Adding a rocket mass heater to an underground greenhouse

Hello---

I live in Eagle River, just north of Anchorage, Alaska. In the spring of '13 we are planning on putting in an earth sheltered green house. Since we want to extend our growing season, we know we will need heat, so the question is: what kind of heat? It might as well be a Rocket Mass Heater since we have lots of wood scraps/branches around.

Next question: Do we use it to heat the soil? Do we place the RMH (rocket mass heater) at the top of the green house or at the bottom. If we put it at the bottom, do we need a cold sink too? Should we try to heat the soil with it? How deep should the pipe go?

Lots of questions!

Cindee

Hi Cindee,

I am also planning to install a Rocket Mass into my greenhouse. I think it is a great idea for growing through the winter because of the slow but constant heat with little wood use. That being said I haven't seen many good examples of functioning greenhouse units with explanations of the effectiveness of heating.

I have read that having cob directly in contact with the stove pipe is good because it will allow the quickest and most complete heat transfer from the pipe, but I've seen plenty that don't do this. I can imagine that if you then had that pipe in a raised bed it would heat the soil which would act as a sufficient thermal mass. Also, the heat is right in the root zone and just above the soil, so if the greenhouse air is cool the plants will still be fine. Here's a video doing that: http://www.youtube.com/watch?v=qtFvdMk3eLM.

As far as depth I don't know what the minimum is but I would definitely play it safe, whatever that means... Maybe build a test before you do the final.

Something to consider is how much of the barrel you leave open to the air. I am contemplating how to best eliminate the loss of heat off of my barrel so that I can store the most heat in the thermal mass. This is something you might want to consider if you are only growing winter crops in the winter. I think it would be a better use of the heat to warm your soil not the air (another trick would be to place row cover over the plants to hold in the radiant heat from the soil). I am imagining covering most of the barrel in cob and also increasing the space between the inner chimney and the barrel so that less heat is lost from the barrel top.

As far as putting the heater on the top or bottom of your greenhouse I don't really understand your orientation. I am going to put mine on the ground along the back wall of my greenhouse so that the thermal mass gets lots of sunlight too. However, we are focusing on the production of spring starts for or farm and not on winter growing so our thermal mass is going to be a 3.5' tall cob bench that the starts can sit on.

I think cold sinks are rarely a bad idea, especially after reading Mike Oehlers book. But, I'm not going to do one because of my high water table.

If you haven't, read the Rocket Mass Heaters book by Ianto Evans and Leslie Jackson.

Cheers,

Alan

A bit of a bummer not having data and directions/experienced people available for Rocket Mass Heater consultation. Guess that's why they call it pioneering.

I'm working on building my RMH with the vent pipe running underneath a Deep Water Culture tank - 4 foot wide by 20 foot long. That makes the vent pipe about 50 foot long with the bends, elbows, etc...
Greenhouse will be 4 foot above the RMH, built above ground (not much help to you, is it?) Have been thinking of building an RMH berm/bench for propagating in the spring. Maybe a vent damper or something so the heat can be directed either underneath the DWC tank or toward the propagating bench. Heating all that water in the winter will keep the fish growing and plants from freezing.

But the fish tank area is another 12 inches or so lower than the RMH. So in the summer I'll be bringing cooler air from around the fish tank through the RMH vent pipes to help cool the mass of water in the DWC. Cool sinking is an idea that I got off this forum (from someones post).

In Alaska, I'd figure you could keep a greenhouse heated to at least grow cold season crops indoors. Using the row covers inside a greenhouse brings the temps something like 500 miles "South". Check out Elliot Colemans "Four Season Harvest" book. Definitely check out the cold sink idea. There is a video out there somewhere that shows how a guy built a deep sink inside his passive greenhouse and put boards over top of it to walk on. Tomatoes in January anyone?

What are you planning on growing?

Hey Alan,

Sounds like we are doing similar builds. GREAT! I need someone to bounce ideas off of. I am using that video as a guide as well, but they don't really answer the green house questions that go with the stove ideas. My slope is very similar to Erica and Ernie's slope, but it looks like they built only one garden bed. We're planning three levels. So I think we've pretty much decided to put the rocket stove at the bottom with a bench attached to the bottom wall since heat rises. It will also be our plant starts bench.

