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Dear Andrew</div>
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I should clarify that the 540 degrees is the outside of the pipe. I understood from your question it might refer to the temperature inside. </div>
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There are two potential 'ideal' applications for this unit: space heating (in which case we want the heat) plus metal pipe chimney heating before leaving the room, and as a heat source for some application, which could include heating a brick wall, water heating,
of running a gas-to-air heater, basically a big box. </div>
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The secondary air could easily be preheated as you suggest. I would make a chamber around the holes (which are the right size) and lead the entrance downwards in a single channel so I could control it. At the moment it is fixed in terms of flow and that has
limitations, though I can add I didn't find much evidence to worry about. It is spectacularly clean. Adding anything would increase the cost and in rural Tajikistan absolute first cost is a serious problem for acquisition. </div>
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That points to two sizes with a different level of complexity and that is OK. The minimalist version at $32 is a great deal, and accessible. In a 'sauna' which is not exactly like a classic swedish system, it would provide room heat and hot water at very low
cost. </div>
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The bottom didn't seem to have a problem regarding the burnout of the char. With the unshielded walls there was some high temperature char in a circle around the core of white ash. We sifted it out and put it into the next burn with great success. In fact
I added it to the fire halfway through and it had no effect on emissions which pleased me greatly. </div>
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Regards </div>
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Crispin </div>
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<div class="PlainText">[Default] On Sun, 13 Mar 2016 16:14:45 +0800,Crispin Pemberton-Pigott<br>
<crispinpigott@outlook.com> wrote:<br>
<br>
>You can see the<br>
>The outside temperature in the centre of the height rises to about 540 C once the pyrolysis layer passes by. This gives it a heating efficiency of about 50% without applying any of the stack heat to another task. To bring this number down and send more into
the axhause it would be necessary to place some sort of ceramic lining in the chamber.
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If the temperature is that low (maybe apart from the final burnout at<br>
the bottom which would need refractory??) why not have an outer skin<br>
of sheet steel in which the secondary air is preheated? This outer<br>
sheet could then be insulated on the outside to keep down overall heat<br>
losses.<br>
<br>
AJH<br>
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