Hi everyone! I'll be filling out the rest of my profile later, I just got too excited reading what I have, and I needed to shoot this off.
I'm currently heating a 4,000sq/ft house in Detroit exclusively with wood. There is a forced air sealed furnace in the basement that only runs $9 a month on the electric ( will be converting that to free DC power, hopefully using a 4kw Peltier module generator - TEG Generator uses thermoelectric modules ), for the fan running 24/7. I also have a fireplace insert on the first floor that I modified with 5 pipes directly *above* the burn box before it vents out the flue. It's an old Black Bart, and the exchange chambers are on the SIDES. No idea how they thought this was efficient. Plus, the blower motor it came with had a starting capacitor the size of my fist. And I roll quarter ton logs around my yard, so I have a decent sized fist. I replaced the blower motor with a 20" Lasko box fan ( Yup, $16 at any walmart or elsewhere ), and a new 5 blade fan from Graingers. That insert costs $6 to run every month. $15 heating bills aren't bad. But I want a $0 bill
Now, I'm thinking of replacing my furnace with a rocket. My main issue is this; would I keep the thermal mass and make an air chamber around that to blower and heat the house with, or some other configuration? I have an almost inexhaustible supply of 100+ year old refractory brick, and I can make cob from industrial hemp shiv/hurd. Size and construction aren't a real concern, as I have slightly over 7' of headroom, and I can go as wide as needed in all directions. I do currently run two coils on it for hot water ( copper held off the burn chamber by 1" ceramics - the old wire insulators from our 101 year old house themselves! -, used during the summer for a few sticks a day to heat the water, and the copper emptied for the winter and left open ended, getting the heat exchange from a PEX coil mounted outside the air exchanger box - get's plenteeee hot still that I don't think the tank's electric has seen an hour's use yet in two years ), and I would like to still incorporate a water heating exchanger as well.
I will need access to a continual temp of around 200F for the peltier generator.
As far as fuel...I have an unlimited supply of kiln dried hardwood rips varying from 1/8" to 2" square, from a moulding mill. I'm thinking about sending all of that through a garden chipper (that can handle up to a few inches in diameter sticks) to make a "pellet" of sorts. This would be placed in a hopper at a slight angle with a large auger attached to a DC rotisserie motor and a variable speed control dial. The auger would slowly drop the biomass down a more steeply angled chute and into the burn chamber.
So...taking all that into considerations....best approach?
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It sounds like you are a good candidate for a batch stove and bell arrangement.
Peterberg has done a lot of excellent work along the lines of what you want to do.
Personally, I think you might be overthinking this a bit, since you pretty much have a working system already. Spending a couple thousand dollars and hundreds of hours of work time in order to save $15 per month on heat seems like a waste of effort to myself. However, if you desire to do it anyway, take a look at this website and read a bit about how convective heat actually flows through a house. Perhaps you will have some other ideas that might serve you better.
As to using the TEG to produce the power for the forced air furnace fan, a TEG requires a fairly constant source of point heat, which a rocket mass heater is not. Only the barrel would be able to maintain temps above 200 degrees, and only so long as there was a *hot* fire blazing in the burn chamber. The point of the RMH is to get the fire very hot, burn through a small wood load quickly, but capture low level heat in the mass for later distribution into the living space; all without overheating that living space. Your high quality TEG would not be able to provide much total power on the relatively short burn cycles of a RMH.
Forced air is a construct of modern HAC. The duct work can be useful for heat circulation but often is not. The indication of your OP is that you may have an older house that has good cold air returns. Returning cold air to the heat source is equally important to distributing the heat to where it is desired. When I was 4 wee moved to a farm with a wood cook stove on one side of the wall and a parlor heater on the other. Heat fro the bath and bedrooms came from leaving the the door open. Based on my fathers experience in the building trades We [I had my own little wheelbarrow] set about digging a basement and installing a wood furnace. People were switching to oil so the furnaces were almost free. but originally he started with the same parlor heater in a sheet metal enclosure and cold air returns made with tar paper between the joists and along the center beam that brought cold air from each room. There was one heat outlet, a 4x4 foot grate in the center of the house about six feet from where the parlor heater used to sit.
The result was no more cold air on the floor. If you opened your door the bedroom warmed up. The heat from a single fire seemed to last twice as long because the residual heat in the stove continued to circulate. When wee came in cold we could lay on our back on the heater grate and warm up.
Now my grandmother's house had a sawdust burner furnace. There was an auger to feed fuel to the fire but no fan. Each room had a hot air outlet at the base of the wall near the center of the hose and a cold air return on an outside wall. Heat was regulated by opening a flapper valve in the outlet in the wall.
What I want you to take away from this is whether you heat a mass for heat storage or not, make sure cold air can passively return to the heat source without having to travel through the house. You could possibly build a mass with alternate flues for the exhaust from a rocket stove or batch heater and the cold air to return to the bottom and exit the top.