Awesome! Thank you for figuring that out for me. Can anyone tell me how THICK I should make the concrete mass that I'll be pouring around the drums for the bench? (Since I'm urban I'm using concrete instead of cob). I was guessing that at the closest points to the drum, I'd probably want it between 1 to 2 inches thick for structural stability? That makes it considerably thicker at the corners... Is that too much mass, or too little? Thanks!
Here"s a view kind of down on the newly modified/opened up manifold. It is now 4-1/2" across for most of the 12" length. Kind of a flattened D shaped opening... I'm hoping that will have sufficient flow for a 6" system?
So, what would be the CSA of a 4-1/4" x 7" rectangular pipe? Anyone? The manifold should flow a bit better than that, I would think...
I'm also going to add some concrete to the floor of the first barrel, to smooth the flow of air into the manifold...
Would it matter if the 6" inlet at A is actually at the bottom of the bell barrel instead of at top?that's where it exits the existing core and manifold, and It seems like it is the exit to the chimney flue being low, that would matter most?
Hi Satamax. Ok, you lost me... Are you saying that I have too much area with that many barrels? What if I delete one from the bench: won't that just reduce the heat I can get out of the system?
Or is the problem just the draft? How would I create a bypass? My exhaust goes out the side wall then vertical outside. I thought this would help with draft since the chimney (flue pipe) walls would always be colder than the air inside the greenhouse...?
What do I need to do to make this system work? It's coooold in the greenhouse! Thanks!
Satamax, I appreciate your help! Sorry for the lag here, but had a death in the family. Now it is time to return to living... Besides, it is going to be in freezing temps end of the week, and I don't want to kill all the tomato plants..
Can you tell me which would be better: a barrel "bell" system after the manifold, or three 7' lengths of 6" pipe? Would I use a pair of fullsize 55gal drums, or the smaller 30gal sized barrels?
Would a 6" pipe going from the manifold into the bell barrel work good or does it need to be bigger? I'm assuming that I should use a pair of whole barrels instead of cutting them in half (how would i seal the "floor" then)? Would i cut the entire ends out between the two barrels, or make a bottom exit from one to the other?
Then the 6" pipe exiting the end of the bell barrels should be located low on the end to force the hot air to expand inside the bells, right? Is there any magic distance for inlet or outlet?
Finally, why couldn't I just mix up quikrete to form the mass around the barrels?
Satamax, that was an awesome link. When I pull things apart to repair, maybe I'll make a bell bench instead of exhaust tubes... Would it work with a fine sand concrete instead of cob covering the bell?
Ok, it's revival time! I'm hoping for some help narrowing down what is needed for fixing my GH RMH. That's because it is starting to get cold, and last year I killed my wife's plamts. ALL of them....
Based on the great responses above from last year, here's what I think I need to do:
1) break out the manifold to provide a better exit for gases from the barrel with a smoother, larger transition.
2) make the exhaust pipe fold back on itself so a total of three 8 foot runs and two 180 degree turns.
3) mix fine sand with portland as thermal mass, to get rid of the air gaps in the rocks I'm currently using.
Will that work?
Do I need to worry about insulating BELOW the RMH, and if so, how? Is the above recommended insulation around the J tunnel to keep the flow going? (I'm not seeing why the menards fire bricks are of concern). Yes, the infeed and tunnel are slightly rectangular, but the vertical chamber is insulated and round... So should I add some firebricks inside, to make the tunnel square instead of rectangle?
And, is there a better non-cob way to build thermal mass, using urban available materials? I'm thinking the manifold restriction is the biggest issue: is there something else I'm missing?
I like the "change one thing at a time" idea, but I think I may have to do more than one improvement before firing it up.. If someone who is experienced would care to give me a list of the needed changes in priority order, I would be amazed and grateful! Thanks, permies!
Ok, Peter, I understand now. I didn't realize that you had jumped from the CSA of the actual manifold to that of the effective value of that rectangle, and was showing the CSA of that relative (and smaller) round pipe. The correlation makes sense to me now.
So, if I broke out the existing mortar bed and moved it offcenter so as to use 6" round pipe the whole way through, would I just use 6" pipe there, or do I need to construct a manifold of some sort leading INTO the 6" exhaust pipe? What dimensions should I use?
And, with a 12" center core and a 55 gal drum, how much space do I need to maintain between the core and the drum on the nearest surface?
I may let that project wait until spring, and just try to get the heat that I *AM* generating, to move more efficiently into the mass.... Any ideas on a better design for my bench? Or on replacement for cob, that could be mixed up from store-bought ingredients? Can I just use a high-sand concrete? Surrounded by brick maybe? Or does solid cinder block work for the mass? Thanks, All!
