Hi all, this is my first post on permies. I'm going to be starting a project that involves cob, straw bale, rocket mass heaters, passive solar, cold sinks, and earth sheltering. I'm hoping to combine these materials and techniques to create a greenhouse in zone 3-4 capable of growing tropical plants. I have experience as a grower at a very old greenhouse in Connecticut that specializes in tropical plants and I think it will be possible. Any other techniques that might help? Ive thought of using a heat tube but thats quite a bit more digging...
Otis, I like the idea of lots of thermal mass arranged inside the greenhouse so as to act like both an absorber and a radiator. Think masonry columns holding up the roof and large stone "landscaping" to create raised beds/lumpy texture. Also, people recommend air to soil heat exchangers...aka a climate battery. Can't wait to see what you do.
That climate battery looks pretty interesting, do you think theres a way to rig it without fans? Id like to have zero electric hookups... i plan on also using raised beds with stone walls for thermal mass and using no till gardening methods.
Welcome Otis, your project sounds very interesting. I'm thinking about something similar for my zone 4a location. At least the tropical plant greenhouse bit. I started with straw bale but ended up thinking it would just be easier to construct with more conventional methods. Not that straw bale isn't the best thing ever, I just didn't know how to handle the interaction of greenhouse humidity and straw.
I kicked around the climate battery idea and the related idea where you draw air from underground tubing into the greenhouse. The climate battery stores heat and you pull it out when you need it. The second just relies on the inherent warmth of the earth to preheat your air. I determined (not 100% scientifically) that a climate battery in the cloudy upper midwest wouldn't create much excess heat in the winter so the "battery" would run out of heat before I run out of winter. I also determined that my deep soil temps are around 49 degrees here so if I use that "heat" to heat my greenhouse I wouldn't be able to keep the temps much over freezing. That's fine for a cool crop but I didn't think bananas would enjoy it. I think both systems need fans to work at a reasonable efficiency.
I'm guessing you've already planned on insulating the foundation to keep from losing heat to the earth around you. It may be worth planning for a thermal curtain at night. Minimizing the heat loss through the glazing would be huge.
Am I right in assuming you are fairly far North (since you say zone 3-4)? What latitude are you at? With your tropical experience I'm keenly interested in how your plants would handle the sunlight available. I've assumed that I need additional light here at 45 degrees North...