Heated Greenhouse

Hi new member here. In spring I'll be setting up a greenhouse. I have an 8.0m x 3.0m tunnel design in polycarbonate and plan to have 2 raised beds running the length of the space with a walkway through the middle. Since the winters in Norway are pretty cold I was hoping to extend the growing season by heating it with compost. I've been pondering a heat exchanger system using those steel cages that hold 1000L water containers filled with compost as the heat source, running the pipes through the soil in the raised beds where it will transfer the heat and return back through the compost. Does anyone have any experience of such a system or perhaps anyone able to offer any advice going forward on pipe size, spacing things like that.

Hi Adam and welcome to Permies!

I just joined Permies a few weeks ago myself, and what a wonderful place this has proven to be.. So many resources and great helpful people working together to improve.

I don’t have any answers for you, but I’m intrested in the replys you’ll get as I’m planning a same kind of project. My future greenhouse is 10m x 3m, polycarbonate as yours and I’m also pondering about the heating options to extend the growing season.. I’m in Finland so probably very similar situation.

Now that I’m here, might as well ask.. What kind of foundation (if any..?) are you planning on doing?

Hi Adam,

Welcome to Permies.

I have a high tunnel measuring approximately 4 m X 8m.   I used to use decomposing straw bales and maybe 500 L of water to keep it warm in the winter.  This tended to work well down to a little below 20 F.   At lower than that I would occasionally use a supplemental LP gas heater. This winter I have put in a permanent concrete block addition to hold a small wood  stove.  I am also enclosing both ends with better doors and windows.  I won’t find out how well this arrangement works until next fall.

Had looked at this in my list of thinking.  Problem are multi-fold from my reading.  Compost containers that small cool to the outside and basically less than half of it will produce decent heat because the outsides cool too much to cook properly.  The answer was to insulate the perimeter of the containers.  The guy was putting 4 containers in a square block and insulating the bottom and the outside perimeter of the square and the top.  To reduce the chance of hitting the lines while turning the compost he was burying the coils vertically rather than horizontally.  He was digging down half a container into another container.  Then playing bucket brigade with the halves of all the rest of the containers.  Then returning the first half removed into the last hole.  Which brings the second problem.  This looked like a major lot of work to regularly turn the piles to keep them running.  Surely there has to be a better answer.

So now my silly thinking on the issue.  

Digging around the coils buried even  vertically is going to be a pain.  What if we did away with them?   Ideally we want to be able to easily remove the heat recovery.  So what if we used heat pipes or heat probes instead of loops to bring the heat up from the compost?   They could then be stabbed down into the compost instead of buried in it.  Thus reducing labor some and risk a bunch.  Heat probes are a pipe inside a pipe.  The water goes down inside pipe and comes up the outside.(borrowing this from a shallow well geothermal heat system but the outside pipe would need to be solid metal so it can be driven into the pile instead of the poly pipes used in the geothermal system.)  The other answer is heat pipes.  They are an evacuated tubes filled with a small amount refrigerant.  Run the water bath around the outside of the top head end.  The refrigerant can be water, alcohol or ammonia or a number of others.  Heat pipes would self regulate how much heat was pulled better but are more complicated to build.  Either way daisy chain a bunch of them together in some combination of parallel and serial to extract the heat.  Monitor outlet water temperature to know if we are pulling too much heat out.  Shut down if the pile is cooling to much.

Still a lot of labor to turn the soil to aerate it.  Can we do away with that too?  What if we built a probe on an air blow gun.  Is it possible to aerate the pile by injection of air in multiple locations one after another.   With 90 psi to 120 psi we should be able to push air in.   Will it just blow back up the outside of the tube or will it spread out and lift an area of the pile while putting air in?  Multiple injection sites and multiple depths.  Or maybe bury a bunch of  vertical tubes when the pile is created.  Tie a bunch of them together in group.  Create 3 or more groups.  Then rather than probing multiple times simply slug the whole pile with air in one tube group.  Use different groups each time to encourage settling and sealing around the unused groups to hopefully not end up with a single air leak up out of the pile.