Byron Campbell wrote:3000° castable / perlite blend, lots of perlite in the blend, and formed around the J-tube core to a thickness of 2 to 3 inches, should be just fine for insulation.
Sorry, no suggestions for a moisture resistant replacement for clay based cob.
Oh, and I used a mix of 6 parts perlite to 4 parts 3000 degree mortar to make my core... Is that what you'd recommend around the j tube?
Also, I've read conflicting things online: some people recommend solid cinder blocks (or hollow ones, filled) for mass, while others claim cinder blocks are more insulative than they are mass...-ish...
Joel Rutledge wrote:Peter how did you come up with 11.28 area for a 12x2.25 rectangle? I see what you are saying about drag, though. I have that part all cemented in though...
According to that simple formula, the rectangle of 12x2.25" is comparable with a round duct of 3.79" diameter as far as aerodynamics are concerned. The csa of that one is 11.28"sq., can't help it but that could well be the bottleneck. A fat chance, I'd say, too bad it is cemented in.
I guess I'm still not understanding how you got a csa of 11.28"... Because 12 x 2.25 = 27. Maybe I have a different understanding of what CSA is: I thought that was the area of the hole... Sorry to be daft...
I do get what you were saying with the drag and comparable size of duct. When building, I assumed the similar area and smooth transition of the 12x2.25 boot would make a good manifold. Should I have used a larger manifold, which would have moved my core offcenter in the drum?
Peter how did you come up with 11.28 area for a 12x2.25 rectangle? I see what you are saying about drag, though. I have that part all cemented in though...
Byron, I thought the perlite mixture was only for the core, not the bench? We don't want to insulate the exhaust, we want to grab its heat... My core is 3000 degree cement with perlite, so there isn't a problem with the core. I built it as the video and others have discussed. What I'm looking for is an urban equivalent of cob for my mass in the bench...
Byron I missed your message. Yes, that is the technique I used for the core, but all I used around the fire bricks for the j tube is solid cinder blocks and bricks. What kind of insulation do I need around it: the perlite cement mixture? How thick? Thanks!
Glenn Herbert wrote:The "manifold" (common term for this area) generally needs to be at least twice the duct cross section for good flow, because of the direction and shape changes.
Uh oh. I thought I was supposed to keep the cross section equal in all pipes... I do plan on reshaping the floor to direct the air more smoothly, but is the cross section going to be something I can overcome?
The boot I used is 12" x 2.25" or 27 square inches cross section. A 6" pipe has 28.3" cross section, which I figured would be close enough... I guess not?
Anyone have any ideas on what to do about the manifold, or other suggestions for the best replacement for cob in the bench? Thank you all!
I wish I'd seen your post before building my RMH for my greenhouse... Among other things, I'm wondering about my core...
I mixed up perlite with Refractory Cement that was already rated for 3000 degree temps. You can get 25 pound buckets of it from Menards. But I didn't mix it the same way you did... I mixed it with water to a crumbly, barely dry consistency, but a lot more water than you did misting it... I was worried it was too dry while I was packing it.
The core ended up very heavy and dense/hard like concrete: is that correct?
What did you do with the pink styrofoam after pouring: scrape out the big chunks then let the edges burn off at first firing? Great idea for an internal form!
Satamax: the burn tunnel and vertical flue are well insulated: firebrick barely even gets warm on the outside after burning, the refractory cement I mixed up insulated to 3000 degrees fahrenheit, and the core has the refractory cement with perlite between the 6" pipe and the 12" pipe.
I don't see why someone would need the "bell" plans: overcomplicated and likely not much efficiency gain. A proper RMH should do the job. I subscribe to the KISS Principle: keep it simple.
The last link you gave was pretty cool: rmh bench in a restaurant. What's with the horizontal drums for exhaust though? Unless they are filled with a just-right amount of rocks, I'd think you would have problems with CSR, expanding the cross section enormously. And wouldn't it be difficult to get ash out of the rock mass later?
I think I'll stick with fixing the known problems with my RMH design... Thanks!
Kyrt Ryder, have you used portland to do this? I have plenty of Portland on hand and can mix it up without the perlite so as to not insulate. Is this more or less efficient than the cob? One to one, sand to portland?
Perhaps for time and cost efficiency, I should mix it a little thin and pour it around rocks, or perhaps mix the rock and gravel in with the cement mixture? That would increase density or space used up, and rock is cheaper than portland. What do you think?
Anyone else have experience with replacements for cob?
Satamax: thanks for the reply. I used 1-1/2" thick firebrick for the burn tunnel, and it insulates great. It gives off nearly no heat to the surrounding mass, which is just used to support the drum.
