So,
February 2014, my older sis and brother in law inform me that they want to build a mostly passive greenhouse on a 6.8 acre parcel of land, attached to their main property, which they purchased some years back. They knew I had some basic knowledge about aquaponics and greenhouses so they set me to the task to research and draw up some plans for them. 6 months later I submit the finished plans to the town (see posted images) and... the town rejected the project. The 6.8 acres are very isolated and cannot even be seen by any neighbors but... 25 years ago the land was a functional cranberry bog and is now categorized as a watershed which doesn't seem possible because the land is in a bowl and no water flows anywhere on the surface. In Plymouth MA, a permanent foundation cannot be built on a watershed. The permanent 4 foot concrete toe wall of a 30'x 28' greenhouse on a 6.8 acre isolated piece of unused land will threaten the integrity of the watershed. What a joke and what a lesson. If you ever get inspired to build or do a thing on your property, just do it. Don't ask. Then maybe film the town tearing it down if need be.
Hows that for a rant.
I guess I should post a note on why I am obsessing over the "heating from below" experiment...
I found these paragraphs in Greenhouse Gardener's Companion by Shane Smith page 52...
http://www.amazon.com/Greenhouse-Gardeners-Companion-Revised-Sunspace/dp/1555914500
"When soil temperatures drop below 45˚ F, roots grow much slower and have a harder time taking up water and nutrients"...
..."research has shown that if soil temperatures are kept around 65˚F, the winter air temperature can drop to 10˚F without any loss in yield. This is especially true with fruiting crops. Many researchers believe that the positive results obtained by heating the soil are due not just to the effects of temperature but also to the effects of faster organic matter decomposition (warmer temperatures wake up decomposition microbes, which creates more CO2), increasing the rate of photosynthesis."
I've found a few papers online where growers have used different methods to heat from below with greatly varying results. Most at least showed at least some improvement in yield so my layman's brain tells me that the important stuff is going on in the soil. But I've chosen to include the wicking bed to keep the roots from becoming too dry from the added heat. We shall test and see.
I'll post a construction change in a week or so, the hole has caved in on both ends, unleveling the base, I think it needs a slight rebuild, but I'm a bit busy at the moment.
After reading a few posts about below grade insulation I've found out this brand of insulation soaks up water like a sponge. -_-
But it's R-value per square inch is too high and space is too limited and... I have big sheets of extra cheap thin painters plastic that I'm just going to spray mount around each of the 5 pieces (5th being the base piece). This is just an in ground test fit photo. After this photo was taken I spray glued some strips of heavy duty tinfoil on to the ends of the uncovered insulation. It might help hold the heat a bit. Once I seal up the cracks with some expanding foam I'll be ready to install the set up for the heat sink venting.
50˚ today in Plymouth.
4 mil plastic sheet folded in half to a size of 11' x 12' and then stapled on edge to make it easier to handle while placing it around the sides/bottom of the foundation hole.
It wasn't too difficult to get in the center of the base and walk it up the cellar stairs. Letting it slide down into the hole with the plastic secured in place was also easy. Insulation, heat sink set up and some back filling will be next.
Not bad/close enough
I've started prepping the pieces for the above ground portion of the greenhouse and have made a few on the spot changes. Instead of building a box unit to channel the air down the outside of the under ground insulated box, I plan on running a 1"–1.5" pvc pipe from the warm air collection fan, down through the middle of the back wall of the green house just behind the black absorption surface, and down into the perforated pipe below the rock thermal bank. This method uses up only a little space within the grow bed/wicking bed so its a much simpler compromise. In this diagram I've drawn in some simple pvc vent pipes that when opened will allow outside air into the greenhouse during both winter and summer months.
These are just a few of the YouTube clips posted by growers and builders/designers that have inspired me to build and test my own system.
https://www.youtube.com/watch?v=pvPVsMGlVVI
A large school built greenhouse in western Canada with pv arrays and an in floor solar thermal storage.
https://www.youtube.com/watch?v=V0M6l3bnzZE
A large wood beam greenhouse in Minnesota focuses on collecting the large mass of sun heated air from within the greenhouse and pumping it through tubes just beneath the grow beds.
This sketch shows the insulated "foundation box" with cut away view of greenhouse on top.
