morpho
Junior Member
Posts: 50
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Post by morpho on Jun 16, 2008 20:18:06 GMT -8
I read in a post here that sand is a good material to store heat in. Could you use sand as your base for a floor with the flue burried in it, then lay large pavers overtop? Would it not work? Would it? How far does the heat travel horizontally through sand, cob, or concrete? How many flue's would you need in a 20x40 floor to actually eliminate cold spots? (not that every corner needs to be toasty warm, but enough that you are not hopping from warm strip to warm strip of floor)
Thanks....anyone.
Morpho
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Post by canyon on Jun 16, 2008 22:27:22 GMT -8
Try your bale trench with pond liner idea with sand instead of water (no need for watertight liner or watertight flue) and you can get an idea of how the heat transfers in how long etc. A lot of heat will be required to dry the sand first and then depending on the sand, it will have 1/2 or less the heat storage per cu/ft than water and you can't move it around. But, I think a sand heat bank floor would be great. I hope someone can share actual experience with that or any hypocaust. However, as it says in the book, don't go right to building a full on hypocaust... try a tested model first.
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Post by Donkey on Jun 17, 2008 10:10:46 GMT -8
Morpho, Good idea. You could use sand, though it tends to shift around over time. The sand could be mixed with a touch of dampened clay soil to kind of glue it in place. Depending on how much clay you can find in your dirt, a mix of something like 1 part soil to 4 or 5 parts sand should do it, this is the mixture used for bread oven cores and around hot rocket stove parts, etc.
Earthen floors are a common thing in the Natural Building world. They are VERY good at storing heat, particularly from solar gain. The base coats are typically quite a lot like road base material. 3/4 inch minus, crusher run is usually mixed with a little clay rich soil and slightly moistened. This mixture is then tamped tightly down to form a firm, level base.
I know of one guy who built a rocket stove hypocaust under his earthen floor. The system was rather large, I think he said he used a 10 inch heat riser... He built it into a particularly small floor, smaller than 80 square feet. I understand that on the first firing, with a still damp floor, it quickly got too hot to walk on comfortably.
Ya know, the more I do this stuff, the less I like in-floor heating systems. They tend to be overly complicated and underly helpful.. The heat provided (while yummy on the feet) tends to strike the body at its narrowest aspect. When stuff goes wrong, usually its damn difficult to get down there and fix it too. That is not to say that floors shouldn't be used for heat storage.. Heavy, dark floors are great for passively storing solar radiation. Better (IMHO) to place active heating systems in walls, or benches, or some such place where either the body has direct contact or at least presents the most surface area to the radiative source.
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Post by larsmith on Aug 29, 2008 5:12:51 GMT -8
I plan to incorporate sand as part of my heat battery.
I've got a fair number of red brick as well as firebrick to use as walls of any heat battery. I'm considering laying up brick "walls" for my heat battery and back-filling the walls with sand ... or making my exhaust channel all brick ( ie: not using black pipe to get from the heater to outside but brick channel only ) and then either covering the whole thing with sand or at least "burming" sand up against the sides of the exhaust channel.
My rocket mass heater is already "under ground" or "under grade" in the all-sand floor of my heater room. I'm just now in the process of adding an 8X8 addition to the side of my house, semi-lean-to style, to house my rocket. The floor is all sand. I dug down into the sand/clay floor, laid down two cement sidewalk tiles ( about 2'X2' each ) and built up the base of the feed box and fire tunnel.
I'm still in the discovery stages as to whether to use 1) firebrck or 2) chimney tile or 3) stove / exhaust pipe or 4) stainless pipe or 5) quarter inch thick steel for my heat riser. Any comments via EMail would be appreciated in this side-issue.
I'm painting anything that's wood in the new room and adjoining wall into my house with a fire retardant paint. When I cut thru the side wall to my old house, as you might imagine, I discovered VERY dry wood and don't care to take any chances with fire being able to touch any of those old studs, planks, etc.
I hope to report back to y'all about my final steps and degree of success with this.
