DIY Geothermal Greenhouse Part 3: Earth Battery Excavation

#112 After starting to build our EMT electrical metal conduit (1.25") greenhouse two years ago, we are finally back to completing this project. We're actually glad we didn't finish it then, as we would not have had the time to learn all that we have about greenhouses since that time. We would have regretted doing/not doing some of the things then, in light of what we'll be doing now.

In this video we are FINISHING what we are calling, "The Big Dig" - excavating 3,200 cubic feet of dirt from underneath the greenhouse with a Mahindra 3016 tractor in order to install a passive solar earth battery (or climate battery/thermal banking/ground to air heat transfer) geothermal system. The idea is to use two high efficiency inline fans to pull hot air from the top of the greenhouse during the heat of the day down through a system of black corrugated drain pipes (600 linear feet) in the ground (300' buried at two feet and 300' at four feet) in order to heat the clay in the ground and return cooler air to the greenhouse. At night the process reverses, effectively warming the greenhouse for the cost of leaving a 75 watt light bulb on. In the summer, spring, and fall, this will help to keep the greenhouse cool(er) on hot days, and in the spring, fall, and winter it will help keep it warm(er) at night.

Background on the project: Our homestead came with metal pipes in the ground from a former 16' x 50' hoop house. It also had water lines run from the farm well (which also needed to be restored) and a 60 amp electric service. In the first video we installed the 1.25" EMT conduit that serves as the frame. In future videos we'll frame the end walls, run electric, and get the plastic cover on in time for winter.

Each rib or section of the greenhouse consists of three 10' pipes, no cutting. They are joined by stock EMT connectors. The two outer angles are 117.3. The ridge angle is 125.4. Sides are 6' tall. Just over 10' to the ridge. 16' wide.

Ultimately, this will be a double wall plastic film greenhouse.


David Mumford: "Wayfaring Stranger"
Jason Shaw: "Landra's Dream"