Ground To Air Heat Transfer System (GAHT) installed in Underground Greenhouse / Wisconsin Walipini

How do people keep their underground greenhouses 'warm' in the winter in Zone 4A? The Wisconsin Walipini has a GAHT system that puts out a steady 50 degrees F virtually year round.

The 'Ground to Air Heat Transfer' System heats the walipini in the winter, even with snow on the ground and sub-zero temperatures outside. In the summer, it works the other way, taking plus 100 degree F temperatures and cooling them to about 50 degrees.

Some people call GAHT systems 'earth batteries. Whatever you call them, they work by storing excess heat in the earth, or even drawing heat FROM the earth, and piping it via a fan or two into the growing space.

In this video, we start at the very beginning, and show the excavation and installation of the pipes below the surface. We then fast forward to the present day and show how it is actually working, with temperatures at 13 F.

This is an overview video. If anyone has specific questions, they'll have to put them in the comment section. They will perhaps be answered in a future video.

Here are links to the fans used in the Walipini:

https://amzn.to/3Gynhnc

Now, that is not the EXACT version. The exact version appears to be discontinued. This is the closest I could find to the version currently used. I note that the brand name is different, but by appearances, its a match. Your mileage may vary, but if its essentially the same thing (and I think it is, but upgraded), I think you'll be pleased. YMMV!

This is the fan being used to blow the heat across the middle of the greenhouse:

https://amzn.to/3CybZ0M

It says it is 'quiet.' Yea, maybe, if its on very low power. If sound is an issue, definitely use the first fans I linked to. It was an issue for me, which is why I looked into to other options. Otherwise, it works fine.