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Post by rectifier on Nov 18, 2011 18:35:29 GMT -8
Starting this thread for discussion about use and modifications of RMH heaters in extreme climates such as that of Canada, Alaska etc...
Elsewhere we were discussing increasing the thermal mass to hold greater amounts of heat. What materials, modern or primitive, make sense? Is containing a large volume of water worth the effort, cost, and flood risk?
Also, system sizing and burn times, does anyone have experience running a RMH in a cold climate and what duty cycle was required? Is a RMH alone capable of keeping a house warm in -35C, or is another heat source required to fill in between firing cycles?
Just trying to pull together some of the discussion and get some of the cold climate ideas collected in one thread.
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Post by Deleted on Nov 19, 2011 1:47:17 GMT -8
The house of my grandparents was heated from a single fireplace with air channels to 8 rooms on two floors. The area has cold winters, sometimes below -25°C. The oven was tiled and the very heavy burn chamber was build from cast iron. The solid fuel burner was later replaced by an oil burner for convenience. While the heat capacity of iron is not high it has a lot mass in a small volume. In relation to the costs and other drawbacks the volumetric heat capacity of iron is the second best to water. Water makes the most sense in decoupling heat production, heat storage and heat delivery.
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Post by Donkey on Nov 19, 2011 12:51:04 GMT -8
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Post by rectifier on Nov 20, 2011 20:52:18 GMT -8
Cast iron is indeed very heavy per unit volume, and it seems to have the 'magical' property of sucking up applied heat at a high rate and storing it. Likely because it is heavy and conductive, allowing it to distribute heat throughout the bulk more effectively than earthen materials. My little cast iron stove manages to remove most of the heat from the exhaust stream with an internal surface area of only about 4 square feet.
Water of course is even better due to the fact that it can transfer heat via convection as well, but is messy and corrosive to metals.
Donkey, those Russian bell heaters are pretty neat and I really need to learn more about them and the 'free gas movement' principles. Going to have to go over Peterberg's bell rocket thread again and try to understand it.
Do you know what the stones right in the flame path are for? It seems they would both quench the flame and retain a bunch of heat that is not easily transferred into the living area. Do you shovel them out and use them to heat up the sauna?
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Post by Deleted on Nov 21, 2011 4:05:01 GMT -8
One could use heat pipes to distribute heat faster within materials of lower conductivity. Creating a heat pipes is simple, one needs just to close the tube while the medium is boiling inside. Mesh is not absolutely needed inside if the heat destination is sufficiently above the source. Welded pipes with water as the medium can operate at fairly high temperatures (above 300°C), if the tube walls are not to thin. Paraffin wax provides one of the highest volumetric heat capacities of the not overly expensive materials. The change in volume from solid to liquid and reverse is high and it can burn. en.wikipedia.org/wiki/Paraffin
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Post by canyon on Dec 4, 2011 11:51:05 GMT -8
So I hope we get some more experience shared from RMH peoples in the great white north. I am only at latitude 59 in Homer Alaska which some people call the banana belt of the north but we have decent winters nonetheless. Freezing temps start in september and proper winter usually in october and last until breakup in April/May. It is a long dark winter and heating is an important part of life here. I have been heating with my RMH for three winters now and am blown away by the dramatic shift in wood consumption going down while my comfort level has gone up. I used to heat with 300 gallons of oil and 3 cords of firewood and now I heat with 2 cords of wood and no oil. Things are very different though, I now am in tune with the bench and what I put into it and when and what the weather is doing. I can prepare by banking up the bench (1-2 days of excessive firing) and my place will not freeze for four or five days in below zero F temps as long as it is not windy (my structure is an experiment in natural construction and I have a lot of unfinished areas/air leaks). That fact alone is so important for people living with wood heat. My place holds a more even base temp but I still need to wear sweaters when it is many hours since firing and it is single digits or less outside unless I camp on the bench like my daughter who can't seem to get off of it (unless there is something like skiing or sledding that is more exciting to do). It is so satisfying to ski home after a crazy day in town and snuggle up to the bench and warm up before finally deciding it is time to start a fire. It is a different way of living than push button temp control. I welcome it, but I recognize that some people want to be more disconnected from their heat and won't be satisfied with a RMH. I have a six inch system with only 24 feet of horizontal bench run and I am heating about 700 square feet. Since I built mine, I have built several teaching others in workshops and have come to really appreciate the value of an 8" system with much more mass. The one we built last month has 55 feet of bench run! I do think that RMH's are great for extreme cold if one is willing to have a relationship with ones heat and with the addition of more mass for the more extreme. Water storage is another whole subject that is complicated and best for situations where the heat needs to be moved around. I have some experience with that to share as well in appropriate threads.
