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Post by Donkey on Dec 14, 2011 8:47:46 GMT -8
All in all, unless you have a specific NEED to move heat around, I wouldn't use water as heat storage medium, REGARDLESS of the numbers and whatnot. The stuff is a hassle, it's dangerous, want's to get out of whatever you put it in and eventually WILL do just that. Cob or brick or steel just stays where you put it and as a general rule, causes no trouble at all. For my time and money, the storage medium I choose is easy to get, inexpensive (better yet, free), easy to work with, stays where you put it and is relatively safe. Cob has been used because it fits ALL these criteria, it can also be formed into ANY shape. Regardless of it's (relative to water) low(ish) specific heat (clay soil, sand) it has so many other advantages that it simply blows away the competition (for me). Choose almost any other storage medium and ask yourself, "how am I going to make this stuff here into a stove?", or "how am I going to include this stuff into the stove that I'm making?". If ANY of you can give me a material that's easier to answer these questions with, I'll be surprised.
That's NOT to say that "cob is the only answer", I would never suggest such a thing. In most cases though, I've found that cob works where other solutions prove too difficult or too expensive, etc.
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Post by Deleted on Dec 14, 2011 9:24:17 GMT -8
Agreed. Cob has a lot hart to beat and some unbeatable properties. For the weaker storage just add some more of it.
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Post by rectifier on Dec 16, 2011 20:55:22 GMT -8
Well put, mintcake - energy per unit volume is much more important than energy per unit mass. This makes other materials sound much better again, whereas by mass water is a clear winner.
Water of course is attractive due to its mobility and the ability to choose the rate you extract heat from your mass - a rock radiates at a standard rate, whereas an insulated water tank can store heat for a prolonged period, or release it very rapidly through heat exchangers.
The easiest way to use water would be to let the exhaust rise through an old gas water heater as it heads for the final chimney. This should extract nearly all the heat from the exhaust (well, at least reduce it to 100C). The water heater would of course have to be sealed up much better to the stovepipe than the gas ones are, as we are dealing with more toxic exhaust gases.
Of course there is the issue of what happens when the water inevitably ends up >100C, and I believe multiple pressure relief valves would be required for safety.
However: - if the water is circulated via pump through radiators, a well designed system will switch on to distribute heat as it approaches the boiling point - running at moderate pressure will elevate boiling point and increase efficiency, this could be achieved cheaply via a rad cap/filler neck cut off a scrap car and a large expansion tank. I'm sure there is a better system used in real boilers that someone could enlighten us on. 13psi is common for vehicles. Remember a hot water tank is rated to the 100psi commonly found in a municipal water system.
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Post by bobsfixit on Mar 25, 2012 19:08:48 GMT -8
First of all thanks for having this site. I have read Ianto Evans book Rocket Mass Heaters and plan on experimenting with our green house before doing one for the house. I live about 30 miles west of Fairbanks, Alaska and have some questions about materials and condensation.
First of all condensation. When the weather is -30F and colder condensation freeze up builds up in sewer pipes and in some boiler vents. This many times will block off the vent. Has anyone had this problem with rocket stoves.
Second Materials. Since condensation is very corrosive how long will the vent pipe last before being eaten away. I have seen furnaces and boilers where the exhaust gas temperature was allowed to get to low and the condensation ate up the stove pipe. Thanks again. Bob
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Post by canyon on Mar 27, 2012 8:07:19 GMT -8
Hi Bob, Glad to welcome another Alaskan! Although I don't see much 30 below, this winter we had a bit of 10 to 20 below down here on the kenai peninsula. With a traditional insulated vertical stack on a tuned rocket for exit temps above 180 F, condensation is not a problem. It is only if you are pushing the limits of efficiency into the condensation range that you see it with the exception of the first few weeks breaking in the system or if you use wet wood. The condensate is corrosive so it is recommended to keep the exit temps above the condensation point to avoid the eating away of your flue. I have not heard of anyone doing a side exit rocket in interior like winter conditions yet so no info there. We do workshops down here building these hands on to give people experience with these materials/methods. No workshops in Fairbanks scheduled this year but we are doing a RMH in a greenhouse in Eagle River this summer. PM me or stay tuned if you want to check some of these out.
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Post by muddome on May 8, 2012 9:51:33 GMT -8
I've added A LOT of rocks to the mass in my bench. Some of them quite large (up to 25 kg). I expect I may have to burn a little longer to get the whole mass toasty warm but hopefully the tradeoff will be that it stays warm much longer too. Our winter temps here often get down to -40. Can't really call it the Great White North though. Some winters there is snow, others there is still dirt blowing around, but always pretty darn cold either way.
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Post by Donkey on Jan 22, 2013 11:09:12 GMT -8
Umm... It's one of my pet peeves, so I've just gotta say... HEAT DOES NOT RISE!! Heated fluids rise (down here on Earth) but heat itself ALWAYS travels in a straight line in all directions. Heat traveling upwards is in the nature of the medium through which heat acts, NOT the nature of heat itself. We've been taught to see it in an inaccurate way, our daily experience tends to back up the illusion... A clearer understanding of the REALITY can really help when designing things that do non-intuitive things with heat.. Like Rocket Stoves. Ok.. Rant off..
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Post by Vortex on Mar 20, 2013 2:22:01 GMT -8
I came across a big list of materials and their relative heat storage characteristics recently but I cant seem to find it anywhere now. It was interesting as it also had the time it took each material to absorb heat and how long it would hold it. I noticed that soapstone and iron had very similar properties. Would be very good to have it in the library if anyone know where to find it.
A builder friend recently gave me a whole set of the heat storage bricks from an electric night storage heater, they're amazingly dense for their size and seem to be made from a mixture of iron slag. Made me wonder about the possibility of using iron fillings and cement, or old railway line which is sold by the foot here for use as farm goat posts.
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Post by Dan (Upstate NY, USA) on Jun 10, 2013 2:00:51 GMT -8
I put a bunch of steel/iron scrap in my heat bench, just to use it up and add some more mass.
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Post by smarty on Jun 26, 2013 9:35:27 GMT -8
I was thinking of filling my bench with talcum powder it is a close relative of soapstone and can be bought in 25kg bags.
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Post by alanidaho on Sept 4, 2013 13:38:50 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 alanidaho on Sept 4, 2013 13:41:42 GMT -8
Canyon, are you saying you would now rather have an 8" system to heat your 700 sq. feet? thanks alan
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