The transition is 2"x12", giving a CSA of 24, compared to the CSA of 28 for a 6" pipe... I didn't feel this little of a difference would affect it much? It seems to draft well...
What is a bell or half barrel bell?
To the other responses: thank you, keep it coming! Maybe I should have titled this "Help fixing my GH RMS"... Oh, and the barrell gets super-hot (can simmer but not quite boil water in a pan on top), and the exhaust is too warm; not giving enough heat into the bench.
To sum up some issues: not enough length of exhaust (mentioned above); I failed to insulate BELOW the RMH and bench; and I don't think the sand and gravel filler is going to do enough to transmit heat to the mass. A 2-hour burn last night didn't give any appreciable heat to the mass, although the heat from the rmh barrel made it nice and toasty! I need to find a better mass, and adjust the length of exhaust while I'm rebuilding...
Any ideas for a better mass for a city-dweller? Some thing I can mix up from mortar, etc...?
And finally, 2 pics of the gasket I used. I took cardboard strips about 2" wide, and taped them to the inside AND outside of the barrel lip. I put a 1/2" layer of the homemade refractory cement (with Portland and sand and perlite) across the area the drum would sit on to level it and give a reference. I should have done this in stages and repeated that step to give a more even, level base, but it still worked out. Then I placed the barrel on the wet cement. I packed more wet cement around the outside up to the top of the cardboard strips, and let it all dry overnight. When I pulled the barrel (the cardboard acts as a spacer AND keeps the cement from sticking to the drum), it left a 1/2" wide channel where the drum sits. After it cured fully, I placed (no adhesive, just loosely pushing it in place) the fireplace gasket material in the channel. It is braided treated fiber that resists up to 500 degrees F. Now when I place the drum upside down on the whole unit, it seems to seal nicely, but is removable when I need it to be! One of the pics also shows the outlet nicely, where the exhaust exits the barrel. In spring, I plan on using more cement to make a smoother bottom and transition the gases out the outlet, but it was going to freeze in a few days, so I skipped that step.
More pictures. Notice the exhaust tube in the pics above? That's what I'm wondering if I need more than just river rock around it...? These pics below show the central core, a 6" tube with a 12" tube, 2" below the top of the barrel in length. There is a mixture of equal parts perlite and refractory cement packed in between while slightly damp. The masonry work below and around the rest of the engine has 1.5 parts Portland, 2 parts perlite, and 2 parts sand; this was mixed a bit wetter for easier working and molding.
Hi! I'm building an RMH for my wife's 12x10 harbor freight greenhouse. We have a 6x8 GH attached to the front as a sort of airlock/buffer for entry during cold weather. I built a 6" RMH using refractory bricks into a 6" system (with the 12" refractory filled vertical) and a 55 gallon drum. But I have some questions on the RMH...
1. Do I need to make the exhaust snake back and forth? Right now it is going straight out, approximately 7' long. Then up. I am thinking of making it go up and out the roof instead, to capture more heat: is this a good idea? But do I NEED to make it snake around, or is straight ok? It seems like it is not giving off very much of the heat from the exhaust, but, I do not have the mass around it yet...
2. What suffices for mass materials around the exhaust? I am in the city, and don't plan on mixing cob (especially in 17 degree weather). I have cinder blocks that I was planning on filling in with rock, and stuffing rock around the exhaust pipe (6"), but is that sufficient? Will the air space between the rocks interrupt the conduction and transference of the heat, into the surrounding materials and then to the greenhouse? Would filling in with sand in addition to the rocks increase efficiency?
3. When burning 1x2 or 2x2 scrap lumber (not treated!), I get smoke backing up and coming out the feed tube. It seems to be because I got a super hot (white hot almost) bed of coals going and the wood above the normal burn zone ignited... Smaller sticks don't seem to do this, possibly because the bed of coals doesn't build up, possibly because of surface area and burn rate...? How do I fix this: any ideas?
4. Can I stack bricks around and/or on the drum to increase the slow release of heat for the greenhouse? Will that interrupt the draft or efficiency of the system?
5. Do I need to surround the mass with cement or stucco or anything? It doesn't need to be "pretty", just useful. It's a greenhouse....
I have basically a 4x6-ish J of refractory bricks, then 6" pipe the rest of the way. Approximately 12"/24"/36" dimensions of the J. I seated the barrel into some door seal cording from a woodstove for sealing the bottom and making it easily removable (when cool). (I can share how I did this easily if you are interested.) BTW, that feature helped when I forgot to burn off the paint outdoors before starting up the first burn....
If you have any ideas, especially for 1, 2, and 4 above, I would sure appreciate it. I've learned a lot from Permies, and hoping to get some of these things corrected.