[Stoves] Draft problems in Kyrgyzstan

[Crispin Pemberton-Pigott]

Dear Friends of Chimney Stoves

There is a plan to install 50 improved stoves in Kyrgyzstan to monitor them through the winter, getting fuel consumption, user feedback and air quality (in some of them) to support a larger program in the coming year.

Many of the installations have a chimney that rises from the stove then exits horizontally through a wall outdoors, that's it. No more draft than that.

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This is a typical issue: limited draft, exiting through a wall that may or may not have a wind blowing against it. Combined with the negative pressure on the lee side of the building, it is enough to reverse the chimney flow at low power and the gases emerge into the house. There are many reports of this happening in Central Asia.

One of the most important changes to make is to create stoves that are very air-tight so that the gas flow is impeded by a restricted entrance, rather than a low temperature. If the temperature is much higher in the chimney, the loss of heat is not necessarily higher, if the flow rate is much lower. This is difficult to understand intuitively because there is a common belief that if the exit temperature is higher, the loss is greater. That is only true when the gas velocity is the same.  If the gas velocity is reduced by a factor of 6 the temperature cam be much higher and the loss reduced. For that reason we are getting routine thermal efficiency readings of >70% at significantly higher flue temperature readings. Those readings should be taken at the roofline - i.e. where the pipe passes through the ceiling which is interpreted to be heated envelope.

The stoves are being placed in homes this month, 5 models. So far the ultra-low smoke versions of the GTZ-7 stove (original design from Mongolia) is a hit not only with the customers but the producers themselves. Producers and project staff are ripping out their own stoves and replacing them with project models! That is what I call a Good Start.

The full drawings of all models are on the newdawnengineering.com website in the Library under Stoves/Kyrgyzstan. Look for the renamed GTZ stove in the Tajikistan folder under /Model 4. There are two versions there, one specifically made for production using only an arc welder and an angle grinder which are the only tools many producers have.

Regards
Crispin
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