So it has been coming together in my head.
I was thinking along the lines of this
http://www.youtube.com/watch?feature=endscreen&NR=1&v=9IYKzpVPMBw. I didn't like the venting system in this design though so I thought that I could do a double glazing using
Solex (as seen here) .
Now I'm thinking that a simple rectangular fully earth bermed on 3 sides with glazing all down the south side. It would look more like a small oddly proportioned earthship from the outside. The roof could be super insulated using a living roof or a steel roof with straw bale insulation. A water collection system would feed a buried reservoir.
In either case the cold sink similar to the one shown in M Ohler's book was to be used. I plan on a foot deeper version with more gravel to bring it up to the correct standing height and while the cold sink will still run down the south wall it will have fingers coming off it in the direction of the north wall. Essentially the coral tanks would be on raised earth beds. Isles ( the cold sink) would allow me to walk all the way around 3 sides of the 4' wide x 12' long coral beds. Under the coral beds in the raised earthen platform I'll bury radiant coils hooked up to the storage tank for the evacuated solar collector. At the bottom of the cold sink I'll install drainage tile which will connect to a sump pump.
All of the exposed ground/dirt will be sprayed with a fibre reinforced thincoat of concrete very similiar to the method they use when building the
ecodome homes. On the U.S. site they show fences and planters built using their sprayer and basalt reinforcement clothe and that would be my approach. The coral tanks them selves will be made of plywood coated in Williams low voc 80% solids by weight 2 part epoxy and standard fiberglass reinforcing cloth. They will need to be built in place.
The south glazing will be 60 degrees and use
Solexx with one layer on top of the 2x6's that form the glazed wall, and one layer on the bottom, which would be inside the greenhouse. A blower system with a manifold up top and a collector down below would blow styro beads ( like are sold/used to fill beanbag chairs) up the manifold to fill the cavities between the studs and glazings forming an insulated wall. Gravity will empty it and it is something that can be easily automated by either a thermostat or photo cell. The bottom door that opens to allow the beads to fall into the collection chamber could be powered by a 12v DC power window module from the junkyard. They are cheap, have plenty of torque and the drivers side on most imports has an auto stop at full open and full closed simplifying the design.
A ground source heat pump will supply the backup heat and it will be installed in a manner that will allow the addition of more greenhouses to be serviced by the one heat pump. I am going to have to spend some time and figure out the best proportions for the design. I will not be targeting my greatest amount of solar gain during the day time as I am more concerned with heat loss at night. That is the case for all passive solar designs but I will be clearly leaning towards heat conservation and stability.
Earth tube heating/cooling would be implemented as per
http://www.mb-soft.com/solar/intake.html
No matter what I do a green house can not supply all of the light I need and I will have to supplement with a lighting system. Corals use a lot of the blue spectrum (420-460nm wavelength) and that is quite strongly filtered out by most any glazing. Even a plain single pane of glass removes a significant amount so the result is that a greenhouse is capable of providing me with only approx 30 to 50% of the light I need. That is still a considerable contribution considering how much hydro is commonly used to power the HID lights in most coral farms. My intention is to use array's of 3 volt LED's with a DC controller so that I can wire them to a PV/battery system. I should be able to get away with producing only the light spectrum of 420 to 460 nm with the ambient light of the greenhouse supplying the rest of the spectrum. Only hands on experience will tell that tale for certain. Regardless, lighting is something every coral farmer is an expert on and it can be scaled as required.
I'll use DC lighting (for ambient/working light) and DC motors though out the design and attempt to operate completely off solar power. For backup it will be on the grid and have a generator.
No single attribute of this idea makes financial sense for this project on it own. But the combined low cost of construction of the building, even lower cost of future greenhouses due to the shared heat pump, low heating costs, ease of expansion and reduced lighting requirements make it appear feasible to do. I am not an engineer though and am in fact mathematically dyslexic so there will be precious little for me to go on except for experience and gut instinct.
My instinct is that it will work. There is nothing new here as these are all common technologies that are just being applied for a new purpose.
A lot of it depends on finding a suitable site to build on. I could build this on the ground and berm it up after construction if need be. That would mean the additional cost of cement walls and foundation though. That is money that could better be used in other parts of the project.
Some additional thoughts are to build a super insulated utilities building that will be the center of the system. It could be quite small fully earth bermed and house the connection to the grid (so I only have to pass one hydro inspection) the heat pump, the electronics and distribution for the power, the generator, the sump that the drainage pipes in the cold sinks feed to, the storage tank(s) for the evacuated solar collector(s), the earth tube heating/cooling collection/distribution system and any other mechanical system. I'd obviously need to run heavily insulated pipes and tubes to distribute the air and fluids from it to the greenhouse but it would allow greenhouses to be added as money or demand allowed forming little clusters. The single systems would be much easier automated and regulated to serve the needs of multiple greenhouses this way.
Now all of that said we have just requested a walk though on a commercial building in the city and if it is a go I'll be changing gears completely.