Another side issue ... I'll hope some will EMail me re: connecting an 8" black pipe to my 55gal heat exchanger. I've got a 35gal drum inside to hold in the insulation so there's only a 1.5" gap between the 2 barrels ... and if I connect an 8" chimney pipe to it, I believe I will be creating a bottleneck right there and need some advice as to my other options. For those of you who have used firebrick as your heat riser, talk to me about what you'd advise.
My rocket stove is only laid up "dry" right now ... no mortar used yet so I'm free to tear it down and re-do it so am open to the benefits of any / all current ( experienced ) advice.
If these topics have been adequately handled in previous threads, please either direct me to a previous thread or EMail me with thoughts / comments.
Respectfully ( and thankfully ) yours Allan Hermon, NY, USA
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Post by Donkey on Aug 29, 2008 18:13:19 GMT -8
Another side issue ... I'll hope some will EMail me re: connecting an 8" black pipe to my 55gal heat exchanger. I've got a 35gal drum inside to hold in the insulation so there's only a 1.5" gap between the 2 barrels ... and if I connect an 8" chimney pipe to it, I believe I will be creating a bottleneck right there and need some advice as to my other options. For those of you who have used firebrick as your heat riser, talk to me about what you'd advise. Good.. You can figure out if the gap is enough by doing the math.. Normally I like to avoid the numbers but here it's just too helpful. I'll have to make some assumptions to do this myself for your system, sight unseen.. Here goes: The 55 gallon barrels that I've got in my yard here are 22" diameter inside dimension.. You are saying that there is a 1.5" gap (all around??) between the large barrel and the small.. This indicates that the inner barrel is 19" diameter, outside dimension.. First figure out the cross sectional area of the two barrels, inside dimension of the large one, outside of the small.. The formula for figuring the area of a circle is PI times Radius Squared.. Or, put simply, the radius (half the diameter) times itself, times 3.14.. Large barrel = 22" diameter = 11" radius.. 11 x 11 = 121 x 3.14 = 379.94 square inches. Same operation on the small barrel gives 283.38 inches square. Subtract the inner volume from the outer to tell us the area of the channel made.. The area I get is about 96.56 square inches. An eight inch stove pipe has an area of 50.24 square inches.. Looks to me like you've got enough and then some to spare.
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Post by Donkey on Aug 30, 2008 8:40:11 GMT -8
I forgot to mention... Steel barrels have those ridges running around them to add strength.. You should measure the inside barrel at its WIDEST POINT, and the outside barrel at its NARROWEST POINT..
The place where I have messed up in the past is in the gap above the heat riser, between it and the barrel. The best (and least math-y) way to get it right (IMHO) is fire up the stove, place the barrel over it and move it up and down till you like it.
Otherwise you have to visualize an invisible cylinder over the top of the riser, as wide as the opening of the riser (8") and as tall as the gap above.. make sure that the imaginary surface area of this cylinder is equal to or greater than that of your size choice.. For an 8" system that would be 50.24 sq. inches.
To figure for the size of the cylinder you multiply circumference of the riser times the height of the gap above.. Or, actually a better way to say that would be to figure out minimum gap size divide the circumference by the minimum area.. So: The circumference of an 8" pipe is PI times Diameter, or 3.14 times 8 = 25.12" Divide the area of our system size by the circumference, 50.24 / 25.12 = 2 inches.
For 8" systems, you need a gap above of no less than 2 inches.
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Post by larsmith on Sept 2, 2008 7:17:22 GMT -8
Donkey, TY for your info. It dawned on me just how much sense it makes that the gap above the HeatRiser and the gap at the exit to the exhaust should be the same. I feel a bit silly for having missed that physical fact and at the same time am thankful for your clarity !!
I've still have yet to decide exactly what to use as heat riser and am open to any/all info which can be provided ( or threads to which I might be directed in any other discussion groups / forums ). I've got plenty of firebrick to use but understand that's not the best option. I've got a chimney liner in good condition I could use. I'm looking for 1/4th inch steel 8" pipe & have found a possible source for it. I've heard of some using StainlessSteel double or triple lined chimney or just a stainless steel pipe. I'm at the point where I need to make a decision. AnyAll help would be greatly appreciated
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Post by Donkey on Sept 3, 2008 13:05:17 GMT -8
I've been greatly impressed with quarter inch steel, eight inch pipe, insulated with perlite/clay. Very much make happy!
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