:39 Dear Dave K Thanks for writing and your questions are good. There is a success story (in my view) next door in rural Zimbabwe. There, the adoption of quite technically simple built-in stoves with chimneys which became successful. They started building more and more elaborate versions of the stove, polishing them with graphite and building in shelves, cupboards and so on. Huge things. Quite remarkable. Something you can try that has not been done (as far as I know) with a Lorena is to use a built-in preheating air sleeve made from a tin can or rolled a roofing offcut. The efficiency of a Lorena is not as bad as many have claimed and it has lots of room for improvement. We built many in the mid-80's in Transkei (through the AT unit based in Umtata). Where water heating is important (people with babies) they are really nice to have and use. Richard Bolis and his wife had a big 4-pot one in their home and trained people in the Tsolo area. For them there was some space heating advantage too. Mainly it was about saving fuel (outside is windy) and getting the smoke out. Generally we got better results using a metal top and a mud/brick bottom. Generally the advice given for Lorena construction has too much draft, too much excess air and therefore a reduced efficiency. It is a problem often created when adding a chimney to what was a low draft fire. There is really no thought given to secondary combustion. Are you interested in improving the stoves or just copying plans available? If you want to make a very low cost stove, i.e. no metal at all, you can burn charcoal but it should be more like a stove+hood than a stove+ close-coupled chimney. You will have trouble controlling a charcoal fire. Control is important because it is purchased fuel. While a great deal of discussion of Lorena type stoves focuses on the 'heat lost into the mass of the stove', think also about the system as a hole, not just one part of it. The main loss is NOT from the heat into the stove body. There is a big gain in performance late in the fire if the stove body retains a lot of heat so don't let your thinking be dominated by this single loss. Most heat is lost be sending the heat up the chimney with high excess air. If you reduce the amount of air flowing into the stove, you increase the temperature of the fire a lot. That burns more of the CO and gives a much higher heat transfer efficiency to the top. Next, the transfer of heat to the pots may be poor. You make heat, you slip most of it past the pot, it continues inside the stove to perhaps a second or third pot, doesn't get transferred well, then heads for the channel to the chimney. It was doing fine inside the channel but didn't get absorbed. Work out how much heat a stove holds. It is not very much. Don't be impressed by claims, ask to see the numbers. The small amount of heat you prevent getting away and keep in the insulated channel is bought at a cost (usually) of a far weaker stove with a much shorter lifetime. Is it worth it?? There is little point (to repeat myself) spending all sorts of time and effort to preserve some little amount of heat going into the stove body when you are building a very inefficient fire inside it to begin with. Any fire that is completely enclosed within the stove should be burning really efficiently. After all, it has all the advantages that an open fire does not. Very little proper testing has been done on clay stoves of that type. There are lots of task-based performance tests, but not detailed analyses that lets you point a finger at the main losses and correct them with the flick of a small flat metal sheet. Simple math: stove mass = 75 kg (that would be a large stove with more than 50 litres of material in it) thermal mass of stove material 0.8 J/g (soil) Average temperature 150 C (that would be a very hot stove) Heat stored in the stove (150-20) x 0.8 x 75,000 = 7.2 MJ = about 1/2 a kg of wood. If the wood used in a cooking session was 5 kg, that is a 10% loss. Reducing the excess air from 1000% to 500% would save 25% of the fuel. Here is a real test manipulated, 5 kg burned: Excess Air / Efficiency / Fuel wasted (kg) 1524% / 17.2% / 4.14 1059% / 36.1% / 3.195 (saved 0.95 kg) 553% / 60.7% / 1.965 (saved 2.175 kg) 283% / 75.4% / 1.23 (saved 2.91 kg) Those numbers were produced by varying the excess air ratio only. Suppose you managed to create a stove that absorbed only 250g worth of wood during a cooking session. That means you are limiting the transfer of heat into the stove body. You can't eliminate it, especially for no cost, but it can be reduced. So you can save 5% of the fuel, but it requires (usually) a lot of work and training and care with a sacrifice of durability and much more frequent maintenance (because low density constructions are inherently fragile). Is it worth it? If you have little money to spend on the stove, make it last as long as possible and concentrate on getting the fire to burn properly with no more air going into it that it needs. It will far outperform the well-insulated Lorena that does not take care of the combustion. You can measure the excess air level in the chimney with just an oxygen meter. Not very special. Regards Crispin -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of dave kuchanny Sent: 04 November 2010 06:21 To: [email protected] Subject: Re: [Stoves] Chimneys Hi Crispin / stovers I've avidly followed your links, posts and advice for some time now, first time to write anything myself. What about the zero cost stoves with chimneys? Surely these are amongst the most desirable in terms of economic effect to IAP and improved efficiency. I have recently been running a study in Zambia on alleviation of IAP from cookingstoves using a participatory approach, not the 'top down' imposition of technologies. I did however showcase and example improved cookstove, promoted through GTZ in Uganda, the mud rocket stove called (I believe) the Lorena. This adobe (anthill soil and grass) based stove uses banana stem as formwork to build the fire box and chimney etc around, and has no financial costs to produce. The construction manual is straightforward, with simple diagrams, and with a 2 pot stove like this one, it is appropriate to the cooking dynamic of the region. It also comes with cleaning and maintenance guidelines to stop the sooting of the chimney becoming an issue. The details are found here; http://www.energyandminerals.go.ug/pdf/gtz/HOUSEHOLD%20Stoves%20Construction%20Manual%20August%202008.pdf There are 2 issues I am aware of, but am looking for greater knowledge and further insights from the group. 1. The stove cooks with small pieces of timber, but the local vernacular is split approximatley 50:50 wood/charcoal, so this will be inconvenient or completely inappropriate to some. Is it possible to use charcoal in stoves such as this, and what changes would be needed? 2. I am aware of the improvement gained by adding insulation. This stove has large mass, insulative in part by the grass in the anthill soil 'mud' body. A fired clay insert that followed the heat pathway through the stove, in place of the banana stem formwork, would mean that initial heat would transfer more directly to the pot, not into the stove body, and increase fuel efficiency. Are there no cost methods to achieve this? What if there are no kilns nearby? Can we cerate this improved insulation by, say, adding vermiculite (not sure if locally available) or other material in larger ammount to the adobe mix surrounding the banana stems? Ash perhaps? Would we then need a stronger binder than the clay soils, like lime? I am working towards briquette manufacture, more improved stoves and biochar potentials in the area but am looking to stagger introduction of these (probable) improvements. There are at present almost no improved stoves and extremely poor charcoaling and wood production methodologies, with little understanding of IAP andthe efferct of smoke. It makes sense for the transition to be gradual and community owned for there to be lasting adoption. Any advice, contacts or cautions would be greatly appreciated. Dave _______________________________________________ The Stoves list has moved to [email protected] - please update your email contacts to reflect the change. Please visit BioEnergy Discussion Lists http://info.bioenergylists.org/ Thank you, Stoves Administrator http://stoves.bioenergylists.org http://info.bioenergylists.org UNSUBSCRIBE HERE; http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
_______________________________________________ The Stoves list has moved to [email protected] - please update your email contacts to reflect the change. Please visit BioEnergy Discussion Lists http://info.bioenergylists.org/ Thank you, Stoves Administrator http://stoves.bioenergylists.org http://info.bioenergylists.org UNSUBSCRIBE HERE; http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
