Friday, January 18, 2008

What is an IAP Stove?

Stoves for reducing indoor air pollution come in two different types - those which have no chimney (so may be intended for use outside, or use a clean enough fuel or design so that if they are inside they need no chimney) and chimney stoves - which evacuate the combustion products from the home. Consider a chimney to be a self powered, passive (no fan needed) smoke removal device - hot air rises, and this drags the smoke up and out too. By facilitating a change to stoves which use a more technologically advanced heat source - ethanol, propane, plant oils, or even electricity - we can usually do without a chimney, but in most situations this is not an option... much of the world will continue to depend on biomass (wood, agricultural waste, and charcoal) for the foreseeable future.

A very common feature of chimney stoves is that in them the fire tends to be totally enclosed - this is how the unburnt smoke is collected and directed up the chimney and out of the house. Without these two things together (as they are in a western wood heating stove as well) you risk having smoke escape into the kitchen - an unacceptable situation. You can put a "hood" (usually sheet metal, maybe with a fan to draw off the smoke) above any non-enclosed stove and perhaps achieve the same IAP goals, but a chimney attached directly to the stove can be much easier to construct than a separate ventilation hood.

Now that your picturing the basic design - enclosed fire plus chimney to the outdoors - next the materials of construction are an important consideration. In the west we are familiar with cast iron and thick steel walled stoves, resulting in a very heavy and expensive stove that provides space heating as well as the cooking function. But metal is very expensive (~$2/kg), not usually easily available where IAP stoves are needed, those customers may not need space heating from their cooking stove so fuel is being wasted, and these types of homemade stoves don't tend to be the most efficient designs. IAP stoves for cooking should be made from all locally available materials, be suitable for construction by local craftsmen, and use just a little fuel as possible. This tends to lead us toward masonry stoves, since nearly every region has supplies of cement (for making concrete), brick, stone, sand, and similar non-metal construction materials - and building with them is familiar to local people. Certainly you will find that commercial IAP cooking stoves in developing countries are often made of sheet metal for the exterior - you can't ship any but the lightest masonry stoves (such as the ONIL, a concrete stove) - but that raises the cost significantly, as does transportation from factory to homes.

For a very locally made stove now we're picturing this concrete/brick/stone box (it can be any shape or size) - and it may be for a home, a restaurant or business (such as a tortillaria), or for institutional use (a school, hospital, orphanage, prison, etc. And it has a chimney, to get the smoke out of the kitchen - admittedly we may just be exporting the smoke so that it is now some one else's problem (I saw this recently in Xela, Guatemala where all of the restaurant stoves in the central market are wood burning, creating a haze over the whole town). We'll discuss later how better stove designs also burn the smoke when used properly, so that there are minimal emissions from the chimney as well.

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