8x12 climate battery greenhouse design input please

To begin, I would like to thank this community for all of the interesting and informative reading over the years.  Having so much time at home during these strange days I thought it was time to join and get some help for a project on our property.
I have been fascinated by the Climate Battery Greenhouses for years and finally decided to build one. I got one of those curved plexiglass aluminum sunrooms for free last summer.  It is 8'x12'.  I have a huge pile of fill on the property that is south facing and I have dug into the side of it and down several feet below grade.  I have to get an excavator in to go down a couple more feet for the battery. I have been reading voraciously about the topic but I am getting conflicting information and as my greenhouse is small I want to scale the design properly. Could any of the knowledge members on here give me some guidance. My current plane is to dig down 6 feet below grade to put in the posts for the frame and the first layer of pipes.  Then back fill 2 feet and another layer of pipe, then 2 more feet for the floor of the greenhouse. Which puts the floor 2 feet below grade.  The courses of pipe I am planning on using 4 inch "big-o" for the runs and some bigger abs pipe for the manifolds at the ends.

My ultimate goal to the run the whole rig off of solar panels and if it keeps things warm enough integrate grow lights for the winter months to raise cold hardy plants

Let me know your thoughts or input on this plan. We are in Zone 5 in Ontario Canada.

Regards
Brayden

Would you please post pictures?  This helps us help you in more ways than one!

My apologies for not posting a picture.  Here is how deep it was two days ago.  I measured this morning and I am only 2 feet below grade at the moment.  4 more to go minimum  I have been using my front end loader to scrape and scoop out what I can as I do not have access to an excavator to date.  I was looking this morning and I think I can go even deeper if I extend the ramp back further but that means moving way more soil than if I have an excavator.  I also forgot to describe my plans to make the retaining wall to the north. I am thinking that if I plant 6x6's in cement at the lowest grade and then pile a row of white cedar logs against the 6x6 posts.  I am thinking 4 of those across that back should suffice. Then I was going to collect smaller rocks from my fence row go between the logs and soil/fill.

Please let me know any further thoughts.

Regards
BRayden

I am an avid greenhouse gardener, because my passive solar house is heated by the seasonally attached greenhouse. Also at the school I work at, we've built many different greenhouse designs over the years.

I am not a fan of sunken greenhouses, because the south wall casts a long shadow over the growing bed surface in the winter, especially in Ontario's northern latitude, where the sun hangs low in the sky in the winter.

Personally I prefer to have the growing beds more or less level with the south wall of the greenhouse, or just a few inches lower than it, to minimise that shaded area in winter. If you are not planning to use the greenhouse from November through February I guess it wouldn't be much of a problem, though, and in fact you could start cold tolerant greens like kale, lettuce and others in September, get them big enough before midwinter, and continue harvesting them through the winter while they just hunker down and don't grow much.

When you say that solar panels will run the whole rig, I don't understand. What power do you need in the greenhouse? I only use electricity in my greenhouse for lights for a minute when I have to go outside to get herbs or salad for dinner. I would also like a fan someday, when the greenhouse gets too hot in the shoulder season of autumn and spring, when nights are too cold to remove the glazing entirely, and the end doors and windows don't provide enough natural ventilation on sunny days.

I don't think it's reasonable to heat a whole greenhouse using a solar electricity. The collection area for the electricity has to be something like 20 to 100 times larger than the same collection area if the sun's energy were collected as heat rather than converted to electricity, stored, and converted back in to heat. This is because of the low efficiency of solar electricity and storage. If you just want to power seedling germination mats of a couple square feet, I guess 50 to 100 square feet of solar panels would do the job. But there are easier and far cheaper ways to do it.  

I very much like having the north side bermed. My greenhouse is attached to my house, which is essentially adobe, so the wall of the house provides thermal mass and stabilisation to the greenhouse. For a freestanding greenhouse like yours, having the north side bermed is great. One thing to consider would be to insulate after a few of feet of earth, so that the greenhouse is not thermally connected to the chilly deep underground (warmer than outside, but colder than you want in a greenhouse).

