Heavy duty thermal mass, geothermal, solar, greenhouse.

I would like thoughts on this. I want to dig a hole down 8 feet. Then pour a foundation. Then build a wooden 2x8 wall. Insulate it and poly on the inside. THEN,,, fill the hole back up. Then build a 2x8 building on top of the basement wall. glaze the south side, maybe some of the east and west walls also. Insulate the rest. Superseal it as well. It should never freeze in there, right? I live in central Saskatchewan -40c, in the winter, and up to +40c in the summer.

Mark,
Evidently it is getting cold is spots from the number of greenhouse inquiries this weekend.

I found this post earlier today Bermed Greenhouse,
the guy does some stuff like you are talking. From your area, I think.

Here is a quote from that page:

The overall dimensions of the greenhouse are 42' X 16'.

The green house is bermed up on the north side with a 6 foot wall. I used recycled patio doors for the glazing.

I heat the concrete walls with the solar panels (that is the tubing in the walls).

When it was -6 F degrees out side it was 46 F inside this past winter.

Here is the link to more information on various Winter arrangements Walipini

Anybody else? I really want to know if anyone has done this, or knows of someone who has. I'm wondering if the geothermal heat plus the solar of course, will keep it from freezing. The walls will be insulated from 8 feet down, right to the top of the greenhouse.

Hi Mark,
I can see that you want people to discuss your greenhouse idea. I'd love to, as I'm a big fan of, and have lived with, greenhouses and thermal mass. But I don't understand your verbal description of your plan. Any chance you could upload a rough sketch? You lost me from the first sentence: is the 8 foot deep hole the entire size of the structure? Or just for a foundation under the walls? Or a narrow deep hole like in a children's book...? And so on, from there. A picture would help a lot.

The hole would be the same size as the greenhouse on top. I'm thinking about 8 feet wide by 12 feet long. The foundation would be pored around in the bottom of a 8 foot hole. A wooded insulated wall built on top of that, up to the ground level,, then the hole filled back up with earth. The greenhouse itself, built on top of the "basement" wall.

With all due respect Mark, I don't think your idea will accomplish anything. My take is you want to create a thermal mass by isolating it from the cold ground. The ground itself is a giant thermal mass but it still manages to freeze over in the winter, so your thermal mass will die by the same fate.
Greenhouses by nature are not very well insulated and with your cold winter you would be hard pressed to keep it even reasonably warm.
This is only my opinion and I could be wrong but sometimes it is best to see all the critical views before making the final decision.
Good luck with whatever decision you choose to make.

Thanks for you input. I don't want to insulate it from the bottom. I don't want to insulate it from the ground,,thats where I want to get my heat from.

Any more thoughts or ideas?

I'll expand on my original thought.
Heat will only transfer from hot to cold. With a greenhouse you would need temperatures in the 20's Celsius range (70'sF). The thermal mass at 8' deep might only have a temperature of 10C or less, so it can't offer up any heat until the greenhouse temperature drops to below this point. When it does give up it's heat it slowly cools and the heat from the earth can't recharge the mass fast enough, so eventually it would drop to below freezing.
The reason geothermal heating systems work is because they use a heat pump and exploit a thermal mass that is many times greater than the structure that is being heated.
The only way you can make your thermal mass work for you is to push into it additional heat such as is done with a rocket mass heater. But with your only other source of heat being solar, there wouldn't be enough heat generated to keep this mass charged up in the dead of winter.

Bud. could a person set up some dark colored solar panels for heating air, inside the greenhouse, and pump the air into the concrete or the earth to help warm the mass?

Miles Flansburg wrote:Bud. could a person set up some dark colored solar panels for heating air, inside the greenhouse, and pump the air into the concrete or the earth to help warm the mass?

I had a private discussion with Mark last night and his intention is to do something along this line using flat plate collectors. This could help somewhat but remember that heat doesn't like to stay put. It will always travel from hot to cold. If you make the earth mass below the greenhouse warmer, the added heat will migrate into the earth that is outside of the greenhouse footprint and therefore you will lose some of that energy. Also for this to work you need reliable sunshine for every day of the week and lots of it. Where I am located in Ontario, the winter months see a lot of cloudy days and you would not be making any additional heat on those days, but the heat lost to the cold temperatures is constant.
Additionally, I don't think you would get enough good hours of sunlight even on a good day to build enough of a solar gain to carry you through the night. In winter the daylight hours drop to about 8 hours per day, but when the sun is low on the horizon (morning and evening) you won't see any warming, so you might only have about 4 hours of good sun per day.
This is only my opinion and I would be tickled pink if someone were to prove me wrong because then we could incorporate this idea and heat our homes for free. But I feel that if it were this easy, somebody would have already done it by now.

OK Thanks Bud.

We're quite a bit further south, but we have a pit greenhouse along the lines of what you're proposing... I have found that in winter, it gets plenty warm in the greenhouse as far as air temperature, but the temperature in the soil beds hovers near freezing. It will climb through the day, though. I have insulated the beds recently, and added some PVC piping, so as to provide some bottom heat. My understanding is that we have enough light in winter to grow cool season crops, but not enough heat down in the root zone. My best advice would be for you to start small and take careful measurements of both air and soil temperatures. Our greenhouse will "hold" a crop in cold weather, but there's not much actual growing going on. Best of luck to you!

Thank-you very much for your input. I'm guessing that your insulated up the walls and well down below the frost line with a r-factor of 25, or more?