Mark Boone

The compost water heater has the advantage of working at night/early morning, you don't have to wait on the sun.  But not very effective in winter unless you move the compost into an insulated barn/shed.

I've been thinking about recovering waste heat with water - for instance using your refrigerator coils to warm water.  Another idea, specifically useful for campers and vanlifers, would be to add a heat exchanger loop to your vehicle's coolant system - it could heat up a 20-gallon (or so) insulated tank of water every time the vehicle is driven - there would have to be safeties built-in to prevent overheating and to turn it off in low water situations, but otherwise, it would just be extracting free heat.  Basically, any system that needs to be cooled down is a possible source of hot water.

You can build up the back ridge on the sole a little bit to keep your heel from sliding back too easily. Use Shoe Goo, Sugru or make it yourself oogoo.

There is nothing particularly new about a ducted fan, or ducted turbine. The efficiencies claimed for this are nonsense - but probably true in a very limited sense. I don't doubt that they could achieve a 600% increase in wind velocity, but that is not the same as saying it is 600% more efficient, in fact I am certain it is substantially less efficient.

The effect of all that ducting is to allow a smaller turbine - all that extra hardware in the ducts allows you to reduce the length of the blades. But is that less expensive than longer blades? One thing I am certain of is that it lowers the overall efficiency of the unit because you lose a lot of energy changing the direction of the wind and doing the other things required to make this work. For example, there have to be one way air valves (or flaps) that shut off the downwind 'collectors', since they would otherwise create negative pressure and lower the effective power delivered to the turbine. Those valves, even in open position, will also lower the final pressure delivered to the turbine. Shoving wind into pipes is never going to be very efficient.

But while I'm making the point that in any meaningful way the efficiency claims are almost certainly bogus - that really has very little relevance. Who cares if it isn't mechanically efficient - is it economical? Like solar panels I'd much rather have units that are only 2% efficient than 17% efficient panels that cost 100 times as much. I'm no more worried about a 'wind spill' than a 'solar spill' so the efficiency of the unit is pretty much moot compared to its economics.

Having the turbine and major moving parts at ground level is a big benefit. As is the unidirectional design. But those features are also present in Darrieus and Savonius wind turbines with a lot less complication. Is this design any better? I'm a little dubious, but it all comes down to cost.

Although his project is two wheeled, you might want to check out Craig Vetter's "last Vetter fairing" project. His goal is to make a practical vehicle that meets his goal of 100 mpg at 70 mph, into a 30 mph headwind, with four bags of groceries - that would be the owners first choice of vehicles in the garage. This is basically a streamlining project. Note that 100mpg is meant in energy cost equivalent - alternative fuels are encouraged - his streamlining is being applied to diesel (biodiesel) and has just begun an electric vehicle project. The project has included regular fuel economy 'races' called The Vetter Fuel Economy Challenge.



Over the last 5 years:

http://www.craigvetter.com/pages/470MPG/Intro%20to%20economy.html
http://www.craigvetter.com/pages/2011-Streamliner/2011-vetter-streamliner-p40.html
http://www.craigvetter.com/pages/2012-Streamliner/2012-vetter-streamliner-p52.html
http://www.craigvetter.com/pages/2013%20Streamliner/2013-vetter-streamliner-Vic-nose--p62.html

Cats by themselves may not have an essential role in permaculture (except as a usurper of native predators) but that kind of misses the point. Humans don't fit into the natural ecology either, at least not since we were a very small population of hunter gatherers. One of permaculture's roles is to better fit us into a beneficial ecological balance - and by 'us' we really need to include the co-species that make up the 'human ecology' - the dogs and cats that evolved in concert with us and live with us in nearly every human culture. I suppose it is arguable that you could include vermin like rats, roaches and lice in the equation too - but I'd rather not.

Among Ohio's techno-Amish (who are pretty flexible about technology as long as it is 'off grid') Lehman's General Store is a favorite. No url since I don't intend this as spam, you can google it. They have a lot of gas and DC appliances - including dual or triple use ones that can switch between them. Good place to find products you can try to source locally or directly from manufacturers.

I've heard of using earthbags filled with other stuff as insulation - such as shredded straw packed between rafters and even bags filled with rice hulls. Even wondered if bags filled with wood chips would work. Clearly they couldn't be structural like dirt filled earth bags, but stacked against a structural wall should be good insulation.