Thank you for sharing your thoughts Rebecca. The solar array will be used to run the fans for the climate battery, watering system and hopefully the grow lights in the deep winter. I agree with you about the south facing side of the greenhouse. The back wall will exceed 10 feet total so my idea is to have a tiered system of racks for plants. I can have plants on the south facing side in the spring/summer and in the winter just the north wall. It will be an interesting experiment for sure.
Regards
Brayden

When thinking about shade from the south wall, don't forget about any snow that may shed off the roof and pile up there.  My greenhouse can accumulate a 6' snow pile and I have to dig it out a couple times a winter.  Even at that, it stays 2' high all winter.

I would pay particular attention to insulating and sealing it.  My N, W and E walls are insulated to R20-24 and the foundation is insulated to R20 as well (Swedish skirt method).  

Also pay attention to preventing moisture from getting into the insulation/walls and think about how you want the condensation to be managed.  If the walls are insulated, most of the condensation will come off of the glazing.  Sounds like with your plexiglass outfit, it won't rot if it gets wet.  Then you can harvest that condensation to water a bed below it.

Lastly, don't forget to include enough ventilation.  The climate battery may negate the need but in the heat of summer, being able to open a vent high and low to let air flow through is very nice.

I am not worried about the snow. I have a tractor and snow blower, which would make short work of any pile. I am going to insulate all the of the walls as much as possible as well.

Regards
Brayden

Thanks for the pic Brayden! I agree with Rebecca, if you insulate your thermal mass from the ground and you collect all the solar gain you can by avoiding shade, your greenhouse might not need any solar electric.

The only thing the picture you posted makes me wonder about is if any of those trees cast a shadow on the south side of your greenhouse?  One solar expert pointed out that if your passive solar devices (not solar electric) have any kind of shade, it will drop the device's efficiency by 40 to 60%. And of course you know to align the green house to solar south (not magnetic south) ....some beginners don't know this so I'm adding the expert obvious for them.

Thank you for all of the input everyone. I have been reading way to much online and I am now beginning to question the climate battery idea for the greenhouse. Getting down deep enough is going to be a major endeavour to really reap the benefit of earth constant temperature. I am still going to put in a single layer of the underground piping as I am deep enough but after reading some more of the wonderful articles on here I am now thinking that integrating water barrels for a thermal battery and integrate that with a rocket mass stove and a solar water heater may be a better way to go. I can not remember which post on here I read but someone brilliant really broke down the math on the climate battery and best case scenario I would be out of usable heat by the middle of the winter.  With the better heat retention capabilities of water and the solar panels I have, plus a rocket mass stove I should be dandy.

Orin, thanks for the heads up on Solar South I will adjust to suit.  The trees are to the west of the greenhouse and I cleared them way back last year to open up more land.  It should not be an issue or a minor one at the worst.
I hope to make some sketches tonight and I can post to share the new plan.

Brayden

I after some wet weather that put the project on hold, I am about to start the next phase. I am now seeking advise on if I need to insulate the underground section of the greenhouse.  The retaining walls are going to be made from 6 inch diameter easter white cedar logs. From what I can see online for a soft wood the R value is 1.4 per inch, which would be roughly 8.5 R value for the walls.  Do I need to put foam in as well?  
As always I appreciate the input.

So the logs will be laying on their sides and will hold back the hill because they're behind the cemented posts?  If that's all correct, I'm picturing these logs just sitting on one another.  So they'd have 8.5 R at the center of each log and then everywhere else there'd be less insulation, down to zero where the logs meet.  Or are you cutting flats on the logs so they fit together better?

I'm thinking I'd want some more insulation behind the logs...

Yes I was planning of just stacking them like that.  I could spray foam or something in the parts between, but it would be way easier to throw some foam boards behind them?  Just trying to save time and expense.

If I'm understanding correctly, I'd probably throw some foam board back there.  Or the fancy fiberglass board that's good for below grade applications but I'm guessing it's more pricey than foam.  

Braydon, it's pretty important to do an engineered concrete wall or concrete block retaining wall if the height of the soil is more than 3 feet or 1 meter between a building and the soil.  Even at 3 feet/1meter there should be some serious construction of a wall to hold back soil because of rain, soil movement, rodents and rodent holes that could send flowing water out of that wall of dirt, saturating the soil the greenhouse is sitting on, and snow load.  Plexiglass should not have great weight against it.  

Not sure where you are, but will plexiglass be okay with the expansion/contraction of cold/heat and soil expansion/contraction?