Tuesday, October 02, 2007

Cookstoves in Uttaranchal

For about ten days at the end of September I had the opportunity to do some consulting for an environmental and public health non-profit located in the foothills of the Indian Himalaya. Aarohi (Hindi for “ascendance”) is situated high among the tiny mountain villages near the small city of Almora in southeastern Uttaranchal. It is some of the most beautiful mountain country I have ever visited.

For a few days I tagged along with Aarohi staff as they visited villagers’ homes on a number of errands pertaining to various initiatives of the NGO. Specifically, I was to take a look at the villagers’ wood fired cookstoves and make recommendations addressing a number of common and interlinked problems.

One of Aarohi’s concerns is the sustainable utilization of forest resources – especially firewood – and they have developed a variety of community-led cooperative management schemes for conserving precious forest resources.

For hundreds of years, villagers existed happily and in balance with forest ecosystems, historically dominated by oak. But with colonization by the British, and later, Indian government “development” programs, roads were built into the forest and heavy logging ensued.

More recently some logging regulations have been put in place, and specifically the oak has been protected in hopes that it will reestablish. Presently the forests are dominated by pine, a lower quality wood than oak hardwood from the perspective of building and cooking.

One reason the villagers don’t like to use pine for cooking is that it produces a lot of smokes when burned. Smoke in villagers’ houses is a serious concern – a concern Aarohi specifically wanted me to address in my study of cookstoves. Their health clinic has seen many of the villagers who suffer from lung and eye ailments brought on by smoke overexposure.

And finally, since the villages are located at fairly high elevation (6,000 - 7,500 ft) in the Himalayan foothills, home heating can be an issue, especially during winter months and the monsoon.

So I had a multi-dimensional problem on my hands: how to provide for efficient home heating and cooking with the minimum firewood consumption and the elimination of smoke in the home.

Observations

My visits to villagers’ homes revealed that three main types of cookstoves being used: mud stove, three-stone in a conventional fireplace, and mud stove-fireplace combination.


Typical mud stove

Traditional fireplace and mud stove-fireplace combination

Typical mud stoves have a large firebox with two openings, and the pot sits on top of raised humps. A conduit from the back of the firebox connects to another opening over which a pot or kettle can be kept warm. Most often these stoves are not equipped with a chimney; accordingly there tends to be a lot of smoke in houses using these stoves.

Photos showing soot accumulation on walls and ceiling. This home, like many others that use the typical mud stove, did not have a chimney because the residents are concerned to keep heat in the house during the cold months.

The traditional fireplace style uses a three-stone arrangement or horseshoe-shaped mud baffle to support the pot. The combo style uses a conduit sculpted into the mud body of the stove to channel the smoke to a warming spot and then up the chimney. Both of these designs result in much less smoke in the home than the typical mud stove.

Pretty much everyone complained of being cold in the winter. Families – typically 6 – 10 people per household – huddle around their stoves to keep warm, though the heat output is apparently not that great.

Research

Like any good academic scientist worth his salt, I secured an internet connection and proceeded to do some research on combustion and stove designs for rural households. I knew the first place to start was the website of Aprovecho, an appropriate technology research center in Oregon. They have been developing robust, inexpensive and efficient stoves for nearly three decades. (I stole the cartoon images below from some of their materials.)

Based on my reading of Aprovecho’s technical papers, I could immediately see how many of the villagers’ stoves could be improved. For example, simply placing a metal grate in the entrance of the firebox to support the burning wood would result in more complete combustion by promoting greater airflow. This, in turn, would mean a hotter fire, less smoke, and greater cooking efficiency.

A grate for supporting the burning fuelwood.

As it turns out, surprisingly, wood does not burn – it’s the hot gases escaping the wood that burn. Heat from the fire volatilizes organic molecules that make up the wood; these in turn combine with oxygen from the air in combustion – a process that, if carried out completely, converts the hydrocarbons into carbon dioxide and water vapor. If combustion is incomplete, a panoply of partially combusted hydrocarbons is given off in what we commonly call “soot” and “smoke.”

