<div dir="ltr"><div>Hi Huck,</div><div><br></div><div>Have you read Sam Baldwins book on Biomass Stoves? He explains a lot about heat transfer. I copied a few sentences from Chapter 3 page 55 (I think) for you:</div><div><br></div><div>"Thus, lightweight walls have the intrinsic potential for much higher </div><div>performance than massive walls due to their lower thermal inertia. </div><div>This </div><div>does not, however, necessarily mean that a lightweight stove will </div><div>automatically </div><div>save energy or that a massive stove cannot. For a lightweight </div><div>stove to save energy its heat loss to the exterior must also be </div><div>minimized </div><div>and the convective and radiant heat transfer to its pot must be </div><div>optimized. </div><div>Conversely, massive stoves can and sometimes do save energy despite </div><div>their </div><div>large wall losses. Such stoves can save energy if the convective and </div><div>radiative heat transfer to the pot is carefully optimized. "</div><div><br></div><div>Best,</div><div><br></div><div>Dean</div><div class="gmail_extra"><br><div class="gmail_quote">On Sat, Nov 1, 2014 at 5:46 PM, Huck Rorick <span dir="ltr"><<a href="mailto:huckrorick@groundwork.org" target="_blank">huckrorick@groundwork.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple"><div><p class="MsoNormal">In Aprovecho’s very well written paper “Design Principles for Wood Burning Cook Stoves” they recommend against high mass stoves such as the Lorena stoves they had worked with many years back.<u></u><u></u></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal">It is obvious to me why you would want an insulated stove to avoid loss of heat from the fire to the outside as opposed to the pot. But I am very puzzled as to why a sheet metal stove would be better than a heavy clay one. It seems to me that heat from the fire will be transmitted much more quickly through the thin walls of a metal stove (without thermal insulation such as ceramic fiber) than through a massive earth wall. To orient myself I checked the thermal conductance of a few materials in Watts/meter/degree Kelvin. Insulating materials such as ceramic fiber are about .03-.04, insulating brick .15, dry earth 1.5, stainless steel 16, and carbon steel 43. Compared to steel the earth is a good insulator. An interesting aside, dry sand is similar to insulating brick at .15.<u></u><u></u></p><p class="MsoNormal"><span style="font-size:11.0pt"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt">The fact that the high mass stove stores the heat in the stove body rather than immediately transferring to the outside air as a metal stove would do wouldn’t seem to change the heat lost from the fire.<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt">Huck<u></u><u></u></span></p><p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:#400040">Huck Rorick</span><span style="font-family:"Times New Roman","serif""><u></u><u></u></span></p><p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:gray">Executive Director<br>Groundwork Institute<br>2640 Silvercrest Street<br>Pinole, CA 94564<br>Phone: <a href="tel:510-222-4111" value="+15102224111" target="_blank">510-222-4111</a><br>email: </span><a href="mailto:huckrorick@groundwork.org" target="_blank"><span style="font-family:"Arial","sans-serif";color:blue">huckrorick@groundwork.org</span></a><span style="font-family:"Times New Roman","serif";color:gray"><br></span><span style="font-family:"Arial","sans-serif";color:gray">Website: </span><u><span style="font-family:"Arial","sans-serif";color:blue"><a href="http://www.groundwork.org" target="_blank"><span style="color:blue">www.groundwork.org</span></a></span></u><span style="font-family:"Arial","sans-serif""> </span><span style="font-size:11.0pt"><u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt"><u></u> <u></u></span></p></div></div><br>_______________________________________________<br>
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