Hi Dave,

Nice find. Interesting concept. Kind of like a heat pump in some ways.

Id imagine a considerable amount of its efficiency is determined by its insulative qualities. I.E. trapping all the heat and funneling as much up the chimney through the "load" without losses through the three paths, conduction, convection and radiation.

I have been doing some metal work as a side hobby for sometime now, and have crafted a number of wood and gas fired devices for different purposes. Doing so has allowed me to better understand and delve into the realm of thermodynamics. I recently helped a friend construct a gas powered forge for use in annealing/quenching and shaping metals, mostly for bladesmithing. We decided to rebuild our first design and implement correct ceramic insulation. Of course it was going to work better, but I was amazed at the heat retained and the corresponding drop in gas consumption. We can shut it up at night at it is still too hot to touch inside 12 hours later.

So insulation is a no brainer, obviously in the right places. The shape of the chimney/updraft would be interesting to play with too. I personally would like to see how a thin rectangular section would respond as opposed to a tubular section, depending on the designs purpose of course.

I found some great simple pdfs on wood fired ovens/chimney design for 3rd world countries if you are interested. Alot of the information is focused on optimising either burn time or heat transmitted through radiation/convection/conduction.

Regards

geothermal ??

Hey Dave,
I'm in the middle of constructing an earthbag single room structure and want to use solar or/and geothermal heat. Of course I've not tested any of these ideas yet, but want to use earth friendly sources of energy.

If you use the chimney and geothermal ideas together that sounds like fun but costly to try.

Good idea for an interesting thread,
wantomake

wantomake,
What are you using for your geothermal heat source?

I have been looking at passive solar (sun heating water in black pipe) which is circulated through to heat the house, and also to run a Sterling engine turning a small generator to provide 12 volt electricity. You get SOME heat and SOME electricity for the cost of running a small electric pump. Works great on sunny days. The sterling engine/ generator combo is just a plus that you get for "free. " (If you don't count the cost of the thing, maintenance fees, etc.) Actually MORE Sterling engines with generators could be added to the system, because once the heat chamber of the Sterling engine is brought up to temp (which causes heat loss in the water) there is very little heat loss in the water to maintain it, and that water can be used again farther down the pipe to run another Sterling engine/ generator combination. By the way, if you have to pump water up to your roof to heat it for a setup like this, the water that comes down off the roof, assisted by gravity should be used to turn a small generator to offset your losses to the system. It requires a small holding tank that is lower on the output side than your pump. The tank is filled and the input from the pump is at the top of the tank. This is not an air tight tank, so has to be refilled occasionally due to evaporation. The output to the house is at the bottom so that water, assisted by gravity "falls" past a generating device to provide 12 volt power. There are several "generating devices" that would work for this on the market, but so far I haven't decided on one.

Dave