I think we also decided that our building will be mostly cob -----IF we can scout some more clay in the area. The north wall will be solid cob, the east wall is our garage wall, our south and west walls will be lots of windows? or greenhouse plastic building material of some kind. Of course we need the roof to shed snow down the mountain.

Doing a test/model is an EXCELLENT idea. If we run our pipe up slope under the growing beds, we are thinking the pipe will have to be deeper at the bottom and shallower at the top. Interesting idea which may take a lot of adjusting.

REALLY, I need to keep really good records about what we are doing. I haven't found anything on the web giving any specific directions about RMH and greenhouses. Mike Oehler's book is good, but.... like you said

I haven't seen many good examples of functioning greenhouse units with explanations of the effectiveness of heating.

So....Luckily I have a guy who's taught with Ianto and Leslie coming to do the workshop of building the RMH. (Lasse Holmes) He's advising us on the greenhouse, but the greenhouse has to be framed in before the stove. So we'll spend this winter making sure our ideas our sound by bouncing them off of folks like you!

Thanks for your ideas---I think we'll probably cover the barrel with cob as well, for similar reasons, but we'll wait for that decision to be final next spring.

Many thanks---
Cindee

Hey Bill---

We enjoy growing peppers, tomatoes, squash, beans in the green house we are borrowing. However, we are realizing that it needs to be way more insulated to extend the season of growing in Alaska. When we build our greenhouse close to or IN the ground against a south facing slope, we may be able to grow broccoli all year. We just don't know since we can't find anyone who's done it already up here.

The main problem is that 90% of our food is imported from the Lower 48, so we are just trying to grow anything to make us less dependent. Once we build it, we can start experimenting.

Send any ideas you have, our direction!
Thanks,

Cindee

Found a link to it on this forum thread: Heating a 7000 sf Greenhouse

Other good stuff on that thread as well.

Thanks, Bill. I just email Rachel (who was thinking about that 7,000 sf greenhouse) and asked her if anything had happened. I had no clue she was considering that.

I'm sure she didn't do a Rocket Mass Heater though. It's just not that common in Alaska yet. That's why I want to build one and show folks what I believe it can do===especially on a south facing slope!

I really appreciate your time!!! (Why didn't I find that?)

Cindee

there is hours and hours of reading somewhere in this forum (read most of it last year before the forums format change) as well as here: http://donkey32.proboards.com/index.cgi

I went through 3 versions of a RMH heater last year to heat the garage. I went with a 6 inch cross sectional area because I was on a bare bones budget. I would highly, highly recommend at least the 8 inch diameter/csa. As someone says somewhere in one of these forums, 6 inches "isnt the most energetic" version possible.

Be prepared for more tinkering and fine tuning than you expect; the ratios of length and cross sectional area are quite important; be willing to revise and rebuild. Each stove is a custom job. have fun.

on edit: a particularly useful thread on rocketstoves.com; http://donkey32.proboards.com/index.cgi?board=discuss&action=display&thread=337

Great RMH forum. Cindee, we hope to see lots of pics of the Alaskan RMH build.

In Alaska you should build the greenhouse with the north wall and roof insulated as all the sun will be to the south you can save heat by not letting the heat go up and out the roof

Mr. Bill A. :I don't generally drift very far away from the Rocket Stoves forum, by now you have noticed that the R.S. forum has lots of 'greenhouse threads'.
I did find my way to this forum/thread and am a little concerned about your plans to employ 'a vent damper or something' to divert the R.S.'s hot exhaust gas
flow from a growing bed to a water tank.

I can see no problem with your Idea as long as there is no way that both pipes could ever be shut of at the same time. A manifold with a sliding door that can
only cover One Pipe at a Time would be fine, but in fact the design of the rocket stove does not allow the use of a closing OR restricting damper EVER !

Basically, I hope that you figured this out on your own and that I am just a worry-wart ! Peace ! For the good of the Craft! B.S.,K.W.! PYROmagical Big AL

Can I get a witness ? How about a report from everyone here about your 'rocket stoves " Big AL !