Rufus Laggren wrote:Thanks for your response. Your testing approach seems about the only responsible way and I'm glad somebody's taking the time/effort. Also, the 1)passive 2)reliable criteria seem pretty good also.
FWIW I'll pass on a link you might find worthwhile some time - www.heatinghelp.com. A small business vehicle, it attracts mostly smart professionals who love their craft. Doesn't relate directly (lot of digital whiz-bang there), but there are some good discussions of heating in general and quality people are good to know; they might have some interest in your version of HVAC, too. Dan Hollohan, the owner, is quite ecletic and a most decent person.
Which makes me think of a Q: Do RMH installs have any condensation issues where the surfaces' temps get below the condensation point for the wood fire gasses?
IIRC 137F. is where natural gas combustion products (don't know about wood fuel) condense onto a surface and lots of thought goes into dealing with that phenomenon. Or do the RMH flue gasses always remain hot enough all the way through to the atmosphere to prevent any condensation?
Rufus
I like that link a lot - we've been getting requests for water-heater information and I would love to send folks to take a Dead Men Steam School workshop.
http://www.heatinghelp.com/seminar/73/Dead-Mens-Steam-Night-School-Parsippany-NJ Wonder if they're open to the permies, or if he requires builder qualifications?
Condensation:
The original
Rocket Mass Heater designs relied entirely on the super-clean combustion design to prevent any problems with creosote.
Ianto likes his exhaust gases as cool as possible, down around 60 degrees F for cob buildings with a lot of thermal mass. This exhaust rolls out and tends to drift downward as a dense fog, and the exit pipe does drip. They exhaust slightly downward to allow drainage of ordinary flue-gas condensation. (CO2 and steam, condenses to carbonated water, plus a few stray ketones.) With adequate drainage, the warm air flowing past at the end of a burn cycle can dry things out pretty nicely. He's working with cob buildings, though, so the walls are completely non-flammable, and going out that way is much easier than creating a custom thru-roof for his EPDM/living roof designs. He's also in a forested valley with pretty convenient (and minimal) prevailing winds.
We tend to keep the exhaust at somewhat higher temperatures for conventional buildings, and use a conventional manufactured chimney through-roof to bring the exhaust out above the roof. It's easier than trying to establish a reliable downwind horizontal draft (the owner-builder may not be able to remember prevailing winds or predict storm winds / eddies). To get reliable vertical draft, you have to maintain warmer exhaust temperatures, as dropping below the dew point also makes the exhaust quite dense. So you do a shorter heat-exchanger, like the masonry heaters' rough working limit of about 20-25 feet, and lose a little more heat to atmosphere, or you bring the last pass back between the barrel and wall to re-heat the chimney gas on its way out. These systems tend to exhaust a clear gas, which turns to white fog a few inches beyond the chimney cap, then dissipates and disappears.
Another situation where the cooler, downward exhaust might be worth doing is in a greenhouse, where conditions (such as damp garden beds) make a cold exhaust temperature highly likely.
There's not a lot of time or space on a modern building site to tweak slopes for drainage, and in the US there's this expectation that all the working bits will be hidden in the basement or attic (like the servants of yesteryear). So high-tech fans or high-temp exhaust is the preferred solution, over-building for reliable installation with minimal disruption of the owner's happy home. These are like taking a pill instead of healthy exercise or diet.
I recently lived in an apartment that was cobbled together over time, and central heat was added as an afterthought: insulated tubes of flexible duct crawling through the attic like a monstrous squid. When we started heating with our
rocket mass heater, we had warm air circulating in the house, and the usual levels of damp for a Pacific NW winter. Moisture would condense in the furnace air ducts even from ordinary room air, in the colder attic, and we had a drip from one of the vents once that we thought was a leak in the roof. We had all the vents closed except the intake. Ended up blocking the air intake haphazardly with brown paper - allowing enough air to circulate to hopefully prevent mold, but limiting that condensation cycle.
Building cheap and thoughtless gives marginal results at best. The larger house on the same property was modeled on an older New England home, and had a number of highly functional features - but still suffered from leaks where a gable gutter had no drainspout and back-flowed up the roof in heavy weather.
One thing to understand about natural building (building with natural materials) is that it traditionally handles damp very differently from industrial building.
Most natural materials are breathable. Softer mortars are used to protect stone, instead of needing expansion joints as with cement-type materials. Aesthetics often include practical elements that make sense with traditional materials, like the blunt trim of thatch creating a softer drip-line. (Replicating this curve in asphalt shingle creates some unique challenges for a roofer.)