Thanks for your input guys, so fast!
Some really good ideas. Although some seem too complicated for me to do right. I love the idea of insulating the bins to the outsides and digging it down a bit to help with the height.  I was thinking to put 2 bins together on each side of the tunnel. On the inside walls how about zig zagging some  25mm black htpe pipes up and fixing them to the cage walls with zip ties. (would this be big enough?) Should keep them out of the way of the pitch fork when turning the pile. steel pipes would be better of course but the cost of the project woud likely run out of control,  running it as 4 separate systems might be useful if something were to leak and i will need to fix it without losing the whole crop. for the same reasons id like to keep the medium as water to avoid any biohazard. I wasnt going to have a base just to dig down where the legs of the structure for a couple of feet or til I hit something substantial bang some rebars into that and set the legs in concrete.
It goes down to -20c here too but I think at those times of year there is so little light nothing would grow anyway. might be best to empty the system for Dec Jan and Feb. We will see how it works before making that decision. It snows up to May here so I was really looking to extend the season a few months rather than grow oranges in January. Also in the location ithere is no electricity, its not impossible to get some there but it will cost. getting air into the pile by means of a couple of 110m pipes with some holes drilled in might be a better option for me.

Here's a scribble i made quickly in an effort to expain things better.

And suddenly I remembered something I read a while back, I couldn’t find it for now but I’ll try to explain. Bear with me, I probably wont ne using the right terms..

This was in Finland, some people had a kind pf a geothermal(?) system in their greenhouse.
The idea was that it made the greenhouse cooler in the summer and warmer in the fall/winter. They had a pipe go from the highest point of the greenhouse, it went down below the greenhouse where there were rows of pipe (i think with small holes to deal with condensation) and then it came back up somewhere at ground level. There was a fan pushing the hot air down the pipe and under the greenhouse.

I’ll try to hunt down the article, there was somekind of drawing made of it that would be better than my explanation.

Hey Saana! That was my original plan actually. So last winteri got reasonably well researched on that. I shelved it because Id have to hire someone to install electricity and do all the groundworks.  Its super smart though. I fear it might not the the right location to do it. I have forest and plan to get a few goats llamas chickens and all  so I'll have all the compost going anyhow thought I might as well try and use that heat.
Thanks for the thought though 😀

Oh okies!

And you were asking about warming with compost, I went completely offtopic. I just started to think about my greenhouse project and a lightbulb appeared and I just had to come and write it here. 😅 I was also planning the geothermal heating/cooling when I was planning year and a half ago, but I had to put the whole project on a shelf for a while.. The greenhouse is in a pile in my garage waiting for assembly. Maybe this year? If not then 2024!

Okay, now lets get back to the topic of heating with compost! I’ll shuffle silently to the side.

Edit for many typos.

Similar situation here. The greenhouse got delivered summer 2021 it's taken me this long to choose a spot for it! When the ground thaws out I'll just go for it. All good ideas welcome

Hi. I came across this forum and thread when searching for how viable a geothermallly heated greenhouse is in Finland, where we live. We've had unheated, summer season, greenhouses in Finland for years but have been considering the geothermal option for our next one. So, and this is really directed to Saana, do you know of geothermal greenhouses that actually work in Finland? Do they keep the temperature above 0 all year round? If so, I'd love to know where I could get more details, or who to contact for more details. Any advice appreciated. Thanks. Jamie

Hi Jamie,

Welcome to Permies.

Jamie Craig wrote:So, and this is really directed to Saana, do you know of geothermal greenhouses that actually work in Finland? Do they keep the temperature above 0 all year round?

Hi Jamie!
I would say that no, they do not keep the temperature above 0C all year round.

What I was looking for with a geothermal system was an extention to the growing season and balancing the temperatures in the summer.

My greenhouse is still in the garage waiting for assembly.

Hi Saana,

Thanks for your reply. I suspected as much. I've seen videos and websites with successful geothermal systems in Canada, where the temperatures are a lot colder than we get in Finland, but they get a lot more light, being a lot further south (Southern Canada). Do you think the light makes the difference?

I guess, in Finland, we just have to accept that the greenhouse gets some downtime in the winter.

Hope your greenhouse makes its way out of the garage soon, maybe this spring?

Jamie

Jamie Craig wrote:Hi Saana,
Thanks for your reply. I suspected as much. I've seen videos and websites with successful geothermal systems in Canada, where the temperatures are a lot colder than we get in Finland, but they get a lot more light, being a lot further south (Southern Canada). Do you think the light makes the difference?

I don't have any actual information about it, so basicly you know more than I do! Maybe you could start a new thread about geothermal systems in greenhouses? We might find other people with more information and maybe someone has some links to articles or something.

Hope your greenhouse makes its way out of the garage soon, maybe this spring?

Oh I hope so too! Thank you!