A grate for supporting the burning embers helps ensure sufficient airflow, providing ample oxygen for complete combustion and thereby reducing the production of soot and smoke. It also encourages a hotter fire, which requires less wood to do the same amount of cooking.

Another brilliant recommendation I found in the Aprovecho literature is the use of a pot skirt. This is an inexpensive device made of sheet metal that can be fabricated locally. Its purpose is to channel the hot combustion gases through a narrow gap surrounding the sides of the pot. This increases heat transfer to the pot and the food inside, the reducing the amount of wood needed for cooking.


A similar effect can also be achieved by recessing the pots into the molded mud stove. This design improvement can also be combined with a chimney to remove smoke from the house.


Another ingenious device for reducing cooking fuel consumption is a haybox. This is an insulating box in which you place your pot of beans, rice, etc. – any food that needs to slow-cook over some hours. Just give the food an initial boil on the stove then pop it in the haybox, which works great to keep the food at or just below simmering temperature.



In sum, my research into designing the optimal cookstove led me to the conclusion that the key is getting as much of the fire’s heat as possible focused right onto the bottom and walls of the pot. Maintaining a good draft is integral to efficient combustion; installing a grate at one end of the fire and a chimney at the other help to ensure adequate draft.

Other than that, the goal is to minimize heat loss to the stove body and surroundings. Many stove builders construct their firebox out of lightweight ceramic tiles, or sheet metal insulated with pumice, ash or perlite, or some other low thermal-mass material. Mud, clay and stone by themselves, that is, without such an insulated firebox, are only OK stove materials, since they have a high thermal mass. This means they will tend to absorb heat energy from the fire. If heat energy is going into warming up your stove body, it’s not going into your food – representing a loss of efficiency and a need for more firewood.

Something else occurred to me as well – the notion that using a cookstove, well designed or otherwise, to try to heat your home in winter isn’t going to work very well, for the reasons I’ve just mentioned. You can either channel heat energy into your food, into your stove body, or send it up the chimney – all bad options if one of your goals is to heat a chilly house on a wintry Himalayan evening.

Yet many households were trying to do just that. The reason the typical mud stove has such large, inefficient openings is because the villagers have been trying to use it for a dual purpose – for cooking and heating. My recent research into the principles of combustion and efficient stove design, however suggested that this design offers the worst of both worlds, rather than the best – kind of like hybrid bicycles, which are too flimsy to take off road like a mountain bike, but are too heavy and put you into a dorky upright posture that prevents you from really hauling ass like you would on a proper road bike.

As any good cyclist knows, you need two bikes for two purposes. (Unless you’re also into downhilling, BMX, dirt jumping, time-trialing, triathlons, touring, and cyclocross, which means you need at least nine bikes, plus something to commute on since locking any of the others to a Berkeley parking meter would amount to kissing it goodbye.)

Anyway, I latched on to the idea that trying to optimize one tool to do two different jobs would result in a tool that does both poorly. How about two tools, each optimized to its own specific purpose?

That question led me straight to Ianto Evans’ and Leslie Jackson’s pioneering work on rocket mass heaters. The rocket heater is a super efficient device, super cheap to build, for combusting wood and storing the heat in a massive thermal battery – a horizontal chimney, if you will, that can be molded using cob (a mixture of mud and straw) into any shape you can imagine. One of the more popular designs is a sofa built right into the wall of the house or cottage. Here I’ve stolen some images of a rocket mass heater from Evans’ and Jackson’s website:


Whereas a well-designed cookstove won’t absorb precious heat energy away from the cookpot, heat absorption into the thermal mass of the rocket heater is exactly what you want. The fire warms the cob body of the heater, which in turn re-radiates the heat into the room. I haven’t seen one of these babies in action, but a trusted friend has experienced a demo of one such heater in Oregon and he vouches for the copious quantities of steady warmth it produces.