Moisture is generally handled with a combination of primary protection (roof overhangs, tall dry foundations), ventilation, and breathability. Higher airflows can be tolerated, or even encouraged, to protect the building materials and inhabitants. Air movement is often handled within the rooms, with cross-breezes (doors or windows that open and shut); hidden cavities are minimized or kept above the ceiling as places for bugs and mice to collect.
Modern building seems enamored of 'waterproof' materials like cement, that can actually still wick moisture or ground-damp, and damp-proof materials like tarpaper and plastic, that can cause condensation problems as moisture migrates toward a cold surface and is stopped there. Trying to limit airflow sometimes results in condensation exactly where you don't want it (wall sockets and chimney liners). Insulating a roof rather than a ceiling can create mold problems due to inadequate ventilation. There are limits to how well-sealed a home can be, and still be durable and healthy.
In most traditional buildings, only secondary heat is circulated as air. Primary heat is radiant, and conductive, stored within thermal mass solutions like passive
solar orientation and masonry heaters/chimneys.
We have a decent
solar aspect on our current home by accident (it was a converted garage belonging to my in-laws), but are giving a lot of thought to passive-solar design for a permanent home. We would like to have a natural building showcase to live in (who wouldn't). But we currently travel for weeks at a time for work, and Ernie dreams of doing coastal disaster relief from a big live-aboard boat, so realistically we will need to design a small home that can take care of itself while we are gone for extended absences. Or content ourselves to live where we are, not where we own.
The passive-solar option can be harder to implement, but it's safer and more sustainable than something that
lights itself on fire while you're gone.
If the building isn't passively comfortable, I'd be tempted to install a small electric heater for the pipes, or hire a responsible neighbor's kid, rather than an electrically-controlled combustion device.
Why do you need to heat the house while you're not in it?
To keep pipes thawed from a distance?
Commuting and literally only there when you're asleep?
Or could you find time to supervise a fire 3 evenings a week, while doing other things like cooking dinner or surfing
online?
(Or is it just the lure of tinkering - spending hundreds of hours to design a workable self-feeding device is its own reward, as opposed to the same hours spent enjoying a good book by a simpler fire?)
I'm going on about this, kinda ponderously. You're right about us preferring simple and solid-state to whizbangery, although I can appreciate a good whizbang as much as the next person when I'm in the mood. But there's something about the hopper-fed idea that looks like a limited solution to me, and I'm trying to put my finger on it.
Just seems to rely on too many complex interacting factors - including waste materials, components, and cheap electricity that may become scarce tomorrow.
Coal-fired furnaces didn't last that long, historically speaking, even when coal was still cheap. District electricity or steam was convenient and tidy in cities, and wood fuel more easily obtained / cheaper, for rural folks. I can see some of the same supply-line issues with pellet fuels. They depend on the grid / home electrical generation, and pellets won't store for very long without being subject to deformation or rot ...
Another factor might be the number of conversions of power. You lose something like 30-70% of your potential energy with every conversion, so a system that depends on both electrical and a processed fuel seems like it is going to have hidden energy costs that are currently masked by cheap electricity, transport, and pellet mass-production. I wouldn't be surprised if pellets are being shipped from China or Mexico at a cost in fuel oil that outshines their fuel value.
A lot of people like pellet stoves, or like the idea of biofuels other than wood.
(Non-wood biofuels is another issue that may be part of my hesitation. It sounds 'green' in theory to save trees by burning agricultural wastes instead, but ... our soils are being depleted while forests are choking on ladder-fuels. Most alternative biofuels are grown on cleared lands, that were once productive forest or prairie. There's also a good argument for the idea that a healthy forest, even a timber or fuel-wood plantation, does more for biomass, oxygen, and tree conservation than a field of ethanol-corn or grassy chaff. Modern paper waste is unsuitable for fuel for the same reasons it's not much good in
compost: too much clay-sizing and heavy metals. It's easier to collect large dung patties than small pellets.
I think in general both biochar and pellets fail Descarte's ethical test: would it still be a good thing if everyone did it? Then again, none of the appropriate technologies really meet this test; the test itself assumes a universal 'good' when nature's 'waste into resource' involves a lot more local balancing of variables. Rocket stoves and rocket mass heaters do very well on small-wood that is currently abundant to excess in North American forests. Similar small fuels can be produced on very small
permaculture plots worldwide through pruning and coppicing. This avoids killing any large trees, either directly for fuels, or while clearing land for fuel plantations. Dried invasive weed bundles make good tinder. But there may be places where noxious wastes can be safely burned as pellets, and there are no other locally abundant small fuels.)