Would be easy to combine with (dirt-filled) earth bag construction by half-filling bags with the lighter 'airy' material, and interleaving the unfilled half of the bag between courses of dirt filled bags - resulting in a double wall tightly tied together. Hopefully such a wall would be stable enough on the outside (insulated side) to take a stucco or cob render after being wrapped in chicken wire.

Perlite or vermiculate to lighten the thermal mass would also make it less efficient - they have a lot of entrained air in them and do a good job of insulating (insulating=slowing down the process of heat transfer) meaning less transfer of heat from the exhaust before it is vented outside. You could compensate by having a longer run through the TM, but that would require more TM which would weigh more overall. There is really no way to escape the need for mass in the thermal mass - except by using costly phase-change materials like paraffin (also flammable).

Two ideas - complex and simple.

From all that I've heard what you need for good TM is direct contact with the exhaust run from a highly heat conductive material - cob being the practical optimum - which in turn is embedded with high mass material for heat accumulation (rock, brick, stone rubble).

For a tiny house on a trailer you need something which is permanently installed - but is low weight when the home is in transport mode.

It really sounds like water could be the answer. Very conductive, plenty of mass, very portable, easily drained out when necessary, safe and nonflammable (but provision would have to be made to safely vent steam in case of overheating). The amount you use would have to be carefully thought out - you can't let it get hotter than 100C (212F), so the total volume would have to be fairly high so that it can absorb a useful number of BTUs without transitioning to steam.

I am imagining a heat bench with a short run of conventional cob/stone TM at the hot end of the exhaust run, but with the remainder essentially a series of water containers with a relatively small amount of cob between containers and in direct contact with the exhaust duct - like a cob honeycomb. It would be quite massive in weight, but a good portion of that mass could be drained out.

But ... Perhaps you should just go simpler.

Your house, all its furnishings, and even the air inside it, is thermal mass. Assuming your tiny house is well insulated, you can just utilize the home itself as your thermal mass. When not in transport mode you can add to the home's mass by using water drums as table supports, end tables, etc. (as a bonus you have a good supply of emergency water). They'll retain the ambient indoor temperature - which in cold weather you can maintain by more frequent firings of a small RMH stove without built in TM. Yes it will be less efficient than a big thermal mass unit that recovers a large amount of the exhaust heat, but it will still be better than a conventional furnace or wood stove.

Chris, I like the idea of a rocket core with all the essential 'plumbing' - just add a barrel and riser and hook up the exhaust. But instead of using cardboard forms, how about paper maché?

You could sculpt the internals in negative - creating the perfect angles, smooth curves, etc., then make a mold of plaster (or resin or whatever). From the mold halves (or as many pieces as you needed to cut it into) you could lay in paper maché. Once dry trim and paper maché the partials together to form a perfect sacrificial form to pour your refractory mix around. Keep your molds and it is easily repeatable.

Great discussion!

Jeremy Bunag wrote:But I'm imagining something like sandbags (or dirtbags) stacked up, with little fissures for air to infiltrate.

Seems to me that that is the last thing to worry about with this kind of construction. Earth bags are the exact same thing as sand bags used to hold back flood waters. Indeed most 'sand bagging' uses local soil rather than sand. Those hand stacked bags lock into each other so tightly that water can't get through even though the bag is made of open weave plastic and filled with permeable soil.

Other thoughts:

Thermal mass structures, especially in 4 season zones, are improved with insulation on the outside. I read of using vermiculite or expanded perlite render to plaster the exterior walls. But the discussion of rice hulls got me thinking - what about an outer row of rice hull bags next to the soil bags? Would they be stable enough to apply an external cob render over them?

There are immense quantities of shredded wood chips/mulch (not talking about leaf mulch) in many areas. A lot is used in gardening as ground cover. But the supply is nearly free if you have a chipper and brush to clear, or are willing to haul it away for others. Would this be useful in bags? It would be a lot better insulator than as thermal mass, and you'd need to be extra careful in providing a vapor barrier. Seems like it could compliment cordwood construction using on site dead trees and underbrush as building material. Most trees aren't suitable for lumber, but they could still provide useful building material.