Recommendations

Sadly I had only ten days to spend in this verdant mountain paradise in the foothills of the Great Himalaya. But before I left I made the following recommendations to Aarohi to address the interdependent problems of cooking, heating, firewood consumption, and smoky interiors:

1. Insulation. Many of the villagers homes had poor insulation, especially the newer homes. The traditional architecture builds with walls of local stone, often finished with a clay plaster, and gorgeous slate roofs insulated from beneath by rough cut wooden slats covered with a thick layer of clay mixed with organic matter. (Homes constructed in this traditional way are reputed to last over 200 years, and with minimal maintenance.)

Newer construction builds with brick-and-mortar, or concrete, or a mixture of these techniques and the traditional stone methods. Roofs are often made of concrete slabs or tin – neither of these insulate as well, or last nearly as long, as the traditional slate roofs. As is the ubiquitous trend under economic globalization and “modernization,” newer construction is “cheaper” but involves substituting fossil energy and materials brought from afar for locally abundant materials and intensive labor.

Whatever the method of construction, an adequately insulated home helps to retain warmth in the winter and “coolth” in the summer. Roof insulation is especially crucial to temperature regulation.


These photos show older, stone farmhouses constructed in the traditional style. The stone walls of the second house have been finished with a clay plaster and lime wash. Its slate roof is insulated, though owing to the age of the building has degraded and could be refurbished.


The times are changing: this older farmhouse constructed in the traditional style, with a slate roof, has a more recent addition with a tin roof.

This newer home has an un-insulated tin roof – note the holes letting in sunlight! When it’s cold, this family retreats to the basement kitchen, a small, cave-like room with one small window that becomes very smoky. Luckily when it’s warm they can cook upstairs with a three-stone arrangement in the chimney and avoid inhaling much smoke during these periods.

A testament to the durability of the old methods: note the crack in this brick and mortar wall, which comprises the newest part of the structure. The old portion just below, made of stacked stone, appears solid, as does the much older section on the bottom left.

2. Optimized cookstoves. Based on my research into the principles of combustion and efficient cookstove design as outlined above, I estimated that fuelwood consumption for cooking could be reduced by perhaps as much as one-third in most households by optimizing stoves specifically for that task.

3. Try out rocket heaters. Rather than trying to heat the home with a cookstove – a task it is ill suited for – install rocket mass heaters. One of the Aarohi staff, Prakhaj, is building a new home and offered his guest room for the site for a prototype rocket heater. Prakhaj is well known and well respected among many of the villagers, so building a prototype rocket heater at his place, if it works, will have huge demonstration potential. If it works for Prakhaj then many of the other villagers are likely to want a rocket heater for their homes, too.

I’ll need to do some more research and run some numbers to verify the following conclusion, but for now I roughly estimate that the use of optimized cookstoves year-round coupled with rocket mass heaters in the cold months will (1) eliminate smoke in the house and (presumably) the accompanying health problems, and (2) keep villagers toasty warm while reducing their annual firewood consumption by perhaps as much as 25%.

Future work

It was bad timing to leave off such an exciting project as this, but I had a long-anticipated date with organic farmer and social activist Debal Deb at his agrarian education center in West Bengal. All is not lost though – one of my colleagues, a permaculturalist from Australia, has taken over construction of the prototype rocket heater. I have implored her to send me photos and detailed descriptions of every step of the process. Hopefully I will be able to present these in future blog posts as the project unfolds.

3 comments:

Anonymous said...

Do you have any comments on the issue of smoke vs malaria?

An thoughts in why people have not been convinced to use more efficient stoves and old style stoves still abound?

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Sweenblog said...

Hey Josh, stumbled across your posting while doing some research for an Engineers Without Boarders project that I'm assisting on (University of Utah, clean cook stoves for Kumari in Nepal). Enjoyed your post and the ideas that you came up with, and insight on broader aspects of the cook stove issue and "development of the under-developed". I'm also an Abbey nut and have a big interest sustainable technologies for the under-developed world while preserving the culture. Curious if you continued with any work in cook stoves or have come across any interesting concepts related to biomass cooking and heating.

Dan Sweeney