We are in a weird in-between era where a lot of back-to-the-landers and starving farmers are commuting to pay the
mortgage, but wanting more of a homestead self-sufficiency level just in case.
Pellet stoves are cool in the way that model trains are cool - a working, 'living' household example of industrial achievement.
As long as there is a local market big enough to support a local pellet-maker who is committed to sourcing and processing suitable local waste fuels, and they are cheaper to run than pure
electric heat, they might be a viable option. Historically, commercial producers often have a much easier time sourcing virgin materials than bothering about collecting waste materials. Trees are pulped for paper, while any self-respecting
permie can get truckloads of wood chip for free (arborist, mill wastes, etc). Most of us don't save our own sawdust for wood putty or fuel pellets. If a fuel is not something I am willing or able to procure for myself, or a trusted local source can make a living supplying to me, the chances of it being locally sustainable drop off quickly.
I am also biased toward things that have been locally sustainable over long periods of history - indigenous technologies. I can't recall any indigenous cultures where an auto-fed stove is a priority (aside from the slight tilt of a fox-stove, or downdraft stove). It comes down to the question of why would you need the fire to tend itself? Leaving fire alone is a form of disrespect that is anathema in many cultures - especially, in many of the cultures that have taught me cool things about efficient and effective fire.
Some cultures have truly ingenious and weird stoves, and the empires tend to develop bizarre furnaces for every conceivable purpose. But most cultures seem to gravitate toward intuitive up-draft stoves that are easy to understand and maintain. I've seen fuels processed into useful shapes to minimize fire tending for a cooking fire, like the Sterno-candle-stove, or the Japanese tea-stove with its special coal-powder briquettes (they look like a thick watering-can nozzle, you light the fire from below with a small amount of tinder), or our barbecue briquettes (minimize time from flame to coals).
But the self-feeding pellet thing is new. Is it a response to the dilemma of needing heat all night, but not staying awake to tend the fire?
Thermal mass does that better, in my opinion. Better return on time spent, if you count the pellet-processing or purchasing.
In the absence of the industrial subsidies for fossil-fueled electricity and processing waste into uniform fuel pellets, I think it will be easier to hand-feed minimally processed fuels than to produce uniform pellets and a hopper that can intelligently disburse them. So it would be a post-modern solution that is viable (fit) for a current niche, but might not remain practical for long. It would be a labor of love.
I have this concern about the rocket mass heaters too - in many places steel barrels and ducting simply aren't in the waste stream, and the expense goes up if you count the time to source or fabricate replacements out of masonry or local resources. With all-masonry materials, the benefits over other masonry heaters are reduced (you lose the quick radiant heat, owner-building becomes more difficult, and the costs go up). I think benefits from other, traditional, masonry heaters (like intuitive fire tending, or being able to see the flames) might outweigh the special benefits of the rocket mass heaters (very clean burn, horizontal heated mass for cheap foundations and comfy resting platforms).
@EAW - I like the idea of using goat or deer pellets as a natural fuel - until I think of the difficulty of potty-training the deer to concentrate their pellets in a useful area. Goats, however, might get really into the idea of lighting their poop on fire. Can it be burned wet? Because potty-training the goats onto the hopper would be a pretty simple solution. (Not sure the poop is a better fuel than a soil-builder, but if they are penned up and concentrating it, and you gotta burn something...)
Seems like the sort of job that Douglas Adams would have assigned to Marvin, the suicidal robot with a brain the size of a planet: would he be more depressed about being used as a ruminant's pooper-scooper, or about hand-feeding the little pellets to the fire?
Or how about a Rube Goldberg conveyor system that the goats poop onto, which first cycles the pellet up over the heat source for drying, and then down toward the hopper and individually toward its fiery doom...
This would be amazing just to see. People watch OMSI's Gravi-Tram do similar circulations for hours, driven by worm-gears; there's another one at Timberline Lodge still keeping kids and dates entertained in the chow line. But the staff know that the little steel ball bearings routinely fall off the tracks, and have to be rescued to keep things in motion. There wasn't even any fire or goats, and it still broke down.
Some things are fun to imagine, and amazing if brought into reality, no matter how briefly.
