where to place rocket mass heater in 'in ground greenhouse'

Attached is a drawing of our future walipini. I am going to pile soil up around the long walls all the way down (couldnt figure out how to make sketchup do it), but leave the windowed end exposed. I plan on putting a rocket mass heater in it, but location is still up in the air. I was hoping someone with more experience running their dragon could help me decide location.

Would the RMH work better in the end of the greenhouse that is underground, or the end that is more exposed? I was thinking that I'd put it in the end near the window to try to keep the exposed end warmer (also closer to the firewood shed), but would it work better on the other end and for what reason? Perhaps the middle of a wall? Or does it matter at all?

Thanks ahead of time for your responses!

Matt,

I would say what you want to grow will play as much of a difference as the dimensions of the structure. For example, if you're growing Bananas right next to the heater, much of the radiant heat may be caught or shaded by those plants, making plants farther away less warm. Insulation and vapor barrier is probably in order to prevent drafts and cold spots, aside from your intended vents.

You're dealing with several types of heat, conductive, which will logarithmically decline as you increment distance from the RMH, radiant heat, which will heat anything in line-of-site, then convective heat which is heat transported by air.

Though, since it's a greenhouse, you're going to have decent humidity, which is nicely thermally conductive. A thing I learned in cooling data centers is efficient layout is best, but if all else fails, blow air around enough and you get rid of the hot and cold spots. That's not necessarily efficient, but it may help in a pinch.

An idea, that's just a theory really is elevating the RMH to the center (vertically of the room). Then you could radiate the heat to the exterior walls, and if coated with a reflective film, reflect the heat all around the room, kind of like a lightbulb. Just a theory, but it might work.

Ernie or Erica Wisner? any ideas?
Allen Lumley?
Mr Wheaton?
anybody else?


I love lots of different ideas! I'm interesting in a discussion as how the RMH would work on either end or center if it would be better on the "cold" end or "warm" end.

how long is the building?

ronald bush, it is 18 by 40 feet, and the walls will be 6 foot tall with a max height inside of 12 feet with the roof peak

matt sorrells wrote:ronald bush, it is 18 by 40 feet, and the walls will be 6 foot tall with a max height inside of 12 feet with the roof peak

I am getting ready to build a greenhouse and want to use RMH heat for it and so have been doing lots of research into in-use designs that seem to work.

I've been looking at photos of greenhouses heated with RMH units and almost all of them that are approximately the size of your design are heated by a RMH placed in the middle of the structure and extended down that middle line.


With a length of 40 feet, the RMH at either end would not radiate much heat all the way to the opposite end.

Depending on the plants grown in this greenhouse, an end placed heater would work if you were, for instance, going to grow kale or other cold tolerant plants that improve in flavor by being colder. They would be planted at the end opposite the heater end.

The arrangement of an end placed RMH would give you zones for growing since the further you get from the heat mass, the colder the greenhouse would get. Which is not in anyway a bad thing, just means a different plant placement plan than a greenhouse with consistent heated space.

Matt Sorrells : I do not own a greenhouse, but I have worked in them, the first thing i learned was there is way to much stoop labor involved in the G'house process .

the usual way of selling with this is hanging baskets off of all the bows, ribs, and hardware of the Frame and Creating sawhorses to get things up off of the floor.

In line with past observations I would recommend that the Rocket Mass Heater RMH and the thermal mass be Tall enough for use as a seed starting , potting and
general work table , with just 1 pass of stove pipe right down the center it can be rather narrow, allowing for more heat to radiate off of the sides.

In the advent of a 'Polar Vortex'The Plantings can be brought in close to the sides of the Thermal bench and covered with a row cover arrangement with a much
simpler cover over the top of the bench, It this situation with so much of the ground and bench being warm the air under the row cover will remain above freezing
for a long Time !

Besides your wood supply in a separate building, I would have a wood bow that was air tight that i Could load up from outside and unload from inside, a high moisture
content greenhouse is not a great place to store the Small very dry thin split wood a RMH thrives on ! Trying to navigate a door or a series of doors while carrying
wood can be the recipe for a disaster ! Certainly do put your rocket stove close to your wood supply !

I am still confused by the picture both the man and the Green house seem to have shadows, is the long axis of your green house facing the sun running east and west,
or is the small end with windows the south facing end ?!

For the good of the craft ! Big AL

Allen,

I may not have gotten the shadows correct, but the long side facing you in the picture is the south side, with the windows and one door facing east. There will be much more soil piled up against the walls.

My first priority is providing more food year round in the greenhouse, but I'd love to produce enough to sell the excess, either fresh or as value added (canned, juiced, or jams...(or the attempt to sell fresh, and when they get close to being too ripe, process 'em!).).

I'm planning a "cold air sink" or cold air/water drain under a walkway down the middle or slightly c shaped inside the greenhouse. I think if the heater were front and center it would take up far too much room, so I've either got my eyeball on the south side or east near the door. Plus if it was in the center, you'd have to have two walkways taking up twice as much room, wouldnt you? Reckon I could place the barrel end of the RMH by the east door and put a long run down the greenhouse and exit on the west end? I was thinking a shorter mass so the exhaust could go up by the barrel to increase draft quickly.

I'm also planning on planting alot in the soil on the bottom plus some shelving in the future to increase floorspace plus some things in the rafters (strawberries!). I've got soil from the forest on the mountain I've hauled in plus a bunch of other things (coffee grounds, wood chips, shredded leaves) to put under the soil to provide nutrients and moisture.

Also, I couldnt get sketchup to do it, but the inside is dug down 6 foot deep on the "deep end" and I'll backfill with good soil a foot or so. I just realized this does not show in the picture and could be confusing. The vast majority of the structure will be underground except the roof and east wall. The floor will be level with the bottom of the door from front to back.

Here is a laughable suggestion of what I was thinking about with the walkway

Matt Sorrells : As has already been suggested, if you place your RMh to one end of the G'house you will certainly end up with temperature zones, You can
that effect with hanging curtains, but tif you do not center your heater you will certainly end up with a lot of your heat stratified at ceiling level while trying
to heat the far end !

Wether you place your RMH on the floor raised bench, or in the floor you are creating a No -Walk environment !

As shown in your sketch the hight of your south facing wall will not allow the Late winter sun to penetrate to heat the mass of your North wall, often this area
is filled with Stacked barrels 2-3 tiers high, even if the two top tiers are warm much of their re-radiation of heat energy will be blocked by the lower tier !

Take from this what you can ! Big AL !

" Plus if it was in the center, you'd have to have two walkways taking up twice as much room, wouldnt you?"

If your greenhouse is 18' wide, you will need to be able to walk in more than one line down the length anyway, to get to everything. You probably wouldn't need to have more than one clear wheelbarrow path, though. Approximately centering the whole unit, heater plus mass, would make sure no area was more than 8' or so from the heat source, which sounds like a good idea to me. Making a raised bed over the duct sounds like making a more comfortable work area and getting some plants even higher into warmer air.

If you don't have your sidewalls built already, I am skeptical, like Allen, about the usefulness of a high south wall which will keep winter sun from touching most of the ground surface. Surely you aren't going to have 6' high plants everywhere? With a 3' wall and sloped roof, you can have comfortable working space everywhere that is farther than a couple of feet from the wall while allowing the maximum winter sun to hit the ground. This would also mean less volume to keep warm. I suppose the sun angle is less of a deal in North Carolina than in upstate New York, but it is still a real factor. I understand the walipini was developed in equatorial mountain regions, where sun angle is hardly a factor, and digging deep on all sides makes perfect sense.