Storing Heat Underground in a Geosolar System.

Verge Permaculture | Jun 30, 2016

As an engineer and permaculture designer living in a cold-climate, I am particularly fascinated with the interplay between thermodynamics and design and with capturing “waste” energy and finding novel, inexpensive and efficient ways to store and/or recapture and re-use it. One of these such systems, is geothermal storage.In late 2015, our consulting company, Adaptive Habitat, was hired to design and install a geosolar heat collection system just north of Calgary, Alberta, underneath a Ready-To-Move (RTM) home. For R&D and monitoring purposes we decided to outfit the system with 11 temperature probes.

We are really pleased with its performance to-date. Here is a summary of how it is designed it and what we have observed so far.This system, which is also called an Annualized Geosolar (AGS) system, basically captures hot air from the attic in the spring, summer and fall and, using a fan, blows it underground beneath the home. The heat from the attic air transfers into the soil as it travels through the underground duct and then migrates slowly through the earth, returning to surface approximately six months later. This heats the crawspace under the home during the winter months. The end result is a reduction in heating bills and increased comfort from a warm floor. Note that, in conventional design, the attic air would be simply discharged to atmosphere through a power vent – so we are not even increasing power consumption with this modification.

Ideally, if you want to put something like this under your home or building, it needs to be thought-out and designed ahead of time. It would be possible to use this system in a retrofit but it would be less efficient and more expensive to install.

To install the system, we dug a trench down the center of the house pad, and used low cost materials such as two 50 gallon drums and 4.5 inch weeping tile for the inlet / outlet and duct work. We also had to bring a duct from the attic down into the crawl space. Material cost was around $3,500 CAD. We did have an excavator dig the trench, but he was there anyways digging the trenches for the eco-septic field that we also designed and installed (more on that in a later post).

Once the duct was laid, we covered and heavily compacted around the ducts both to eliminate settling and improve contact with the soil

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