I'm able to get a high tunnel for free. Has anyone incorporated this as a topper for a walipini? I'm in southern VA - 7a = 7b. I'm aware of problems as well as advantages aka air flow, but not having a solid north wall seems to be an exception. Currently, this is a trussed 14' at it's peak.
That would be a cool greenhouse to be inside of. If you can keep it warm enough you could grow some pretty tall trees (banana ). I don't have any direct experience but my guess is that you may get the same amount of solarenergy through a high tunnel or a normal walipini roof. But the heat loss through the high tunnel could be worse due to greater surface area.
So if you have the same glazing between the two options, the high tunnel would likely lose a fair bit more heat at night and in the winter. Unless you can find a way to insulate the North part of the high tunnel and maybe the North half of the E and W walls. You could also potentially have a reflective inner surface on the North side of the high tunnel to bounce light down that would otherwise enter the South side and exit the North side without hitting a plant. That would give you more solar gain with the high tunnel option.
You'd also have more cubic feet of air to heat/cool/ventilate under a high tunnel which could be good or bad.
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Are you working with flat land or a hillside? If the north side of the high tunnel is buffered by digging down or into a hillside and burning the north wall with the removed earth You can have both the advantage of the walipini and the ventilation of a high tunnel.
I'm going to take advantage of a hill and am playing with several ideas. I want to have a "vestibule" for lack of a better descriptor, on the north side entrance, since I have read untold comments about the north wall heat loss. I want to have a buffer zone on the north wall, which will also be an area to store tools etc. A ramp (wheelbarrow width) going down to a door, opening into the actual greenhouse and level on either side for storage. I am playing with that entire area being covered in a fashion similar to a wofati, embracing the sides. This is planning stage, so I'm playing with a ridiculous amount of ideas. I also want to be able to remove the glass/ poly roof in total during the summer. We have extremely high humidity in the summer and I see no point in fighting it. I know, so much to consider and so many options.
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