If this interests you, I recommend checking out this video of Russ Finch, a farmer who grows citruses (orange, lemons, etc), figs, pomegranates in his sunken greenhouse in the middle of Nebraska in the snow/20F, and uses geothermal heating (long tubes buried underground) to heat it (and his house) during the winter months, and cool in the summer months. Really interesting story/concept and I'm hoping to replicate on a small scale when I renovate my back yard in the coming years.
The tubes are called earth tubes or ground-earth heat exchangers. If you look for geothermal heating you'll end up getting the wrong information, mostly for ground source heat pumps. The earth tubes aren't strictly speaking geothermal though, they're massive thermal reservoirs that you're taping into. You extract heat and then putting it back later either from day-night cycles or seasonal cycles.
Well it does not have the heat pump. So you will only ever get the temperature the ground is at. In his case the temperature of the ground is 11C. Which I guess is fine for the greenhouse with the additional sun gain.
This is nowhere near enough for human habitation comfort let alone hot water.
Yea, the difference is in capex cost and capabilities so the best you'll get is the ground temperature. Ideally you put a ground source heat pump but the energy needed to run it is high, COP for a ground source heat pump is like 3-6, cop on earth tubes are like 30 because you're only running a fan but you get whatever temperature the ground is.
A friend/acquaintance of mine who lives a few miles from me built a setup based on this, here in southern Ontario. It's pretty neat. Big tubes into the ground and fans to run into/out of them to circular air from ground heat storage.
Ended up costing him quite a bit to build even though he did a lot of the work himself. But he does have a full season growing setup though, and a swimming pool in there. Not sure how much if any supplemental heating he uses; but he's got various citrus, bananas, etc. growing.
No way! Do you think he’d be interested in visitors? I’m in southern Ontario and I’ve wanted to visit Russ Finch’s for a long time but would love to see something closer to home…
I haven't spoken to him in a while, but I could ask. I think he's mulled it over before and spoken of touring to the local area (Hamilton) permaculture guild, so he might be open to it. I can try to reach out.
Note that they hardened those citrus trees over many generations by gradually moving them north. While they were able to produce oranges, etc., I believe it became economically inviable over the course of the 20th C. What I wonder about is if any of those citrus varieties still exist today?
I know that the rootstock they commonly use for many citrus in the USA (Flying Dragon) is hardy down to nearly subzero Fahrenheit but the fruit doesn’t taste very good!
Curious if you could replace a backyard patio with a sunken greenhouse. You can harvest year round, small backyards could still utilize the space as a patio if the greenhouse is covered in thick enough glass panels, and if functional it would look nice.
If you're ever near Taos, New Mexico, check out the Earth Ships -- a community of homes each built around a similar concept, with a large thermal mass and south-facing windows allowing year-round gardening.
Hmm I had a similar idea to this because I want to be able to grow cilantro in the summer without it bolting which it does when it gets hot here. I was thinking I could dig a pit or trench and cover it with plastic or glass and hopefully keep it relatively cool in the summer when its 100+ degrees outside.
The easier approach to try first is just to plant it on the shady side of something that grows tall. Mine did much better this year mulched and growing in the shadow of tomatoes, cucumbers etc.
I also confirmed that I've got too much sun for my cucumbers, and that they do better with some shade.
My parsley would always bolt and this has been the first year it’s been excellent - in the most shaded of my garden beds. Coriander in that same bed still bolts though!
Ya, shade helps a bit but not enough, that's why I was thinking of the trench idea because during the summer cilantro is impossible here. I really want salsa with all my own tomatoes, jalapenos, onions and cilantro at the same time though!
Yes. I suggest the book "The Chinese Greenhouse". A very straightforward look at constructing a partially sunken greenhouse.
Chiras, D. D., Chiras, F., & Rao, A. (2020). The chinese greenhouse: Design and build a low-cost, passive solar greenhouse. New Society Publishers.
> Originally developed in China to feed millions, Chinese greenhouses are earth-sheltered, solar-heated, east-west oriented, intelligently glazed, and well-insulated. They have proven highly effective in growing warm-weather vegetables and fruits like green peppers and tomatoes in cold climates through fall, winter, and early spring using passive solar energy as the sole heat source.
I visited a very high-tech greenhouse a couple of years ago here in Australia and one of their solutions was very low-tech: in summer, to manage the heat somewhat, they sprayed the glass roof/walls with a chalky mixture which impeded heat coming through slightly.
These design ideas are old. It’s more that our civilization did not value this and never planned housing like this. There are other patterns that can harvest sun, rain and wind.
North facing can work well if you’re in a place that recieves too much sun. With flat ground in hot arid climate, an Eartship design for a house can be the hill providing the thermal mass.
Water harvesting is also a part of permaculture design. It depends on variability of the rain, the slope you are working with. I have a two-volume book from Brad Lancaster with all about design patterns for harvesting and managing water, whether too much or not enough. O
In the article, he discusses putting in French drains. If berming into a hillside, having French drains that are lower than the sunken green house would do the trick. You could have two symmetric drains that start on the middle of the back (north) berm, follow around the side walls, and then drain out on either end below the low/south wall.
French drains are good for normal amounts of moisture, but once you're talking about a structure installed at a low point and receive an inch or two of rain in less than 24 hours, the drains and ground will be saturated and then you're gonna have a bad time.
I'm only thinking of this because of the extreme amount of rain we've been having in the Bay Area this past week. Normally it wouldn't be a big concern.
From what I remember, the Bay Area doesn’t have enough porous layers to absorb water. It’s rocky ground and bedrock.
You don’t need to put the sunken greenhouse at the lowest point. Layer some berms below the greenhouse on the slope — effectively form swales — and plant some things there.
Another possible solution is to dig out a cistern.
Here is an example from India, where much of the water is concentrated in monsoon storms. Even with such heavy rain, there are cities suffering from drought. https://youtu.be/AvV-L8MdhO4
They have two storage tanks, and the excess goes into the onsite well to recharge ground water, instead of washing into the streets, contributing to flood conditions.
On the other hand San Francisco’s hardiness zone is 10a, 10b. If there is enough sun, it can support zone 10 tropical plants without a greenhouse, sunken or otherwise.
I mean, siting is everything. I’d only build one of these in a hill. I’ve got an earth-bermed house in a hillside in rural Wisconsin. There were terrible floods in the area in 2018, but the drains around the house sent all the water down the hill to the creek.
https://www.youtube.com/watch?v=ZD_3_gsgsnk