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Post by Deleted on Dec 6, 2011 6:53:30 GMT -8
Without any changes to the RMH design one could turn it easily in to a very convenient oil heater or plainly get rid of some waste oil and take value from it. Simply by placing a pot style burner in the stack and letting an oil feeder dropping oil into the hot pot. The feeder could be driven by gravity or other means. An extremely simple pot design is described here by Bruce Woodford. journeytoforever.org/biofuel_library/ethanol_motherearth/me8.htmlI've ran a short test without a feeder, just a bit oil soaked cat litter at the pot's bottom. Such a burner works nicely once it became hot.
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Post by hinotama on Dec 9, 2011 12:41:02 GMT -8
I am not in an EXTREMELY cold environment, but I want to use water because it has specific heat, which I think is J/kg, that is about 4 times higher than things like rock and iron. I think that is right, anyway.
Where I live, pumps are very easy to get ahold of and they are extremely reliable, so moving a mass of warm matter from place to place is not so hard, given a reasonable amount of time. For me, the biggest problem is humidity because I am well... afraid to use a closed system.
I want to use safe temperatures and safe pressures, and that is possible. If you can do those things, then water is a great medium for heat storage and transfer.
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Post by Donkey on Dec 10, 2011 17:25:55 GMT -8
Water is good medium for moving heat around but I disagree with common knowledge, that water is a good heat storage medium. Regardless of it's high specific heat, water has a relatively low phase change temperature which means you can't get a lot of heat into it before it does something (potentially) dangerous. Massive materials, even ones with (compared to water) poor specific heat but EXTREMELY high phase change temperature can be made to store more BTUs per unit mass.. When it comes to transferring heat, the DIFFERENCE in temperature means everything. Heat flows much like a rock rolling down hill, the steeper the slope (difference in temperature) the faster it will roll. So getting a rock (with inferior specific heat compared with water) up to a MUCH higher temperature will do more for you in the long run than a necessarily larger volume of water for the same BTUs of storage and slower and/or less efficient transfer.
It is IMPORTANT to remember, all this stuff is contextual, if you take a particular solution out of it's particular context, you may have a duck when you really needed a goat instead.
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Post by pinhead on Dec 11, 2011 16:46:37 GMT -8
After a lot of reading and investigating, I completely agree with Donkey.
I'd use oil before water.
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Post by Deleted on Dec 12, 2011 5:07:09 GMT -8
With regards to the general temperature range of wood burning stoves I dare to disagree.
With the energy needed to bring water to it's boiling point:
iron ~ 930°C granite ~ 530°C sand ~500°C brick ~ 497°C concrete ~ 475°C aluminum ~ 466°C paraffin wax ~ 167°C
For practical reasons its virtually only paraffin wax (boiling above 250°C), which could actually store more energy, but has drawbacks too. One could however store more energy per volume.
I agree that retrieving the energy from water may be not so easy.
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Post by Deleted on Dec 12, 2011 9:43:21 GMT -8
At high-altitude other storage media become more favorable, as the boiling point of water will become even lower.
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Post by mintcake on Dec 13, 2011 12:11:18 GMT -8
One could however store more energy per volume. And surely this is the point? Assuming that you're not building on stilts, then mass is a much lesser problem than volume (or price) isn't it? Adjusting your figures for densities I found (care of google, :-) ) then I get: water 1g/cm3 100°C iron 7.87g/cm3 ~ 127°C granite 2.7g/cm3 ~ 196°C sand 1.6g/cm3 ~312° brick ~2g/cm3 ~ 248°C (firebrick 2.4g/cm3 ~ 207°C) concrete 2.3g.cm3 ~ 206°C aluminum 2.7g/cm3 ~ 172°C paraffin wax 0.9g/cm3 ~ 185°C Actually, I expect that no one is going to want to buy that much iron or aluminium, but volume for volume, they both beat parafin wax (and don't burn so well, either).
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Post by Deleted on Dec 14, 2011 2:33:09 GMT -8
I should have left an empty line to separate "One could however store more energy per volume" from what I said about paraffin.
To express it more clearly: Paraffin could beat water in respect to mass by higher temperatures. Other storage stuff can do this only by volume.
As you said there is virtually only iron and aluminium. The other stuff would require to much effort for insulating the high temperatures or has other problems.
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Post by Deleted on Dec 14, 2011 3:42:44 GMT -8
For practical reasons it is very hard to find applicable stuff that could actually beat water as storage media. Paraffin has a safety problem. Water has problems with safety and corrosion and thus requires safety precautions and maintenance. Very high heat has a safety problem too. The clear winner would be iron. While not actually able to beat water under normal conditions not having safety and maintenance problems may be a big plus for some stuff.
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